Positive Electrode Active Material Spheroidality Stress Concentration
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in charge and discharge capacity, cycle performance, reliability, safety, and cost due to breakage of positive electrode active materials during pressure application and repeated charging and discharging.
Innovation Solution
A positive electrode active material with a smooth surface and nearly spherical shape is developed, characterized by a median solidity of 0.96 or higher, a fractal dimension of 1.143 or less, and a circularity of 0.7 or more, containing lithium, a transition metal, and optionally halogen, magnesium, nickel, and aluminum, to alleviate stress concentration and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pressure is applied to increase density and adhesion, then electrode density and adhesion are improved, but positive electrode active material breakage occurs
Solution Approach 1:
The patent applies spheroidality by controlling the positive electrode active material particles to have a spherical shape with a circularity of 0.7 or more. This spherical morphology reduces stress concentration during pressure application and charging/discharging cycles, preventing particle breakage while maintaining good electrode density and adhesion properties
2Ease of manufacture
If conventional positive electrode active materials are used, then manufacturing is simpler, but breakage occurs during pressure application and charging/discharging
Solution Approach 1:
The patent applies parameter changes by specifying precise geometric parameters (solidity ≥0.96, circularity ≥0.7, fractal dimension ≤1.143) and compositional parameters (Li content, transition metal content, optional halogen/magnesium/nickel/aluminum content) of the positive electrode active material. These parameter optimizations enhance structural stability and reliability during cycling while maintaining manufacturing feasibility through controlled particle formation processes
3Productivity
If repeated charging and discharging are performed, then battery capacity is utilized, but cracking and breakage of active material occur
Solution Approach 1:
The spherical shape with high circularity (≥0.7) distributes mechanical stress uniformly during volume expansion and contraction in charging/discharging cycles, preventing crack initiation and propagation. This maintains structural integrity while enabling high charge and discharge capacity utilization
Solution Approach 2:
The optimized geometric parameters (solidity, circularity, fractal dimension) and compositional parameters create a structurally stable positive electrode active material that can withstand repeated charging/discharging cycles without cracking or breakage, enabling sustained high productivity
Data Source
AI summary
The breakage or cracking of a positive electrode active material due to pressure application, repeated charging and discharging, or the like is likely to cause dissolution of a transition metal, an excessive side reaction, and the like. With a crack, unevenness, a step, roughness, or the like on the surface of a positive electrode active material, stress tends to be concentrated on part, which easily causes breakage. By contrast, with a smooth surface and a nearly spherical shape, stress concentration is alleviated; thus, breakage is unlikely to occur. Therefore, a positive electrode active material with a smooth surface and little unevenness is formed. For example, when the positive electrode active material is subjected to image analysis using a microscope image, the median value of the solidity is larger than or equal to 0.96. Alternatively, the median value of the fractal dimension of the positive electrode active material is smaller than or equal to 1.143. Alternatively, the median value of the circularity of the positive electrode active material is larger than or equal to 0.7.