Patent Application
20220140332
One embodiment of the present invention relates to a method of analyzing a lithium composite oxide. One embodiment of the present invention relates to an object or a manufacturing method. One embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.
Note that in this specification, a power storage device refers to every element and device having a function of storing power. Examples of the power storage device include a storage battery (also referred to as a secondary battery) such as a lithium-ion secondary battery, a lithium-ion capacitor, and an electric double layer capacitor.
In addition, electronic devices in this specification mean all devices including power storage devices, and electro-optical devices including power storage devices, information terminal devices including power storage devices, and the like are all electronic devices.
In recent years, a variety of power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries have been actively developed. In particular, demands for lithium-ion secondary batteries with high output and high capacity have rapidly grown with the development of the semiconductor industry, for portable information terminals such as mobile phones, smartphones, and laptop computers; portable music players; digital cameras; medical equipment; next-generation clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), and plug-in hybrid electric vehicles (PHEV); and the like. The lithium-ion secondary batteries are essential as rechargeable energy supply sources for the modern information society.
Thus, improvement of a positive electrode active material has been studied to increase the cycle characteristics and the capacity of the lithium-ion secondary battery (Patent Document 1 and Patent Document 2).
The performance required for power storage devices includes safe operation under a variety of environments and longer-term reliability.
Various aspects of lithium ion secondary batteries and positive electrode active materials used in them such as capacity, cycle performances, charge-discharge characteristics, reliability, safety, and cost are desired to be improved; a lithium composite oxide LiMO2 (M is two or more metals including Co), in which a part of LiCoO2 is substituted by other elements, has been developed.
However, the number of the substitution elements is very small; the method to reveal the structure of the lithium composite oxide has not been invented yet. If the structure of the lithium composite oxide is revealed, it may help to develop materials and to clarify the mechanisms such as charge-discharge characteristics and reliability.
In view of the above, an object of one embodiment of the present invention is to provide a method to analyze a lithium composite oxide. An object is to provide a positive electrode active material particle which hardly deteriorates. An object of one embodiment of the present invention is to provide a novel positive electrode active material particle. An object of one embodiment of the present invention is to provide a power storage device which hardly deteriorates. An object of one embodiment of the present invention is to provide a highly safe power storage device. An object of one embodiment of the present invention is to provide a novel power storage device.
Note that the description of these objects does not preclude the existence of other objects. One embodiment of the present invention does not have to achieve all these objects. Note that other objects can be taken from the description of the specification, the drawings, and the claims.
One embodiment of the present invention is a method to analyze substitution positions of a Ni atom and a Mg atom in a compound represented by a chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2. The method includes a first calculation step of calculating stabilization energy of the compound represented by the chemical formula when a Ni atom and a Mg atom each independently substitute for a Li atom and/or a Co atom contained in a LiCoO2 crystal. The method includes a second calculation step of calculating the stabilization energy of the compound represented by the chemical formula when cation occupancy of Li sites is changed. The method includes a first measurement step of measuring charge-discharge efficiency in the first cycle and charge-discharge efficiency in the n-th cycle of the compound represented by the chemical formula (n is an integer greater than or equal to 2). In the chemical formula, x+y<1, a+b<1, and x, y, a, and b each independently represent a real number greater than or equal to 0 and less than or equal to 1.
In the above structure, the measurement step includes at least a step of making a sample and a step of mechanical measurement. Owing to a combination of calculation and measurement, calculation results and the validity of events expected from the calculation results can be evaluated, which enables detail analysis.
In the above structure, in the first calculation step and the second calculation step, a GGA+U(DFT-D2) method is preferably used.
In the above structure, the cation occupancy is preferably changed at least within a range of 80% to 100% for calculation
In the above structure, n is preferably 2.
In the above structure, it is preferable that in the chemical formula, 0<x+a≤0.015 and 0<y+b≤0.06
In the above structure, in the second calculation step, when the Ni atom and the Mg atom substitute for the same kind of atoms in the LiCoO2 crystal, the stabilization energy of the case where the same kind of atoms exists in the same layer in the LiCoO2 crystal and the stabilization energy of the case where the same kind of atoms exists in different layers in the LiCoO2 crystal are preferably calculated.
According to one embodiment of the present invention, a method to analyze a lithium composite oxide can be provided. A positive electrode active material particle which hardly deteriorates can be provided. A novel positive electrode active material particle can be provided. A power storage device which hardly deteriorates can be provided. A highly safe power storage device can be provided. A novel power storage device can be provided.
FIG. 10A1, FIG. 10A2, FIG. 10B1, and FIG. 10B2 are diagrams showing examples of a secondary battery.
Embodiments of the present invention are described in detail below with reference to the drawings. Note that the present invention is not limited to the following description, and it is readily understood by those skilled in the art that modes and details of the present invention can be modified in various ways. In addition, the present invention should not be construed as being limited to the description of embodiments below.
In the crystallography, a bar is placed over a number in the expression of crystal planes and orientations; however, in this specification and the like, crystal planes and orientations are expressed by placing a minus sign (−) before a number because of expression limitations. Furthermore, an individual direction which shows an orientation in a crystal is denoted by “[ ]”, a set direction which shows all of the equivalent orientations is denoted by “< >”, an individual plane which shows a crystal plane is denoted by “( )”, and a set plane having equivalent symmetry is denoted by “{ }”.
As a positive electrode material, a lithium composite oxide in which a part of LiCoO2 is substituted by other elements has been developed. The number of the substitution elements is too small; it is difficult to analyze the crystal structure of the lithium composite oxide. The present inventors have found that the crystal structure can be analyzed efficiently and in detail through analysis of the crystal structure using a combination of chemical calculations and experiments.
When LiCoO2 is doped with a metal element, a Li site or a Co site in a crystal of LiCoO2 may be substituted by the metal element; however, at the moment, it is difficult to analyze which site is substituted through a measurement. In the case of doping with a plurality of metal elements, each doped metal may be substituted for a Li site or a Co site, which makes the situation complex. Thus, it is effective to estimate, through chemical calculation, the site for which the doped metal is substituted by calculating the stabilization energy of the crystal structure with an arrangement of cation sites. An analysis method of a substitution position of a doped element in a lithium composite oxide is described below using an example of a calculation on a material represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2, which is an example of a lithium composite oxide in which LiCoO2 is doped with Mg and Ni. In the above chemical formula, x+y<1 and a+b<1.
A concept of a crystal model is preferably made by an experimenter and calculations are preferably carried out with a computer. When a concept of a crystal model is made by an experimenter, relations between a crystal condition and parameters become clear, which enables the following analyses to be performed in detail. The calculation amount is enormous; calculation results can be obtained fast with a computer. The following calculation example is explained on the assumption that the crystal structure of LiCoO2 (R-3m (O3)) is made by an experimenter and calculations are carried out with a computer.
[Calculation Example of Stabilization Energy of Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+e)O2]
A model is made in which LiCoO2 with a crystal structure of R-3m (O3), which is a basic structure of LiCoO2, is doped with Mg and Ni, and the stabilization energy thereof is calculated; through this, the crystal structure of Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 can be analyzed.
Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is a compound in which Mg and Ni are used as substitution elements for (a) metal element(s) of LiCoO2 (one or both of Li and metal). The following crystal models are considered as the combinations of the substitution sites of Mg and Ni.
Li in the same Li layer are substituted by Mg and Ni.
Li in different Li layers are substituted by Mg and Ni.
Co in the same Co layer are substituted by Mg and Ni.
Co in different Co layers are substituted by Mg and Ni.
Li in a Li layer is substituted by Mg and Co in a Co layer is substituted by Ni.
Li in a Li layer is substituted by Ni and Co in a Co layer is substituted by Mg.
The stabilization energy of the crystal structure in each of the above combinations of the substitution sites is calculated, whereby what crystal structure Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 can form can be analyzed. The stabilization energy can be estimated with the following formulae. A model is assumed here in which a Li atom and a Co atom are substituted by one Mg atom and one Ni atom in LiCoO2 which consists of 48 Li atoms, 48 Co atoms, and 96 oxygen atoms (192 atoms in total).
<Case where Two Li Sites are Substituted by One Mg and One Ni>
(Equation 1)
ΔE=[E_total{(Li46Mg1Ni1Co48O96)+2×E_atom(Li)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 1)
<Case where One Li Site is Substituted by One Mg and Co Site is Substituted by One Ni>
(Equation 2)
ΔE=[E_total{(Li47Mg1Ni1Co47O96)+E_atom(Li)+E_atom(Co)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 2)
<Case where Two Co Sites are Substituted by One Mg and One Ni>
(Equation 3)
ΔE=[E_total{(Li48Mg1Ni1Co46O96)+2×E_atom(Co)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 3)
Symbols in Formula 1 to Formula 3 are as follows.
ΔE: stabilization energy.
E_total (Li46Mg1Ni1Co48O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which two Li are substituted by one Mg and one Ni.
E_total (Li47Mg1Ni1Co47O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which one Li is substituted by one Mg and one Co is substituted by one Ni.
E_total (Li48Mg1Ni1Co46O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which two Co are substituted by one Mg and one Ni.
E_total (Li48Co48O96): the energy of the model of a LiCoO2 crystal (192 atoms in total).
E_atom (Li): the energy of one Li atom.
E_atom (Co): the energy of one Co atom.
E_atom (Mg): the energy of one Mg atom.
E_atom (Ni): the energy of one Ni atom.
The stabilization energy of each combination of the substitution sites by Mg and Ni is calculated and the results are compared, whereby a stable crystal structure can be estimated. The smaller the stabilization energy which is calculated from Formulae (1) to (3) is, the more stable the crystal model is and the more likely Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is to form the model.
The LDA+U method, the GGA+U(DFT-D2) method, or the like can be used for the calculation; the GGA+U(DFT-D2) method is preferably used. The GGA+U(DFT-D2) method can accurately estimate the stabilization energy since the GGA+U(DFT-D2) method can more accurately estimate the Van der Waals force than the LDA+U method.
Stabilization energy is influenced by the position where an atom is substituted. For example, in
In the above formula, a model having 192 atoms in a crystal is used for the calculation; a user of this invention can extend the tendency of the calculation result to the bulk crystal. It is assumed that a model with a different number of atoms shows a similar tendency; the tendency of the calculation result can also be extended to a model with a different number of atoms. For example, when a model in which Li in the same Li layer are substituted by Mg and Ni has a lower stabilization energy than a model in which Co in the same Co layer are substituted by Mg and Ni, a similar tendency is assumed to be shown in the bulk crystal and a model with a different number of atoms; the tendency of the calculation result can be extended.
The stabilization energy of each crystal model is calculated and the results are compared as described above; through this, what crystal structure Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 forms can be analyzed. The calculation and the comparison of the stabilization energy estimate a lithium composite oxide with a cation site occupancy of 100%; however, behavior and change in the crystal structure of the lithium composite oxide used to a positive electrode are not considered on calculation. When the lithium composite oxide is used as a positive electrode material, behavior during charging and discharging is preferably considered. Considering behavior during charging and discharging enables detailed analysis to be conducted.
[Calculation of Stabilization Energy when Cation Occupancy of Li Site is Changed]
In order to estimate a change of the crystal structure of a lithium composite oxide during charging and discharging a secondary battery when the lithium composite oxide is used as a positive electrode material of the secondary battery, the stabilization energy of the lithium composite oxide from which Li is extracted, that is, the stabilization energy when cation occupancy of Li sites is changed is calculated. Extraction of Li from a lithium composite oxide is assumed to be behavior occurring in a positive electrode of a secondary battery during charging. The stabilization energy of a lithium composite oxide with Li extracted is estimated as the stabilization energy during charging.
Formulae to calculate the stabilization energy when cation occupancy of Li sites is changed are shown below.
<Case where Two Li Sites are Substituted by One Mg and One Ni>
(Equation 4)
ΔEC=[EC_total{(Li46-zMg1Ni1Co48O96)+z×E_atom(Li)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 4)
<Case where One Li Site is Substituted by One Mg and Co Site is Substituted by One Ni>
(Equation 5)
ΔEC=[EC_total{(Li47-zMg1Ni1Co47O96)+z×E_atom(Li)+E_atom(Co)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 5)
<Case where Two Co Sites are Substituted by One Mg and One Ni>
(Equation 6)
ΔEC=[EC_total{(Li48-zMg1Ni1Co46O96)+z×E_atom(Li)+2×E_atom(Co)}−{E_total(Li48Co48O96)+E_atom(Mg)+E_atom(Ni)} (Formula 6)
Symbols in Formula 4 to Formula 6 are as follows. Descriptions of symbols which are the same as those in Formula 1 to Formula 3 are omitted.
ΔEC: the stabilization energy when cation occupancy of Li sites is changed.
EC_total (Li46-zMg1Ni1Co48O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which two Li are substituted by one Mg and one Ni and z Li is/are extracted. Note that z is an integer satisfying 0≤z≤46.
EC_total (Li47-zMg1Ni1Co47O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which one Li is substituted by one Mg and one Co is substituted by one Ni. Note that z is an integer satisfying 0≤z≤47.
EC_total (Li48-zMg1Ni1Co46O96): in a LiCoO2 crystal (192 atoms in total), the energy of the model in which two Co are substituted by one Mg and one Ni and z Li is/are extracted. Note that z is an integer satisfying 0≤z≤48.
In Formulae 4 to 6, z means an extracted Li number. When the value of z is changed, it means that the cation occupancy of Li sites in a lithium composite oxide crystal is changed. In each model, ΔEC is calculated with respect to z, and ΔEC is plotted with respect to the cation occupancy of Li sites or z, whereby the stabilization energy during charging can be estimated.
As shown in
The cation occupancy is preferably changed at least between more than or equal to 80% and less than or equal to 100% to plot ΔEC. The cation occupancy is preferably changed between more than or equal to 50% and less than or equal to 100%, more preferably between more than or equal to 0% and less than or equal to 100%. With these conditions, events occurring during charging can be identified.
By making the plot, a crystal structure of a lithium composite oxide can be analyzed through the aforementioned ΔE and ΔEC. In the above example, the positions of a Ni atom and a Mg atom when Mg and Ni are added to LiCoO2 can be analyzed.
In Formula 4 to Formula 6, z is changed to perform calculation; a plurality of calculations (48 ways at maximum in the above example) on one model is required, which may increase calculation cost. On the other hand, ΔE calculated with Formula 1 to Formula 3 requires a small number of relations between a Mg atom and a Ni atom (approximately up to the fourth proximity) considered with respect to one model, which needs low calculation cost. Thus, ΔE is calculated and appropriate models are selected; then ΔEC of the appropriate model is calculated to make the plot, whereby a crystal structure or substitution positions of a Ni atom and a Mg atom can be analyzed efficiently.
It is expected that a graph showing a relation in which ΔEC increases as z increases is obtained when ΔEC is plotted with respect to the cation occupancy of Li sites or z. When graphs of a plurality of models are made, the magnitude relation between the models is reversed depending on z. For example, with the calculation results in which ΔEC of a model A is smaller than ΔEC of a model B in the range of the cation occupancy of more than or equal to 95% and less than or equal to 100%, whereas ΔEC of the model A is larger than ΔEC of the model B in the range of the cation occupancy of more than or equal to 0% and less than 95%, Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 presumably has the structure of the model A when the cation occupancy is more than or equal to 95% and less than or equal to 100%, and has the structure of the model B when the cation occupancy is more than or equal to 0% and less than 95%. In other words, a charging presumably changes the crystal structure. The event caused by charging is preferably analyzed with the following measurement.
The charge-discharge efficiency of a secondary battery shows approximately 100% when appropriate electrodes are selected, unless materials such as electrode materials and an electrolyte deteriorate, short-circuits occur, and metal lithium precipitates, for example. When a deterioration factor described above does not exist and charge-discharge efficiency falls short of 100%, a crystal structure change of a positive electrode during charging or discharging material can be estimated. Charge-discharge efficiency is calculated from the ratio of a discharging capacity to a charging capacity; when energy supplied by charging is used for something other than Li extraction, charge-discharge efficiency decreases. When a crystal model of a positive electrode material changes, decrease of charge-discharge efficiency is observed. Thus, change of a crystal model of a lithium composite oxide can be analyzed by measuring charge-discharge efficiency.
To analyze change of a crystal model accurately, the deterioration factors are preferably few. Thus, the charge-discharge efficiency in the first cycle is preferably measured. When a crystal model changes, events occurring in a crystal can be analyzed in detail by analyzing whether the change is reversible or irreversible. Thus, the charge-discharge efficiency in the second cycle is more preferably measured in addition to the charge-discharge efficiency in the first cycle. When the second measurement shows a similar result of the first measurement, events occurring in a crystal are presumably reversible. On the other hand, when the second measurement shows a different result from the first measurement, for example, the charge-discharge efficiency in the first cycle is less than 100% and the charge-discharge efficiency in the second cycle is 100%, the events occurred in a crystal are presumably irreversible and occurred only at the first cycle. Analysis can be conducted in more detail by comparing the charge-discharge efficiency in the first cycle and that in the second cycle.
If deterioration factors are few, the charge-discharge efficiency in the third and the subsequent cycles can be compared with that in the first cycle. Charge-discharge efficiency in any cycle can be compared such as the second and after the third cycle. When events occurring in a crystal are irreversible, the events may be observed only at the first cycle. Thus, the charge-discharge efficiency in the first cycle is preferably measured. Considering deterioration factors, the charge-discharge efficiency in the first cycle and that in the second cycle are more preferably compared.
To measure the charge-discharge efficiency of a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2, it is necessary to synthesize the compound firstly. Then, the synthesized compound is used to make a battery cell and the charge-discharge efficiency of the battery cell is measured. Measuring charge-discharge efficiency needs these steps. When measurements such as an XRD measurement, which do not relate to charging, discharging, an electrolyte, and the like, are conducted on the compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2, a battery cell need not be made. When the measurement relating to a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is conducted, at least a step to synthesize the compound and a step to measure the characteristics of the compound are needed. To measure charge-discharge efficiency, a step to make a battery cell is also needed. Other steps may be included for measurement.
Analysis is conducted with a combination of ΔE, ΔEC, and measurement of charge-discharge efficiency described in this embodiment, whereby the crystal structure and substitution positions of a lithium composite oxide can be accurately analyzed. A plurality of calculation methods is used to perform calculation efficiently and analysis is conducted with a combination of measurements; these are the features of this invention. Calculation and measurement are combined, which makes it possible to evaluate the validity of a calculation result and events expected from the calculation result; detail analysis can be conducted. A compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 has especially good characteristics in the ranges of 0<x+a≤0.015 and 0<y+b≤0.06; however, the crystal structure thereof is difficult to analyze in detail only with measurement since Mg and Ni are slightly contained. Thus, the analysis method of one embodiment of the present invention can be suitably used. Based on an analysis result from calculation and measurement, another analysis with calculation and measurement is conducted, whereby more accurate analysis can be conducted. The calculations and measurements shown in this embodiment can be repeated. Based on the results from the calculations and the measurements shown in this embodiment, an additional analysis can be conducted.
A measurement of charge-discharge efficiency is described as an example of measurement; a dQ/dV measurement, an XRD measurement, a magnetization measurement, a Li NMR measurement, and the like can be used as the measurements of one embodiment of the present invention. The measurements of one embodiment of the present invention are not limited to them.
This embodiment can be implemented in appropriate combination with any of the other embodiments.
An example of a method to make a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is described using
As shown in Step S11 in
In this embodiment, lithium fluoride LiF is prepared as the fluorine source and the lithium source, and magnesium fluoride MgF2 is prepared as the fluorine source and the magnesium source (Step S11 in
In addition, in the case where the following mixing and grinding steps are performed by a wet process, a solvent is prepared. As the solvent, ketone such as acetone; alcohol such as ethanol or isopropanol; ether; dioxane; acetonitrile; N-methyl-2-pyrrolidone (NMP); or the like can be used. An aprotic solvent that hardly reacts with lithium is further preferably used. In this embodiment, acetone is used (see Step S11 in
Next, the materials of the mixture 902 are mixed and ground (Step S12 in
The materials mixed and ground in the above are collected (Step S13 in
For example, D50 of the mixture 902 is preferably greater than or equal to 600 nm and less than or equal to 20 μm, further preferably greater than or equal to 1 μm and less than or equal to 10 μm. When mixed with a composite oxide containing lithium, a transition metal, and oxygen in the later step, the mixture 902 pulverized to such a small size is easily attached to surfaces of composite oxide particles uniformly. The mixture 902 is preferably attached to the surfaces of the composite oxide particles uniformly because both halogen and magnesium are easily distributed to the superficial portion of the composite oxide particles after heating. When there is a region containing neither halogen nor magnesium in the superficial portion, the above-described pseudo-spinel crystal structure in the charged state is less likely to be formed.
Next, a lithium source is prepared as shown in Step S25. A composite oxide containing lithium, a transition metal, and oxygen that is synthesized in advance may be used as Step S25.
For example, as lithium cobaltate synthesized in advance, a lithium cobaltate particle (product name: CELLSEED C-10N) manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. can be used. This is lithium cobaltate in which the average particle diameter (D50) is approximately 12 μm, and in the impurity analysis by a glow discharge mass spectroscopy method (GD-MS), the magnesium concentration and the fluorine concentration are less than or equal to 50 ppm wt, the calcium concentration, the aluminum concentration, and the silicon concentration are less than or equal to 100 ppm wt, the nickel concentration is less than or equal to 150 ppm wt, the sulfur concentration is less than or equal to 500 ppm wt, the arsenic concentration is less than or equal to 1100 ppm wt, and the concentrations of elements other than lithium, cobalt, and oxygen are less than or equal to 150 ppm wt.
The composite oxide including lithium, the transition metal, and oxygen in Step S25 preferably has a layered rock-salt crystal structure with few defects and distortions. Therefore, the composite oxide is preferably a composite oxide with few impurities. In the case where the composite oxide including lithium, the transition metal, and oxygen includes a lot of impurities, the crystal structure is highly likely to have a lot of defects or distortions.
Next, the mixture 902 and the composite oxide including lithium, the transition metal, and oxygen are mixed (Step S31 in
The condition of the mixing in Step S31 is preferably milder than that of the mixing in Step S12 not to damage the particles of the composite oxide. For example, a condition with a lower rotation frequency or shorter time than the mixing in Step S12 is preferable. In addition, it can be said that the dry process has a milder condition than the wet process. For example, a ball mill, a bead mill, or the like can be used for the mixing. When the ball mill is used, a zirconia ball is preferably used as media, for example.
The materials mixed in the above are collected (Step S32 in
Next, the mixture 903 is heated (Step S34 in
The annealing is preferably performed at an appropriate temperature for an appropriate time. The appropriate temperature and time depend on the conditions such as the particle size and the composition of the composite oxide including lithium, the transition metal, and oxygen in Step S25. In the case where the particle size is small, the annealing is preferably performed at a lower temperature or for a shorter time than the case where the particle size is large, in some cases.
When the average particle diameter (D50) of the particles in Step S25 is approximately 12 μm, for example, an annealing temperature is preferably higher than or equal to 600° C. and lower than or equal to 950° C., for example. The annealing time is preferably longer than or equal to 3 hours, further preferably longer than or equal to 10 hours, still further preferably longer than or equal to 60 hours, for example.
On the other hand, when the average particle diameter (D50) of the particles in Step S25 is approximately 5 μm, the annealing temperature is preferably higher than or equal to 600° C. and lower than or equal to 950° C., for example. The annealing time is preferably longer than or equal to 1 hour and shorter than or equal to 10 hours, further preferably approximately 2 hours, for example.
The temperature decreasing time after the annealing is, for example, preferably longer than or equal to 10 hours and shorter than or equal to 50 hours.
It is considered that when the mixture 903 is annealed, a material having a low melting point (e.g., lithium fluoride, which has a melting point of 848° C.) in the mixture 902 is melted first and distributed to the superficial portion of the composite oxide particle. Next, the existence of the melted material decreases the melting points of other materials, presumably resulting in melting of the other materials. For example, magnesium fluoride (melting point: 1263° C.) is presumably melted and distributed to the superficial portion of the composite oxide particle.
The elements included in the mixture 903 are diffused faster in the superficial portion and the vicinity of the grain boundary than inside the composite oxide particles. Therefore, the concentrations of magnesium and halogen in the superficial portion and the vicinity of the grain boundary are higher than those of magnesium and halogen inside the composite oxide particles.
The materials annealed in the above manner are collected (Step S35 in
Next, as shown in Step S50, the mixture 904 and pulverized nickel hydroxide are mixed. Then, the mixed materials are collected (Step S51). The pulverized nickel hydroxide is formed in advance by Step S15 for mixing nickel hydroxide and acetone and Step S16 for collecting the mixture. Through Step S16, the pulverized nickel hydroxide is obtained (Step S17).
The materials mixed in Step S50 are collected in Step S51, whereby a mixture 905 is obtained (Step S52 in
Then, the obtained mixture is heated (Step S53 in
As for the heating time, the time for keeping the heating temperature within a predetermined range is preferably longer than or equal to 1 hour and shorter than or equal to 80 hours.
The heating temperature is lower than 1000° C., preferably higher than or equal to 700° C. and lower than or equal to 950° C., further preferably approximately 850° C.
The heating is preferably performed in an oxygen-containing atmosphere.
In this embodiment, the heating temperature is 850° C. and kept for 2 hours, the temperature rising rate is 200° C./h, and the flow rate of oxygen is 10 L/min.
Here, the heating temperature in Step S53 is preferably lower than the heating temperature in Step S34.
Next, cooled particles are collected (Step S54 in
The positive electrode active material 100A-1 obtained by the above manufacturing method is described.
A material with a layered rock-salt crystal structure, such as lithium cobaltate (LiCoO2), is known to have a high discharge capacity and excel as a positive electrode active material of a secondary battery. As an example of the material with a layered rock-salt crystal structure, a composite oxide represented by LiMO2 is given. As an example of the element M, one or more elements selected from Co and Ni can be given. As another example of the element M, in addition to one or more elements selected from Co and Ni, one or more elements selected from Al and Mg can be given.
It is known that the Jahn-Teller effect in a transition metal compound varies in degree according to the number of electrons in the d orbital of the transition metal.
In a compound containing nickel, distortion is likely to be caused because of the Jahn-Teller effect in some cases. Accordingly, when high-voltage charging and discharging are performed on LiNiO2, the crystal structure might be disordered because of the distortion. The influence of the Jahn-Teller effect is suggested to be small in LiCoO2; hence, LiCoO2 is preferable because the resistance to high-voltage charging and discharging is higher in some cases.
Positive electrode active materials are described with reference to
A compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 can have small difference of CoO2 layers through repetitions of high-voltage charging and discharging. Furthermore, change in volume can be small. Thus, the compound can achieve excellent cycle performances. In addition, the compound can have a stable crystal structure in a high-voltage charged state. Thus, in the compound, a short circuit is less likely to occur while the high-voltage charged state is maintained. This is preferable because the safety is further improved. It is particularly preferable to satisfy 0<x+a≤0.015 and 0<y+b≤0.06, in which case the compound shows good performances.
In the compound, there is a small difference in change in the crystal structure and volume in comparison with the same number of transition metal atoms between a sufficiently discharged state and a high-voltage charged state.
The crystal structure with a charge depth of 0 (discharged state) in
Note that in the pseudo-spinel crystal structure, oxygen is tetracoordinated to a light element such as lithium in some cases. Also in that case, the ion arrangement has symmetry similar to that of the spinel crystal structure.
The pseudo-spinel crystal structure can also be regarded as a crystal structure that contains Li between layers at random but is similar to a CdCl2 type crystal structure. The crystal structure similar to the CdCl2 type crystal structure is close to a crystal structure of lithium nickel oxide when charged up to a charge depth of 0.94 (Li0.06NiO2); however, pure lithium cobaltate or a layered rock-salt positive electrode active material containing a large amount of cobalt is known not to have this crystal structure generally.
Anions of a layered rock-salt crystal and anions of a rock-salt crystal have cubic closest packed structures (face-centered cubic lattice structures). Anions of a pseudo-spinel crystal are also presumed to have cubic closest packed structures. When the pseudo-spinel crystal is in contact with the layered rock-salt crystal and the rock-salt crystal, there is a crystal plane at which orientations of cubic closest packed structures composed of anions are aligned. Note that a space group of the layered rock-salt crystal and the pseudo-spinel crystal is R-3m, which is different from a space group Fm-3m of a rock-salt crystal (a space group of a general rock-salt crystal) and a space group Fd-3m of a rock-salt crystal (a space group of a rock-salt crystal having the simplest symmetry); thus, the Miller index of the crystal plane satisfying the above conditions in the layered rock-salt crystal and the pseudo-spinel crystal is different from that in the rock-salt crystal. In this specification, a state where the orientations of the cubic closest packed structures composed of anions in the layered rock-salt crystal, the pseudo-spinel crystal, and the rock-salt crystal are aligned is referred to as a state where crystal orientations are substantially aligned in some cases.
In the positive electrode active material 100A-1, a change in the crystal structure when the positive electrode active material 100A-1 is charged with a high voltage and a large amount of lithium is extracted is inhibited as compared with the positive electrode active material 100C. As indicated by the dotted lines in
More specifically, the structure of the positive electrode active material 100A-1 is highly stable even when a charging voltage is high. For example, at a charge voltage that makes the positive electrode active material 100C have the H1-3 type crystal structure, for example, at a voltage of approximately 4.6 V with reference to the potential of lithium metal, the positive electrode active material 100A-1 can have the R-3m (O3) crystal structure. Moreover, in a higher charge voltage region, for example, at voltages of approximately 4.65 V to 4.7 V with reference to the potential of lithium metal, the pseudo-spinel crystal structure can be obtained. At a much higher charging voltage, the H1-3 type crystal is eventually observed in some cases. In the case where graphite, for instance, is used as a negative electrode active material in a secondary battery, when the voltage of the secondary battery ranges from 4.3 V to 4.5 V, for example, the R-3m (O3) crystal structure can be maintained. In a higher charging voltage region, for example, at voltages of 4.35 V to 4.55 V with reference to the potential of lithium metal, the pseudo-spinel crystal structure can be obtained.
Thus, in the positive electrode active material 100A-1, the crystal structure is less likely to be disordered even when charging and discharging are repeated at a high voltage.
Note that in the unit cell of the pseudo-spinel crystal structure, coordinates of cobalt and oxygen can be represented by Co (0, 0, 0.5) and O (0, 0, x) within the range of 0.20≤x≤0.25.
A slight amount of magnesium existing between the CoO2 layers, i.e., in lithium sites at random, has an effect of inhibiting a difference in the CoO2 layers. Thus, the existence of magnesium between the CoO2 layers makes it easier to obtain the pseudo-spinel crystal structure. Therefore, magnesium is preferably distributed in the entire particle of the positive electrode active material 100A-1. In addition, to distribute magnesium in the entire particle, heat treatment is preferably performed in the formation process of the positive electrode active material 100A-1.
However, cation mixing occurs when the heat treatment temperature is excessively high, so that magnesium is highly likely to enter the cobalt sites. Magnesium in the cobalt sites eliminates the effect of maintaining the R-3m structure. Furthermore, when the heat treatment temperature is excessively high, adverse effects such as reduction of cobalt to be divalent and transpiration of lithium are concerned.
In view of the above, a halogen compound such as a fluorine compound is preferably added to lithium cobaltate before the heat treatment for distributing magnesium in the entire particle. The addition of the halogen compound decreases the melting point of lithium cobaltate. The decrease in the melting point makes it easier to distribute magnesium in the entire particle at a temperature at which the cation mixing is unlikely to occur. Furthermore, when the fluorine compound exists, it is expected that the corrosion resistance to hydrofluoric acid generated by decomposition of an electrolyte solution is improved.
When the magnesium concentration is higher than a predetermined value, the effect of stabilizing a crystal structure becomes small in some cases. This is probably because magnesium enters the cobalt sites in addition to the lithium sites. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times, preferably larger than 0.01 times and less than 0.04 times, still further preferably approximately 0.02 times the number of cobalt atoms. The magnesium concentration described here may be a value obtained by element analysis on the entire particle of the positive electrode active material using ICP-MS or the like, or may be a value based on the ratio of the raw materials mixed in the formation process of the positive electrode active material, for example.
The number of nickel atoms in the positive electrode active material 100A-1 of one embodiment of the present invention is preferably 7.5% or less, further preferably 0.05% to 40%, still further preferably 0.1% to 2% of the number of cobalt atoms. The nickel concentration described here may be a value obtained by element analysis on the entire particle of the positive electrode active material using ICP-MS or the like, or may be a value based on the ratio of the raw materials mixed in the process of forming the positive electrode active material, for example.
The detail structure of the positive electrode active material 100A-1 can be analyzed with the analysis methods shown in Embodiment 1.
A too large particle size of the positive electrode active material 100A-1 causes problems such as difficulty in lithium diffusion and too much surface roughness of an active material layer in coating to a current collector. By contrast, a too small particle size causes problems such as difficulty in loading the active material layer in coating to the current collector and overreaction with an electrolyte solution. Therefore, an average particle size (D50, also referred to as median diameter) is preferably more than or equal to 1 μm and less than or equal to 100 μm, further preferably more than or equal to 2 μm and less than or equal to 40 μm, still further preferably more than or equal to 5 μm and less than or equal to 30 μm.
Whether or not a positive electrode active material is the positive electrode active material having the pseudo-spinel crystal structure when charged with a high voltage can be determined by analyzing a high-voltage charged positive electrode using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like. The XRD is particularly preferable because the symmetry of a transition metal such as cobalt contained in the positive electrode active material can be analyzed with high resolution, the degrees of crystallinity and the crystal orientations can be compared, the distortion of lattice periodicity and the crystallite size can be analyzed, and a positive electrode obtained by disassembling a secondary battery can be measured without any change with sufficient accuracy, for example.
As described so far, the positive electrode active material 100A-1 has a feature of a small change in the crystal structure between the high-voltage charged state and the discharged state. A material where 50 wt % or more of the crystal structure greatly changes between the high-voltage charged state and the discharged state is not preferable because the material cannot withstand a high-voltage charging and discharging. In addition, it should be noted that a target crystal structure is not obtained in some cases only by adding impurity elements. For example, although the positive electrode active material that is lithium cobaltate containing magnesium and fluorine is a commonality, the positive electrode active material has 60 wt % or more of the pseudo-spinel crystal structure in some cases, and has 50 wt % or more of the H1-3 type crystal structure in other cases, when charged with a high voltage. Furthermore, at a predetermined voltage, the positive electrode active material has almost 100 wt % of the pseudo-spinel crystal structure, and with an increase in the predetermined voltage, the H1-3 type crystal structure is generated in some cases. The crystal structure of the positive electrode active material 100A-1 is preferably analyzed with XRD or the like. It is more preferable to analyze it with the analysis methods described in Embodiment 1. The combination of the analysis methods and measurement such as XRD enables more detail analysis.
Note that a positive electrode active material in the high-voltage charged state or the discharged state sometimes causes a change in the crystal structure when exposed to the air. For example, the pseudo-spinel crystal structure changes into the H1-3 type crystal structure in some cases. Thus, all samples are preferably handled in an inert atmosphere such as an argon atmosphere.
A positive electrode active material (lithium cobaltate) shown in
As shown in
Furthermore, when the charge depth is 1, LiCoO2 has the crystal structure of the space group P-3 μml, and one CoO2 layer exists in a unit cell. Thus, this crystal structure is referred to as an O1-type crystal structure in some cases.
Moreover, lithium cobaltate when the charge depth is approximately 0.88 has the crystal structure of the space group R-3m. This structure can also be regarded as a structure in which CoO2 structures such as P-3 μml (O1) and LiCoO2 structures such as R-3m (O3) are alternately stacked. Thus, this crystal structure is referred to as an H1-3 type crystal structure in some cases. Note that the number of cobalt atoms per unit cell in the actual H1-3 type crystal structure is twice as large as that of cobalt atoms per unit cell in other structures. However, in this specification including
For the H1-3 type crystal structure, as disclosed in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell can be expressed as follows, for example: Co (0, 0, 0.42150±0.00016), O1 (0, 0, 0.27671±0.00045), and O2 (0, 0, 0.11535±0.00045). Note that O1 and O2 are each an oxygen atom. In this manner, the H1-3 type crystal structure is represented by a unit cell including one cobalt and two oxygen. Meanwhile, the pseudo-spinel crystal structure of one embodiment of the present invention shown in
When charging with a high voltage of 4.6 V or higher based on the redox potential of a lithium metal or charging with a large charge depth of 0.8 or more and discharging are repeated, the crystal structure of lithium cobaltate changes (i.e., a non-equilibrium phase change occurs) repeatedly between the H1-3 type crystal structure and the R-3m (O3) structure in a discharged state.
However, there is a large difference in the position of the CoO2 layer between these two crystal structures. As indicated by the dotted lines and the arrows in
A difference in volume is also large. A difference in volume in comparison with the same number of cobalt atoms between the H1-3 type crystal structure and the O3-type crystal structure in the discharged state is 3.0% or more.
In addition, a structure in which CoO2 layers are continuous, such as P-3 μml (O1), included in the H1-3 type crystal structure is highly likely to be unstable.
Thus, the repeated high-voltage charging and discharging break the crystal structure of lithium cobaltate. The break of the crystal structure degrades the cycle performance. This is probably because the break of the crystal structure reduces sites where lithium can stably exist and makes it difficult to insert and extract lithium.
In this embodiment, examples of materials that can be used for a secondary battery containing the positive electrode active material 100 described in
The positive electrode includes a positive electrode active material layer and a positive electrode current collector.
The positive electrode active material layer includes a positive electrode active material particle. The positive electrode active material layer may contain a conductive additive and a binder.
As the positive electrode active material particle, the positive electrode active material 100 can be used. As the positive electrode active material 100, the lithium composite oxide described in the above embodiment, such as a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 and the positive electrode active material 100A-1, can be used. In the chemical formula, it is preferable to satisfy 0<x+a≤0.015 and 0<y+b≤0.06. A secondary battery with the compound hardly deteriorates and thus has good safety.
Examples of the conductive additive include a carbon material, a metal material, and a conductive ceramic material. Alternatively, a fiber material may be used as the conductive additive. The content of the conductive additive to the total amount of the active material layer is preferably greater than or equal to 1 wt % and less than or equal to 10 wt %, further preferably greater than or equal to 1 wt % and less than or equal to 5 wt %.
A network for electric conduction can be formed in the electrode by the conductive additive. The conductive additive also allows the maintenance of a path for electric conduction between the positive electrode active materials. The addition of the conductive additive to the active material layer increases the electric conductivity of the active material layer.
Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fiber. As carbon fiber, mesophase pitch-based carbon fiber and isotropic pitch-based carbon fiber can be used. Furthermore, as carbon fiber, carbon nanofiber and carbon nanotube can be used. Carbon nanotube can be formed by, for example, a vapor deposition method. Other examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite (black lead) particles, graphene, and fullerene. Alternatively, metal powder or metal fibers of copper, nickel, aluminum, silver, gold, or the like, a conductive ceramic material, or the like can be used.
Alternatively, a graphene compound may be used as the conductive additive.
A graphene compound has excellent electrical characteristics of high conductivity and excellent physical properties of high flexibility and high mechanical strength in some cases. Furthermore, a graphene compound has a planar shape. A graphene compound enables low-resistance surface contact. Furthermore, a graphene compound has extremely high conductivity even with a small thickness in some cases and thus allows a conductive path to be formed in an active material layer efficiently even with a small amount. Thus, a graphene compound is preferably used as the conductive additive, in which case the area where the active material and the conductive additive are in contact with each other can be increased. In addition, the graphene compound is preferable because electrical resistance can be reduced in some cases. Here, it is particularly preferable to use, for example, graphene, multilayer graphene, graphene quantum dot, or reduced graphene oxide (hereinafter, RGO) as a graphene compound. Note that RGO refers to a compound obtained by reducing graphene oxide (GO), for example.
In the case where an active material particle with a small particle diameter (e.g., 1 μm or less) is used, the specific surface area of the active material particle is large and thus more conductive paths for connecting the active material particles are needed. In such a case, a graphene compound that can efficiently form a conductive path even in a small amount is particularly preferably used.
A cross-sectional structure example of an active material layer 200 containing a graphene compound as a conductive additive is described below.
The longitudinal cross section of the active material layer 200 in
Here, the plurality of graphene compounds are bonded to each other to form a net-like graphene compound sheet (hereinafter, referred to as a graphene compound net or a graphene net). The graphene net covering the active material can function as a binder for bonding active materials. The amount of binder can thus be reduced, or the binder does not have to be used. This can increase the proportion of the active material in the electrode volume or the electrode weight. That is to say, the capacity of the power storage device can be increased.
Here, it is preferable to perform reduction after a layer to be the active material layer 200 is formed in such a manner that graphene oxide is used as the graphene compound 201 and mixed with an active material. When graphene oxide with extremely high dispersibility in a polar solvent is used for the formation of the graphene compounds 201, the graphene compounds 201 can be substantially uniformly dispersed in the active material layer 200. The solvent is removed by volatilization from a dispersion medium containing the uniformly-dispersed graphene oxide to reduce the graphene oxide; hence, the graphene compounds 201 remaining in the active material layer 200 are partly overlap with each other and are dispersed such that surface contact is made, thereby forming a three-dimensional conduction path. Note that graphene oxide can be reduced either by heat treatment or with the use of a reducing agent, for example.
Unlike a particle of conductive additive such as acetylene black, which makes point contact with an active material, the graphene compound 201 is capable of making low-resistance surface contact; accordingly, the electrical conduction between the particles of the positive electrode active material 100 and the graphene compound 201 can be improved with a smaller amount of the graphene compound 201 than that of a normal conductive additive. This can increase the proportion of the positive electrode active material 100 in the active material layer 200. This can increase discharge capacity of the power storage device.
As the binder, a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer can be used, for example. Alternatively, fluororubber can be used as the binder.
For the binder, for example, water-soluble polymers are preferably used. As the water-soluble polymers, for example, a polysaccharide can be used. As the polysaccharide, for example, a cellulose derivative such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose or starch can be used. It is further preferred that such water-soluble polymers be used in combination with any of the above rubber materials.
Alternatively, as the binder, a material such as polystyrene, poly(methyl acrylate), poly(methyl methacrylate) (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene-propylene-diene polymer, polyvinyl acetate, or nitrocellulose is preferably used.
A plurality of the above materials may be used in combination for the binder.
For example, a material having a significant viscosity modifying effect and another material may be used in combination. For example, a rubber material or the like has high adhesion or high elasticity but may have difficulty in viscosity modification when mixed in a solvent. In such a case, a rubber material or the like is preferably mixed with a material having a significant viscosity modifying effect, for example. As a material having a significant viscosity modifying effect, for example, a water-soluble polymer is preferably used. An example of a water-soluble polymer having an especially significant viscosity modifying effect is the above-mentioned polysaccharide; for example, a cellulose derivative such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, or regenerated cellulose, or starch can be used.
Note that a cellulose derivative such as carboxymethyl cellulose obtains a higher solubility when converted into a salt such as a sodium salt or an ammonium salt of carboxymethyl cellulose, and accordingly, easily exerts an effect as a viscosity modifier. The high solubility can also increase the dispersibility of an active material and other components in the formation of slurry for an electrode. In this specification, cellulose and a cellulose derivative used as a binder of an electrode include salts thereof.
The water-soluble polymers stabilize viscosity by being dissolved in water and allow stable dispersion of the active material and another material combined as a binder, such as styrene-butadiene rubber, in an aqueous solution. Furthermore, a water-soluble polymer is expected to be easily and stably adsorbed to an active material surface because it has a functional group. Many cellulose derivatives such as carboxymethyl cellulose have functional groups such as a hydroxyl group and a carboxyl group. Because of functional groups, polymers are expected to interact with each other and cover an active material surface in a large area.
In the case where the binder covering or being in contact with the active material surface forms a film, the film is expected to serve as a passivation film to suppress the decomposition of the electrolyte solution. Here, the passivation film refers to a film without electronic conductivity or a film with extremely low electric conductivity, and can suppress the decomposition of an electrolyte solution at a potential at which a battery reaction occurs in the case where the passivation film is formed on the active material surface, for example. It is preferred that the passivation film can conduct lithium ions while suppressing electric conduction.
The positive electrode current collector can be formed using a material that has high conductivity, such as a metal like stainless steel, gold, platinum, aluminum, and titanium, or an alloy thereof. It is preferred that a material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Alternatively, it is possible to use an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added. Still alternatively, the positive electrode current collector may be formed using a metal element that forms silicide by reacting with silicon. Examples of the metal element that forms silicide by reacting with silicon include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can have any of various shapes including a foil-like shape, a plate-like shape (sheet-like shape), a net-like shape, a punching-metal shape, and an expanded-metal shape. The current collector preferably has a thickness of greater than or equal to 5 μm and less than or equal to 30 μm.
The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may contain a conductive additive and a binder.
As a negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.
For the negative electrode active material, an element that enables charge-discharge reactions by an alloying reaction and a dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, and the like can be used. Such elements have higher capacity than carbon. In particular, silicon has a high theoretical capacity of 4200 mAh/g. For this reason, silicon is preferably used as the negative electrode active material. Alternatively, a compound containing any of the above elements may be used. Examples of the compound include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, an element that enables charge-discharge reactions by an alloying reaction and a dealloying reaction with lithium and a compound containing the element, for example, may be referred to as an alloy-based material.
In this specification and the like, SiO refers, for example, to silicon monoxide. Note that SiO can alternatively be expressed as SiOx. Here, x preferably has an approximate value of 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less.
As the carbon-based material, graphite, graphitizing carbon (soft carbon), non-graphitizing carbon (hard carbon), carbon nanotube, graphene, carbon black, and the like may be used.
Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include meso-carbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. As artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB is preferably used because it may have a spherical shape. Moreover, MCMB may preferably be used because it is relatively easy to have a small surface area. Examples of natural graphite include flake graphite and spherical natural graphite.
Graphite has a low potential substantially equal to that of a lithium metal (higher than or equal to 0.05 V and lower than or equal to 0.3 V vs. Li/Li+) when lithium ions are intercalated into graphite (while a lithium-graphite intercalayer compound is formed). For this reason, a lithium-ion secondary battery can have a high operating voltage. In addition, graphite is preferred because of its advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher level of safety than that of a lithium metal.
Alternatively, for the negative electrode active material, oxide such as titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O12), lithium-graphite intercalation compound (LixC6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), or molybdenum oxide (MoO2) can be used.
Still alternatively, for the negative electrode active material, Li3-xMxN (M=Co, Ni, or Cu) with a Li3N structure, which is a nitride containing lithium and a transition metal, can be used. For example, Li2.6Co0.4N3 is preferable because of high charge and discharge capacity (900 mAh/g and 1890 mAh/cm3).
A nitride containing lithium and a transition metal is preferably used, in which case lithium ions are contained in the negative electrode active material and thus the negative electrode active material can be used in combination with a material for a positive electrode active material which does not contain lithium ions, such as V2O5 or Cr3O8. Note that in the case of using a material containing lithium ions as a positive electrode active material, the nitride containing lithium and a transition metal can be used for the negative electrode active material by extracting the lithium ions contained in the positive electrode active material in advance.
Alternatively, a material that causes a conversion reaction can be used for the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used. Other examples of the material that causes a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, sulfides such as CoS0.89, NiS, and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.
For the conductive additive and the binder that can be included in the negative electrode active material layer, materials similar to those of the conductive additive and the binder that can be included in the positive electrode active material layer can be used.
For the negative electrode current collector, a material similar to that of the positive electrode current collector can be used. Note that a material which is not alloyed with carrier ions such as lithium is preferably used for the negative electrode current collector.
The electrolyte solution contains a solvent and an electrolyte. As the solvent of the electrolyte solution, an aprotic organic solvent is preferably used. For example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone can be used, or two or more of these solvents can be used in an appropriate combination in an appropriate ratio.
The use of one or more kinds of ionic liquids (room temperature molten salts) which have non-flammability and non-volatility as a solvent of the electrolyte solution can prevent a power storage device from exploding or catching fire even when the power storage device internally shorts out or the internal temperature increases owing to overcharging or the like. An ionic liquid contains a cation and an anion, specifically, an organic cation and an anion. Examples of the organic cation used for the electrolyte solution include aliphatic onium cations such as a quaternary ammonium cation, a tertiary sulfonium cation, and a quaternary phosphonium cation, and aromatic cations such as an imidazolium cation and a pyridinium cation. Examples of the anion used for the electrolyte solution include a monovalent amide-based anion, a monovalent methide-based anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, and a perfluoroalkylphosphate anion.
As an electrolyte dissolved in the above-described solvent, one of lithium salts such as LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B10Cl10, Li2B12Cl12, LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2) (CF3SO2), and LiN(C2F5SO2)2 can be used, or two or more of these lithium salts can be used in an appropriate combination in an appropriate ratio.
The electrolyte solution used for a power storage device is preferably highly purified and contains a small amount of dust particles and elements other than the constituent elements of the electrolyte solution (hereinafter, also simply referred to as impurities). Specifically, the weight ratio of impurities to the electrolyte solution is less than or equal to 1%, preferably less than or equal to 0.1%, further preferably less than or equal to 0.01%.
Furthermore, an additive agent such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or a dinitrile compound such as succinonitrile or adiponitrile may be added to the electrolyte solution. The concentration of the additive agent in the whole solvent is, for example, higher than or equal to 0.1 weight % and lower than or equal to 5 weight %.
Alternatively, a polymer gelled electrolyte obtained in such a manner that a polymer is swelled with an electrolyte solution may be used.
When a polymer gel electrolyte is used, safety against liquid leakage and the like is improved. Furthermore, a secondary battery can be thinner and more lightweight.
As a polymer that undergoes gelation, a silicone gel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide-based gel, a polypropylene oxide-based gel, a fluorine-based polymer gel, or the like can be used. Examples of the polymer include a polymer having a polyalkylene oxide structure, such as polyethylene oxide (PEO); PVDF; polyacrylonitrile; and a copolymer containing any of them. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP) can be used. The formed polymer may be porous.
Instead of the electrolyte solution, a solid electrolyte including an inorganic material such as a sulfide-based inorganic material or an oxide-based inorganic material, or a solid electrolyte including a high-molecular material such as a PEO (polyethylene oxide)-based high-molecular material may alternatively be used. When the solid electrolyte is used, a separator and a spacer are not necessary. Furthermore, the battery can be entirely solidified; therefore, there is no possibility of liquid leakage and thus the safety of the battery is dramatically increased.
In this embodiment, examples of a shape of a secondary battery containing the positive electrode active material 100 described in the above embodiment are described. For the materials used for the secondary battery described in this embodiment, the description of the above embodiment can be referred to.
First, an example of a coin secondary battery is described.
In a coin secondary battery 300, a positive electrode can 301 doubling as a positive electrode terminal and a negative electrode can 302 doubling as a negative electrode terminal are insulated from each other and sealed by a gasket 303 made of polypropylene or the like. A positive electrode 304 includes a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector 305. A negative electrode 307 includes a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector 308.
Note that only one surface of each of the positive electrode 304 and the negative electrode 307 used for the coin secondary battery 300 is provided with an active material layer.
For the positive electrode can 301 and the negative electrode can 302, a metal having corrosion resistance to an electrolyte solution, such as nickel, aluminum, or titanium, an alloy of such metals, or an alloy of such a metal and another metal (e.g., stainless steel) can be used. Alternatively, the positive electrode can 301 and the negative electrode can 302 are preferably covered with nickel, aluminum, or the like in order to prevent corrosion due to the electrolyte solution. The positive electrode can 301 and the negative electrode can 302 are electrically connected to the positive electrode 304 and the negative electrode 307, respectively.
The negative electrode 307, the positive electrode 304, and a separator 310 are immersed in the electrolyte solution. Then, as shown in
When the positive electrode active material particle described in the above embodiment is used in the positive electrode 304, the coin secondary battery 300 with little deterioration and high safety can be obtained.
The secondary battery preferably includes a separator. As the separator, for example, fiber containing cellulose such as paper; nonwoven fabric; glass fiber; ceramics; synthetic fiber using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane; or the like can be used. The separator is preferably formed to have an envelope-like shape to wrap one of the positive electrode and the negative electrode.
The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, a mixture thereof, or the like. Examples of the ceramic-based material include aluminum oxide particles and silicon oxide particles. Examples of the fluorine-based material include PVDF and polytetrafluoroethylene. Examples of the polyamide-based material include nylon and aramid (meta-based aramid and para-based aramid).
Deterioration of the separator in charging and discharging at a high voltage can be suppressed and thus the reliability of the secondary battery can be improved because oxidation resistance is improved when the separator is coated with the ceramic-based material. In addition, when the separator is coated with the fluorine-based material, the separator is easily brought into close contact with an electrode, resulting in high output characteristics. When the separator is coated with the polyamide-based material, in particular, aramid, the safety of the secondary battery is improved because heat resistance is improved.
For example, both surfaces of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid. Alternatively, a surface of the polypropylene film that is in contact with the positive electrode may be coated with the mixed material of aluminum oxide and aramid, and a surface of the polypropylene film that is in contact with the negative electrode may be coated with the fluorine-based material.
With the use of a separator having a multilayer structure, the capacity per volume of the secondary battery can be increased because the safety of the secondary battery can be maintained even when the total thickness of the separator is small.
Examples of cylindrical secondary batteries are described with reference to
Since a positive electrode and a negative electrode that are used for a cylindrical storage battery are wound, active materials are preferably formed on both surfaces of a current collector. A positive electrode terminal (positive electrode current collecting lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collecting lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be formed using a metal material such as aluminum. The positive electrode terminal 603 and the negative electrode terminal 607 are resistance-welded to a safety valve mechanism 612 and the bottom of the battery can 602, respectively. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 through a positive temperature coefficient (PTC) element 611. The safety valve mechanism 612 cuts off electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611, which serves as a thermally sensitive resistor whose resistance increases as temperature rises, limits the amount of current by increasing the resistance, in order to prevent abnormal heat generation. Barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used for the PTC element.
Alternatively, as shown in
When the positive electrode active material 100 described in the above embodiment is used in the positive electrode 604, the cylindrical secondary battery 600 with little deterioration and high safety can be obtained.
Other structural examples of power storage devices are described with reference to
The circuit board 900 includes a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 951, the terminal 952, the antenna 914, the antenna 915, and the circuit 912. Note that a plurality of terminals 911 may be provided and each of the plurality of terminals 911 may serve as a control signal input terminal, a power supply terminal, and the like.
The circuit 912 may be provided on the rear surface of the circuit board 900. Note that the shapes of the antenna 914 and the antenna 915 are not limited to coil shapes, and may be linear shapes or plate shapes, for example. An antenna such as a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic-field antenna, or a dielectric antenna may be used. Alternatively, the antenna 914 or the antenna 915 may be a flat-plate conductor. This flat-plate conductor can serve as one of conductors for electric field coupling. That is, the antenna 914 or the antenna 915 may serve as one of two conductors of a capacitor. Thus, electric power can be transmitted and received not only by an electromagnetic field or a magnetic field but also by an electric field.
The line width of the antenna 914 is preferably larger than the line width of the antenna 915. This makes it possible to increase the amount of power received by the antenna 914.
The power storage device includes a layer 916 between the secondary battery 913, and the antenna 914 and the antenna 915. The layer 916 has a function of, for example, blocking an electromagnetic field from the secondary battery 913. As the layer 916, for example, a magnetic body can be used.
Note that the structure of the power storage device is not limited to that shown in
For example, as shown in FIG. 10A1 and FIG. 10A2, an antenna may be provided for each of a pair of opposing surfaces of the secondary battery 913 shown in
As shown in FIG. 10A1, the antenna 914 is provided on one of the pair of surfaces of the secondary battery 913 with the layer 916 located therebetween, and as shown in FIG. 10A2, an antenna 915 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 located therebetween. The layer 917 has a function of, for example, blocking an electromagnetic field from the secondary battery 913. As the layer 917, for example, a magnetic body can be used.
With the above structure, both the antenna 914 and the antenna 915 can be increased in size.
Alternatively, as shown in FIG. 10B1 and FIG. 10B2, a pair of opposing surfaces of the secondary battery 913 in
As shown in FIG. 10B1, the antenna 914 and the antenna 915 are provided on one of the opposing surfaces of the secondary battery 913 with the layer 916 interposed therebetween, and as shown in FIG. 10B2, an antenna 918 is provided on the other of the opposing surfaces of the secondary battery 913 with the layer 917 interposed therebetween. The antenna 918 has a function of communicating data with an external device, for example. An antenna with a shape that can be applied to the antenna 914 and the antenna 915, for example, can be used as the antenna 918. As a system for communication using the antenna 918 between the power storage device and another device, a response method that can be used between the power storage device and another device, such as NFC, can be employed.
Alternatively, as shown in
The display device 920 may display, for example, an image showing whether charging is being carried out, an image showing the amount of stored power, or the like. As the display device 920, electronic paper, a liquid crystal display device, an electroluminescent (EL) display device, or the like can be used. For example, the use of electronic paper can reduce power consumption of the display device 920.
Alternatively, as shown in
The sensor 921 has a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays. With the sensor 921, for example, data on an environment (e.g., temperature) where the storage device is placed can be determined and stored in a memory inside the circuit 912.
Furthermore, structure examples of the secondary battery 913 are described using
The secondary battery 913 shown in
Note that as shown in
For the housing 930a, an insulating material such as an organic resin can be used. In particular, when a material such as an organic resin is used for the side on which an antenna is formed, blocking of an electric field from the secondary battery 913 can be inhibited. When an electric field is not significantly blocked by the housing 930a, an antenna such as the antenna 914 and the antenna 915 may be provided inside the housing 930a. For the housing 930b, a metal material can be used, for example.
The negative electrode 931 is connected to the terminal 911 shown in
When the positive electrode active material particle described in the above embodiment is used in the positive electrode 932, the secondary battery 913 with little deterioration and high safety can be obtained.
Next, examples of laminated secondary batteries are described with reference to
A laminated secondary battery 980 is described using
Note that the number of stacks each including the negative electrode 994, the positive electrode 995, and the separator 996 may be determined as appropriate depending on required capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) through one of a lead electrode 997 and a lead electrode 998. The positive electrode 995 is connected to a positive electrode current collector (not shown) through the other of the lead electrode 997 and the lead electrode 998.
As shown in
For the film 981 and the film 982 having a depressed portion, a metal material such as aluminum or a resin material can be used, for example. With the use of a resin material for the film 981 and the film 982 having a depressed portion, the film 981 and the film 982 having a depressed portion can be changed in their forms when external force is applied; thus, a flexible storage battery can be formed.
Although
When the positive electrode active material particle described in the above embodiment is used in the positive electrode 995, the secondary battery 980 with little deterioration and high safety can be obtained.
In addition,
A laminated secondary battery 500 shown in
In the laminated secondary battery 500 shown in
As the exterior body 509 of the laminated secondary battery 500, for example, a laminate film having a three-layer structure can be employed in which a highly flexible metal thin film of aluminum, stainless steel, copper, nickel, or the like is provided over a film formed of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film of a polyamide-based resin, a polyester-based resin, or the like is provided over the metal thin film as the outer surface of the exterior body.
In
Here, an example of a method of manufacturing the laminated secondary battery whose external view is shown in
First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked.
After that, the negative electrode 506, the separator 507, and the positive electrode 503 are placed over the exterior body 509.
Subsequently, the exterior body 509 is folded along a dashed line as shown in
Next, the electrolyte solution 508 is introduced into the inside of the exterior body 509 from the inlet provided for the exterior body 509. The electrolyte solution 508 is preferably introduced in a reduced pressure atmosphere or in an inert gas atmosphere. Lastly, the inlet is sealed by bonding. In this manner, the secondary battery 500 that is a laminated secondary battery can be manufactured.
When the positive electrode active material particle described in the above embodiment is used in the positive electrode 503, the secondary battery 500 with little deterioration and high safety can be obtained.
Next, examples of bendable secondary batteries are described with reference to
The positive electrode 211a and the negative electrode 211b included in the secondary battery 250 are described with reference to
As shown in
The positive electrodes 211a and the negative electrodes 211b are stacked so that surfaces of the positive electrodes 211a on each of which the positive electrode active material layer is not formed are in contact with each other and that surfaces of the negative electrodes 211b on each of which the negative electrode active material is not formed are in contact with each other.
Furthermore, the separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material is formed and the surface of the negative electrode 211b on which the negative electrode active material is formed. In
In addition, as shown in
Next, the exterior body 251 is described with reference to FIG. 19B1, FIG. 19B2,
The exterior body 251 has a film-like shape and is folded in half so as to sandwich the positive electrodes 211a and the negative electrodes 211b. The exterior body 251 includes a folded portion 261, a pair of seal portions 262, and a seal portion 263. The pair of seal portions 262 is provided with the positive electrodes 211a and the negative electrodes 211b positioned therebetween and thus can also be referred to as side seals. The seal portion 263 includes portions overlapping with the lead 212a and the lead 212b and can also be referred to as a top seal.
Part of the exterior body 251 that overlaps with the positive electrodes 211a and the negative electrodes 211b preferably has a wave shape in which crest lines 271 and trough lines 272 are alternately arranged. The seal portions 262 and the seal portion 263 of the exterior body 251 are preferably flat.
FIG. 19B1 is a cross section cut along a portion overlapping with the crest line 271, and FIG. 19B2 is a cross section cut along a portion overlapping with the trough line 272. FIG. 19B1 and FIG. 19B2 correspond to cross sections of the battery 250, the positive electrodes 211a, and the negative electrodes 211b in the width direction.
Here, the distance between end portions of the positive electrode 211a and the negative electrode 211b in the width direction and the seal portion 262, that is, the distance between the end portions of the positive electrode 211a and the negative electrode 211b and the seal portion 262 is referred to as a distance La. When the battery 250 changes in shape, for example, is bent, the positive electrode 211a and the negative electrode 211b change in shape such that the positions thereof are shifted from each other in the length direction as described later. At the time, if the distance La is too short, the exterior body 251 and the positive electrode 211a and the negative electrode 211b are rubbed hard against each other, so that the exterior body 251 is damaged in some cases. In particular, when a metal film of the exterior body 251 is exposed, the metal film might be corroded by the electrolyte solution. Therefore, the distance La is preferably set as long as possible. However, if the distance La is too long, the volume of the battery 250 is increased.
The distance La between the positive and negative electrodes 211a and 211b and the seal portion 262 is preferably increased as the total thickness of the stacked positive electrodes 211a and negative electrodes 211b is increased.
More specifically, when the total thickness of the stacked positive electrodes 211a and negative electrodes 211b is referred to as a thickness t, the distance La is preferably 0.8 times or more and 3.0 times or less, further preferably 0.9 times or more and 2.5 times or less, still further preferably 1.0 times or more and 2.0 times or less as large as the thickness t. When the distance La is in the above range, a compact battery highly reliable for bending can be obtained.
Furthermore, when the distance between the pair of seal portions 262 is referred to as a distance Lb, it is preferred that the distance Lb be sufficiently longer than the widths of the positive electrode 211a and the negative electrode 211b (here, a width Wb of the negative electrode 211b). In this case, even when the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251 by change in the shape of the battery 250 such as repeated bending, the position of part of the positive electrode 211a and the negative electrode 211b can be shifted in the width direction; thus, the positive and negative electrodes 211a and 211b and the exterior body 251 can be effectively prevented from being rubbed against each other.
For example, the difference between the distance La between the pair of seal portions 262 and the width Wb of the negative electrode 211b is preferably 1.6 times or more and 6.0 times or less, further preferably 1.8 times or more and 5.0 times or less, still further preferably 2.0 times or more and 4.0 times or less as large as the total thickness t of the positive electrode 211a and the negative electrode 211b.
In other words, the distance Lb, the width Wb, and the thickness t preferably satisfy the relationship of Formula 7 below.
Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, further preferably 1.0 or more and 2.0 or less.
When the battery 250 is bent, part of the exterior body 251 positioned on the outer side in bending is stretched and the other part positioned on the inner side changes its shape as it is squashed. More specifically, the part of the exterior body 251 positioned on the outer side in bending changes its shape such that the wave amplitude becomes smaller and the length of the wave period becomes larger. In contrast, the part of the exterior body 251 positioned on the inner side changes its shape such that the wave amplitude becomes larger and the length of the wave period becomes smaller. When the exterior body 251 changes its shape in this manner, stress applied to the exterior body 251 with bending is relieved, so that a material itself of the exterior body 251 does not need to be stretched or squashed. As a result, the battery 250 can be bent with weak force without damage to the exterior body 251.
Furthermore, as shown in
Furthermore, the space 273 is provided between the positive electrode 211a and the negative electrode 211b and the exterior body 251, whereby the positive electrode 211a and the negative electrode 211b located on an inner side can be shifted relatively without being in contact with the exterior body 251 when the battery 250 is bent.
In the battery 250 shown in
In this embodiment, examples of electronic devices each including the secondary battery of one embodiment of the present invention are described.
First,
In addition, a flexible secondary battery can be incorporated along a curved inside/outside wall surface of a house or a building or a curved interior/exterior surface of an automobile.
The portable information terminal 7200 is capable of executing a variety of applications such as mobile phone calls, e-mailing, viewing and editing texts, music reproduction, Internet communication, and a computer game.
The display surface of the display portion 7202 is curved, and images can be displayed on the curved display surface. In addition, the display portion 7202 includes a touch sensor, and operation can be performed by touching the screen with a finger, a stylus, or the like. For example, by touching an icon 7207 displayed on the display portion 7202, application can be started.
With the operation button 7205, a variety of functions such as time setting, power on/off, on/off of wireless communication, setting and cancellation of a silent mode, and setting and cancellation of a power saving mode can be performed. For example, the functions of the operation button 7205 can be set freely by setting the operation system incorporated in the portable information terminal 7200.
The portable information terminal 7200 can employ near field communication that is a communication method based on an existing communication standard. In that case, for example, mutual communication between the portable information terminal 7200 and a headset capable of wireless communication can be performed, and thus hands-free calling is possible.
Moreover, the portable information terminal 7200 includes the input/output terminal 7206, and data can be directly transmitted to and received from another information terminal through a connector. In addition, charging with the input/output terminal 7206 is possible. Note that the charging operation may be performed by wireless power feeding without using the input/output terminal 7206.
The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. For example, the secondary battery 7104 shown in
The portable information terminal 7200 preferably includes a sensor. As the sensor, for example, a human body sensor such as a fingerprint sensor, a pulse sensor, or a body temperature sensor, a touch sensor, a pressure sensitive sensor, or an acceleration sensor is preferably mounted.
The display surface of the display portion 7304 is curved, and images can be displayed on the curved display surface. A display state of the display device 7300 can be changed by, for example, near field communication, which is a communication method based on an existing communication standard.
The display device 7300 includes an input/output terminal, and data can be directly transmitted to and received from another information terminal with a connector. In addition, charging with the input/output terminal is possible. Note that the charge operation may be performed by wireless power feeding without using the input/output terminal.
Next,
The tablet terminal 9600 includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 is provided across the housing 9630a and the housing 9630b over the movable portion 9640.
Part of the display portion 9631 can be a touch panel region and data can be input when a displayed operation key is touched. When a position where a keyboard display switching button is displayed on the touch panel is touched with a finger, a stylus, or the like, keyboard buttons can be displayed on the display portion 9631.
The display mode changing switch 9626 can switch the display between a portrait mode and a landscape mode, and between monochrome display and color display, for example. With the power saving mode changing switch 9625, display luminance can be optimized in accordance with the amount of external light in use, which is detected with an optical sensor incorporated in the tablet terminal 9600. Another detection device including a sensor for detecting inclination, such as a gyroscope sensor or an acceleration sensor, may be incorporated in the tablet terminal, in addition to the optical sensor.
The tablet terminal is closed in
Note that the tablet terminal 9600 can be folded in half, thus, the tablet terminal 9600 can be folded so that the housing 9630a and the housing 9630b overlap with each other when not in use. Thus, the display portion 9631 can be protected owing to the holding, which increases the durability of the tablet terminal 9600. With the power storage unit 9635 including the secondary battery of one embodiment of the present invention which has high capacity and excellent cycle characteristics, the tablet terminal which can be used for a long time for a long period can be provided.
The tablet terminal shown in
The solar cell 9633, which is attached on the surface of the tablet terminal, supplies electric power to a touch panel, a display portion, an image signal processor, and the like. Note that the solar cell 9633 can be provided on one surface or both surfaces of the housing 9630 and the power storage unit 9635 can be charged efficiently.
The structure and operation of the charging-discharging control circuit 9634 shown in
First, an operation example in which electric power is generated by the solar cell 9633 using external light is described. The voltage of electric power generated by the solar cell is raised or lowered by the DC-DC converter 9636 to a voltage for charging the power storage unit 9635. When the display portion 9631 is operated with the electric power from the solar cell 9633, the switch SW1 is turned on and the voltage is raised or lowered by the converter 9637 to a voltage needed for the display portion 9631. When display on the display portion 9631 is not performed, the switch SW1 is turned off and the switch SW2 is turned on, so that the power storage unit 9635 is charged.
Note that the solar cell 9633 is described as an example of a power generation unit; however, one embodiment of the present invention is not limited to this example. The power storage unit 9635 may be charged using another power generation unit such as a piezoelectric element or a thermoelectric conversion element (Peltier element). For example, the charging may be performed with a non-contact power transmission module that performs charging by transmitting and receiving power wirelessly (without contact), or with a combination of other charging units.
A semiconductor display device such as a liquid crystal display device, a light-emitting device in which a light-emitting element such as an organic EL element is provided in each pixel, an electrophoresis display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display) can be used for the display portion 8002.
Note that the display device includes, in its category, all of information display devices for personal computers, advertisement displays, and the like besides TV broadcast reception.
In
Note that although the installation lighting device 8100 provided in the ceiling 8104 is shown in
As the light source 8102, an artificial light source that emits light artificially by using electric power can be used. Specifically, an incandescent lamp, a discharge lamp such as a fluorescent lamp, and light-emitting elements such as an LED and an organic EL element are given as examples of the artificial light source.
In
Note that although the split-type air conditioner including the indoor unit and the outdoor unit is illustrated in
In
In addition, in a time period when electronic devices are not used, particularly when the proportion of the amount of electric power which is actually used to the total amount of electric power which can be supplied from a commercial power supply source (such a proportion is referred to as a usage rate of electric power) is low, electric power is stored in the secondary battery, whereby the usage rate of electric power can be reduced in a time period other than the above time period. For example, in the case of the electric refrigerator-freezer 8300, electric power is stored in the secondary battery 8304 in night time when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed. On the other hand, in daytime when the temperature is high and the refrigerator door 8302 and the freezer door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power supply; thus, the usage rate of electric power in daytime can be reduced.
The secondary battery of one embodiment of the present invention can be used in a variety of electronic devices as well as the above electronic devices. According to one embodiment of the present invention, the secondary battery can have little deterioration and high safety. Thus, when the secondary battery of one embodiment of the present invention is used in the electronic devices described in this embodiment, electronic devices with longer lifetime and higher safety can be obtained. This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment, examples of vehicles each including the secondary battery of one embodiment of the present invention are described.
The use of secondary batteries in vehicles enables production of next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).
The secondary battery can also supply electric power to a display device included in the automobile 8400, such as a speedometer or a tachometer. Furthermore, the secondary battery can supply electric power to a semiconductor device included in the automobile 8400, such as a navigation system.
Furthermore, although not shown, the vehicle may include a power receiving device so that it can be charged by being supplied with electric power from an above-ground power transmitting device in a contactless manner. In the case of the contactless power feeding system, by fitting a power transmitting device in a road or an exterior wall, charging can be performed not only when the vehicle is stopped but also when driven. In addition, the contactless charging system may be utilized to perform transmission and reception of electric power between vehicles. Furthermore, a solar cell may be provided in the exterior of the vehicle to charge the secondary battery when the vehicle stops or moves. To supply electric power in such a contactless manner, an electromagnetic induction method or a magnetic resonance method can be used.
Furthermore, in the motor scooter 8600 shown in
According to one embodiment of the present invention, the secondary battery can have little deterioration and high safety. Thus, when the secondary battery is mounted on a vehicle, a reduction in mileage, acceleration performance, or the like can be inhibited. In addition, a highly safe vehicle can be achieved. Furthermore, the secondary battery included in the vehicle can be used as a power source for supplying electric power to products other than the vehicle. In such a case, the use of a commercial power supply can be avoided at peak time of electric power demand, for example. Avoiding the use of a commercial power supply at peak time of electric power demand can contribute to energy saving and reduction in carbon dioxide emissions. Moreover, the secondary battery with little deterioration and high safety can be used for a long period; thus, the use amount of rare metals such as cobalt can be reduced.
This embodiment can be implemented in appropriate combination with the other embodiments.
In this example, an analysis of substitution positions of a Ni atom and a Mg atom in a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is described.
Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 is a compound in which Mg and Ni are added to LiCoO2 as substitution elements. When the one Mg atom and the one Ni atom are substituted for metal atoms contained in LiCoO2, combinations of substitution sites are presumably the above combinations. These are described again below.
Li in the same Li layer are substituted by Mg and Ni: Condition (A).
Li in different Li layers are substituted by Mg and Ni: Condition (B).
Co in the same Co layer are substituted by Mg and Ni: Condition (C).
Co in different Co layers are substituted by Mg and Ni: Condition (D).
Li in a Li layer is substituted by Mg and Co in a Co layer is substituted by Ni: Condition (E).
Li in a Li layer is substituted by Ni and Co in a Co layer is substituted by Mg: Condition (F).
As for the combinations of the substitution sites above, the stabilization energy ΔE of the combinations in which Ni and Mg have a relation of the first proximity to the third or the fourth proximity was calculated using Formulae 1 to 3. The calculation conditions of LiCoO2 are shown in Table 1 and the calculation results of ΔE are shown in
Note that VSAP in Table 1 shows Vienna Ab initio Simulation Package (bought from VASP Software GmbH).
[Calculation of Stabilization Energy (ΔEC) when Cation Occupancy of Li Sites is Changed]
ΔEC was calculated to estimate energy change in charging. According to
According to
The above results suggest that in a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2, Mg and Ni are substituted for a Li site and a Co site respectively immediately after the synthesis, and Ni moves to a Li site to relax instability through charging. That is, it is suggested that the substitution position of Ni changed between before and after charging. In other words, it is suggested that the event of a Ni movement from a Co site to a Li site by charging occurred.
To confirm whether the event of a Ni movement from a Co site to a Li site by charging actually occurs or not, a compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 was made and charge-discharge efficiency of a secondary battery using the compound was measured.
<Making of a Compound Represented by Chemical Formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2>
A compound represented by the chemical formula Li(1−x−y)Co(1−a−b)Ni(x+a)Mg(y+b)O2 was made as the positive electrode active material 100A-1 with reference to the flowchart in
First, the mixture 902 containing magnesium and fluorine was formed (Step S11 to Step S14). First, LiF and MgF2 were weighted so that the molar ratio of LiF to MgF2 was LiF:MgF2=1:3, acetone was added as a solvent, and the materials were mixed and ground by a wet process. The mixing and the grinding were performed in a ball mill using a zirconia ball at 400 rpm for 12 hour. The material that has been subjected to the treatment was collected to be the mixture 902.
Next, nickel hydroxide, which is a metal source, and acetone were mixed to form pulverized nickel hydroxide (Step S15 to Step S17).
Next, lithium cobaltate was prepared as a composite oxide containing lithium and cobalt. Specifically, CELLSEED C-10N manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. was prepared (Step S25).
Next, in Step S31, the materials were weighed so that the number of atoms of magnesium in the mixture 902 was 2.0 mol % of the number of atoms of cobalt in the lithium cobaltate. The mixing was performed by a dry method. The mixing was performed in a ball mill using a zirconia ball at 150 rpm for 1 hour.
Next, each of the mixtures 903 was put in an alumina crucible and annealed at 850° C. using a muffle furnace in an oxygen atmosphere for 60 hours (Step S34). At the time of annealing, the alumina crucible was covered with a lid. The flow rate of oxygen was 10 L/min. The temperature rise was 200° C./hr, and it took longer than or equal to 10 hours to lower the temperature. The material subjected to the heat treatment was collected and filtered (Step S35), and the mixture 904 was obtained (Step S36).
Next, nickel hydroxide, which is a metal source, and acetone were mixed to form pulverized nickel hydroxide (Step S15 to Step S17).
Next, in Step S50, nickel hydroxide and the mixture 903 were weighed so that the number of nickel atoms contained in nickel hydroxide was w mol % of the sum of the number of cobalt atoms and the number of nickel atoms contained in the mixture 903. Each sample has different w, as shown in Table 2 below. The weighed mixture 903 and nickel hydroxide were mixed. The mixing was performed by a dry method. The mixing was performed in a ball mill using a zirconia ball at 150 rpm for 1 hour.
Next, the materials that has been subjected to the treatment were collected to obtain the mixtures 905 (Step S51 and Step S52).
Next, the mixture 905 was put in an alumina crucible and annealed at 850° C. using a muffle furnace in an oxygen atmosphere for 60 hours (Step S53). At the time of annealing, the alumina crucible was covered with a lid. The flow rate of oxygen was 10 L/min. The temperature rise was 200° C./hr, and it took longer than or equal to 10 hours to lower the temperature. The material after the heat treatment was collected and filtered (Step S54), and Sample 1 to Sample 3 were obtained (Step S55).
Next, Sample 1 to Sample 3 obtained above were used as positive electrode active materials to make respective positive electrodes. A current collector that was coated with slurry in which the positive electrode active material, AB, and PVDF were mixed at the active material:AB:PVDF=95:3:2 (weight ratio) was used. As a solvent of the slurry, NMP was used.
After the current collector was coated with the slurry, the solvent was volatilized. Then, pressure was applied at 210 kN/m, and then pressure was applied at 1467 kN/m. Through the above process, the positive electrode was obtained. The load amount of the positive electrode was approximately 7 mg/cm2 and an electrode density was 3.8 g/cc.
Using the fabricated positive electrodes, CR2032 type coin battery cells (diameter: 20 mm, height: 3.2 mm) were fabricated.
A lithium metal was used for a counter electrode.
As an electrolyte contained in the electrolyte solution, 1 mol/L lithium hexafluorophosphate (LiPF6) was used. As the electrolyte solution, an electrolyte solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at EC:DEC=3:7 (volume ratio) was used. Note that for secondary batteries used for evaluating the charge-discharge efficiency, 2 wt % of vinylene carbonate (VC) was added to the electrolytic solution.
As a separator, 25-μm-thick polypropylene was used.
A positive electrode can and a negative electrode can that are formed using stainless steel (SUS) were used.
The charge-discharge efficiency in the first cycle and that in the second cycle of the battery cells using obtained Sample 1 to Sample 3 were measured.
The calculation result and the measurement result suggest that, according to only
100: positive electrode active material, 100A-1: positive electrode active material, 100C: positive electrode active material, 200: active material layer, 201: graphene compound, 211a: positive electrode, 211b: negative electrode, 212a: lead, 212b: lead, 214: separator, 215a: bonding portion, 215b: bonding portion, 217: fixing member, 250: battery, 251: exterior body, 261: folded portion, 262: seal portion, 263: seal portion, 271: crest line, 272: crest line, 273: space, 300: secondary battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 600: secondary battery, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 612: safety valve mechanism, 613: conductive plate, 614: conductive plate, 615: module, 616: wiring, 617: temperature control device, 900: circuit substrate, 902: mixture, 903: mixture, 904: mixture, 905: mixture, 910: label, 911: terminal, 912: circuit, 913: secondary battery, 914: antenna, 915: antenna, 916: layer, 917: layer, 918: antenna, 919: terminal, 920: display device, 921: sensor, 922: terminal, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 932: positive electrode, 933: separator, 950: wound body, 951: terminal, 952: terminal, 980: secondary battery, 981: film, 982: film, 993: wound body, 994: negative electrode, 995: positive electrode, 996: separator, 997: lead electrode, 998: lead electrode, 7100: portable display device, 7101: housing, 7102: display portion, 7103: operation button, 7104: secondary battery, 7200: portable information terminal, 7201: housing, 7202: display portion, 7203: band, 7204: buckle, 7205: operation button, 7206: input/output terminal, 7207: icon, 7300: display device, 7304: display portion, 7400: mobile phone, 7401: housing, 7402: display portion, 7403: operation button, 7404: external connection port, 7405: speaker, 7406: microphone, 7407: secondary battery, 7408: lead electrode, 7409: current collector, 8000: display device, 8001: housing, 8002: display portion, 8003: speaker portion, 8004: secondary battery, 8021: charging device, 8022: cable, 8024: secondary battery, 8100: lighting device, 8101: housing, 8102: light source, 8103: secondary battery, 8104: ceiling, 8105: side wall, 8106: floor, 8107: window, 8200: indoor unit, 8201: housing, 8202: air outlet, 8203: secondary battery, 8204: outdoor unit, 8300: electric refrigerator-freezer, 8301: housing, 8302: refrigerator door, 8303: freezer door, 8304: secondary battery, 8400: automobile, 8401: headlight, 8406: electric motor, 8500: automobile, 8600: scooter, 8601: side mirror, 8602: secondary battery, 8603: direction indicator, 8604: storage unit under seat storage, 9600: tablet terminal, 9625: switch, 9626: display mode changing switch, 9627: power switch, 9628: operation switch, 9629: fastener, 9630: housing, 9630a: housing, 9630b: housing, 9631: display portion, 9633: solar cell, 9634: charging-discharging control circuit, 9635: power storage unit, 9636: DC-DC converter, 9637: converter, 9640: movable portion
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-015036 | Jan 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/050459 | 1/22/2020 | WO | 00 |
