Positive electrode layer, lithium ion battery, and method for manufacturing positive electrode layer

Abstract

The present disclosure provides a positive electrode layer, which is a positive electrode layer used in a lithium ion battery, has a single crystal system active material composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O as a positive electrode active material, the single crystal system active material includes a long side and a short side, an angle formed by the long side and the short side is 60° or more and 120° or less, and a length ratio of the long side to the short side, that is, an aspect ratio is 1.2 or more, the long side of the single crystal system active material extends along a (003) plane, and an inclination of the long side direction with respect to an in-plane direction of the positive electrode layer is 50° or more and 90° or less B The ratio (N B / N A ) of the number N A of the single crystal system active material to the total number of the single crystal system active material and a polycrystal system active material is 20% or more.

Description

Technical Field

[0001] This disclosure relates to a positive electrode layer for lithium-ion batteries, a lithium-ion battery, and a method for manufacturing the positive electrode layer. Background Technology

[0002] In recent years, battery development has been booming. For example, in the automotive industry, development is underway for batteries used in battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs). Active materials containing transition metals such as Ni, Co, and Mn are known to be used as positive electrode materials in batteries.

[0003] Techniques for orienting active material particles in a specific direction have been proposed (e.g., Japanese Patent Application Publication No. 2020-87597, Japanese Patent Application Publication No. 2012-156129, Japanese Patent Application Publication No. 2012-99405). Summary of the Invention

[0004] There is a demand for high-performance batteries. This disclosure was made in view of the above-mentioned realities, and its main objective is to provide a positive electrode layer for lithium-ion batteries with good rate characteristics. In addition, the rate characteristics in this disclosure are expressed as the ratio of the battery capacity when the battery is discharged at a large (high-rate) discharge current value to the battery capacity when the battery is discharged at a small (low-rate) discharge current value (high-rate capacity retention rate), and the larger the ratio (the less likely the battery capacity will decrease even at high rates), the more preferred.

[0005] [1] A positive electrode layer, which is used in lithium-ion batteries.

[0006] The positive electrode layer has a single-crystal active material as the positive electrode active material, which is composed of crystalline primary particles containing Li, TM (TM is a transition metal) and O.

[0007] In the cross-sectional image of the positive electrode layer obtained using a scanning electron microscope

[0008] The single-crystal active material comprises a long side and a short side, the angle between the long side and the short side being 60° or more and 120° or less, and the aspect ratio (length to width) of the long side to the short side being 1.2 or more.

[0009] The long edge (003) of the single-crystal active material extends.

[0010] The number N of the single-crystal active material in which the inclination of the long side direction relative to the in-plane direction of the positive electrode layer is more than 50° and less than 90°. B The number N of the single-crystal active material A proportion (N) B / N A The percentage is over 20%.

[0011] [2] According to the positive electrode layer described in [1], the length of the long side of the single crystal active material is 0.5 μm or more.

[0012] [3] According to the positive electrode layer described in [1] or [2], the ratio (N) B / N A The percentage is between 28% and 50%.

[0013] [4] According to any one of [1] to [3], the primary particle has a Li x Ni a Co b Mn c O y (In the formula, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1) represents the composition.

[0014] [5] A lithium-ion battery comprising any one of [1] to [4] a positive electrode layer.

[0015] [6] A method for manufacturing a positive electrode layer, which is a method for manufacturing a positive electrode layer as described in any one of [1] to [4], includes a coating process and an orientation process.

[0016] In the coating process, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material, wherein the positive electrode active material contains the single-crystal active material.

[0017] In the orientation process, the positive electrode layer precursor is exposed to a magnetic field, causing the single-crystal active material to be oriented with its long side direction tilted at an angle of 50° or more and 90° or less relative to the in-plane direction of the positive electrode layer.

[0018] According to this disclosure, a positive electrode layer for lithium-ion batteries with good rate characteristics can be provided. Attached Figure Description

[0019] The features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will now be described with reference to the accompanying drawings, wherein the same symbols denote the same elements.

[0020] Figure 1This is a schematic diagram of a cross-sectional image of the positive electrode layer obtained by scanning electron microscopy.

[0021] Figure 2 yes Figure 1 A magnified view of the single-crystal active substance P within the dashed box.

[0022] Figure 3 This is a schematic diagram showing the crystal structure of the single-crystal active material P in the cathode layer of this disclosure.

[0023] Figure 4 This is a schematic diagram illustrating the orientation process in the manufacturing method of the positive electrode layer of this disclosure.

[0024] Figure 5 This is a schematic cross-sectional view illustrating the lithium-ion battery of this disclosure. Detailed Implementation

[0025] The present disclosure will now be described in detail with reference to the accompanying drawings. The drawings shown below are illustrative, and for ease of understanding, the size and shape of the parts are sometimes exaggerated.

[0026] A. Positive electrode layer

[0027] The positive electrode layer in this disclosure is a positive electrode layer for lithium-ion batteries. The positive electrode layer has a single-crystal active material composed of crystalline primary particles containing Li, TM (TM being a transition metal), and O as the positive electrode active material. In a cross-sectional image of the positive electrode layer obtained using a scanning electron microscope, the single-crystal active material includes a long side and a short side, the angle between the long side and the short side being 60° or more and 120° or less, and the length-to-width ratio (length-to-width ratio) of the long side to the short side is 1.2 or more. The long side of the single-crystal active material extends along the (003) plane, and the inclination of the long side direction relative to the in-plane direction of the positive electrode layer is 50° or more and 90° or less. The number N of such single-crystal active materials is... B The number N of the above-mentioned single-crystal active material A proportion (N) B / N A The percentage is over 20%.

[0028] Figure 1 This is a schematic diagram of a cross-sectional image (hereinafter also referred to as a cross-sectional SEM image) of the positive electrode layer in this disclosure obtained by scanning electron microscopy. Figure 2 yes Figure 1 A magnified view of the single-crystal active substance P within the dashed box. Figure 3 This is a schematic diagram showing the crystal structure of the single-crystal active material P in the cathode layer of this disclosure. (See diagram for reference.) Figure 1As shown, the positive electrode layer 1 of this disclosure has a single-crystal active material P composed of crystalline primary particles containing Li, TM (TM is a transition metal) and O as the positive electrode active material. Figure 2 As shown, in the cross-sectional SEM image of the positive electrode layer 1, the single-crystal active material P includes a long side a and a short side b, the angle θ between the long side a and the short side b is 60° or more and 120° or less, and the length ratio of the long side a to the short side b, i.e., the aspect ratio, is 1.2 or more. In this disclosure, the long side a of the single-crystal active material P extends along the (003) plane. Figure 3 As shown, the (003) face is a crystal face where lithium ions do not enter or leave.

[0029] As mentioned above, there is a need for a positive electrode layer for lithium-ion batteries with good rate characteristics. In contrast, in this disclosure, as... Figures 1-3 As shown, by tilting the single-crystal active material P with its long side a relative to the in-plane direction D of the positive electrode layer 1... P A roughly perpendicular orientation (between 50° and 90°) allows lithium ions to move towards the positive electrode active material within the positive electrode layer 1 in the direction of the thickness D of the positive electrode layer 1. T The direction of lithium ion diffusion is approximately the same as that of lithium ions within the single-crystal active material P. Therefore, the diffusion path of lithium ions can be effectively ensured, improving the rate characteristics. Furthermore, while Japanese Patent Application Publication 2020-87597 describes the orientation of active material particles having a core and a shell, this disclosure differs in that the orientation of the single-crystal active material along its length is directly aligned. Additionally, aspects regarding the effectiveness of the lithium ion diffusion path are not described.

[0030] Furthermore, in this specification, the cross-sectional SEM image of the positive electrode layer is obtained, for example, by exposing the cross-section of the positive electrode layer using an ion milling apparatus and observing the cross-section of the positive electrode layer using a scanning electron microscope. The magnification of the cross-sectional SEM image can be, for example, 2000x or more and 20000x or less. As the scanning electron microscope, the SEM apparatus "Product Name SU8230" manufactured by Hitachi High Technology Co., Ltd. can be used. Various dimension measurements and shape analyses in the cross-sectional SEM image can be performed, for example, using image analysis software such as "ImageJ".

[0031] The positive electrode layer will be described in detail below.

[0032] 1. Positive electrode active material

[0033] (1) Positive electrode active material

[0034] The positive electrode layer of this disclosure includes a positive electrode active material. The positive electrode active material of this disclosure comprises a single-crystal active material composed of crystalline primary particles containing Li, TM (TM being a transition metal), and O. In a cross-sectional image of the aforementioned positive electrode layer obtained using a scanning electron microscope, the single-crystal active material includes a long side and a short side, the angle between the long side and the short side being 60° or more and 120° or less, and the length-to-width ratio (length-to-width ratio) of the long side to the short side being 1.2 or more. The long side of the single-crystal active material extends along the (003) plane, and the inclination of the long side direction relative to the in-plane direction of the positive electrode layer is 50° or more and 90° or less. The number N of such single-crystal active materials is... B The number N of active materials relative to the single crystal system A proportion (N) B / N A The percentage is over 20%.

[0035] Monocrystalline active materials are not the same as so-called polycrystalline active materials (active materials formed by the seamless aggregation of multiple primary particles). Monocrystalline active materials typically do not aggregate and exist as a single, independent particle. Ideally, monocrystalline active materials should not show grain boundaries in SEM observations (magnification: approximately 10,000 to 30,000 times).

[0036] Compared to polycrystalline active materials, monocrystalline active materials have the advantage of less degradation over time. Furthermore, polycrystalline active materials, composed of secondary particles, are prone to fracture, easily exposing newly formed internal surfaces. These newly formed surfaces come into contact with and react with the electrolyte, thereby generating resistive components. On the other hand, the positive electrode active material of the positive electrode layer disclosed herein comprises a monocrystalline active material. Compared to polycrystalline active materials, monocrystalline active materials are less susceptible to stress and fracture, thus suppressing the increase in resistance associated with charging and discharging.

[0037] The primary particles disclosed herein contain Li, TM (TM being a transition metal), and O. A primary particle may contain one, two, three, or more transition metals.

[0038] Transition metals are metals belonging to groups 3 through 11 of the periodic table. A primary particle may contain a transition metal belonging to period 3, 4, or 5. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0039] The primary particles preferably contain at least Ni as TM. This is because a positive electrode active material with good capacity characteristics can be obtained. The molar ratio of Ni to TM (all transition metals contained in the primary particles) is, for example, 0.25 or more, 0.33 or more, 0.50 or more, 0.70 or more, or 0.80 or more. By increasing the proportion of Ni, the capacity characteristics are improved.

[0040] The primary particles preferably contain at least one of Co and Mn as TM.

[0041] The primary particle may contain Co as TM, or it may not contain Co. The molar ratio of Co to TM (all transition metals contained in the primary particle) is, for example, 0 or more, 0.05 or more, or 0.10 or more. On the other hand, the molar ratio of Co to TM is, for example, 0.40 or less, or 0.20 or less.

[0042] The primary particle may contain Mn as TM, or it may not contain Mn. The molar ratio of Mn to TM (all transition metals contained in the primary particle) is, for example, 0 or more, 0.05 or more, or 0.10 or more. On the other hand, the molar ratio of Mn to TM is, for example, 0.40 or less, or 0.20 or less.

[0043] The primary particle preferably contains at least one of Ni, Co, and Mn as TM. The molar ratio of the total of Ni, Co, and Mn to TM (all transition metals contained in the primary particle) is, for example, 0.80 or more, 0.90 or more, or 0.95 or more. In addition, "the total of Ni, Co, and Mn" also includes the case where the proportion of one or two of Ni, Co, and Mn is 0.

[0044] In addition to Li and TM, primary particles may also contain other metals M besides Li and TM. 1 (Including semi-metals). As other metals M 1 For example, metals belonging to groups 12 through 14 in the periodic table can be cited. Examples of metals belonging to groups 12 through 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0045] There are no particular restrictions on the composition of primary particles; for example, they can be composed of the general formula Li. x Ni a Co b Mn c O y The composition represented by (0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1).

[0046] The x mentioned above represents the molar ratio of Li relative to the total of Ni, Co, and Mn, which is typically 0.1 or higher, but can be 0.4 or higher, 0.6 or higher, 0.8 or higher, 1.0 or higher, or 1.05 or higher. On the other hand, the x mentioned above is typically 1.5 or lower, but can be 1.4 or lower, or 1.2 or lower.

[0047] The y mentioned above represents the molar ratio of O to the total of Ni, Co, and Mn, which is typically 1.5 or higher, but can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher. On the other hand, the y mentioned above is typically 2.1 or lower, and can be 2.0 or lower.

[0048] The term 'a' above represents the molar ratio of Ni to the total molar ratio of Ni, Co, and Mn, which is typically 0.5 or higher, but can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher. On the other hand, the term 'a' above is typically 1.0 or lower, and can be 0.9 or lower.

[0049] The 'b' mentioned above represents the molar ratio of Co relative to the total of Ni, Co, and Mn, which is typically 0 or higher, but can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. On the other hand, the 'b' mentioned above is typically 0.30 or lower, but can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0050] The 'c' mentioned above represents the molar ratio of Mn to the total of Ni, Co, and Mn, and is typically 0 or higher, but can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. On the other hand, the 'c' mentioned above is typically 0.30 or lower, but can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0051] In the above formula, the molar ratios of Ni (a), Co (b), and Mn (c) satisfy the relationship a + b + c = 1.0.

[0052] The positive electrode active material disclosed herein, for example, has a composition of LiNi 0.90 Mn 0.10 O2, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.4 O2, LiNi 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.1 Co 0.1 Mn 0.2 O2, LiNi 0.1 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.9 Co 0.05 Mn 0.05 O2 represents the composition.

[0053] In this disclosure, the composition of the positive electrode active material can be determined, for example, by dissolving the positive electrode active material in acid and measuring it using ICP emission spectroscopy (ICP-OES).

[0054] As a primary particle crystal structure, layered rock salt is preferred. The crystal structure of layered rock salt is usually classified into space group R-3m.

[0055] In this disclosure, such as Figure 1 and Figure 2 As shown, in a cross-sectional image of the cathode layer obtained using a scanning electron microscope (SEM), the single-crystal active material P composed of primary particles includes a long side a and a short side b. The angle θ between the long side a and the short side b is 60° or more and 120° or less, and the aspect ratio (length ratio of the long side a to the short side b) is 1.2 or more. Furthermore, in the cross-sectional SEM image of the cathode layer, the long side a appears to be the longest side of the single-crystal active material P. The short side b connects to the end of the long side a. The short side b represents the longest side in the cross-sectional SEM image among the sides connected to the long side a. The short side b extends from the end of the long side a in a direction intersecting the direction in which the long side a extends. Both the long side a and the short side b can extend in a straight line. Alternatively, both the long side a and the short side b can be curved. In the case of a curved side, the length of the side represents the distance between the two ends of the side.

[0056] In this disclosure, in the cross-sectional SEM image of the cathode layer, the direction of the long side a is relative to the in-plane direction D of the cathode layer. P The number of single-crystal active substances P with a tilt of 50° or more and 90° or less. B The amount N of active material P relative to the single crystal system A proportion (N) B / N A The content is 20% or more. That is, in this disclosure, more than 20% of the single-crystal active material P is in the in-plane direction D relative to the positive electrode layer. P Oriented in a roughly vertical direction.

[0057] Ratio (N) B / N A The specific measurement method is as follows. First, in the cross-sectional SEM image of the positive electrode layer, 100 single-crystal active materials P(N) containing both a long side and a short side, with the angle between the long side and the short side being greater than 60° and less than 120°, and the aspect ratio (length to width ratio) of the long side to the short side being greater than 1.2, are randomly extracted. A =100). For each of the 100 extracted single-crystal active substances P, such as Figure 2 As shown, the direction of the long side a is measured relative to the in-plane direction D of the positive electrode layer. P tilt θ D The tilt θ in 100 single-crystal active materials P D The number of single-crystal active substances P with an angle greater than 50° and less than 90° is defined as N. B Therefore, the ratio (N) can be calculated. B / N A ).

[0058] The long side of the single-crystal active material disclosed herein extends along the (003) plane. By adjusting the ratio (N... B / N A Setting it to 20% or higher allows lithium ions to move in the direction of the positive electrode active material within the positive electrode layer (the thickness direction D of the positive electrode layer). T The direction of lithium ion diffusion within a single particle is approximately the same as that of the (003) plane in single-crystal active materials. Therefore, the diffusion path of lithium ions can be effectively ensured, and the rate characteristics are improved.

[0059] The above ratio (N) B / N A The percentage (N) can be above 28% or above 36%. On the other hand, the aforementioned percentage (N) B / N A For example, it can be below 90%, below 80%, below 70%, below 60%, or below 50%.

[0060] The number N of single-crystal active materials whose inclination along the long side a relative to the in-plane direction of the positive electrode layer is greater than 0° and less than 50°. C The number N of active materials relative to the single crystal system A proportion (N) C / N A For example, it could be 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more. On the other hand, the above proportions (N) C / N A It is usually below 80%, but it can be below 70% or even below 60%.

[0061] The aspect ratio of single-crystal active materials can be 1.2 or higher, and can be 1.3 or higher, 1.4 or higher, 1.6 or higher, 1.8 or higher, 2.0 or higher, 2.5 or higher, 3.0 or higher, 3.5 or higher, 4.0 or higher, 4.5 or higher, 5.0 or higher, 5.5 or higher, 6.0 or higher, 6.5 or higher, or 7.0 or higher. The aspect ratio can also be below 10.0, below 9.0, or below 8.0.

[0062] The long side 'a' of the single-crystal active material can be, for example, 0.5 μm or more, 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 3.5 μm or more, or 4.0 μm or more. The long side 'a' can also be less than 6.0 μm or less than 5.0 μm.

[0063] For single-crystal active materials, the short side b can be 0.2 μm or more, or 0.5 μm or more, or 0.8 μm or more, or 1.0 μm or more, or 1.5 μm or more, or 1.7 μm or more, or 1.9 μm or more. The short side b can be 5.0 μm or less, or 4.0 μm or less, or 3.0 μm or less, or 2.0 μm or less.

[0064] In single-crystal active materials, the angle (interior angle) θ between the long side a and the short side b is greater than 60° and less than 120°, can be greater than 70° and less than 110°, or can be greater than 80° and less than 100°.

[0065] In this disclosure, the long side a extends along the (003) plane. The (003) plane can be determined in a high-angle scattering annular dark-field scanning transmission microscope (HAADF-STEM) image. For example, a powder containing a single-crystal active material is embedded in epoxy resin. For example, a sample is prepared by thinning the powder for each resin using an argon ion milling method. First, the single-crystal active material is extracted at low magnification. The long side a of the single-crystal active material is determined. Then, the single-crystal active material is observed at high magnification, thereby determining the (003) plane. When the angle between the (003) plane and the long side a is 0° to 30°, the long side a is considered to extend along the (003) plane. In the STEM image, if the long side a extends along the (003) plane in one or more of the randomly extracted single-crystal active materials, it is considered that the long side a extends along the (003) plane in the entire powder.

[0066] The angle between the long side a of the single-crystal active material and the (003) plane can be, for example, less than 25°, less than 15°, less than 10°, less than 5°, less than 3°, or less than 1°. Among 10 single-crystal active materials randomly extracted from the STEM image, the proportion of single-crystal active materials with the long side a along the (003) plane can be, for example, more than 20%, more than 30%, more than 40%, more than 50%, more than 60%, more than 70%, more than 80%, or more than 90%.

[0067] The shape of a single-crystal active material can be, for example, polyhedral. The shape of a single-crystal active material can also be, for example, hexahedral, octahedral, etc. The shape of a single-crystal active material can also be, for example, cuboid.

[0068] Primary particles, for example, possess crystal structures belonging to space group R-3m. The space group to which the crystal structure belongs is determined by XRD (X-ray Diffraction) patterns. The XRD patterns are obtained by powder XRD determination under the following conditions.

[0069] Analysis method: Wide-angle method

[0070] Measurement apparatus: SmartLabII (manufactured by Rigaku Corporation)

[0071] Measurement angle: 10°~120°

[0072] Tube: CuKα

[0073] Tube voltage: 45kV

[0074] Tube current: 200mA

[0075] Determination method: Continuous method

[0076] Step size: 0.02

[0077] Speed: 2° / minute

[0078] IS: 1 / 2

[0079] RS: 20mm

[0080] Detection mode: One-dimensional

[0081] The single-crystal active material disclosed herein preferably has no coating layer formed on its surface. Examples of coating layers include carbon coatings.

[0082] The positive electrode active material disclosed herein may or may not include a polycrystalline active material (polycrystalline particles) composed of secondary particles of the aforementioned primary particles. The proportion of monocrystalline active material in the positive electrode active material is, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. On the other hand, the proportion of monocrystalline active material in the positive electrode active material is, for example, 100% by weight or less.

[0083] The content of the positive electrode active material in the positive electrode layer can be, for example, 20% by weight or more, 30% by weight or more, 40% by weight or more, 50% by weight or more, 60% by weight or more, or 70% by weight or more. If the content of the positive electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the content of the positive electrode active material can be, for example, 95% by weight or less, 90% by weight or less, or 80% by weight or less. If the content of the positive electrode active material is too high, the ionic conductivity and electronic conductivity in the positive electrode layer may decrease. The content of the positive electrode active material in the positive electrode layer refers to the content of the positive electrode active material when the total solid composition of the positive electrode layer is set to 100% by weight.

[0084] (2) Method for manufacturing positive electrode active material

[0085] The positive electrode active material disclosed herein can be manufactured by the following steps: a step of synthesizing a transition metal hydroxide, a calcination step of subjecting a mixture of the transition metal hydroxide, a Li source and a molten salt (flux) to heat treatment, and a pulverization step of pulverizing the calcined material.

[0086] (a) Transition metal hydroxide synthesis process

[0087] Transition metal hydroxides are precursors for positive electrode active materials. Transition metal hydroxides can be obtained by crystallization of various transition metal compounds in a solvent to form precipitates.

[0088] There are no particular limitations on the synthesis method of transition metal hydroxides; for example, the following methods can be used. First, prepare an aqueous solution of the transition metal hydroxide as a raw material. For example, a method for preparing the aqueous solution can be to dissolve a water-soluble transition metal compound in water. For example, metal salts such as sulfates and nitrates can be used as transition metal compounds. For example, NiSO4 and Ni(NO3)2 can be used as Ni sources. For example, CoSO4, Co(NO3)2, and Co(NO3)3 can be used as Co sources. For example, MnSO4 and Mn(NO3)2 can be used as Mn sources. The composition of the aqueous solution is adjusted appropriately according to the target positive electrode active material.

[0089] Next, a certain amount of NH3 aqueous solution is added to the reaction vessel, and nitrogen replacement is carried out while stirring with a stirrer to create a non-oxidizing atmosphere. Then, sodium hydroxide aqueous solution is added to the reaction vessel to maintain an alkaline pH. While controlling the temperature, the above-mentioned raw material aqueous solution is added dropwise to the reaction vessel, thus forming a reaction solution. By adjusting the pH of the reaction solution, a precipitate (crystal) of transition metal hydroxide can be formed.

[0090] After the precipitation reaction is completed, pre-firing is performed. The pre-firing conditions are, for example, a temperature of 120°C or higher and 220°C or lower, a time of 4 hours or higher and 10 hours or lower, and a pressure of 0.2 MPa or higher and 1.0 MPa or lower.

[0091] After pre-firing, the washed material is filtered to remove the transition metal hydroxide, which is then dried. The drying temperature is, for example, above 100°C and below 150°C. The drying time is, for example, above 8 hours and below 24 hours.

[0092] (b) Firing process

[0093] The obtained transition metal hydroxide, Li source, and molten salt are mixed to obtain a mixture. The Li source is a lithium compound, for example, at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride. The molar ratio of Li in the Li source to TM contained in the transition metal hydroxide is, for example, 0.8 or more and 1.2 or less, 0.9 or more and 1.1 or less, or 1.0.

[0094] The above mixture typically contains a molten salt. The presence of a molten salt in the mixture allows for sufficient primary particle growth. The molar ratio of Li in the molten salt to TM in the transition metal hydroxide is typically 0.1 or more and 1.0 or less, and can be 0.2 or more and 0.6 or less. The molten salt can be a lithium compound of the same type as the Li source. For example, lithium hydroxide is used as the molten salt. When lithium hydroxide is used as the Li source, by ensuring that the amount of lithium hydroxide added is sufficient relative to the stoichiometry of the target positive electrode active material compared to the transition metal hydroxide, lithium hydroxide functions as a flux, allowing for sufficient primary particle growth. The molar ratio of Li in the Li source and the molten salt to TM in the transition metal hydroxide is, for example, 1.1 or more and 2.0 or less, and can be 1.2 or more and 1.6 or less. The mixing method of the transition metal hydroxide, Li source, and molten salt is arbitrary. For example, mixing can be done using a mortar.

[0095] In this disclosure, a mixture containing a transition metal hydroxide, a Li source, and a molten salt is subjected to heat treatment. The firing temperature is, for example, 500°C or higher and 1100°C or lower, or 650°C or higher and 1100°C or lower, or 700°C or higher and 900°C or lower. In this disclosure, it is preferable to perform multi-stage firing of the mixture containing the transition metal hydroxide, Li source, and molten salt at multiple firing temperatures. This is because it is easy to obtain the aforementioned single-crystal active material with the specific shape described above. For example, it is preferable to fire at a predetermined firing temperature T1 for a predetermined time, then raise the temperature to the firing temperature T2 of the next firing stage, and fire at the firing temperature T2 for a predetermined time. The aforementioned firing temperature T1 is, for example, 500°C or higher and 650°C or lower, or 500°C or higher and 600°C or lower. The aforementioned firing temperature T2 is higher than the firing temperature T1, for example, 650°C or higher and 1100°C or lower, or 750°C or higher and 1000°C or lower. The firing process can be carried out in two stages, three stages, or more than four stages. The total firing time in each stage can be, for example, more than 5 hours and less than 18 hours, or more than 8 hours and less than 15 hours.

[0096] In the case of multi-stage firing, molten salt can be added to the mixture in such a way that the Li / TM (molar ratio) in the mixture increases with each firing stage. For example, for a mixture containing a transition metal hydroxide and a Li source, after firing at a predetermined firing temperature T1 for a predetermined time, molten salt is added, and the temperature is raised to the firing temperature T2 for the next firing stage. Then, firing is carried out at the firing temperature T2 for a predetermined time. Alternatively, molten salt can be added before the final firing stage, such that the molar ratio of Li in the Li source and molten salt to TM in the transition metal hydroxide falls within the range mentioned above. Firing can be performed using any heat treatment furnace, such as a muffle furnace, electric furnace, etc.

[0097] Next, the calcined material is pulverized to a specified particle size, for example, an average particle size of less than 0.2 μm. This pulverization can be performed using an agate mortar. The pulverized material is then dispersed in pure water and stirred to perform washing. The washed slurry is then filtered, rinsed, and vacuum dried.

[0098] The resulting dry powder can be subjected to post-annealing (re-firing). Post-annealing is carried out in an oxygen atmosphere. The firing temperature in post-annealing is, for example, above 500°C and below 800°C, and the firing time is, for example, above 1 hour and below 5 hours.

[0099] (c) Crushing process

[0100] Next, the calcined material is pulverized to a specified particle size. This pulverization can be performed using an agate mortar and pestle or a grinding mill such as a laboratory mill. After pulverization, further processing such as grading and granulation can be carried out. This yields a positive electrode active material with a specified composition and containing single-crystal active material.

[0101] 2. Positive electrode layer

[0102] The positive electrode layer contains the aforementioned positive electrode active material, and may also contain conductive materials and binders as needed. The positive electrode layer may contain an electrolyte. The electrolyte may be, for example, the electrolyte solution described later. Alternatively, the positive electrode layer may contain a solid electrolyte.

[0103] Examples of conductive materials include graphite, acetylene black (AB), Ketjen black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene sheets (GF). The content of the conductive material in the positive electrode layer can be, for example, more than 0.1 parts by weight and less than 10 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0104] Examples of binders include polyvinylidene fluoride (PVdF), PVdF-HFP copolymer, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and their derivatives. The binder content in the positive electrode layer may be, for example, 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0105] The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[0106] The positive electrode layer can be formed, for example, by the method described in "C. Method for manufacturing the positive electrode layer".

[0107] In the cross-sectional SEM image of the cathode layer in this disclosure, there may be single-crystal active materials that cannot be observed with the specific shape described above. Examples of such single-crystal active materials include those that have substantially the same shape as single-crystal active materials observed with the specific shape, but when the cross-section of the cathode layer is exposed, the portion at the end of the active material particles is cut off, thus resulting in small particles or particles that look like dots.

[0108] B. Lithium-ion batteries

[0109] The lithium-ion battery disclosed herein includes the aforementioned positive electrode layer for lithium-ion batteries. That is, in this disclosure, a battery in which a positive electrode layer, an electrolyte layer, and a negative electrode layer are sequentially stacked can be provided, wherein the positive electrode layer is the aforementioned positive electrode layer. Figure 5 This is a schematic cross-sectional view illustrating the lithium-ion battery of this disclosure. Figure 5 The lithium-ion battery 10 shown is along the thickness direction D T It has a negative current collector 5, a negative electrode layer 4, an electrolyte layer 3, a positive electrode layer 1, and a positive current collector 2 in sequence. The negative current collector 5 and the negative electrode layer 4 constitute the negative electrode AN, and the positive electrode layer 1 and the positive current collector 2 constitute the positive electrode CA.

[0110] According to this disclosure, the lithium-ion battery has the above-mentioned positive electrode layer, thus its rate characteristics become good.

[0111] 1. Positive electrode layer

[0112] As the positive electrode layer, it is the same as the content recorded in "A. Positive Electrode Layer".

[0113] 2. Negative electrode layer

[0114] The negative electrode layer contains at least a negative electrode active material, and may contain at least one of an electrolyte, a conductive material, and a binder, depending on the requirements. Examples of negative electrode active materials include silicon-based active materials such as Si and Si alloys, tin and tin alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; and metallic lithium and lithium alloys.

[0115] The negative electrode active material can be in particle or sheet form. The average particle size of the negative electrode active material can be, for example, 1 μm or more. Alternatively, the average particle size of the negative electrode active material can be, for example, 30 μm or less.

[0116] Regarding the conductive materials, adhesives, and electrolytes used in the negative electrode layer, examples can be made of the same materials as those described in the positive electrode layer.

[0117] 3. Electrolyte layer

[0118] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte).

[0119] As an example of an electrolyte, a non-aqueous electrolyte can be cited. Non-aqueous electrolytes, for example, contain lithium salts and non-aqueous solvents. Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0120] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The non-aqueous solvent can be a mixture of cyclic carbonates such as EC and PC, which have high dielectric constants and high viscosity, and chain carbonates such as DMC, DEC, and EMC, which have low dielectric constants and low viscosity. The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.3 M or more and 5 M or less. Furthermore, the non-aqueous electrolyte may contain ionic liquids. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidineonium salts, morpholinium salts, phosphonium salts, and imidazolium salts.

[0121] Other examples of electrolytes include aqueous electrolytes. Aqueous electrolytes are electrolytes whose main component contains water as a solvent. The proportion of water to the total solvent is, for example, 50% by mass or more, or even 70% by mass or more. Examples of lithium salts used in aqueous electrolytes include bis(fluorosulfonyl)imide lithium and bis(trifluoromethanesulfonyl)imide lithium, which are imide-based electrolytes. The concentration of the lithium salt in the aqueous electrolyte is, for example, 1 M or more and 25 M or less.

[0122] The electrolyte layer may include a membrane impregnated with the electrolyte. By providing the membrane, the occurrence of internal short circuits can be suppressed. The membrane may be, for example, a porous membrane. Examples of membrane materials include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. Furthermore, the electrolyte layer may contain a solid electrolyte. Examples of solid electrolytes include organic electrolytes such as polymer electrolytes and gel electrolytes, and inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes.

[0123] 4. Positive current collector

[0124] Materials used as positive current collectors include, for example, SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be, for example, foil-like, mesh-like, or porous. There are no particular limitations on the top-view shape of the positive current collector; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The positive current collector can be a structure with a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0125] 5. Negative current collector

[0126] Materials used as negative current collectors include, for example, SUS, aluminum, copper, nickel, iron, titanium, and carbon. Furthermore, the thickness of the negative current collector varies depending on its shape, typically ranging from 1 μm to 50 μm. The shape of the negative current collector can be, for example, foil or plate. There are no particular limitations on the top-view shape of the negative current collector; examples include circular, elliptical, rectangular, and arbitrary polygonal shapes. The negative current collector can also have a structure with a buffer layer, elastic layer, or PTC thermistor layer disposed on its surface.

[0127] 6. Lithium-ion batteries

[0128] The battery disclosed herein can have an outer casing that houses the power generation elements (positive electrode layer, electrolyte layer, and negative electrode layer). Examples of such outer casings include shell-type outer casings and laminated outer casings.

[0129] The lithium-ion battery disclosed herein is typically a secondary battery. When the positive electrode layer, electrolyte layer, and negative electrode layer are considered as a power generation unit, the lithium-ion battery of this disclosure can be a single cell with only one power generation unit, or a stacked battery with two or more power generation units. The stacked battery can be a unipolar stacked battery (parallel-connected stacked battery) or a bipolar stacked battery (series-connected stacked battery).

[0130] There are no particular limitations on the applications of lithium-ion batteries; examples include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred for use as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can be used as power sources for mobile bodies other than vehicles (such as railways, ships, and aircraft), and also for electrical products such as information processing devices.

[0131] C. Manufacturing method of the positive electrode layer

[0132] The method for manufacturing the positive electrode layer disclosed herein includes a coating process and an orientation process. In the coating process, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material and a solvent. The positive electrode active material contains the single-crystal active material. In the orientation process, the positive electrode layer precursor is exposed to a magnetic field, and the single-crystal active material is oriented such that the inclination of the long side direction relative to the in-plane direction of the positive electrode layer is 50° or more and 90° or less.

[0133] According to this disclosure, it is possible to easily orient the single-crystal active material in a manner in which the tilt of the long side is approximately perpendicular (between 50° and 90°) to the in-plane direction of the cathode layer.

[0134] 1. Coating process

[0135] In this process, for example, the positive electrode active material containing the aforementioned single-crystal active material is mixed with a solvent to obtain a positive electrode slurry, and the positive electrode slurry is coated onto a positive electrode current collector, thereby obtaining a positive electrode layer precursor as a coating layer on the positive electrode current collector. The single-crystal active material and the positive electrode active material are the same as those described in "A. Positive Electrode Layer 1. Positive Electrode Active Material".

[0136] Examples of solvents include N-methylpyrrolidone (NMP), tetrahydronaphthalene, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene.

[0137] 2. Orientation process

[0138] This process exposes the aforementioned cathode layer precursor to a magnetic field, causing the aforementioned single-crystal active material to be oriented with its long side direction tilted at an angle of 50° or more and 90° or less relative to the in-plane direction of the aforementioned cathode layer. Figure 4 This is a schematic diagram illustrating the application of a magnetic field in this process. For example... Figure 4 As shown, in the above coating process, for example, by coating a slurry containing a single-crystal active material P onto the positive electrode current collector 2, a structure 20 having a positive electrode current collector 2 and a positive electrode layer precursor 1' is obtained. Then, by fixing the S pole 30a and N pole 30b of a neodymium magnet to the left and right sides of the structure 20 and exposing it to a magnetic field, the orientation of the long side of the single-crystal active material P can be adjusted to be approximately perpendicular to the in-plane direction of the positive electrode layer (the in-plane direction of the current collector). The magnitude of the magnetic field is, for example, 5 Tesla or more and 10 Tesla or less. The exposure time to the magnetic field is, for example, 1 minute or more and 2 hours or less, or 1 minute or more and 1 hour or less, or 3 minutes or more and 1 hour or less. In addition, when drying and pressing are performed without an orientation process, the above ratio (N B / N A It is usually less than 20%.

[0139] After the orientation process, drying and pressing processes can be performed as needed. For example, rolling and flat pressing can be used for pressing. The above-described positive electrode layer is manufactured using these methods.

[0140] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are merely illustrative, and any technical solutions that have a substantially the same structure and achieve the same effect as the technical concept described in the claims of this disclosure are included within the technical scope of this disclosure.

[0141] Example 1

[0142] Synthesis of positive electrode active material

[0143] The following method is used to obtain a product with LiNi 0.90 Mn 0.10 O2 represents the composition of the positive electrode active material.

[0144] Preparation of raw material aqueous solution

[0145] First, a raw material aqueous solution was prepared by dissolving NiSO4 and MnSO4 in ion-exchanged water. The ratio of NiSO4 to MnSO4 was adjusted to a Ni / Mn ratio of 90 / 10 atm%. The concentration of the raw material aqueous solution (the number of moles of raw material (total solute) relative to the raw material aqueous solution) was 0.2 mol%.

[0146] Dehydration and pre-firing

[0147] A prescribed amount of NH3 aqueous solution was added to the reaction vessel, and the mixture was stirred while nitrogen was purged. NaOH was then added to the reaction vessel to adjust the pH of the aqueous solution to alkaline. While maintaining a constant pH and temperature within the reaction vessel, the raw material aqueous solution was added dropwise, thereby precipitating the transition metal hydroxide. After the precipitation reaction was complete, the precipitate was dehydrated and pre-calcined under the following temperature and pressure conditions.

[0148] Temperature: 120℃

[0149] • Duration: 8 hours

[0150] Pressure: 1.0 MPa

[0151] Precursor recovery

[0152] After pre-calcination, the precipitate is washed with water. The washed material is filtered to remove the transition metal hydroxide. Then, it is dried at 110°C for 12 hours to evaporate the moisture (dried product). This prepares the precursor.

[0153] Mixing Li feedstock and molten salt

[0154] The obtained precursor (transition metal hydroxide) and LiOH as a Li source were mixed in a mortar. The LiOH as a Li source was mixed such that the molar ratio (Li content in the Li source to the total amount of transition metal species (Ni, Mn) in the transition metal hydroxide) was 1.0. Furthermore, the LiOH as a molten salt was mixed such that the molar ratio (Li content in the molten salt to the total amount of transition metal species in the transition metal hydroxide) was 0.2. That is, the total amount of LiOH added was mixed such that the molar ratio (Li content in the LiOH to the total amount of transition metal species in the transition metal hydroxide) was 1.2. As a result, excess lithium compounds formed during calcination formed a molten salt, thereby promoting the single crystallization of the positive electrode active material.

[0155] Firing

[0156] The mixture was subjected to heat treatment (firing). After firing at 500°C for 3 hours in a muffle furnace, it was then fired at 780°C for 12 hours (firing process). Next, the fired material was pulverized to a particle size of less than 0.2 mm using an agate mortar and pestle, dispersed in 500 mL of pure water, and vigorously stirred for 1 minute to obtain a slurry. The slurry was filtered through a Buchner funnel and filter paper, washed with 500 mL of pure water, and the resulting filter cake was vacuum dried at 90°C. After drying, the dried powder was fired at 500°C for 3 hours under oxygen flow (re-firing). The fired material was then pulverized (crushed) using an agate mortar and pestle to a specified particle size. Thus, a product with LiNi composition was obtained.0.90 Mn 0.10 O2 represents the constituent particles.

[0157] Positive electrode production

[0158] Using a film applicator with a film thickness adjustment function (Allgood Co., Ltd.), a positive electrode slurry containing the aforementioned particles as positive electrode active material, acetylene black, and NMP solvent is coated onto an aluminum foil serving as the positive electrode current collector, resulting in a structure having a positive electrode current collector and a positive electrode layer precursor (coating process). Neodymium magnets are fixed to the left and right sides of the structure, and the structure is exposed to a magnetic field of approximately 5 Tesla for 1 hour (alignment process). After exposure to the magnetic field, the structure is dried for 5 minutes using a hot plate at 80°C to evaporate the NMP solvent, followed by a pressing process (three pressing processes using a 3-ton roller press). Thus, a positive electrode having a positive electrode current collector (aluminum foil) and a positive electrode layer is obtained.

[0159] The obtained positive electrode was cut in the thickness direction by ion milling to expose the cross-section of the positive electrode layer. The cross-section of the positive electrode layer was observed using a scanning electron microscope (SEM, Hitachi High Technology Corporation SU8230) at an accelerating voltage of 1 kV. In the cross-sectional SEM image, a single-crystal active material composed of crystalline primary particles was observed. One hundred portions were randomly selected that had line segments that could be identified as short and long sides, an angle between the short and long sides of 60° or more and 120° or less, and an aspect ratio (length to width) of 1.2 or more for the long side to the short side (i.e., N...). A =100). The number N of primary particles whose long side orientation is tilted by 50° or more but less than 90° relative to the in-plane orientation of the cathode layer (the in-plane orientation of the metal foil) in 100 single-crystal active materials. B Perform the counting. Calculate the quantity N. B Relative to the quantity N A proportion (N) B / N A The results are shown in Table 1.

[0160] Battery manufacturing

[0161] Prepare lithium metal foil as the negative electrode. Prepare a 1M LiPF6 solution as the electrolyte, wherein LiPF6 is used as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are contained as solvents in a ratio of EC / DMC / EMC = 3 / 4 / 3 vol%. Using the above positive electrode, electrolyte, and negative electrode, fabricate a button cell with an electrode area of ​​16 mm in diameter.

[0162] Example 2

[0163] In the synthesis of the positive electrode active material, lithium compound (LiOH), serving as a molten salt, was mixed in a molar ratio of 0.6 between the total amount of Li in the molten salt and the total amount of transition metals contained in the transition metal hydroxide. Otherwise, the positive electrode active material was synthesized using the same method as in Example 1. Specifically, the total amount of LiOH added was mixed in a molar ratio of 1.6 between the total amount of Li in the LiOH and the total amount of transition metals contained in the transition metal hydroxide. Using the obtained positive electrode active material, the structure was exposed to a magnetic field for 3 minutes during the alignment process when fabricating the positive electrode. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A button cell with the same structure as in Example 1 was obtained, except that the obtained positive electrode was also used.

[0164] Example 3

[0165] In the synthesis of the positive electrode active material, lithium compound (LiOH), serving as a molten salt, was mixed in a molar ratio of 0.6 to the total amount of Li in the molten salt relative to the total amount of transition metals contained in the transition metal hydroxide. Otherwise, the positive electrode active material was synthesized using the same method as in Example 1. Specifically, the total amount of LiOH added was mixed in a molar ratio of 1.6 to the total amount of Li in the LiOH relative to the total amount of transition metals contained in the transition metal hydroxide. Using the obtained positive electrode active material, the structure was exposed to a magnetic field for 1 minute during the alignment process when fabricating the positive electrode. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A button cell with the same structure as in Example 1 was obtained, except that the obtained positive electrode was also used.

[0166] Comparative Example 1

[0167] Except that the alignment process is omitted during the fabrication of the positive electrode, the positive electrode is fabricated using the same method as in Example 1. A button cell with the same structure as in Example 1 is obtained, except that the obtained positive electrode is not used.

[0168] Comparative Example 2

[0169] During the fabrication of the positive electrode, neodymium magnets were fixed at the top and bottom of the structure in the alignment process, and the structure was exposed to a magnetic field of approximately 5 Tesla for 20 seconds. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A button cell with the same structure as in Example 1 was obtained except that the obtained positive electrode was used.

[0170] evaluate

[0171] Using the obtained button cells, a capacity evaluation test was conducted under the following conditions.

[0172] Ambient temperature: 25℃

[0173] Current rate: 0.1C

[0174] Voltage range: 4.3V~3.0V

[0175] After measuring the initial discharge capacity of the button cell at a rate of 0.1C, it was charged again using CCCV and discharged at a rate of 1C. In the initial capacity test, the 0.1C discharge capacity (in mAhg) per gram of positive electrode active material was calculated by dividing the capacity (mAh) obtained during the initial charge-discharge process by the weight (in g) of the positive electrode active material contained in the electrode of the button cell. -1 Similarly, the 1C discharge capacity was calculated. From this, the 1C discharge capacity / 0.1C discharge capacity was calculated as the rate characteristic. The results are shown in Table 1.

[0176] Table 1

[0177]

[0178] As shown in Table 1, N was confirmed. B / N A Batteries with a positive electrode layer of 20% or more (Examples 1-3) and those with N B / N A Compared to batteries with a positive electrode layer of less than 20% (Comparative Example 1 and Comparative Example 2), the rate characteristics are higher.

Claims

1. A positive electrode layer, used in lithium-ion batteries. The positive electrode layer has a single-crystal active material as the positive electrode active material. The single-crystal active material is composed of crystalline primary particles containing Li, TM, and O. TM is a transition metal. In the cross-sectional image of the positive electrode layer obtained using a scanning electron microscope The single-crystal active material comprises a long side and a short side, wherein the angle between the long side and the short side is 60° or more and 120° or less, and the aspect ratio (length to width) of the long side to the short side is 1.2 or more. The long edge (003) of the single-crystal active material extends. The number N of the single-crystal active material in which the inclination of the long side direction relative to the in-plane direction of the positive electrode layer is more than 50° and less than 90°. B The number N of the single-crystal active material A The proportion N B / N A It is over 20%.

2. The positive electrode layer according to claim 1, The length of the long side of the single-crystal active material is 0.5 μm or more.

3. The positive electrode layer according to claim 1, The ratio N B / N A It is between 28% and 50%.

4. The positive electrode layer according to claim 1, The primary particle has Li x Ni a Co b Mn c O y The composition is represented by the formula, where 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, and 1.5≤y≤2.

1.

5. A lithium-ion battery comprising a positive electrode layer according to any one of claims 1 to 4.

6. A method for manufacturing a positive electrode layer, comprising a coating step and an alignment step, as described in any one of claims 1 to 4. In the coating process, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material, wherein the positive electrode active material contains the single-crystal active material. In the orientation process, the positive electrode layer precursor is exposed to a magnetic field, causing the single-crystal active material to be oriented with its long side direction tilted at an angle of 50° or more and 90° or less relative to the in-plane direction of the positive electrode layer.

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