Patent Application
20230246198
One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, manufacture, or a composition (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 electronic devices in this specification generally mean 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, air batteries, and all-solid-state batteries have been actively developed. In particular, demand for lithium-ion secondary batteries with high output and high capacity has rapidly grown with the development of the semiconductor industry, and the lithium-ion secondary batteries are essential as rechargeable energy supply sources for today's information society.
As the demand expands, the lithium-ion secondary batteries are required to have higher performance. Thus, the positive electrode active material has been improved to enhance the capacity and cycle performance of lithium-ion secondary batteries (e.g., Patent Document 1).
Moreover, among the lithium-ion secondary batteries, an all-solid-state battery having higher safety has been developed. A thin-film secondary battery in which a positive electrode, an electrolyte, and a negative electrode are formed by PVD (physical vapor deposition), CVD (chemical vapor deposition), or the like is one kind of all-solid-state battery (e.g., Patent Document 2).
There is room for improvements in a variety of aspects of thin-film secondary batteries, such as charge and discharge characteristics, cycle performance, reliability, safety, and costs. For example, regarding cycle performance, a crystal structure of a positive electrode active material may be broken as charge and discharge are repeated, which might lead to a reduction in charge and discharge capacity. Moreover, a side reaction may occur, for example, at the interface between a positive electrode active material and an electrolyte or the interface between a positive electrode active material and a positive electrode current collector, which might also lead to a reduction in charge and discharge capacity.
In view of the above, an object of one embodiment of the present invention is to provide a positive electrode for a secondary battery in which a side reaction does not easily occur, for example, at the interface between a positive electrode active material and an electrolyte or the interface between a positive electrode active material and a positive electrode current collector even when charge and discharge are repeated. Another object is to provide a positive electrode for a secondary battery, which has a crystal structure that is not easily broken even when charge and discharge are repeated. Another object is to provide a positive electrode for a secondary battery, which has excellent charge and discharge cycle performance. Another object is to provide a positive electrode for a secondary battery, which has high charge and discharge capacity. Another object is to provide a positive electrode for a secondary battery, in which a decrease in capacity in charge and discharge cycles is inhibited. Another object is to provide a secondary battery with excellent charge and discharge cycle performance. Another object is to provide a secondary battery with high charge and discharge capacity. Another object is to provide a highly safe or reliable secondary battery.
Another object of one embodiment of the present invention is to provide a novel material, novel active material particles, a novel power storage device, or a manufacturing method thereof.
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. Other objects can be derived from the description of the specification, the drawings, and the claims.
In one embodiment of the present invention, a cap layer is provided over a positive electrode active material layer in order to make a crystal structure less likely to be broken, inhibit a side reaction, and improve cycle performance.
One embodiment of the present invention is a positive electrode for a secondary battery, which includes a base film, a positive electrode active material layer, and a cap layer. At least one of the base film and the cap layer contains titanium oxynitride. The positive electrode active material layer contains lithium cobalt oxide. The cap layer contains a titanium compound containing oxygen.
In the above, a crystal structure included in the base film and a crystal structure included in the positive electrode active material layer each preferably have a plane where only anions are arranged.
In the above, the base film and the positive electrode active material layer each preferably have a crystal structure where cations and anions are alternately arranged.
One embodiment of the present invention is a secondary battery including the above positive electrode for a secondary battery, a solid electrolyte, and a negative electrode.
One embodiment of the present invention is an electronic device including the above secondary battery.
One embodiment of the present invention is an electronic device including the above secondary battery and a lithium-ion secondary battery which includes a positive electrode, a negative electrode, an electrolytic solution, and a separator.
One embodiment of the present invention can provide a positive electrode for a secondary battery in which a side reaction does not easily occur, for example, at the interface between a positive electrode active material and an electrolyte or the interface between a positive electrode active material and a positive electrode current collector even when charge and discharge are repeated. A positive electrode for a secondary battery, which has a crystal structure that is not easily broken even when charge and discharge are repeated, can be provided. A positive electrode for a secondary battery, which has excellent charge and discharge cycle performance, can be provided. A positive electrode for a secondary battery, which has high charge and discharge capacity, can be provided. A positive electrode for a secondary battery, in which a decrease in capacity in charge and discharge cycles is inhibited, can be provided. A secondary battery with excellent charge and discharge cycle performance can be provided. A secondary battery with high charge and discharge capacity can be provided. A highly safe or reliable secondary battery can be provided.
One embodiment of the present invention can provide a novel material, novel active material particles, a novel power storage device, or a manufacturing method thereof.
Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not have to have all of these effects. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like.
Embodiments of the present invention will be 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 the embodiments below.
The Miller index is used for the expression of crystal planes and orientations in this specification and the like. An individual plane representing a crystal plane is denoted by “( )”. An orientation is denoted by “[ ]”. A reciprocal lattice point is represented using a similar index without parentheses or brackets. In the crystallography, a bar is placed over a number in the expression of crystal planes, orientations, and space groups; however, in this specification and the like, because of application format limitations, crystal planes, orientations, and space groups are sometimes expressed by placing a minus sign (−) before a number instead of placing a bar over the number.
In this specification and the like, a layered rock-salt crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure in which a rock-salt ion arrangement where cations and anions are alternately arranged is included and the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that lithium can be two-dimensionally diffused. Note that a defect such as a cation or anion vacancy may exist. Moreover, in the layered rock-salt crystal structure, strictly, a lattice of a rock-salt crystal is distorted in some cases.
In this specification and the like, a rock-salt crystal structure refers to a structure in which cations and anions are alternately arranged. Note that a cation or anion vacancy may exist.
Anions of a layered rock-salt crystal and anions of a rock-salt crystal have a cubic closest packed structure (face-centered cubic lattice structure). When the layered rock-salt crystal and the rock-salt crystal are in contact with each other, 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 is R-3m, which is different from a space group Fm-3m of a rock-salt crystal; thus, the Miller index of the crystal plane satisfying the above conditions in the layered rock-salt 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 and the rock-salt crystal are aligned is sometimes referred to as a state where crystal orientations are substantially aligned.
Whether the crystal orientations in two regions are substantially aligned with each other can be judged from a TEM (transmission electron microscope) image, a STEM (scanning transmission electron microscope) image, a HAADF-STEM (high-angle annular dark field scanning transmission electron microscope) image, an ABF-STEM (annular bright-field scanning transmission electron microscope) image, and the like. X-ray diffraction (XRD), electron diffraction, neutron diffraction, and the like can also be used for judging. When the crystal orientations are substantially aligned with each other, a state where an angle between the orientations of lines in each of which cations and anions are alternately arranged is less than or equal to 5°, or less than or equal to 2.5° is observed from a TEM image and the like. Note that in a TEM image and the like, a light element typified by oxygen or fluorine cannot be clearly observed in some cases; in such a case, alignment of orientations can be judged by arrangement of metal elements.
In this specification and the like, theoretical capacity of a positive electrode active material refers to the amount of electricity at the time when lithium that can be inserted and extracted and is contained in the positive electrode active material is all extracted. For example, the theoretical capacity of LiCoO2 is 274 mAh/g, the theoretical capacity of LiNiO2 is 274 mAh/g, and the theoretical capacity of LiMn2O4 is 148 mAh/g.
In this specification and the like, charge depth at the time when lithium that can be inserted and extracted is all inserted is 0, and charge depth at the time when lithium that can be inserted and extracted and is contained in a positive electrode active material is all extracted is 1.
In this specification and the like, the expression “planes are parallel to each other” refers to not only the case where the planes are exactly parallel numerically but also the case where an angle formed between the planes is 5° or less, or 2.5° or less.
A positive electrode for a secondary battery of one embodiment of the present invention will be described with reference to
The base film 104 is provided between the positive electrode current collector 103 and the positive electrode active material layer 101. The base film 104 has a function of increasing conductivity between the positive electrode current collector 103 and the positive electrode active material layer 101. Alternatively, the base film 104 has a function of inhibiting a side reaction such as oxidation of the positive electrode current collector 103 due to oxygen contained in the positive electrode active material layer 101 or the like or diffusion of a metal atom included in the positive electrode current collector 103 into the positive electrode active material layer 101. Alternatively, the base film 104 has a function of stabilizing a crystal structure included in the positive electrode active material layer 101.
For the base film 104, a material having conductivity is preferably used. Moreover, a material that is likely to inhibit oxidation is preferably used. For example, it is possible to use a titanium compound such as titanium oxide, titanium nitride, titanium oxide in which nitrogen is substituted for part of oxygen, titanium nitride in which oxygen is substituted for part of nitrogen, or titanium oxynitride (TiOxNy, where 0<x<2 and 0<y<1). Titanium nitride is particularly preferable because it has high conductivity and has a high capability of inhibiting oxidation.
The cap layer 102 is provided over the positive electrode active material layer 101. The cap layer 102 has a function of inhibiting a side reaction between the positive electrode active material layer 101 and an electrolyte. Alternatively, the cap layer 102 has a function of stabilizing a crystal structure included in the positive electrode active material layer 101.
For the cap layer 102, a titanium compound is preferably used. For example, it is preferable to use titanium oxide, titanium nitride, titanium oxide in which nitrogen is substituted for part of oxygen, titanium nitride in which oxygen is substituted for part of nitrogen, or titanium oxynitride (TiOxNy, where 0<x<2 and 0<y<1). Titanium and oxygen are materials that can be contained in a solid electrolyte. Therefore, titanium oxide is particularly preferable for the cap layer 102.
Note that in this specification and the like, an electrolyte refers to not only a solid electrolyte but also an electrolytic solution in which lithium salt is dissolved in a liquid solvent and an electrolytic solution in which lithium salt is dissolved in a gelled compound.
The positive electrode active material layer 101 contains lithium, a transition metal M, and oxygen. In other words, the positive electrode active material layer 101 includes a composite oxide containing lithium and the transition metal M.
As the transition metal M contained in the positive electrode active material layer 101, a metal that can form, together with lithium, a layered rock-salt composite oxide belonging to the space group R-3m is preferably used. As the transition metal M, one or more of manganese, cobalt, and nickel can be used, for example. That is, as the transition metal contained in the positive electrode active material layer 101, only cobalt may be used; only nickel may be used; two metals of cobalt and manganese or cobalt and nickel may be used; or three metals of cobalt, manganese, and nickel may be used. In other words, the positive electrode active material layer 101 can include a composite oxide containing lithium and the transition metal M, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which manganese is substituted for part of cobalt, lithium cobalt oxide in which nickel is substituted for part of cobalt, or lithium nickel-manganese-cobalt oxide.
In addition to the above, the positive electrode active material layer 101 may contain an element other than the transition metal M, such as magnesium, fluorine, or aluminum. Such elements further stabilize a crystal structure included in the positive electrode active material layer 101 in some cases. In other words, the positive electrode active material layer 101 can contain lithium cobalt oxide to which magnesium and fluorine are added, lithium nickel-cobalt oxide to which magnesium and fluorine are added, lithium cobalt-aluminum oxide to which magnesium and fluorine are added, lithium nickel-cobalt-aluminum oxide, lithium nickel-cobalt-aluminum oxide to which magnesium and fluorine are added, or the like.
When the positive electrode active material layer 101 contains lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine, given that the proportion of cobalt atoms included in the positive electrode active material layer 101 is 100, the proportion of nickel atoms is preferably greater than or equal to 0.05 and less than or equal to 2, further preferably greater than or equal to 0.1 and less than or equal to 1.5, and still further preferably greater than or equal to 0.1 and less than or equal to 0.9, for example. Given that the proportion of cobalt atoms included in the positive electrode active material layer 101 is 100, the proportion of aluminum atoms is preferably greater than or equal to 0.05 and less than or equal to 2, further preferably greater than or equal to 0.1 and less than or equal to 1.5, and still further preferably greater than or equal to 0.1 and less than or equal to 0.9, for example. Given that the proportion of cobalt atoms included in the positive electrode active material layer 101 is 100, the proportion of magnesium atoms is preferably greater than or equal to 0.1 and less than or equal to 6, further preferably greater than or equal to 0.3 and less than or equal to 3, for example. Given that the proportion of magnesium atoms included in the positive electrode active material layer 101 is 1, the proportion of fluorine atoms is preferably greater than or equal to 2 and less than or equal to 3.9, for example.
When nickel, aluminum, and magnesium are contained at the above concentrations, a stable crystal structure can be maintained even if charge and discharge are repeated at high voltage. Thus, the positive electrode active material layer 101 can have high capacity and excellent charge and discharge cycle performance.
The molar concentrations of cobalt, nickel, aluminum, and magnesium can be measured by inductively coupled plasma mass spectrometry (ICP-MS), for example. The molar concentration of fluorine can be measured by glow discharge mass spectrometry (GD-MS), for example.
Here, the results of calculating a crystal structure at the interface between the positive electrode active material layer 101 and the base film 104 in the case where lithium cobalt oxide is used for the positive electrode active material layer 101 will be described with reference to
Both these diagrams selectively show the interface between the positive electrode active material layer 101 and the base film 104. Other calculation conditions are listed in Table 1.
In the case of
In the rock-salt crystal structure that belongs to the space group Fm-3m, a plane where only anions are arranged exists parallel to the (111) plane. In titanium nitride, only nitrogen atoms are arranged on a plane parallel to the (111) plane. In the layered rock-salt crystal structure that belongs to the space group R-3m, a plane where only anions are arranged exists parallel to the (001) plane. In lithium cobalt oxide, only oxygen atoms are arranged on a plane parallel to the (001) plane.
When the (111) plane of titanium nitride and the (001) plane of lithium cobalt oxide are parallel to each other, planes where only anions are arranged are parallel to each other in both of these materials, so that the crystal structure is likely to become stable.
The rock-salt crystal structure that belongs to the space group Fm-3m and the layered rock-salt crystal structure that belongs to the space group R-3m can each be regarded as a crystal structure in which cations and anions are alternately arranged. Thus, when lithium cobalt oxide having a layered rock-salt crystal structure is stacked over titanium nitride having a rock-salt crystal structure, orientation of crystals in the base film 104 and orientation of crystals in the positive electrode active material layer 101 are likely to be substantially aligned with each other.
Meanwhile, in the case of
As described above, titanium nitride is particularly preferable for the base film 104 when lithium cobalt oxide having a layered rock-salt crystal structure is used for the positive electrode active material layer 101.
Although
This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment, a secondary battery including the positive electrode for a secondary battery described in Embodiment 1, and a manufacturing method of the secondary battery will be described with reference to
The secondary battery 200 is a thin-film battery including the positive electrode 100 described in the foregoing embodiment, in which a solid electrolyte layer 203 is formed over the positive electrode 100 and a negative electrode 212 is formed over the solid electrolyte layer 203. The negative electrode 212 includes a negative electrode current collector 205 and a negative electrode active material layer 204. As illustrated in
The base film 214 is provided between the negative electrode current collector 205 and the negative electrode active material layer 204. The base film 214 has a function of increasing conductivity between the negative electrode current collector 205 and the negative electrode active material layer 204. Alternatively, the base film 214 has a function of suppressing excessive expansion of the negative electrode active material layer. Alternatively, the base film 214 has a function of inhibiting a side reaction between the negative electrode current collector 205 and the negative electrode active material layer 204.
For the base film 214, it is preferable to use a material having conductivity. It is preferable to use a material capable of suppressing excessive expansion of the negative electrode active material layer. It is preferable to use a material that is likely to inhibit a side reaction. For example, it is preferable to use a titanium compound such as titanium oxide, titanium nitride, titanium oxide in which nitrogen is substituted for part of oxygen, titanium nitride in which oxygen is substituted for part of nitrogen, or titanium oxynitride (TiOxNy, where 0<x<2 and 0<y<1). Titanium nitride is particularly preferable because it has high conductivity and has a high capability of inhibiting a side reaction.
The cap layer 209 is provided between the negative electrode active material layer 204 and the solid electrolyte layer 203. The cap layer 209 has a function of inhibiting a side reaction between the negative electrode active material layer 204 and the solid electrolyte layer 203.
For the cap layer 209, titanium or a titanium compound is preferably used. As the titanium compound, it is preferable to use titanium oxide, titanium nitride, titanium oxide in which nitrogen is substituted for part of oxygen, titanium nitride in which oxygen is substituted for part of nitrogen, or titanium oxynitride (TiOxNy, where 0<x<2 and 0<y<1), for example. Titanium is a material that can be contained in a solid electrolyte. Therefore, titanium and a titanium compound are particularly preferable for the cap layer 209.
For the negative electrode active material layer 204, silicon, carbon, titanium oxide, vanadium oxide, indium oxide, zinc oxide, tin oxide, nickel oxide, or the like can be used. A material that is alloyed with lithium, such as tin, gallium, or aluminum can be used. Alternatively, an oxide of such a metal that is alloyed with lithium may be used. A lithium titanium oxide (Li4Ti5O12, LiTi2O4, or the like) may be used; in particular, a material containing silicon and oxygen (also referred to as a SiOx film) is preferable. A lithium metal may also be used for the negative electrode active material layer 204. Alternatively, a mixture of these materials may be used. A mixture of a silicon particle and carbon, for example, is preferable because of having favorable reliability and a relatively high energy density per volume.
The solid electrolyte layer 203 is provided between the positive electrode 100 and the negative electrode 212. Examples of materials for the solid electrolyte layer 203 include Li0.35La0.55TiO3, La(2/3−A)Li3ATiO3, Li3PO4, LixPO(4−B)NB, LiNb(1−A)Ta(A)WO6, Li7La3Zr2O12, Li(1+A)Al(A)Ti(2−A)(PO4)3, Li(1+A)Al(A)Ge(2−A)(PO4)3, and LiNbO2. Note that A>0 and B>0. As a deposition method, a sputtering method, an evaporation method, or the like can be used.
A compound containing titanium is preferably used for the solid electrolyte layer 203. Since the cap layer 102 included in the positive electrode 100 and the cap layer 209 included in the negative electrode 212 contain titanium, the secondary battery can be easily manufactured when a material containing titanium is also used for the solid electrolyte layer 203.
In addition, SiOC (0<C≤2) can also be used for the solid electrolyte layer 203. SiOC (0<C≤2) may be used for the solid electrolyte layer 203, and SiOC (0<C≤2) may also be used for the negative electrode active material layer 204. In this case, the ratio of oxygen to silicon (O/Si) in SiOC is preferably higher in the solid electrolyte layer 203 than in the negative electrode active material layer 204. With this structure, conductive ions (particularly lithium ions) in the solid electrolyte layer 203 are likely to diffuse, and conductive ions (particularly lithium ions) in the negative electrode active material layer 204 are likely to be extracted or accumulated, whereby a solid-state secondary battery with favorable characteristics can be obtained. When the solid electrolyte layer 203 and the negative electrode active material layer 204 are formed using materials containing the same components as described above, a secondary battery can be manufactured easily.
The solid electrolyte layer 203 may have a stacked-layer structure. In the case of a stacked-layer structure, a material in which nitrogen is added to lithium phosphate (Li3PO4) (the material is also referred to as Li3PO(4-Z)NZ:LiPON) may be stacked as one of the layers. Note that Z>0.
As illustrated in
As illustrated in
In the secondary battery 200, a protective layer 206 is preferably formed over the positive electrode 100, the solid electrolyte layer 203, and the negative electrode 210.
Films for forming these layers can be formed using metal masks. The positive electrode current collector 103, the base film 104, the positive electrode active material layer 101, the cap layer 102, the solid electrolyte layer 203, the cap layer 209, the negative electrode active material layer 204, the base film 214, and the negative electrode current collector 205 can be selectively formed by a sputtering method. Furthermore, the solid electrolyte layer 203 may be selectively formed using a metal mask by a co-evaporation method.
As illustrated in
In
As illustrated in
Each of the positive electrode and the negative electrode included in the secondary battery of one embodiment of the present invention may have a stacked-layer structure of active material layers and cap layers. For example, as illustrated in
As illustrated in
As illustrated in
Although the secondary battery in which not only the positive electrode but also the solid electrolyte layer and the negative electrode are formed of thin films is described in
As illustrated in
In addition, as illustrated in
As illustrated in
Next, a flow example of a method for manufacturing the secondary battery 200 illustrated in
First, the positive electrode current collector 103 is formed over the substrate 110 (S1). As a deposition method, a sputtering method, an evaporation method, or the like can be used. A substrate having conductivity may be used as the current collector. For the positive electrode current collector 103, it is possible to use a material having high conductivity, for example, a metal such as gold, platinum, aluminum, titanium, copper, magnesium, iron, cobalt, nickel, zinc, germanium, indium, silver, or palladium or an alloy thereof. It is also possible to use aluminum to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added. Alternatively, the positive electrode current collector 103 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.
As the substrate 110, a ceramic substrate, a glass substrate, a resin substrate, a silicon substrate, a metal substrate, or the like can be used. When a flexible material is used for the substrate 110, a flexible thin-film secondary battery can be manufactured.
The positive electrode current collector 103 using a material having high conductivity can serve as both a substrate and a positive electrode current collector. In this case, a metal substrate of titanium or copper is preferably used, for example. In the case where the base film 104 is provided, the base film 104 inhibits oxidation of the positive electrode current collector 103 due to oxygen contained in the positive electrode active material layer 101 or the like or diffusion of metal atoms. Accordingly, a material that is easily oxidized or a material including a metal atom that is easily diffused can be used for the positive electrode current collector 103.
Next, the base film 104 is formed (S2). As a deposition method for the base film 104, a sputtering method, an evaporation method, or the like can be used. For example, in the case where titanium nitride is used for the base film 104, titanium nitride can be deposited by a reactive sputtering method using a titanium target and a nitrogen gas.
Then, the positive electrode active material layer 101 is formed (S3). The positive electrode active material layer 101 can be formed by a sputtering method using a sputtering target that includes, as its main component, an oxide containing lithium and one or more of manganese, cobalt, and nickel, for example. It is possible to use, for example, a sputtering target including lithium cobalt oxide (LiCoO2, LiCo2O4, or the like) as its main component, a sputtering target including a lithium manganese oxide (LiMnO2, LiMn2O4, or the like) as its main component, or a sputtering target including a lithium nickel oxide (LiNiO2, LiNi2O4, or the like) as its main component. Alternatively, the positive electrode active material layer 101 may be formed by a vacuum evaporation method.
In a sputtering method, with use of a metal mask, film deposition can be selectively performed. Alternatively, the positive electrode active material layer 101 may be patterned by being selectively removed by dry etching or wet etching using a resist mask or the like.
To form the positive electrode active material layer 101 containing magnesium, fluorine, aluminum, or the like, the positive electrode active material layer 101 may be formed using a sputtering target that contains magnesium, fluorine, aluminum, or the like in addition to lithium and one or more of manganese, cobalt, and nickel. Alternatively, film deposition may be performed using a sputtering target that includes, as its main component, an oxide containing lithium and one or more of manganese, cobalt, and nickel; after that, magnesium, fluorine, aluminum, or the like may be deposited by a vacuum evaporation method; then, annealing may be performed.
Subsequently, the cap layer 102 is formed over the positive electrode active material layer 101 (S4). As a deposition method for the cap layer 102, a sputtering method, an evaporation method, or the like can be used. For example, in the case where titanium oxide is used for the cap layer 102, titanium oxide can be deposited by a reactive sputtering method using a titanium target and an oxygen gas. Titanium oxide can also be deposited by sputtering of a titanium oxide target.
The positive electrode active material layer 101 and the cap layer 102 are preferably formed at a high temperature (500° C. or higher). The positive electrode 100 with higher crystallinity can be manufactured.
Next, the solid electrolyte layer 203 is formed over the positive electrode active material layer 101 (S5).
A compound containing titanium is preferably used for the solid electrolyte layer 203. Since the cap layer 102 included in the positive electrode 100 contains titanium, the secondary battery can be easily manufactured when a material containing titanium is also used for the solid electrolyte layer 203. As a deposition method, a sputtering method, an evaporation method, or the like can be used.
Then, the negative electrode active material layer 204 is formed over the solid electrolyte layer 203 (S6). As a deposition method, a sputtering method, an evaporation method, or the like can be used.
Next, the negative electrode current collector 205 is formed over the negative electrode active material layer 204 (S7). As a material of the negative electrode current collector 205, one or more kinds of conductive materials selected from aluminum, titanium, copper, gold, chromium, tungsten, molybdenum, nickel, silver, and the like are used. As a deposition method, a sputtering method, an evaporation method, or the like can be used. In a sputtering method, with use of a metal mask, film deposition can be selectively performed. A conductive film may be patterned by being selectively removed by dry etching or wet etching using a resist mask or the like.
In the case where the positive electrode current collector 103 or the negative electrode current collector 205 is formed by a sputtering method, at least one of the positive electrode active material layer 101 and the negative electrode active material layer 204 is preferably formed by a sputtering method. A sputtering apparatus is capable of successive film deposition in one chamber or using a plurality of chambers and can also be a multi-chamber manufacturing apparatus or an in-line manufacturing apparatus. A sputtering method is a manufacturing method that uses a chamber and a sputtering target and is suitable for mass production. In addition, a sputtering method enables thin formation and thus excels in film deposition properties.
Then, the protective layer 206 is preferably formed over the positive electrode 100, the solid electrolyte layer 203, and the negative electrode 210 (S8). For the protective layer 206, it is possible to use a metal oxide containing one kind or two or more kinds selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, neodymium, lanthanum, magnesium, and the like. It is also possible to use silicon nitride oxide, silicon nitride, or the like. The protective layer 206 can be formed by a sputtering method.
For film deposition of each layer described in this embodiment, a gas phase method (a vacuum evaporation method, a thermal spraying method, a pulsed laser deposition method (PLD method), an ion plating method, a cold spray method, or an aerosol deposition method) can also be used without limitation to a sputtering method. Note that an aerosol deposition (AD) method is a method in which film deposition is performed without heating a substrate. The aerosol means microparticles dispersed in a gas. Alternatively, a CVD method or an ALD (Atomic Layer Deposition) method may be used.
Through the above-described steps, the secondary battery 200 of one embodiment of the present invention can be manufactured.
This embodiment can be implemented in appropriate combination with the other embodiments.
In order to increase the output voltage of a thin-film secondary battery, secondary batteries can be connected in series. While the example of the secondary battery of the single cell is described in Embodiment 2, an example of manufacturing thin-film secondary batteries in which a plurality of cells are connected in series is described in this embodiment.
Then, a second negative electrode active material layer, a second solid electrolyte layer 213, a second positive electrode active material layer, and a second positive electrode current collector 215 are formed in this order over a region of the negative electrode current collector 205 that does not overlap with a first negative electrode active material layer. Lastly, the protective layer 206 is formed (
This embodiment can be implemented in appropriate combination with the other embodiments.
A plurality of positive electrodes and a plurality of negative electrodes can be stacked to form a multi-layer secondary battery to increase an output voltage or a discharge capacity of a thin-film secondary battery. While the example of the secondary battery of the single-layer cell is described in Embodiment 2, an example of a thin-film battery of a multi-layer cell is described in this embodiment.
Furthermore, a second cell is formed in such a manner that a second negative electrode active material layer 204, a solid electrolyte layer, a cap layer, a positive electrode active material layer, a base film, and a positive electrode current collector layer are sequentially formed over the negative electrode current collector 205.
Moreover, a third cell is formed in such a manner that a third base film, a positive electrode active material layer, a cap layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are sequentially formed over the second positive electrode current collector.
Lastly, the protective layer 206 is formed in
Note that the solid electrolyte layer 203, the second solid electrolyte layer, and the third solid electrolyte layer are preferably formed using the same material, leading to a reduction in the manufacturing cost.
To reduce the number of manufacturing steps, in
This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment,
The mask alignment chamber 891 includes at least a stage 851 and a substrate transfer mechanism 852.
The first transfer chamber 871 includes a substrate cassette raising and lowering mechanism, the second transfer chamber 872 includes a substrate transfer mechanism 853, and the third transfer chamber 873 includes a substrate transfer mechanism 854.
Each of the first deposition chamber 892, the second deposition chamber 874, the second material supply chamber 894, the first material supply chamber 895, the third material supply chamber 896, the mask alignment chamber 891, the first transfer chamber 871, the second transfer chamber 872, and the third transfer chamber 873 is connected to an exhaust mechanism. The exhaust mechanism is selected in accordance with usage of the respective chambers, and may be, for example, an exhaust mechanism including a pump having an adsorption unit, such as a cryopump, a sputtering ion pump, or a titanium sublimation pump, an exhaust mechanism including a turbo molecular pump provided with a cold trap, or the like.
In a process of film deposition on the substrate, the substrate 850 or the substrate cassette is set in the load lock chamber 870, and transferred to the mask alignment chamber 891 by the substrate transfer mechanism 852. A mask to be used is picked up among a plurality of masks set in advance in the mask alignment chamber 891, and its position is aligned with the substrate over the stage 851. After the position alignment, the gate 880 is opened, and the mask and the substrate 850 are transferred to the first transfer chamber 871 by the substrate transfer mechanism 852. After the mask and the substrate 850 are transferred to the first transfer chamber 871, the gate 881 is opened, and they are transferred to the second transfer chamber 872 by the substrate transfer mechanism 853.
The first deposition chamber 892 provided next to the second transfer chamber 872 through the gate 882 is a sputtering deposition chamber. The sputtering deposition chamber has a mechanism of applying voltage to the sputtering target by switching an RF power supply and a pulsed DC power supply. Furthermore, two or three kinds of sputtering targets can be set. In this embodiment, a single crystal silicon target, a sputtering target including lithium cobalt oxide (LiCoO2) as its main component, and a titanium target are set. It is possible to provide a substrate heating mechanism in the first deposition chamber 892 and perform film deposition while heating is performed up to a heater temperature of 700° C.
The negative electrode active material layer can be formed by a sputtering method using a single crystal silicon target. An SiOx film formed by a reactive sputtering method using an Ar gas and an O2 gas may be used as the negative electrode active material layer. A silicon nitride film formed by a reactive sputtering method using an Ar gas and an N2 gas can be used as a sealing film. The positive electrode active material layer can be formed by a sputtering method using a sputtering target including lithium cobalt oxide (LiCoO2) as its main component. A conductive film to be a current collector can be formed by a sputtering method using a titanium target. A titanium nitride film formed by a reactive sputtering method using an Ar gas and an N2 gas can be formed as the cap layer or the base film.
In the case where the positive electrode active material layer is formed, the mask and the substrate in an overlapped state are transferred from the second transfer chamber 872 to the first deposition chamber 892 by the substrate transfer mechanism 853, the gate 882 is closed, and then film deposition is performed by a sputtering method. After the deposition, the gate 882 and the gate 883 are opened, transferring to the heating chamber 893 is performed, the gate 883 is closed, and then heating can be performed. For this heat treatment in the heating chamber 893, an RTA (Rapid Thermal Anneal) apparatus, a resistance heating furnace, or a microwave heating apparatus can be used. As the RTA apparatus, a GRTA (Gas Rapid Thermal Anneal) apparatus or an LRTA (Lamp Rapid Thermal Anneal) apparatus can be used. The heat treatment in the heating chamber 893 can be performed in an atmosphere of nitrogen, oxygen, a rare gas, or dry air. In addition, heating time is longer than or equal to 1 minute and shorter than or equal to 24 hours.
After the film deposition or the heat treatment, the substrate and the mask are returned to the mask alignment chamber 891 and position alignment for a new mask is performed. The substrate and the mask after being subjected to the position alignment are transferred to the first transfer chamber 871 by the substrate transfer mechanism 852. The substrate is transferred by the raising and lowering mechanism of the first transfer chamber 871, the gate 884 is opened, and transferring to the third transfer chamber 873 is performed by the substrate transfer mechanism 854.
In the second deposition chamber 874 which is connected to the third transfer chamber 873 through the gate 885, film deposition by evaporation is performed.
The second deposition chamber 874 is connected to the second material supply chamber 894 through the gate 886. The second deposition chamber 874 is connected to the first material supply chamber 895 through the gate 888. The second deposition chamber 874 is connected to the third material supply chamber 896 through the gate 887. Thus, ternary co-evaporation is possible in the second deposition chamber 874.
In a process of evaporation, first, the substrate is provided in a substrate holding portion 845. The substrate holding portion 845 is connected to a rotation mechanism 865. Then, a first evaporation material 855 is heated to some extent in the first material supply chamber 895, the gate 888 is opened when the evaporation rate becomes stable, and an arm 862 is extended so that the evaporation source 856 is transferred and stopped below the substrate. The evaporation source 856 includes the first evaporation material 855, a heater 857, and a container for storing the first evaporation material 855. Also in the second material supply chamber 894, a second evaporation material is heated to some extent, the gate 886 is opened when the evaporation rate becomes stable, and an arm 861 is extended so that the evaporation source is transferred and stopped below the substrate.
After that, a shutter 868 and an evaporation source shutter 869 are opened, and co-evaporation is performed. During the evaporation, the rotation mechanism 865 is rotated in order to improve the uniformity of the thickness. The substrate after being subjected to the evaporation is transferred to the mask alignment chamber 891 on the same route. In the case where the substrate is extracted from the manufacturing apparatus, the substrate is transferred from the mask alignment chamber 891 to the load lock chamber 870 and extracted.
The second deposition chamber 874 may include an imaging unit 863 such as a CCD camera. With the provision of the imaging unit 863, the position of the substrate 850 can be confirmed.
In the second deposition chamber 874, the thickness of a film deposited on a substrate surface can be estimated from results of measurements by a film thickness measurement mechanism 867. The film thickness measurement mechanism 867 may include a crystal oscillator, for example.
Note that in order to control the evaporation of the vaporized evaporation material, the shutter 868 is provided so as to overlap with the substrate until the vaporization rate of the evaporation material becomes stable, and the evaporation source shutter 869 is provided to overlap with the evaporation source 856 and the evaporation boat 858 until the vaporization rate of the evaporation material becomes stable.
In the evaporation source 856, an example of a resistance heating method is shown, but an EB (Electron Beam) evaporation method may be employed. In addition, although an example of a crucible as the container for the evaporation source 856 is shown, an evaporation boat may be used. As the first evaporation material 855, an organic material is put into the crucible heated by the heater 857. In the case where pellet-like or particle-like SiO or the like is used as the evaporation material, the evaporation boat 858 is used. The evaporation boat 858 is composed of three parts, and obtained by overlapping a member having a concave surface, a middle lid having two openings, and a top lid having one opening. Note that the evaporation may be performed after the middle lid is removed. The evaporation boat 858 functions as a resistor when current flows therethrough, and has a mechanism of heating itself.
Although an example of a multi-chamber apparatus is described in this embodiment, there is no particular limitation and an in-line manufacturing apparatus may be used.
This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment, an example of a thin-film secondary battery including a battery control circuit or the like is described.
The terminal 911 is connected to a device to which electric power of the thin-film-type solid-state secondary battery is supplied, for example. For example, the terminal 911 is connected to a display device, a sensor, or the like.
The layer 916 has a function of blocking an electromagnetic field from the secondary battery 913, for example. As the layer 916, for example, a magnetic body can be used.
A substrate having flexibility is preferably used as the substrate 900.
By using a substrate having flexibility as the substrate 900, a thin battery control circuit can be achieved. As illustrated in
Another example of a thin-film secondary battery including a battery control circuit or the like is described with reference to
As illustrated in
This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment, examples of electronic devices using thin-film secondary batteries are described with reference to
An ID 3002 and a photograph 3003 of a worker who wears a management badge are displayed on the IC card 3000. A signal such as an authentication signal can be transmitted from the antenna using the electric power charged in the thin-film-type secondary battery 3001.
An active matrix display device may be provided to display the ID 3002 and the photograph 3003. As examples of the active matrix display device, a reflective liquid crystal display device, an organic EL display device, electronic paper, or the like can be given. An image (a moving image or a still image) or time can be displayed on the active matrix display device. Electric power for the active matrix display device can be supplied from the thin-film-type secondary battery 3001.
A plastic substrate is used for the IC card, and thus an organic EL display device using a flexible substrate is preferable.
A solar cell may be provided instead of the photograph 3003. By irradiation with external light, light can be absorbed to generate electric power, and the thin-film-type secondary battery 3001 can be charged with the electric power.
Without limitation to the IC card, the thin-film-type secondary battery can be used for a power supply of an in-vehicle wireless sensor, a secondary battery for a MEMS device, or the like.
For example, the secondary battery of one embodiment of the present invention can be incorporated in a glasses-type device 400 as illustrated in
Furthermore, the secondary battery of one embodiment of the present invention can be incorporated in a headset-type device 401. The headset-type device 401 includes at least a microphone portion 401a, a flexible pipe 401b, and an earphone portion 401c. The secondary battery can be provided in the flexible pipe 401b or the earphone portion 401c. When the secondary battery of one embodiment of the present invention is included, a structure that can support space saving due to a reduction in the size of a housing can be achieved.
The secondary battery of one embodiment of the present invention can also be incorporated in a device 402 that can be directly attached to a human body. A secondary battery 402b can be provided in a thin housing 402a of the device 402. When the secondary battery of one embodiment of the present invention is included, a structure that can support space saving due to a reduction in the size of a housing can be achieved.
The secondary battery of one embodiment of the present invention can also be incorporated in a device 403 that can be attached to clothing. A secondary battery 403b can be provided in a thin housing 403a of the device 403. When the secondary battery of one embodiment of the present invention is included, a structure that can support space saving due to a reduction in the size of a housing can be achieved.
Furthermore, the secondary battery of one embodiment of the present invention can be incorporated in a belt-type device 406. The belt-type device 406 includes a belt portion 406a and a wireless power feeding and receiving portion 406b, and the secondary battery can be incorporated in the belt portion 406a. When the secondary battery of one embodiment of the present invention is included, a structure that can support space saving due to a reduction in the size of a housing can be achieved.
The secondary battery of one embodiment of the present invention can also be incorporated in a watch-type device 405. The watch-type device 405 includes a display portion 405a and a belt portion 405b, and the secondary battery can be provided in the display portion 405a or the belt portion 405b. When the secondary battery of one embodiment of the present invention is included, a structure that can support space saving due to a reduction in the size of a housing can be achieved.
The display portion 405a can display various kinds of information such as reception information of an e-mail or an incoming call in addition to time.
Since the watch-type device 405 is a type of wearable device that is directly wrapped around an arm, a sensor that measures pulse, blood pressure, or the like of a user can be incorporated therein. Data on the exercise quantity and health of the user can be accumulated and used for health maintenance.
This embodiment can be implemented in appropriate combination with the other embodiments.
In this embodiment, electronic devices each using the secondary battery including the positive electrode of one embodiment of the present invention are described with reference to
The display panel 702 mounted in the housing 701 doubling as a bezel includes a rectangular display region. The display region has a curved surface. The display panel 702 preferably has flexibility. Note that the display region may be non-rectangular.
The bands 705A and 705B are connected to the housing 701. The clasp 703 is connected to the band 705A. The band 705A and the housing 701 are connected such that a connection portion rotates via a pin. In a similar manner, the band 705B and the housing 701 are connected to each other and the band 705A and the clasp 703 are connected to each other.
The secondary battery 750 has flexibility. Thus, the band 705A can be formed so as to incorporate the secondary battery 750. For example, the secondary battery 750 is set in a mold that the outside shape of the band 705A fits and a material of the band 705A is poured in the mold and cured, so that the band 705A illustrated in
In the case where a rubber material is used as the material for the band 705A, rubber is cured through heat treatment. For example, in the case where fluorine rubber is used as a rubber material, it is cured through heat treatment at 170° C. for 10 minutes. In the case where silicone rubber is used as a rubber material, it is cured through heat treatment at 150° C. for 10 minutes.
Examples of the material used for the band 705A include fluorine rubber, silicone rubber, fluorosilicone rubber, and urethane rubber.
Note that the portable information terminal 700 illustrated in
The housing 701 can include a speaker, a sensor (a sensor having a function of measuring force, 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), a microphone, and the like. Note that the portable information terminal 700 can be manufactured using a light-emitting element for the display panel 702.
Although
For example, the cleaning robot 6300 can analyze images taken by the cameras 6303 to judge whether there are obstacles such as a wall, furniture, or a step. When an object that is likely to be caught in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 internally includes the secondary battery of one embodiment of the present invention and a semiconductor device or an electronic component. The cleaning robot 6300 including the secondary battery of one embodiment of the present invention can be a highly reliable electronic device that can operate for a long time.
The microphone 6402 has a function of detecting a speaking voice of a user, an environmental sound, and the like. The speaker 6404 has a function of outputting sound. The robot 6400 can communicate with a user with the use of the microphone 6402 and the speaker 6404.
The display portion 6405 has a function of displaying various kinds of information. The robot 6400 can display information desired by a user on the display portion 6405. A touch panel may be incorporated in the display portion 6405. Moreover, the display portion 6405 may be a detachable information terminal, in which case charging and data communication can be performed when the display portion 6405 is set at the home position of the robot 6400.
The upper camera 6403 and the lower camera 6406 each have a function of taking images of the surroundings of the robot 6400. The obstacle sensor 6407 can detect an obstacle in the direction where the robot 6400 advances with the moving mechanism 6408. The robot 6400 can move safely by recognizing the surroundings with the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.
The robot 6400 internally includes the secondary battery 6409 of one embodiment of the present invention and a semiconductor device or an electronic component. The robot 6400 including the secondary battery of one embodiment of the present invention can be a highly reliable electronic device that can operate for a long time.
For example, image data taken by the camera 6502 is stored in an electronic component 6504. The electronic component 6504 can analyze the image data to detect whether there are obstacles when the flying object moves. Moreover, the electronic component 6504 can estimate the remaining battery level from a change in the power storage capacity of the secondary battery 6503. The flying object 6500 internally includes the secondary battery 6503 of one embodiment of the present invention. The flying object 6500 including the secondary battery of one embodiment of the present invention can be a highly reliable electronic device that can operate for a long time.
One embodiment of the present invention may be an electronic device or a system including the thin-film battery described in the foregoing embodiment and another secondary battery. There is no particular limitation on the other secondary battery; for example, a lithium-ion secondary battery including a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a bulk all-solid-state secondary battery can be used. Note that in this specification and the like, a system refers to a system combining individual components. A secondary battery is included as one of the components.
At this time, the key 7163 preferably includes the thin-film battery described in the foregoing embodiment, in which case the key can be made thinner and more lightweight. As a secondary battery for driving the automobile 7160, a secondary battery that can easily have higher discharge capacity, e.g., a lithium-ion secondary battery including a positive electrode, a negative electrode, an electrolytic solution, and a separator, or a bulk all-solid-state secondary battery is preferably used.
This embodiment can be implemented in appropriate combination with the other embodiments.
A device described in this embodiment includes at least a biosensor and a solid-state secondary battery that supplies electric power to the biosensor, and can obtain various kinds of biological data using infrared light and visible light and make the memory store the data. Such biological data can be used for both user's personal authentication uses and health care uses. The secondary battery of one embodiment of the present invention has a high discharge capacity, a high cycle performance, and a high level of safety. Thus, the device has a high level of safety and can be used for a long time.
The biosensor is a sensor for obtaining biological data and obtains biological data that can be used for health care uses. Examples of biological data include pulse waves, blood glucose levels, oxygen saturation levels, and neutral fat concentrations. The data is stored in the memory.
Furthermore, the device described in this embodiment is preferably provided with a unit for obtaining other biological data. Examples of such biological data include internal biological data such as an electrocardiogram, a blood pressure, and a body temperature and superficial biological data such as facial expression, a complexion, and a pupil. In addition, data on the number of steps taken, exercise intensity, a height difference in a movement, and a meal (e.g., calorie intake and nutrients) are important for health care. The use of a plurality of kinds of biological data and the like enables complex management of physical conditions, leading to not only daily health management but also early detection of injuries and diseases.
Blood pressure can be calculated from an electrocardiogram and a difference in timing of two pulsations of a pulse wave (a period of pulse wave propagation time), for example. A high blood pressure results in a short pulse wave propagation time, whereas a low blood pressure results in a long pulse wave propagation time. The body conditions of the user can be estimated from a relationship between the heart rate and the blood pressure that are calculated from the electrocardiogram and the pulse wave. For example, when both the heart rate and the blood pressure are high, it can be estimated that the user is nervous or excited, whereas when both the heart rate and the blood pressure are low, it can be estimated that the user is relaxed. When the state where the blood pressure is low and the heart rate is high is continued, the user might suffer from a heart disease or the like.
The user can check the biological data measured with the electronic device, one's own body conditions estimated on the basis of the data, and the like at any time; thus, health awareness is improved. This may inspire the user to reconsider the daily habits, for example, to avoid over-eating and over-drinking, get enough exercise, manage one's physical conditions, and have a medical examination at a medical institution as necessary.
Data may be shared among a plurality of biosensors.
As the predetermined conditions of the embedded device illustrated in
The device embedded into the living body, which is illustrated in
The biosensor 80b incorporated in the device may have a function of storing obtained data in a temporary memory incorporated in the device. Alternatively, the data obtained by the biosensor may be transmitted to a portable data terminal 85 in
The pair of electrodes 83 is provided in parts of a housing 82 with a display portion 81a therebetween. A display portion 81b is a curved region. The electrodes 83 function as electrodes for obtaining biological data.
Providing the pair of electrodes 83 in the longitudinal direction of the housing 82 as illustrated in
An example of the usage state of the portable data terminal 89 is illustrated. The display portion 81a can display electrocardiogram data 88a, heart-rate data 88b, and the like, which are obtained with the pair of electrodes 83.
This function is not necessary when the biosensor 80a is embedded in the user's body as illustrated in
The camera 84 can capture an image of the user's face, for example. Biological data on facial expression, a pupil, a complexion, and the like can be obtained from the image of the user's face.
The microphone 86 can obtain the user's voice. Voiceprint data that can be used for voiceprint authentication can be obtained from the obtained voice data. When voice data is regularly obtained and a change in voice quality is monitored, the voice data can be utilized for health management. Needless to say, talking on a video call with a doctor at the medical institution 87 is possible with use of the microphone 86, the camera 84, and the speaker.
With use of the device illustrated in
This embodiment can be implemented in appropriate combination with the other embodiments.
In this example, a secondary battery of one embodiment of the present invention, which includes a base film and a cap layer, and a secondary battery as a comparative example, which does not include a base film or a cap layer, were fabricated and the charge and discharge characteristics and cycle performance thereof were evaluated.
Sample 1 of one embodiment of the present invention was fabricated in the following manner. First, a titanium sheet was used to serve as both a substrate and a positive electrode current collector layer. As the titanium sheet, a non mirror rolled foil with a thickness of 0.1 mm and a purity of 99.5% was used after being processed by etching to be a diameter of 12 mm.
As a base film, titanium nitride (TiN) was deposited to 20 nm by a sputtering method over the titanium sheet. The sputtering conditions were as follows.
Target: titanium target, diameter of 100 mm
Sputtering power supply and output: DC power supply, 500 W
Atmosphere: argon flow rate of 12.0 sccm, nitrogen flow rate of 28 sccm, and pressure of 0.4 Pa
Deposition time: 8 minutes
Deposition temperature: set to 600° C.
Deposition rate: 2.5 nm/min
Next, as a positive electrode active material layer, lithium cobalt oxide (LiCoO2) was deposited to 1000 nm by a sputtering method. The sputtering conditions were as follows.
Target: lithium cobalt oxide target, diameter of 100 mm
Sputtering power supply and output: RF power supply, 500 W
Atmosphere: argon flow rate of 40 sccm, oxygen flow rate of 10 sccm, and pressure of 0.4 Pa
Deposition time: 461 minutes
Deposition temperature: set to 600° C.
Deposition rate: 2.2 nm/min
Next, as a cap layer, titanium oxide (TiOx) was deposited to approximately 20 nm by a sputtering method. The sputtering conditions were as follows.
Target: titanium target, diameter of 100 mm
Sputtering power supply and output: DC power supply, 500 W
Atmosphere: argon flow rate of 24 sccm, oxygen flow rate of 16 sccm, and pressure of 0.4 Pa
Deposition time: 27.7 minutes
Deposition temperature: set to 600° C. (an actual substrate temperature of approximately 400° C.)
Deposition rate: 0.72 nm/min
In addition, Sample 2, which does not include a base film, and Sample 3, in which titanium oxide (TiOx) is deposited as a base film, were fabricated. Sample 2 and Sample 3 were fabricated in a manner similar to that for Sample 1 except for the base film.
As other comparative examples, Sample 4 to Sample 6, each of which does not include a cap layer, were fabricated. Sample 4 to Sample 6 were fabricated in a manner similar to that for Samples 1 to 3 except that the cap layer was not deposited.
Table 2 shows fabrication conditions of the samples.
Next, with use of the samples as positive electrodes, CR2032 type coin battery cells (a diameter of 20 mm, a height of 3.2 mm) were fabricated.
A lithium metal was used for a counter electrode.
As an electrolyte contained in an electrolytic solution, 1 mol/L of lithium hexafluorophosphate (LiPF6) was used. As the electrolytic solution, a 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 and 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 were formed using stainless steel (SUS) were used.
The initial characteristics were measured under conditions of CCCV charging, 0.2 C, 4.2 V, and a cutoff current of 0.1 C. Discharging was performed at 0.2 C with a cutoff voltage of 2.5 V. Note that here, 1 C was set to 137 mA/g, which was a current value per weight of the positive electrode active material. The measurement temperature was set to 25° C. The measurement results of the initial characteristics are shown in Table 3,
According to Table 3,
Next, the charge and discharge cycle performance of these battery cells was evaluated. Charge and discharge in the measurement of the cycle performance were performed in a manner similar to that for the measurement of the initial characteristics. The cycle performance results are shown in
According to
This indicates that the provision of the cap layer results in fabrication of a secondary battery with favorable charge and discharge cycle performance. It is also found that better charge and discharge cycle performance is achieved in the case where the base film, particularly titanium nitride, is included than in the case where the base film is not provided.
In this example, a secondary battery of one embodiment of the present invention, which includes a cap layer, and a secondary battery as a comparative example, which does not include a cap layer, were fabricated, and the characteristics thereof were analyzed by TEM, electron energy loss spectroscopy (EELS), nanobeam electron diffraction, impedance measurement, and the like to evaluate the cycle performance thereof
Sample 11 of one embodiment of the present invention was fabricated in the following manner. First, a titanium sheet with a thickness of 100 μm was used to serve as both a substrate and a positive electrode current collector layer.
As a base film, titanium nitride (TiN) was deposited to 20 nm by a sputtering method over the titanium sheet. The sputtering conditions were as follows.
Target: titanium target, diameter of 2 inches
Sputtering power supply and output: RF power supply, 100 W
Atmosphere: argon flow rate of 3.0 sccm, nitrogen flow rate of 7 sccm, and pressure of 0.5 Pa
Deposition time: 15 minutes
Deposition temperature: set to 600° C.
Target-substrate distance: 75 mm
Next, as a positive electrode active material layer, lithium cobalt oxide (LiCoO2) was deposited to 900 nm by a sputtering method. The sputtering conditions were as follows.
Target: lithium cobalt oxide target, diameter of 2 inches
Sputtering power supply and output: RF power supply, 200 W
Atmosphere: argon flow rate of 10 sccm and pressure of 0.5 Pa
Deposition time: 109 minutes
Deposition temperature: set to 600° C.
Target-substrate distance: 75 mm
Deposition rate: 9.2 nm/min
Next, as a cap layer, titanium oxide (TiO2) was deposited to 20 nm by a sputtering method. The sputtering conditions were as follows.
Target: titanium target, diameter of 100 mm
Sputtering power supply and output: DC power supply, 500 W
Atmosphere: argon flow rate of 24 sccm, oxygen flow rate of 16 sccm, and pressure of 0.4 Pa
Deposition time: 27.7 minutes
Deposition temperature: set to 600° C. (an actual substrate temperature of approximately 400° C.)
Deposition rate: 0.72 nm/min
As a comparative example, Sample 12, which does not include a cap layer, was fabricated. Sample 12 was fabricated in a manner similar to that for Sample 11 except for the cap layer.
Table 4 shows fabrication conditions of the samples.
TEM images were taken under the following conditions.
Pretreatment of sample: Slicing by an FIB method (μ-sampling method)
Transmission electron microscope: JEM-ARM200F manufactured by JEOL Ltd.
Observation condition, acceleration voltage: 200 kV
Magnification accuracy: ±3%
Then, the electron state of cobalt in the samples after charge and discharge was analyzed using EELS, and the valence was calculated from L3/L2 with reference to Non-Patent Document 1. The measurement conditions of EELS were as follows.
Element analysis (point analysis)
Scanning transmission electron microscope: JEM-ARM200F manufactured by JEOL Ltd.
Acceleration voltage: 200 kV
Beam diameter: approximately 0.1 nmϕ
Element analysis apparatus: Quantum ER manufactured by Gatan Inc.
Photoelectron spectrometer: MOS detector array
Taking time: 30 seconds
EELS analysis points of Sample 11 after charge and discharge are represented by *1 and *2 in
Table 5 and Table 6 clearly show that reduction of cobalt in the crystal grain is suppressed more in Sample 11 including the cap layer. This suggests that degradation of a layered rock-salt crystal structure can be suppressed by providing the cap layer.
Next, the crystal structures of the grain boundary of lithium cobalt oxide and the vicinity thereof were analyzed by nanobeam electron diffraction.
As described above, the lattice constant of Sample 11 not including the cap layer after charge and discharge tends to be larger than the lattice constant of lithium cobalt oxide before charge and discharge. This is probably due to reduction of cobalt.
In contrast, in Sample 12 including the cap layer, the a-axis tends to be small on average even after charge and discharge. This indicates that cobalt has a large valence and reduction of cobalt is suppressed.
Next, secondary batteries were fabricated using Sample 11 and Sample 12, and their charge and discharge cycle performance was evaluated.
With use of Sample 11 and Sample 12 as positive electrodes and a lithium metal as a counter electrode, CR2032 type coin battery cells (a diameter of 20 mm and a height of 3.2 mm) were fabricated.
As an electrolyte included in an electrolytic solution, 1 mol/L lithium hexafluorophosphate (LiPF6) was used. As the electrolytic solution, a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC=3:7 and vinylene carbonate (VC) was added as an additive at 2 wt % was used.
As a separator, 25-μm-thick polypropylene was used.
A positive electrode can and a negative electrode can that were formed using stainless steel (SUS) were used.
A cycle test was performed under the following conditions. The charge voltage was set to 4.2 V. The measurement temperature was set to 25° C. CC/CV charging (0.2 C, 0.1 Ccut) and CC discharging (0.1 C, 2.5 Vcut) were performed, and a 10-minute break was taken before the next charging. Note that 1 C was set to 137 mA/g in this example and the like.
The impedance of each secondary battery was measured in the above charge and discharge cycle test.
In this example, an electrochemical phenomenon generated in the secondary battery of one embodiment of the present invention is analyzed with an equivalent circuit shown in
Here, Rs is the electric resistance of an electrode and the resistance of an electrolytic solution. The electric resistance of the electrode includes all simple electric resistances included in the coin cell. The resistance of the electrolytic solution refers to the diffusive resistance of ions in the solution.
R1 is denoted by Rf or Rsurface in some cases, which means a high-frequency component of the impedance of the secondary battery. R1 includes the diffusive resistance of lithium ions at the interface between the positive electrode and the electrolytic solution.
CPE1 (constant phase element, electric double layer capacitance) is the capacitance that reproduces the behavior on a porous electrode.
R2 is denoted by Rct in some cases, which means a low-frequency component. R2 includes the resistance in the process (charge transfer) in which Li ions are inserted into and extracted from a positive electrode active material layer (LiCoO2 in this example).
Ws1 is the resistance with lithium diffusion in a solid.
The graph of
The impedance of Sample 11 is shown in
The comparison of the impedance of Sample 12 between the second cycle and the 50th cycle shows a significant increase in R1 (high-frequency component) as shown in
In contrast, the comparison of the impedance of Sample 11 between the second cycle and the 50th cycle shows a relatively small increase in R1 as shown in
100: positive electrode, 101: positive electrode active material layer, 102: cap layer, 103: positive electrode current collector, 104: base film, 110: substrate, 111: substrate, 200: secondary battery, 201: secondary battery, 202: secondary battery, 203: solid electrolyte layer, 204: negative electrode active material layer, 205: negative electrode current collector, 206: protective layer, 209: cap layer, 210: negative electrode, 211: negative electrode, 212: negative electrode, 213: solid electrolyte layer, 214: base film, 215: positive electrode current collector, 220: separator, 221: electrolytic solution, 222: exterior body, 223a: lead electrode, 223b: lead electrode, 230: secondary battery, 231: secondary battery
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-187370 | Oct 2019 | JP | national |
| 2019-199752 | Nov 2019 | JP | national |
| 2020-127004 | Jul 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/059076 | 9/29/2020 | WO |
