Layered Graphite Negative Electrode for Cycle Life and Capacity
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary batteries face challenges in achieving both superior charge/discharge cycle characteristics and higher capacity due to issues with packing density, electrolyte permeability, and contact points between active material particles, particularly when using materials like silicon with large expansion/contraction.
Innovation Solution
A negative electrode structure featuring alternately placed first and second active material layers with different graphite particle contents and porosities, where the first layer has a higher content of graphite particles with smaller internal porosity and the second layer has a higher content of graphite particles with larger internal porosity, optimized to maintain permeability and packing density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a region of low packing density is formed at a part of the active material layer to improve electrolyte permeability, then charge/discharge cycle characteristic is improved, but battery capacity is reduced
Solution Approach 1:
The patent applies local quality by creating regions with different packing densities within the active material layer. Specifically, it forms a low packing density region at the width-direction center portion and high packing density regions at other portions, allowing each region to serve its optimal function: the low density region ensures electrolyte permeability and cycle stability, while the high density regions maximize capacity.
Solution Approach 2:
The patent segments the active material layer into distinct regions with different packing densities arranged in a stripe pattern. This segmentation allows the electrode to simultaneously achieve good electrolyte penetration (through low density regions) and high capacity (through high density regions), resolving the contradiction between cycle life and capacity.
2Reliability
If a groove is formed on the surface of the negative electrode active material layer to improve electrolyte permeability, then charge/discharge cycle characteristic is improved, but packing density at the groove portion becomes large making permeability improvement difficult
Solution Approach 1:
Instead of forming a groove (removing material) to improve permeability, the patent inverts the approach by controlling the packing density distribution during layer formation. It creates low packing density regions through controlled application conditions rather than mechanical removal, achieving permeability improvement without the drawbacks of groove structures.
3Quantity of substance
If the electrode plate surface is covered by active material particles with small particle size to increase capacity, then battery capacity is improved, but movement of electrolyte solution from within the active material layer is restricted reducing charge/discharge cycle characteristic
Solution Approach 1:
The patent applies local quality by using small particle size active materials specifically at the width-direction center portion where electrolyte penetration is most critical for cycle life, while using larger particle sizes at other portions to maximize capacity. This spatial differentiation of particle sizes allows simultaneous optimization of both capacity and cycle characteristics.
4Quantity of substance
If active material with large expansion/contraction such as silicon is used to increase capacity, then battery capacity is improved, but contact points between active material particles are reduced making it difficult to secure conductivity
Solution Approach 1:
The patent uses composite materials by combining silicon-based active materials with conductive carbon materials in specific ratios and distributions. This composite structure maintains high capacity from the silicon while the carbon network preserves conductivity even as silicon expands and contracts during cycling, resolving the contradiction between capacity and electrical conductivity.
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 charge/discharge cycle characteristics and maintains higher capacity by ensuring effective electrolyte permeation and reduced electrical resistance, while securing adhesion between the current collector and active materials.
Implementation Method 1
an internal porosity of the graphite particles A is smaller than an internal porosity of the graphite particles B
Data Source
AI summary
A negative electrode for nonaqueous electrolyte secondary batteries with a negative electrode collector and a negative electrode active material layer thereon, with respect to the negative electrode active layer, first active material layers (X) and second active material layers (Y) are alternately arranged on the negative electrode collector, the first and second active material layers containing, as a negative electrode active material, graphite particles A and graphite particles B, while being different from each other in the content of the graphite particles A relative to the total mass of the graphite particles A and the graphite particles B. The internal void fraction of the graphite particles A is lower than the internal void fraction of the graphite particles B; the content of the graphite particles A in the first active material layers (X) is higher than the content of the graphite particles A in the second active material layers (Y).