Analysis method for lithium composite oxides

Abstract

To provide an analytical method of lithium composite oxide.SOLUTION: Disclosed is an analytical method of substitution sites of Ni atom and Mg atom in a compound represented by a chemical formula Li(1-x-y)Co(1-a-b)Ni(x+a)Mg(y+b)O2, wherein the analytical method includes: a first calculation step of calculating a stabilization energy obtained when Ni atom and Mg atom are replaced by a desired Li atom or Co atom included in LiCoO2 crystal; a second calculation step of calculating a stabilization energy of the compound represented by the chemical formula on changing cation occupancy in Li sites; and a first measurement step of measuring the first charge-discharge efficiency and the n-th charge-discharge efficiency of the compound represented by the chemical formula. Here, n is an integer of 2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a method for analyzing a lithium composite oxide, or to an object or manufacturing method thereof. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. Another embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or a manufacturing method thereof.

[0002] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, storage batteries (also called secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors.

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like. [Background technology]

[0004] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-capacity lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, as they are used in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, and next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs).

[0005] Therefore, improvements in the positive electrode active material have been investigated in order to improve the cycle characteristics and increase the capacity of lithium ion secondary batteries (Patent Documents 1 and 2).

[0006] Furthermore, the characteristics required of the power storage device include safety in various operating environments and improved long-term reliability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-018914 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-076454 [Non-patent literature]

[0008] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3- and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2(0.0≦x≦1.0)”, Physical Review B, 80(16);165114 Summary of the Invention [Problem to be solved by the invention]

[0009] There is a demand for improvements in various aspects of lithium ion secondary batteries and the positive electrode active materials used therein, such as capacity, cycle characteristics, charge / discharge characteristics, reliability, safety, and cost. ODevelopment is underway on a lithium composite oxide LiMO2 (where M is two or more metals including Co) in which part of the O2 is replaced with a different element.

[0010] However, because the substitution elements are present in trace amounts, no method has yet been developed to clarify the structure of lithium composite oxides. If the structure of lithium composite oxides could be clarified, it would be helpful in materials development and in elucidating the mechanisms behind their charge-discharge characteristics and reliability.

[0011] In view of the above, an object of one embodiment of the present invention is to provide a method for analyzing a lithium composite oxide. Another object is to provide positive electrode active material particles that are less likely to deteriorate. Another object of one embodiment of the present invention is to provide novel positive electrode active material particles. Another object of one embodiment of the present invention is to provide a power storage device that is less likely to deteriorate. Another object of one embodiment of the present invention is to provide a highly safe power storage device. Another object of one embodiment of the present invention is to provide a novel power storage device.

[0012] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims. [Means for solving the problem]

[0013] One aspect of the present invention is a compound of formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b)A method for analyzing the substitution positions of Ni atoms and Mg atoms in a compound represented by O2. In the chemical formula, x + y < 1 and a + b < 1, and x, y, a, and b each independently represent a real number from 0 to 1, and a first calculation step of calculating the stabilization energy of a compound represented by the chemical formula obtained when the Ni atom and the Mg atom are each independently substituted for any Li atom or Co atom contained in the LiCoO2 crystal; a second calculation step of calculating the stabilization energy of a compound represented by the chemical formula when the cation occupancy of the Li site is changed; and a first measurement step of measuring the initial charge-discharge efficiency and the charge-discharge efficiency at the nth time (n is an integer of 2 or more) of a compound represented by the chemical formula. It is a method for analyzing the substitution positions of Ni atoms and Mg atoms.

[0014] In the above configuration, the measurement step includes at least a step of preparing a sample and a step of performing a mechanical measurement. By combining calculation and measurement, the validity of the calculation results and the phenomena predicted from the calculation results can be evaluated, so detailed analysis can be performed.

[0015] Also, in the above configuration, it is preferable to use the GGA+U(DFT-D2) method in the first calculation step and the second calculation step.

[0016] Also, in the above configuration, it is preferable to perform the calculation by changing the cation occupancy in the range of at least 80% or more and 100% or less.

[0017] Also, in the above configuration, it is preferable that n = 2

[0018] Also, in the above configuration, in the above chemical formula, it is preferable that 0 < x + a ≤ 0.015 and 0 < y + b ≤ 0.06.

[0019] Also, in the above configuration, in the second calculation step, when the Ni atom and the Mg atom are substituted for the same type of atom in the LiCoO2 crystal, it is further preferable to have a step of calculating the stabilization energy when the same type of atom is present in the same layer and in a different layer in the LiCoO2 crystal, respectively. [Effects of the Invention]

[0020] According to one embodiment of the present invention, a method for analyzing a lithium composite oxide can be provided. Furthermore, positive electrode active material particles that are less likely to deteriorate can be provided. Furthermore, novel positive electrode active material particles can be provided. Furthermore, a power storage device that is less likely to deteriorate can be provided. Furthermore, a highly safe power storage device can be provided. Furthermore, a novel power storage device can be provided. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating an example of the crystal structure of LiCoO2. [Figure 2] 2A and 2B are diagrams illustrating examples of the crystal structure of lithium composite oxides. [Figure 3] FIG. 3 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 4] FIG. 4 is a diagram illustrating the crystal structure and magnetism of a conventional positive electrode active material. [Figure 5] FIG. 5 is a diagram illustrating the crystal structure and magnetism of the positive electrode active material. [Figure 6] 6A and 6B are cross-sectional views of an active material layer in which a graphene compound is used as the conductive additive. [Figure 7] 7A and 7B are diagrams illustrating a coin-type secondary battery. [Figure 8] 8A and 8B are diagrams illustrating a cylindrical secondary battery, FIG. 8C is a perspective view of a battery module, and FIG. 8D is a top view of the battery module. [Figure 9] 9A and 9B are diagrams illustrating an example of a secondary battery. [Figure 10] 10A1, 10A2, 10B1, and 10B2 are diagrams illustrating examples of secondary batteries. [Figure 11] 11A and 11B are diagrams illustrating an example of a secondary battery. [Figure 12] 12A and 12B are diagrams illustrating an example of a secondary battery. [Figure 13]FIG. 13 is a diagram illustrating an example of a secondary battery. [Figure 14] 14A, 14B, and 14C are diagrams illustrating a laminated secondary battery. [Figure 15] 15A and 15B are diagrams illustrating a laminated secondary battery. [Figure 16] FIG. 16 is a diagram showing the appearance of a secondary battery. [Figure 17] FIG. 17 is a diagram showing the appearance of a secondary battery. [Figure 18] 18A, 18B, and 18C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 19] FIG. 19A is a top view of a bendable secondary battery, FIG. 19B1 is a cross-sectional view taken along chain lines C1C2, FIG. 19B2 is a cross-sectional view taken along chain lines C3C4, FIG. 19C is a cross-sectional view taken along chain lines A1A2, and FIG. 19D is a cross-sectional view taken along chain lines B1B2 when bent. [Figure 20] FIG. 20A is a perspective view of a secondary battery, and FIG. 20B is a perspective view of a secondary battery. [Figure 21] Figure 21A is an oblique view of an electronic device, Figure 21B is an oblique view of an electronic device, Figure 21C is an oblique view of a secondary battery, Figure 21D is an oblique view of an electronic device, Figure 21E is an oblique view of a secondary battery, and Figures 21F and 21G are oblique views illustrating an example of an electronic device. [Figure 22] 22A is a top view of the electronic device in an open state, FIG. 22B is a top view of the electronic device in a closed state, and FIG. 22C is a diagram illustrating a block diagram of the electronic device. [Figure 23] FIG. 23 is a diagram illustrating an example of an electronic device. [Figure 24] 24A, 24B, and 24C are diagrams illustrating an example of an electronic device. [Figure 25] FIG. 25 is a diagram illustrating the calculation results of the stabilization energy according to the example. [Figure 26] FIG. 26 is a diagram for explaining the calculation results of the stabilization energy according to the example. [Figure 27]FIG. 27 is a diagram illustrating the charge / discharge efficiency according to the example. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0023] In addition, in crystallography, crystal planes and directions are represented by numbers with a superscript bar, but in this specification and elsewhere, due to limitations on notation in applications, crystal planes and directions are represented by a minus sign (-) before the number instead of a bar above it. Also, individual directions indicating directions within a crystal are represented by [ ], collective directions indicating all equivalent directions are represented by < >, individual planes indicating crystal planes are represented by ( ), and collective planes with equivalent symmetry are represented by {}.

[0024] (Embodiment 1) Development of lithium composite oxides, in which a portion of LiCoO2 is replaced with a different element, is underway as a positive electrode material. Because the content of the replacement element is small, analysis of the crystalline structure of lithium composite oxides is difficult. The inventors discovered that analysis of the crystalline structure can be performed efficiently and in more detail by combining chemical calculations and experiments.

[0025] [Calculation of stabilization energy for different substitution positions] When a metal element is doped into LiCoO2, it is expected that it will substitute for either the Li site or the Co site in the LiCoO2 crystal, but it is currently difficult to analyze by measurement which site has been substituted. Furthermore, when there are multiple metal elements to be doped, the situation becomes even more complicated as each of the doped metals can substitute for either the Li site or the Co site. Therefore, it is effective to use chemical calculations to determine the stabilization energy of the crystal structure depending on the arrangement of each cation site, thereby estimating the site that the doped metal will substitute for. Below, we will look at an example of a lithium composite oxide in which LiCoO2 is doped with Mg and Ni, with the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The analytical method for the substitution position of the doping element in the lithium composite oxide will be explained using the calculation of a substance represented by O2 as an example. Note that in the above chemical formula, x+y<1 and a+b<1.

[0026] It is preferable that the experimenter creates an outline of the crystal model and then performs various calculations using a computer. By creating an outline of the crystal model, the crystal conditions and the relationships between various parameters become clear, allowing for subsequent detailed analysis. Furthermore, since the amount of calculation required is enormous, using a computer to process the calculation results can be obtained quickly. In the following calculation example, the crystal structure of LiCoO2 (R-3m(O3)) is created by the experimenter, and various calculations are performed using a computer.

[0027] [Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) Calculation example of O2 stabilization energy] By creating a model in which Mg and Ni are doped into LiCoO2, which has the crystal structure of R-3m(O3), the basic structure of LiCoO2, and calculating the stabilization energy, Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b)It is possible to analyze the crystal structure of O2. Figure 1 shows a crystal model of R-3m(O3), which is the basic structure of LiCoO2. Figure 1 shows the crystal structure of LiCoO2 (total number of atoms: 192), which consists of 48 Li atoms, 48 ​​Co atoms, and 96 oxygen atoms.

[0028] Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) O2 is a compound in which Mg and Ni are used as substitution elements for the metal elements (Li and / or metal) in LiCoO2. Here, several crystal models are possible for the combination of the substitution sites of the Mg and Ni, as shown below. When Li in the same Li layer is replaced with Mg and Ni When Li in different Li layers is replaced with Mg and Ni When Co in the same Co layer is replaced by Mg and Ni When Co in different Co layers is replaced by Mg and Ni When Li in the Li layer is replaced with Mg and Co in the Co layer is replaced with Ni When Li in the Li layer is replaced with Ni and Co in the Co layer is replaced with Mg

[0029] Figures 2A and 2B show examples of the substitution positions of Mg and Ni in a LiCoO2 crystal. Figure 2A shows the case where Li in the same Li layer is substituted with Mg and Ni, while Figure 2B shows the case where Li in a different Li layer is substituted with Mg and Ni.

[0030] Here, by calculating the stabilization energy of the crystal structure for each combination of the above substitution sites, Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) It is possible to analyze what kind of crystal structure O2 can take. The stabilization energy can be estimated using the following formula. Here, we consider a model in which a Li atom or Co atom in LiCoO2 (total number of atoms: 192) consisting of 48 Li atoms, 48 ​​Co atoms, and 96 oxygen atoms is replaced by one Mg atom and one Ni atom.

[0031] <When two Li sites are substituted with one Mg and one Ni> (Equation 1) ΔE = [E_total{(Li 46 Mg1Ni1Co 48 O 96 ) + 2 × E_atom(Li)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 1)

[0032] <When one Li site is substituted with one Mg and one Co site is substituted with one Ni> (Equation 2) ΔE = [E_total{(Li 47 Mg1Ni1Co 47 O 96 ) + E_atom(Li) + E_atom(Co)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 2)

[0033] <When two Co sites are substituted with one Mg and one Ni> (Equation 3) ΔE = [E_total{(Li<00贯穿00038>Mg1Ni1Co 46 O 96 ) + 2 × E_atom(Co)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 3)

[0034] The symbols in the above Equations 1 to 3 are as follows. · ΔE: Stabilization energy. · E_total(Li 46 Mg1Ni1Co 48 O 96): Energy of a model in which two Li atoms are replaced with one Mg atom and one Ni atom in a LiCoO2 crystal (total number of atoms: 192). E_total(Li 47 Mg1Ni1Co 47 O 96 ): Energy of a model in which one Li atom is replaced with one Mg atom and one Co atom is replaced with one Ni atom in a LiCoO2 crystal (total number of atoms: 192). E_total(Li 48 Mg1Ni1Co 46 O 96 ): Energy of a model in which two Co atoms are replaced with one Mg atom and one Ni atom in a LiCoO2 crystal (total number of atoms: 192). E_total(Li 48 Co 48 O 96 ): Energy of a LiCoO2 crystal (total number of atoms: 192) model. E_atom(Li): Energy of one Li atom. ·E_atom(Co): Energy of one Co atom. ·E_atom(Mg): Energy of one Mg atom. ·E_atom(Ni): Energy of one Ni atom.

[0035] By calculating and comparing the stabilization energy for each combination of Mg and Ni substitution sites, it is possible to estimate the stable crystal structure. The smaller the stabilization energy value calculated from equations (1) to (3), the more stable the crystal model is. (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) This indicates that O2 is the most likely option.

[0036] The above calculations can be performed using the LDA+U method or the GGA+U (DFT-D2) method, but the GGA+U (DFT-D2) method is preferred. The GGA+U (DFT-D2) method can estimate the van der Waals forces more accurately than the LDA+U method, and therefore can estimate the stabilization energy more accurately.

[0037] The stabilization energy is also affected by the position of the atom substitution. For example, in FIG. 2A, if Mg is substituted at the Li(a) site and Ni is substituted at the Li(b) site (first nearest neighbor), and if Mg is substituted at the Li(a) site and Ni is substituted at the Li(c) site (second nearest neighbor), the stabilization energy may change, even though the Li in the same Li layer is substituted with Mg and Ni. Therefore, when calculating the stabilization energy, it is preferable to perform calculations taking into account not only the layer of the substituted atom but also the positional relationship of the substituted atoms. Furthermore, when analyzing which layer Mg and Ni are substituted into, it is preferable to calculate and compare the stabilization energies for the first to third nearest neighbors for each of the six crystal models shown above. It is even more preferable to calculate and compare the stabilization energies for the first to fourth nearest neighbors.

[0038] While the above calculation formula is based on a model with 192 atoms in the crystal, the user of the present invention can consider the trends in the calculation results by extending them to bulk crystals. Furthermore, since similar trends are expected to be observed when using models with different numbers of atoms, the trends in the calculation results can also be applied to models with different numbers of atoms. For example, if the stabilization energy of a model in which Li in the same Li layer is substituted with Mg and Ni is lower than the stabilization energy of a model in which Co in the same Co layer is substituted with Mg and Ni, the results are expected to show similar trends in bulk crystals and models with other numbers of atoms, and the trends in the calculation results can be applied.

[0039] As mentioned above, by calculating and comparing the stabilization energies of each crystal model, Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b)It is possible to analyze what crystal structures O2 can take. In addition, the calculation and comparison of the above stabilization energy estimate the state of the lithium composite oxide when the occupancy rate of the cation site is 100%, but the calculation is performed without considering the behavior and changes in the crystal structure when the lithium composite oxide is used as the positive electrode. When treating the lithium composite oxide as a positive electrode material, it is preferable to consider the behavior during charge and discharge. By considering the behavior during charge and discharge, more detailed analysis can be performed.

[0040] [Calculation of stabilization energy when changing the cation occupancy rate of the Li site] When using a lithium composite oxide as a positive electrode material for a secondary battery, in order to estimate what changes occur in the crystal structure of the lithium composite oxide due to charge and discharge of the secondary battery, the stabilization energy when Li is extracted from the lithium composite oxide, that is, a method of calculating the stabilization energy when changing the cation occupancy rate of the Li site can be mentioned. The extraction of Li from the lithium composite oxide assumes the behavior that occurs at the positive electrode when the secondary battery is charged. Therefore, the stabilization energy when Li is extracted from the lithium composite oxide estimates the stabilization energy during charging.

[0041] The calculation formula used for calculating the stabilization energy when changing the cation occupancy rate of the Li site is shown below.

[0042] [[ID=

[14] ]<When 2 Li sites are replaced by 1 Mg and 1 Ni> (Equation 4) ΔE C =[E C _total{(Li 46-z Mg1Ni1Co 48 O 96 ) + z × E_atom(Li)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 4)

[0043] <When one Li site is replaced by one Mg and one Co site is replaced by one Ni> (Equation 5) ΔE C =[E C _total{(Li 47-z Mg1Ni1Co 47 O 96 ) + z×E_atom(Li) + E_atom(Co)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 5)

[0044] <When two Co sites are replaced by one Mg and one Ni> (Equation 6) ΔE C =[E C _total{(Li 48-z Mg1Ni1Co 46 O 96 ) + z×E_atom(Li) + 2×E_atom(Co)} - {E_total(Li 48 Co 48 O 96 ) + E_atom(Mg) + E_atom(Ni)} ··· (Equation 6)

[0045] The symbols in the above Equations 4 to 6 are as follows. The explanations of the symbols similar to those used in Equations 1 to 3 are omitted.

[0046] ·ΔE C : The stabilization energy when the cation occupancy of the Li site is changed. ·E C _total(Li 46-z Mg1Ni1Co 48 O 96 ): The energy when z Li are extracted in the model where two Li in the LiCoO2 crystal (total number of atoms 192) are replaced by one Mg and one Ni. Here, z is an integer satisfying 0 ≦ z ≦ 46. ·E C _total(Li 47-z Mg1Ni1Co 47 O 96): Energy of a model in which one Li atom is replaced with one Mg atom and one Co atom is replaced with one Ni atom in a LiCoO2 crystal (total number of atoms: 192). Note that z is an integer satisfying the range 0≦z≦47. E C _total(Li 48-z Mg1Ni1Co 46 O 96 ): The energy when z Li atoms are extracted from a LiCoO2 crystal (total number of atoms: 192) in which two Co atoms are replaced with one Mg atom and one Ni atom. z is an integer satisfying the condition 0≦z≦48.

[0047] In the above equations 4 to 6, z represents the number of extracted Li atoms. Therefore, changing the value of z corresponds to changing the cation occupancy rate of the Li site in the lithium composite oxide crystal. ΔE C Calculate the cation occupancy of the Li site or ΔE for each value of z. C By plotting this, the stabilization energy during charging can be estimated.

[0048] As shown in Figure 1, LiCoO2 crystals have a structure in which Li ions and Co ions are stacked alternately. Therefore, as the number of cations on the Li site decreases, the energy (E C _total(Li 46-z Mg1Ni1Co 48 O 96 ), E C _total(Li 47-z Mg1Ni1Co 47 O 96 ) and E C _total(Li 48-z Mg1Ni1Co 46 O 96 )), the influence of the van der Waals force between the Co layers is thought to be greater. C To calculate ΔE, it is preferable to use a functional that takes van der Waals forces into account. COther functionals that can be used include OPTB88, DFT-D3, and DFT-TS. Functionals that can be used in one embodiment of the present invention are not limited to these.

[0049] The cation occupancy is changed from at least 80% to 100%. C It is preferable to plot the above. It is more preferable to plot the above between 50% and 100%, and even more preferable to plot the above between 0% and 100%. By using this configuration, it is possible to grasp the phenomena that occur during charging.

[0050] By creating this plot, the crystal structure of the lithium composite oxide can be analyzed from both the above-mentioned ΔE and ΔEc. In the above example, the substitution positions of Ni atoms and Mg atoms when Mg and Ni are added to LiCoO2 can be analyzed.

[0051] Since calculations are performed by changing the value of z in Equations 4 to 6, multiple calculations (up to 48 in the above example) must be performed for one model, which can increase the calculation cost. On the other hand, ΔE calculated by Equations 1 to 3 requires only a small number of relationships between Mg atoms and Ni atoms (up to roughly the fourth nearest neighbor) to be considered for one model, so the calculation cost is low. Therefore, after calculating ΔE and examining appropriate models, ΔEc is calculated for only those appropriate models, and the above-mentioned plots are created, allowing for efficient analysis of the crystal structure or the substitution positions of Ni atoms and Mg atoms.

[0052] Here, ΔE C When plotting, as the value of z increases, ΔE C It is expected that a graph of the relationship will be obtained in which the ΔE of a certain model increases. When the graph is created for multiple models, the relationship between the magnitude of each model may be reversed depending on the value of z. For example, when the cation occupancy is in the range of 95% to 100%, the ΔE of a certain model A is C ΔE of Model B CHowever, in the range of cation occupancy of 0% or more and less than 95%, ΔE C is the ΔE of Model B C If the calculation result is greater than , when the cation occupancy is in the range of 95% to 100%, Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) O2 is expected to have a structure of Model A, but when the cation occupancy is in the range of 0% or more and less than 95%, it is expected to have a structure of Model B. In other words, it is expected that a change in the crystal structure occurs due to charging. To analyze such phenomena caused by charging, it is preferable to perform the following measurements.

[0053] [Measurement of first charge / discharge efficiency and second charge / discharge efficiency] The charge / discharge efficiency of secondary batteries can be approximately 100% by selecting appropriate electrodes, provided that there is no material degradation of the electrode materials or electrolyte, short circuits, or deposition of metallic lithium. If the charge / discharge efficiency is below 100% even without the aforementioned degradation factors, a change in the crystal structure of the positive electrode material during charge or discharge can be inferred. Furthermore, since charge / discharge efficiency is calculated from the ratio of discharge capacity to charge capacity, if the energy applied during charging is used for purposes other than the extraction of Li, the charge / discharge efficiency will decrease. Therefore, if there is a change in the crystal model of the positive electrode material, a decrease in charge / discharge efficiency can be observed. Therefore, by measuring the charge / discharge efficiency, changes in the crystal model of the lithium composite oxide can be analyzed.

[0054] To analyze changes in the crystal model more accurately, it is preferable to minimize the above-mentioned degradation factors. Therefore, it is preferable to measure the initial charge / discharge efficiency. Furthermore, if the crystal model changes, analyzing whether the change is reversible or irreversible allows for a more detailed analysis of the phenomena occurring in the crystal. Therefore, it is more preferable to measure not only the initial charge / discharge efficiency but also the second charge / discharge efficiency. If the second measurement yields the same results as the first, it can be assumed that the phenomena occurring in the crystal are reversible. On the other hand, if the second measurement differs from the first measurement—for example, if the initial charge / discharge efficiency is less than 100% but the second charge / discharge efficiency is 100%—it can be assumed that the phenomena occurring in the crystal are irreversible and occur only in the first measurement. In this way, comparing the initial and second charge / discharge efficiencies allows for a more detailed analysis.

[0055] If the factors of deterioration are few, it is acceptable to compare the charge-discharge efficiency between the first and third or later cycles. It is also acceptable to compare the charge-discharge efficiency between any number of cycles, such as the second and third or later cycles. However, if the phenomenon occurring in the crystal is irreversible, the phenomenon may only be observed the first time. Therefore, it is preferable to measure the charge-discharge efficiency for the first time. Furthermore, considering the factors of deterioration, it is more preferable to compare the first and second cycles.

[0056] Also, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) To measure the charge-discharge efficiency of a compound represented by the formula Li, it is first necessary to synthesize the compound. Next, a battery cell is made using the synthesized compound, and then the charge-discharge efficiency of the battery cell is measured. These steps are necessary to measure the charge-discharge efficiency. (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) When performing measurements that are not related to charge / discharge or electrolyte, such as XRD measurement of O2, it is not necessary to prepare a battery cell. (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b)When measuring a compound represented by O₂, at least a step of synthesizing the compound and a step of measuring the properties of the compound are required. When measuring the charge-discharge efficiency, a step of fabricating a battery cell is further required. Note that other steps may be included for the measurement.

[0057] By combining and analyzing the measurements of ΔE, ΔEc, and charge-discharge efficiency described in this embodiment, the crystal structure and substitution positions of the lithium composite oxide can be accurately analyzed. Efficiently performing calculations using multiple calculation methods and further combining measurements for analysis is a feature of the present invention. By combining calculations and measurements, the validity of the calculation results and the phenomena predicted from the calculation results can be evaluated, enabling detailed analysis. Particularly for the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The compound represented by O₂ has particularly good properties when 0 < x + a ≤ 0.015 and 0 < y + b ≤ 0.06. However, since the mixing amounts of Mg and Ni are small, it is currently difficult to analyze the detailed crystal structure only by measurement. Therefore, the analysis method of one aspect of the present invention can be preferably used. Also, based on the analysis results obtained from calculations and measurements, performing analysis by calculation and measurement again can enable more accurate analysis. Therefore, the calculations and measurements shown in this embodiment may be repeated. Further, additional analysis may be performed based on the results obtained from the calculations and measurements shown in this embodiment.

[0058] Also, although the measurement of charge-discharge efficiency has been described as an example of measurement, as the measurement of one aspect of the present invention, dQ / dV measurement, XRD measurement, magnetization measurement, Li NMR measurement, etc. can also be used. The measurement of one aspect of the present invention is not limited to these.

[0059] This embodiment can be used in appropriate combination with other embodiments.

[0060] (Embodiment 2) Using FIG. 3, for the chemical formula Li (1-x-y)Co (1-a-b) Ni (x+a) Mg (y+b) An example of a method for producing a compound represented by O2 will be described.

[0061] As shown in step S11 of Figure 3, first, lithium fluoride, which is a fluorine source, and magnesium fluoride, which is a magnesium source, are prepared as materials for the mixture 902. Lithium fluoride is preferable because it has a relatively low melting point of 848°C and is easily melted in the annealing step described below. Lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can also be used as both a fluorine source and a magnesium source.

[0062] In this embodiment, lithium fluoride LiF is prepared as the fluorine source and lithium source, and magnesium fluoride MgF2 is prepared as the fluorine source and magnesium source (Step S11 in FIG. 3). The molar ratio of lithium fluoride LiF to magnesium fluoride MgF2 is preferably LiF:MgF2=u:1 (0≦u≦1.9), more preferably LiF:MgF2=x:1 (0.1≦u≦0.5), and even more preferably LiF:MgF2=u:1 (u=near 0.33).

[0063] If the subsequent mixing and grinding steps are performed wet, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used (see step S11 in FIG. 3).

[0064] Next, the materials for the mixture 902 are mixed and pulverized (step S12 in FIG. 3). Mixing can be performed by either a dry or wet method, but a wet method is preferred because it allows for finer pulverization. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the medium. It is preferable to thoroughly perform this mixing and pulverization process to finely pulverize the mixture 902.

[0065] The mixed and crushed materials are collected (step S13 in FIG. 3) to obtain a mixture 902 (step S14 in FIG. 3).

[0066] The D50 of the mixture 902 is preferably, for example, 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. Such a finely pulverized mixture 902 facilitates uniform adhesion of the mixture 902 to the surface of the composite oxide particles when mixed with a composite oxide containing lithium, a transition metal, and oxygen in a subsequent process. Uniform adhesion of the mixture 902 to the surface of the composite oxide particles is preferable because it facilitates thorough distribution of halogen and magnesium throughout the surface layer of the composite oxide particles after heating. If there are regions in the surface layer that do not contain halogen and magnesium, it may be difficult to form the pseudospinel crystal structure described above in a charged state.

[0067] Next, a lithium source is prepared as shown in step S25. In step S25, a composite oxide containing lithium, a transition metal, and oxygen that has been synthesized in advance is used.

[0068] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as pre-synthesized lithium cobalt oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0069] The composite oxide containing lithium, a transition metal, and oxygen in step S25 preferably has a layered rock-salt crystal structure with few defects and strain. Therefore, a composite oxide with few impurities is preferred. If the composite oxide containing lithium, a transition metal, and oxygen contains a large amount of impurities, it is likely to have a crystal structure with many defects or strains.

[0070] Next, the mixture 902 is mixed with a composite oxide containing lithium, a transition metal, and oxygen (step S31 in FIG. 3). The ratio of the number of transition metal atoms TM in the composite oxide containing lithium, a transition metal, and oxygen to the number of magnesium atoms MgMix1 in the mixture 902 is preferably TM:MgMix1=1:v (0.005≦v≦0.05), more preferably TM:MgMix1=1:v (0.007≦v≦0.04), and even more preferably about TM:MgMix1=1:0.02.

[0071] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the composite oxide particles. For example, the mixing conditions are preferably lower in rotation speed or shorter in time than those in step S12. It can also be said that dry mixing conditions are milder than wet mixing. For example, a ball mill, bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media.

[0072] The mixed materials are collected (step S32 in FIG. 3) to obtain a mixture 903 (step S33 in FIG. 3).

[0073] Next, the mixture 903 is heated (step S34 in FIG. 3). This step is sometimes called annealing or second heating to distinguish it from the previous heating step.

[0074] The annealing is preferably performed at an appropriate temperature and time. The appropriate temperature and time vary depending on conditions such as the size and composition of the composite oxide particles containing lithium, transition metal, and oxygen in step S25. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large.

[0075] For example, when the average particle size (D50) of the particles in step S25 is about 12 μm, the annealing temperature is preferably, for example, 600° C. or more and 950° C. or less. The annealing time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0076] On the other hand, when the average particle size (D50) of the particles in step S25 is about 5 μm, the annealing temperature is preferably, for example, 600° C. to 950° C. The annealing time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0077] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0078] When mixture 903 is annealed, it is believed that the material with the lowest melting point in mixture 902 (e.g., lithium fluoride, melting point 848°C) melts first and distributes to the surface layer of the composite oxide particles. Next, the presence of this molten material lowers the melting points of other materials, which then melts them. For example, magnesium fluoride (melting point 1263°C) melts and distributes to the surface layer of the composite oxide particles.

[0079] The diffusion of elements contained in this mixture 903 is faster in the surface layer and near the grain boundaries than inside the composite oxide particles, so the magnesium and halogen concentrations are higher in the surface layer and near the grain boundaries than inside.

[0080] The annealed material is collected (step S35 in FIG. 3) to obtain a mixture 904 (step S36 in FIG. 3).

[0081] Next, as shown in step S50, the mixture 904 and the pulverized nickel hydroxide are mixed. Then, the mixed material is recovered (step S51). The pulverized nickel hydroxide is previously subjected to step S15 in which nickel hydroxide is mixed with acetone and step S16 in which it is recovered. By step S16, pulverized nickel hydroxide is obtained (step S17).

[0082] The materials mixed in step S50 are collected in step S51 to obtain a mixture 905 (step S52 in FIG. 3).

[0083] Next, the resulting mixture is heated (step S53 in FIG. 3).

[0084] The heating time is preferably set to a holding time within the heating temperature range of 1 hour to 80 hours.

[0085] The heating temperature is less than 1000°C, preferably 700°C or higher and 950°C or lower, and more preferably about 850°C.

[0086] The heating is preferably carried out in an atmosphere containing oxygen.

[0087] In this embodiment, the heating temperature is set to 850° C. and is maintained for two hours, the temperature is increased at 200° C. / h, and the oxygen flow rate is set to 10 L / min.

[0088] The heating temperature in step S53 is preferably lower than the heating temperature in step S34.

[0089] <Steps S54 and S55> Next, the cooled particles are collected (step S54 in FIG. 3). Furthermore, it is preferable to sieve the particles. (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) A positive electrode active material 100A-1, which is an example of a compound represented by O2, can be produced (step S55 in FIG. 3).

[0090] The positive electrode active material 100A-1 obtained by the above-described manufacturing method will be described.

[0091] [Positive electrode active material structure] Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock-salt crystal structure is a composite oxide represented by LiMO2. Examples of element M include one or more selected from Co and Ni. Examples of element M include one or more selected from Co and Ni, as well as one or more selected from Al and Mg.

[0092] It is known that the strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal.

[0093] In a compound having nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charge and discharge are performed at a high voltage in LiNiO₂, there is a concern that the crystal structure may collapse due to the distortion. In LiCoO₂, it is suggested that the influence of the Jahn-Teller effect is small, and it may be more resistant to charge and discharge at a high voltage, which is preferable.

[0094] Using FIGS. 4 and 5, the positive electrode active material will be described. In FIGS. 4 and 5, the case where cobalt is used as the transition metal included in the positive electrode active material will be described.

[0095] Chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The compound represented by O₂ can reduce the shift of the CoO₂ layer in repeated charge and discharge at a high voltage. Furthermore, the volume change can be reduced. Therefore, the compound can achieve excellent cycle characteristics. In addition, the compound can have a stable crystal structure in the charged state at a high voltage. Therefore, when the compound maintains the charged state at a high voltage, a short circuit is less likely to occur. In such a case, since the safety is further improved, it is preferable. Particularly, it is preferable when 0 < x + a ≤ 0.015 and 0 < y + b ≤ 0.06 because the characteristics are good.

[0096] In this compound, the change in the crystal structure and the volume difference when compared per the same number of transition metal atoms in the fully discharged state and the state charged at a high voltage are small.

[0097] The crystal structure of the positive electrode active material 100A-1 before and after charge and discharge is shown in FIG. 5. The positive electrode active material 100A-1 is a complex oxide represented by the chemical formula Li (1-x-y) [[ID=२6]]Co (1-a-b) Ni (x+a) Mg (y+b) O₂.

[0098] The crystal structure at a charge depth of 0 (discharged state) in Figure 5 is the same as in Figure 4, R-3m(O3). On the other hand, when the cathode active material 100A-1 is fully charged, it has a crystal structure different from the H1-3 crystal structure. This structure belongs to the space group R-3m. Although it is not a spinel crystal structure, ions such as cobalt and magnesium occupy six oxygen coordination sites, and the arrangement of cations has a symmetry similar to that of a spinel structure. Therefore, this structure is referred to as a pseudo-spinel crystal structure in this specification. In the pseudo-spinel crystal structure shown in Figure 5, lithium is omitted to explain the symmetry of the cobalt atoms and the oxygen atoms. However, in reality, lithium is present between the CoO2 layers at, for example, 20 atomic % or less relative to cobalt. In both the O3 crystal structure and the pseudo-spinel crystal structure, magnesium is preferably present in a dilute form between the CoO2 layers, i.e., at the lithium sites. Furthermore, halogens such as fluorine may be present randomly and dilutely at the oxygen sites.

[0099] In addition, in the pseudospinel crystal structure, light elements such as lithium may occupy the oxygen tetracoordination site, and in this case too, the arrangement of ions has a symmetry similar to that of the spinel structure.

[0100] It can also be said that the pseudospinel crystal structure has random Li between the layers, but is similar to the CdCl2 crystal structure. This CdCl2-like crystal structure was observed when lithium nickel oxide was charged to a depth of charge of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0101] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in pseudospinel crystals also have a cubic close-packed structure. When these crystals contact, there are crystal planes where the cubic close-packed structures formed by the anions are aligned. However, the space group of layered rock salt crystals and pseudospinel crystals is R-3m, which is different from the space groups of rock salt crystals, Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and pseudospinel crystals and rock salt crystals. In this specification, when the cubic close-packed structures formed by the anions are aligned in layered rock salt crystals, pseudospinel crystals, and rock salt crystals, the crystal orientations may be said to be approximately aligned.

[0102] In positive electrode active material 100A-1, when a large amount of lithium is released during high-voltage charging, the change in the crystal structure is more suppressed than in positive electrode active material 100C. For example, as shown by the dotted line in Figure 4, there is almost no displacement of the CoO2 layers in these crystal structures.

[0103] More specifically, the cathode active material 100A-1 exhibits high structural stability even at high charging voltages. For example, the cathode active material 100C exhibits a charging voltage range where the R-3m(O3) crystal structure can be maintained even at charging voltages of approximately 4.6 V relative to the potential of lithium metal, where the H1-3 crystal structure is formed. Furthermore, even at higher charging voltages, such as 4.65 to 4.7 V relative to the potential of lithium metal, a pseudo-spinel crystal structure can be formed. Furthermore, the H1-3 crystal structure can sometimes only be observed at higher charging voltages. In addition, when graphite is used as the anode active material in a secondary battery, a charging voltage range where the R-3m(O3) crystal structure can be maintained exists, even at secondary battery voltages of 4.3 V to 4.5 V, where the pseudo-spinel crystal structure can be formed. Furthermore, even at higher charging voltages, such as 4.35 V to 4.55 V relative to the potential of lithium metal, a pseudo-spinel crystal structure can be formed.

[0104] Therefore, in the positive electrode active material 100A-1, the crystal structure is not easily broken even when the material is repeatedly charged and discharged at a high voltage.

[0105] The pseudospinel crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), with 0.20≦x≦0.25.

[0106] Magnesium, which is present randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers. Therefore, the presence of magnesium between the CoO2 layers tends to form a pseudo-spinel crystal structure. Therefore, it is preferable that magnesium be distributed throughout the particles of the positive electrode active material 100A-1. In addition, to distribute magnesium throughout the particles, it is preferable to perform a heat treatment during the production process of the positive electrode active material 100A-1.

[0107] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. If magnesium is present at the cobalt site, it will no longer be effective in maintaining the R-3m structure. Furthermore, if the heat treatment temperature is too high, there are concerns that adverse effects such as cobalt being reduced to a divalent state and lithium evaporating may occur.

[0108] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0109] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably approximately 0.02. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the production process of the positive electrode active material.

[0110] The number of nickel atoms in the positive electrode active material 100A-1 is preferably 7.5% or less of the number of cobalt atoms, more preferably 0.05% to 4%, and even more preferably 0.1% to 2%. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0111] A more detailed structure of positive electrode active material 100A-1 can be analyzed by the analytical method shown in the first embodiment.

[0112] ≪Particle size≫ If the particle size of the positive electrode active material 100A-1 is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector arise. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte occur. Therefore, the average particle size (D50: also referred to as median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0113] <Analysis method> Whether a certain positive electrode active material exhibits a pseudospinel crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0114] As described above, the positive electrode active material 100A-1 is characterized by minimal change in its crystal structure between a high-voltage charged state and a discharged state. Materials in which a crystal structure that exhibits a significant change between a high-voltage charged state and a discharged state occupies 50 wt% or more of the charged state is undesirable because they cannot withstand high-voltage charging and discharging. It should be noted that the desired crystal structure may not be achieved simply by adding impurity elements. For example, even if both materials share the common feature of being lithium cobalt oxide containing magnesium and fluorine, there are cases in which a pseudo-spinel crystal structure occupies 60 wt% or more of the charged state at a high voltage, and cases in which an H1-3 crystal structure occupies 50 wt% or more of the charged state at a high voltage. Furthermore, at a certain voltage, the pseudo-spinel crystal structure may be nearly 100 wt%, and further increasing the voltage may result in the H1-3 crystal structure. Therefore, it is preferable to analyze the crystal structure of the positive electrode active material 100A-1 using XRD or the like. Furthermore, it is even more preferable to perform the analysis using the analytical method described in the first embodiment. By combining this with measurements such as XRD, a more detailed analysis can be performed.

[0115] However, when positive electrode active materials are charged or discharged at high voltage, their crystal structure may change when exposed to air. For example, they may change from a pseudospinel crystal structure to an H1-3 crystal structure. Therefore, it is recommended that all samples be handled in an inert atmosphere such as an argon atmosphere.

[0116] <Comparative example of positive electrode active material (LiCoO2)> The positive electrode active material (lithium cobalt oxide) shown in Fig. 4 is lithium cobalt oxide (LiCoO) to which no halogen or magnesium is added using a manufacturing method described below. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Fig. 4 changes depending on the depth of charge.

[0117] As shown in Figure 4, lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0118] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0119] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.88 has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as an H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 5 and other parts of this specification, for ease of comparison with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0120] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 type crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as will be described later, the pseudospinel type crystal structure of one embodiment of the present invention shown in FIG. 5 is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the pseudospinel structure and the H1-3 type structure, and that the pseudospinel structure changes less from the O3 structure than the H1-3 type structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (good of fitness) value is smaller in Rietveld analysis of XRD.

[0121] When lithium cobalt oxide is repeatedly charged and discharged at a high voltage of 4.6 V or higher, based on the redox potential of lithium metal, or at a deep charge depth of 0.8 or higher, the crystal structure of the lithium cobalt oxide changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0122] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 4, in the H1-3 type crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0123] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0124] In addition, the structure in which CoO2 layers such as P-3m1(O1) with the H1-3 type crystal structure are continuous is likely to be unstable.

[0125] Therefore, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobalt oxide collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is thought to be because when the crystal structure collapses, the sites where lithium can exist stably decrease, and it becomes difficult for lithium to be inserted and extracted.

[0126] (Embodiment 3) In this embodiment, an example of a material that can be used for a secondary battery having a positive electrode active material 100 shown in FIGS. 6A and 6B will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example. Note that the positive electrode active material 100 has the chemical formula Li (1-x-y) Co (1-a-b) Ni [[ID=1×5]] (x+a) Mg (y+b) compound represented by O2 and the positive electrode active material 100A-1 can be used.

[0127] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0128] <Positive electrode active material layer> The positive electrode active material layer has positive electrode active material particles. Further, the positive electrode active material layer may have a conductive assistant and a binder.

[0129] As the positive electrode active material particles, the positive electrode active material 100 can be used. The lithium composite oxide described in the previous embodiment for the positive electrode active material 100, for example, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) compound represented by O2 and the positive electrode active material 100A-1 can be used. In the chemical formula, it is preferable that 0 < x + a ≤ 0.015 and 0 < y + b ≤ 0.06. By using this compound, a secondary battery with less deterioration and high safety can be obtained.

[0130] The conductive additive may be a carbon material, a metal material, a conductive ceramic material, or the like. Alternatively, a fibrous material may be used as the conductive additive. The content of the conductive additive relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, more preferably 1 wt% to 5 wt%.

[0131] The conductive additive can form an electrically conductive network in the electrode. The conductive additive can maintain an electrical conduction path between the positive electrode active materials. By adding the conductive additive to the active material layer, an active material layer with high electrical conductivity can be realized.

[0132] Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fibers. Examples of the carbon fibers that can be used include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Examples of the carbon fibers that can be used include carbon nanofibers and carbon nanotubes. Carbon nanotubes can be produced by, for example, vapor phase growth methods. Examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite particles, graphene, and fullerene. Examples of the conductive additive include metal powders and metal fibers such as copper, nickel, aluminum, silver, and gold, and conductive ceramic materials.

[0133] A graphene compound may also be used as the conductive additive.

[0134] Graphene compounds may have excellent electrical properties, such as high electrical conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds also have a planar shape. Graphene compounds enable surface contact with low contact resistance. Even when thin, they can have very high electrical conductivity, allowing a small amount to efficiently form a conductive path within the active material layer. Therefore, using graphene compounds as a conductive additive is preferable because it can increase the contact area between the active material and the conductive additive. It is also preferable because it can reduce electrical resistance. Here, graphene compounds such as graphene, multigraphene, graphene quantum dots, or reduced graphene oxide (hereinafter, RGO) are particularly preferable. Here, RGO refers to a compound obtained by reducing graphene oxide (GO).

[0135] When using active material particles with a small particle size, for example, active material particles of 1 μm or less, the specific surface area of ​​the active material particles is large, and more conductive paths connecting the active material particles are required. In such cases, it is particularly preferable to use a graphene compound that can efficiently form conductive paths even in a small amount.

[0136] As an example, a cross-sectional configuration example in which a graphene compound is used as a conductive additive in the active material layer 200 will be described below.

[0137] FIG. 6A shows a longitudinal cross-sectional view of an active material layer 200. The active material layer 200 includes granular positive electrode active material 100, a graphene compound 201 as a conductive additive, and a binder (not shown). Here, graphene or multi-graphene may be used as the graphene compound 201, for example. Here, the graphene compound 201 preferably has a sheet-like shape. Alternatively, the graphene compound 201 may be a sheet-like shape formed by partially overlapping a plurality of multi-graphenes and / or a plurality of graphenes.

[0138] In a longitudinal cross section of the active material layer 200, as shown in Fig. 6A, sheet-like graphene compounds 201 are dispersed approximately uniformly within the active material layer 200. In Fig. 6A, the graphene compounds 201 are schematically represented by thick lines, but in reality, they are thin films having a thickness corresponding to a single layer or multiple layers of carbon molecules. The plurality of graphene compounds 201 are formed so as to wrap around or cover the plurality of granular positive electrode active material 100, or to adhere to the surfaces of the plurality of granular positive electrode active material 100, and are therefore in surface contact with each other.

[0139] Here, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphene compounds together. When an active material is covered with a graphene net, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or no binder can be used, thereby improving the ratio of the active material to the electrode volume or weight. In other words, the capacity of the power storage device can be increased.

[0140] Here, it is preferable to use graphene oxide as the graphene compound 201, mix it with an active material to form a layer that will become the active material layer 200, and then reduce it. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene compound 201, it is possible to disperse the graphene compound 201 approximately uniformly inside the active material layer 200. Since the solvent is volatilized and removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compound 201 remaining in the active material layer 200 is dispersed to the extent that it partially overlaps and is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of the graphene oxide may be performed by, for example, heat treatment or using a reducing agent.

[0141] Therefore, unlike a granular conductive additive such as acetylene black that makes point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance, and therefore can improve the electrical conductivity between the granular positive electrode active material 100 and the graphene compound 201 with a smaller amount than that of a typical conductive additive. This allows the proportion of the positive electrode active material 100 in the active material layer 200 to be increased, thereby increasing the discharge capacity of the power storage device.

[0142] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0143] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of water-soluble polymers that can be used include polysaccharides. Examples of polysaccharides that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0144] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0145] The binder may be used in combination with two or more of the above.

[0146] For example, a material with particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjusting effect. Furthermore, as water-soluble polymers with particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch may be used.

[0147] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium salts or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials and other components when preparing electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0148] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl groups and carboxyl groups. Because of these functional groups, the polymers are expected to interact with each other and widely cover the surface of the active material.

[0149] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and have the effect of suppressing decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0150] <Positive electrode current collector> The positive electrode current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The positive electrode current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate (sheet), mesh, punched metal, or expanded metal, as appropriate. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0151] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive additive and a binder.

[0152] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0153] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. For this reason, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called alloy-based materials.

[0154] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO x Here, x preferably has a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0155] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0156] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0157] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05V to 0.3V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0158] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0159] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0160] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0161] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0162] The conductive additive and binder that can be contained in the negative electrode active material layer can be the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer.

[0163] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0164] [Electrolyte] The electrolytic solution contains a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, or sultone, or any combination and ratio of two or more of these.

[0165] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the electricity storage device. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0166] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these.

[0167] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular dust and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0168] The electrolyte may contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1% by weight to 5% by weight based on the total weight of the solvent.

[0169] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0170] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0171] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0172] In addition, instead of an electrolyte solution, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymer materials such as polyethylene oxide (PEO) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.

[0173] (Fourth embodiment) In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the previous embodiment will be described. The description in the previous embodiment can be referred to for materials used in the secondary battery described in this embodiment.

[0174] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. Fig. 7A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 7B is a cross-sectional view thereof.

[0175] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0176] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0177] Positive electrode can 301 and negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, it is preferable to coat them with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0178] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 7B, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-type secondary battery 300.

[0179] By using the positive electrode active material particles described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can be made less susceptible to deterioration and highly safe.

[0180] [Separator] The secondary battery preferably has a separator. Examples of the separator include fibers containing cellulose, such as paper, nonwoven fabrics, glass fibers, ceramics, and synthetic fibers made of nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably formed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0181] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0182] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0183] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0184] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0185] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Figures 8A to 8D. As shown in Figures 8A and 8B, a cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0186] FIG. 8B is a schematic diagram showing the cross section of a cylindrical secondary battery. Inside a hollow cylindrical battery can 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal that is corrosion-resistant to the electrolyte, such as nickel, aluminum, or titanium, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel). Furthermore, a coating of nickel, aluminum, or the like is preferable to prevent corrosion by the electrolyte. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The non-aqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0187] Because the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active materials on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element can be made of barium titanate (BaTiO3)-based semiconductor ceramics or the like.

[0188] 8C , a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between conductive plates 613 and 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0189] FIG. 8D is a top view of the module 615. For clarity, the conductive plate 613 is shown with a dotted line. As shown in FIG. 8D, the module 615 may have conductive wires 616 that electrically connect the multiple secondary batteries 600. A conductive plate can be superimposed on the conductive wires 616. A temperature control device 617 may also be provided between the multiple secondary batteries 600. When the secondary batteries 600 are overheated, they can be cooled by the temperature control device 617, and when the secondary batteries 600 are too cold, they can be heated by the temperature control device 617. This makes it less likely that the performance of the module 615 will be affected by the outside temperature.

[0190] By using the positive electrode active material 100 described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 can be made less susceptible to deterioration and highly safe.

[0191] [Structure example of power storage device] Another structural example of the power storage device will be described with reference to FIGS.

[0192] 9A and 9B are diagrams showing the appearance of a power storage device. The power storage device has a circuit board 900 and a secondary battery 913. A label 910 is attached to the secondary battery 913. Furthermore, as shown in FIG. 9B, the power storage device has a terminal 951, a terminal 952, an antenna 914, and an antenna 915.

[0193] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to a terminal 951, a terminal 952, an antenna 914, an antenna 915, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0194] The circuit 912 may be provided on the back surface of the circuit board 900. The antennas 914 and 915 are not limited to being coil-shaped, and may be, for example, wire-shaped or plate-shaped. Also, antennas such as a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 or 915 may be a flat-plate conductor. This flat-plate conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 or 915 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

[0195] The line width of the antenna 914 is preferably larger than the line width of the antenna 915. This allows the amount of power received by the antenna 914 to be increased.

[0196] The power storage device includes a layer 916 between the antenna 914, the antenna 915, and the secondary battery 913. The layer 916 has a function of shielding, for example, an electromagnetic field generated by the secondary battery 913. The layer 916 can be formed using, for example, a magnetic material.

[0197] The structure of the electricity storage device is not limited to that shown in FIG.

[0198] For example, as shown in Fig. 10A1 and Fig. 10A2, an antenna may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in Fig. 9A and Fig. 9B. Fig. 10A1 is an external view of the pair of surfaces as seen from one side, and Fig. 10A2 is an external view of the pair of surfaces as seen from the other side. Note that the description of the power storage device shown in Fig. 9A and Fig. 9B can be used as appropriate for the same parts as those of the power storage device shown in Fig. 9A and Fig. 9B.

[0199] 10A1, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in Fig. 10A2, an antenna 915 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The layer 917 has a function of shielding, for example, an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0200] By using the above structure, the size of both the antenna 914 and the antenna 915 can be increased.

[0201] Alternatively, as shown in Figures 10B1 and 10B2, a separate antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 9A and 9B. Figure 10B1 is an external view of the pair of surfaces as seen from one side, and Figure 10B2 is an external view of the pair of surfaces as seen from the other side. Note that the description of the power storage device shown in Figures 9A and 9B can be used as appropriate for the same parts as those of the power storage device shown in Figures 9A and 9B.

[0202] 10B1, antennas 914 and 915 are provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in FIG. 10B2, antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The antenna 918 has a function of, for example, performing data communication with an external device. For example, an antenna having a shape applicable to the antennas 914 and 915 can be used as the antenna 918. As a communication method between the power storage device and another device via the antenna 918, a response method that can be used between the power storage device and another device, such as NFC, can be used.

[0203] 11A, a display device 920 may be provided on the secondary battery 913 shown in FIGS. 9A and 9B. The display device 920 is electrically connected to a terminal 911 via a terminal 919. Note that the label 910 does not necessarily have to be provided on the portion where the display device 920 is provided. Note that the description of the power storage device shown in FIGS. 9A and 9B can be used as appropriate for the same portions as those of the power storage device shown in FIGS. 9A and 9B.

[0204] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored power. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0205] 11B, a sensor 921 may be provided in the secondary battery 913 shown in FIGS. 9A and 9B. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. Note that the description of the power storage device shown in FIGS. 9A and 9B can be used as appropriate for the same parts as those of the power storage device shown in FIGS. 9A and 9B.

[0206] The sensor 921 may have a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared ray. By providing the sensor 921, for example, data indicating the environment in which the power storage device is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0207] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0208] A secondary battery 913 shown in Fig. 12A has a wound body 950 in which terminals 951 and 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in Fig. 12A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (such as aluminum) or a resin material.

[0209] 12B, the housing 930 shown in Fig. 12A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 12B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0210] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, antennas such as the antenna 914 and the antenna 915 may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0211] 13 shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0212] 9 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG.

[0213] By using the positive electrode active material particles described in the above embodiment for the positive electrode 932, the secondary battery 913 can be less susceptible to deterioration and highly safe.

[0214] [Laminated secondary battery] Next, examples of laminated secondary batteries will be described with reference to Figures 14 to 19. If a laminated secondary battery has a flexible configuration, and is mounted in an electronic device having at least a flexible portion, the secondary battery can also be bent in accordance with deformation of the electronic device.

[0215] A laminated secondary battery 980 will be described using Fig. 14. The laminated secondary battery 980 has a wound body 993 shown in Fig. 14A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. The wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 on top of each other with the separator 996 sandwiched therebetween, similar to the wound body 950 described in Fig. 13, and winding the laminated sheet.

[0216] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed depending on the required capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0217] 14B, a film 981 serving as an exterior body and a film 982 having a recess are bonded together by thermocompression or the like to form a space, and the above-described wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 14C. The wound body 993 has lead electrodes 997 and 998, and is impregnated with an electrolyte solution between the film 981 and the film 982 having a recess.

[0218] For example, a metal material such as aluminum or a resin material can be used for film 981 and film 982 having recesses. If a resin material is used as the material for film 981 and film 982 having recesses, film 981 and film 982 having recesses can be deformed when an external force is applied, and a flexible storage battery can be produced.

[0219] Although FIGS. 14B and 14C show an example in which two films are used, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0220] By using the positive electrode active material particles described in the above embodiment for the positive electrode 995, the secondary battery 980 can be one that is less susceptible to deterioration and has high safety.

[0221] Furthermore, although Figure 14 describes an example of a secondary battery 980 having a wound body in a space formed by a film that serves as an outer casing, it may also be a secondary battery having multiple strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing, as shown in Figure 15, for example.

[0222] 15A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte solution 508, and an exterior body 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. The exterior body 509 is filled with the electrolyte solution 508. The electrolyte solution described in Embodiment 2 can be used as the electrolyte solution 508.

[0223] 15A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged so as to be partially exposed to the outside from the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the exterior body 509, and a lead electrode may be used and ultrasonically bonded to the positive electrode current collector 501 or the negative electrode current collector 504 so as to expose the lead electrode to the outside.

[0224] In the laminated secondary battery 500, the exterior body 509 can be a three-layer laminate film having a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and further having an insulating synthetic resin film made of polyamide-based resin, polyester-based resin, or the like provided on the metal thin film as the outer surface of the exterior body.

[0225] 15B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 15A shows an example configured with two current collectors, but in reality, it is configured with multiple electrode layers.

[0226] In FIG. 15B, the number of electrode layers is 16 as an example. Note that even if the number of electrode layers is 16, the secondary battery 500 remains flexible. FIG. 15B shows a structure with a total of 16 layers, including eight layers of negative electrode current collectors 504 and eight layers of positive electrode current collectors 501. Note that FIG. 15B also shows a cross section of the negative electrode lead-out portion, in which eight layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16 and may be more or less. When the number of electrode layers is large, a secondary battery with a larger capacity can be obtained. Furthermore, when the number of electrode layers is small, a secondary battery can be made thinner and have excellent flexibility.

[0227] 16 and 17 show examples of the external appearance of a laminated secondary battery 500. The battery 500 includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0228] FIG. 18A shows the appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The areas and shapes of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 18A.

[0229] [Method for manufacturing laminated secondary batteries] Here, an example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 16 will be described with reference to FIGS. 18B and 18C.

[0230] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 18B shows the stacked negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0231] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0232] Next, as shown in Fig. 18C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that electrolyte 508 can be introduced later.

[0233] Next, electrolytic solution 508 is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. Introduction of electrolytic solution 508 is preferably performed under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, secondary battery 500, which is a laminated secondary battery, can be produced.

[0234] By using the positive electrode active material particles described in the above embodiment for the positive electrode 503, the secondary battery 500 can be one that is less susceptible to deterioration and has high safety.

[0235] [Bendable secondary battery] Next, an example of a bendable secondary battery will be described with reference to FIGS.

[0236] FIG. 19A shows a schematic top view of a bendable battery 250. FIGS. 19B1, 19B2, and 19C are schematic cross-sectional views taken along chain lines C1-C2, C3-C4, and A1-A2 in FIG. 19A, respectively. The battery 250 includes an exterior housing 251 and a positive electrode 211a and a negative electrode 211b housed within the exterior housing 251. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior housing 251. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed within the area surrounded by the exterior housing 251.

[0237] The positive electrode 211a and the negative electrode 211b of the battery 250 will be described with reference to Fig. 20. Fig. 20A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 20B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0238] 20A, battery 250 has a plurality of rectangular positive electrodes 211a, a plurality of rectangular negative electrodes 211b, and a plurality of separators 214. Positive electrode 211a and negative electrode 211b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of positive electrode 211a in the portion other than the tab, and a negative electrode active material layer is formed on one surface of negative electrode 211b in the portion other than the tab.

[0239] The positive electrode 211a and the negative electrode 211b are stacked so that the surfaces of the positive electrode 211a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

[0240] Furthermore, a separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material is formed and the surface of the negative electrode 211b on which the negative electrode active material is formed. In Fig. 20, the separator 214 is indicated by a dotted line for ease of viewing.

[0241] 20B, the positive electrodes 211a and the lead 212a are electrically connected at a joint 215a, and the negative electrodes 211b and the lead 212b are electrically connected at a joint 215b.

[0242] Next, the exterior body 251 will be described with reference to FIGS. 19B1, 19B2, 19C, and 19D.

[0243] The exterior body 251 has a film-like shape and is folded in two to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b, and can also be called side seals. The sealing portion 263 has a portion that overlaps with the lead 212a and the lead 212b, and can also be called a top seal.

[0244] The exterior body 251 preferably has a wave shape in which ridge lines 271 and valley lines 272 are alternately arranged in the portions overlapping the positive electrode 211a and the negative electrode 211b. Furthermore, the seal portions 262 and 263 of the exterior body 251 are preferably flat.

[0245] Fig. 19B1 is a cross section taken at a portion overlapping with ridge line 271, and Fig. 19B2 is a cross section taken at a portion overlapping with valley line 272. Fig. 19B1 and Fig. 19B2 both correspond to widthwise cross sections of battery 250, positive electrode 211a, and negative electrode 211b.

[0246] Here, the distance La is defined as the distance between the widthwise ends of the positive electrode 211a and the negative electrode 211b, i.e., the ends of the positive electrode 211a and the negative electrode 211b, and the seal portion 262. When the battery 250 is deformed, such as by bending, the positive electrode 211a and the negative electrode 211b deform so as to be displaced from each other in the longitudinal direction, as described below. In this case, if the distance La is too short, the exterior body 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, resulting in damage to the exterior body 251. In particular, if the metal film of the exterior body 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the battery 250 increases.

[0247] Furthermore, it is preferable that the distance La between the positive electrode 211a and the negative electrode 211b and the seal portion 262 is increased as the total thickness of the stacked positive electrode 211a and the negative electrode 211b increases.

[0248] More specifically, when the total thickness of the stacked positive electrode 211a and negative electrode 211b is thickness t, the distance La is preferably 0.8 to 3.0 times, more preferably 0.9 to 2.5 times, and even more preferably 1.0 to 2.0 times the thickness t. By setting the distance La in this range, a compact battery with high reliability against bending can be realized.

[0249] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to make distance Lb sufficiently larger than the width of the positive electrode 211a and the negative electrode 211b (here, width Wb of the negative electrode 211b). This allows parts of the positive electrode 211a and the negative electrode 211b to shift in the width direction even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251 when the battery 250 is repeatedly deformed, such as by bending, so that rubbing between the positive electrode 211a and the negative electrode 211b and the exterior body 251 can be effectively prevented.

[0250] For example, it is preferable that the difference between the distance La between the pair of seal portions 262 and the width Wb of the negative electrode 211b is 1.6 to 6.0 times, preferably 1.8 to 5.0 times, and more preferably 2.0 to 4.0 times the thickness t of the positive electrode 211a and the negative electrode 211b.

[0251] In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following formula 7.

[0252]

number

[0253] Here, a satisfies the range of 0.8 to 3.0, preferably 0.9 to 2.5, and more preferably 1.0 to 2.0.

[0254] 19C is a cross section including lead 212a, and corresponds to a cross section in the longitudinal direction of battery 250, positive electrode 211a, and negative electrode 211b. As shown in FIG. 19C, it is preferable that a space 273 be formed between exterior body 251 and the longitudinal ends of positive electrode 211a and negative electrode 211b at bent portion 261.

[0255] Figure 19D shows a schematic cross-sectional view of the bent battery 250. Figure 19D corresponds to the cross section taken along the cutting line B1-B2 in Figure 19A.

[0256] When the battery 250 is bent, a portion of the exterior body 251 located on the outside of the bend expands, and another portion located on the inside contracts. More specifically, the portion located on the outside of the exterior body 251 deforms so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the portion located on the inside of the exterior body 251 deforms so that the wave amplitude becomes larger and the wave period becomes smaller. In this way, the deformation of the exterior body 251 relieves the stress applied to the exterior body 251 due to bending, so the material that constitutes the exterior body 251 itself does not need to expand or contract. As a result, the battery 250 can be bent with a small force without damaging the exterior body 251.

[0257] 19D, when the battery 250 is bent, the positive electrodes 211a and the negative electrodes 211b are displaced relative to each other. At this time, because one end of each of the stacked positive electrodes 211a and negative electrodes 211b on the sealing portion 263 side is fixed by the fixing member 217, the amount of displacement increases toward the bending portion 261. This relieves stress on the positive electrodes 211a and negative electrodes 211b, and the positive electrodes 211a and negative electrodes 211b themselves do not need to expand or contract. As a result, the battery 250 can be bent without damaging the positive electrodes 211a and negative electrodes 211b.

[0258] Furthermore, by providing the space 273 between the positive electrode 211a and the negative electrode 211b and the exterior body 251, when the battery is bent, the positive electrode 211a and the negative electrode 211b located on the inside can be relatively displaced without coming into contact with the exterior body 251.

[0259] 19 and 20 is a battery that is resistant to damage to the exterior body, the positive electrode 211a, and the negative electrode 211b, etc., even when repeatedly bent and stretched, and the battery characteristics are also resistant to deterioration. By using the positive electrode active material particles described in the previous embodiment for the positive electrode 211a of the battery 250, it is possible to obtain a secondary battery that is even less susceptible to deterioration and is therefore safer.

[0260] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on an electronic device will be described.

[0261] First, an example of mounting the bendable secondary battery described in part of embodiment 3 in an electronic device is shown in Fig. 21. Examples of electronic devices to which the bendable secondary battery is applied include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, sound reproduction devices, and large game machines such as pachinko machines.

[0262] Furthermore, a secondary battery having a flexible shape can be incorporated into the inner or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0263] 21A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 also includes a secondary battery 7407.

[0264] FIG. 21B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided inside is also bent. FIG. 21C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode 7408 electrically connected to a current collector 7409.

[0265] FIG. 21D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. FIG. 21E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's wrist in a bent state, the housing deforms, changing the curvature of part or all of the secondary battery 7104. The degree of bending at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surfaces of the housing or secondary battery 7104 change within a radius of curvature range of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature of the main surfaces of the secondary battery 7104 is within a range of 40 mm to 150 mm.

[0266] 21F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0267] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0268] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with a touch sensor, and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0269] The operation button 7205 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0270] The mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is also possible by communicating with a wirelessly enabled headset.

[0271] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0272] The secondary battery of one embodiment of the present invention is included in the display portion 7202 of the mobile information terminal 7200. For example, the secondary battery 7104 shown in FIG. 21E can be incorporated into the housing 7201 in a curved state or into the band 7203 in a bendable state.

[0273] The portable information terminal 7200 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or other human body sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0274] 21G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0275] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0276] The display device 7300 also has an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may also be performed by wireless power supply without using the input / output terminal.

[0277] Next, an example of a foldable tablet terminal is shown in FIGS. 22A and 22B. The tablet terminal 9600 shown in FIGS. 22A and 22B includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display unit 9631, a display mode selector switch 9626, a power switch 9627, a power saving mode selector switch 9625, a fastener 9629, and an operation switch 9628. Using a flexible panel for the display unit 9631 allows the tablet terminal to have a larger display area. FIG. 22A shows the tablet terminal 9600 in an open state, and FIG. 22B shows the tablet terminal 9600 in a closed state.

[0278] The tablet terminal 9600 also includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housing 9630a and the housing 9630b.

[0279] A part of the display portion 9631 can be a touch panel area, and data can be input by touching displayed operation keys. Furthermore, keyboard buttons can be displayed on the display portion 9631 by touching a position on the touch panel where a keyboard display switch button is displayed with a finger or a stylus.

[0280] Furthermore, a display mode switch 9626 can switch the display orientation between portrait and landscape, and can select between black and white and color display. A power saving mode switch 9625 can optimize the display brightness according to the amount of external light during use detected by an optical sensor built into the tablet terminal 9600. The tablet terminal may be equipped with not only an optical sensor but also other detection devices such as a gyroscope, an acceleration sensor, or other sensors that detect tilt.

[0281] 22B shows the tablet terminal in a closed state, which includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. In addition, a secondary battery according to one embodiment of the present invention is used as a power storage unit 9635.

[0282] Note that the tablet terminal 9600 can be folded in half, and thus can be folded so that the housing 9630a and the housing 9630b overlap each other when not in use. By folding, the display portion 9631 can be protected, thereby improving durability of the tablet terminal 9600. Furthermore, the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, and therefore, a tablet terminal that can be used for a long period of time can be provided.

[0283] In addition, the tablet terminals shown in Figures 22A and 22B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch input operations or editing information displayed on the display unit, and controlling processing using various software (programs).

[0284] A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display unit, a video signal processor, etc. The solar cell 9633 can be provided on one or both surfaces of the housing 9630, and can be configured to efficiently charge the power storage unit 9635.

[0285] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 22B will be described with reference to a block diagram in Fig. 22C. Fig. 22C shows a solar cell 9633, a power storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 22B.

[0286] First, an example of operation when power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 9636 to a voltage for charging a power storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, a switch SW1 is turned on, and the converter 9637 steps up or steps down the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, SW1 is turned off and SW2 is turned on to charge the power storage unit 9635.

[0287] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and the power storage unit 9635 may be charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be used.

[0288] FIG. 23 illustrates an example of another electronic device. In FIG. 23, a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one embodiment of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power source.

[0289] The display unit 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0290] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0291] 23 , a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. Although FIG. 23 illustrates the case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0292] Note that although Figure 23 illustrates an example of a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided in places other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device.

[0293] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include discharge lamps such as incandescent lamps and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0294] 23 , an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although FIG. 23 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or can use power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0295] Note that although FIG. 23 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, a secondary battery according to one embodiment of the present invention can also be used in an integrated-type air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing.

[0296] 23 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 23 , the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 of one embodiment of the present invention as an uninterruptible power source.

[0297] Furthermore, by storing power in the secondary battery during time periods when electronic devices are not in use, particularly during time periods when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these time periods. For example, in the case of electric refrigerator-freezer 8300, power is stored in secondary battery 8304 during the night when the temperature is low and refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature rises and refrigerator door 8302 and freezer door 8303 are opened and closed, secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0298] In addition to the electronic devices described above, the secondary battery of one embodiment of the present invention can be mounted in various electronic devices. According to one embodiment of the present invention, a secondary battery with less deterioration and higher safety can be obtained. Therefore, by mounting the secondary battery of one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and higher safety. This embodiment can be implemented in combination with other embodiments as appropriate.

[0299] (Embodiment 6) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0300] By installing a secondary battery in a vehicle, next-generation clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), and plug-in hybrid electric vehicles (PHEV) can be realized.

[0301] 24A illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 24A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery. The secondary battery not only drives the electric motor 8406 but also supplies power to a light-emitting device such as a headlight 8401 or a room light (not shown).

[0302] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0303] The automobile 8500 shown in FIG. 24B can charge its secondary battery by receiving power from an external charging facility using a plug-in system, a wireless power supply system, or the like. FIG. 24B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged via a cable 8022 from a ground-mounted charging device 8021. The charging method and connector specifications may be determined appropriately using a predetermined system such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0304] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0305] 24C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 24C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0306] 24C, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0307] According to one embodiment of the present invention, a secondary battery with little deterioration and high safety can be obtained. Therefore, by installing the secondary battery in a vehicle, deterioration of cruising range, acceleration performance, and the like can be suppressed. Furthermore, a vehicle with high safety can be obtained. Furthermore, a secondary battery installed in a vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. Avoiding the use of a commercial power source during peak power demand can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, since a secondary battery with little deterioration and high safety can be used for a long period of time, the amount of rare metals used, such as cobalt, can be reduced.

[0308] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0309] In this example, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The analysis of the substitution positions of Ni and Mg atoms in the compound represented by O2 will be explained.

[0310] [Calculation of stabilization energy (ΔE) for different substitution positions] Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) O2 is LiC O It is a compound in which Mg and Ni are added as substitution elements to O2. Here, one Mg atom and one Ni atom are LiC O When substituting for a metal atom with O2, the combinations of substitution sites are considered to be the same as those mentioned above. When Li in the same Li layer is replaced with Mg and Ni, condition (A) When Li in different Li layers is replaced with Mg and Ni, condition (B) When Co in the same Co layer is replaced by Mg and Ni, condition (C) When Co in different Co layers is replaced by Mg and Ni, condition (D) When Li in the Li layer is replaced by Mg and CoNi in the Co layer, condition (E) When Li in the Li layer is replaced with Ni and Co in the Co layer is replaced with Mg, condition (F)

[0311] For the above combinations of substitution sites, the stabilization energy ΔE was calculated for each combination where Ni and Mg are first to third or fourth nearest neighbors using the above formulas 1 to 3. The calculation conditions for LiCoO2 are shown in Table 1, and the calculation results of ΔE are shown in Figure 25. Note that (A) to (E) in Figure 25 represent the calculation results under the above conditions (A) to (E). Because the ionic radius of the Mg ion is larger than the ionic radius of the Co ion, it is expected that a large amount of energy is required for Mg to be substituted at the Co site. Therefore, the stabilization energy under condition (F) is expected to be large.

[0312] In Table 1, VSAP stands for Vienna Ab initio Simulation Package (purchased from VASP Software GmbH).

[0313] [Table 1]

[0314] Figure 25 shows that conditions (A), (B), and (E) tend to have low stabilization energies, while conditions (C) and (D) have high stabilization energies and are unstable. This suggests that Mg and Ni are unlikely to substitute at the Co site. On the other hand, condition (E) has the lowest stabilization energy, suggesting that Ni at the Co site is stabilized by the presence of Mg substituted at the Li site. Furthermore, conditions (A) and (B) have similar stabilization energies, suggesting that their stabilization energies are slightly higher than condition (E).

[0315] [Stabilization energy (ΔE C ) calculation] To estimate the energy change during charging, ΔE C From Figure 25, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The crystal structure of the compound represented by O2 is likely to be under conditions (A), (B), and (E). Therefore, for conditions (B) and (E), ΔE C Figure 26 shows the ΔE C The calculation cost was reduced by using the graph in Fig. 25, which plots the cation occupancy of the Li site.

[0316] As can be seen from Figure 26, under condition (E), as the cation occupancy rate of the Li site decreases, ΔE CIn addition, when the Li site occupancy rate is 100%, which is the state before charging, condition (E) has a larger ΔE than condition (B). C is smaller than that of condition (B) when the Li site occupancy is 98% or less. C It was also found that condition (B) has a minimum when the occupancy of the Li site is 96%. This suggests that condition (B) is more stable when charging begins.

[0317] From this result, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) Immediately after synthesis, the compound represented by O2 has Mg substituted at the Li site and Ni substituted at the Co site, but it is suggested that Ni moves to the Li site upon charging, alleviating instability. In other words, it is suggested that the substitution position of Ni changes before and after charging. In other words, it is suggested that the phenomenon of "Ni moving from the Co site to the Li site upon charging" occurs.

[0318] [Charge / discharge efficiency measurement] To confirm whether the phenomenon of Ni migrating from the Co site to the Li site upon charging actually occurs, we used a compound with the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) A compound represented by O2 was prepared, and the charge-discharge efficiency of a secondary battery using the compound was measured.

[0319] <Chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) Preparation of compounds represented by O2> As the positive electrode active material 100A-1, a compound having the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b)A compound represented by the formula O2 was prepared. As will be described later, Samples 1 to 3 were prepared by varying the amount of nickel hydroxide Ni(OH)2 mixed. Two identical samples were prepared for each sample, and the charge-discharge efficiency of Samples 1 to 3 was measured twice.

[0320] First, a mixture 902 containing magnesium and fluorine was prepared (steps S11 to S14). LiF and MgF2 were weighed out so that the molar ratio was LiF:MgF2 = 1:3, and acetone was added as a solvent, followed by wet mixing and pulverization. The mixing and pulverization were carried out in a ball mill using zirconia balls at 400 rpm for 12 hours. The processed material was recovered and designated mixture 902.

[0321] Next, nickel hydroxide, which is a metal source, was mixed with acetone to prepare finely powdered nickel hydroxide (steps S15 to S17).

[0322] Next, lithium cobalt oxide was prepared as a composite oxide containing lithium and cobalt. More specifically, Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd. was prepared (step S25).

[0323] Next, in step S31, the atomic weight of magnesium in the mixture 902 was weighed out so that the atomic weight of magnesium in the mixture 902 was 2.0 mol% relative to the atomic weight of cobalt in the lithium cobalt oxide. Mixing was performed by dry mixing. Mixing was performed in a ball mill using zirconia balls at 150 rpm for 1 hour.

[0324] Next, the mixture 903 was placed in an alumina crucible and annealed in a muffle furnace in an oxygen atmosphere at 850°C for 60 hours (step S34). During the annealing, the alumina crucible was covered with a lid. The oxygen flow rate was 10 L / min. The temperature was increased at a rate of 200°C / hr and decreased over 10 hours or more. The material after the heat treatment was recovered and sieved (step S35), and mixture 904 was obtained (step S36).

[0325] Next, nickel hydroxide, which is a metal source, was mixed with acetone to prepare finely powdered nickel hydroxide (steps S15 to S17).

[0326] Next, in step S50, the atomic weight of nickel in nickel hydroxide was weighed out so that it was w mol% relative to the sum of the atomic weights of cobalt and nickel in mixture 903. w differs for each sample and is as shown in Table 2 below. The weighed mixture 903 and nickel hydroxide were mixed together. Mixing was performed by dry mixing. Mixing was performed in a ball mill using zirconia balls at 150 rpm for 1 hour.

[0327] [Table 2]

[0328] Next, the treated material was collected to obtain a mixture 905 (steps S51 and S52).

[0329] Next, the mixture 905 was placed in an alumina crucible and annealed in a muffle furnace in an oxygen atmosphere at 850°C for 60 hours (step S53). During annealing, the alumina crucible was covered with a lid. The oxygen flow rate was 10 L / min. The temperature was increased at 200°C / hr and decreased over 10 hours or more. The material after the heat treatment was recovered and sieved (step S54), and Samples 1 to 3 were obtained (step S55).

[0330] <Battery cell production> Next, each of Samples 1 to 3 obtained above was used as the positive electrode active material to fabricate a positive electrode. The positive electrode active material, AB, and PVDF were mixed in a weight ratio of active material:AB:PVDF=95:3:2, and the slurry was coated onto a current collector. NMP was used as the solvent for the slurry.

[0331] After the slurry was applied to the current collector, the solvent was evaporated. After that, a pressure of 210 kN / m was applied, and then a pressure of 1467 kN / m was applied. A positive electrode was obtained through these steps. The loading amount of the positive electrode was approximately 7 mg / cm. 2 The electrode density was set to 3.8 g / cc.

[0332] Using the prepared positive electrode, a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0333] The counter electrode was made of lithium metal.

[0334] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7. For the secondary batteries used to evaluate the charge / discharge efficiency, 2 wt% vinylene carbonate (VC) was added to the electrolytic solution.

[0335] The separator was made of polypropylene with a thickness of 25 μm.

[0336] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0337] <Charge / discharge efficiency measurement> The initial and second charge-discharge efficiencies of battery cells fabricated using each of the obtained Samples 1 to 3 were measured. The results are shown in Figure 27. The charge-discharge efficiency was measured under the conditions of 25°C, with CCCV charging (0.5C, 4.6V, cut-off current 0.05C) and CC discharging (0.5C, 2.5V), and the charge-discharge rate was 200mA / g. The charge-discharge efficiency (%) = (discharge capacity / charge capacity) × 100.

[0338] Figure 27 shows that the initial charge-discharge efficiency for Samples 1 to 3 was less than 100%. This result suggests that Ni, which had previously substituted for the Co layer before charging, migrated to other sites during charging. Analysis of this data in conjunction with the calculation results suggests that the phenomenon of Ni migrating from the Co site to the Li site during charging is occurring. Furthermore, the initial charge-discharge efficiency tended to decrease as the amount of Ni(OH)2 added increased. Because the discharge capacity is thought to decrease due to Ni migrating to the Li site, samples with higher Ni concentrations are expected to show a greater decrease in charge-discharge efficiency (difference from 100%). This tendency is therefore thought to reflect the above-mentioned phenomenon. Furthermore, the second charge-discharge efficiency for Samples 1 to 3 was approximately 100%. This suggests that this phenomenon is irreversible and occurs only during the initial charge.

[0339] From the above calculation results and measurement results, in Figure 25 alone, the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) The compound represented by O2 has the most stable structure in which Mg is substituted at the Li site and Ni is substituted at the Co site, but ΔE C The calculation of ΔE and the measurement results of charge / discharge efficiency suggested that the compound is more stable when Mg and Ni are substituted at the Li site after charging. Therefore, it was suggested that the compound has a structure in which Mg is substituted at the Li site and Ni is substituted at the Co site at the time of synthesis, but when charging is performed, Ni moves to the Li site and the structure changes. In addition to calculating ΔE C By calculating ΔE and measuring the charge / discharge efficiency, as described above, it is possible to analyze the structure of the lithium composite oxide more accurately by performing not only calculations but also actual measurements, and therefore analysis can be performed from both calculation and experiment. In addition, by calculating ΔE, it is possible to efficiently C It was found that the calculation of the above equation can reduce the calculation cost. Furthermore, since the validity of the phenomenon occurring in the compound can be examined by calculation, the measurement can be performed efficiently. Therefore, the number of samples and the time required for measurement can be reduced. [Explanation of symbols]

[0340] 100: positive electrode active material, 100A-1: positive electrode active material, 100C: positive electrode active material, 200: active material layer, 201: graphene compound, 211a: positive electrode, 211b: negative electrode, 212a: lead, 212b: lead, 214: separator, 215a: joint portion, 215b: joint portion, 217: fixing member, 250: battery, 251: exterior body, 261: folded portion, 262: sealing portion, 263: sealing portion, 271: ridge line, 272: valley line, 273: space, 300: secondary battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode Active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 600: secondary battery, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: P TC element, 612: safety valve mechanism, 613: conductive plate, 614: conductive plate, 615: module, 616: conducting wire, 617: temperature control device, 900: circuit board, 902: mixture, 903: mixture, 904: mixture, 905: mixture, 910: label, 911: terminal, 912: circuit, 913: secondary battery, 914: antenna, 915: antenna, 916: layer, 917: layer, 918: antenna, 919: terminal, 920: display device, 921: sensor, 922: terminal, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 932: positive electrode, 933: separator, 9 50: wound body, 951: terminal, 952: terminal, 980: secondary battery, 981: film, 982: film, 993: wound body, 994: negative electrode, 995: positive electrode, 996: separator, 997: lead electrode, 998: lead electrode, 7100: portable display device, 7101: housing, 7102: display unit, 7103: operation button, 7104: secondary battery, 7200: portable information terminal, 7201: housing, 7202: display unit, 7203: band, 7204: buckle, 7205: operation button, 7206: input / output terminal, 7207: icon, 7300: display device, 7304: display unit,7400: mobile phone, 7401: housing, 7402: display unit, 7403: operation button, 7404: external connection port, 7405: speaker, 7406: microphone, 7407: secondary battery, 7408: lead electrode, 7409: current collector, 8000: display device, 8001: housing, 8002: display unit, 8003: speaker unit, 8004: secondary battery, 8021: Charging device, 8022: cable, 8024: secondary battery, 8100: lighting device, 8101: housing, 8102: light source, 8103: secondary battery, 8104: ceiling, 8105: side wall, 8106: floor, 8107: window, 8200: indoor unit, 8201: housing, 8202: air outlet, 8203: secondary battery, 8204: outdoor unit, 8300: electric refrigerator-freezer, 8301: Housing, 8302: refrigerator compartment door, 8303: freezer compartment door, 8304: secondary battery, 8400: automobile, 8401: headlight, 8406: electric motor, 8500: automobile, 8600: scooter, 8601: side mirror, 8602: secondary battery, 8603: turn signal light, 8604: under-seat storage, 9600: tablet terminal, 9625: switch, 9626: display mode selector switch, 9627: power switch, 9628: operation switch, 9629: fastener, 9630: housing, 9630a: housing, 9630b: housing, 9631: display unit, 9633: solar cell, 9634: charge / discharge control circuit, 9635: power storage unit, 9636: DCDC converter, 9637: converter, 9640: moving part,

Claims

1. LiCoO ２ The compound is a compound with Ni and Mg atoms added as substitution elements of the formula Li （１－ｘ－ｙ） Co （１－ａ－ｂ） Ni （ｘ＋ａ） Mg （ｙ＋ｂ） O ２ In the compound represented by the formula (0<x+a≦0.015 and 0<y+b≦0.06), a first step of calculating first stabilization energies of the compound represented by the chemical formula for substitution positions where Li atoms in the same Li layer are substituted with the Ni atoms and the Mg atoms, substitution positions where Li atoms in a different Li layer are substituted with the Ni atoms and the Mg atoms, substitution positions where Co atoms in the same Co layer are substituted with the Ni atoms and the Mg atoms, substitution positions where Co atoms in a different Co layer are substituted with the Ni atoms and the Mg atoms, substitution positions where Li atoms in the Li layer are substituted with the Mg atoms and Co atoms in the Co layer are substituted with the Ni atoms, and substitution positions where Li atoms in the Li layer are substituted with the Ni atoms and Co atoms in the Co layer are substituted with the Mg atoms; a second step of calculating a second stabilization energy of the compound represented by the chemical formula when the cation occupancy of the Li site is changed for the substitution position having the lowest first stabilization energy and the substitution position having the second lowest first stabilization energy, A method for analyzing a lithium composite oxide, which estimates the structure of the compound after charging.

2. In claim 1, The method for analyzing a lithium composite oxide, wherein the Ni atom and the Mg atom in the first step have a combination of first nearest neighbors to third nearest neighbors.

3. In claim 1 or claim 2, The method for analyzing a lithium composite oxide includes changing the cation occupancy rate in a range of at least 80% to 100% and performing calculations.

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