High-Ni Cathode Particle Structure for Density and Crack Stability
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Solution Overview
Problem
High Ni positive electrode active materials face issues with structural degradation due to volume changes during charging and discharging, leading to cracks and reduced conductivity, and existing solutions for mid Ni materials fail to address these issues effectively in high Ni materials with high nickel content.
Innovation Solution
A high Ni positive electrode active material is developed with a secondary particle structure formed by aggregating primary particles of specific sizes and compositions, including lithium transition metal composite oxides with additives like aluminum, zirconium, and cobalt, which maintains crystallinity and improves density and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high Ni positive electrode active material is formed in a secondary particle structure, then rolling density is improved and cracks during rolling are minimized, but volume change during charge and discharge causes structural degradation and crack formation
Solution Approach 1:
The positive electrode active material is divided into multiple primary particles (1-5 μm) aggregated into a secondary particle structure. This segmentation allows the material to maintain high rolling density while the smaller primary particles experience reduced volume change stress during lithium insertion/extraction, preventing crack formation and structural degradation.
Solution Approach 2:
Different regions of the particle structure are optimized for different functions: the internal primary particles provide structural stability and accommodate volume changes, while the external surface maintains high density for efficient lithium ion transport. This local optimization resolves the contradiction between rolling density and structural stability.
2Stability of the object's composition
If a single particle structure is used, then structural stability is improved, but particle diameter distribution increases and specific surface area decreases leading to poor cell resistance characteristics
Solution Approach 1:
Instead of using a single large particle, the invention segments the active material into multiple smaller primary particles (1-5 μm) that aggregate to form a secondary particle. This segmentation maintains structural stability while increasing specific surface area and reducing particle diameter distribution, thereby improving cell resistance characteristics.
Solution Approach 2:
The invention creates a composite particle structure where multiple primary particles with controlled size distribution aggregate to form a secondary particle. This composite structure combines the structural stability of larger particles with the high surface area and low resistance characteristics of smaller particles.
3Manufacturing precision
If heat treatment is performed at higher temperature to prepare micron-level primary particles in secondary structure, then rolling density is improved, but layered structure degenerates into rock salt structure causing decreased crystallinity and performance
Solution Approach 1:
The invention optimizes the heat treatment temperature parameter to a specific range (700-900°C) that is sufficient to achieve micron-level primary particle formation and high rolling density, but below the threshold that causes layered structure degradation to rock salt structure. This precise parameter control resolves the contradiction between rolling density and crystallinity.
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.