High-Ni Cathode Secondary Particles for Density and Structural 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 secondary particles are not effective for high Ni materials with excellent capacity properties.
Innovation Solution
A high Ni positive electrode active material is developed with a secondary particle structure where primary particles are aggregated, coated with cobalt and boron, and has a specific composition to maintain crystallinity, improving density and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If high Ni positive electrode active material is formed in secondary particle structure, then rolling density is improved, but volume change during charge-discharge causes cracks and structural degradation
Solution Approach 1:
The positive electrode active material is divided into primary particles (0.5-5 μm) that aggregate to form secondary particles (10-20 μm). This segmentation allows the material to achieve high rolling density through aggregation while maintaining structural integrity at the primary particle level, reducing crack formation during charge-discharge cycles.
Solution Approach 2:
The invention uses a composite structure where multiple primary particles are aggregated to form secondary particles. This composite approach combines the benefits of high density (from aggregation) with the advantages of smaller particle sizes (lower volume change), creating a hierarchical structure that resolves the contradiction between rolling density and structural stability.
2Reliability
If high Ni positive electrode active material is formed as single particle, then structural degradation is reduced, but particle diameter distribution increases and specific surface area decreases
Solution Approach 1:
Instead of forming single large particles, the invention segments the material into multiple primary particles (0.5-5 μm) that aggregate into secondary particles. This segmentation maintains narrow particle diameter distribution at the primary particle level while achieving the structural stability benefits of smaller particles through the aggregated structure.
3Volume of stationary object
If heat treatment temperature is increased to prepare micron-level primary particle secondary structure, then rolling density is improved, but layered structure degenerates into rock salt structure
Solution Approach 1:
The invention optimizes the heat treatment temperature parameter to a specific range (900-1100°C) that is sufficient to achieve micron-level primary particle aggregation and high rolling density, but controlled enough to prevent excessive degradation of the layered structure into rock salt structure. This parameter optimization resolves the contradiction between density improvement and crystallinity maintenance.
Data Source
Figure 1(A)~1(B)
Figure 2(A)~2(B)
Figure 3(A)~3(B)
AI summary
The present invention relates to a positive electrode active material, and to a positive electrode active material capable of resolving 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.