Patent Application
20220166016
The present disclosure relates to a composite metal oxide for a lithium secondary battery containing a doping element, a positive electrode active material for a lithium secondary battery prepared therefrom, and a lithium secondary battery including the same. More specifically, the present disclosure relates to a composite metal oxide for a lithium secondary battery containing a doping element such that the lithium secondary battery exhibits high capacity and at the same time, suppresses micro cracks to improves lifespan characteristics thereof, and relates to a positive electrode active material for a lithium secondary battery prepared therefrom, and a lithium secondary battery including the same.
With development of portable mobile electronic devices such as smart phones, MP3 players, and tablet PCs, demand for secondary batteries capable of storing electrical energy therein is increasing explosively. In particular, with advent of electric vehicles, medium and large sized energy storage systems, and portable devices requiring high energy density, the demand for lithium secondary batteries is increasing.
With the increase in the demand for the lithium secondary battery, various research and development for improving characteristics of a positive electrode active material used in the lithium secondary battery are being conducted. For example, in Korean Patent Application Publication No. 10-2014-0119621 (Application No. 10-2013-0150315), a secondary battery is disclosed in which high voltage capacity and long lifespan characteristic are achieved by using a lithium excess positive electrode active material preparation precursor to control a type and composition of a metal substituted in the precursor, and control a type and amount of a metal as added.
A purpose of the present disclosure is to provide a composite metal oxide for a lithium secondary battery containing a novel doping element to suppress micro cracks to achieve an improved lifespan characteristic of the battery, and to provide a positive electrode active material for a lithium secondary battery prepared therefrom, and a lithium secondary battery including the same.
Another purpose of the present disclosure is to provide a composite metal oxide for a lithium secondary battery containing a doping element in which the doping element is added to the composite metal oxide using a novel method to achieve an optimal effect based on a content and a composition of the doping element relative to the composite metal oxide, such that the battery has the long-term lifespan characteristic and improved safety while electrochemical characteristic of high capacity thereof is maintained, and to provide a positive electrode active material for a lithium secondary battery prepared therefrom, and a lithium secondary battery including the same.
Purposes of the present disclosure are not limited to the above-mentioned purpose.
In one aspect of the present disclosure, there is provided a positive electrode active material comprising secondary particles, wherein each secondary particle is an agglomerate of a plurality of primary particles, wherein the primary particles include: first primary particles constituting a core portion A of each secondary particle; and second primary particles constituting a shell portion of each secondary particle, wherein the shell portion surrounds the core portion, wherein an average length of a long side of a longitudinal cross-section of each first primary particle is defined as a1, and an average length of a short side thereof perpendicular to the long side is defined as a2, wherein a1 is equal to or larger than a2, wherein an average length of a long side of a longitudinal cross-section of each second primary particle is defined as b1, and an average length of a short side thereof perpendicular to the long side is defined as b2, wherein b1 is larger than b2, wherein a ratio b1/b2 is in a range of 2 to 25.
In one implementation of the positive electrode active material, after a battery including the positive electrode active material has been subjected to multiple charging/discharging cycles, a micro crack including a space between the first primary particle or a space between the second primary particles occurs in the secondary particle, wherein when the battery including the positive electrode active material has been subjected to 100 charging/discharging cycles where each cycle includes a charging of the battery to 4.3V under 0.5 C constant current and a discharging of the battery to 2.7V under 0.5 C constant current, and then the battery is discharged to 0.27V, an area of the micro crack is equal to or smaller than 13% of an entire area of a longitudinal cross section of the secondary particle.
In one implementation of the positive electrode active material, each of 90% or greater of the second primary particles has b1 in a range of 0.1 μm to 2.0 μm, and b2 in a range of 0.01 μm to 0.8 μm.
In one implementation of the positive electrode active material, each of 90% or greater of the second primary particles has a b1/b2 in a range of 2 to 15, and has b2 in a range of 0.01 μm to 0.25 μm.
In one implementation of the positive electrode active material, at least some of the second primary particles has a rod shape having an aspect ratio, wherein each of 50% or greater of the second primary particles having the rod shape is oriented toward a surface of the secondary particle.
In one implementation of the positive electrode active material, each of an average length of a2 of each of 90% or greater of the first primary particles and an average length of b2 each of 90% or greater of the second primary particles is in a range of 0.01 μm to 0.8 μm.
In one implementation of the positive electrode active material, a ratio b1/a1 is in a range of 1 to 3.5, and a ratio b2/a2 is in a range of 0.8 to 1.5.
In one implementation of the positive electrode active material, each primary particle contains nickel (Ni), M1 and M2, wherein M1 includes at least one of manganese (Mn), cobalt (Co), and aluminum (Al), wherein a content of nickel (Ni) is greater than or equal to 80 mol %, wherein M2 acts as a doping element, wherein a content thereof is in a range of 0.05 mol % to 2 mol %.
In one implementation of the positive electrode active material, M2 includes at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb) and antimony (Sb).
In one implementation of the positive electrode active material, M2 includes at least two doping elements selected from tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb) and antimony (Sb), wherein the two doping elements are co-doped into the positive electrode active material.
In one implementation of the positive electrode active material, when M2 is tantalum (Ta), a ratio b2/a2 is in a range of 0.5 to 1.2, and b2 is in a range of 0.01 μm to 0.6 μm; when M2 is tungsten (W), the ratio b2/a2 is in a range of 0.5 to 2, and b2 is in a range of 0.005 μm to 0.5 μm; when M2 is molybdenum (Mo), the ratio b2/a2 is in a range of 0.7 to 1.5, and b2 is in a range of 0.02 μm to 0.7 μm; when M2 is niobium (Nb), the ratio b2/a2 is in a range of 0.5 to 1.5, and b2 is in a range of 0.02 μm to 0.7 μm; or when M2 is antimony (Sb), the ratio b2/a2 is in a range of 0.5 to 1.5, and b2 is in a range of 0.01 μm to 0.5 μm.
In one implementation of the positive electrode active material, M2 includes: one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb); and at least one of tin (Sn), hafnium (Hf), silicon (Si), zirconium (Zr), calcium (Ca), germanium (Ge), gallium (Ga), indium (In), ruthenium (Ru), tellurium (Te), iron (Fe), chromium (Cr), vanadium (V), and titanium (Ti), wherein M2 includes at least two doping elements.
In one implementation of the positive electrode active material, after a battery including the positive electrode active material has been subjected to 100 charging/discharging cycles where each cycle includes a charging of the battery to 4.3V under 0.5 C constant current and a discharging of the battery to 2.7V under 0.5 C constant current, Rct of the positive electrode active material is in a range of 10Ω to 30Ω.
In one implementation of the positive electrode active material, when the positive electrode active material is subjected to X-ray diffraction analysis using a device with 45 kV and 40 mA output and a Cu Ka beam source at a scan rate of 1 degree per minute and at a step size spacing of 0.0131, a ratio of an intensity of a peak 003 to an intensity of a peak 104 is in a range of 2 to 2.2.
In one implementation of the positive electrode active material, the positive electrode active material includes a compound containing a metal, lithium, a doping element, and oxygen, wherein the positive electrode active material is prepared by mixing a composite metal oxide containing the metal, the doping element, and a lithium compound containing the lithium with each other and then performing calcination of the mixture, wherein the metal includes: nickel (Ni); and at least one of cobalt (Co), manganese (Mn), and aluminum (Al), wherein the doping element includes at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb), wherein a content of nickel (Ni) is greater than or equal to 80 mol %, and a content of the doping element is in a range of 0.05 mol % to 2 mol %.
In one implementation of the positive electrode active material, the positive electrode active material is prepared by performing calcination of the mixture at least one time in a temperature range of 700° C. to 800° C., wherein each of 90% or greater of the second primary particles in the positive electrode active material after the calcination has b2 in a range of 0.01 μm to 0.8 μm.
In another aspect of the present disclosure, there is provided a composite metal oxide for a lithium secondary battery as a precursor of the positive electrode active material as defined above, wherein the composite metal oxide is a spherical agglomerate of particles prepared via agglomeration of a plurality of micro-particles, wherein the composite metal oxide is mixed with a lithium compound and then calcination of the mixture is carried out at a temperature range of 700° C. to 800° C., thereby producing the positive electrode active material, wherein the micro-particles of the composite metal oxide include: first micro-particles constituting a core portion of the agglomerate of particles; and second micro-particles constituting a shell portion surrounding the core portion of the agglomerate of particles, wherein an aspect ratio of the second micro-particle is equal to an aspect ratio of the second primary particle of the positive electrode active material.
In still another aspect of the present disclosure, there is provided a positive electrode for a secondary battery including the positive electrode active material as defined above. In still yet another aspect of the present disclosure, there is provided a lithium secondary battery including the positive electrode as defined above.
In still yet another aspect of the present disclosure, there is provided a battery module including the lithium secondary battery as defined above as a unit cell.
In still yet another aspect of the present disclosure, there is provided a battery pack including the battery module as defined above, wherein the battery pack is used as a power source for an medium and large sized apparatus, wherein the medium and large sized apparatus is selected from a group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.
According to the present disclosure as described above, the positive electrode active material according to the present disclosure includes the secondary particles, each second particle as the agglomerate of a plurality of primary particles, wherein the secondary particle includes Ni at the high content level and the doping element.
Further, according to another aspect of the present disclosure, the composite metal oxide for a lithium secondary battery containing the doping element may be realized in which the shape of the composite metal oxide may be controlled and the micro cracks may be suppressed such that long-term lifespan characteristics and stability of the battery may be maintained and the electrochemical characteristics thereof may be improved. Further, the positive electrode active material for a lithium secondary battery as prepared therefrom, and the lithium secondary battery including the same may be realized.
Further, according to still another aspect of the present disclosure, when a mixture of the composite metal oxide containing nickel at the high content level and having a rod shape, and the lithium compound is calcined at a high temperature, the shape of the composite metal oxide may be maintained in a relatively unchanged manner, and thus the micro-structure may be stably maintained, thereby producing the positive electrode active material for a lithium secondary battery with improved stability and electrochemical characteristic. Further, the lithium secondary battery including the same may be realized.
Specific details of other embodiments are included in the detailed description and drawings.
Advantages and features of the present disclosure, and how to achieve the advantages and features will become apparent with reference to the embodiments as described below in detail in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments as disclosed below, but may be implemented in a variety of different forms. Unless otherwise specified in following descriptions, all of numbers, values, and/or expressions indicating ingredients, reaction conditions, and contents of ingredients in the present disclosure are, in essence, approximations thereof based on various uncertainties in measurements which occur in obtaining the numbers, values, and/or expressions. Thus, the numbers, values and/or expressions should be understood as being modified by a term “about” in all instances. Further, where a numerical range is disclosed in the present description, the range is continuous and includes a minimum value and a maximum value of the range, unless otherwise indicated. Further, where the number or the value refers to an integer, the range includes all of integers included between the minimum and the maximum of the range, unless otherwise indicated.
Further, in the present disclosure, when a variable is included in a range, the variable will be understood to include all values within a stated range including stated endpoints of the range. For example, a range of “5 to 10” includes values of 5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc. It will be understood that the variable includes any value between valid integers in a stated range such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9, etc. For example, a range “10% to 30%” includes all of integer values such as 10%, 11%, 12%, 13%, 30%, etc. as well as any subranges such as 10% to 15%, 12% to 18%, or 20% to 30%, etc. It will be understood that the range includes any value between valid integers within the stated range such as 10.5%, 15.5%, 25.5%, etc.
In one embodiment, an average value of diameters or sizes of particles in an agglomerate of various particles such as primary particles and secondary particles is expressed. However, the present disclosure is not limited thereto. Generally, a diameter representing a maximum value of a distribution of the particle diameters, a median diameter corresponding to a median value of an integral distribution curve thereof, and various average diameters (number average, length average, area average, mass average, volume average, etc.) may be used. In the present disclosure, unless otherwise specified, an average size and an average particle diameter may respectively refer to a number average size and a number average diameter, and may mean a D50 (a particle diameter at a point where a distribution percentage is 50%).
Referring to
An average length of a long side of a longitudinal cross-section of each first primary particle 110 is a1, and an average length of a short side thereof perpendicular to the long side a1 is a2, wherein a1 is equal to or larger than a2 (a1≥a2). An average length of a long side of a longitudinal cross-section of each second primary particle 120 is b1, and an average length of a short side thereof perpendicular to the long side b1 is b2, wherein b1 is larger than b2 (b1>b2) and a ratio b1/b2 is in a range of 2 to 25. Specifically, each of 90% or greater of the second primary particles may have a ratio b1/b2 in a range of 2 to 25.
The positive electrode active material according to the present embodiment may be used for an positive electrode for a lithium secondary battery. In the positive electrode active material according to the present embodiment, the secondary particle 200 may be approximately spherical. The first primary particles 110 may constitutes the core portion A of the secondary particle 200. The second primary particles 120 may constitutes the shell portion B of the secondary particle 200. The second primary particle 120 may have a rod shape having a longitudinal cross section having a long side and a short side perpendicular to the long side, wherein an average length of the long side is b1, and an average length of the short side is b2. At least some of the second primary particles 120 may be oriented in a radial direction. The radial direction means a direction R from a center c of the secondary particle 200 toward a surface of the secondary particle 200 as shown in
For example, the second primary particle 120 may be oriented such that the long side is parallel to the radial direction. Thus, diffusion of lithium ions from the surface of the secondary particle 200 into the inside thereof may be promoted. Further, the second primary particle 120 may be oriented in a parallel manner to a movement direction of lithium ions. This may reduce a volume change of the secondary particle 200 during expansion and contraction of the secondary particle 200 due to repeated reversible charging and discharging of the secondary battery. Cracks that may occur between the primary particles 100 may be suppressed. For example, a spacing between the primary particles may be reduced according to a shape change of the primary particles 100 due to a volume change accompanying the electrochemical reaction, so that the lifespan characteristic of the secondary battery may be improved. For example, the direction R from the center c of the secondary particle 200 toward the surface of the secondary particle 200 may be parallel to a direction of an a-axis direction of the primary particle 100, and a c-axis direction of the primary particle 100 may be perpendicular to the a-axis direction.
For example, a maximum change percentage along the a-axis of the primary particle 100 after a charge/discharge cycle may be approximately 2.1%, while a maximum change percentage along the c-axis thereof may be approximately 4.5%. This phenomenon may be caused by the primary particles, particularly, the second primary particles 120 constituting the shell portion of the secondary particle 200 rather than the first primary particles 110 constituting the core portion of the secondary particle 200. In general, micro-cracks may occur due to anisotropic volume changes along the a-axis and the c-axis of the second primary particle 120, thereby reducing the capacity and lifespan characteristics after the cycles.
On the contrary, in an embodiment of the present disclosure, the second primary particle 120 may contain a doping element, and a ratio between contents of the doping element and a transition metal may be controlled such that the ratio b1/b2 of the second primary particle 120 may be in a range of 2 to 25, and the second primary particle 120 has a rod shape having an aspect ratio in the above range. Thus, a stable micro-structure may be maintained even in anisotropic contraction along the a-axis and the c-axis. Preferably, the ratio b1/b2 of the second primary particle 120 may be in a range of 2 to 20, or 2 to 18, or 2 to 15, or 2 to 13, or 2 to 11.
In the present embodiment, the secondary particle 200 may be formed by agglomeration of the first primary particles 110 and the second primary particles 120. The first primary particle 110 may have an average length a1 of along side of a longitudinal cross section thereof and an average length a2 of a short side thereof. The second primary particle 120 may have an average length b1 of a long side of a longitudinal cross section thereof and an average length b2 of a short side of the longitudinal cross section thereof. The positive electrode active material according to the present embodiment may include nickel (Ni) at a high content level. Controlling the shapes of the first primary particle 110 and the second primary particle 120 may allow the cycle characteristics and stability of the battery to be improved and allow the battery to have high electrochemical capacity. The first primary particles 110 may constitute the core portion A of the secondary particle 200, while the second primary particles 120 may constitute the shell portion B of the secondary particle 200, so that the second primary particles 120 surround an outer surface of the agglomerate of the first primary particles 110.
Each of 90% or greater of the second primary particles 120 may have the ratio b1/b2 in a range of 2 to 25. When each of 90% or greater of the second primary particles 120 constituting the shell portion of the secondary particle 200 may have the ratio b1/b2 in a range of 2 to 25, lithium ions may move smoothly from the surface of the secondary particle 200 to the center c thereof. A morphology of the secondary particle 200 may be efficiently adjusted to control reversibility of a volume change that occurs during charging and discharging of the secondary battery, so that an overall shape of the secondary particle 200 may be maintained. Specifically, the ratio b1/b2 may be in a range of 2 to 15, more specifically, 2.2 to 11.
Further, in the second primary particle 120, b1 may be 2.0 μm or smaller. When b1 of the second primary particle 120 is larger than 2.0 μm, the lifespan characteristic of the secondary battery may be deteriorated. Specifically, b1 may be in a range of 0.005 μm to 2.0 μm, or 0.01 μm to 2.0 μm, 0.05 μm to 2.0 μm, 0.1 μm to 2.0 μm, 0.05 μm to 1.5 μm, 0.05 μm to 1.2 μm, or 0.1 μm to 1.2 μm.
Each of 90% or greater of the second primary particles of the second primary particle 120 may have b1 in a range of 0.1 μm to 2.0 μm, and b2 in a range of 0.01 μm to 0.8 μm. When each of b1 and b2 of the second primary particle 120 is controlled to be in the above range, orientations of the second primary particles 120 constituting the secondary particle 200 may be further uniform.
Each of an average length of a2 of each of 90% or greater of the first primary particles 110 and an average length of b2 of each of 90% or greater of the second primary particles 120 may be in a range of 0.01 μm to 0.8 μm. For example, a2 as the short side length of the first primary particle 110 may be similar to b2 as the short side length of the second primary particle 120. The first primary particles 110 and the second primary particles 120 may constitute the core portion A and the shell portion B of the secondary particle 200, respectively. Specifically, the average length of b2 of each of 90% or greater of the second primary particles 120 may be in a range of 0.015 μm to 0.8μ m, or 0.02 μm to 0.6 μm, or 0.03 μm to 0.5 μm, or 0.03 μm to 0.25 μm. Further, a ratio b1/a1 may be in a range of 1 to 3.5, while a ratio b2/a2 may be in a range of 0.8 to 1.5.
When, in the secondary particle 200, each of 90% or greater of the first primary particles 110 and each of 90% or greater of the second primary particles 120 have the dimensions in the above-described range, the first primary particles 110 constitute the core portion of the secondary particle 200 to guide the second primary particles 120 to be oriented along the first primary particles 110. The second secondary particles 120 may surround the outer surface of the agglomerate of the first primary particles 110, so that the secondary particle 200 may have a stable micro-structure and the electrochemical characteristic and lifespan characteristic of the battery may be improved.
After the battery including the positive electrode active material has been subjected to multiple charging/discharging cycles, micro cracks may occur in a space between the first primary particles 110 or between the second primary particles 120 in the secondary particle 200.
A manner in which the micro crack according to the present embodiment affects the lifespan of the battery may be related to a crack path. The crack path means a path along which a first crack between the first primary particles 110 and a second crack between the second primary particles 120 are connected to each other, and the second crack extends to the outermost surface of the secondary particle 200. For example, in the secondary particle 200 according to the present embodiment, micro cracks and crack paths may be prevented from occurring inside the secondary particle 200 after 100 cycles, thereby improving lifespan and thermal stability.
Specifically, the positive electrode active material according to the present embodiment has been subjected to 100 charging/discharging cycles where each cycle includes a charging of the battery to 4.3V under 0.5 C constant current (CC) or constant current and constant voltage (CV) and a discharging of the battery to 2.7V under 0.5 C constant current. Then, when the battery is discharged to 0.27V, an area of the micro crack may be equal to or smaller than 13% of an area of a longitudinal cross section of the secondary particle. Thus, the crack path may be prevented from occurring. Specifically, the area of micro crack after the 100 cycles may be in a range of 2% to 8%, more specifically, 3% to 7% of an area of a longitudinal cross section of the secondary particle.
The positive electrode active material has been subjected to 100 charging/discharging cycles where each cycle includes a charging of the battery to 4.3V under 0.5 C constant current (CC) and a discharging of the battery to 2.7V under 0.5 C constant current. Then, when the battery is discharged to 0.27V, the area of the microcrack may be measured. In this connection, the area of the micro crack including both the spacing between the first primary particles 110 and the spacing between the second primary particles 120 may be equal to or smaller than 13% of a total area of a longitudinal cross section of the secondary particle. Specifically, the area of the micro crack may be equal to or smaller than 10% of a total area of a longitudinal cross section of the secondary particle. More specifically, the area of the micro crack may be in a range of 0.05% to 10%, more specifically, 1% to 8% of the total area of a longitudinal cross section of the secondary particle. Further, the area of the micro crack may be increased as a content of nickel (Ni) increases.
In general, when the secondary battery using the positive electrode active material has been subjected to multiple charge/discharge cycles for a long period of time, the secondary particle constituting the positive electrode active material repeatedly expands and contracts. In the process of performing the cycles, a volume of each of the primary particles constituting the secondary particle may not be reversibly recovered, or a side reaction may occur due to electrolyte invasion into a space between the primary particles, such that the micro-structure of the primary particles is destroyed, which causes a decrease in lifespan or a rapid decrease in capacity.
The crack path may include a path along which the first crack as a separation space occurring between the first primary particles 110 of the core portion A, the second crack as a separation space occurring between the second primary particles 120 of the shell portion B are connected to each other, and then the second crack connected to the first crack extends to the outer surface of the secondary particle. When the crack path occurs, electrolyte may invade into the core portion A of the secondary particle 200, thereby causing the collapse of the micro-structure of the secondary particle 200.
On the contrary, the positive electrode active material according to the present embodiment may be prepared using a novel doping element. Further, shapes and arrangements of the first primary particles 110 and the second primary particles 120 constituting the positive electrode active material may be controlled using a novel method such that the occurrence of the crack paths in the secondary particle 200 may be suppressed even after cycles for a long time. For example, controlling the secondary particle 200 so that the area of the micro-crack is equal to or smaller than 13% of a total area of a longitudinal cross section of the secondary particle may allow the crack path including the connection between the first crack and the second crack and the extension to the outer surface of the secondary particle 200 to be prevented from occurring in the secondary particle.
In the present embodiment, the primary particle 100 may contain nickel (Ni) and, M1 and M2, wherein M1 includes at least one of manganese (Mn), cobalt (Co) and aluminum (Al), wherein a content of nickel (Ni) may be equal to or greater than 80 mol %, wherein a content of M2 as a doping element may be in a range of 0.05 mol % to 2 mol %. Preferably, the content of M2 may be in a range of 0.05 mol % to 1.5 mol %, or 0.05 mol % to 1.2 mol %, or 0.05 mol % to 1 mol %, or 0.1 mol % to 1.7 mol %, or 0.1 mol % to 1.5 mol %, or 0.1 mol % to 1.2 mol %, or 0.1 mol % to 0.5 mol %, or 0.5 mol % to 1.5 mol %, or 0.5 mol % to 1.2 mol %.
The positive electrode active material according to the present embodiment may contain nickel (Ni) at a high content level which is 80 mol % or greater, and 0.05 mol % to 2 mol % of the doping element. Thus, the battery including the same may exhibit high capacity, and have improved lifespan characteristic and thermal stability at the same time. When the content of nickel (Ni) is smaller than 80 mol %, the battery may not exhibit high capacity. When the content of the doping element is in the above range, the doping element may allow the secondary particle 200 to be structurally stabilized via interaction thereof with a transition metal such as nickel.
In one embodiment of the present disclosure, the positive electrode active material may be prepared by mixing a first composite metal oxide containing nickel (Ni), M1 and M2 with a lithium compound and performing calcination of the mixture in a temperature range of 700° C. to 800° C., or may be prepared by mixing a second composite metal oxide containing nickel (Ni) and M1 with M2 and lithium compound and performing calcination of the mixture in a temperature range of 700° C. to 800° C. Each of the first and second composite metal oxides, and the positive electrode active material prepared by the calcination of the first or second composite metal oxide may be composed of agglomerated particles prepared by agglomerating a plurality of micro-particles. The positive electrode active material may be prepared by calcination of a mixture of the first or second composite metal oxide and a lithium compound at a high temperature, for example, in a temperature range of 700° C. to 800° C.
In general, in a process of mixing the first or second composite metal oxide with a lithium compound, and of calcination of the mixture, micro-particles constituting the first or second composite metal oxide may be agglomerated with each other. As a result, the primary particles constituting the positive electrode active material may have a volume larger than that of the micro-particles constituting the first or second composite metal oxide before the calcination. As such, when the battery including the positive electrode active material in which the volume of the primary particles is increased is subjected to the charging and discharging cycle, micro-particle arrangement of the first or second composite metal oxide before the calcination may not be maintained in the secondary particle as the agglomerate of the primary particles due to a difference between volume changes in the long and short sides thereof. Further, when the battery is subjected to the charging and discharging cycle, the micro crack including the separation space between the primary particles may occur and further, the micro crack may gradually accumulate, thereby causing the collapse of the micro-structure and deterioration of the lifespan characteristic.
On the contrary, after the positive electrode active material according to the present embodiment has been subjected to calcination at a high temperature in a temperature range of 700° C. to 800° C., an original shape and size (for example, micro-particles) of the first or second composite metal oxide before the calcination may be maintained in calcinated the positive electrode active material. Further, the primary particles constituting the positive electrode active material may have a similar orientation to that of each of the primary particles constituting the first or second composite metal oxide. Therefore, after the positive electrode active material according to the present embodiment has been subjected to a plurality of cycles, the positive electrode active material may exhibit a high retention characteristic, and may maintain a stable micro-structure such that the micro cracks hardly occur.
In the present embodiment, the first composite metal oxide may be prepared by mixing nickel (Ni) and M1 and M2 and calcination of the mixture. The second composite metal oxide may be prepared by mixing nickel (Ni) and M1, and then adding M2 thereto, and then calcination of the mixture. M2 may act as the doping element and may be added at 0.05 mol % to 2 mol % based on a total content of the positive electrode active material. As in the first composite metal oxide, M2 and nickel (Ni) and M1 may be subjected to co-precipitation at the same time. Alternatively, as in the second composite metal oxide nickel, (Ni) and M1 may be subjected to co-precipitation, and then M2 present in a solid state and having a particle size of 2 μm or smaller and a lithium compound may be added thereto, and the mixture may be subjected to calcination.
M2 may include at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb). Specifically, when M2 is tantalum (Ta), the ratio b2/a2 may be in a range of 0.5 to 1.2, and b2 may be in a range of 0.01 μm to 0.6 μm; when M2 is tungsten (W), the ratio b2/a2 may be in a range of 0.5 to 2, and b2 may be in a range of 0.005 μm to 0.5 μm; when M2 is molybdenum (Mo), the ratio b2/a2 may be in a range of 0.7 to 1.5, and b2 may be in a range of 0.02 μm to 0.7 μm; when M2 is niobium (Nb), the ratio b2/a2 may be in a range of 0.5 to 1.5, and b2 may be in a range of 0.02 μm to 0.7 μm; and when M2 is antimony (Sb), the ratio b2/a2 may be in a range of 0.5 to 1.5, and b2 may be in a range of 0.01 μm to 0.5 μm.
Alternatively, M2 may include at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb) and antimony (Sb), and at least one of tin (Sn), hafnium (Hf), silicon (Si), zirconium (Zr), calcium (Ca), germanium (Ge), gallium (Ga), indium (In), ruthenium (Ru), tellurium (Te), iron (Fe), chromium (Cr), vanadium (V) and titanium (Ti). That is, M2 may be composed of at least two different doping elements.
For example, in the positive electrode active material according to the present embodiment, M2 as the doping element may include one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb), and at least one auxiliary element selected from tin (Sn), hafnium (Hf), silicon (Si), zirconium (Zr), calcium (Ca), germanium (Ge), gallium (Ga), indium (In), ruthenium (Ru), tellurium (Te), iron (Fe), chromium (Cr), vanadium (V) and titanium (Ti) to supplement a function of one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb).
After the battery including the positive electrode active material has been subjected to 100 cycles in which each cycle includes charging of the battery to 4.3V under 0.5 C constant current and discharging of the battery to 2.7V under 0.5 C constant current, Rct of the positive electrode active material may be in a range of 10Ω to 30Ω. After the battery including the positive electrode active material according to the present embodiment has been subjected to a plurality of cycles, that Rct of the positive electrode active material may be maintained within the above-mentioned range because the change of the micro-structure of the positive electrode active material is controlled.
Further, when the positive electrode active material after the calcination at a temperature of 730° C. or lower is subjected to X-ray diffraction analysis using a device with 45 kV, and 40 mA output and a Cu Ka beam source at a scan rate of 1 degree per minute and at a step size spacing of 0.0131, a ratio of intensity of peak 003 to intensity of peak 104 may be in a range of 2 to 2.2. In the X-ray diffraction analysis, the positive electrode active material as a measurement target sample may be prepared to minimize an effect of errors due to other equipment, sample preparation details, etc. For example, the beam source for measuring the positive electrode active material may have an area smaller than the area of the positive electrode active material and may be configured to minimize a preferred orientation.
The positive electrode active material may be a compound containing the metal, lithium, the doping element, and oxygen. The positive electrode active material may be prepared by providing a composite metal oxide containing 80 mol % or greater of nickel (Ni) as the metal, adding 0.05 mol % to 2 mol % of the doping element including at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb) % and a lithium compound containing lithium to the composite metal oxide and then calcination of the mixture. The positive electrode active material may be prepared via calcination at least one time in the temperature range of 700° C. to 800° C. The average length of b2 of the second primary particle in the positive electrode active material after the calcination may be in a range of 0.01 μm to 0.8 μm.
In general, when the mixture of the composite metal oxide containing 80 mol % or greater of nickel (Ni) and the lithium compound is calcined at a high temperature, the volume of the primary particles constituting the secondary particles expands. In particular, the second primary particle in which a difference between aspect ratios of the primary particles is larger has a large volume change, such that the micro-structure of the secondary particle may be unstable.
On the contrary, although the positive electrode active material according to the present embodiment contains nickel (Ni) at a higher content level which is 80 mol % or greater, each of 90% or greater of the second primary particles has the average length of b2 which is maintained at 0.01 μm to 0.25 μm even after calcination in the temperature range of 700° C. to 800° C. at the high temperature. This may stabilize the micro-structure of the secondary particle such that the characteristic of the positive electrode active material may be further improved. More specifically, the average length of b2 may be in a range of 0.01 μm to 0.7 μm, or 0.01 μm to 0.3 μm, 0.02 μm to 0.3 μm, or 0.02 μm to 0.2 μm.
According to another aspect of the present disclosure, embodiments of the present disclosure relate to a composite metal oxide for a lithium secondary battery as a precursor of the above-described positive electrode active material. The composite metal oxide may be a spherical agglomerate of particles as prepared via agglomeration of a plurality of micro-particles. The composite metal oxide may be mixed with lithium compound and then calcination of the mixture may be carried out at a temperature range of 700° C. to 800° C., thereby producing the positive electrode active material. The micro-particles of the composite metal oxide may include the first micro-particles constituting a core portion of the agglomerate of particles, and the second micro-particles surrounding the first micro-particles and constituting a shell portion of the agglomerate of particles. A aspect ratio of the second micro-particle may correspond to the aspect ratio of the second primary particle of the positive electrode active material. Thus, the composite metal oxide for the lithium secondary battery may be prepared.
The composite metal oxide according to the present embodiment may be subjected to calcination at a high temperature such as, for example, a temperature range of 700° C. to 800° C., thereby producing the positive electrode active material. The composite metal oxide hardly changes in volume during the calcination process. Thus, the size and shape of the composite metal oxide may be maintained to be substantially the same as those of the positive electrode active material. The co-precipitation of the composite metal oxide may allow at least some of the micro-particles to be oriented to have directionality while the micro-particles are agglomerated with each other. The composite metal oxide may have a thermodynamically stable structure. This structure is maintained even during the calcination, thereby improving the electrochemical and lifespan characteristics of the positive electrode active material.
The composite metal oxide may contain a metal, wherein the metal includes at least one of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). Further, the composite metal oxide may be mixed with a doping element and a lithium compound and then the mixture may be subjected to calcination, thereby producing the positive electrode active material.
The doping element may include at least one of tantalum (Ta), tungsten (W), molybdenum (Mo), niobium (Nb), and antimony (Sb). The content of nickel (Ni) may be in a range of 80 mol % or greater, and the content of the doping element may be in a range of of 0.05 mol % to 2 mol %.
According to still another aspect of the present disclosure, embodiments of the present disclosure relate to a positive electrode for a secondary battery containing the above-described positive electrode active material, and to a lithium secondary battery including the positive electrode.
According to still yet further aspect of the present disclosure, embodiments of the present disclosure relate to a battery module including the lithium secondary battery as a unit cell.
Further, according to still yet further aspect of the present disclosure, embodiments of the present disclosure relate to a battery pack including the battery module, wherein the battery pack may be used as a power source for a medium and large sized apparatus, wherein the medium and large sized apparatus may be selected from a group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and systems for power storage.
Present Examples and Comparative Examples of the present disclosure are described below. However, the following Examples are only preferred embodiments of the present disclosure. The scope of the right of the present disclosure is not limited to the following Examples.
(1) Positive Electrode Active Material Based on Ta Dopant Content
10 liters of distilled water was put into a co-precipitation reactor (capacity 47 L, and an output of a rotary motor 750 W or greater), and then N2 gas was supplied to the reactor at a flow rate of 6 liters/min. While a temperature of the reactor was maintained at 45° C., stirring was carried out at 350 rpm. Nickel sulfate aqueous solution (NiSO46H2O, Samchun Chemicals), and cobalt sulfate aqueous solution (CoSO47H2O, Samchun Chemicals) were mixed with each other such that a molar ratio of nickel (Ni) and cobalt (Co) was 9:1, thereby preparing a metal solution having a concentration of 2M. The prepared metal solution was continuously input to the reactor for 24 hours at 0.561 liter/hour. 16M concentration of ammonia solution (NH4OH, JUNSEI) was continuously input to the reactor for 24 hours at 0.08 L/hour. 4M concentration of sodium hydroxide solution (NaOH, Samchun Chemicals) was continuously input to the reactor for 24 hours at 0.60 L/hour. While maintaining pH in the reactor in a range of 10 to 12, co-precipitation was performed to prepare Ni0.9Co0.1(OH)2 composite metal hydroxide.
The prepared Ni0.9Co0.1(OH)2 metal complex hydroxide was washed several times with distilled water, filtered, and dried in a vacuum dryer at 110° C. for 12 hours to prepare the Ni0.9Co0.1(OH)2 metal complex hydroxide in a powder form. After mixing the Ni0.9Co0.1(OH)2 metal complex hydroxide prepared in the powder form and a lithium hydroxide (LiOH) with each other at a molar ratio of 1:1.01, the mixture was heated at a temperature increase rate of 2° C./min and was maintained at 450° C. for 5 hours. In this way, preliminary calcination was performed. Subsequently, main calcination was carried out at 730° C. for 10 hours to prepare positive electrode active material powders. This Preparation Example is shown in Table 1.
10 liters of distilled water was put into a co-precipitation reactor (capacity 47 L, and an output of a rotary motor 750 W or greater), and then N2 gas was supplied to the reactor at a flow rate of 6 liters/min. While a temperature of the reactor was maintained at 45° C., stirring was carried out at 350 rpm. Nickel sulfate aqueous solution (NiSO46H2O, Samchun Chemicals), and cobalt sulfate aqueous solution (CoSO47H2O, Samchun Chemicals) were mixed with each other such that a molar ratio of nickel (Ni) and cobalt (Co) was 9:1, thereby preparing a metal solution having a concentration of 2M. The prepared metal solution was continuously input to the reactor for 24 hours at 0.08 liter/hour. 16M concentration of ammonia solution (NH4OH, JUNSEI) was continuously input to the reactor for 24 hours at 0.11 L/hour. 4M concentration of sodium hydroxide solution (NaOH, Samchun Chemicals) was continuously input to the reactor for 24 hours at 0.60 L/hour. While maintaining pH in the reactor in a range of 10 to 12, co-precipitation was performed to prepare Ni0.9Co0.1(OH)2 composite metal hydroxide.
The prepared Ni0.9Co0.1(OH)2 metal complex hydroxide was washed several times with distilled water, filtered, and dried in a vacuum dryer at 110° C. for 12 hours to prepare the Ni0.9Co0.1(OH)2 metal complex hydroxide in a powder form. We used a ball mill to prepare tantalum oxide (Ta2O5) powders so that an average particle size thereof was 2 μm or smaller. The Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form, the tantalum oxide (Ta2O5), and lithium hydroxide (LiOH) were mixed with each other at a molar ratio of 0.9995:0.00025:1.01. Then, the mixture was heated at a temperature increase rate of 2° C./min and was maintained at 450° C. for 5 hours. In this way, preliminary calcination was performed. Subsequently, main calcination was carried out at 730° C. for 10 hours to prepare positive electrode active material powders. This Preparation Example is shown in Table 1.
Each of positive electrode active material powders of Preparation Example 3 to Preparation Example 6 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, tantalum oxide (Ta2O5), and lithium hydroxide (LiOH) were mixed with each other at each of molar ratios as shown in the following Table 1. These Preparation Examples are shown in Table 1.
A positive electrode active material powder of Preparation Example 7 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, aluminum hydroxide (Al(OH)3), and lithium hydroxide (LiOH) were mixed with each other at a molar ratio as shown in the following Table 1. These Preparation Examples are shown in Table 1.
(2) Positive Electrode Active Material Based on Calcination Temperature and Calcination Duration
We prepared each of positive electrode active material powders of Preparation Example 8 to Preparation Example 11 in the same way as in Preparation Example 2 except that only the calcination temperature in Preparation Example 1 was changed based on Table 2 below.
These Preparation Examples are shown in Table 2.
Each of positive electrode active material powders of Preparation Example 12 to Preparation Example 15 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, tantalum oxide (Ta2O5), and lithium hydroxide (LiOH) were mixed with each other at each of molar ratios as shown in the following Table 2, and the mixture was calcinated at a calcination temperature as shown in the following Table 2. These Preparation Examples are shown in Table 2.
Each of positive electrode active material powders of Preparation Example 16 to Preparation Example 19 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, aluminum hydroxide (Al(OH)3), and lithium hydroxide (LiOH) were mixed with each other at each of molar ratios as shown in the following Table 2, and the mixture was calcinated at a calcination temperature as shown in the following Table 2. These Preparation Examples are shown in Table 2.
We prepared each of positive electrode active material powders of Preparation Example 20 to Preparation Example 21 in the same way as in Preparation Example 2 except that only the calcination temperature in Preparation Example 1 was changed based on Table 3 below. These Preparation Examples are shown in Table 3.
Each of positive electrode active material powders of Preparation Example 22 to Preparation Example 23 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, tantalum oxide (Ta2O5), and lithium hydroxide (LiOH) were mixed with each other at each of molar ratios as shown in the following Table 3, and the mixture was calcinated at a calcination temperature as shown in the following Table 3. These Preparation Examples are shown in Table 3.
Each of positive electrode active material powders of Preparation Example 24 to Preparation Example 25 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, aluminum hydroxide (Al(OH)3), and lithium hydroxide (LiOH) were mixed with each other at each of molar ratios as shown in the following Table 3, and the mixture was calcinated at a calcination temperature as shown in the following Table 3. These Preparation Examples are shown in Table 3.
(3) Positive Electrode Active Material Based on Dopant Type and Dopant Content
Each of positive electrode active material powders of Preparation Example 26 to Preparation Example 41 was prepared in the same manner as in Preparation Example 2 except that when the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, tantalum oxide (Ta2O5), and lithium hydroxide (LiOH) were mixed with each other in Preparation Example 2, tantalum oxide (Ta2O5) as the dopant compound was replaced with each of niobium pentoxide (Nb2O5) (Preparation Example 26 to Preparation Example 29), molybdenum trioxide (MoO3) (Preparation Example 30 to Preparation Example 33), tungsten trioxide (WO3) (Preparation Example 34 to Preparation Example 37), and antimony trioxide (Sb2O3) (Preparation Example 38 to Preparation Example 41) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in a following Table 4. These Preparation Examples are shown in Table 4. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller.
(4) Positive Electrode Active Material Based on Type of Composite Metal Hydroxide
Each of positive electrode active material powders of Preparation Example 42 to Preparation Example 61 was prepared in the same manner as in Preparation Example 2 except that the Ni0.9Co0.1(OH)2 composite metal oxide prepared in the powder form in Preparation Example 2, aluminum hydroxide (Al(OH)3), lithium hydroxide (LiOH), and the dopant compound were mixed with each other, wherein the dopant compound employed each of tantalum oxide (Ta2O5) (Preparation Example 42 to Preparation Example 45), niobium pentoxide (Nb2O5) (Preparation Example 46 to Preparation Example 49), molybdenum trioxide (MoO3) (Preparation Example 50 to Preparation Example 53), tungsten trioxide (WO3) (Preparation Example 54 to Preparation Example 57), and antimony trioxide (Sb2O3) (Preparation Example 58 to Preparation Example 61) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in a following Table 5. These Preparation Examples are shown in Table 5. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller.
10 liters of distilled water was put into a co-precipitation reactor (capacity 47 L, and an output of a rotary motor 750 W or greater), and then N2 gas was supplied to the reactor at a flow rate of 6 liters/min. While a temperature of the reactor was maintained at 45° C., stirring was carried out at 350 rpm. Nickel sulfate aqueous solution (NiSO46H2O, Samchun Chemicals), and cobalt sulfate aqueous solution (CoSO47H2O, Samchun Chemicals) were mixed with each other such that a molar ratio of nickel (Ni) and cobalt (Co) was 96:4, thereby preparing a metal solution having a concentration of 2M. The prepared metal solution was continuously input to the reactor for 24 hours at 0.561 liter/hour. 16M concentration of ammonia solution (NH4OH, JUNSEI) was continuously input to the reactor for 24 hours at 0.11 L/hour. 4M concentration of sodium hydroxide solution (NaOH, Samchun Chemicals) was continuously input to the reactor for 24 hours at 0.60 L/hour. While maintaining pH in the reactor in a range of 10 to 12, co-precipitation was performed to prepare Ni0.96Co0.04(OH)2 composite metal hydroxide.
The prepared Ni0.96Co0.04(OH)2 metal complex hydroxide was washed several times with distilled water, filtered, and dried in a vacuum dryer at 110° C. for 12 hours to prepare the Ni0.96Co0.04(OH)2 metal complex hydroxide in a powder form. After mixing the Ni0.96Co0.04(OH)2 metal complex hydroxide prepared in the powder form and a lithium hydroxide (LiOH) with each other at a molar ratio of 1:1.01, the mixture was heated at a temperature increase rate of 2° C./min and was maintained at 450° C. for 5 hours. In this way, preliminary calcination was performed. Subsequently, main calcination was carried out at 700° C. for 10 hours to prepare positive electrode active material powders. This Preparation Example is shown in Table 6.
Each of positive electrode active material powders of Preparation Example 63 to Preparation Example 78 was prepared in the same manner as in Preparation Example 62 except that the Ni0.96Co0.04(OH)2 composite metal oxide prepared in the powder form in Preparation Example 62, lithium hydroxide (LiOH), and the dopant compound were mixed with each other, wherein the dopant compound employed each of tantalum oxide (Ta2O5) (Preparation Example 63 to Preparation Example 66), niobium pentoxide (Nb2O5) (Preparation Example 67 to Preparation Example 70), molybdenum trioxide (MoO3) (Preparation Example 71 to Preparation Example 74), and tungsten trioxide (WO3) (Preparation Example 75 to Preparation Example 78) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in the following Table 6. These Preparation Examples are shown in Table 6. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller.
A positive electrode active material powder of Preparation Example 79 was prepared in the same manner as in Preparation Example 62 except that the Ni0.96Co0.04(OH)2 composite metal oxide prepared in the powder form in Preparation Example 62, aluminum hydroxide (Al(OH)3), and lithium hydroxide (LiOH) were mixed with each other at a molar ratio as shown in Table 7 below, and calcination of the mixture was carried out at 700° C. Preparation Example 79 is shown in Table 7.
Each of positive electrode active material powders of Preparation Example 80 to Preparation Example 95 was prepared in the same manner as in Preparation Example 62 except that the Ni0.96Co0.04(OH)2 composite metal oxide prepared in the powder form in Preparation Example 62, aluminum hydroxide (Al(OH)3), lithium hydroxide (LiOH), and the dopant compound were mixed with each other, wherein the dopant compound employed each of tantalum oxide (Ta2O5) (Preparation Example 80 to Preparation Example 83), niobium pentoxide (Nb2O5) (Preparation Example 84 to Preparation Example 87), molybdenum trioxide (MoO3) (Preparation Example 88 to Preparation Example 91), and tungsten trioxide (WO3) (Preparation Example 92 to Preparation Example 95) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in the following Table 7. These Preparation Examples are shown in Table 7. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller
10 liters of distilled water was put into a co-precipitation reactor (capacity 47 L, and an output of a rotary motor 750 W or greater), and then N2 gas was supplied to the reactor at a flow rate of 6 liters/min. While a temperature of the reactor was maintained at 45° C., stirring was carried out at 350 rpm. Nickel sulfate aqueous solution (NiSO46H2O, Samchun Chemicals), cobalt sulfate aqueous solution (CoSO47H2O, Samchun Chemicals), and manganese sulfate aqueous solution (MnSO4H2O, Samchun Chemicals) were mixed with each other such that a molar ratio of nickel (Ni), cobalt (Co), and manganese (Mn) was 95:2.5:2.5, thereby preparing a metal solution having a concentration of 2M. The prepared metal solution was continuously input to the reactor for 24 hours at 0.561 liter/hour. 16M concentration of ammonia solution (NH4OH, JUNSEI) was continuously input to the reactor for 24 hours at 0.08 L/hour. 4M concentration of sodium hydroxide solution (NaOH, Samchun Chemicals) was continuously input to the reactor for 24 hours at 0.60 L/hour. While maintaining pH in the reactor in a range of 10 to 12, co-precipitation was performed to prepare Ni0.95Co0.025Mn0.025(OH)2 composite metal hydroxide.
The prepared Ni0.95Co0.025Mn0.025(OH)2 metal complex hydroxide was washed several times with distilled water, filtered, and dried in a vacuum dryer at 110° C. for 12 hours to prepare the Ni0.95Co0.025Mn0.025(OH)2 metal complex hydroxide in a powder form. After mixing the Ni0.95Co0.025Mn0.025(OH)2 metal complex hydroxide prepared in the powder form and a lithium hydroxide (LiOH) with each other at a molar ratio of 1:1.01, the mixture was heated at a temperature increase rate of 2° C./min and was maintained at 450° C. for 5 hours. In this way, preliminary calcination was performed. Subsequently, main calcination was carried out at 730° C. for 10 hours to prepare positive electrode active material powders. This Preparation Example is shown in Table 8.
Each of positive electrode active material powders of Preparation Example 97 to Preparation Example 112 was prepared in the same manner as in Preparation Example 96 except that the Ni0.95Co0.025Mn0.025(OH)2 composite metal oxide prepared in the powder form in Preparation Example 96, lithium hydroxide (LiOH), and the dopant compound were mixed with each other, wherein the dopant compound employed each of tantalum oxide (Ta2O5) (Preparation Example 97 to Preparation Example 100), niobium pentoxide (Nb2O5) (Preparation Example 101 to Preparation Example 104), molybdenum trioxide (MoO3) (Preparation Example 105 to Preparation Example 108), and tungsten trioxide (WO3) (Preparation Example 109 to Preparation Example 112) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in the following Table 8. These Preparation Examples are shown in Table 8. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller.
10 liters of distilled water was put into a co-precipitation reactor (capacity 47 L, and an output of a rotary motor 750 W or greater), and then N2 gas was supplied to the reactor at a flow rate of 6 liters/min. While a temperature of the reactor was maintained at 45° C., stirring was carried out at 350 rpm. Nickel sulfate aqueous solution (NiSO46H2O, Samchun Chemicals), cobalt sulfate aqueous solution (CoSO47H2O, Samchun Chemicals), and manganese sulfate aqueous solution (MnSO4H2O, Samchun Chemicals) were mixed with each other such that a molar ratio of nickel (Ni), cobalt (Co), and manganese (Mn) was 90:5:5, thereby preparing a metal solution having a concentration of 2M. The prepared metal solution was continuously input to the reactor for 24 hours at 0.561 liter/hour. 16M concentration of ammonia solution (NH4OH, JUNSEI) was continuously input to the reactor for 24 hours at 0.08 L/hour. 4M concentration of sodium hydroxide solution (NaOH, Samchun Chemicals) was continuously input to the reactor for 24 hours at 0.60 L/hour. While maintaining pH in the reactor in a range of 10 to 12, co-precipitation was performed to prepare Ni0.9Co0.05Mn0.005(OH)2 composite metal hydroxide.
The prepared Ni0.9Co0.05Mn0.005(OH)2 metal complex hydroxide was washed several times with distilled water, filtered, and dried in a vacuum dryer at 110° C. for 12 hours to prepare the Ni0.9Co0.05Mn0.05(OH)2 metal complex hydroxide in a powder form. After mixing the Ni0.9Co0.05Mn0.05(OH)2 metal complex hydroxide prepared in the powder form and a lithium hydroxide (LiOH) with each other at a molar ratio of 1:1.01, the mixture was heated at a temperature increase rate of 2° C./min and was maintained at 450° C. for 5 hours. In this way, preliminary calcination was performed. Subsequently, main calcination was carried out at 750° C. for 10 hours to prepare positive electrode active material powders. This Preparation Example is shown in Table 9.
Each of positive electrode active material powders of Preparation Example 114 to Preparation Example 129 was prepared in the same manner as in Preparation Example 113 except that the Ni0.9Co0.05Mn0.05(OH)2 composite metal oxide prepared in the powder form in Preparation Example 113, lithium hydroxide (LiOH), and the dopant compound were mixed with each other, wherein the dopant compound employed each of tantalum oxide (Ta2O5) (Preparation Example 114 to Preparation Example 117), niobium pentoxide (Nb2O5) (Preparation Example 118 to Preparation Example 121), molybdenum trioxide (MoO3) (Preparation Example 122 to Preparation Example 125), and tungsten trioxide (WO3) (Preparation Example 126 to Preparation Example 129) which was added at each content (0.05 mol %, 0.5 mol %, 1 mol % and 2 mol %) shown in the following Table 9. These Preparation Examples are shown in Table 9. The dopant compound was prepared in a powder form using a ball mill so that an average particle size thereof was 2 μm or smaller.
A half-cell and a pouch-type full-cell were prepared via a following method using each of the positive electrode active materials according to Preparation Example 1 to Preparation Example 100.
To prepare the half-cell and the full-cell, 1 g of the positive electrode active material in the powder form prepared according to each of Preparation Example 1 to Preparation Example 100, poly(vinylidene fluoride), and carbon black were added to 0.4 g of N-methyl pyrrolidone at a weight ratio of 90:4.5:5.5. The mixture was uniformly stirred to prepare a positive electrode slurry. The prepared positive electrode slurry was coated on an aluminum foil, which in turn was subjected to roll pressing and vacuum drying. In this manner, a positive electrode was prepared.
When preparing the half-cell, the prepared positive electrode slurry was coated on the aluminum foil such that a loading level of the positive electrode active material was approximately 3.5 mg/cm2 to prepare the positive electrode (when the aluminum foil having the positive electrode active material coated thereon was sampled into a square of 1 cm2, a weight of only the positive electrode active material in the positive electrode was 5 mg). An electrolyte solution was prepared by uniformly dissolving vinylene carbonate (VC) 2 wt %, and lithium salt 1.2 mol/L LiPF6 as an additive into ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=3:7 v/v) as a solvent. Lio was used as a negative electrode. Thus, a 2032-coin type half-cell (hereinafter, half-cell) was prepared.
When preparing the full-cell, the prepared positive electrode slurry was coated on the aluminum foil such that a loading level of the positive electrode active material was approximately 8.5 mg/cm2 to prepare the positive electrode. Graphite slurry was coated on a copper foil so that a loading level thereof was 6.5 mg/cm2, followed by roll pressing and vacuum drying to prepare a negative electrode. An electrolyte solution was prepared by uniformly dissolving vinylene carbonate (VC) 2 wt %, and lithium salt 1.2 mol/L LiPF6 as an additive into ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=3:7 v/v) as a solvent. The positive electrode, a separator (Celgard, Model 2320), and the negative electrode were stacked into a pouch-type battery case, and the case was filled with the prepared electrolyte and was sealed to prepare a pouch-type full-cell.
(1) Identification of Capacity and Cycle Characteristics Using Half-Cell
The prepared half-cell was subjected to a charge/discharge cycle in which the half-cell was charged to 4.3V and discharged to 2.7V under a constant current of 0.5 C (1 C being 180 mA/g) at 30° C. The prepared half-cell was subjected to 100 cycles. Then, retention was identified (hereinafter, 2.7 V-4.3V).
(2) Identification of Capacity and Cycle Characteristics Using Full-Cell
The prepared full-cell was subjected to a charge/discharge cycle in which the cell was discharged to 3.0V voltage and was charged to 4.2V under a 1 C constant current at 25° C. to identify capacity and retention.
(3) Identification of Microstructure of Composite Metal Oxide (Precursor) and Positive Electrode Active Material Using SEM
The microstructure of each of the positive electrode active material according to each of Preparation Examples and the composite metal oxide (precursor) before the preliminary calcination of the positive electrode active material was identified using SEM (Nova Nano SEM 450, FEI).
In a following description, the micro-structure, surface characteristic, and electrochemical characteristic of the positive electrode active material according to each of Preparation Example 1 to Preparation Example 102 were identified.
Table 10 shows the capacity of each of Preparation Example 1 to Preparation Example 7 using the half-cell and the retention thereof after the cycle.
In
Referring to
On the contrary, referring to
That is, we examined the shape of the secondary particle and the primary particles based on the SEM image and the capacity and retention of the battery including the same. It could be identified that as the content of the tantalum (Ta) increased, the primary particles constituting the shell portion of the secondary particle had a smaller width. Accordingly, it could be identified that the electrochemical characteristics such as capacity and retention after the cycle did not have the same tendency as that of the shape. It could be identified that in the present embodiment, the content of the tantalum (Ta) in a range of 0.5 mol % to 2 mol % exhibited excellent characteristics in capacity and retention after the cycles.
Referring to
Referring to
That is, the retention based on NCA89 where 1 mol % of aluminum (Al) was added to nickel (Ni) and cobalt (Co) was relatively similar to the retention based on NC9010 where only nickel (Ni) and cobalt (Co) were present. On the contrary, NC9010-Ta1 and NCA89 were compared with each other. That is, NC9010-Ta1 where 1 ml of tantalum (Ta) was added at the content of 1 mol % exhibited better retention than NCA89 where aluminum (Al) was added at the content of 1 mol % exhibited. That is, it was identified that when the content of nickel (Ni) was constant, NC9010-Ta1 having tantalum (Ta) exhibited the better lifespan characteristic, compared to NC9010 without aluminum (Al) and NCA89 with aluminum (Al) added thereto.
Referring to
The positive electrode active material may undergo a continuous phase change: H1 (hexagonal 1)->M (monoclinic)->H2 (hexagonal 2)->H3 (hexagonal 3) during the charging process. During the last H2->H3 change, a sudden anisotropic volume change occurs. In this connection, the volume change proceeds gently up to 4.15 V as the voltage before the H2->H3 phase transition starts, and then the cell volume rapidly decreases at 4.2 V where the H2->H3 phase transition starts.
At approximately 4.1 V after charging to 4.3 V at which the rapid volume change begins, micro cracks occurred in the micro-structure of secondary particles of NCA89, whereas micro cracks did not occur in NC9010-Ta1. That is, it is considered that in NC9010-Ta1, the primary particles are oriented and aligned in the secondary particle so that micro cracks in the micro-structure due to the anisotropic volume change did not occur.
Referring to
Referring to
In
That is, the overall volume changes of Preparation Example 4 (NC9010-Ta1) and Preparation Example 7 (NCA89) during one cycle is similar to each other (see
Table 12 below represents the area fraction % of microcracks occurring in Preparation Example 7 (NCA89) and Preparation Example 4 (NC9010-Ta1) while performing one cycle from charge to discharge in an order of 3.9V->4.1V->4.3V->4.1V->3.9V->2.7V.
Referring to Table 12 and
Table 13 shows capacity and retention after 100 cycles for NC9010 (Preparation Example 1, Preparation Examples 8 to 11), NC9010-Ta1 (Preparation Example 4, Preparation Example 12 to Preparation Example 15), and NCA89 (Preparation Example 7, Preparation Example 16 to Preparation Example 19) using half-cells, based on the calcination temperature.
Referring to Table 13 and
Referring to
Referring to
That is, it could be identified that the shapes of primary and secondary particles were controlled by doping the tantalum (Ta), and that the controlled shapes had an effect on capacity and retention after the cycles. Further, it could be identified that the doping of the tantalum (Ta) allowed the shapes of primary and secondary particles in NC9010-Ta1 to be maintained relatively unchanged even after the calcination at high temperature, compared to NC9010 and NCA89. Accordingly, the unchanged shape may have the effect on the characteristics of capacity and retention.
Table 14 below shows a temperature-based value of (003)/(104) ratio of each of NC9010-Ta1 and NCA89 using XRD.
NC9010-Ta1 exhibited excellent electrochemical characteristics at the calcination temperature in a range of 730° C. to 790° C. In this connection, it could be identified that the primary particles (second primary particles) constituting the shell portion of the secondary particle had a rod-shaped having an aspect ratio, and at the same time, lithium ion movement was effectively performed when 50% or greater thereof had the above orientation. Further, it could be identified that when the calcination temperature was 850° C., the grain was changed to a polygonal shape, and thus, the percentage of the second primary particles having the above orientation was reduced to 24.16%. That is, it was identified that in the present embodiment, the addition of tantalum (Ta) as a dopant allowed the second primary particle as the primary particles constituting the shell portion of the secondary particle to have the rod shape rather than a polygonal form, and at the same time, allowed 50% or greater of the second primary particles to have the orientation (that is, 50% or greater of the second primary particles had an orientation toward the surface of the second particle), so that the electrochemical performance was further improved.
Each of NC9010, NC9010-Ta1, and NCA89 was subjected to the calcination at 730° C. while varying the calcination duration to 5 hours, 10 hours, and 20 hours, such that the positive electrode active material was prepared. Table 15 shows the result of identifying capacity and retention after 100 cycles of the half-cells prepared using the positive electrode active materials.
Referring to Table 15, and
Referring to Table 15 and
Referring to
Table 16 shows the results of identifying capacity and retention of the half-cells using NCA89 and NC9010, based on the dopant type and content.
Referring to Table 16,
Referring to
Table 17 below shows resistance values Rsf and Rct based on a content of each dopant.
Referring to Table 17, it may be identified that the resistance value increases as the number of cycles increases. The resistance value of NCA89 in which the dopant was not contained was significantly increased, compared to other positive electrode active materials to which the dopant was added. That is, as the cycle increased, the resistance value increased due to the increase in the separation space between the primary particles, that is, the micro cracks in the secondary particles. The micro crack was suppressed when the dopant was added. Further, as the dopant content increased, the micro crack formation was suppressed. However, when the dopant concentration was 2 mol %, the effect was reduced. Further, it could be identified that the dopants exhibited approximately similar effects.
Referring to
Referring to
Referring to
Hereinafter, in order to identify whether the effect of the dopant based on the type and content of the transition element constituting the positive electrode active material exhibited a similar trend as that in NC9010, various positive electrode active materials were prepared while changing the type and content of the transition metal, and then tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), and antimony (Sb) as the doping elements were added thereto at various contents. Then, whether capacity and retention were improved was identified.
Table 18 shows capacity and retention after 100 cycles of the half-cell containing NCA89, based on the dopant type and the dopant content. Table 19 shows the capacity and retention after 100 cycles when 1 mol % of each dopant is contained in each of NC9010 and NCA89.
Table 20 shows capacity and retention after 100 cycles of the half-cell containing NC9604, based on the dopant type and the dopant content.
Table 21 shows capacity and retention after 100 cycles of the half-cell containing NCA95, based on the dopant type and the dopant content.
Referring to Table 17 to Table 21, it could be identified that similarly to the above-described NC9010, in each of NCA89, NC9604, and NCA95, when each of tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), and antimony (Sb) was contained, the retention after the cycles was excellent, compared to that when each of tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), and antimony (Sb) was not contained. Referring to
Referring to Table 18 and Table 19, it could be identified that when the same content, that is, 1 mol % of each of tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), and antimony (Sb) was added to each of NC9010 and NCA89 which have different types of transition metals, NC9010 and NCA89 exhibited excellent capacity and 100-cycle retention in the similar manner.
Table 22 below shows the results of identifying capacity and retention of the half-cell including NCM95 based on the dopant type and content.
Table 23 below shows the results of identifying capacity and retention of the half-cell including NCM90 based on the dopant type and content.
Referring to Table 22 and Table 23, it could be identified that similarly to the above-mentioned NC9010, in each of NCM 95 and NCM 90, the retention after the cycles when each of tantalum (Ta), niobium (Nb), molybdenum (Mo) and tungsten (W) was contained was superior to that when each of tantalum (Ta), niobium (Nb), molybdenum (Mo) and tungsten (W) was not contained. That is, even when manganese (Mn) is included as a transition metal in addition to nickel (Ni) and cobalt (Co), the effect based on the dopant content exhibited a similar tendency.
Each of NCA89, NC9010-Ta1 (730° C. calcination), NC9010-Ta1 (750° C. calcination), and NC9010-Nb1 (730° C. calcination) was used to prepare each pouch-type full-cell (electrolyte EC:EMC VC). Table 24 below shows the capacity and retention after 100 cycles of each pouch-type full-cell.
Referring to Table 24,
Hereinafter, the results of identifying the size of the primary particles constituting the secondary particle in the positive electrode active material prepared according to the above-described Preparation Examples are set forth. The size of the primary particle was photographed multiple times using an SEM having excellent resolution, and 5 clear images were selected and then samples for measurement were obtained, based on the images. The size of each of the primary particles constituting the secondary particle of each of the positive electrode active materials was measured using the 5 samples as obtained. The size of the primary particle was measured based on the longest length of the long side. The longest length among the lengths perpendicular to the long side was measured and defined as the length of the short side. An average value was calculated based on the measurements.
As shown in
Table 25 below shows an average length of each of the long side and the short side of each of the first and second primary particles.
Referring to Table 25, it could be identified that in the secondary particle free of the dopant, b1/b2 in the second primary particle was small, and accordingly, the percentage of the of the second primary particles having the orientation toward the center of the secondary particle was reduced. On the contrary, when the second primary particle contained the dopant, and thus b1/b2 was larger, the percentage of the of the second primary particles having the orientation toward the center of the secondary particle was increased, and, accordingly, the retention after 100 cycles under 0.5 C was excellent. Further, it could be identified that the value of b1/b2 of the second primary particle was greater than 1.82 and smaller than or equal to 10.41.
Table 26 and Table 27 show the short side length b2 of the second primary particle of each of NC9010 and NC9010-Ta1 and the capacity thereof, based on the calcination temperature and the calcination duration. Table 28 shows the short side length b2 and the long side length b1 of the second primary particle, based on the calcination temperature and calcination duration, and based on the nickel content when 1 mol % of the dopant is added.
0.102
0.185
0.172
0.149
Table 26 and Table 27 show only the short side length of the second primary particle. This is because when increasing the calcination temperature or increasing the calcination duration, the shape of the first primary particle hardly changes, and only the short side length in the second primary particle changes to increase the volume, and the long side length of the second primary particle hardly changes. Referring to Table 26 and
Referring to Table 24 and
Referring to Table 28, it could be identified that NC9010-Ta1 containing dopant had relatively smaller values of the short side length b2 and the short side length b1 of the second primary particle regardless of the calcination duration and the calcination temperature, compared to those in NCA89. Further, it could be identified that although NC9604-Ta1, NC9604-Nb1, and NC9604-W1 had the nickel (Ni) content which was higher than that of NCA89, each of NC9604-Ta1, NC9604-Nb1, and NC9604-W1 had relatively smaller values of the short side length b2 and the short side length b1 of the second primary particle than those of NCA89.
It could be identified that as the calcination duration ofNC9010-Ta1 increased, the short side length b2 and the short side length b1 of the second primary particle of NC9010-Ta1 remained almost unchanged, and b1/b2 had a value of approximately 4 to 6.
Further, it could be identified that when the calcination duration was 10 hours, and as the calcination temperature increased, b1 hardly changed, but b2 increased as the temperature increased from 750° C. to 770° C., and b2 was constant as the temperature increased from 770° C. to 790° C. That is, it could be identified that in the second primary particle, only the b2 was affected by the calcination temperature and the calcination duration, and b1 had little change.
It could be identified that even though NC9604-Ta1 was calcined at a relatively low calcination temperature, NC9010-Ta1 exhibited the relatively smaller b2 and b1, compared to those in NC9604-Ta1. This is believed to be because NC9604-Ta1 has a high nickel (Ni) content and is relatively vulnerable to high temperatures.
The positive electrode active material according to an embodiment of the present disclosure may contain the dopant to control the shape and the orientation of the primary particles constituting the secondary particle. Accordingly, thermal stability thereof against high temperatures may be improved. Further, the positive electrode active material may maintain the structural stability of the micro-structure during the cycles and may suppress the micro cracks, thereby improving the long-term lifespan characteristic.
Those of ordinary skill in the technical field to which the present disclosure belongs will be able to understand that the present disclosure may be implemented in other specific forms without changing its technical idea or essential characteristics. Therefore, it should be understood that the embodiments as described above are illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the following claims rather than the detailed description. All changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted to be included in the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2019-0009515 | Jan 2019 | KR | national |
| 10-2020-0010140 | Jan 2020 | KR | national |
This application is a national stage of pending International Application No. PCT/KR2020/001305, which was filed on Jan. 28, 2020 and claims priority to Korean Patent Application Nos. 10-2019-0009515 and 10-2020-0010140 filed on Jan. 24, 2019 and Jan. 28, 2020 in the Korean Intellectual Property Office, the disclosures of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2020/001305 | 1/28/2020 | WO | 00 |
