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DE-102025130138-A1 - ACTIVE MATERIAL FOR THE CATHOD OF A LITHIUM-ION SECONDARY BATTERY

DE102025130138A1DE 102025130138 A1DE102025130138 A1DE 102025130138A1DE-102025130138-A1

Abstract

An active material of the cathode for a lithium-ion secondary battery contains single-crystal particles. A crack group is generated in a cross-section of the single-crystal particle. The crack group comprises two or more cracks. The crack group includes a section in which two or more cracks extend parallel to each other. The active material of the cathode satisfies the relationship "3% ≤ L/D". "L" denotes the length of the crack. "D" denotes the diameter of the smallest circumscribing circle of the single-crystal particle in the cross-section.

Inventors

  • Ryosuke OHSAWA
  • Taku Kinoshita
  • Yuji MAHARA

Assignees

  • TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date
20260513
Application Date
20250730
Priority Date
20241113

Claims (5)

  1. Active material of the cathode for a lithium-ion secondary battery, wherein the active material of the cathode contains a single crystal particle, wherein a crack group is generated in a cross-section of the single crystal particle, the crack group comprises two or more cracks, the crack group comprises a section in which two or more of the cracks extend parallel, and a relationship of 3% ≤ L/D is satisfied, where L denotes the length of the cracks and D denotes the diameter of a smallest circumscribing circle of the single crystal particle in cross-section.
  2. Active material of the cathode after Claim 1 , where the crack group comprises four or more to eight or fewer cracks.
  3. Active material of the cathode after Claim 1 or 2 , where a relationship of 6% ≤ L/D ≤ 52% is satisfied.
  4. Active material of the cathode after Claim 1 or 2 , wherein the active material of the cathode consists of the single crystal particles, which make up 50% or more of the proportion, and the polycrystal particles, which make up the remainder.
  5. Active material of the cathode after Claim 1 or 2 , where the composition of the active material of the cathode is expressed by the general formula Li x Ni a Co b Mn c O y and 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.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention The present disclosure relates to an active material for the cathode of a lithium-ion secondary battery. 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 material for cathodes has been proposed. Single-crystallization is expected to improve storage properties, for example. This is attributed to the fact that single-crystal particles have a smaller specific surface area compared to polycrystal particles. However, there is still room for improvement regarding the initial resistance of single-crystal particles. The purpose of this disclosure is to reduce the initial resistance. 1. An active material of the cathode, or for the cathode of a lithium-ion secondary battery, contains a single-crystal particle. A crack group is generated in a cross-section of the single-crystal particle. The crack group comprises two or more cracks. The crack group includes a section in which two or more of the cracks extend parallel to each other. The active material of the cathode satisfies the relationship "3% ≤ L/D". "L" denotes the length of the cracks. "D" denotes the diameter of a smallest circumscribing circle of the single-crystal particle in the cross-section. The formation of the crack group in the single-crystal particle is expected to reduce the initial resistance. It is assumed that a diffusion path for ions forms within the single-crystal particle as the electrolyte solution penetrates the particle through the crack group. The number of cracks is also referred to as the "crack count." The length of the cracks is also referred to as the "crack length." The active material of the cathode for a lithium-ion secondary battery can be abbreviated as "cathode active material." The lithium-ion secondary battery can be abbreviated as "battery." 2. The active material of the cathode, or for the cathode according to point “1” above, may, for example, have the following configuration. The crack group comprises four or more up to eight or fewer cracks. The single-crystal particles repeatedly expand and contract due to repeated charging and discharging cycles. These volume changes within the single-crystal particles can lead to stress concentrations. It is possible that cracks in the single-crystal particles caused by these stress concentrations contribute to a reduction in capacity. The premature formation of four or more cracks in the single-crystal particles before charging and discharging cycles in the battery can be expected to improve cycle life, in addition to reducing initial resistance. This is thought to be because the cracks mitigate the stress concentration. 3. The active material of the cathode according to point “1” or “2” above may, for example, have the following configuration. The active material of the cathode satisfies the relationship “6% ≤ L/D ≤ 52%”. If the relationship “6% ≤ L/D ≤ 52%” is fulfilled, an improvement in cycle characteristics can be expected in addition to a reduction in initial resistance. 4. The active material of the cathode according to one of the preceding points “1” to “3” may, for example, have the following configuration. The active material for the cathode consists of single-crystal particles, which constitute a proportion of 50% or more, and polycrystalline particles, which constitute the remainder. The active material for the cathode can contain polycrystalline particles in addition to single-crystal particles. Since the proportion of single-crystal particles is 50% or more, an improvement in cycle properties can be expected, for example. 5. The active material of the cathode, according to one of the points "1" to "4" mentioned above, can, for example, have the following configuration. The composition of the active material of the cathode is expressed by the general formula "Li x Ni a Co b Mn c O y ". In the general formula, "x, a, b, c and y" satisfy the 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 also "1.5 ≤ y ≤ 2.1". Since the Ni content “a” is, for example, 0.5 or more, an increase in the initial discharge capacity is to be expected. An embodiment of the present disclosure (hereinafter referred to as "present embodiment") and an example of the present disclosure (hereinafter referred to as "present example") are described. It should be noted, however, that the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are exemplary in every respect. The present embodiment and the present example are not limiting. The technical scope of the present disclosure includes all modifications in the sense and scope that correspond to the description of the claims. For example, it is