Lithium Ion Battery Negative Electrode Hardness via Porous Fillers
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Solution Overview
Problem
Lithium ion secondary batteries with graphite-based negative electrodes face challenges in high rate tolerance due to the softness of graphite particles, which leads to crushing and increased resistance during charging and discharging, and existing methods to enhance hardness, such as high-pressure compression, compromise electrolyte permeation.
Innovation Solution
Incorporating inorganic filler particles and lithium titanate (LTO) particles with specific size ratios into the negative electrode mixture layer to improve hardness and create permeation paths for the electrolyte, while maintaining effective electrolyte access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the negative electrode mixture layer is compressed at high pressure to increase hardness, then the negative electrode becomes harder and more resistant to crushing, but the voids in the negative electrode mixture layer are crushed and electrolyte solution permeation is reduced
Solution Approach 1:
The patent utilizes porous inorganic filler particles with specific pore structures that maintain void spaces within the negative electrode mixture layer. These porous materials provide both mechanical strength to prevent graphite particle crushing and maintain electrolyte permeation pathways, resolving the contradiction between hardness and electrolyte access.
Solution Approach 2:
The patent creates a composite negative electrode mixture layer combining graphite particles with porous inorganic filler particles. This composite structure leverages the softness of graphite for lithium insertion while the porous inorganic filler provides structural support and maintains electrolyte pathways, achieving both hardness and permeation simultaneously.
2Strength
If the negative electrode mixture layer is compressed to improve hardness, then resistance to crushing increases, but high rate tolerance does not improve as expected
Solution Approach 1:
The porous inorganic filler particles maintain open void structures that facilitate rapid electrolyte penetration during high rate charging and discharging. This porosity enables sustained high rate tolerance while the filler particles simultaneously provide structural hardness to prevent particle crushing during expansion and contraction cycles.
Solution Approach 2:
The patent changes the physical and chemical parameters of the negative electrode by introducing porous inorganic fillers with specific surface areas, pore sizes, and distributions. These parameter changes enable the electrode to maintain both mechanical integrity at high rates and adequate electrolyte access, improving high rate tolerance beyond what compression alone achieves.
3Quantity of substance
If graphite particles are used in the negative electrode mixture layer, then capacity is maintained, but the softness of graphite particles causes crushing during charging and discharging
Solution Approach 1:
The patent forms a composite where graphite particles (providing lithium storage capacity) are combined with porous inorganic filler particles (providing structural support). The inorganic filler acts as a rigid framework that prevents graphite particle crushing during charging and discharging while maintaining the graphite's lithium insertion capability.
Solution Approach 2:
The porous inorganic filler particles serve as an intermediary structural support between the soft graphite particles and the external mechanical stresses during charging and discharging. This intermediary framework protects the graphite particles from crushing while allowing lithium ions to access the graphite for capacity maintenance.
Data Source
AI summary
A lithium ion secondary battery includes at least a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer. The negative electrode mixture layer is formed on a surface of the negative electrode current collector. The negative electrode mixture layer includes graphite particles, inorganic filler particles, lithium titanate particles, and a water-based binder. The inorganic filler particles have an average primary particle size that is ½ or less of an average primary particle size of the graphite particles. The lithium titanate particles have an average primary particle size of 1 μm or less. A ratio of an average primary particle size of the lithium titanate particles with respect to an average primary particle size of the inorganic filler particles is one or less.