Layered Nickel Cathode Surface Chemistry for High-Voltage Cycling
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Solution Overview
Problem
Existing positive-electrode active materials for nonaqueous electrolyte secondary batteries face challenges in maintaining charge/discharge capacities and cycle characteristics at high voltages, particularly due to the addition of aluminum compounds which can lead to capacity reduction and structural deterioration.
Innovation Solution
A positive-electrode active material comprising lithium transition metal composite oxide particles with a layered structure, containing nickel, and oxides adhering to the surface, including lithium-aluminum and lithium-boron oxides, where the aluminum is present as a solid solution in the surface layer and diffuses through grain boundaries, optimizing the molar ratios and particle diameter distribution of the aluminum compound to enhance cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum compound is added to improve cycle characteristics at high voltage, then charge/discharge cycle characteristics are improved, but charge/discharge capacity is reduced
Solution Approach 1:
The patent applies local quality by creating a concentrated aluminum region specifically at the grain boundaries between primary particles near the surface of secondary particles, rather than uniformly distributing aluminum throughout the material. This localized aluminum enrichment (with higher concentration than the matrix phase) provides protective effects at the critical surface regions where cycle degradation occurs, while maintaining higher charge/discharge capacity in the bulk material regions.
2Stability of the object's composition
If aluminum compound is added to stabilize structure at high voltage, then structural stability is improved, but charge/discharge capacity is reduced
Solution Approach 1:
The patent implements local quality by concentrating aluminum at grain boundaries between primary particles near the secondary particle surface, creating a localized protective barrier that stabilizes the crystal structure at these critical regions during high-voltage cycling, while preserving charge/discharge capacity in the interior regions of the particles.
3Reliability
If oxide coating is applied to surface to improve cycle characteristics, then cycle characteristics are improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the formation of aluminum-containing oxide coating with the existing sintering process by adding aluminum compound to the starting mixture and performing heat treatment. This integration combines the coating formation step with the standard manufacturing process, avoiding the need for separate coating operations and reducing overall manufacturing complexity while still achieving the protective surface layer.
Solution Approach 2:
The patent applies preliminary action by incorporating aluminum compound into the starting material mixture before sintering, so that the aluminum-containing oxide coating forms during the standard heat treatment process. This preliminary incorporation of aluminum allows the protective coating to be formed as part of the normal manufacturing sequence, rather than requiring post-processing coating steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution effectively stabilizes the lithium transition metal composite oxide structure, improving charge/discharge capacities and cycle characteristics at high voltages while minimizing capacity reduction, by ensuring sufficient aluminum presence in the surface layer and efficient diffusion through grain boundaries.
Implementation Method 1
aluminum is present as a solid solution in a surface layer and diffuses through grain boundaries
Data Source
AI summary
Provided is a positive-electrode active material for a nonaqueous electrolyte secondary battery, including a lithium transition metal composite oxide particle having a layered structure and containing nickel, and an oxide containing lithium and aluminum and an oxide containing lithium and boron adhering to a surface of the lithium transition metal composite oxide particle. The lithium transition metal composite oxide particle includes a secondary particle formed by aggregation of primary particles containing a solid solution of aluminum in a surface layer. The lithium transition metal composite oxide particles have a composition with a difference of more than 0.22 mol % and less than 0.6 mol % between a ratio of the number of moles of aluminum in the solid solution in the surface layer of the primary particles relative to a total number of moles of metal other than lithium and a ratio of the number of moles of aluminum present in a region other than the surface layer of the primary particles relative to the total number of moles of metal other than lithium.