Positive electrode active material, positive electrode plate, and lithium-ion battery

Abstract

To provide a positive electrode active material, a positive electrode plate, and a lithium-ion battery that improve the output characteristics of a lithium-ion battery. [Solution] Composition formula: Li a Ni b Co c Mn d W x Ag y O2(0.6≦a≦1.4, b+c+d+x+y=1, 0

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material, a positive electrode plate, and a lithium-ion battery. [Background technology]

[0002] Lithium-ion batteries are widely used in electric vehicles, hybrid vehicles, small electronic devices (smartphones, laptops), and energy equipment, among other things.

[0003] In recent years, with the increasing demand for improved performance in electric vehicles (HEV, PHEV, BEV), lithium batteries have been required to have even higher output. Therefore, technologies that can achieve even higher output are needed.

[0004] Patent Document 1 discloses a positive electrode active material used in a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is a lithium-nickel-cobalt-manganese composite oxide, and the lithium-nickel-cobalt-manganese composite oxide contains tungsten and niobium. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-140787 [Overview of the project] [Problems that the invention aims to solve]

[0006] The positive electrode active material described in Patent Document 1 can impart excellent output characteristics to lithium-ion secondary batteries by substituting a portion of NCM (lithium nickel-cobalt-manganate) with W (tungsten) and Nb (niobium). However, the development of technologies that can further increase output is expected.

[0007] An object to be solved by one embodiment of the present disclosure is to provide a positive electrode active material for improving the output characteristics of a lithium-ion battery, a positive electrode plate including the same, and a lithium-ion battery. **Means for Solving the Problems**

[0008] Means for solving the above problems include the following aspects. <1> Composition formula: Li a Ni b Co c Mn d W x Ag y A positive electrode active material represented by O2 (0.6 ≤ a ≤ 1.4, b + c + d + x + y = 1, 0 < x < 0.100, 0 < y < 0.100, 0 < x + y ≤ 0.075, 0.333 ≤ x / y ≤ 2.000). <2> The positive electrode active material according to <1>, wherein 0.025 ≤ x ≤ 0.050 and 0.500 ≤ x / y ≤ 2.0. <3> A positive electrode plate including a positive electrode current collector foil and a positive electrode composite material layer including the positive electrode active material according to <1> or <2>. <4> A lithium-ion battery including the positive electrode plate according to <3>. **Advantages of the Invention**

[0009] According to one embodiment of the present disclosure, there are provided a positive electrode active material for improving the output characteristics of a lithium-ion battery, a positive electrode plate, and a lithium-ion battery. **Brief Description of the Drawings**

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an example of the structure of the positive electrode active material of the present disclosure. **Modes for Carrying Out the Invention**

[0011] Hereinafter, embodiments of the present disclosure will be described.

[0012] In this specification, a numerical range indicated by "~" represents a range that includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In a numerical range described stepwise in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerically described range. In the numerical range described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0013] <Cathode active material> The cathode active material of the present disclosure has a composition formula: Li a Ni b Co c Mn d W x Ag y O2 (0.6 ≤ a ≤ 1.4, b + c + d + x + y = 1, 0 < x < 0.100, 0 < y < 0.100, 0 < x + y ≤ 0.075, 0.333 ≤ x / y ≤ 2.000), which is a cathode active material.

[0014] With the above configuration, the diffusibility of lithium ions in the cathode active material solid phase is improved. Therefore, the output characteristics of the lithium ion battery can be improved.

[0015] FIG. 1 is a schematic diagram showing an example of the structure of the cathode active material of the present disclosure. As shown in FIG. 1, the cathode active material of the present disclosure has a structure in which a part of the Ni (nickel) sites of NCM (lithium nickel cobalt manganese oxide) 523 is substituted with W (tungsten) and Ag (silver). The cathode active material shown in FIG. 1 is co-substituted with 5 mol% of W and 5 mol% of Ag with respect to 100 mol% of the cathode active material, and has a composition formula: Li 0.67 Ni 0.4 Co 0.2 Mn 0.3 W 0.05 Ag 0.05 O2, which is a cathode active material.

[0016] In the positive electrode active material of this disclosure, the molar ratio a of Li is in the range of 0.6 to 1.4, preferably 0.6 to 1.2, more preferably 0.6 to 1.0, and even more preferably 0.6 to 0.8. A molar ratio a of Li in the range of 0.6 to 1.4 tends to stabilize the crystal structure of the positive electrode active material.

[0017] In the positive electrode active material of this disclosure, the sum of the molar ratios of Ni (b), Co (c), Mn (d), W (x), and Ag (y) (b+c+d+x+y) is 1. The molar ratios of Ni (b), Co (c), and Mn (d) are not particularly limited as long as b+c+d+x+y=1. Within the above range, the molar ratio of Ni (b) is preferably 0.3 to 0.8, the molar ratio of Co (c) is preferably 0.1 to 0.5, and the molar ratio of Mn (d) is preferably 0.1 to 0.5.

[0018] In the positive electrode active material of this disclosure, the molar ratio x of W is greater than 0 and less than 0.100. If the molar ratio x of W is 0.100 or higher, the crystal structure of the positive electrode active material becomes unstable, and it may not be possible to obtain a positive electrode active material cosubstituted with W and Ag.

[0019] The molar ratio x of W is preferably 0.025 to 0.050, more preferably 0.025 to 0.040, and even more preferably 0.025 to 0.030. A molar ratio x of W of 0.025 to 0.050 allows the co-substitution effect of W and Ag to be more pronounced, further improving the diffusibility of lithium ions within the positive electrode active material solid phase.

[0020] In the positive electrode active material of this disclosure, the molar ratio y of Ag is greater than 0 and less than 0.100. If the molar ratio y of Ag is 0.100 or higher, the crystal structure of the positive electrode active material becomes unstable, and a positive electrode active material cosubstituted with W and Ag cannot be obtained.

[0021] The molar ratio y of Ag is preferably 0.005 to 0.050, more preferably 0.005 to 0.040, and even more preferably 0.005 to 0.030. A molar ratio y of Ag of 0.005 to 0.050 allows the W and Ag co-substitution effect to be more pronounced, further improving the diffusibility of lithium ions within the positive electrode active material solid phase.

[0022] In the positive electrode active material of this disclosure, the sum of the molar ratios of W and Ag (x+y) is greater than 0 and less than or equal to 0.075. If the sum of the molar ratios of W and Ag (x+y) exceeds 0.075, the crystal structure of the positive electrode active material becomes unstable, and a positive electrode active material cosubstituted with W and Ag cannot be obtained. The range of the sum of the molar ratios (x+y) is preferably 0.030 to 0.075.

[0023] The sum of the molar ratios of W and Ag (x+y) is preferably 0.030 to 0.075, more preferably 0.030 to 0.065, and even more preferably 0.030 to 0.060. A sum of the molar ratios of W and Ag (x+y) of 0.030 to 0.075 allows for improved lithium ion diffusivity within the solid phase of the positive electrode active material while maintaining structural stability, without causing phase separation or structural decomposition of the positive electrode active material.

[0024] In the positive electrode active material of this disclosure, the molar ratio of W to Ag (x / y) is between 0.333 and 2.000. If the molar ratio of W to Ag (x / y) is less than 0.333, the crystal structure of the positive electrode active material becomes unstable, and it is often not possible to obtain a positive electrode active material cosubstituted with W and Ag. When the molar ratio of W to Ag (x / y) exceeds 2.000, the co-substitution effect of W and Ag decreases, and the diffusivity of lithium ions within the solid phase of the positive electrode active material decreases.

[0025] The molar ratio of W to Ag (x / y) is preferably 0.500 to 2.0, more preferably 0.075 to 2.0, and even more preferably 0.1 to 0.2. A molar ratio of W to Ag (x / y) of 0.500 to 2.0 allows the co-substitution effect of W and Ag to be more pronounced, further improving the diffusivity of lithium ions within the positive electrode active material solid phase.

[0026] (Method for manufacturing positive electrode active material) The positive electrode active material of this disclosure can be manufactured by any method, for example, by uniformly mixing oxides or precursor metal salts of each metal constituting the positive electrode active material with a Li salt in a predetermined mixing ratio, and then calcining the mixture in an oxidizing atmosphere. Examples of metal salts include hydroxides, nitrates, sulfates, carbonates, etc. The metal salt may also be a composite metal salt prepared in advance by coprecipitation or the like. Examples of Li salts include lithium hydroxide (anhydrous or monohydrate), lithium carbonate, lithium nitrate, lithium oxide, etc.

[0027] Firing is usually carried out in an oxidizing atmosphere (for example, in air). The firing temperature is typically 600°C to 1200°C, preferably 700°C to 1100°C, more preferably 800°C to 1000°C, and even more preferably 850°C to 950°C. If the firing temperature is too low, unreacted raw materials may remain in the positive electrode active material, and a positive electrode active material with the desired composition ratio may not be obtained. If the firing temperature is too high, by-products are more likely to be generated, and a positive electrode active material with the desired composition ratio may not be obtained.

[0028] The firing time is usually 10 to 30 hours, preferably 10 to 25 hours, more preferably 15 to 25 hours, and even more preferably 15 to 20 hours. When the firing time is 10 to 30 hours, the interparticle diffusion reaction of the mixture proceeds sufficiently, resulting in excellent productivity.

[0029] The firing process may be carried out multiple times at the same or different firing temperatures and for the same or different firing times. After firing, it is preferable to crush and classify the fired material to adjust the particle size.

[0030] The positive electrode active material of this disclosure can be manufactured as follows:

[0031] First, an aqueous solution of NiSO4, CoSO4, and MnSO4 dissolved in a predetermined composition ratio is added dropwise to pure water while stirring. Next, the temperature of the aqueous solution is raised to 70°C while stirring to obtain a precipitate (complex metal salt). This aqueous solution is filtered to remove the precipitate, and it is heat-treated in an oxygen atmosphere at 300°C to obtain a Ni-Co-Mn complex oxide. Next, the obtained Ni-Co-Mn composite oxide is mixed with LiOH, WO3, and AgNO3 and then calcined. The firing conditions are 900°C for 20 hours under an oxygen atmosphere. This yields W / Ag cosubstituted NCM (lithium nickel cobalt manganese oxide), which is the positive electrode active material of this disclosure. In W / Ag co-substituted NCM, the amounts of W and Ag can be adjusted by matching the amount of WO3 and AgNO3 mixed in this calcination process to the desired composition ratio.

[0032] (Diffusion coefficient of lithium ions in positive electrode active material) The positive electrode active material of this disclosure has a lithium ion diffusion coefficient of 2.58 cm² at room temperature (300 K). 2 ·s -1 ~4.00cm 2 ·s -1 Preferably, it is 2.78 cm 2 ·s -1 ~3.80cm 2 ·s -1 It is more preferable that it be 2.98 cm 2 ·s -1 ~3.60cm 2 ·s -1 It is even more preferable that the diffusion coefficient of lithium ions at room temperature (300K) is 2.58 cm². 2 ·s -1 ~4.00cm 2 ·s -1 This allows it to become a lithium-ion battery with high output characteristics.

[0033] The diffusion coefficient of lithium ions in the positive electrode active material is obtained by molecular dynamics (MD) calculation. The force field used in the molecular dynamics calculation can be a classical force field, a first-principles density functional theory (DFT), or a machine learning force field obtained by machine learning the results of DFT calculations. While DFT is preferable because it predicts the lithium ion diffusion coefficient with higher accuracy than classical force fields, it is computationally intensive. Therefore, a machine learning force field obtained by machine learning the results of DFT calculations can be used as a force field that offers similar computational accuracy to DFT while reducing computation time. In this embodiment, the data also uses a machine learning force field obtained by machine learning the results of DFT calculations. Here, the machine learning force field is a graph neural network (GNN) force field, and the GNN is M3GNet. The accuracy of M3GNet has been confirmed by Chi Chen (Chi Chen et al. Nat. Compt. Sci. 2 (2022) 718-728) as being among the most accurate GNN force fields.

[0034] The diffusion coefficient of lithium ions in the positive electrode active material can be determined specifically as follows using molecular dynamics calculations (MD method) with a GNN force field.

[0035] First, we calculate the stable atomic configuration for 1280 atoms (number of atoms per compositional formula of NCM523 (=4) × 320 cells) of NCM523, which has a crystal structure belonging to the space group R-3m, using first-principles density functional theory (DFT). The calculation conditions are as follows. Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions

[0036] Next, the stable atomic arrangement of a structure in which some lithium ions of the structurally optimized NCM523 are missing will be calculated using first-principles density functional theory (DFT). The calculation conditions will be as follows. Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions

[0037] Next, some of the nickel sites in the NCM523 model, which have a partial lithium ion deficiency, are replaced with W atoms and Ag atoms, and the stable atomic arrangement of the structure is calculated using first-principles density functional theory (DFT). The calculation conditions are as follows: Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions

[0038] Next, we evaluate the stability of the crystal structure of the NCM model with elemental substitution. The evaluation involves inputting the model data into crystal structure plotting software, obtaining the XRD diffraction pattern of the structural model using the implementation function, and if diffraction peaks not present in the NCM523 crystal structure are observed (for example, diffraction peaks with a relative intensity of 5 or less in the low-angle region of 2θ = 10° ± 0.5° or less), the structure is evaluated as unstable.

[0039] Next, for the models evaluated as structurally stable, the diffusion coefficient of lithium ions is determined. Specifically, the mean square displacement is calculated from the change in lithium ions in the crystal structure over time. <r 2 Calculate (t)> (using equation (1) below), and from the slope of the mean squared displacement with respect to time, the diffusion coefficient D of lithium ions is obtained. Li Calculate (using formula (2) below).

[0040]

number

[0041] During the ceremony, <r 2 (t)> is the mean squared displacement at time t, N is the number of lithium ions, t is the elapsed time (seconds), t0 is the initial time (seconds), r i (t) represents the position coordinates of lithium ion i at time t, and <> represents the average over time t.

[0042]

number

[0043] In the formula, D Li The diffusion coefficient of lithium ions, <r 2 (t)> represents the mean squared displacement at time t.

[0044] The diffusion coefficient of lithium ions can be calculated, for example, under the temperature conditions of 700K, 800K, 900K, 1,000K, 1,100K, 1,200K, 1,300K, and 1,400K. The calculation conditions are as follows: ·Force field: GNN force field • Ensemble: NVT (constant particle number, lattice volume, temperature) • Time step: 2fs • Number of steps: 100,000 steps ·Calculation time: 200ps

[0045] Next, plot the lithium ion diffusion coefficients at each temperature, with the vertical axis representing the lithium ion diffusion coefficient at each temperature (logD) and the horizontal axis representing the reciprocal of the temperature (1 / T) (Aleunius plot). By extrapolating this plot to 300K (room temperature), the lithium ion diffusion coefficient at 300K (room temperature) can be obtained.

[0046] As described above, the diffusion coefficient of lithium ions in the positive electrode active material at 300K (room temperature) can be calculated.

[0047] <Positive plate> The positive electrode plate of this disclosure comprises a positive electrode current collector foil and a positive electrode composite layer containing the positive electrode active material of this disclosure.

[0048] -Positive current collector foil- The positive electrode current collector foil may be made of aluminum, aluminum alloy, stainless steel, or the like. The thickness of the positive electrode current collector foil may be, for example, 5 μm to 30 μm.

[0049] -Positive electrode composite layer- The positive electrode composite layer may include the positive electrode active material of this disclosure, as well as a conductive additive and a binder. The content of the positive electrode active material may be, for example, 85% to 95% by mass relative to the total mass of the positive electrode composite layer.

[0050] Examples of conductive additives include acetylene black, Ketjenblack, vapor-processed carbon fiber (VGCF®), and carbon nanotubes (CNTs). The content of the conductive additive may be 0.5% to 1.0% by mass relative to the total mass of the positive electrode composite layer.

[0051] Examples of binders include polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride (modified PVDF), and polytetrafluoroethylene (PTFE). Among these, polyvinylidene fluoride (PVDF) is preferred from the viewpoint of excellent binding properties and chemical stability. A single binder may be used, or two or more may be used in combination. The binder content may be 2.5% to 7.5% by mass relative to the total mass of the first cathode composite layer.

[0052] The thickness of the positive electrode composite layer is, for example, 25 μm to 35 μm.

[0053] <Lithium-ion battery> The lithium-ion battery of this disclosure includes the positive electrode plate. In addition to the positive electrode plate, the lithium-ion battery of this disclosure may also include a negative electrode plate.

[0054] (Negative electrode plate) The negative electrode plate may comprise a negative electrode current collector foil and a negative electrode composite layer formed on the negative electrode current collector foil. Copper foil is preferred as the negative electrode current collector foil. The negative electrode composite layer may contain a negative electrode active material and a binder.

[0055] The negative electrode active material may be a carbon-based active material such as graphite; or lithium titanate (e.g., Li4Ti5O 12 Oxide-based active materials such as ) and Si-based active materials such as elemental Si, SiO, SiC, and Si alloys can be used. Volume average particle size D of the negative electrode active material 50 The particle size may be between 0.1 μm and 100 μm. The content of the negative electrode active material may be between 92.5% by mass and 99.5% by mass relative to the total mass of the negative electrode composite layer.

[0056] In addition to polyvinylidene fluoride (PVDF), other binders such as styrene-butadiene rubber (SBR), polyacrylic acid, and polyimide can be used. The binder content may be 0.5% to 2.0% by mass relative to the total mass of the negative electrode composite layer. The binder may also contain carboxymethylcellulose (CMC) as a thickening agent.

[0057] (Method of manufacturing lithium ions) The lithium-ion battery of this disclosure can be manufactured by stacking a positive electrode plate and a negative electrode plate with a separator in between.

[0058] The positive electrode plate or negative electrode plate is obtained by applying a positive electrode composite slurry or a negative electrode composite slurry onto the positive electrode current collector foil or a negative electrode current collector foil, drying it, and pressing it to form a positive electrode composite layer or a negative electrode composite layer.

[0059] A positive electrode mixture slurry or a negative electrode mixture slurry is obtained by adding a solvent to a mixture of positive electrode active material or negative electrode active material and a binder in a predetermined mixing ratio (composition ratio) (in the case of a positive electrode mixture, a conductive additive is also added) and kneading the mixture.

[0060] As solvents, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), etc., can be used.

[0061] Mixing can be carried out by appropriately selecting from among mixing methods such as planetary mixers, sand mills, ball mills, gyroscopic mills, roll mills, extruders, and dispersers.

[0062] The slurry can be applied using die coating, doctor blade coating, gravure coating, etc.

[0063] Drying can be carried out by natural drying, reduced-pressure drying, or heat drying. If the slurry contains NMP, heat drying at 80°C to 135°C is acceptable.

[0064] Pressing can be done using a roll press, a flat plate press, etc. A roll press may be used, with a pressure of 0.01 t / cm to 1.0 t / cm and a temperature of 80°C to 135°C.

[0065] Lamination may be performed manually or using a lamination device. As a separator, porous resin sheets such as polyethylene or polypropylene can be used.

[0066] The lithium-ion battery of this disclosure may include a non-aqueous electrolyte, the non-aqueous electrolyte comprising an electrolyte and a non-aqueous solvent.

[0067] Examples of electrolytes include LiPF6, LiBF4, LiAsF6, LiSbF6, Li(CF3SO2)2N, Li(C2F5SO2)2N, LiTaF6, LiClO4, and LiCF3SO3. Electrolytes may be used individually or in combination of two or more.

[0068] Examples of non-aqueous solvents include cyclic carbonate solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC); linear carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); ether solvents such as 1,2-dimethoxyethane, tetrahydrofuran, and dioxolane; γ-butyrolactone; acetonitrile; and others. Non-aqueous solvents may be used individually or in mixtures of two or more. When using both a cyclic carbonate solvent and a linear carbonate solvent, the mixing ratio of the cyclic carbonate solvent to the linear carbonate solvent may be, for example, 1:9 to 5:5 by volume.

[0069] The concentration of the solid electrolyte in the non-aqueous solvent may be between 1.0 mol / L and 1.2 mol / L.

[0070] The lithium-ion battery of this disclosure can be in various shapes, such as cylindrical, stacked, or coin-shaped. An electrode group, in which a positive electrode plate and a negative electrode plate are stacked with a separator in between, is completed as a lithium-ion battery by converging the positive electrode current collector foil and the negative electrode current collector foil at their ends, connecting them to the positive electrode terminal and the negative electrode terminal via leads, and sealing them together with a non-aqueous electrolyte in an outer case. [Examples]

[0071] The embodiments of this disclosure will be specifically described below with reference to examples. The embodiments of this disclosure are not limited to the following examples.

[0072] <Example 1> The diffusion coefficient of lithium ions in the positive electrode active material was determined by following the steps (1) to (7) below. (1) First, a structurally stable NCM523 structural model (M1) was constructed using first-principles density functional theory (DFT) calculations. The calculation conditions were as follows: • 1280 atoms (number of atoms per NCM523 chemical formula (=4) × 320 cells) Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions (2) Next, using M1, an NCM523 structural model (M2) without elemental substitution was constructed in which 33 mol% lithium ions were missing from 100 mol% of the positive electrode active material. The lithium ions to be missing were selected randomly. The calculation conditions were as follows. Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions (3) Next, using M2, the Ni sites were substituted with W and Ag atoms to construct an NCM structural model (M3) with elemental substitution. The number of substitutions was adjusted to match the empirical formula shown in Table 1. The calculation conditions were as follows: Software: VASP • Pseudopotential: Plane wave basis (PAW) method • k-points: 1x1x1 mesh • Exchange-correlation functional: GGA-PBE + U method • Use periodic boundary conditions (4) Next, the information from M1 to M3 was input into the crystal structure plotting software VESTA, and the XRD diffraction pattern of each structural model was obtained using the software's implementation function to evaluate the structural stability of NCM with elemental substitution. If diffraction peaks not present in the crystal structure of NCM523 were observed in the XRD diffraction pattern (determined by whether or not diffraction peaks with a diffraction intensity of 5 or less exist in the low-angle region of 2θ = 10° ± 0.5° or less), the structure was evaluated as structurally unstable and NCM with elemental substitution could not exist (indicated as "×" in Table 1), and the subsequent steps were not performed. If no diffraction peaks not present in the crystal structure of NCM523 were observed in the XRD diffraction pattern, the structure was evaluated as stable (indicated as "○" in Table 1). (5) Molecular dynamics calculations using the GNN force field were performed using M3. The calculation conditions were as follows: ·Force field: M3GNET • Calculation temperatures: 8 points: 700K, 800K, 900K, 1,000K, 1,100K, 1,200K, 1,300K, and 1,400K • Ensemble: NVT (constant particle number, lattice volume, temperature) • Time step: 2fs • Number of steps: 100,000 steps ·Calculation time: 200ps (6) The mean square displacement was calculated from the change in the distance traveled by lithium ions over time (Equation (1)), and the diffusion coefficient of lithium ions at each calculation temperature was determined (Equation (2)).

[0073]

number

[0074]

number

[0075] In formula (1), <r 2 (t)> is the mean squared displacement at time t, N is the number of lithium ions, t is the elapsed time (seconds), t0 is the initial time (seconds), r i(t) is the position coordinate of lithium ion i at time t, and <> represents the average with respect to time t. In equation (2), D Li The diffusion coefficient of lithium ions, <r 2 (t)> represents the mean squared displacement at time t.

[0076] (7) Arrhenius plots were created from the lithium ion diffusion coefficient values ​​at each calculation temperature, and the lithium ion diffusion coefficient at 300K (room temperature) was calculated by extrapolating the Arrhenius plots to 300K. The results are shown in Table 1.

[0077] <Examples 2-6 and Comparative Examples 1-20> A model was created in the same manner as in Example 1, except for the composition shown in Table 1. For structurally stable models, the diffusion coefficient of lithium ions in the positive electrode active material at 300 K (room temperature) was determined. The results are shown in Table 1. Comparative Example 1 shows the diffusion coefficient of lithium ions in the structural model M2 described above.

[0078] [Table 1]

[0079] The results in Table 1 show that the W / Ag cosubstituted cathode active materials of Examples 1-6 are structurally stable and exhibit superior lithium ion diffusion in the solid phase compared to the W-only substituted and Ag-only substituted materials of Comparative Examples 1-9. In particular, cathode active materials with a W content of 0.025 ≤ x ≤ 0.050 in molar ratio and a W content relative to Ag of 0.500 ≤ x / y ≤ 2.0 tended to exhibit even better lithium ion diffusion (Examples 3-6). The lithium ion diffusivity of the W / Ag cosubstituted cathode active material in Example 4 is higher than that of the W-only substituted product in Comparative Example 4 and the Ag-only substituted product in Comparative Example 8, confirming the synergistic effect of cosubstituted material.

[0080] <Reference example 1> An aqueous solution of NiSO4, CoSO4, and MnSO4 in a composition ratio of 5:2:3 is added dropwise to pure water while stirring. Next, the aqueous solution is heated to 70°C while stirring to obtain a precipitate. This aqueous solution is filtered to remove the precipitate, and then heat-treated in an oxygen atmosphere at 300°C to obtain a Ni-Co-Mn composite oxide. Next, the obtained Ni-Co-Mn composite oxide is mixed with LiOH, WO3, and AgNO3 in a composition ratio of 1.0:1.15:0.003:0.006 and then calcined. The firing conditions are 900°C for 20 hours under an oxygen atmosphere. This yields the positive electrode active material of Example 1.

[0081] <Reference example 2> The positive electrode active material of Example 2 can be obtained in the same manner as in Reference Example 1, except that the Ni-Co-Mn composite oxide, LiOH, WO3, and AgNO3 are mixed in a composition ratio of 1.0:1.15:0.003:0.009 and then calcined.

[0082] <Reference example 3> The positive electrode active material of Example 3 can be obtained in the same manner as in Reference Example 1, except that Ni-Co-Mn composite oxide, LiOH, WO3, and AgNO3 are mixed in a composition ratio of 1.0:1.15:0.025:0.013 and then calcined.

[0083] <Reference example 4> The positive electrode active material of Example 4 can be obtained in the same manner as in Reference Example 1, except that the Ni-Co-Mn composite oxide, LiOH, WO3, and AgNO3 are mixed in a composition ratio of 1.0:1.15:0.025:0.025 and then calcined.

[0084] <Reference example 5> The positive electrode active material of Example 5 can be obtained in the same manner as in Reference Example 1, except that the Ni-Co-Mn composite oxide, LiOH, WO3, and AgNO3 are mixed in a composition ratio of 1.0:1.15:0.025:0.050 and then calcined.

[0085] <Reference example 6> The positive electrode active material of Example 6 can be obtained in the same manner as in Reference Example 1, except that the Ni-Co-Mn composite oxide, LiOH, WO3, and AgNO3 are mixed in a composition ratio of 1.0:1.15:0.050:0.025 and then calcined.

Claims

1. Composition formula: Li ａ Ni ｂ Co ｃ Mn ｄ W ｘ Ag ｙ O ２ The positive electrode active material is represented by (0.6 ≤ a ≤ 1.4, b + c + d + x + y = 1, 0 < x < 0.100, 0 < y < 0.100, 0 < x + y ≤ 0.075, 0.333 ≤ x / y ≤ 2.000).

2. The positive electrode active material according to claim 1, wherein 0.025 ≤ x ≤ 0.050 and 0.500 ≤ x / y ≤ 2.

0.

3. Positive electrode current collector foil, A positive electrode composite layer comprising the positive electrode active material described in claim 1 or claim 2, A positive electrode plate equipped with the following features.

4. A lithium-ion battery comprising the positive electrode plate described in claim 3.

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