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 that can suppress the increase in resistance associated with the charging and discharging of the battery. [Solution] In this disclosure, 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 microscope, 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 materials 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 0° or more and 30° or less. B The proportion (N B / N A The above problem is solved by providing a positive electrode layer in which ) is 50% 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] In recent years, techniques have been proposed to orient active material particles or specific crystal planes in active materials in specific directions. For example, Patent Document 1 discloses plate-like particles for positive electrode active material of a lithium secondary battery, formed as a polycrystalline material consisting of numerous primary crystal particles having a layered rock salt structure, wherein the (003) plane of the primary crystal particles within the plate-like particles is oriented parallel to the plate surface of the plate-like particles. Patent Document 2 discloses a method for manufacturing an energy storage device, comprising the steps of using a material having anisotropic magnetic susceptibility, such as an olivine-type oxide containing a transition metal element, as active material particles, applying a slurry containing active material particles to a current collector, and leaving the current collector coated with the slurry in a magnetic field. Patent Document 3 discloses a non-aqueous electrolyte secondary battery in which a graphite-based negative electrode active material is arranged such that its longitudinal direction aligns with the plane direction of the current collector when a magnetic field is applied. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2012 / 046557 [Patent Document 2] Japanese Patent Publication No. 2022-66604 [Patent Document 3] Japanese Patent Publication No. 2015-138644 [Overview of the project] [Problems that the invention aims to solve]

[0005] From the perspective of improving battery performance, there is a need to suppress the increase in resistance associated with battery charging and discharging. This disclosure has been made in view of the above circumstances, and its main objective is to provide a positive electrode layer for lithium-ion batteries that can suppress the increase in resistance associated with battery charging and discharging. [Means for solving the problem]

[0006] [1] A positive electrode layer used in lithium-ion batteries, The above 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 above 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 above single-crystal active material extends along the (003) plane, Number N of the above single-crystal active materials 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 0° or more and 30° or less. B The proportion (N B / N A A positive electrode layer in which ) is 50% or more.

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

[0008] [3] The above percentage (N B / N A A positive electrode layer as described in [1] or [2], wherein the content of ) is 56% or more and 65% or less.

[0009] [4] The outer shape of the above-mentioned single crystal active material is rectangular parallelepiped, and the positive electrode layer according to any one of [1] to [3].

[0010] [5] The above primary particles contain at least Ni as the above TM, and the positive electrode layer according to any one of [1] to [4].

[0011] [6] The above primary particles contain at least one of Co and Mn as the above TM, and the positive electrode layer according to any one of [1] to [5]. [[ID=1,8]]

[0012] [7] The molar ratio of the above Ni to the above TM is 0.5 or more, and the positive electrode layer according to [5].

[0013] [8] The proportion of the above single crystal active material in the above positive electrode active material is 50% by weight or more, and the positive electrode layer according to any one of [1] to [7].

[0014] [9] The above primary particles have a layered rock salt type crystal structure, and the positive electrode layer according to any one of [1] to [8].

[0015]

[10] The above 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), and the positive electrode layer according to any one of [1] to [9].

[0016]

[11] A lithium ion battery including the positive electrode layer according to any one of [1] to

[10] .

[0017]

[12] A method for manufacturing a positive electrode layer, which is described in any of [1] to

[10] , A coating step to obtain a cathode layer precursor by coating a cathode slurry containing the above-mentioned single-crystal active material and the above-mentioned 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 such that the inclination of the long side direction with respect to the in-plane direction of the positive electrode layer is 0° or more and 30° or less. [Effects of the Invention]

[0018] According to this disclosure, it is possible to provide a positive electrode layer for a lithium-ion battery that can suppress the increase in resistance associated with the charging and discharging of the battery. [Brief explanation of the drawing]

[0019] [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 manufacturing process of 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. [Figure 6] This is a schematic cross-sectional view illustrating a lithium-ion battery as described in this disclosure. [Modes for carrying out the invention]

[0020] 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.

[0021] 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 0° or more and 30° or less. B The proportion (N B / N A ) is 50% or more.

[0022] 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.

[0023] As mentioned above, there is a need for a positive electrode layer that can suppress the increase in resistance associated with battery charging and discharging. In particular, while layered positive electrode active materials containing Ni are expected to increase discharge capacity, charging and discharging inevitably cause contraction and expansion of the crystal lattice in the stacking direction (c-axis direction), resulting in the severance of conductive paths and deterioration of the crystal structure, which tends to increase resistance. This is presumed to be because, during charging, Li ions are extracted from the Li layer, causing the Li layer to contract in the stacking direction (c-axis direction), and an exchange phenomenon (cation mixing) occurs between Li ions in the Li layer and Ni ions in the transition metal layer, causing part of the layered structure to change into a rock salt structure. In particular, the increase in resistance becomes noticeable when charging and discharging includes high potential regions of 4.1V or higher.

[0024] In contrast, in this disclosure, the positive electrode active material has a single-crystal active material P composed of crystalline primary particles, and in the cross-sectional SEM image of the positive electrode layer 1, the single-crystal active material P has a predetermined shape, and the long side a of the single-crystal active material P extends along the (003) plane. Since the single-crystal active material is long along the (003) plane, i.e., the Li layer is wide, it is thought that the desorption of Li ions from the Li layer can proceed relatively slowly. It is thought that the Li ions remaining in the Li layer function as pillars, so to speak, which mitigates the shrinkage of the Li layer and makes structural degradation less likely to occur. However, even when such a single-crystal active material P is used, there are cases where the increase in resistance due to charging and discharging cannot be sufficiently suppressed. In this disclosure, as shown in Figures 1 to 3, the single-crystal active material P has a slope of the long side a in the in-plane direction D of the positive electrode layer 1. P By orienting the plane to be approximately parallel to (0° to 30°), the plane (003) where lithium ions do not enter or leave is positioned in the direction of lithium ion diffusion within the positive electrode layer (the thickness direction of the positive electrode layer D). T The particles are oriented approximately perpendicular to the ) . This improves the durability of the crystal structure of the primary particles even after repeated charging and discharging, and suppresses the increase in resistance associated with charging and discharging of lithium-ion batteries. Note that Patent Document 1 does not describe adjusting the orientation of plate-like particles. For this reason, the resistance of the battery tends to increase with charging and discharging.

[0025] In this disclosure, the single-crystal active material is oriented so that its longitudinal direction (the inclination of the long side a) is substantially parallel to the in-plane direction of the positive electrode layer. Compared to a case where the longitudinal direction of the primary particles is not adjusted, the direction of expansion and contraction of the single-crystal active material during battery charging and discharging is aligned. Furthermore, the force applied to the single-crystal active material during expansion and contraction is smaller compared to a single-crystal active material oriented so that its longitudinal direction is perpendicular to the plane of the positive electrode layer. For these reasons, cracking of the single-crystal active material can be suppressed, and the increase in resistance during battery charging and discharging can be suppressed.

[0026] 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".

[0027] The positive electrode layer will be described in detail below.

[0028] 1.Cathode 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 0° and 30°. B The proportion (NB / N A ) is 50% or more.

[0029] 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).

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The primary particles preferably contain at least one of Co and Mn as TM.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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).

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The positive electrode active material in this disclosure is, for example, LiNi 0.90 Mn 0.10 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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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 0° and 30° is N. B The proportion (N B / N A ) is 50% or more. In other words, in this disclosure, 50% 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 in a direction approximately parallel to it.

[0051] 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 materials P whose temperature is between 0° and 30° is N B This means that the proportion (N B / N A Calculate ).

[0052] In this disclosure, the single-crystal active material has its long side extending along the (003) plane. B / N A By setting the (003) plane of the single-crystal active material to 50% or more, the (003) plane of the single-crystal active material can be arranged substantially parallel to the in-plane direction of the positive electrode layer, thereby suppressing the increase in battery resistance that occurs with charging and discharging of the lithium-ion battery.

[0053] The above percentage (N B / N A ) may be 56% or more, or 58% or more. On the other hand, the above proportion (NB / N A ) is, for example, 100% or less, may be 99% or less, may be 95% or less, may be 90% or less, may be 80% or less, may be 70% or less, may be 65% or less.

[0054] The number N of single crystal active materials A The ratio of the number N of single crystal active materials with an inclination of more than 30° and 50° or less in the long side a direction with respect to the in-plane direction of the positive electrode layer to the number N of single crystal active materials C (N C / N A ) is, for example, 40% or less, may be 30% or less.

[0055] The number N of single crystal active materials A The ratio of the number N of single crystal active materials with an inclination of more than 50° and 90° or less in the long side a direction with respect to the in-plane direction of the positive electrode layer to the number N of single crystal active materials D (N D / N A ) is, for example, 20% or less, may be 10% or less.

[0056] The aspect ratio of the single crystal active material is 1.2 or more, may be 1.3 or more, may be 1.4 or more, may be 1.6 or more, may be 1.8 or more, may be 2.0 or more, may be 2.5 or more, may be 3.0 or more, may be 3.5 or more, may be 4.0 or more, may be 4.5 or more, may be 5.0 or more, may be 5.5 or more, may be 6.0 or more, may be the aspect ratio may be 6.5 or more, may be 7.0 or more. For example, the aspect ratio may be 10.0 or less, may be 9.0 or less, may be 8.0 or less.

[0057] The longest side a of the single-crystal active material is, for example, 0.5 μm or more, may be 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 longest side a is, for example, 6.0 μm or less, may be 5.0 μm or less.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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

[0064] 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.

[0065] 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.

[0066] 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.

[0067] (3) 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.

[0068] (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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] (b) Firing process The obtained transition metal hydroxide, the Li source, and the molten salt (flux) 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] (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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] The positive electrode layer can be formed, for example, by the method described in "C. Method for Manufacturing the Positive Electrode Layer".

[0085] 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.

[0086] 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.

[0087] According to this disclosure, since the lithium-ion battery has the above-described positive electrode layer, it is possible to suppress the increase in resistance associated with the charging and discharging of the battery.

[0088] 1. Positive electrode layer The positive electrode layer is the same as described in "A. Positive Electrode Layer".

[0089] 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.

[0090] 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.

[0091] The conductive material, binder, and electrolyte used in the negative electrode layer are the same as those described for the positive electrode layer above.

[0092] 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).

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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).

[0101] Figure 6 is a schematic cross-sectional view illustrating a case where the lithium-ion battery in this disclosure is a bipolar battery. The lithium-ion battery 10 shown in Figure 6 has a plurality of stacked power generation units P. Each power generation unit P has a positive electrode layer 1, a negative electrode layer 4, and an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 4. The lithium-ion battery 10 shown in Figure 6 has bipolar electrodes BP (BP1 to BP29) as electrodes. Furthermore, the lithium-ion battery 10 has a positive electrode end electrode CA and a negative electrode end electrode AN. The bipolar electrode BP has a current collector 6, a positive electrode layer 1, and a negative electrode layer 4. The positive electrode layer 1 is located on one surface of the current collector 6, and the negative electrode layer 4 is located on the other surface of the current collector 6. The positive electrode end electrode CA has a current collector 6 and a positive electrode layer 1. This positive electrode layer 1 is located on one surface of the current collector 6. The negative electrode end electrode AN has a current collector 6 and a negative electrode layer 4. This negative electrode layer 4 is located on one surface of the current collector 6.

[0102] The lithium-ion battery 10 in this disclosure may have only one bipolar electrode BP, or it may have two or more. On the other hand, the battery in this disclosure may not have a bipolar electrode.

[0103] 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.

[0104] 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 0° or more and 30° or less.

[0105] According to this disclosure, a single-crystal active material can be easily oriented such that the inclination of its long side is substantially parallel (0° to 30°) to the in-plane direction of the positive electrode layer.

[0106] 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".

[0107] Examples of solvents include N-methylpyrrolidone (NMP), tetralin, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and may contain two or more of these components.

[0108] 2. Orientation process In this process, by exposing the above-mentioned cathode layer precursor to a magnetic field, the above-mentioned single crystal active material is oriented such that the inclination of the long side direction with respect to the in-plane direction of the above-mentioned cathode layer is 0° or more and 30° or less. FIG. 4 is a schematic diagram showing a state where a magnetic field is applied in this process. As shown in FIG. 4, in the above-mentioned coating process, for example, by coating a slurry containing a single crystal active material P on the cathode current collector 2, a structure 20 having the cathode current collector 2 and the cathode layer precursor 1' is obtained. Thereafter, the S pole 30a and the N pole 30b of a neodymium magnet are fixed above and below the structure 20, and by exposing it to a magnetic field, the orientation of the long side direction of the single crystal active material P can be adjusted to be substantially parallel to the in-plane direction of the cathode layer (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 time for exposure to the magnetic field is, for example, 1 minute or more and 2 minutes or less, and may be 1 minute or more and 10 minutes or less.

[0109] After the orientation process, if necessary, a drying process and a pressing process are performed. Examples of the pressing process include roller pressing and flat plate pressing. In addition, when the drying process and the pressing process are performed without performing the orientation process, the above ratio (N B / N A ) is usually less than 50%, and may be 40% or less. By the above method, the above-mentioned cathode layer is manufactured.

[0110] Note that the present disclosure is not limited to the above embodiment. The above embodiment is an example, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same operational effects is included in the technical scope of the present disclosure.

Example

[0111] (Example 1) [Synthesis of Cathode Active Material] By the method shown below, a cathode active material having a composition represented by LiNi 0.90 Mn 0.10 O2 was obtained.

[0112] [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 was set to 0.2 mol%.

[0113] <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 subjected to dehydration and calcination under the following temperature and pressure conditions. · Temperature: 120 °C · Time: 8 hours · Pressure: 1.0 MPa

[0114] <Precursor Recovery>[[]] After calcination, the precipitate was washed with water. The washed product was filtered to take out the transition metal hydroxide. Next, it was dried at 110 °C for 12 hours to evaporate the moisture (dried product). Thereby, a precursor was prepared. [[ID=2C]]

[0115] <Mixing of Li Raw Material and Molten Salt>[[]] The obtained precursor (transition metal hydroxide) and LiOH as a Li source were mixed in a mortar. LiOH as a Li source was mixed so that the ratio (molar ratio) of Li contained in the Li source to the total amount of transition metal species (Ni, Mn) contained in the transition metal hydroxide was 1.0. Further, LiOH as a molten salt was mixed so that the ratio (molar ratio) of Li of the molten salt to the total amount of transition metal species contained in the transition metal hydroxide was 0.6. That is, the total addition amount of LiOH was set to an amount such that the ratio (molar ratio) of Li contained in LiOH to the total amount of transition metal species contained in the transition metal hydroxide was 1.6. Thereby, during firing, an excessive lithium compound forms a molten salt, promoting the crystallization of the positive electrode active material into single crystals.

[0116] ​​​ <Firing> The mixture was subjected to heat treatment (calcination). It was calcined in a muffle oven at 500°C for 3 hours, then at 780°C for 12 hours (calcination process). Next, the calcined material was crushed in an agate mortar to a particle size of 0.2 mm or less, 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, rinsed with 500 mL of pure water, and the resulting cake was vacuum-dried at 90°C. After drying, the resulting dried powder was calcined at 500°C for 3 hours under oxygen flow (re-calcination). The calcined material was pulverized in an agate mortar and crushed to a predetermined particle size (pulverization). As a result, LiNi 0.90 Mn 0.10 Particles having a composition represented by O2 were obtained.

[0117] [Fabrication of the positive electrode] A slurry for the positive electrode, containing the above-mentioned particles as the positive electrode active material, acetylene black, and NMP solvent, was coated onto aluminum foil, which serves as the positive electrode current collector, using a film applicator with film thickness adjustment capabilities (Allgood Co., Ltd.) to obtain a structure having a positive electrode current collector and a positive electrode layer precursor (coating process). Neodymium magnets were fixed above and below the structure, and the structure was exposed to a magnetic field of approximately 5 Tesla for 10 minutes (orientation process). After exposure to the magnetic field, the structure was dried on an 80°C hot plate for 5 minutes to remove the NMP solvent, and then pressed (three presses using a 3-ton roll press). This resulted in obtaining a positive electrode having a positive electrode current collector (aluminum foil) and a positive electrode layer.

[0118] The obtained positive electrode was cut in the thickness direction by ion milling to obtain a cross-section of the positive electrode layer. The cross-section of the positive electrode layer was observed using a scanning electron microscope (Hitachi High-Tech Scanning Electron Microscope SU8230) at an acceleration voltage of 1 kV. In the cross-sectional SEM image, a single-crystal active material composed of crystalline primary particles was observed. 100 single-crystal active materials were randomly selected that had portions that could be identified as line segments of two sides, a short side and a long side, an angle between the short side and the long side between 60° and 120°, and an aspect ratio (ratio of the length of the long side to the length of the short side) of 1.2 or more (i.e., N A=100). N is the number of primary particles among the 100 single-crystal active materials whose tilt in the direction of the long side relative to the in-plane direction of the positive electrode layer (in-plane direction of the metal foil) is between 0° and 30°. 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.

[0119] [Battery construction] A negative electrode composite paste containing natural graphite, the negative electrode active material, was coated onto the surface of a metal foil negative electrode current collector using a film applicator with film thickness adjustment function (manufactured by AllGrid Co., Ltd.). The negative electrode was then dried in a dryer at 80°C for 5 minutes to produce a negative electrode with a negative electrode layer on the negative electrode current collector. 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%. The positive electrode, separator, and negative electrode were laminated, the separator was impregnated with the electrolyte, and a small laminate cell was fabricated with the power generation element housed in an Al laminate film pouch.

[0120] (Example 2) The 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 laminate cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0121] (Example 3) The 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 1 minute. A laminate cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0122] (Comparative Example 1) The positive electrode was prepared in the same manner as in Example 1, except that the orientation step was omitted during the preparation of the positive electrode. A laminate cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0123] (Comparative Example 2) The 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 20 seconds. A laminate cell having the same configuration as in Example 1 was obtained, except that the obtained positive electrode was used.

[0124] [evaluation] For the laminated cells, the IV resistance was measured after the initial aging and after a 100-cycle test. The 100-cycle test was performed under the following conditions. Ambient temperature: 60℃ Number of cycles: 100 Current rate: 0.3C Voltage range: 4.25V to 2.5V

[0125] The laminated cells were charged to 50% of their state of charge (SOC), then discharged and charged at 25°C with currents of 0.3C, 0.5C, 0.7C, and 1.0C. The average resistance estimated from the voltage drop / rise after 1 second was defined as the IV resistance (after initial aging). The above measurements were performed after 100 cycles of testing (after 100 cycles). The results are shown in Table 1.

[0126] [Table 1]

[0127] As shown in Table 1, N B / N A Batteries having a positive electrode layer of 50% or more (Examples 1 to 3) are N B / N A It was confirmed that this can suppress the increase in resistance after cycling compared to batteries with a positive electrode layer of less than 50% (Comparative Example 1 and Comparative Example 2). [Explanation of Symbols]

[0128] 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 0° or more and 30° or less is N. Ｂ The proportion (N Ｂ / N Ａ A positive electrode layer in which ) makes up 50% 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 56% or more and 65% or less.

4. The positive electrode layer according to claim 1, wherein the outer shape of the single-crystal active material is a rectangular parallelepiped.

5. The positive electrode layer according to claim 1, wherein the primary particles include at least Ni as TM.

6. The positive electrode layer according to claim 5, wherein the primary particles contain at least one of Co and Mn as TM.

7. The positive electrode layer according to claim 5, wherein the molar ratio of Ni to TM is 0.5 or more.

8. The positive electrode layer according to claim 1, wherein the proportion of the single-crystal active material in the positive electrode active material is 50% by weight or more.

9. The positive electrode layer according to claim 1, wherein the primary particles have a layered rock salt type crystalline structure.

10. 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 a composition represented by

11. A lithium-ion battery comprising a positive electrode layer according to any one of claims 1 to 10.

12. A method for manufacturing a positive electrode layer according to any one of claims 1 to 10, 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 0° or more and 30° or less in the direction of the long side with respect to the in-plane direction of the positive electrode layer.

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