Gradient Electrode Structure for Uniform Lithium Ion Diffusion
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Solution Overview
Problem
Lithium ion secondary batteries face deterioration in cycle characteristics due to non-uniform charge-discharge reactions within the electrode mixture layer, particularly near the separator, leading to reduced energy density and increased production costs when the mixture layer thickness is increased.
Innovation Solution
The battery is designed with a structure where at least three resistance components (diffusion and ohmic resistances, reaction resistances) have lower values near the current collector compared to the separator, ensuring a uniform reaction in the thickness direction of the mixture layer, achieved by varying void rates, conductive auxiliary agent content, binder content, and particle sizes across different layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the mixture layer is increased to improve energy density and reduce production cost, then the capacity per unit electrode area is increased, but the uniformity of charge-discharge reaction in the thickness direction deteriorates due to higher frequency of use of active material near the separator
Solution Approach 1:
The invention applies local quality by creating a gradient structure in the mixture layer where the void rate varies through the thickness direction. Specifically, the void rate is set to be 10-30% near the separator and 5-20% near the current collector, with a gradual transition in between. This spatial variation in void rate creates different local properties that compensate for the non-uniform reaction frequency, reducing the overuse of active material near the separator while maintaining high capacity per unit area.
2Ease of manufacture
If the mixture layer is thickened to reduce production cost, then the amount of active material is increased, but the cycle characteristics deteriorate due to non-uniform reaction and active material deterioration near the separator
Solution Approach 1:
The invention applies parameter changes by systematically varying the void rate parameter through the thickness direction of the mixture layer. The void rate is controlled to decrease from the separator side toward the current collector side, with specific ranges defined for different regions. This parameter gradient allows the use of thicker mixture layers with more active material while maintaining uniform reaction distribution, thereby improving cycle characteristics without sacrificing production cost benefits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the uniformity of charge-discharge reactions and improves cycle characteristics by maintaining a low difference in solid phase lithium ion concentration between the current collector and separator positions, thereby extending battery life and maintaining high capacity retention rates.
Implementation Method 1
diffusion resistance of lithium ions in the nonaqueous electrolytic solution which permeates at least one of the positive electrode and the negative electrode
Implementation Method 2
ohmic resistance of the mixture layer of the positive electrode; ohmic resistance of the mixture layer of the negative electrode
Implementation Method 3
reaction resistance on a surface of the active material of the positive electrode; reaction resistance on a surface of the active material of the negative electrode
Data Source
AI summary
A lithium ion secondary battery that includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution. Among resistance values of at least three of the following resistance components: diffusion resistance of Li ions in the nonaqueous electrolytic solution; ohmic resistance of the nonaqueous electrolytic solution; ohmic resistance of a positive electrode mixture layer, ohmic resistance of a negative electrode mixture layer; reaction resistance of a surface of a positive electrode active material, reaction resistance of a surface of a negative electrode active material; and diffusion resistance of Li ions in the positive electrode mixture layer, diffusion resistance of Li ions in the negative electrode mixture layer, the resistance values at a position of a mixture layer nearest a current collector are smaller than the resistance values at a position of a mixture layer nearest a separator.