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

Abstract

The primary objective of this disclosure is to provide a positive electrode layer for lithium-ion batteries with good rate characteristics. [Solution] In this disclosure, a positive electrode layer used in a lithium-ion battery has a positive electrode active material comprising a single-crystal active material composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O, wherein the single-crystal active material includes a long side and a short side, the angle between the long side and the short side is 60° or more and 120° or less, and the aspect ratio, which is the ratio of the length of the long side to the length of the short side, is 1.2 or more, the long side of the single-crystal active material extends along the (003) plane, and the number of single-crystal active materials N A The number of single-crystal active materials N in which the inclination in the long-side direction with respect to the in-plane direction of the positive electrode layer is 50° or more and 90° or less. B The proportion (N B / N A The above problem is solved by providing a positive electrode layer in which ) 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 a positive electrode layer. [Background technology]

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

[0003] Techniques have been proposed to orient active material particles in a specific direction (for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-87597 [Patent Document 2] Japanese Patent Publication No. 2012-156129 [Patent Document 3] Japanese Patent Publication No. 2012-99405 [Overview of the project] [Problems that the invention aims to solve]

[0005] There is a demand for higher performance batteries. This disclosure has been made in view of the above circumstances, and its main purpose is to provide a positive electrode layer for lithium-ion batteries that has good rate characteristics. In this disclosure, rate characteristics refer to the ratio of the battery capacity when the battery is discharged with a large (high-rate) discharge current value to the battery capacity when the battery is discharged with a small (low-rate) discharge current value (high-rate capacity retention rate), and a larger ratio (battery capacity does not decrease easily even at high rates) is preferable.

Means for Solving the Problem

[0006] [1] A positive electrode layer used in a lithium-ion battery, wherein the positive electrode layer has, as a positive electrode active material, a single crystal system active material composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O, In a cross-sectional observation image of the positive electrode layer by a scanning electron microscope, 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 6%uB0 or more and 12%uB0 or less, and an aspect ratio, which is a ratio of the length of the long side to the length of the short side, is 1.2 or more, the long side of the single crystal system active material extends along the (003) plane, the number N of the single crystal system active materials A with respect to the number N of the single crystal system active materials having an inclination of 5%uB0 or more and 9%uB0 or less in the long side direction with respect to the in-plane direction of the positive electrode layer B of the ratio (N B / N A ) is 20% or more, a positive electrode layer.

[0007] [2] The positive electrode layer according to [1], wherein the length of the long side of the single crystal system active material is 0.5 %u3BCm or more.

[0008] [3] The positive electrode layer according to [1] or [2], wherein the ratio (N B / N A ) is 28% or more and 50% or less.

[0009] [4] The primary particles have a composition represented by Li x Ni a Co b Mn c O y (where 0.1 %u2264 x %u2264 1.5, 0.5 %u2264 a %u2264 1.0, 0 %u2264 b %u2264 0.3, 0 %u2264 c %u2264 0.3, a + b + c = 1.0, 1.5 %u2264 y %u2264 2.1), the positive electrode layer according to any one of [1] to [3]. [5] A lithium-ion battery comprising a positive electrode layer as described in any of [1] through [4]. [6] A method for manufacturing a positive electrode layer, which is described in any of [1] to [4], A coating step to obtain a cathode layer precursor by coating a cathode slurry containing the aforementioned single-crystal active material and the aforementioned cathode active material, A method for manufacturing a positive electrode layer, comprising: an orientation step of oriented the positive electrode layer precursor under a magnetic field so that the tilt of the single-crystal active material is 50° or more and 90° or less in the direction of the long side with respect to the in-plane direction of the positive electrode layer. [Effects of the Invention]

[0010] According to this disclosure, a positive electrode layer for lithium-ion batteries with good rate characteristics can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a cross-sectional image of the positive electrode layer in this disclosure, obtained by scanning electron microscopy. [Figure 2] Figure 1 shows a magnified view of the single-crystal active material P within the dotted line frame. [Figure 3] This is a schematic diagram showing the crystal structure of the single-crystal active material P in the positive electrode layer in this disclosure. [Figure 4] This is a schematic diagram illustrating the orientation step in the method for manufacturing the cathode layer in this disclosure. [Figure 5] This is a schematic cross-sectional view illustrating a lithium-ion battery as described in this disclosure. [Modes for carrying out the invention]

[0012] The present disclosure will be described in detail below with reference to the drawings. The following figures are illustrative and may be exaggerated in size and shape for ease of understanding.

[0013] A. Positive electrode layer The positive electrode layer in this disclosure is a positive electrode layer used in a lithium-ion battery, wherein the positive electrode layer has a single-crystal active material composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O as the positive electrode active material, and in a cross-sectional observation image of the positive electrode layer by scanning electron microscopy, the single-crystal active material includes a long side and a short side, the angle between the long side and the short side is 60° or more and 120° or less, and the aspect ratio, which is the ratio of the length of the long side to the length of the short side, is 1.2 or more, the long side of the single-crystal active material extends along the (003) plane, and the number of the single-crystal active material N A The number of single-crystal active materials N such that the inclination in the long-side direction with respect to the in-plane direction of the positive electrode layer is 50° or more and 90° or less. B The proportion (N B / N A ) is 20% or more.

[0014] Figure 1 is a schematic diagram of a scanning electron microscope (SEM) cross-sectional image (hereinafter also referred to as a cross-sectional SEM image) of the positive electrode layer in this disclosure. Figure 2 is an enlarged view of the single-crystal active material P within the dotted frame in Figure 1. Figure 3 is a schematic diagram showing the crystal structure of the single-crystal active material P in the positive electrode layer in this disclosure. As shown in Figure 1, the positive electrode layer 1 in this disclosure has a single-crystal active material P as the positive electrode active material, which is composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O. As shown in Figure 2, 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 aspect ratio, which is the ratio of the length of the long side a to the length of the short side b, is 1.2 or more. In this disclosure, the long side a of the single-crystal active material P extends along the (003) plane. As shown in Figure 3, the (003) plane is a crystal plane where lithium ions do not enter or leave the crystal.

[0015] As described above, there is a need for a positive electrode layer for lithium-ion batteries with good rate characteristics. In response to this, as shown in Figures 1 to 3, the single-crystal active material P is such that the slope of the long side a is in the in-plane direction D of the positive electrode layer 1. PBy orienting the lithium ions to be approximately perpendicular to the positive electrode (50° to 90°), the lithium ions move in the direction (the thickness direction of the positive electrode layer D) towards the positive electrode active material within the positive electrode layer. T ) and the direction in which lithium ions diffuse within the single-crystal active material can be made substantially the same. Therefore, the diffusion path of lithium ions can be efficiently secured, and the rate characteristics are improved. Note that while Patent Document 1 orients active material particles having core particles and a shell layer, this disclosure differs in that the longitudinal direction of the single-crystal active material is directly aligned. Furthermore, there is no description of how to make the diffusion path of lithium ions efficient.

[0016] In this specification, the cross-sectional SEM image of the positive electrode layer is obtained, for example, by performing cross-sectional processing on the positive electrode layer using an ion milling device and observing the cross-section of the positive electrode layer with a scanning electron microscope. The magnification of the cross-sectional SEM image may be, for example, 2000x or more and 20000x or less. As the scanning electron microscope, the SEM device "product name SU8230" manufactured by Hitachi High-Technologies Corporation can be used. Various dimensional measurements and shape analyses of the cross-sectional SEM image can be performed, for example, using image analysis software such as "ImageJ".

[0017] The positive electrode layer will be described in detail below.

[0018] 1.Cathode active material (1) Positive electrode active material The positive electrode layer in this disclosure includes a positive electrode active material. The positive electrode active material in this disclosure includes a single-crystal active material composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O. In a cross-sectional image of the positive electrode layer obtained by scanning electron microscopy, the single-crystal active material includes a long side and a short side, the angle between the long side and the short side is 60° or more and 120° or less, the aspect ratio, which is the ratio of the length of the long side to the length of the short side, is 1.2 or more, the long side of the single-crystal active material extends along the (003) plane, and the number of single-crystal active materials N A The number of single-crystal active materials N in which the inclination in the long-side direction with respect to the in-plane direction of the positive electrode layer is between 50° and 90°.B The proportion (N B / N A ) is 20% or more

[0019] A single-crystal active material is defined as a material that is not a polycrystalline active material (an active material in which numerous primary particles are aggregated without gaps). Single-crystal active materials typically exist as independent particles, not aggregated. It is preferable that no grain boundaries are visible in single-crystal active materials under SEM observation (magnification: approximately 10,000 to 30,000 times).

[0020] Single-crystal active materials have the advantage of being less prone to degradation over time compared to polycrystalline active materials. Furthermore, polycrystalline active materials, composed of secondary particles, are prone to cracking, and newly formed internal surfaces are easily exposed. These newly formed surfaces come into contact with the electrolyte and react, generating resistive components. On the other hand, the positive electrode layer in this disclosure contains a single-crystal active material. Because single-crystal active materials are less susceptible to stress and cracking compared to polycrystalline active materials, they can suppress the increase in resistance associated with charging and discharging compared to polycrystalline active materials.

[0021] The primary particles in this disclosure contain Li, TM (where TM is a transition metal), and O. The primary particles may contain one transition metal, two transition metals, three transition metals, or four or more transition metals.

[0022] Transition metals are metals belonging to groups 3 through 11 of the periodic table. The transition metals included in the primary particles may belong to the third, fourth, or fifth period. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0023] The primary particles preferably contain at least Ni as TM, because this allows for the acquisition of a positive electrode active material with good capacitance characteristics. The molar ratio of Ni to TM (all transition metals contained in the primary particles) is, for example, 0.25 or higher, may be 0.33 or higher, 0.50 or higher, 0.70 or higher, or 0.80 or higher. Increasing the proportion of Ni improves the capacitance characteristics.

[0024] The primary particles preferably contain at least one of Co and Mn as TM.

[0025] The primary particles may or may not contain Co as TM. The molar ratio of Co to TM (all transition metals contained in the primary particles) may be, 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 may be, for example, 0.40 or less, or 0.20 or less.

[0026] The primary particles may or may not contain Mn as TM. The molar ratio of Mn to TM (all transition metals contained in the primary particles) may be, for example, 0 or greater, 0.05 or greater, or 0.10 or greater. On the other hand, the molar ratio of Mn to TM may be, for example, 0.40 or less, or 0.20 or less.

[0027] The primary particles preferably contain at least one of Ni, Co, and Mn as TM. The molar ratio of the total Ni, Co, and Mn to TM (all transition metals contained in the primary particles) is, for example, 0.80 or higher, may be 0.90 or higher, or 0.95 or higher. Note that "total Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0028] The primary particles consist of Li and TM, as well as other metals M other than Li and TM. 1 It may contain (including metalloids). Other metals M 1Examples of such metals include those belonging to groups 12 through 14 of the periodic table. Examples of metals belonging to groups 12 through 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0029] The composition of the primary particles is not particularly limited, but for example, Li x Ni a Co b Mn c O y The composition may also be 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).

[0030] The above x represents the molar ratio of Li to the total of Ni, Co, and Mn, and is usually 0.1 or greater, but may be 0.4 or greater, 0.6 or greater, 0.8 or greater, 1.0 or greater, or 1.05 or greater. On the other hand, the above x is usually 1.5 or less, but may be 1.4 or less, or 1.2 or less.

[0031] The above y represents the molar ratio of O to the total of Ni, Co, and Mn, and is usually 1.5 or higher, but may be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher. On the other hand, the above y is usually 2.1 or lower, but may be 2.0 or lower.

[0032] The above value a represents the molar ratio of Ni to the total of Ni, Co, and Mn, and is usually 0.5 or higher, but may be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher. On the other hand, the above value a is usually 1.0 or lower, but may be 0.9 or lower.

[0033] The above b represents the molar ratio of Co to the total of Ni, Co, and Mn, and is usually 0 or greater, but may be 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, or 0.075 or greater. On the other hand, the above b is usually 0.30 or less, but may be 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less.

[0034] The above value c represents the molar ratio of Mn to the total of Ni, Co, and Mn, and is usually 0 or greater, but may be 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, 0.05 or greater, 0.06 or greater, 0.07 or greater, or 0.075 or greater. On the other hand, the above value c is usually 0.30 or less, but may be 0.25 or less, 0.20 or less, 0.15 or less, 0.10 or less, 0.09 or less, or 0.08 or less.

[0035] In the above equation, the molar ratios a of Ni, b of Co, and c of Mn satisfy the relationship a + b + c = 1.0.

[0036] The positive electrode active material in this disclosure is, for example, LiNi 0.90 Mn00. 10 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.5 Co 0.3 Mn 0.2 O2, LiLiLi 0.5 Co 0.4 Mn 0.1 O2, LiLiLi 0.5 Co 0.1 Mn 0.4 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi0.6 Co 0.3 Mn 0.1 O2, LiLiLi 0.6 Co 0.1 Mn 0.3 O2, LiLiLi 0.7 Co 0.1 Mn 0.2 O2, LiLiLi 0.7 Co 0.2 Mn 0.1 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 O2, or LiLi 0.9 Co 0.05 Mn 0.05 It has a composition represented by O2.

[0037] In this disclosure, the composition of the positive electrode active material can be determined, for example, by dissolving the positive electrode active material in an acid and measuring it by ICP emission spectrometry (ICP-OES).

[0038] The layered rock salt type is preferred as the crystal structure of the primary particles. The layered rock salt type crystal structure is usually assigned to the space group R-3m.

[0039] In this disclosure, as shown in Figures 1 and 2, the single-crystal active material P composed of primary particles includes a long side a and a short side b in a cross-sectional image of the positive electrode layer obtained by scanning electron microscopy, 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, which is the ratio of the length of the long side a to the length of the short side b, is 1.2 or more. The long side a is the longest side of the single-crystal active material P as it appears in the cross-sectional SEM image of the positive electrode layer. The short side b is connected to the end of the long side a. The short side b is the longest side among the sides connected to the long side a as it appears in the cross-sectional SEM image. 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. The long side a and the short side b may each extend in a straight line. On the other hand, the long side a and the short side b may each be curved. If the side is curved, the length of the side indicates the distance between the two ends of the side.

[0040] In this disclosure, the number of single-crystal active materials P in the cross-sectional SEM image of the positive electrode layer is N. A In the in-plane direction D of the positive electrode layer P The number of single-crystal active materials P whose inclination in the direction of the longer side a is between 50° and 90° is N. B The proportion (N B / N A ) is 20% or more. That is, in this disclosure, 20% or more of the single-crystal active material P is in the in-plane direction D of the positive electrode layer. P It is oriented approximately perpendicular to the given direction.

[0041] Ratio (N B / N A The specific measurement method for ) is as follows: First, 100 single-crystal active materials P are randomly selected from the cross-sectional SEM image of the positive electrode layer, including the long side and the short side, the angle between the long side and the short side being 60° or more and 120° or less, and the aspect ratio, which is the ratio of the length of the long side to the length of the short side, being 1.2 or more (N A (=100 pieces). For each of the 100 extracted single-crystal active materials P, the in-plane direction D of the positive electrode layer is as shown in Figure 2. P The slope θ in the direction of the longer side a relative to the curve D The inclination θ is measured among 100 single-crystal active materials P. D The number of single-crystal active material P whose temperature is between 50° and 90° is N B This means that the proportion (N B / N A Calculate ).

[0042] In this disclosure, the single-crystal active material has its long side extending along the (003) plane. B / N A By making the ratio 20% or more, lithium ions move in the direction toward the positive electrode active material within the positive electrode layer (the thickness direction of the positive electrode layer D). T The direction in which lithium ions diffuse within the primary particles (the (003) plane direction of the single-crystal active material) can be made substantially the same. Therefore, the diffusion path of lithium ions can be efficiently secured, and the rate characteristics are improved.

[0043] The above percentage (NB / N A ) may be 28% or more, and may be 36% or more. On the other hand, the above ratio (N B / N A ) is, for example, 90% or less, and may be 80% or less, 70% or less, 60% or less, or 50% or less.

[0044] The number N of single-crystalline active materials A The number N of single-crystalline active materials with an inclination of 0° or more and less than 50° in the long-side a direction with respect to the in-plane direction of the positive electrode layer C The ratio (N C / N A ) is, for example, 10% or more, and may be 20% or more, 30% or more, 40% or more, or 50% or more. On the other hand, the above ratio (N C / N A ) is usually 80% or less, and may be 70% or less, or 60% or less.

[0045] The aspect ratio of the single-crystalline active material is 1.2 or more, and may be 1.3 or more, 1.4 or more, 1.6 or more, 1.8 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, 5.0 or more, 5.5 or more, 6.0 or more, 6.5 or more, or 7.0 or more. The aspect ratio may be, for example, 10.0 or less, 9.0 or less, or 8.0 or less. <​​​

[0047] The short side b of the single-crystal active material is, for example, 0.2 μm or more, may be 0.5 μm or more, 0.8 μm or more, 1.0 μm or more, 1.5 μm or more, 1.7 μm or more, or 1.9 μm or more. The short side b is, for example, 5.0 μm or less, may be 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less.

[0048] In a single-crystal active material, the angle (interior angle) θ between the longer side a and the shorter side b is 60° or more and 120° or less, and may also be 70° or more and 110° or less, or 80° or more and 100° or less.

[0049] In this disclosure, the long side a extends along the (003) plane. The (003) plane can be identified in high-angle scattering annular dark-field scanning transmission microscope (HAADF-STEM) images. For example, a powder containing a single-crystal active material is embedded in an epoxy resin. A sample is prepared by thinning the powder together with the resin, for example, by argon ion milling. First, the single-crystal active material is extracted at low magnification. The long side a of the single-crystal active material is identified. Next, the (003) plane is identified by observing the single-crystal active material at high magnification. If the angle between the (003) plane and the long side a is between 0° and 30°, the long side a is considered to extend along the (003) plane. In a STEM image, if one or more of the ten randomly selected single-crystal active materials have their long side a extending along the (003) plane, then the long side a of the entire powder is considered to extend along the (003) plane.

[0050] The angle between the long side a and the (003) plane in a single-crystal active material is, for example, 25° or less, but may also be 15° or less, 10° or less, 5° or less, 3° or less, or 1° or less. Among 10 single-crystal active materials randomly extracted from a STEM image, the proportion of single-crystal active materials whose long side a aligns with the (003) plane may be, for example, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0051] The external shape of the single-crystal active material may be, for example, polyhedral. The external shape of the single-crystal active material may also be, for example, hexahedral, octahedral, or the like. The external shape of the single-crystal active material may also be, for example, rectangular parallelepiped.

[0052] The primary particles have a crystal structure that belongs to, for example, the space group R-3m. The space group to which the crystal structure belongs is determined by the XRD (X-Ray Diffraction) pattern. The XRD pattern is obtained by powder XRD measurement, and the measurement conditions are as follows. Analysis method: Wide-angle method Measurement device: Smart Lab II (manufactured by Rigaku Corporation) Measurement angle: 10° to 120° Tube:CuKα Tube voltage: 45kV Tube current: 200mA Measurement method: Continuous method Step: 0.02 Speed: 2° / min IS:1 / 2 RS: 20mm Detection mode: 1D

[0053] In this disclosure, it is preferable that the single-crystal active material does not have a coating layer formed on its surface. Examples of coating layers include carbon coating layers.

[0054] The positive electrode active material in this disclosure may or may not contain a polycrystalline active material (polycrystalline particles) composed of secondary particles of the primary particles described above. The proportion of single-crystal active material in the positive electrode active material is, for example, 50% by weight or more, may be 60% by weight or more, may be 70% by weight or more, may be 80% by weight or more, or may be 90% by weight or more. On the other hand, the proportion of single-crystal active material in the positive electrode active material is, for example, 100% by weight or less.

[0055] The content of the positive electrode active material in the positive electrode layer is, for example, 20% by weight or more, but may be 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, a sufficient energy density may not be obtained. On the other hand, the content of the positive electrode active material is, for example, 95% by weight or less, but may be 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 relatively decrease. The content of the positive electrode active material in the positive electrode layer is the content of the positive electrode active material when the total solid content of the positive electrode layer is taken as 100% by weight.

[0056] (2) Method for producing positive electrode active material The positive electrode active material in this disclosure can be manufactured by performing a step of synthesizing a transition metal hydroxide, a calcination step of heating a mixture of the transition metal hydroxide, a Li source, and a molten salt (flux), and a pulverization step of pulverizing the calcined material.

[0057] (a) Transition metal hydroxide synthesis process Transition metal hydroxides are precursors to positive electrode active materials. These transition metal hydroxides may also be obtained by dissolving multiple types of transition metal compounds in a solvent and then crystallizing them to form a precipitate.

[0058] The method for synthesizing transition metal hydroxides is not particularly limited, but examples include the following. First, an aqueous solution of the raw materials for the transition metal hydroxide is prepared. A method for preparing the aqueous solution of the raw materials is, for example, to dissolve a water-soluble transition metal compound in water. Examples of transition metal compounds include metal salts such as sulfates and nitrates. Examples of Ni sources include NiSO4 and Ni(NO3)2. Examples of Co sources include CoSO4, Co(NO3)2, and Co(NO3)3. Examples of Mn sources include MnSO4 and Mn(NO3)2. The composition of the aqueous solution of the raw materials is appropriately adjusted according to the desired cathode active material.

[0059] Next, a fixed amount of NH3 aqueous solution is added to the reaction vessel, and while stirring with a stirrer or the like, nitrogen is purged to create a non-oxidizing atmosphere. Subsequently, sodium hydroxide aqueous solution is added to the reaction vessel to maintain an alkaline pH, and while controlling the temperature, the above raw material aqueous solution is added dropwise to the reaction vessel to form the reaction solution. By adjusting the pH of the reaction solution, a precipitate (crystallized product) of transition metal hydroxide can be formed.

[0060] After the precipitation reaction is complete, calcination is performed. The conditions for calcination are, for example, a temperature of 120°C to 220°C, a time of 4 hours to 10 hours, and a pressure of 0.2 MPa to 1.0 MPa.

[0061] After calcination, the material is washed with water, filtered to extract the transition metal hydroxide, and then dried. The drying temperature is, for example, between 100°C and 150°C. The drying time is, for example, between 8 hours and 24 hours.

[0062] (b) Firing process The obtained transition metal hydroxide, the Li source, and the molten salt are mixed to obtain a mixture. The Li source is a lithium compound, and examples include 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, and may be 0.9 or more and 1.1 or less, or 1.0.

[0063] The above mixture typically contains a molten salt. The inclusion of a molten salt in the mixture allows for sufficient grain growth of primary particles. 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, but may also be 0.2 or more and 0.6 or less. The molten salt may 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 adding lithium hydroxide in excess of the stoichiometric ratio of the target positive electrode active material relative to the transition metal hydroxide, the lithium hydroxide functions as a flux, allowing for sufficient grain growth of primary particles. The molar ratio of Li in the Li source and molten salt to TM in the transition metal hydroxide is, for example, 1.1 or more and 2.0 or less, but may also be 1.2 or more and 1.6 or less. The method of mixing the transition metal hydroxide, Li source, and molten salt is arbitrary. For example, they may be mixed in a mortar.

[0064] 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 to 1100°C, may be 650°C to 1100°C, or 700°C to 900°C. In this disclosure, it is preferable to perform multi-stage firing of the mixture containing the transition metal hydroxide, the Li source, and the molten salt at multiple firing temperatures. This is because it is easier to obtain a single-crystal active material with the specific shape described above. For example, it is preferable to fire the mixture 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 the mixture at the firing temperature T2 for a predetermined time. The firing temperature T1 described above is, for example, 500°C to 650°C, or 500°C to 600°C. The firing temperature T2 mentioned above 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 may be a two-stage firing, a three-stage firing, or four or more stages. The total firing time for each firing stage may be, for example, 5 hours or more and 18 hours or less, or 8 hours or more and 15 hours or less.

[0065] When performing multi-stage firing, molten salt may be added to the mixture so that the Li / TM (molar ratio) in the mixture increases with each firing stage. For example, a mixture containing a transition metal hydroxide and a Li source is fired at a predetermined firing temperature T1 for a predetermined time, then molten salt is added, and the temperature is raised to the firing temperature T2 for the next firing stage. Next, firing is performed at the firing temperature T2 for a predetermined time. By the final firing stage, molten salt may be added so that the molar ratio of Li in the Li source and molten salt to TM in the transition metal hydroxide falls within the range described above. Any heat treatment furnace can be used for firing, such as a muffle furnace or an electric furnace.

[0066] Next, the calcined material is ground to a predetermined particle size, for example, an average particle diameter of 0.2 μm or less. This grinding may be done using an agate mortar and pestle. Next, the ground material is dispersed in pure water and washed by stirring. The slurry after washing is filtered, rinsed, and vacuum dried.

[0067] The resulting dried powder may be post-annealed (re-calcined). Post-annealing is carried out in an oxygen atmosphere. The calcination temperature during post-annealing is, for example, between 500°C and 800°C, and the calcination time is, for example, between 1 hour and 5 hours.

[0068] (c) Grinding process Next, the calcined material is crushed and broken down to a predetermined particle size. This crushing may be done using an agate mortar or a mill such as a lab mill. After crushing, classification, sizing, etc., may be further performed. Through the above steps, a positive electrode active material having a predetermined composition and containing a single-crystal active material is obtained.

[0069] 2. Positive electrode layer The positive electrode layer contains the positive electrode active material described above, and may further contain conductive materials and binders as needed. The positive electrode layer may also contain an electrolyte. The electrolyte is, for example, the electrolyte solution described later. On the other hand, the positive electrode layer may also contain a solid electrolyte.

[0070] Examples of conductive materials include graphite, acetylene black (AB), Ketjenblack (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF). The content of the conductive material 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.

[0071] Examples of binders include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and derivatives thereof. 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.

[0072] The thickness of the positive electrode layer may 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.

[0073] The positive electrode layer can be formed, for example, by the method described in "C. Method for Manufacturing the Positive Electrode Layer".

[0074] In the cross-sectional SEM images of the cathode layer in this disclosure, there may be single-crystal active material that is not observed in the specific shape described above. Examples of such single-crystal active material include particles that have substantially the same external shape as the single-crystal active material observed in the specific shape, but appear as small particles or dots because they were cut at the edges of the active material particles when the cathode layer was cross-sectionalized.

[0075] B. Lithium-ion batteries The lithium-ion battery in this disclosure includes a positive electrode layer for the lithium-ion battery described above. That is, the disclosure provides a battery in which a positive electrode layer, an electrolyte layer, and a negative electrode layer are stacked in this order, and the positive electrode layer is the positive electrode layer described above. Figure 5 is a schematic cross-sectional view illustrating a lithium-ion battery in this disclosure. The lithium-ion battery 10 shown in Figure 5 has a negative electrode current collector 5, a negative electrode layer 4, an electrolyte layer 3, a positive electrode layer 1, and a positive electrode current collector 2, with the thickness direction D T In this order, the negative electrode current collector 5 and negative electrode layer 4 constitute the negative electrode AN, and the positive electrode layer 1 and positive electrode current collector 2 constitute the positive electrode CA.

[0076] According to this disclosure, the lithium-ion battery has the above-described positive electrode layer, resulting in good rate characteristics.

[0077] 1. Positive electrode layer The positive electrode layer is the same as described in "A. Positive Electrode Layer".

[0078] 2. Negative electrode layer The negative electrode layer includes at least a negative electrode active material and may optionally include at least one of an electrolyte, a conductive material, and a binder. 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; metallic lithium and lithium alloys.

[0079] The negative electrode active material may be in the form of parts or sheets, for example. The average particle size of the negative electrode active material particles may be, for example, 1 μm or more. The average particle size of the negative electrode active material may be, for example, 30 μm or less.

[0080] The conductive material, binder, and electrolyte used in the negative electrode layer are the same as those described for the positive electrode layer above.

[0081] 3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte solution).

[0082] An example of an electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte contains, for example, a lithium salt and a non-aqueous solvent. 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.

[0083] Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The non-aqueous solvent may be a mixture of cyclic carbonates such as EC and PC, which have high dielectric constant and high viscosity, and linear carbonates such as DMC, DEC, and EMC, which have low dielectric constant 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. The non-aqueous electrolyte may also contain an ionic liquid. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, and imidazolium salts.

[0084] Another example of an electrolyte is an aqueous electrolyte. An aqueous electrolyte is an electrolyte that contains water as the main component of the solvent. The proportion of water to the total solvent is, for example, 50% by mass or more, and may be 70% by mass or more. Examples of lithium salts used in aqueous electrolytes include imide-based electrolytes such as lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The concentration of the lithium salt in the aqueous electrolyte is, for example, 1M or more and 25M or less.

[0085] The electrolyte layer may include a separator impregnated with the aforementioned electrolyte. Providing a separator can suppress the occurrence of internal short circuits. The separator is, for example, a porous membrane. Examples of separator materials include polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, polyamide, and other resins. The electrolyte layer may also 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.

[0086] 4. Positive electrode current collector Examples of materials for the positive electrode current collector include SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. Examples of shapes for the positive electrode current collector include foil, mesh, and porous shapes. The planar shape of the positive electrode current collector is not particularly limited, but examples include circular, elliptical, rectangular, and any polygonal shape. The positive electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer on its surface.

[0087] 5.Negative electrode current collector Examples of materials for the negative electrode current collector include SUS, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the negative electrode current collector varies depending on its shape, but is typically between 1 μm and 50 μm. The shape of the negative electrode current collector may be, for example, foil-like or plate-like. The planar shape of the negative electrode current collector is not particularly limited, but examples include circular, elliptical, rectangular, and any polygonal shape. The negative electrode current collector may have a buffer layer, an elastic layer, or a PTC thermistor layer on its surface.

[0088] 6. Lithium-ion batteries The battery in this disclosure may have an outer casing that houses the power generation elements (positive electrode layer, electrolyte layer, negative electrode layer). Examples of outer casings include a case-type outer casing and a laminate-type outer casing.

[0089] The lithium-ion battery in this disclosure is typically a secondary battery. When a set of a positive electrode layer, an electrolyte layer, and a negative electrode layer is considered as a power generation unit, the lithium-ion battery in this disclosure may be a single cell having only one power generation unit, or a stacked battery having two or more power generation units. The stacked battery may be a monopolar stacked battery (a stacked battery connected in parallel) or a bipolar stacked battery (a stacked battery connected in series).

[0090] The applications of lithium-ion batteries are not particularly limited, but examples include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, their use as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs) is preferred. Batteries may also be used as power sources for mobile devices other than vehicles (e.g., trains, ships, aircraft), or as power sources for electrical products such as information processing devices.

[0091] C. Method for manufacturing the positive electrode layer The method for manufacturing a positive electrode layer in this disclosure is a method for manufacturing a positive electrode layer as described above, comprising: a coating step of obtaining a positive electrode layer precursor by coating a positive electrode slurry containing the positive electrode active material including the single-crystal active material and a solvent; and an orientation step of oriented the positive electrode layer precursor under a magnetic field so that the single-crystal active material is oriented such that the inclination in the direction of the long side with respect to the in-plane direction of the positive electrode layer is 50° or more and 90° or less.

[0092] According to this disclosure, a single-crystal active material can be easily oriented such that the inclination of its long side is substantially perpendicular (50° to 90°) to the in-plane direction of the positive electrode layer.

[0093] 1. Coating process In this process, for example, the positive electrode active material containing the single-crystal active material and the solvent are mixed to obtain a positive electrode slurry, and the positive electrode slurry is coated onto the positive electrode current collector to obtain a coating layer, which is a positive electrode layer precursor, on the positive electrode current collector. The single-crystal active material and positive electrode active material are the same as those described in "A. Positive Electrode Layer 1. Positive Electrode Active Material".

[0094] Examples of solvents include N-methylpyrrolidone (NMP), tetralin, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene.

[0095] 2. Orientation process This process involves exposing the positive electrode layer precursor to a magnetic field to orient the single-crystal active material such that the inclination of its long side direction relative to the in-plane direction of the positive electrode layer is between 50° and 90°. Figure 4 is a schematic diagram showing how the magnetic field is applied in this process. As shown in Figure 4, in the coating process, for example, a slurry containing the single-crystal active material P is coated onto the positive electrode current collector 2 to obtain a structure 20 having the positive electrode current collector 2 and the positive electrode layer precursor 1'. Subsequently, the south pole 30a and north pole 30b of neodymium magnets are fixed to the left and right sides of the structure 20 and exposed to a magnetic field to adjust the orientation of the long side direction of the single-crystal active material P to be approximately perpendicular to the in-plane direction of the positive electrode layer (in-plane direction of the current collector). The magnitude of the magnetic field is, for example, between 5 Tesla and 10 Tesla. The exposure time under a magnetic field may be, 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. Note that if drying and pressing are performed without the orientation process, the above ratio (N) B / N A ) is usually less than 20%.

[0096] After the orientation process, drying and pressing treatments may be performed as needed. Examples of pressing treatments include roller pressing and flat plate pressing. The above-described positive electrode layer is manufactured by the above method.

[0097] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0098] (Example 1) [Synthesis of positive electrode active material] By the method shown below, LiNi 0.90 Mn 0.10 A positive electrode active material having a composition represented by O2 was obtained.

[0099] <Preparation of Aqueous Raw Material Solution> First, an aqueous raw material solution was prepared by dissolving NiSO4 and MnSO4 in ion-exchanged water. The mixing ratio of NiSO4 and MnSO4 was adjusted so that the Ni / Mn ratio was 90 / 10 atm%. The concentration of the aqueous raw material solution (the number of moles of the raw materials (total solutes) relative to the aqueous raw material solution) was set to 0.2 mol%.

[0100] <Dehydration and Calcination> A predetermined amount of aqueous NH3 solution was placed in a reaction vessel, and while stirring the inside of the reaction vessel with a stirrer, it was purged with nitrogen. NaOH was added to the reaction vessel to adjust the pH of the aqueous solution to be alkaline. While controlling the inside of the reaction vessel to a constant pH and controlling the temperature, an aqueous raw material solution was dropped to precipitate a transition metal hydroxide. After the precipitation reaction was completed, the precipitate was dehydrated and calcined under the following temperature and pressure conditions. · Temperature: 120 °C · Time: 8 hours · Pressure: 1.0 MPa

[0101] <​​​​​​​​

[0103] <Firing> The mixture was heat-treated (fired). After firing at 500 °C for 3 hours in a muffler furnace, it was fired at 780 °C for 12 hours (firing process). Next, the fired product was crushed in an agate mortar to a particle size of 0.2 mm or less, then dispersed in 500 mL of pure water, and vigorously stirred for 1 minute to obtain a slurry. After filtering the above slurry with a Buchner funnel and filter paper, it was rinsed with 500 mL of pure water, and the obtained cake was vacuum dried at 90 °C. After drying, the obtained dry powder was fired at 500 °C for 3 hours under an oxygen flow (re-firing). The fired product was crushed in an agate mortar and crushed to a predetermined particle size (crushing). Thereby, LiNi 0.90 Mn 0.10 Particles having a composition represented by O2 were obtained.

[0104] [Production of positive electrode] A positive electrode slurry containing the above particles as a positive electrode active material, acetylene black, and an NMP solvent was applied onto an aluminum foil, which is a positive electrode current collector, using a film applicator with a film thickness adjustment function (All Good Co., Ltd.) to obtain a structure having a positive electrode current collector and a positive electrode layer precursor (coating process). Neodymium magnets were fixed to the left and right side surfaces of the structure, and the structure was exposed to a magnetic field of about 5 Tesla for 1 hour (orientation process). After exposure to the magnetic field, a drying treatment was performed for 5 minutes on a hot plate at 80 °C to remove the NMP solvent, and then a pressing treatment (three pressing treatments using a 3-ton roll press) was performed. Thereby, a positive electrode having a positive electrode current collector (aluminum foil) and a positive electrode layer was obtained.

[0105] <00​A (=100). The number of primary particles among the 100 single-crystal active materials whose inclination in the direction of the long side with respect to the in-plane direction of the positive electrode layer (in-plane direction of the metal foil) is between 50° and 90° is N. B The number N was counted. A For a number N B The proportion (N B / N A The result was calculated. The results are shown in Table 1.

[0106] [Battery construction] A metallic lithium foil was prepared as the negative electrode. A 1M LiPF6 solution was prepared as the electrolyte, containing LiPF6 as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents in the ratio EC / DMC / EMC = 3 / 4 / 3 vol%. Using the above positive electrode, electrolyte, and negative electrode, a coin cell with an electrode area of ​​16 mm in diameter was fabricated.

[0107] (Example 2) In the synthesis of the positive electrode active material, a lithium compound (LiOH) was mixed as the molten salt such that the ratio of Li in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide (molar ratio) was 0.6. In other words, the total amount of LiOH added was mixed so that the ratio of Li in the LiOH to the total amount of transition metal species contained in the transition metal hydroxide (molar ratio) was 1.6. Using the obtained positive electrode active material, a positive electrode was fabricated in the same manner as in Example 1, except that the exposure time of the structure to the magnetic field during the orientation process was set to 3 minutes. A coin cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0108] (Example 3) In the synthesis of the positive electrode active material, a lithium compound (LiOH) was mixed as the molten salt such that the ratio of Li in the molten salt to the total amount of transition metal species contained in the transition metal hydroxide (molar ratio) was 0.6. In other words, the total amount of LiOH added was mixed so that the ratio of Li in the LiOH to the total amount of transition metal species contained in the transition metal hydroxide (molar ratio) was 1.6. Using the obtained positive electrode active material, a positive electrode was fabricated in the same manner as in Example 1, except that the exposure time of the structure to the magnetic field during the orientation process was 1 minute. A coin cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0109] (Comparative Example 1) The positive electrode was fabricated in the same manner as in Example 1, except that the orientation step was omitted during the fabrication of the positive electrode. A coin cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0110] (Comparative Example 2) The positive electrode was fabricated in the same manner as in Example 1, except that neodymium magnets were fixed to the top and bottom of the structure during the orientation process, and the structure was exposed to a magnetic field of approximately 5 Tesla for 20 seconds. A coin cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0111] [evaluation] Using the obtained coin cells, capacity evaluation tests were conducted under the following conditions. Ambient temperature: 25℃ Current rate: 0.1C Voltage range: 4.3V to 3.0V

[0112] The initial discharge capacity of the coin cell was measured at a 0.1C rate, then it was recharged using CCCV and discharged at a 1C rate. In the initial capacity test, the electrical capacity (mAh) obtained during the discharge process of the first charge-discharge was divided by the weight (in grams) of the positive electrode active material contained in the electrodes of the coin cell to determine the 0.1C discharge capacity (in mAhg) per gram of positive electrode active material. -1The following was calculated: Similarly, the 1C discharge capacity was calculated. Based on this, the rate characteristic was calculated as 1C discharge capacity / 0.1C discharge capacity. The results are shown in Table 1.

[0113] [Table 1]

[0114] As shown in Table 1, N B / N A Batteries having a positive electrode layer of 20% or more (Examples 1 to 3) are N B / N A It was confirmed that the rate characteristics were superior compared to batteries with a positive electrode layer of less than 20% (Comparative Example 1 and Comparative Example 2). [Explanation of Symbols]

[0115] 1…Positive electrode layer 2...Positive electrode current collector 3...Electrolyte layer 4…Negative electrode layer 5...Negative electrode current collector 10…Lithium-ion battery

Claims

1. A positive electrode layer used in lithium-ion batteries, The positive electrode layer has a single-crystal active material composed of crystalline primary particles containing Li, TM (where TM is a transition metal), and O as the positive electrode active material. In the cross-sectional image of the positive electrode layer obtained by scanning electron microscopy, The single-crystal active material includes a long side and a short side, the angle between the long side and the short side is 60° or more and 120° or less, and the aspect ratio, which is the ratio of the length of the long side to the length of the short side, is 1.2 or more. The long side of the single-crystal active material extends along the (003) plane, The number of the single-crystal active material N Ａ The number of single-crystal active materials such that the inclination in the long-side direction with respect to the in-plane direction of the positive electrode layer is 50° or more and 90° or less is N. Ｂ The proportion (N Ｂ / N Ａ A positive electrode layer in which ) makes up 20% or more.

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

3. The aforementioned ratio (N Ｂ / N Ａ The positive electrode layer according to claim 1, wherein the amount of ) is 28% or more and 50% or less.

4. The primary particles are Li ｘ Ni ａ Co ｂ Mn ｃ O ｙ (where 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), the positive electrode layer according to claim 1, having the composition represented by the formula.

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 according to any one of claims 1 to 5, A coating step to obtain a cathode layer precursor by coating a cathode slurry containing the aforementioned single-crystal active material and the aforementioned cathode active material, A method for manufacturing a positive electrode layer, comprising: an orientation step of oriented the positive electrode layer precursor under a magnetic field so that the single-crystal active material is oriented such that the inclination in the direction of the long side with respect to the in-plane direction of the positive electrode layer is 50° or more and 90° or less.

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