Lithium Ion Battery Electrode Void Ratio Gradient for Energy Density
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in increasing energy density without reducing output, as reducing void ratios in electrodes increases diffusion resistance, and methods to enhance reaction areas with smaller active material particles require more conductive agents and binders, making it difficult to densely fill active material particles.
Innovation Solution
The lithium ion secondary battery features an active material mix layer on both surfaces of a current collector with a smaller void ratio in the current collector and surface regions compared to the intermediate region, allowing for a two-directional increase in the reaction area with the electrolyte while maintaining output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the void ratio in an electrode is reduced and active material particles are densely filled to increase energy density, then the energy density is improved, but the diffusion resistance of Li ions increases resulting in output reduction
Solution Approach 1:
The patent applies local quality by creating different void ratio zones within the active material mix layer. The first region (near current collector) has a first void ratio optimized for Li ion diffusion and electrical connection, while the second region (near surface) has a second void ratio optimized for particle filling density. This spatial variation in structural properties resolves the contradiction between energy density and output by allowing each region to perform its specific function optimally.
2Productivity
If the sizes of active material particles are reduced to increase the reaction area with electrolyte, then the reaction resistance is reduced improving output, but the amounts of conductive assisting agent and binder must be increased making it difficult to densely fill active material particles
Solution Approach 1:
The patent resolves this contradiction by assigning different void ratio characteristics to different regions. The first region near the current collector maintains higher void ratio to ensure sufficient conductive assisting agent and binder for maintaining electrical continuity and mechanical strength, enabling good output performance. The second region near the surface uses lower void ratio to maximize active material particle filling density, achieving high energy density. This regional differentiation allows small particles to be used throughout while maintaining both output and energy density.
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 enables a high energy density while maintaining output by reducing diffusion resistance and increasing the reaction area, preventing output degradation, thus improving volume energy density.
Implementation Method 1
a diffusion resistance of Li ions increases
Data Source
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AI summary
Provided is a lithium ion secondary battery capable of realizing a high energy density while maintaining output. A lithium ion secondary battery D1 according to the present invention includes an electrode having an active material mix layer 31 on both surfaces of a current collector 35. The active material mix layer 31 has a smaller void ratio in a current collector side region 34 of the active material mix layer 31 and a surface side region 32 of the active material mix layer 31 than in an intermediate region 33 between the current collector side region 34 and the surface side region 32 of the active material mix layer 31.