Negative Electrode Current Collector Thickness Optimization
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Solution Overview
Problem
There is a need for lithium ion secondary batteries and related devices to be smaller, lighter, and achieve higher energy density while maintaining excellent battery characteristics, with a focus on preventing the negative electrode current collector from breaking due to expansion and shrinkage of the active material during charging and discharging.
Innovation Solution
A negative electrode for lithium ion secondary batteries is designed with a current collector that satisfies specific displacement ratio and expansion coefficient conditions, ensuring the collector remains intact even with material expansion and shrinkage, and is combined with a negative electrode active material layer containing carbon and silicon materials to enhance energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of the negative electrode current collector is reduced to make the battery smaller and lighter, then the battery size and weight are improved, but the current collector becomes more susceptible to breaking due to expansion and shrinkage of the active material
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness of the negative electrode current collector to specific ranges (3-8 μm for copper foil, 5-10 μm for copper-clad steel foil) based on the expansion coefficient of the active material. This quantitative parameter optimization allows the collector to be thin enough to reduce battery weight while thick enough to withstand expansion-shrinkage stresses, thus resolving the contradiction between weight reduction and reliability maintenance.
2Quantity of substance
If the negative electrode active material layer has high expansion coefficient to increase energy density, then the energy density is improved, but the current collector is more likely to break due to larger expansion and shrinkage
Solution Approach 1:
The patent establishes a quantitative relationship between the expansion coefficient of the active material layer (X%) and the current collector thickness through the formula D2≤21.947×(X/100)−24.643, where D2 is the displacement amount in a piercing test. This parameter change approach allows the battery design to accommodate higher expansion coefficients (110-125%) that increase energy density while automatically adjusting the collector thickness to prevent breaking, thus resolving the contradiction between energy density and reliability.
Data Source
AI summary
A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode current collector satisfies:(D2/D1)≥0.968 (1),D2≥21.947*(X/100)−24.643 (2),110≤X≤125 (3), andwhere D1 is a first displacement amount in a first piercing test at a first piercing speed of 0.1 mm/min or more; D2 is a second displacement amount in a second piercing test at a second piercing speed of less than 0.1 mm/min; and X is an expansion coefficient (%) of the negative electrode active material layer.