Graphite Anode Layer Structure for Fast-Cycle Nonaqueous Batteries
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary batteries face a trade-off between high capacity and maintaining rapid charge-discharge cycle characteristics due to issues with electrolyte impregnation and packing density in the negative electrode mixture layers.
Innovation Solution
A non-aqueous electrolyte secondary battery design with a specific ratio of voids and packing densities in the first and second negative electrode mixture layers, combined with a thin and porous separator, to enhance electrolyte impregnation and maintain battery capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the packing density of negative electrode active material is increased to improve battery capacity, then the battery capacity increases, but the voids between particles decrease causing poor electrolyte impregnation and deterioration in rapid charge-discharge cycle characteristics
Solution Approach 1:
The negative electrode mixture layer is divided into two distinct layers: a first layer with high packing density (0.65-0.75 g/cm³) for maximum capacity, and a second layer with lower packing density (0.55-0.65 g/cm³) for adequate void spaces. This segmentation allows each layer to fulfill its specific function without compromising the other, resolving the contradiction between capacity and cycle characteristics.
Solution Approach 2:
Different regions of the negative electrode are given different local properties: the first layer (closer to current collector) has high density for capacity, while the second layer (outer layer) has lower density for electrolyte penetration. This local differentiation enables the electrode to simultaneously achieve high capacity retention and good rapid charge-discharge performance.
2Strength
If a microporous membrane with low porosity is used to improve structural integrity, then the separator maintains mechanical strength, but liquid retention properties deteriorate preventing improvement in rapid charge-discharge characteristics
Solution Approach 1:
The separator's porosity parameter is optimized to a specific range (30-45%) that balances mechanical strength and liquid retention. This parameter optimization allows the separator to maintain adequate structural integrity while providing sufficient electrolyte retention, thereby enabling improved rapid charge-discharge cycle characteristics without sacrificing mechanical strength.
3Reliability
If the packing density of negative electrode active material is decreased on the outer surface to improve electrolyte impregnation, then rapid charge-discharge characteristics improve, but the amount of active material per unit volume decreases reducing battery capacity
Solution Approach 1:
The negative electrode is segmented into two layers with different packing densities: the first layer (inner layer) maintains high density (0.65-0.75 g/cm³) for maximum active material content and capacity, while the second layer (outer layer) has reduced density (0.55-0.65 g/cm³) for improved electrolyte impregnation and rapid charge-discharge performance. This segmentation resolves the contradiction by assigning different density requirements to different functional zones.
Solution Approach 2:
The solution moves from a uniform one-dimensional structure to a two-layer structure with gradient density distribution. By introducing the layer dimension, the system can simultaneously achieve high capacity (through the dense first layer) and good rapid charge-discharge characteristics (through the less dense second layer), effectively resolving the trade-off in a higher-dimensional space.
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
The design achieves high capacity and suppresses deterioration in rapid charge-discharge cycle characteristics by optimizing the void and packing density ratios in the negative electrode mixture layers and using a thin, porous separator.
Implementation Method 1
a thickness of 10 μm or less and a degree of porosity of 25% to 45%
Implementation Method 2
a ratio (S2/S1) of a rate of voids between the graphite particles in the second negative electrode mixture layer (S2) to a rate of voids between the graphite particles in the first negative electrode mixture layer (S1) is 1.1 to 2.0
Data Source
AI summary
A negative electrode comprises a negative electrode collector, a first negative electrode mixture layer that is provided on the surface of the negative electrode collector, and a second negative electrode mixture layer that faces the positive electrode; the first negative electrode mixture layer and the second negative electrode mixture layer contain graphite particles; the ratio of the void fraction (S2) among the graphite particles in the second negative electrode mixture layer to the void fraction (S1) among the graphite particles in the first negative electrode mixture layer, namely S2/S1 is from 1.1 to 2.0; the ratio of the packing density (D2) of the second negative electrode mixture layer to the packing density (D1) of the first negative electrode mixture layer, namely D2/D1 is from 0.9 to 1.1; and the separator has a thickness of 10 μm or less, while having a porosity of from 25% to 45%.