Graphite Anode Particle Mixing for Battery Cycle Endurance
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Solution Overview
Problem
Spheroidized graphite particles used in negative electrodes of non-aqueous electrolyte secondary batteries face issues with cycle endurance due to repeated volume changes causing loss of contact points between particles, leading to discontinuity of conductive paths and decreased capacity retention.
Innovation Solution
A method involving the use of a mixture of first and second graphite particles with specific particle size distributions and circularity relationships, where the second graphite particles are smaller and have equal or lesser circularity than the first, forming conductive paths and maintaining contact points, thereby enhancing cycle endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spheroidized graphite particles are used to improve packing properties and energy density, then particle stability and pore formation are enhanced, but cycle endurance deteriorates due to loss of contact points between particles
Solution Approach 1:
The patent applies the nesting principle by placing smaller graphite particles (second particles) inside the gaps between larger graphite particles (first particles). This nested arrangement ensures that smaller particles fill the void spaces, creating additional contact points and maintaining conductive paths even when larger particles undergo volume changes during charge-discharge cycles. The hierarchical structure resembles nested dolls, where smaller elements are positioned within the spaces of larger elements to enhance overall structural stability.
Solution Approach 2:
The patent applies local quality by creating regions with different particle size characteristics. The negative electrode contains both large graphite particles (providing structural stability and capacity) and small graphite particles (filling gaps and maintaining conductive networks). This local variation in particle size distribution ensures that different regions of the electrode serve complementary functions: larger particles provide bulk capacity while smaller particles ensure continuous conductivity, thereby resolving the contradiction between maintaining contact points and accommodating volume changes.
2Reliability
If conductive material such as carbon black is added to form conductive paths, then conductivity is improved, but energy density decreases due to non-active material addition
Solution Approach 1:
The patent applies parameter changes by altering the particle size parameter of the conductive material. Instead of using conventional carbon black with particle sizes in the micrometer or sub-micrometer range, the invention uses graphite particles with controlled smaller sizes (0.1-10 μm). This parameter change allows the conductive material to also function as active material, simultaneously providing conductivity and lithium storage capacity. The smaller graphite particles can intercalate lithium ions while maintaining the conductive network, thereby improving energy density compared to traditional carbon black additives.
Solution Approach 2:
The patent applies universality by making the smaller graphite particles serve dual functions: as conductive material forming continuous paths between larger particles, and as active material contributing to battery capacity. These smaller graphite particles are not merely inert conductive additives like traditional carbon black; they actively participate in lithium insertion-extraction reactions. This multi-functionality resolves the contradiction by eliminating the need to choose between conductivity and energy density, as the same material provides both benefits.
Data Source
AI summary
A negative electrode active material is prepared by mixing a first graphite particle and a second graphite particle. A negative electrode including the negative electrode active material is produced. A non-aqueous electrolyte secondary battery including the negative electrode, a positive electrode, and an electrolyte solution is produced. The first graphite particle has a first number-based particle size distribution. The second graphite particle has a second number-based particle size distribution. A relationship of “D250/D150≤0.50” is satisfied. D150 is a D50 in the first number-based particle size distribution. D250 is a D50 in the second number-based particle size distribution. A relationship of “R2≤R1” is satisfied. R1 is an arithmetic mean of circularity of the first graphite particle. R2 is an arithmetic mean of circularity of the second graphite particle.