Positive electrode active material for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary battery

Abstract

A positive electrode active material for nonaqueous electrolyte secondary batteries according to the present disclosure contains a first positive electrode active material 10. The first positive electrode active material 10 includes: a first lithium transition metal composite oxide 11 in which the total content of Ni and Mn is 80 mol% or more with respect to the total molar amount of metal elements excluding Li and which has a single particle shape; and a coating layer 12 which coats at least a portion of the surface of the first lithium transition metal composite oxide 11. The first lithium transition metal composite oxide 11 has a volume-based median diameter of 0.5-5.0 μm and a crystallite size of 370-1,500 Å. The coating layer 12 contains an organic ferroelectric that has a spontaneous polarization which exceeds 15 μC / cm2.

Description

Positive electrode active material for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries

[0001] This disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

[0002] As a lithium-ion secondary battery with excellent output characteristics, Patent Document 1 discloses a lithium-ion secondary battery comprising an electrode composite layer containing an electrode active material and an organic ferroelectric material having a relative permittivity of 25 or more. In this lithium-ion secondary battery, the electrode composite layer is formed by adding an organic ferroelectric material to an electrode composite paste used to produce the electrode composite layer.

[0003] Patent No. 6187506

[0004] Conventional cathodes, particularly those using cathode active materials containing lithium transition metal composite oxides with single-particle shapes, have suffered from a decrease in charge / discharge capacity at high current values.

[0005] This disclosure provides a technology that can suppress the decrease in charge / discharge capacity at high current values ​​in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape.

[0006] The positive electrode active material for a non-aqueous electrolyte secondary battery of the present disclosure comprises a first positive electrode active material, the first positive electrode active material comprising a first lithium transition metal composite oxide having a single-particle shape and a total content of Ni and Mn of 80 mol% or more relative to the total molar amount of metal elements excluding Li, and a coating layer covering at least a portion of the surface of the first lithium transition metal composite oxide, the first lithium transition metal composite oxide having a volume-based median diameter of 0.5 μm or more and 5.0 μm or less, and a crystallite size of 370 Å or more and 1500 Å or less, and the coating layer having a spontaneous polarization of 15 μC / cm 2 Includes organic ferroelectrics exceeding [a certain level].

[0007] According to the technology disclosed herein, it is possible to suppress the decrease in charge / discharge capacity at high current values ​​in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape.

[0008] Figure 1 is a cross-sectional view showing the schematic configuration of the first positive electrode active material included in the positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1. Figure 2 is a schematic diagram illustrating an example of a single particle. Figure 3 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte secondary battery in Embodiment 2.

[0009] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0010] (Embodiment 1) The positive electrode active material for the non-aqueous electrolyte secondary battery in Embodiment 1 includes a first positive electrode active material.

[0011] Figure 1 is a cross-sectional view showing the schematic configuration of the first positive electrode active material included in the positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1. The first positive electrode active material 10 includes a first lithium transition metal composite oxide 11 having a single-particle shape and a total content of Ni and Mn of 80 mol% or more relative to the total molar amount of metal elements excluding Li, and a coating layer 12 that covers at least a part of the surface of the first lithium transition metal composite oxide 11. The first lithium transition metal composite oxide 11 has a volume-based median diameter (D50) of 0.5 μm or more and 5.0 μm or less, and a crystallite size of 370 Å or more and 1500 Å or less. The coating layer 12 has a spontaneous polarization of 15 μC / cm 2 Includes organic ferroelectrics exceeding [a certain level].

[0012] In this specification, a single particle refers to a particle formed from a single primary particle, not a secondary particle formed by the aggregation of many (e.g., 1000 or more) primary particles. In other words, there are substantially no particle interfaces of primary particles within the particle. Note that particles formed by the aggregation of 10 or fewer primary particles approximate a single particle shape and can be considered substantially as single particles. A single particle may be a single-crystal particle with substantially no grain boundaries within its interior, or a polycrystalline particle with several grain boundaries within its interior. Figure 2 is a schematic diagram illustrating an example of a single particle. Figure 2 shows a single-crystal particle 11A with substantially no grain boundaries within its interior and a polycrystalline particle 11B with several grain boundaries within its interior. Crystal planes can be distinguished, for example, by the difference in contrast observed when the particle cross-section is viewed at 3000x magnification using a scanning ion microscope (SIM).

[0013] When a lithium transition metal composite oxide having a combined content of Ni and Mn of 80 mol% or more relative to the total molar amount of metal elements excluding Li is used as a positive electrode active material, effects such as improved battery cycle characteristics and durability can be obtained. However, when the above lithium transition metal composite oxide having a single-particle shape is used as a positive electrode active material, the ion diffusion distance tends to be relatively long, which tends to degrade the rate characteristics. In other words, when the above lithium transition metal composite oxide having a single-particle shape is used as a positive electrode active material, the charge and discharge capacity of the battery at high current values ​​tends to decrease. The first positive electrode active material 10 contained in the positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1 has a combined content of Ni and Mn of 80 mol% or more relative to the total molar amount of metal elements excluding Li, and at least a part of the surface of the first lithium transition metal composite oxide 11 having a single-particle shape has a spontaneous polarization of 15 μC / cm². 2The coating layer 12 contains an organic ferroelectric material exceeding 15 μC / cm². This coating layer 12 effectively assists ion diffusion at the interface of the first positive electrode active material 10, thereby suppressing the decrease in the battery's charge / discharge capacity at high current values. The effect of the ferroelectric material in suppressing the decrease in charge / discharge capacity at high current values ​​is achieved when the spontaneous polarization is 15 μC / cm². 2 This can be specifically obtained by having an organic ferroelectric material exceeding a certain value present so as to coat at least a portion of the surface of the first lithium transition metal composite oxide 11. The spontaneous polarization of the organic ferroelectric material contained in the coating layer 12 is, for example, 25 μC / cm². 2 The following is also acceptable.

[0014] As described above, the D50 of the first lithium transition metal composite oxide 11 is between 0.5 μm and 5.0 μm. In this case, the spontaneous polarization is 15 μC / cm². 2 The above effects can be obtained by the coating layer 12 containing an organic ferroelectric material exceeding the specified range. On the other hand, if the coating layer 12 is provided to a single particle where D50 falls outside the range, or to a secondary particle formed by the aggregation of many primary particles, the above effects of the coating layer 12 are small or substantially ineffective. The D50 of the first lithium transition metal composite oxide 11 is preferably 0.7 μm to 3.5 μm, more preferably 0.8 μm to 3.0 μm. Since the coating layer 12 present on the particle surface does not substantially affect the D50 of the first positive electrode active material 10, the D50 of the first positive electrode active material 10 and the D50 of the first lithium transition metal composite oxide 11 are substantially the same.

[0015] In this specification, D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. The particle size distribution of the first lithium transition metal composite oxide 11 can be measured using a laser diffraction particle size distribution analyzer (for example, the MT3000II manufactured by Microtrac-Bell Corporation) with water as the dispersion medium.

[0016] The crystallite size of the first lithium transition metal composite oxide 11 is 370 Å or more and 1500 Å or less, preferably 370 Å or more and 1000 Å or less, more preferably 370 Å or more and 750 Å or less. If the crystallite size is within this range, the above-described effect of the coating layer 12 can be obtained. Since the coating layer 12 present on the particle surface does not substantially affect the crystallite size of the first positive electrode active material 10, the crystallite sizes of the first positive electrode active material 10 and the first lithium transition metal composite oxide 11 are substantially the same. The crystallite size is calculated by the Scherrer's equation represented by the following formula from the half-value width of the diffraction peak of the (104) plane in the X-ray diffraction pattern obtained by X-ray diffraction. In the following formula, s is the crystallite size, λ is the wavelength of the X-ray, B is the half-value width of the diffraction peak of the (104) plane, θ is the diffraction angle (rad), and K is the Scherrer constant. In this specification, K is set to 0.9. s = Kλ / Bcosθ

[0017] The X-ray diffraction pattern is obtained by the powder X-ray diffraction method under the following conditions using a powder X-ray diffractometer (RINT-TTR manufactured by Rigaku Corporation, X-ray source Cu-Kα). Measurement range: 15 - 120° Scan speed: 4° / min Analysis range: 30 - 120° Background: B-Spline Profile function: Split-type pseudo-Voigt function Binding condition: Li(3a) + Ni(3a) = 1 Ni(3a) + Ni(3b) = α (α is the Ni content ratio of each) ICSD No.: 98 - 009 - 4814

[0018] The BET specific surface area of the first lithium transition metal composite oxide 11 is, for example, 0.5 m 2 / g or more and 4 m 2 / g or less, and more preferably 0.9 m 2 / g or more and 3 m 2 / g or less. Since the secondary particles containing a large number of primary particles have voids inside the particles, the specific surface area is relatively large even if the particle size is large. On the other hand, since the single particles have no voids inside the particles, the BET specific surface area becomes smaller as the particle size increases. Since the coating layer 12 present on the particle surface does not substantially affect the BET specific surface area of the first positive electrode active material 10, the BET specific surface areas of the first positive electrode active material 10 and the first lithium transition metal composite oxide 11 are substantially the same.

[0019] The BET specific surface area can be measured using a Tristar II 3020 manufactured by Shimadzu Corporation under the following conditions: Number of measurement points: 11 points (P / P0: 0.05 to 0.3) Warm Free Space: Measured Equilibration Interval: 5s Analysis Adsorbent: N2 Analysis Bath Temp: 77.3K (liquid nitrogen temperature) Cold Free Space: Measured Low Pressure Done: None Analysis method: BET multi-point method

[0020] The first lithium transition metal composite oxide preferably has a layered rock salt structure. When the coating layer 12 is applied to a composite oxide with a layered rock salt structure, the above-mentioned effects of the coating layer 12 become more pronounced. Examples of layered rock salt structures include a layered rock salt structure belonging to space group R-3m and a layered rock salt structure belonging to space group C2 / m. Among these, a layered rock salt structure belonging to space group R-3m is preferred from the viewpoint of increasing capacity and crystalline structure stability.

[0021] The first lithium transition metal composite oxide 11 contains Ni and Mn as essential metal elements. The total content of Ni and Mn is 80 mol% or more, preferably 90 mol% or more, relative to the total molar amount of metal elements excluding Li. If the ratio of Ni and Mn to the metal elements excluding Li is 80 mol% or more, the above effects of the coating layer 12 can be obtained, and a high-capacity first positive electrode active material 10 can be obtained relatively inexpensively. When the first lithium transition metal composite oxide 11 contains Ni, Mn, and Co, their total content is preferably 90 mol% or more, or 95 mol% or more, relative to the total molar amount of metal elements excluding Li. The first lithium transition metal composite oxide 11 may contain substantially only Ni and Mn as transition metal elements.

[0022] Ni is preferably present in the largest amount among the metal elements other than Li that constitute the first lithium transition metal composite oxide 11. From the viewpoint of increasing capacity, the Ni content in the first lithium transition metal composite oxide 11 is preferably 50 mol% or more, more preferably 65 mol% or more, and particularly preferably 70 mol% or more or 75 mol% or more, relative to the total molar amount of the metal elements excluding Li. From the viewpoint of improving durability and suppressing resistance increase, the upper limit of the Ni content is preferably 90 mol% and more preferably 85 mol% or 80 mol%, relative to the total molar amount of the metal elements excluding Li. Examples of a suitable range for the Ni content are 60 mol% to 90 mol%, or 70 mol% to 90 mol%, or 70 mol% to 85 mol%, or 75 mol% to 85 mol%.

[0023] Mn is preferably the second most abundant element, after Ni, among the metal elements other than Li that constitute the first lithium transition metal composite oxide 11. Mn stabilizes the crystal structure of the first lithium transition metal composite oxide 11. The Mn content in the first lithium transition metal composite oxide 11 is, for example, 5 mol% to 50 mol%, or 10 mol% to 35 mol%, or 15 mol% to 30 mol%, relative to the total molar amount of the metal elements excluding Li. The first lithium transition metal composite oxide 11 may also contain Co in a smaller proportion than Ni. The Co content is preferably less than or equal to the Mn content, for example, 15 mol% or less, or 10 mol% or less, or 5 mol% or less, or 3 mol% or less.

[0024] The first lithium transition metal composite oxide 11 may further contain small amounts of elements other than Ni, Mn, and Co. Suitable other elements include at least one selected from the group consisting of Mg, Al, Ca, Nb, Sr, Zr, W, S, and P. These elements may be contained within the particles of the first lithium transition metal composite oxide or present on the particle surface. When these elements are included, for example, side reactions with the electrolyte are suppressed, improving the battery's durability. The first lithium transition metal composite oxide 11 may contain these elements in an amount of 0.01 mol% to 5 mol% relative to the total amount of Ni and Mn. The element content in the first positive electrode active material 10 can be measured using an ICP emission spectrometer (for example, a CIROS-120 manufactured by SPECTRO).

[0025] Many of the single particles of the first lithium transition metal composite oxide 11 are, for example, angular particles. The particle cross-section of each single particle has a polygonal shape including sides with a length of, for example, 1.5 μm or more. At least three interior angles θ of the polygon are, for example, 45° or more and 160° or less. The length of the longest side is, for example, 3 μm or more and 20 μm or less, and may be 3 μm or more and 15 μm or less. All of the interior angles θ of the polygon may be 45° or more and 160° or less, 60° or more and 150° or less, or 70° or more and 130° or less, and there may be three or more interior angles θ of 90° or less.

[0026] The average porosity of a single particle of the first lithium transition metal composite oxide 11 may be 1% or less, or 0.3% or less. Average porosity refers to the average value of the proportion of voids in each single particle and is measured by the method described later. Each single particle is a dense particle with few voids, and the average porosity may be less than 1%.

[0027] The average porosity of single particles of the first lithium transition metal composite oxide 11 is measured by the following method: (1) An ion milling device (e.g., Hitachi High-Tech Corporation, IM4000PLUS) is used to expose a cross-section of the layer containing the first positive electrode active material 10, for example, the positive electrode active material layer in a non-aqueous electrolyte secondary battery. (2) A scanning electron microscope (SEM) is used to capture a backscattered electron image of the exposed cross-section of the positive electrode active material layer. The magnification for capturing the backscattered electron image is 1,000 to 10,000 times. (3) The SEM image of the cross-section of the positive electrode active material layer is imported into a computer and color-coded into two colors based on contrast using image analysis software, with the color with lower contrast representing voids. (4) The void area of ​​100 particles randomly selected from the processed image is determined, and the ratio of the void area to the cross-sectional area of ​​the particles (porosity) is calculated and averaged.

[0028] The organic ferroelectric material contained in the coating layer 12 includes, for example, croconic acid. Croconic acid has a concentration of 21 μC / cm². 2 Because it has spontaneous polarization, it can more effectively assist in the diffusion of ions at the interface of the first positive electrode active material 10. Therefore, the decrease in the battery's charge / discharge capacity at high current values ​​can be more suppressed.

[0029] The coating layer 12 may contain croconic acid and other organic ferroelectrics other than croconic acid, or it may contain only croconic acid as the organic ferroelectric.

[0030] The mass ratio of the organic ferroelectric material to the first lithium transition metal composite oxide 11 is, for example, 0.1% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 3% by mass or less. By including the organic ferroelectric material in such a mass ratio, the diffusion of ions at the interface of the first positive electrode active material 10 can be more effectively assisted. Therefore, the decrease in the battery's charge and discharge capacity at high current values ​​can be more suppressed.

[0031] The mass ratio of the organic ferroelectric to the first lithium transition metal composite oxide 11 can be determined by elemental mapping of a layer containing the first positive electrode active material 10, for example, the cross-section of the positive electrode active material layer in a non-aqueous electrolyte secondary battery. The elemental map can be obtained by energy-dispersive X-ray spectroscopy (STEM-EDX) using a scanning transmission electron microscope in combination.

[0032] The coating layer 12 may contain other components other than the organic ferroelectric, or may be formed only of the organic ferroelectric. For example, the coating layer 12 may be formed by the organic ferroelectric adhering to the surface of the first lithium transition metal composite oxide 11. Thereby, since the organic ferroelectric can more effectively assist the diffusion of ions at the interface of the first positive electrode active material 10, it is possible to further suppress the decrease in the charge-discharge capacity of the battery at a high current value.

[0033] The coating layer 12 may contain, as other components other than the organic ferroelectric, for example, at least one selected from the group consisting of inorganic phosphoric acid and organic phosphoric acid that can form a film with high voltage durability. In this case, the proportion of other components contained in the coating layer 12 is desirably, for example, 1.0 mass% or less.

[0034] The positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1 may further contain a second positive electrode active material in addition to the first positive electrode active material 10. The second positive electrode active material contains secondary particles formed by aggregation of primary particles of a second lithium transition metal composite oxide. By further containing the second positive electrode active material in addition to the first positive electrode active material 10, for example, by changing the mixing ratio of the first positive electrode active material 10 and the second positive electrode active material, the required battery performance can be realized.

[0035] In the second positive electrode active material, a coating layer may not be provided on the surface of the secondary particles, or at least a part of the surface of the secondary particles may be coated with a coating layer.

[0036] The second lithium transition metal composite oxide may have the same composition as the first lithium transition metal composite oxide 11. This allows for efficient production of the positive electrode active material for the non-aqueous electrolyte secondary battery in Embodiment 1, and further reduces manufacturing costs.

[0037] The second lithium transition metal composite oxide may have a different composition from the first lithium transition metal composite oxide 11. This allows for the selection of compositions for the first lithium transition metal composite oxide and the second lithium transition metal composite oxide according to the required battery performance.

[0038] The following describes an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1. In particular, the method for producing the first positive electrode active material 10 will be described. The first positive electrode active material 10 in this embodiment is produced by a step of forming a first lithium transition metal composite oxide having a single-particle shape with a total content of Ni and Mn of 80 mol% or more relative to the total molar amount of metal elements excluding Li, a volume-based median diameter of 0.5 μm or more and 5.0 μm or less, and a crystallite size of 370 Å or more and 1500 Å or less, and a step of forming a coating layer that covers at least a part of the surface of the first lithium transition metal composite oxide. The step of forming the first lithium transition metal composite oxide includes, for example, a synthesis step, a washing step, a drying step, and a crushing step.

[0039] In the synthesis process, a metal hydroxide containing Ni and Mn, where the combined amount of Ni and Mn is 80 mol% or more relative to the total molar amount of metal elements excluding Li, is mixed with a Li compound, and the resulting mixture is calcined to obtain a first lithium transition metal composite oxide. Examples of Li compounds include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH・H2O, LiH, and LiF.

[0040] Metal hydroxides can be obtained, for example, by stirring a solution of a metal salt containing Ni, Mn, and optionally any other metal element, and adding an alkaline solution such as sodium hydroxide dropwise to adjust the pH to the alkaline side (for example, 8.5 to 12.5) to allow precipitation (coprecipitation). Alternatively, metal oxides obtained by heat-treating metal hydroxides may be used instead of metal hydroxides. Since smaller particle sizes of metal hydroxides facilitate the growth of primary particles and the acquisition of single particles, the D50 of the metal hydroxide is preferably 7 μm or less, and more preferably 5 μm or less.

[0041] The metal hydroxide and the Li compound are mixed in a ratio such that, for example, the molar ratio of the metal element excluding Li to Li is 1:0.98 to 1:1.1. When mixing the metal hydroxide and the Li compound, Ca compounds, Sr compounds, W compounds, etc., may be added. Examples of Ca compounds include CaO, Ca(OH)2, and CaCO3. Examples of Sr compounds include SrO, Sr(OH)2, and SrCO3. Examples of W compounds include WO3, Li2WO4, Li4WO5, and Li6W2O9.

[0042] A mixture of metal hydroxide and a Li compound, etc., is calcined, for example, under an oxygen atmosphere (e.g., under a gas flow with an oxygen concentration of 80% or higher). The calcination may be multi-stage. An example of calcination conditions is to set the heating rate in the temperature range of 450°C to 680°C to 1.0°C / min to 5.5°C / min, and the maximum temperature reached to 850°C to 1100°C. The heating rate from 680°C to the maximum temperature may be 0.1°C / min to 3.5°C / min. The holding time at the maximum temperature may be 1 hour to 30 hours. By adjusting the calcination conditions, single particles can be produced and their particle size can be adjusted. For example, increasing the maximum temperature makes it easier to obtain single particles, and their particle size tends to be larger. The calcination may be carried out in air or under an inert gas atmosphere such as nitrogen.

[0043] In the washing step, the first lithium transition metal composite oxide obtained in the synthesis step is washed with water and dehydrated to obtain a cake-like composition. Washing and dehydration can be carried out by known methods and conditions. Ca compounds, Sr compounds, W compounds, etc., may be added to the cake-like composition. In the drying step, the cake-like composition obtained in the washing step is dried to obtain a powder-like composition. The drying step may be carried out under a vacuum atmosphere. For example, the drying temperature is 150°C to 400°C, and the drying time is 0.5 hours to 15 hours. The washing step can be omitted.

[0044] The powdered composition obtained in the drying process is crushed using a pulverizer such as a jet mill. Crushing with a jet mill can be performed, for example, using a PJM-80 (manufactured by Nippon Pneumatic) under the following conditions: Compressed air consumption: 0.5 Nm³ 3 Gas supply pressure per minute: 0.53 MPa; Processing capacity: 2000 g / hour

[0045] A first lithium transition metal composite oxide having a single-particle shape, obtained through a crushing process, is mixed with a coating layer material containing an organic ferroelectric such as croconic acid to form a coating layer containing the organic ferroelectric on at least a portion of the surface of the first lithium transition metal composite oxide having a single-particle shape. A specific method is, for example, to dissolve the organic ferroelectric material in an organic solvent, add the lithium transition metal composite oxide particles, and heat and stir the resulting liquid at a temperature above the boiling point of the solvent.

[0046] The first positive electrode active material 10 can be obtained by the above method.

[0047] (Embodiment 2) The non-aqueous electrolyte secondary battery in Embodiment 2 comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode contains the positive electrode active material for non-aqueous electrolyte secondary batteries in Embodiment 1. By including the positive electrode active material for non-aqueous electrolyte secondary batteries in Embodiment 1, the non-aqueous electrolyte secondary battery in Embodiment 2 can suppress the decrease in charge / discharge capacity at high current values.

[0048] Figure 3 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte secondary battery in Embodiment 2. The secondary battery 100 comprises a container 1, an electrode group 4, and an electrolyte (not shown). The electrolyte is the non-aqueous electrolyte in Embodiment 1. The electrode group 4 has a wound structure. The electrode group 4 is housed in the container 1. The electrode group 4 has a positive electrode 5, a negative electrode 6, and a pair of separators 7. The electrode group 4 is impregnated with the electrolyte. The opening of the container 1 is sealed with a sealing plate 2. The positive electrode 5 has a positive electrode current collector 5a and a positive electrode active material layer 5b. One end of a positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back surface of the sealing plate 2. An insulating packing 3 is arranged around the sealing plate 2. The negative electrode 6 has a negative electrode current collector 6a and a negative electrode active material layer 6b. One end of a negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. Insulating rings 8 are positioned on the upper and lower surfaces of the electrode group 4, respectively.

[0049] The components of the secondary battery 100 will be described in detail below.

[0050] As the positive electrode current collector 5a, a sheet or film made of a metallic material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable materials for the positive electrode current collector 5a because they are inexpensive and easy to make into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material such as carbon may be coated on the surface of the positive electrode current collector 5a as a conductive auxiliary material.

[0051] The positive electrode active material layer 5b includes the positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1. The positive electrode active material layer 5b may further include another positive electrode active material different from the positive electrode active material for a non-aqueous electrolyte secondary battery in Embodiment 1. The other positive electrode active material can be any material having the ability to intercept and release lithium ions, and examples of such materials that can be used include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides.

[0052] The positive electrode active material layer 5b may contain other materials such as conductive additives and binders.

[0053] Conductive additives are used to reduce the resistance of the positive electrode 5. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene.

[0054] A binder is used to improve the binding properties of the materials constituting the positive electrode 5. Possible binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide.

[0055] As the negative electrode current collector 6a, a sheet or film made of a metallic material such as stainless steel, nickel, copper, or alloys thereof may be used. The sheet or film may be porous or non-porous. As the sheet or film, metal foil, metal mesh, etc., may be used. A carbon material such as carbon may be coated on the surface of the negative electrode current collector 6a as a conductive auxiliary material.

[0056] The negative electrode active material layer 6b contains a negative electrode active material. The negative electrode active material may be a material having the ability to intercept and release lithium ions. The negative electrode active material includes, for example, at least one selected from the group consisting of metallic lithium, carbon materials, and materials capable of forming alloys with lithium. Examples of carbon materials include graphite. Examples of materials capable of forming alloys with lithium include silicon, silicon-containing oxides, tin, zinc alloys, bismuth, and germanium. One of these negative electrode active materials may be used, or two or more may be used in combination.

[0057] The negative electrode active material layer 6b may contain at least one selected from the group consisting of graphite and silicon as the negative electrode active material. Alternatively, only graphite may be included in the negative electrode active material layer 6b. Graphite is recommended because it does not degrade easily even when repeatedly charged and discharged at great depths. Other carbon materials may be used as the negative electrode active material. Silicon exhibits a larger capacity than graphite, which is advantageous for increasing the capacity of the secondary battery 100.

[0058] The negative electrode 6 (negative electrode active material layer 6b) may contain metallic lithium as the negative electrode active material.

[0059] The negative electrode active material layer 6b may contain other materials such as conductive additives and binders. Materials that can be used in the positive electrode active material layer 5b can also be used in the negative electrode active material layer 6b as conductive additives and binders.

[0060] The electrolyte, for example, contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolyte may be, for example, 0.5 mol / liter or more and 2 mol / liter or less. By controlling the lithium salt concentration within the above range, an electrolyte with excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0061] Examples of lithium salts that can be used include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One of these electrolyte salts may be used, or two or more may be used in combination.

[0062] The non-aqueous solvent is not particularly limited, and examples include cyclic carbonate esters, linear carbonate esters, and cyclic carboxylic acid esters.

[0063] Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC).

[0064] Examples of linear carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0065] Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0066] The non-aqueous solvent may be used alone or in combination of two or more types. The non-aqueous solvent may also contain ethylene carbonate. This can increase the solubility of electrolytes such as lithium salts in the non-aqueous solvent.

[0067] Typically, it is desirable to interpose a separator between the positive and negative electrodes. The separator 7 has high ion permeability and appropriate mechanical strength and insulating properties. As the separator 7, a microporous thin film, woven fabric, and nonwoven fabric can be used. As the material of the separator 7, for example, a polymer can be used. The polymer may be polyolefin such as polypropylene and polyethylene.

[0068] The electrolyte is impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may also fill the internal space of the container 1. Due to the action of the electrolyte, lithium ions can move between the positive electrode 5 and the negative electrode 6.

[0069] The separator 7 is lithium ion conductive. The material of the separator 7 is not particularly limited as long as the passage of lithium ions is permitted. The material of the separator 7 may be at least one selected from the group consisting of gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 7 is made of these materials, the safety of the secondary battery 100 can be sufficiently ensured. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resin and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric.

[0070] Container 1 is, for example, a metal container such as aluminum or stainless steel. Container 1 may have a cylindrical shape or a rectangular tube shape.

[0071] The electrode group 4 may be wound in a cylindrical shape or in an elliptical shape.

[0072] The shape of the secondary battery 100 is not particularly limited. In this disclosure, as an example of the structure of a non-aqueous electrolyte secondary battery according to Embodiment 2, a configuration example shown in Figure 3 is described, namely a secondary battery in which an electrode group in which a positive electrode and a negative electrode are wound around a separator, and an electrolyte are housed in an outer casing. However, the secondary battery according to this disclosure is not limited to this configuration example. The secondary battery according to this disclosure may take any form, such as cylindrical, prismatic, coin-shaped, button-shaped, laminated, etc. Furthermore, as the electrode group in the secondary battery according to this disclosure, other forms of electrode groups may be used instead of wound electrode groups, such as laminated electrode groups in which a positive electrode and a negative electrode are stacked around a separator.

[0073] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0074] (Technology 1) A first lithium transition metal composite oxide comprising a first positive electrode active material, wherein the combined content of Ni and Mn relative to the total molar amount of metal elements excluding Li is 80 mol% or more, and which has a single-particle shape; and a coating layer covering at least a portion of the surface of the first lithium transition metal composite oxide, wherein the first lithium transition metal composite oxide has a volume-based median diameter of 0.5 μm or more and 5.0 μm or less, and a crystallite size of 370 Å or more and 1500 Å or less, and the coating layer has a spontaneous polarization of 15 μC / cm 2 A positive electrode active material for non-aqueous electrolyte secondary batteries containing an organic ferroelectric material exceeding [a certain value].

[0075] According to Technology 1, in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape, the decrease in charge / discharge capacity at high current values ​​can be suppressed.

[0076] (Technology 2) The organic ferroelectric material is a positive electrode active material for a non-aqueous electrolyte secondary battery according to Technology 1, comprising croconic acid.

[0077] According to Technology 2, in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape, the decrease in charge / discharge capacity at high current values ​​can be further suppressed.

[0078] (Technology 3) The positive electrode active material for a non-aqueous electrolyte secondary battery according to Technology 1 or 2, wherein the mass ratio of the organic ferroelectric material to the first lithium transition metal composite oxide is 0.1% by mass or more and 5% by mass or less.

[0079] According to Technology 3, in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape, the decrease in charge / discharge capacity at high current values ​​can be further suppressed.

[0080] (Technical 4) The organic ferroelectric material is attached to the surface of the first lithium transition metal composite oxide, and is a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Technical 1 to 3.

[0081] According to Technology 4, in a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape, the decrease in charge / discharge capacity at high current values ​​can be further suppressed.

[0082] (Technical 5) The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Technical 1 to 4, wherein the first lithium transition metal composite oxide further comprises at least one selected from the group consisting of Mg, Al, Ca, Nb, Sr, Zr, W, S, and P.

[0083] According to technology 5, battery durability can be improved.

[0084] (Technical 6) The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Technical 1 to 5, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery further comprises a second positive electrode active material, and the second positive electrode active material comprises secondary particles formed by the aggregation of primary particles of a second lithium transition metal composite oxide.

[0085] According to Technology 6, the required battery performance can be achieved.

[0086] (Technical 7) The second lithium transition metal composite oxide has the same composition as the first lithium transition metal composite oxide, wherein it is a positive electrode active material for a non-aqueous electrolyte secondary battery as described in Technical 6.

[0087] According to Technology 7, positive electrode active materials for non-aqueous electrolyte secondary batteries can be manufactured efficiently, and manufacturing costs can be reduced.

[0088] (Technical 8) A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of Technical 1 to 7.

[0089] According to Technology 8, in a battery using a positive electrode active material containing a lithium transition metal composite oxide having a single-particle shape, the decrease in charge / discharge capacity at high current values ​​can be suppressed.

[0090] The present disclosure will be described in more detail below with reference to examples, comparative examples, and reference examples. The following examples are merely illustrative and not limited to any one aspect.

[0091] [Preparation of positive electrode active material and positive electrode slurry for non-aqueous electrolyte secondary batteries] (Example 1) LiNi 0.8 Co0.1 Mn 0.1 A first lithium transition metal composite oxide (NCM) having an O2 composition was prepared. Specifically, LiOH and Ni obtained by coprecipitation. 0.8 Co 0.1 Mn 0.1 A mixture was obtained by mixing (OH)2 powder with Li such that the molar ratio of Li to the total amount of Ni, Mn, and Co was Li:(Mn+Ni+Co) = 1:1.1. This mixture was calcined in two stages under an oxygen stream with an oxygen concentration of 90% or more (flow rate of 0.15 L / min to 0.2 L / min per 1 L of furnace volume). Specifically, the temperature was raised from room temperature to 650°C over 5 hours, and then raised from 650°C to 850°C over 2 hours. After that, it was held at 850°C for 12 hours to obtain the first lithium transition metal composite oxide.

[0092] The obtained first lithium transition metal composite oxide was washed with water to remove excess lithium, and after drying the washed composite oxide, it was crushed using a jet mill. This yielded a first lithium transition metal composite oxide having a single-particle shape.

[0093] Croconic acid was added to the obtained first lithium transition metal composite oxide in a quantity of 1% by mass, and the mixture was mixed with ethanol and then heated to remove the croconic acid. This yielded a first positive electrode active material in which at least a portion of the surface of the first lithium transition metal composite oxide, which has a single-particle shape, was coated with a coating layer consisting of croconic acid. This first positive electrode active material was used as the positive electrode active material for the non-aqueous electrolyte secondary battery of Example 1.

[0094] SEM observation of the first positive electrode active material confirmed that most of the particles of the first lithium transition metal composite oxide are single particles composed of one primary particle. The D50, crystallite size, and BET specific surface area of ​​the first lithium transition metal composite oxide (first positive electrode active material) were measured using the above method, and the results were: D50 4.6 μm, crystallite size 500 Å, and BET specific surface area 0.6 m². 2 The value was / g. The crystal structure of the first lithium transition metal composite oxide is a layered rock salt structure belonging to space group R-3m.

[0095] The positive electrode slurry for Example 1 was prepared by stirring the positive electrode active material for a non-aqueous electrolyte secondary battery from Example 1, acetylene black (AB), and polyvinylidene fluoride (PVDF) with N-methyl-2-pyrrolidone (NMP). The mass ratio of these materials in the positive electrode slurry was positive electrode active material:AB:PVDF = 92:3:2.

[0096] (Comparative Example 1) A positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1, except that a coating layer was not formed. Specifically, a first lithium transition metal composite oxide having a single-particle shape was used as the positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 1.

[0097] A positive electrode slurry for Comparative Example 1 was prepared in the same manner as in Example 1, except that the positive electrode active material for a non-aqueous electrolyte secondary battery from Comparative Example 1 was used.

[0098] (Comparative Example 2) LiNi 0.8 Co 0.1 Mn 0.1 Comparative Example 2 used a lithium transition metal composite oxide (NCM) having an O2 composition, specifically a general secondary particle type positive electrode active material particle containing several thousand to tens of thousands of primary particles. In other words, the positive electrode active material for the non-aqueous electrolyte secondary battery in Comparative Example 2 did not have a coating layer on the surface of the particles. The general secondary particle type positive electrode active material particle used in Comparative Example 2 can be obtained by firing at a lower temperature than the firing temperature used to produce the first lithium transition metal composite oxide having a single particle shape in Example 1.

[0099] A positive electrode slurry for Comparative Example 2 was prepared in the same manner as in Example 1, except that the positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 2 was used.

[0100] (Comparative Example 3) Croconic acid was added to the positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 in an amount of 0.25% by mass relative to the lithium transition metal composite oxide to form a coating layer. The method for forming the coating layer was the same as in Example 1. The obtained particles were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 3.

[0101] A positive electrode slurry for Comparative Example 3 was prepared in the same manner as in Example 1, except that the positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 3 was used.

[0102] (Comparative Example 4) Croconic acid was added to the positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 in an amount of 0.5% by mass relative to the lithium transition metal composite oxide to form a coating layer. The method for forming the coating layer was the same as in Example 1. The obtained particles were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 4.

[0103] A positive electrode slurry for Comparative Example 4 was prepared in the same manner as in Example 1, except that the positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 4 was used.

[0104] (Comparative Example 5) Croconic acid was added to the positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 in an amount of 1% by mass relative to the lithium transition metal composite oxide to form a coating layer. The method for forming the coating layer was the same as in Example 1. The obtained particles were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 5.

[0105] A positive electrode slurry for Comparative Example 5 was prepared in the same manner as in Example 1, except that the positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 5 was used.

[0106] (Comparative Example 6) The positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 6. That is, the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 6 did not have a coating layer on the surface of the particles.

[0107] In Comparative Example 6, unlike Example 1, croconic acid was added as a component of the positive electrode active material layer. The positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 6, acetylene black (AB), polyvinylidene fluoride (PVDF), and croconic acid were mixed with N-methyl-2-pyrrolidone (NMP) and stirred to prepare the positive electrode slurry of Comparative Example 6. The mass ratio of these materials in the positive electrode slurry was positive electrode active material:AB:PVDF:croconic acid = 92:3:2:0.23. In the positive electrode slurry of Comparative Example 6, the mass ratio of croconic acid to lithium transition metal composite oxide (i.e., positive electrode active material) was 0.25% by mass.

[0108] (Comparative Example 7) The positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 7. That is, the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 7 did not have a coating layer on the surface of the particles.

[0109] In Comparative Example 7, unlike Example 1, croconic acid was added as a component of the positive electrode active material layer. The positive electrode active material for a non-aqueous electrolyte secondary battery of Comparative Example 7, acetylene black (AB), polyvinylidene fluoride (PVDF), and croconic acid were mixed with N-methyl-2-pyrrolidone (NMP) and stirred to prepare the positive electrode slurry of Comparative Example 7. The mass ratio of these materials in the positive electrode slurry was positive electrode active material:AB:PVDF:croconic acid = 92:3:2:0.46. In the positive electrode slurry of Comparative Example 7, the mass ratio of croconic acid to the first lithium transition metal composite oxide (i.e., positive electrode active material) was 0.5% by mass.

[0110] (Comparative Example 8) The positive electrode active material particles of a general secondary particle type NCM used in Comparative Example 2 were used as the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 8. In other words, the positive electrode active material for a non-aqueous electrolyte secondary battery in Comparative Example 8 did not have a coating layer on the surface of the particles.

[0111] In Comparative Example 8, unlike Example 1, croconic acid was added as a component of the positive electrode active material layer. The positive electrode active material for the non-aqueous electrolyte secondary battery of Comparative Example 8, acetylene black (AB), polyvinylidene fluoride (PVDF), and croconic acid were mixed with N-methyl-2-pyrrolidone (NMP) and stirred to prepare the positive electrode slurry of Comparative Example 8. The mass ratio of these materials in the positive electrode slurry was positive electrode active material:AB:PVDF:croconic acid = 92:3:2:0.92. In the positive electrode slurry of Comparative Example 8, the mass ratio of croconic acid to the first lithium transition metal composite oxide (i.e., positive electrode active material) was 1% by mass.

[0112] [Preparation of test cells] Test cells were prepared using the positive electrode slurries of Example 1 and Comparative Examples 1 to 8, respectively, according to the following procedure.

[0113] A positive electrode slurry was applied to the surface of an aluminum foil (1.45 cm x 1.45 cm), the coating film was dried, and then the foil was rolled to form a positive electrode active material layer. In this way, a positive electrode was obtained.

[0114] Laminated half-cells were fabricated using Li metal foil (2 cm x 2 cm, 200 μm thick) as the positive electrode and counter electrode, a separator, and a non-aqueous electrolyte. A polyethylene separator (Celgard, #2320) was used as the separator.

[0115] Based on the above, evaluation cells for Example 1 and Comparative Examples 1 to 8 were obtained.

[0116] [Charge and Discharge Test] A charge and discharge test was performed on each evaluation cell according to the following procedure. Each evaluation cell was charged with a constant current of 1C at an ambient temperature of 45°C until the voltage reached 4.3V. Then, it was discharged with a constant current of 1C until the voltage reached 2.5V. The charge and discharge capacities at this time were measured. The same charge and discharge test was performed with current values ​​of 2C, 3C, and 4C, and the charge and discharge capacities at each current value were measured. The measurement results are shown in Table 1. Note that in Table 1, the ratio of the charge and discharge capacities to the result at a current value of 1C is shown as the baseline (100.0).

[0117] [Confirmation of Particle Morphology] Using the cross-section of the positive electrode active material layer of the fabricated test cell, the particle cross-section of the positive electrode active material was observed at 3000x magnification by SIM to confirm the crystal plane inside the particle. This confirmed whether the positive electrode active materials of Example 1 and Comparative Examples 1 to 8 contained single particles.

[0118]

[0119] As shown in Table 1, the battery of Example 1, which used the positive electrode active material of Example 1, comprising a single-particle NCM and a coating layer containing croconic acid covering at least a portion of the surface of the NCM, was able to suppress the decrease in charge / discharge capacity at high current values ​​more effectively than the battery of Comparative Example 1, which used a single-particle NCM without a coating layer as the positive electrode active material. Thus, when a lithium transition metal composite oxide having a single-particle shape is used, the spontaneous polarization is 15 μC / cm². 2 It was confirmed that by providing a coating layer containing an organic ferroelectric material exceeding a certain value, the decrease in charge / discharge capacity at high current values ​​can be effectively suppressed.

[0120] Comparing Comparative Examples 2 to 5, when the lithium transition metal composite oxide does not have a single-particle shape, the spontaneous polarization is 15 μC / cm². 2 It can be seen that coating layers containing organic ferroelectrics exceeding a certain value do not provide much effect in suppressing the decrease in charge / discharge capacity at high current values. Furthermore, comparing Comparative Examples 2, 6 to 8, the spontaneous polarization was 15 μC / cm². 2 When an organic ferroelectric material exceeding a certain value was added as a component of the positive electrode active material layer, the charge-discharge capacity at high current values ​​actually decreased compared to Comparative Example 2, in which no such material was added.

[0121] From the above results, the effect of ferroelectric materials on suppressing the decrease in charge / discharge capacity at high current values ​​is observed when spontaneous polarization is 15 μC / cm². 2 It was confirmed that this effect can be specifically obtained by having an organic ferroelectric material exceeding a certain value present so as to coat at least a portion of the surface of a lithium transition metal composite oxide having a single-particle shape.

[0122] The technology disclosed herein is useful, for example, in lithium-ion secondary batteries.

Claims

1. A first positive electrode active material comprising: a first lithium transition metal composite oxide having a single-particle shape and containing 80 mol% or more of Ni and Mn in total relative to the total molar amount of metal elements excluding Li; and a coating layer covering at least a portion of the surface of the first lithium transition metal composite oxide, wherein the first lithium transition metal composite oxide has a volume-based median diameter of 0.5 μm or more and 5.0 μm or less, and a crystallite size of 370 Å or more and 1500 Å or less; and the coating layer has a spontaneous polarization of 15 μC / cm². 2 A positive electrode active material for non-aqueous electrolyte secondary batteries containing an organic ferroelectric material exceeding [a certain value].

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the organic ferroelectric material comprises croconic acid.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the mass ratio of the organic ferroelectric material to the first lithium transition metal composite oxide is 0.1% by mass or more and 5% by mass or less.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the organic ferroelectric material is attached to the surface of the first lithium transition metal composite oxide.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first lithium transition metal composite oxide further comprises at least one selected from the group consisting of Mg, Al, Ca, Nb, Sr, Zr, W, S, and P.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery further comprises a second positive electrode active material, the second positive electrode active material comprising secondary particles formed by the aggregation of primary particles of a second lithium transition metal composite oxide.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the second lithium transition metal composite oxide has the same composition as the first lithium transition metal composite oxide.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 7.

Images