High-Ni Cathode Surface Layer for Capacity Retention
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Solution Overview
Problem
Existing positive electrode active materials for non-aqueous electrolyte secondary batteries with high Ni content (>80 mol %) face instability in their layered structure, leading to decreased battery capacity during charge/discharge cycles.
Innovation Solution
Incorporating a lithium transition metal composite oxide with a high Ni content (>80 mol %) and adding Al and Sr to form a surface modification layer on the composite oxide, which stabilizes the surface structure and inhibits reactions with the electrolyte.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the proportion of Ni to the total number of mole of metal elements excluding Li is increased to 80 mol % or more to obtain high discharge capacity, then the discharge capacity is improved, but the layered structure becomes unstable and battery capacity decreases during charge/discharge
Solution Approach 1:
The patent applies local quality by creating a surface modification layer with specific composition (Al and Sr elements) on the surface of the lithium transition metal composite oxide particles. This surface layer has different properties from the bulk material, providing local structural stability and protection against electrolyte reactions, while the high-Ni bulk material maintains high discharge capacity.
Solution Approach 2:
The patent uses composite materials by combining the high-Ni lithium transition metal composite oxide with a surface modification layer containing Al and Sr elements. This composite structure integrates the high capacity advantage of high-Ni materials with the structural stability and electrochemical resistance provided by the Al-Sr surface layer.
2Quantity of substance
If the proportion of Ni to the total number of mole of metal elements excluding Li is increased to 80 mol % or more to obtain high discharge capacity, then the discharge capacity is improved, but the battery capacity decreases during charge/discharge cycles
Solution Approach 1:
The surface modification layer with Al and Sr elements provides local protection at the particle surface, preventing electrolyte degradation and maintaining structural integrity during cycling. This local quality enhancement ensures reliable capacity retention while the high-Ni bulk provides high discharge capacity.
Solution Approach 2:
The surface modification layer is formed in advance before battery assembly, creating a pre-protective barrier that prevents harmful reactions between the high-Ni material and the electrolyte during subsequent charge/discharge cycles. This preliminary action ensures stable capacity retention from the first cycle.
3Quantity of substance
If high Ni content (>80 mol %) is used to achieve high capacity, then the capacity is improved, but the layered structure becomes unstable and reacts with electrolyte
Solution Approach 1:
The surface modification layer containing Al and Sr elements acts as an intermediary between the high-Ni lithium transition metal composite oxide and the electrolyte. This intermediate layer prevents direct contact and harmful reactions between the high-Ni material and the electrolyte, while still allowing lithium ion transport.
Solution Approach 2:
The surface modification layer creates an inert environment around the high-Ni material, protecting it from electrolyte degradation and unwanted side reactions. This protective atmosphere allows the high-Ni material to maintain its structural stability and electrochemical performance.
Data Source
AI summary
This positive electrode active material for nonaqueous electrolyte secondary batteries comprises a lithium-transition metal composite oxide and a surface modification layer. The lithium transition metal composite oxide contains at least Al and 80 mol % or more Ni with reference to the total number of moles of metal elements excluding Li, and the surface modification layer contains at least Sr and is formed on the surface of primary particles of the lithium-transition metal composite oxide.