DE-102025133041-A1 - Cathode active material for lithium-ion secondary battery

Abstract

The present invention relates to an active cathode material for a lithium-ion secondary battery. The active cathode material for a lithium-ion secondary battery comprises a lithium transition metal compound oxide. The crystal structure of the lithium transition metal compound oxide belongs to the space group R-3m. The lithium transition metal compound oxide contains Ni₄⁺ .

Inventors

• Kenji YOKOE

Assignees

• TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date

20260513

Application Date

20250819

Priority Date

20241113

Claims (5)

1. Active cathode material for a lithium-ion secondary battery, wherein the active cathode material contains a lithium transition metal compound oxide, wherein the crystal structure of the lithium transition metal compound oxide belongs to a space group R-3m and the lithium transition metal compound oxide contains Ni 4+ .
2. Active cathode material according to Claim 1 , wherein the crystal structure includes a 3a site and a 3b site, the 3a site contains Li + and Ni 2+ and the 3b site contains Ni 4+ and Ni 3+ .
3. Active cathode material according to Claim 2 , where the ratio of the amount of substance of Ni 4+ to the amount of substance of Ni 3+ is 0.09 to 0.35.
4. Active cathode material according to Claim 2 or 3 , where the ratio of the amount of substance Ni 4+ to the amount of substance Ni 2+ is 2.7 to 7.2.
5. Active cathode material according to Claim 2 or 3 , where the composition of the lithium transition metal compound oxide is given by the general formula Li z N 1-ca Co c Mn a O d is expressed where, in the general formula, z, a, c and d satisfy the following relationships: 0.1 ≤ z ≤ 1.5, 0.5 ≤ 1-ca ≤ 1.0, 0 ≤ c ≤ 0.3, 0 ≤ a ≤ 0.3 and 1.5 ≤ d ≤ 2.1.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to an active cathode material for a lithium-ion secondary battery. 2. Description of the state of the art The Japanese unpublished patent application No. 2008-257992 ( JP 2008-257992 A ) reveals a lithium-nickel-cobalt-manganese composite oxide with a layer. SUMMARY OF THE INVENTION A lithium transition metal compound oxide can exhibit a layered structure. This layered structure comprises 3a sites and 3b sites. The 3a sites and 3b sites are layered alternately along the c-axis. The 3a sites contain lithium ions (Li + ). The 3b sites contain transition metal ions (TM). If the 3b sites contain a nickel ion (Ni), it is generally assumed that the Ni ion tends to become trivalent (Ni3 + ). JP 2008-257992 A It is revealed that the valence of Ni ions can be fixed to divalent by ensuring that the occupation rate or degree of other metal ions besides Ni, cobalt (Co), and manganese (Mn) at the 3b sites is 5% or less. In the battery, the lithium transition metal compound oxide is charged. In a highly charged state, the valence of Ni changes from divalent ( Ni²⁺ ) to tetravalent ( Ni⁴⁺ ). The ionic radius differs between divalent and tetravalent ions. Consequently, in a highly charged state, the 3b site can contract rapidly along the c-axis. This sudden contraction of the crystal structures can lead to irreversible structural changes (e.g., transformation into a rock salt structure or similar). Irreversible structural changes are associated with a deterioration of capacity. Therefore, it is possible that the desired cycle characteristics cannot be achieved. The aim of the present invention is to improve the cycle properties. 1. An active cathode material for a lithium-ion secondary battery contains a lithium transition metal compound oxide. The crystal structure of the lithium transition metal compound oxide belongs to the space group R-3m. The lithium transition metal compound oxide contains Ni₄⁺ . The layered structure belongs to the space group R-3m. In the present invention, tetravalent Ni ions are introduced into the crystal structure before the battery is first charged. It is assumed that even if a valence change with respect to the tetravalent Ni occurs during charging, the contraction in the c-axis direction is mitigated because the tetravalent Ni ions are initially present. The cycle life is expected to be improved by reducing irreversible structural changes in a highly charged state. In the following, "active cathode material for lithium-ion secondary batteries" can be abbreviated to "active cathode material". 2. The active cathode material according to point “1” above may, for example, have the following configuration. The crystal structure includes a 3a site and a 3b site. The 3a site contains Li + and Ni2 + . The 3b site contains Ni4 + and Ni3 + . For example, a divalent Ni ion ( Ni²⁺ ) can be transferred to the 3a site. This phenomenon, in which Ni ions are transferred to the 3a site, is also referred to as "cation mixing" (CM). The 3b site can contain tetravalent and trivalent Ni ions. 3. The active cathode material according to point “2” above can, for example, comprise the following configuration. The ratio of the amount of Ni 4+ to the amount of Ni 3+ is 0.09 to 0.35. The ratio of the amount of substance of Ni 4+ to the amount of substance of Ni 3+ is also referred to as the molar ratio "Ni 4+ /Ni 3+ ". An improvement in cycle properties can be expected if the molar ratio "Ni 4+ /Ni 3+ " is in the range of 0.09 to 0.35. 4. The active cathode material according to point “2” or “3” above may, for example, comprise the following configuration. The ratio of the amount of Ni 4+ to the amount of Ni 2+ is 2.7 to 7.2. In the following, the ratio of the amount of substance of Ni 4+ to the amount of substance of Ni 2+ is also referred to as the molar ratio "Ni 4+ /Ni 2+ ". If the molar ratio "Ni 4+ /Ni 2+ " is in the range of 2.7 to 7.2 If the location is favorable, an improvement in cycle characteristics can be expected. 5. The active cathode material according to any of the preceding points “1” to “4” may, for example, comprise the following configuration. A composition of the lithium transition metal composite oxide is expressed by the general formula “Li z Ni 1-ca Co c Mn a O d ”. In the general formula, “z”, a, c and d” satisfy the relationships “0.1 ≤ z ≤ 1.5”, “0.5 ≤ 1-ca ≤ 1.0”, “0 ≤ c ≤ 0.3, 0 ≤ a ≤ 0.3”, and “1.5 ≤ d ≤ 2.1”. An embodiment of the present invention (hereinafter referred to as "present embodiment") and an example of the present invention (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 invention. 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 p