Cathode Active Material Structure for High-Ni Crack Resistance
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Solution Overview
Problem
High Ni positive electrode active materials face issues of structural degradation due to volume changes during charge and discharge, leading to cracks and reduced conductivity, and existing solutions for secondary and single particles fail to address these issues effectively, particularly in high-capacity batteries.
Innovation Solution
A positive electrode active material composed of secondary particles with micron-level primary particles, incorporating lithium transition metal composite oxides with aluminum, yttrium, and zirconium, and a specific composition, which maintains crystallinity and improves density and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high Ni positive electrode active material is formed in secondary particle structure, then capacity properties are improved, but structural degradation and crack formation occur due to volume change
Solution Approach 1:
The positive electrode active material is divided into primary particles (0.5-5 μm) that aggregate to form secondary particles (10-30 μm). This segmentation allows the primary particles to individually accommodate volume changes during lithium insertion/extraction, reducing stress concentration and crack formation in the overall structure while maintaining high capacity through the secondary particle configuration.
Solution Approach 2:
The patent uses a composite structure where multiple primary particles with specific size ranges aggregate to form secondary particles. This composite architecture combines the benefits of small primary particles (low volume change, high surface area) with the advantages of larger secondary particles (high rolling density, good conductivity), resolving the contradiction between capacity and structural stability.
2Reliability
If positive electrode active material is prepared as single particle, then crack development is minimized, but particle diameter distribution increases and specific surface area decreases
Solution Approach 1:
Instead of using single large particles, the material is segmented into multiple small primary particles (0.5-5 μm) that aggregate to form secondary particles. This segmentation ensures uniform particle size distribution while maintaining crack resistance, as each primary particle individually accommodates volume changes without developing large cracks.
Solution Approach 2:
The structure follows a nested configuration where primary particles are aggregated to form secondary particles. This nested structure allows the smaller primary particles to be contained within the larger secondary particle framework, achieving both uniform size distribution and crack resistance simultaneously.
3Volume of stationary object
If primary particle diameter is increased to micron level, then rolling density improves, but heat treatment temperature must be increased causing layered structure degradation
Solution Approach 1:
The patent optimizes the primary particle size parameter to 0.5-5 μm, which is sufficiently small to allow effective heat treatment at moderate temperatures (900-1000°C) without causing layered structure degradation into rock salt structure. This parameter optimization achieves high rolling density through secondary particle formation while avoiding the temperature-induced structural degradation that occurs with larger micron-level particles.
Data Source
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AI summary
The present invention relates to a positive electrode active material, and to a positive electrode active material which may resolve both an issue of a typical secondary particle and an issue of a single particle, wherein the positive electrode active material includes a particle, such as a typical single particle, as a primary particle, and a secondary particle formed by aggregation of a plurality of primary particles, and may thus improve energy density through excellent density characteristics as well as cell characteristics, such as improved lifetime and reduced gas generation amount of a lithium secondary battery, and a positive electrode and a lithium secondary battery which include the same.