Positive Electrode Active Material Suppressing DCR Increase
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face increased direct current resistance (DCR) after high-temperature cycles, leading to degraded output characteristics despite previous techniques aimed at suppressing reaction between the positive electrode active material and electrolytic solution.
Innovation Solution
A positive electrode active material comprising secondary particles formed by aggregation of lithium transition metal oxide primary particles, with rare-earth compound secondary particles adhering to recesses between primary particles and tungsten-containing compounds at the interfaces of these particles, which helps in suppressing surface alteration and cracking during charge-discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a group III element is provided on surfaces of base particles to suppress reaction with electrolytic solution, then charge storage characteristics are improved, but DCR increases after high-temperature cycles
Solution Approach 1:
The coating structure is segmented into multiple functional layers: a group III element-containing compound layer (suppressing electrolyte reaction) and a rare-earth compound layer (suppressing surface alteration and cracking at high temperatures). This segmentation allows each layer to perform its specific function without interfering with the other, resolving the contradiction between charge storage characteristics and high-temperature stability.
Solution Approach 2:
The invention uses composite coating materials combining group III element-containing compounds (such as aluminum oxide, gallium oxide) with rare-earth compounds (such as lanthanum oxide, cerium oxide). This composite structure provides both the electrolyte reaction suppression benefit of group III elements and the high-temperature structural stability of rare-earth compounds, thereby preventing DCR increase while maintaining charge storage characteristics.
2Productivity
If fine particles containing lithium tungstate are formed on surfaces of primary particles to increase initial discharge capacity, then resistance of positive electrode is reduced, but DCR increases after high-temperature cycles
Solution Approach 1:
The rare-earth compound is specifically located at the particle surfaces and interfaces where surface alteration and cracking occur during high-temperature cycles. This local placement provides targeted protection at the critical locations without affecting the bulk electrode properties, thereby maintaining initial discharge capacity while preventing high-temperature DCR increase.
Solution Approach 2:
The rare-earth compound coating is applied in advance before the battery undergoes high-temperature cycling. This preliminary protective layer prevents surface alteration and cracking from occurring in the first place, thereby preventing the subsequent increase in DCR while allowing the electrode to maintain its initial discharge capacity and low resistance characteristics.
Data Source
AI summary
There is provided a positive electrode active material for a nonaqueous electrolyte secondary battery capable of suppressing an increase in DCR during cycles. There is provided a positive electrode active material for a nonaqueous electrolyte secondary battery that includes a secondary particle formed by aggregation of primary particles formed of a lithium transition metal oxide. A rare-earth compound secondary particle formed by aggregation of particles formed of a rare-earth compound adheres to a recess formed between primary particles adjacent to each other on a surface of the secondary particle, and the rare-earth compound secondary particle adheres to both the primary particles adjacent to each other in the recess. A tungsten-containing compound adheres to an interface of primary particles inside the secondary particle formed of the lithium transition metal oxide.