DE-102025138907-A1 - Cathode for lithium-ion secondary battery

Abstract

A cathode for a lithium-ion secondary battery comprises a layer of active cathode material. The active cathode material contains single-crystal particles. One hundred single-crystal particles, randomly selected from a scanning electron microscope image of a cross-section of the active cathode material layer, comprise at least one first particle with a depression and at least one second particle with a protrusion. The following relationships are satisfied: "0.01 ≤ d/D1 ≤ 0.56" and "0.01 ≤ h/D2 ≤ 0.58", where "d" is the depth of the depression of the first particle, "D1" is the diameter of the smallest circumscribing circle of the first particle, "h" is the height of the protrusion of the second particle, and "D2" is the diameter of the smallest circumscribing circle of the second particle.

Inventors

• Ryosuke OHSAWA
• Taku Kinoshita
• Yuji MAHARA

Assignees

• TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date

20260513

Application Date

20250925

Priority Date

20241113

Claims (5)

1. Cathode for a lithium-ion secondary battery, wherein the cathode comprises a layer of active cathode material, wherein: the layer of more active cathode material contains an active cathode material; the active cathode material contains single-crystal particles; one hundred single-crystal particles randomly selected from a scanning electron microscope image of a cross-section of the layer of active cathode material comprise at least one first particle with a depression and at least one second particle with a protrusion; and the following relationships are satisfied: 0,01 ≤ d / D1 ≤ 0,56 and 0,01 ≤ h / D2 ≤ 0,58, where d represents the depth of the depression of the first particle, D1 represents the diameter of a least circumscribing circle of the first particle, h represents the height of the elevation of the second particle, and D2 represents the diameter of a least circumscribing circle of the second particle.
2. cathode after Claim 1 , wherein the randomly selected hundred single-crystal particles include at least one third particle that has the depression and the elevation.
3. cathode after Claim 1 or 2 , wherein the active cathode material contains 50% or more of the number of single crystal particles, the remainder consisting of polycrystalline particles.
4. cathode after Claim 1 or 2 , wherein the active cathode material contains a lithium transition metal composite oxide.
5. cathode after Claim 4 , wherein the active cathode material has a composition that is represented by the following general formula: Li x Ni a Co b Mn c O y where x, a, b, c and y satisfy the following relationships: 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.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention The present disclosure relates to cathodes for lithium-ion secondary batteries. 2. Description of the state of the art The Japanese unpublished patent application No. 2023-036570 ( JP 2023-036570 A ) reveals a ternary cathode material with large grains and a single-crystal morphology. SUMMARY OF THE INVENTION Single-crystallization of active cathode material has been proposed. Since single-crystal particles have a smaller specific surface area than polycrystalline particles, they are expected to improve cycle properties. However, there is still room for improvement regarding the initial resistance. The aim of the present invention is to reduce the initial resistance. 1. A cathode for a lithium-ion secondary battery comprises a layer of active cathode material. The active cathode material contains single-crystal particles. One hundred single-crystal particles, randomly selected from a scanning electron microscope image of a cross-section of the active cathode material layer, comprise at least one first particle with a depression and at least one second particle with a protrusion. The following relationships are satisfied: "0.01 ≤ d/D1 ≤ 0.56" and "0.01 ≤ h/D2 ≤ 0.58", where "d" is the depth of the depression of the first particle, "D1" is the diameter of the smallest circumscribing circle of the first particle, "h" is the height of the protrusion of the second particle, and "D2" is the diameter of the smallest circumscribing circle of the second particle. Single-crystal particles typically have a smooth surface. These particles can be densely packed within the layer of active cathode material. It is assumed that gaps are less likely to form between the single-crystal particles, through which an electrolyte solution could diffuse. Consequently, the initial resistance may increase. The active cathode material layer of the present invention contains single-crystal particles with specific shapes. Specifically, the active cathode material layer contains the first particle and the second particle. The depression of the first particle and the protrusion of the second particle can form gaps in the active cathode material layer through which the electrolyte solution can diffuse. Furthermore, the depression and protrusion each have a suitable size relative to the size of the single-crystal particles. This facilitates the diffusion of the electrolyte solution. Consequently, a reduction in the initial resistance can be expected. Hereinafter, the “cathode for a lithium-ion secondary battery” can simply be referred to as the “cathode.” 2. The cathode according to point “1” above may, for example, have the following configuration. The randomly selected one hundred single-crystal particles include at least one third particle that has the depression and the protrusion. A single crystal particle can exhibit both depressions and elevations. 3. The cathode according to point “1” or “ 2” above may, for example, comprise the following configuration. The active cathode material contains 50% or more of the number of single-crystal particles, with the remainder consisting of polycrystalline particles. The higher the numerical proportion of single crystal particles, the more likely it is that, for example, the cycle characteristics will improve. 4. The cathode according to any of the preceding points “1” to “3” may, for example, comprise the following configuration. The active cathode material contains a lithium transition metal composite oxide. 5. The cathode according to any of the preceding points “1” to “4” may, for example, have the following configuration. The active cathode material has a composition represented by the following general formula: “Li x Ni a Co b Mn c O y ”. In the general formula, “x, a, b, c and y” satisfy the following relationships: “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”. Since the Ni composition fraction or composition ratio or ratio fraction “a” is 0.5 or more, an increase in the initial discharge capacity can be expected, for example. An embodiment of the present invention (hereinafter also referred to as the "present embodiment") and an example of the present invention (hereinafter also referred to as the "present example") are described. However, the present embodiment and the present example are not intended to limit the technical scope of the present invention. The present embodiment and the present example serve in every respect for illustrative purposes. The present embodiment and the present example are not limiting. The technical scope of the present invention includes all modifications that fall within the meaning and scope that correspond to the claims. For example, it is originally intended that any configurations can be extracted from the embodiment and combined as desired. BRIEF DESCRIPTION OF THE DRAWINGS Features, advantages and technical and industrial significance of exemp