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

Abstract

This disclosure relates to a positive electrode layer, a lithium-ion battery, and a method for manufacturing the positive electrode layer. The main objective of this disclosure is to provide a positive electrode layer for a lithium-ion battery that can suppress the increase in resistance that occurs during charging and discharging of the battery. This disclosure addresses this problem by providing a positive electrode layer as described below. The positive electrode layer is used in a lithium-ion battery and has a monocrystalline active material as the positive electrode active material. This monocrystalline active material is composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O. In a cross-sectional image of the positive electrode layer obtained using a scanning electron microscope, the monocrystalline active material includes a long side and a short side, the angle formed by the long side and the short side is 60° or more and 120° or less, and the aspect ratio (length ratio of the long side to the short side) is 1.2 or more. The long side of the monocrystalline active material extends along the (003) plane, and the angle of inclination of the long side direction relative to the in-plane direction of the positive electrode layer is 0° or more and 30° or less. The number N of such monocrystalline active materials is... B The number N of the single-crystal active material A proportion (N) B / N A The percentage is over 50%.

Description

Technical Field

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

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

[0003] In recent years, techniques have been proposed to orient active material particles and specific crystal faces within the active material along specific directions. For example, Patent Document 1 discloses plate-shaped particles for the positive electrode active material of a lithium secondary battery, which are formed as polycrystalline materials composed of multiple primary crystallized particles having a layered rock salt structure, with the (003) face of the primary crystallized particles within the plate-shaped particles oriented parallel to the plate face of the plate-shaped particles. Patent Document 2 discloses a method for manufacturing an energy storage device, comprising: using an anisotropic material with magnetic susceptibility, such as an olivine-type oxide containing a transition metal element, as active material particles; coating a slurry containing the active material particles onto a current collector; and placing 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, by applying a magnetic field, the length direction of the graphite-based negative electrode active material is aligned with the surface direction of the current collector.

[0004] [Existing Technical Documents]

[0005] [Patent Literature]

[0006] [Patent Document 1] International Publication No. 2012 / 046557

[0007] [Patent Document 2] Japanese Patent Application Publication No. 2022-66604

[0008] [Patent Document 3] Japanese Patent Application Publication No. 2015-138644 Summary of the Invention

[0009] From the viewpoint of improving battery performance, it is necessary to suppress the increase in resistance that accompanies battery charging and discharging. This disclosure was made in view of the aforementioned practical situation, and its main objective is to provide a positive electrode layer for lithium-ion batteries capable of suppressing the increase in resistance that accompanies battery charging and discharging.

[0010] [1] A positive electrode layer, which is used as a positive electrode layer in lithium-ion batteries.

[0011] The positive electrode layer has a single-crystal active material as the positive electrode active material, which is composed of crystalline primary particles containing Li, TM (TM is a transition metal) and O.

[0012] In the cross-sectional image of the positive electrode layer obtained using a scanning electron microscope

[0013] The single-crystal active material comprises a long side and a short side, wherein the angle formed by the long side and the short side is 60° or more and 120° or less, and the aspect ratio (length ratio of the long side to the short side) is 1.2 or more.

[0014] The long side of the single-crystal active material extends along the (003) plane.

[0015] The number N of single-crystal active materials whose orientation of the long side is at an angle of 0° or more and less than 30° relative to the in-plane direction of the positive electrode layer. B The number N of the single-crystal active material A proportion (N) B / N A The percentage is over 50%.

[0016] [2] Based on the positive electrode layer described in [1],

[0017] The length of the long side of the single-crystal active material is 0.5 μm or more.

[0018] [3] According to the positive electrode layer described in [1] or [2],

[0019] The ratio (N) B / N A The percentage is between 56% and 65%.

[0020] [4] The positive electrode layer according to any one of [1] to [3],

[0021] The single-crystal active material has a rectangular parallelepiped shape.

[0022] [5] The positive electrode layer according to any one of [1] to [4],

[0023] The primary particle contains at least Ni as the TM.

[0024] [6] The positive electrode layer according to any one of [1] to [5],

[0025] The primary particle contains at least one of Co and Mn as the TM.

[0026] [7] Based on the positive electrode layer described in [5],

[0027] The molar ratio of Ni to TM is 0.5 or higher.

[0028] [8] The positive electrode layer according to any one of [1] to [7],

[0029] The proportion of the single-crystal active material in the positive electrode active material is more than 50% by weight.

[0030] [9] The positive electrode layer according to any one of [1] to [8],

[0031] The primary particles have a layered rock salt-type crystal structure.

[0032]

[10] The positive electrode layer according to any one of [1] to [9],

[0033] The primary particle has Li x Ni a Co b Mn c O y (In the formula, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1) represents the composition.

[0034]

[11] A lithium-ion battery comprising a positive electrode layer as described in any one of [1] to

[10] .

[0035]

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

[10] , includes a coating process and an orientation process.

[0036] In the coating process, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material, wherein the positive electrode active material contains the single-crystal active material.

[0037] In the orientation process, the positive electrode layer precursor is exposed to a magnetic field to orient the single-crystal active material such that the angle between the direction of the long side and the in-plane direction of the positive electrode layer is 0° or more and 30° or less.

[0038] According to this disclosure, a positive electrode layer for lithium-ion batteries can be provided that can suppress the increase in resistance that accompanies battery charging and discharging. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a cross-sectional image of the positive electrode layer in this disclosure obtained using a scanning electron microscope.

[0040] Figure 2 yes Figure 1A magnified view of the single-crystal active substance P within the dashed box.

[0041] Figure 3 This is a schematic diagram showing the crystal structure of the single-crystal active material P in the positive electrode layer of this disclosure.

[0042] Figure 4 This is a schematic diagram illustrating the manufacturing process of the positive electrode layer in this disclosure.

[0043] Figure 5 This is a schematic cross-sectional view illustrating the lithium-ion battery of this disclosure.

[0044] Figure 6 This is a schematic cross-sectional view illustrating the lithium-ion battery of this disclosure.

[0045] [Explanation of reference numerals in the attached figures]

[0046] 1… Positive electrode layer

[0047] 2…Positive current collector

[0048] 3…Electrolyte layer

[0049] 4… Negative electrode layer

[0050] 5… Negative current collector

[0051] 10…Lithium-ion batteries Detailed Implementation

[0052] The present disclosure will now be described in detail with the aid of accompanying drawings. The figures shown below are illustrative, and the size and shape of the parts are sometimes exaggerated for ease of understanding.

[0053] A. Positive electrode layer

[0054] The positive electrode layer disclosed herein is a positive electrode layer used in lithium-ion batteries. The positive electrode layer has a single-crystal active material as the positive electrode active material. This single-crystal active material is composed of crystalline primary particles containing Li, TM (TM is a transition metal), and O. In a cross-sectional image of the positive electrode layer obtained using a scanning electron microscope, the single-crystal active material includes a long side and a short side. The angle formed by the long side and the short side is 60° or more and 120° or less. Furthermore, the aspect ratio (length ratio of the long side to the short side) is 1.2 or more. The long side of the single-crystal active material extends along the (003) plane. The number N of single-crystal active materials whose direction of the long side has an inclination angle of 0° or more and 30° or less relative to the in-plane direction of the positive electrode layer is... B The number N of the single-crystal active material A proportion (N) B / N A The percentage is over 50%.

[0055] Figure 1 This is a schematic diagram of a cross-sectional image (hereinafter also referred to as a cross-sectional SEM image) of the positive electrode layer in this disclosure obtained by scanning electron microscopy. Figure 2 yes Figure 1 A magnified view of the single-crystal active substance P within the dashed box. Figure 3 This is a schematic diagram showing the crystal structure of the single-crystal active material P in the positive electrode layer of this disclosure. (Example) Figure 1 As shown, the positive electrode layer 1 in this disclosure has a single-crystal active material P composed of crystalline primary particles containing Li, TM (TM is a transition metal) and O as the positive electrode active material. Figure 2 As shown, in the cross-sectional SEM image of the positive electrode layer 1, the single-crystal active material P includes a long side a and a short side b, the angle θ formed by the long side a and the short side b is 60° or more and 120° or less, and the aspect ratio La / Lb, 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. Figure 3 As shown, the (003) face is a crystal face that does not produce lithium ion ingress and egress.

[0056] As mentioned above, a cathode layer capable of suppressing the increase in resistance accompanying battery charging and discharging is required. In particular, layered cathode active materials containing Ni are expected to increase discharge capacity. However, since charging and discharging inevitably lead to the contraction and expansion of the crystal lattice along the stacking direction (c-axis), the resulting interruption of conductive pathways and degradation of the crystal structure easily result in high resistivity. This is presumably because, during charging, Li ions are pulled out from the Li layer, causing the Li layer to contract along the stacking direction (c-axis), resulting in an exchange phenomenon (cation mixing) between Li ions in the Li layer and Ni ions in the transition metal layer. This causes a portion of the layered structure to change towards a rock salt structure. High resistivity becomes particularly pronounced when charging and discharging in high potential regions, such as above 4.1V.

[0057] In contrast, in this disclosure, the positive electrode active material is a single-crystal active material P composed of crystalline primary particles. In a cross-sectional SEM image of the positive electrode layer 1, the single-crystal active material P has a defined shape, with its long side a extending along the (003) plane. It is believed that when the single-crystal active material is longer along the (003) plane, the Li layer is broad, and therefore the detachment of Li ions from the Li layer proceeds relatively slowly. It is believed that the Li ions remaining in the Li layer act as so-called pillars, thus mitigating the shrinkage of the Li layer and making structural degradation less likely. However, even when using such a single-crystal active material P, it is sometimes not possible to sufficiently suppress the increase in resistance accompanying charge and discharge. In this disclosure, as Figures 1-3As shown, by tilting the single-crystal active material P with its long side a relative to the in-plane direction D of the positive electrode layer 1... P The orientation is changed to be approximately parallel (above 0° and below 30°) so that the (003) surface, which does not allow lithium ions to enter or leave the cathode layer, is aligned with the direction of lithium ion diffusion within the cathode layer (the thickness direction of the cathode layer). T The primary particles are oriented in a roughly vertical direction. Therefore, even with repeated charging and discharging, the durability of the crystal structure is improved, suppressing the increase in resistance associated with the charging and discharging of the lithium-ion battery. Furthermore, Patent Document 1 does not describe adjusting the orientation of the plate-shaped particles. Therefore, the battery resistance tends to increase with charging and discharging.

[0058] In this disclosure, the monocrystalline active material is oriented such that its length direction (long side a) is approximately parallel to the in-plane direction of the positive electrode layer. Therefore, compared to the case where the length direction of the primary particles is not adjusted, the direction of expansion and contraction of the monocrystalline active material during battery charging and discharging is consistent. Furthermore, compared to monocrystalline active materials oriented with their length direction orthogonal to the plane of the positive electrode layer, the force exerted on the monocrystalline active material during its expansion and contraction is smaller when oriented in this manner. For these reasons, the breakage of the monocrystalline active material can be suppressed, and the increase in resistance during battery charging and discharging can be suppressed.

[0059] Furthermore, in this specification, the cross-sectional SEM image of the positive electrode layer is obtained, for example, by performing cross-sectional alignment processing on the positive electrode layer using an ion milling apparatus and observing the cross-section of the positive electrode layer using a scanning electron microscope. The magnification of the cross-sectional SEM image can be, for example, 2000x or more and 20000x or less. As the scanning electron microscope, the SEM apparatus "Product Name SU8230" manufactured by Hitachi High Technologies Co., Ltd. can be used. Various dimensional measurements and shape analyses in the cross-sectional SEM image can be performed, for example, using image analysis software such as "ImageJ".

[0060] The positive electrode layer is described in detail below.

[0061] 1. Positive electrode active material

[0062] The positive electrode layer of this disclosure includes a positive electrode active material. The positive electrode active material of this disclosure includes a single-crystal active material, which is composed of crystalline primary particles containing Li, TM (TM being a transition metal), and O. In a cross-sectional image of the positive electrode layer obtained using a scanning electron microscope, the single-crystal active material includes a long side and a short side, the angle formed by the long side and the short side being 60° or more and 120° or less, and the aspect ratio (length ratio of the long side to the short side) is 1.2 or more. The long side of the single-crystal active material extends along the (003) plane, and the angle of inclination of the long side direction relative to the in-plane direction of the positive electrode layer is 0° or more and 30° or less. The number N of such single-crystal active materials is... B The number N of active materials relative to the single crystal system A proportion (N) B / N A The percentage is over 50%.

[0063] The term "monocrystalline active material" refers to active materials that are not polycrystalline (active materials in which multiple primary particles are aggregated without gaps). Monocrystalline active materials typically exist as independent, single particles without aggregation. Ideally, monocrystalline active materials should not have visible grain boundaries when observed using SEM (magnification: approximately 10,000 to 30,000 times).

[0064] Compared to polycrystalline active materials, monocrystalline active materials have the advantage of less degradation over time. Furthermore, polycrystalline active materials, composed of secondary particles, are prone to fracture, easily exposing newly formed internal surfaces. These newly formed surfaces react with the electrolyte, generating resistive components. On the other hand, the positive electrode active material in the positive electrode layer of this disclosure comprises a monocrystalline active material. Monocrystalline active materials are less likely to exert stress on polycrystalline active materials, thus making them less prone to fracture; therefore, compared to polycrystalline active materials, they can suppress the increase in resistance accompanying charge and discharge.

[0065] The primary particles in this disclosure contain Li, TM (TM being a transition metal), and O. A primary particle may contain one, two, three, or more transition metals.

[0066] Transition metals are metals belonging to groups 3 through 11 of the periodic table. A primary particle may contain a transition metal belonging to period 3, 4, or 5. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, La, and W.

[0067] The primary particles preferably contain at least Ni as TM. This is because a positive electrode active material with good capacity characteristics can be obtained. The molar ratio of Ni to TM (all transition metals contained in the primary particles) is, for example, 0.25 or more, 0.33 or more, 0.50 or more, 0.70 or more, or 0.80 or more. By increasing the proportion of Ni, the capacity characteristics are improved.

[0068] The primary particles preferably contain at least one of Co and Mn as TM.

[0069] In a primary particle, TM may or may not contain Co. The molar ratio of Co to TM (all transition metals contained in the primary particle) is, for example, 0 or more, 0.05 or more, or 0.10 or more. On the other hand, the molar ratio of Co to TM is, for example, 0.40 or less, or 0.20 or less.

[0070] In a primary particle, TM may or may not contain Mn. The molar ratio of Mn to TM (all transition metals contained in the primary particle) is, for example, 0 or more, 0.05 or more, or 0.10 or more. On the other hand, the molar ratio of Mn to TM is, for example, 0.40 or less, or 0.20 or less.

[0071] In the primary particle, TM preferably contains at least one of Ni, Co, and Mn. The molar ratio of the total of Ni, Co, and Mn to TM (all transition metals contained in the primary particle) is, for example, 0.80 or more, 0.90 or more, or 0.95 or more. Furthermore, the phrase "total of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0072] Primary particles can also contain other metals besides Li and TM, such as M. 1 (Including semi-metals). As other metals M 1 For example, metals belonging to groups 12 to 14 in the periodic table can be cited. Examples of metals belonging to groups 12 to 14 include Zn, Al, Si, Ga, Ge, In, and Sn.

[0073] The composition of primary particles is not particularly limited; for example, it can be based on the general formula Li. x Ni a Co b Mn c O yThe composition represented by (0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1).

[0074] The x represents the molar ratio of Li relative to the total of Ni, Co, and Mn, which is typically 0.1 or more, but can be 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, or 1.05 or more. On the other hand, the x is typically 1.5 or less, 1.4 or less, or 1.2 or less.

[0075] The y represents the molar ratio of O to the total of Ni, Co, and Mn, which is typically 1.5 or higher, but can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher. On the other hand, the y is typically 2.1 or lower, and can be 2.0 or lower.

[0076] The term 'a' represents the molar ratio of Ni to the total of Ni, Co, and Mn, and is typically 0.5 or higher, but can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher. On the other hand, 'a' is typically 1.0 or lower, and can be 0.9 or lower.

[0077] The b represents the molar ratio of Co relative to the total of Ni, Co, and Mn, and is typically 0 or higher, but can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. On the other hand, the b is typically 0.30 or lower, but can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0078] The 'c' represents the molar ratio of Mn to the total of Ni, Co, and Mn, and is typically 0 or higher, but can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. Conversely, the 'c' is typically 0.30 or lower, but can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0079] In the formula, the molar ratios of Ni (a), Co (b), and Mn (c) satisfy the relationship a + b + c = 1.0.

[0080] The positive electrode active material in this disclosure, for example, has LiNi 0.90 Mn 0.10 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, or LiNi 0.9 Co 0.05 Mn 0.05 O2 represents the composition.

[0081] In this disclosure, the composition of the positive electrode active material can be determined, for example, by dissolving the positive electrode active material in acid and measuring it using ICP emission spectroscopy (ICP-OES).

[0082] As a primary particle crystal structure, layered rock salt is preferred. The crystal structure of layered rock salt is usually classified into space group R-3m.

[0083] In this disclosure, such as Figure 1 and Figure 2As shown, the single-crystal active material P, composed of primary particles, in a cross-sectional image of the cathode layer obtained using a scanning electron microscope, includes a long side a and a short side b. The angle θ formed by the long side a and the short side b is 60° or more and 120° or less, and the aspect ratio (length ratio of the long side a to the short side b) is 1.2 or more. Furthermore, the long side a in the cross-sectional SEM image of the cathode layer appears to be the longest side of the single-crystal active material P. The short side b connects to the end of the long side a. The short side b represents the longest side in the cross-sectional SEM image among the sides connected to the long side a. The short side b extends from the end of the long side a in a direction intersecting the direction in which the long side a extends. The long side a and the short side b can extend in a straight line. On the other hand, the long side a and the short side b can be curved. In the case of a curved side, the length of the side represents the distance between the two ends of the side.

[0084] In this disclosure, in the cross-sectional SEM image of the cathode layer, the direction of the long side a is relative to the in-plane direction D of the cathode layer. P The number N of single-crystal active material P with a tilt angle of 0° or more and 30° or less B The amount N of active material P relative to the single crystal system A proportion (N) B / N A The content of the single-crystal active material P is 50% or more. That is, in this disclosure, more than 50% of the single-crystal active material P is in the in-plane direction D relative to the positive electrode layer. P Oriented in roughly parallel directions.

[0085] Ratio (N) B / N A The specific measurement method is as follows. First, in the cross-sectional SEM image of the positive electrode layer, 100 single-crystal active materials P(N) containing both a long side and a short side, with the angle between the long side and the short side being greater than 60° and less than 120°, and the ratio of the length of the long side to the length of the short side (i.e., the aspect ratio) being greater than 1.2, are randomly selected. A =100). For each of the 100 extracted single-crystal active substances P, such as Figure 2 As shown, the direction of the long side a is measured relative to the in-plane direction D of the positive electrode layer. P Inclination angle θ D The tilt angle θ of 100 single-crystal active materials P D The number of single-crystal active substances P with a temperature above 0° and below 30° is denoted as N. B Therefore, the ratio (N) can be calculated. B / N A ).

[0086] In this disclosure, the long side of the single-crystal active material extends along the (003) plane. By making the ratio (N... B / N AWith a content of over 50%, the (003) surface of the single-crystal active material can be arranged approximately parallel to the in-plane direction of the positive electrode layer, which can suppress the increase in battery resistance as the lithium-ion battery is charged and discharged.

[0087] The ratio (N) B / N A The percentage (N) can be 56% or more, or 58% or more. On the other hand, the percentage (N) B / N A For example, it can be below 100%, below 99%, below 95%, below 90%, below 80%, below 70%, or below 65%.

[0088] The number N of single-crystal active materials whose inclination angle relative to the in-plane direction of the long side a is greater than 30° and less than 50° with respect to the in-plane direction of the positive electrode layer. C The number N of active materials relative to the single crystal system A proportion (N) C / N A For example, it can be below 40%, or below 30%.

[0089] The number N of single-crystal active materials whose inclination angle relative to the in-plane direction of the long side a is greater than 50° and less than 90° with respect to the in-plane direction of the positive electrode layer. D The number N of active materials relative to the single crystal system A proportion (N) D / N A For example, it can be below 20%, or below 10%.

[0090] The aspect ratio of single-crystal active materials is 1.2 or higher, and can be 1.3 or higher, 1.4 or higher, 1.6 or higher, 1.8 or higher, 2.0 or higher, 2.5 or higher, 3.0 or higher, 3.5 or higher, 4.0 or higher, 4.5 or higher, 5.0 or higher, 5.5 or higher, 6.0 or higher, 6.5 or higher, or 7.0 or higher. An aspect ratio of, for example, can be below 10.0, below 9.0, or below 8.0.

[0091] For single-crystal active materials, the long side 'a' can be 0.5 μm or more, or 1.0 μm or more, or 1.5 μm or more, or 2.0 μm or more, or 2.5 μm or more, or 3.0 μm or more, or 3.5 μm or more, or 4.0 μm or more. The long side 'a' can be 6.0 μm or less, or 5.0 μm or less.

[0092] For single-crystal active materials, the short side b can be 0.2 μm or more, or 0.5 μm or more, or 0.8 μm or more, or 1.0 μm or more, or 1.5 μm or more, or 1.7 μm or more, or 1.9 μm or more. The short side b can be 5.0 μm or less, or 4.0 μm or less, or 3.0 μm or less, or 2.0 μm or less.

[0093] In single-crystal active materials, the angle (interior angle) θ formed by the long side a and the short side b is greater than 60° and less than 120°, greater than 70° and less than 110°, or greater than 80° and less than 100°.

[0094] In this disclosure, the long side a extends along the (003) plane. The (003) plane can be determined in a high-angle scattering annular dark-field scanning transmission microscope (HAADF-STEM) image. For example, a powder containing a single-crystal active material is embedded in epoxy resin. For example, a sample is prepared by thinning the powder together with the resin using an argon ion milling method. First, the single-crystal active material is extracted at low magnification. The long side a of the single-crystal active material is determined. Next, the (003) plane is determined by observing the single-crystal active material at high magnification. When the angle formed by the (003) plane and the long side a is 0° to 30°, the long side a is considered to extend along the (003) plane. In the STEM image, if the long side a extends along the (003) plane in one or more of the randomly selected single-crystal active materials, the long side a is considered to extend along the (003) plane throughout the entire powder.

[0095] The angle formed by the long side a and the (003) plane in the single-crystal active material is, for example, less than 25°, less than 15°, less than 10°, less than 5°, less than 3°, or less than 1°. Among 10 single-crystal active materials randomly selected from the STEM image, the proportion of single-crystal active materials with the long side a along the (003) plane can be, for example, more than 20%, more than 30%, more than 40%, more than 50%, more than 60%, more than 70%, more than 80%, or more than 90%.

[0096] The shape of a single-crystal active material can be, for example, polyhedral. The shape of a single-crystal active material can also be hexahedral, octahedral, etc. The shape of a single-crystal active material can also be cuboid.

[0097] Primary particles, for example, possess crystal structures belonging to space group R-3m. The space group to which the crystal structure belongs is determined by XRD (X-Ray Diffraction) plots. XRD plots are obtained through powder XRD measurements under the following conditions:

[0098] Analysis method: Wide-angle method

[0099] Measurement apparatus: Smart Lab II (manufactured by Rigaku Corporation)

[0100] Measurement angle: 10° to 120°

[0101] Tube: CuKα

[0102] Tube voltage: 45kV

[0103] Tube current: 200mA

[0104] Determination method: Continuous method

[0105] Step size: 0.02°

[0106] Speed: 2° / minute

[0107] IS: 1 / 2

[0108] RS: 20mm

[0109] Detection mode: One-dimensional

[0110] The single-crystal active material in this disclosure preferably has no coating layer formed on its surface. Examples of coating layers include carbon coatings.

[0111] The positive electrode active material in this disclosure may include a polycrystalline active material (polycrystalline particles) composed of secondary particles of the primary particles, or it may not include it. The proportion of monocrystalline active material in the positive electrode active material is, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. On the other hand, the proportion of monocrystalline active material in the positive electrode active material is, for example, 100% by weight or less.

[0112] The content of the positive electrode active material in the positive electrode layer can be, for example, 20% by weight or more, 30% by weight or more, 40% by weight or more, 50% by weight or more, 60% by weight or more, or 70% by weight or more. If the content of the positive electrode active material is too low, there is a possibility that insufficient energy density may not be obtained. On the other hand, the content of the positive electrode active material can be, for example, 95% by weight or less, 90% by weight or less, or 80% by weight or less. If the content of the positive electrode active material is too high, there is a possibility that the ionic conductivity and electronic conductivity in the positive electrode layer may be relatively reduced. 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 composition of the positive electrode layer is set to 100% by weight.

[0113] Method for manufacturing positive electrode active material

[0114] The positive electrode active material disclosed herein can be manufactured by performing a process of synthesizing a transition metal hydroxide, a calcination process of heating a mixture of the transition metal hydroxide, a Li source and a molten salt (flux), and a pulverization process of pulverizing the calcined material.

[0115] (a) Transition metal hydroxide synthesis process

[0116] Transition metal hydroxides are precursors for positive electrode active materials. Transition metal hydroxides can be obtained by crystallization of various transition metal compounds in a solvent to form precipitates.

[0117] There are no particular limitations on the synthesis method of transition metal hydroxides; for example, the following methods can be used. First, prepare an aqueous solution of the transition metal hydroxide as a raw material. For example, a method for preparing the aqueous solution can be to dissolve a water-soluble transition metal compound in water. For example, metal salts such as sulfates and nitrates can be used as transition metal compounds. For example, NiSO4 and Ni(NO3)2 can be used as Ni sources. For example, CoSO4, Co(NO3)2, and Co(NO3)3 can be used as Co sources. For example, MnSO4 and Mn(NO3)2 can be used as Mn sources. The composition of the aqueous solution can be appropriately adjusted according to the target positive electrode active material.

[0118] Next, a certain amount of NH3 aqueous solution is added to the reaction vessel, and while stirring with a stirrer, nitrogen is used to replace the NH3 to create a non-oxidizing atmosphere. Then, sodium hydroxide aqueous solution is added to the reaction vessel to maintain an alkaline pH, the temperature is controlled, and the raw material aqueous solution is added dropwise to the reaction vessel, thereby forming a reaction solution. By adjusting the pH of the reaction solution, a precipitate (crystal) of transition metal hydroxide can be formed.

[0119] After the precipitation reaction is completed, pre-firing is performed. The pre-firing conditions are, for example, a temperature of 120°C or higher and 220°C or lower, a time of 4 hours or higher and 10 hours or lower, and a pressure of 0.2 MPa or higher and 1.0 MPa or lower.

[0120] The precipitate, after pre-calcination and water washing, is filtered to remove the transition metal hydroxides, and then dried. The drying temperature is, for example, above 100°C and below 150°C. The drying time is, for example, above 8 hours and below 24 hours.

[0121] (b) Firing process

[0122] The obtained transition metal hydroxide, Li source, and molten salt (flux) are mixed to obtain a mixture. The Li source is a lithium compound, for example, at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride. The molar ratio of Li in the Li source to TM contained in the transition metal hydroxide is, for example, 0.8 or more and 1.2 or less, 0.9 or more and 1.1 or less, or 1.0.

[0123] The mixture typically contains a molten salt. The presence of a molten salt in the mixture allows for sufficient primary particle growth. The molar ratio of Li in the molten salt to TM in the transition metal hydroxide is typically 0.1 or more and 1.0 or less, and can be 0.2 or more and 0.6 or less. The molten salt can be a lithium compound of the same type as the Li source. For example, lithium hydroxide is used as the molten salt. When lithium hydroxide is used as the Li source, by ensuring that the amount of lithium hydroxide added relative to the transition metal hydroxide is less than the stoichiometric ratio of the target positive electrode active material, lithium hydroxide acts as a flux, allowing for sufficient primary particle growth. The molar ratio of the total Li in the Li source and the molten salt to TM in the transition metal hydroxide is, for example, 1.1 or more and 2.0 or less, and can be 1.2 or more and 1.6 or less. The mixing method of the transition metal hydroxide, the Li source, and the molten salt is arbitrary. For example, it can be mixed using a mortar and pestle.

[0124] In this disclosure, a mixture containing a transition metal hydroxide, a Li source, and a molten salt is subjected to heat treatment. The firing temperature is, for example, 500°C or higher and 1100°C or lower, or 650°C or higher and 1100°C or lower, or 700°C or higher and 900°C or lower. In this disclosure, it is preferable to perform multi-stage firing of the mixture containing the transition metal hydroxide, Li source, and molten salt at various 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 at a predetermined firing temperature T1 for a predetermined time, then raise the temperature to the firing temperature T2 for the next firing stage, and fire at the firing temperature T2 for a predetermined time. The firing temperature T1 is, for example, 500°C or higher and 650°C or lower, or 500°C or higher and 600°C or lower. The firing temperature T2 is higher than the firing temperature T1, for example, 650°C or higher and 1100°C or lower, or 750°C or higher and 1000°C or lower. Firing can be done in two stages, three stages, or four or more stages. The total firing time for each stage can be, for example, more than 5 hours and less than 18 hours, or more than 8 hours and less than 15 hours.

[0125] In the case of multi-stage firing, molten salt can be added to the mixture in such a way that the Li / TM (molar ratio) in the mixture increases with each firing stage. For example, for a mixture containing a transition metal hydroxide and a Li source, after firing at a predetermined firing temperature T1 for a predetermined time, molten salt is added, and the temperature is raised to the firing temperature T2 for the next firing stage. Then, firing is carried out at the firing temperature T2 for a predetermined time. Molten salt can be added such that the total molar ratio of Li in the Li source and molten salt relative to the TM in the transition metal hydroxide is within the range described until the final firing stage. Firing can be performed using any heat treatment furnace, such as a muffle furnace, electric furnace, etc.

[0126] Next, the calcined material is pulverized to a specified particle size, for example, an average particle size of less than 0.2 μm. This pulverization can be performed using an agate mortar. Then, the pulverized material is washed by dispersing it in pure water and stirring. The washed slurry is then filtered, rinsed, and vacuum dried.

[0127] The resulting dry powder can be subjected to post-annealing (re-firing). Post-annealing is carried out in an oxygen atmosphere. The firing temperature in post-annealing is, for example, above 500°C and below 800°C, and the firing time is, for example, above 1 hour and below 5 hours.

[0128] (c) Crushing process

[0129] Next, the calcined material is pulverized to a specified particle size. This pulverization can be performed using an agate mortar and pestle or a grinding mill such as a laboratory mill. After pulverization, further processing such as grading and granulation can be carried out. Through the above process, a positive electrode active material with a specified composition and containing single-crystal active material is obtained.

[0130] 2. Positive electrode layer

[0131] The positive electrode layer contains the aforementioned positive electrode active material, and may further contain conductive materials and binders as needed. The positive electrode layer may also contain an electrolyte. The electrolyte may be, for example, the electrolyte solution described later. Alternatively, the positive electrode layer may contain a solid electrolyte.

[0132] Examples of conductive materials include graphite, acetylene black (AB), Ketjen black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene sheets (GF). The content of the conductive material in the positive electrode layer relative to 100 parts by weight of the positive electrode active material can be, for example, 0.1 parts by weight or more and 10 parts by weight or less.

[0133] Examples of binders include polyvinylidene fluoride (PVdF), PVdF-HFP copolymer, polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ethers, and their derivatives. The binder content in the positive electrode layer may be, for example, 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0134] The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[0135] The positive electrode layer can be formed, for example, by the method described in "C. Method for manufacturing the positive electrode layer".

[0136] In the cross-sectional SEM images of the cathode layer in this disclosure, there may also be single-crystal active materials that are not observed in the specific shape described. Examples of such single-crystal active materials include those that, although having substantially the same shape as single-crystal active materials observed in the specific shape, appear as small particles or dots because the portions at the ends of the active material particles are cut off during cross-sectional alignment of the cathode layer.

[0137] B. Lithium-ion batteries

[0138] The lithium-ion battery disclosed herein includes the positive electrode layer used in lithium-ion batteries. That is, this disclosure provides a battery in which a positive electrode layer, an electrolyte layer, and a negative electrode layer are stacked sequentially, and the positive electrode layer is the aforementioned positive electrode layer. Figure 5 This is a schematic cross-sectional view illustrating the lithium-ion battery of this disclosure. Figure 5 The lithium-ion battery 10 shown is along the thickness direction D T It has a negative current collector 5, a negative electrode layer 4, an electrolyte layer 3, a positive electrode layer 1, and a positive current collector 2 in sequence. The negative current collector 5 and the negative electrode layer 4 constitute the negative electrode AN, and the positive electrode layer 1 and the positive current collector 2 constitute the positive electrode CA.

[0139] According to this disclosure, the lithium-ion battery has the aforementioned positive electrode layer, thus enabling the suppression of resistance increase accompanying battery charging and discharging.

[0140] 1. Positive electrode layer

[0141] As the positive electrode layer, it is the same as the content recorded in "A. Positive Electrode Layer".

[0142] 2. Negative electrode layer

[0143] The negative electrode layer contains at least a negative electrode active material, and may also contain at least one of an electrolyte, a conductive material, and a binder, as needed. Examples of negative electrode active materials include silicon and Si alloys, tin and tin alloys, silicon-based active materials such as 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.

[0144] The negative electrode active material can be in particle or sheet form. The average particle size of the negative electrode active material can be, for example, 1 μm or more. Alternatively, the average particle size of the negative electrode active material can be, for example, 30 μm or less.

[0145] Regarding the conductive materials, adhesives, and electrolytes used in the negative electrode layer, examples can be made of the same substances described in the description of the positive electrode layer.

[0146] 3. Electrolyte layer

[0147] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. The electrolyte is, for example, a liquid electrolyte (electrolyte).

[0148] As an example of an electrolyte, non-aqueous electrolytes can be cited. Non-aqueous electrolytes, for example, contain lithium salts and non-aqueous solvents. Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0149] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Non-aqueous solvents can also be mixtures of cyclic carbonates such as EC and PC, which have high dielectric constants and high viscosity, and chain carbonates such as DMC, DEC, and EMC, which have low dielectric constants and low viscosity. The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.3 M or more and 5 M or less. Furthermore, the non-aqueous electrolyte may contain ionic liquids. Examples of ionic liquids include sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidineonium salts, morpholinium salts, phosphonium salts, and imidazolium salts.

[0150] Other examples of electrolytes include aqueous electrolytes. Aqueous electrolytes are electrolytes whose main component contains water as a solvent. The proportion of water to the total solvent is, for example, 50% by mass or more, and can be 70% by mass or more. Examples of lithium salts used in aqueous electrolytes include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, which are imide-based electrolytes. The concentration of the lithium salt in the aqueous electrolyte is, for example, 1 M or more and 25 M or less.

[0151] The electrolyte layer may also include a membrane capable of impregnating the electrolyte. By providing a membrane, the occurrence of internal short circuits can be suppressed. The membrane may be, for example, a porous membrane. Examples of membrane materials include resins such as polyethylene, polypropylene, polyester, polyvinyl alcohol, cellulose, and polyamide. Furthermore, the electrolyte layer may 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.

[0152] 4. Positive current collector

[0153] Materials used for the positive current collector include, for example, stainless steel (SUS), Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be, for example, foil-like, mesh-like, or porous. The top view shape of the positive current collector is not particularly limited; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The positive current collector can also be composed of a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0154] 5. Negative current collector

[0155] Materials used for the negative current collector include, for example, stainless steel (SUS), aluminum, copper, nickel, iron, titanium, and carbon. Furthermore, the thickness of the negative current collector varies depending on its shape, typically ranging from 1 μm to 50 μm. The shape of the negative current collector can be, for example, foil or plate. The top view shape of the negative current collector is not particularly limited; examples include circular, elliptical, rectangular, and arbitrary polygonal shapes. The negative current collector can also be configured with a buffer layer, elastic layer, or PTC thermistor layer disposed on its surface.

[0156] 6. Lithium-ion batteries

[0157] The battery disclosed herein may have an outer casing that houses the power generation elements (positive electrode layer, electrolyte layer, and negative electrode layer). Examples of such outer casings include shell-type outer casings and laminated outer casings.

[0158] The lithium-ion batteries disclosed herein are typically secondary batteries. When the positive electrode layer, electrolyte layer, and negative electrode layer are used as a set as a power generation unit, the lithium-ion battery disclosed herein can be a single cell with only one power generation unit, or a stacked battery with two or more power generation units. The stacked battery can be a unipolar stacked battery (parallel-connected stacked battery) or a bipolar stacked battery (series-connected stacked battery).

[0159] Figure 6 This is a schematic cross-sectional view illustrating the case where the lithium-ion battery in this disclosure is a bipolar battery. Figure 6 The lithium-ion battery 10 shown 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. Figure 6 The lithium-ion battery 10 shown has bipolar electrodes BP (BP1~BP29) as electrodes. Furthermore, the lithium-ion battery 10 has a positive electrode side end electrode CA and a negative electrode side 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 disposed on one surface of the current collector 6, and the negative electrode layer 4 is disposed on the other surface of the current collector 6. The positive electrode side end electrode CA has a current collector 6 and a positive electrode layer 1. The positive electrode layer 1 is disposed on one surface of the current collector 6. The negative electrode side end electrode AN has a current collector 6 and a negative electrode layer 4. The negative electrode layer 4 is disposed on one surface of the current collector 6.

[0160] The lithium-ion battery 10 of this disclosure may have only one bipolar electrode BP, or it may have two or more bipolar electrodes BP. On the other hand, the battery of this disclosure may also not have bipolar electrodes.

[0161] The applications of lithium-ion batteries are not particularly limited; examples include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred for use as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can be used as power sources for mobile bodies other than vehicles (such as trains, ships, and airplanes), and also as power sources for electrical products such as information processing devices.

[0162] C. Manufacturing method of the positive electrode layer

[0163] The method for manufacturing the positive electrode layer disclosed herein includes a coating step and an orientation step. In the coating step, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material and a solvent. The positive electrode active material contains the single-crystal active material. In the orientation step, the positive electrode layer precursor is exposed to a magnetic field to orient the single-crystal active material such that the angle between the direction of the long side and the in-plane direction of the positive electrode layer is 0° or more and 30° or less.

[0164] According to this disclosure, a single-crystal active material can be easily oriented such that the long side is tilted relative to the in-plane direction of the cathode layer and becomes approximately parallel (0° or more and 30° or less).

[0165] 1. Coating process

[0166] In this process, for example, a positive electrode slurry is obtained by mixing the positive electrode active material containing the single-crystal active material with a solvent, and the positive electrode slurry is coated onto a positive electrode current collector, thereby obtaining a positive electrode layer precursor as a coating layer on the positive electrode current collector. The single-crystal active material and the positive electrode active material are the same as those described in "A. Positive Electrode Layer 1. Positive Electrode Active Material".

[0167] Examples of solvents include N-methylpyrrolidone (NMP), tetrahydronaphthalene, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and may contain two or more of these components.

[0168] 2. Orientation process

[0169] This process exposes the cathode layer precursor to a magnetic field, causing the single-crystal active material to be oriented with an angle of 0° or more and 30° or less relative to the in-plane direction of the cathode layer, with the direction of the long side being the inclination angle of the long side relative to the in-plane direction of the cathode layer. Figure 4 This is a schematic diagram showing the application of a magnetic field in this process. For example... Figure 4 As shown, in the coating process, for example, a structure 20 having a positive current collector 2 and a positive electrode layer precursor 1′ is obtained by coating a slurry containing a single-crystal active material P onto the positive current collector 2. Then, the S pole 30a and N pole 30b of neodymium magnets are fixed above and below the structure 20, exposing it to a magnetic field. This allows the orientation of the long side of the single-crystal active material P to be adjusted to be approximately parallel to the in-plane direction of the positive electrode layer (the in-plane direction of the current collector). The magnitude of the magnetic field is, for example, 5 Tesla or more and 10 Tesla or less. The exposure time to the magnetic field is, for example, 1 minute or more and 20 minutes or less, and can be 1 minute or more and 10 minutes or less.

[0170] After the orientation process, drying and pressing are performed as needed. Examples of pressing include roller pressing and flat pressing. Furthermore, if drying and pressing are performed without an orientation process, the ratio (N) B / N A The content is usually less than 50%, and sometimes less than 40%. The above method can be used to manufacture the positive electrode layer.

[0171] Furthermore, this disclosure is not limited to the described embodiments. The described embodiments are illustrative and are embodiments that have substantially the same structure and achieve the same effect as the technical concept described in the claims of this disclosure. Regardless of the embodiment, it is included in the technical scope of this disclosure.

[0172] Example

[0173] (Example 1)

[0174] Synthesis of positive electrode active materials

[0175] The following method is used to obtain LiNi 0.90 Mn 0.10 O2 represents the composition of the positive electrode active material.

[0176] <Preparation of raw material aqueous solution>

[0177] First, a raw material aqueous solution was prepared by dissolving NiSO4 and MnSO4 in ion-exchanged water. The mixing ratio of NiSO4 and MnSO4 was adjusted to achieve a Ni / Mn ratio of 90 atomic% / 10 atomic%. The concentration of the raw material aqueous solution was set to 0.2 mol%.

[0178] <Dehydration and Pre-firing>

[0179] A prescribed amount of NH3 aqueous solution was added to the reaction vessel, and nitrogen was purged while stirring. NaOH was added to the reaction vessel to adjust the pH of the aqueous solution to alkaline. The pH of the reaction vessel was controlled to maintain a specific level, the temperature was controlled, and the raw material aqueous solution was added dropwise, thereby precipitating the transition metal hydroxide. After the precipitation reaction was completed, the precipitate was dehydrated and pre-calcined under the following temperature and pressure conditions.

[0180] Temperature: 120℃

[0181] • Duration: 8 hours

[0182] Pressure: 1.0 MPa

[0183] <Precursor Recycling>

[0184] After pre - calcination, the precipitate is washed with water. The washed precipitate is filtered to obtain the transition metal hydroxide. Then, it is dried at 110 °C for 12 hours to evaporate the moisture (the dried product). Thus, the precursor is prepared.

[0185] <Mixing of Li raw material and molten salt>

[0186] The obtained precursor (transition metal hydroxide) and LiOH as the Li source are mixed in a mortar. LiOH as the Li source is mixed in such a way that the proportion (molar ratio) of Li contained in the Li source to the total amount of transition metals (Ni, Mn) contained in the transition metal hydroxide is 1.0. Further, LiOH as the molten salt is mixed in such a way that the proportion (molar ratio) of Li in the molten salt to the total amount of transition metals contained in the transition metal hydroxide is 0.6. That is, the total addition amount of LiOH is set to a quantity such that the proportion (molar ratio) of Li contained in LiOH to the total amount of transition metals contained in the transition metal hydroxide is 1.6. Thus, during firing, the excess lithium compound forms a molten salt, thereby promoting the single - crystallization of the positive electrode active material.

[0187] <Firing>

[0188] The mixture is subjected to heat treatment (firing). After firing at 500 °C for 3 hours using a muffle furnace, it is fired at 780 °C for 12 hours (firing process). Then, after the fired product is pulverized to a particle size of 0.2 mm or less using an agate mortar, it is dispersed in 500 mL of pure water and vigorously stirred for 1 minute to obtain a slurry. The slurry is filtered using a Buchner funnel and filter paper, washed with 500 mL of pure water, and the obtained filter cake is vacuum - dried at 90 °C. After drying, the obtained dry powder is fired at 500 °C for 3 hours in an oxygen flow (re - firing). The fired product is pulverized using an agate mortar and crushed to a specified particle size (pulverization). Thus, particles with a composition represented by LiNi 0.90 Mn 0.10 O2 are obtained.

[0189] [Fabrication of positive electrode]

[0190] A slurry for the positive electrode, comprising the particles (as the positive electrode active material), acetylene black, and NMP solvent, is coated onto an aluminum foil serving as the positive electrode current collector using a film coating applicator (Allgood Co., Ltd.) equipped with a film thickness adjustment function, resulting in a structure having a positive electrode current collector and a positive electrode layer precursor (coating process). Neodymium magnets are fixed above and below the structure, and the structure is exposed to a magnetic field of approximately 5 Tesla for 10 minutes (orientation process). After exposure to the magnetic field, the structure is dried for 5 minutes using a heating plate at 80°C to allow the NMP solvent to disperse, followed by a pressing process (three pressing processes using a 3-ton roller press). Thus, a positive electrode having a positive electrode current collector (aluminum foil) and a positive electrode layer is obtained.

[0191] The obtained positive electrode was cut in the thickness direction by ion milling to align the cross-section of the positive electrode layer. The cross-section of the positive electrode layer was observed using a scanning electron microscope (SEM, Hitachi High Technology Co., Ltd. SU8230) at an accelerating voltage of 1kV. In the cross-sectional SEM image, a single-crystal active material composed of crystalline primary particles was observed. One hundred portions of single-crystal active material (i.e., N1) were randomly selected, each containing a line segment that can be identified as having a short and a long side, an angle between the short and long sides of 60° and 120°, and an aspect ratio (length to width ratio) of 1.2 or higher. A =100). Count the number N of primary particles among 100 single-crystal active materials whose long side has an angle of inclination of 0° or more but less than 30° relative to the in-plane direction of the positive electrode layer (the in-plane direction of the metal foil). B Calculate the number N. B Relative to the number N A proportion (N) B / N A The results are shown in Table 1.

[0192] [Battery Manufacturing]

[0193] A negative electrode paste containing natural graphite as the negative electrode active material was applied to the surface of a metal foil serving as the negative electrode current collector using a film coating applicator (manufactured by Allgood Co., Ltd.) with a film thickness adjustment function. Then, the negative electrode with a negative electrode layer on the negative electrode current collector was fabricated by drying at 80°C for 5 minutes using a dryer. A 1M LiPF6 solution containing LiPF6 as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents in a ratio of EC / DMC / EMC = 3 / 4 / 3 vol%. The positive electrode, separator, and negative electrode were stacked, with the separator impregnated with the electrolyte, to fabricate a small laminated battery containing power-generating elements housed in a pouch made of Al laminated film.

[0194] (Example 2)

[0195] In fabricating the positive electrode, the structure was exposed to a magnetic field for 3 minutes during the alignment process. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A laminated cell with the same structure as in Example 1 was obtained, except that the obtained positive electrode was used.

[0196] (Example 3)

[0197] In fabricating the positive electrode, the structure was exposed to a magnetic field for 1 minute during the alignment process. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A laminated cell with the same structure as in Example 1 was obtained, except that the obtained positive electrode was used.

[0198] (Comparative Example 1)

[0199] Except that no orientation process was performed during the fabrication of the positive electrode, the positive electrode was fabricated using the same method as in Example 1. A laminated battery having the same structure as in Example 1 was obtained, except that the obtained positive electrode was not used.

[0200] (Comparative Example 2)

[0201] In fabricating the positive electrode, the exposure time of the structure to a magnetic field was set to 20 seconds during the alignment process. Otherwise, the positive electrode was fabricated using the same method as in Example 1. A laminated cell with the same structure as in Example 1 was obtained except that the obtained positive electrode was used.

[0202] [evaluate]

[0203] For laminated cells, IV resistance was measured after initial aging and after 100 cycles of cycling testing. The cycling test was conducted for 100 cycles under the following conditions.

[0204] Ambient temperature: 60℃

[0205] Number of cycles: 100

[0206] Current ratio: 0.3C

[0207] Voltage range: 4.25V to 2.5V

[0208] After charging the laminated battery to 50% SOC, it was discharged and charged at 25°C with currents of 0.3C, 0.5C, 0.7C, and 1.0C. The average resistance estimated based on the potential drop / rise after 1 second was taken as the IV resistance (after initial aging). The measurements were performed after 100 cycles of cycling. The results are shown in Table 1.

[0209]

[0210] As shown in Table 1, it was confirmed that: N B / N A A battery with a positive electrode layer of 50% or more (Examples 1-3), and having N B / N A Compared to batteries with a positive electrode layer of less than 50% (Comparative Example 1 and Comparative Example 2), the resistance increase after cycling can be suppressed.

Claims

1. A positive electrode layer used in lithium-ion batteries. The positive electrode layer has a single-crystal active material as the positive electrode active material. The single-crystal active material is composed of crystalline primary particles containing Li, TM, and O, where TM is a transition metal. In the cross-sectional image of the positive electrode layer obtained using a scanning electron microscope The single-crystal active material comprises a long side and a short side, wherein the angle formed by the long side and the short side is 60° or more and 120° or less, and the aspect ratio (length ratio of the long side to the short side) is 1.2 or more. The long side of the single-crystal active material extends along the (003) plane. The number N of single-crystal active materials whose orientation of the long side is at an angle of 0° or more and less than 30° relative to the in-plane direction of the positive electrode layer. B The number N of the single-crystal active material A The proportion N B / N A It is over 50%.

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

3. The positive electrode layer according to claim 1, The ratio N B / N A It is between 56% and 65%.

4. The positive electrode layer according to claim 1, The single-crystal active material has a rectangular parallelepiped shape.

5. The positive electrode layer according to claim 1, The primary particle contains at least Ni as the TM.

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

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

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

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

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

1.

11. A lithium-ion battery comprising the positive electrode layer as described in any one of claims 1 to 10.

12. A method for manufacturing a positive electrode layer, comprising a coating step and an alignment step, of any one of claims 1 to 10. In the coating process, a positive electrode layer precursor is obtained by coating a positive electrode slurry containing the positive electrode active material, wherein the positive electrode active material contains the single-crystal active material. In the orientation process, the positive electrode layer precursor is exposed to a magnetic field to orient the single-crystal active material such that the angle between the direction of the long side and the in-plane direction of the positive electrode layer is 0° or more and 30° or less.

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