Gradient Silicon-Graphite Negative Electrode for Battery Discharge Rate
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries with silicon materials as negative electrode active materials face challenges in achieving high discharge rate characteristics due to volume expansion issues during charging and discharging.
Innovation Solution
A negative electrode structure with a mixture layer containing graphite and silicon, where a first region with a higher silicon content and lower density is designed to facilitate lithium ion conductivity by creating pores, improving discharge rate characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode active material to increase capacity, then the battery capacity is improved, but the discharge rate characteristics deteriorate due to volume expansion issues
Solution Approach 1:
The negative electrode mixture layer is divided into a first region (remote from current collector) with high silicon content and a second region (adjacent to current collector) with low silicon content. This segmentation allows the high-capacity silicon material to be distributed strategically while maintaining good discharge rate characteristics through the graphite-rich second region that provides stable ion transport pathways.
Solution Approach 2:
Different regions of the mixture layer are given different compositions: the first region has high silicon content (60-90 mass%) for maximum capacity, while the second region has low silicon content (0-40 mass%) for stable discharge performance. This local quality variation optimizes both capacity and discharge rate characteristics in their respective zones.
2Quantity of substance
If the mixture layer density is increased to improve capacity, then the energy density is improved, but the lithium ion conductivity deteriorates
Solution Approach 1:
The mixture layer exhibits local density variation: the first region has lower density (providing higher porosity and lithium ion conductivity) while the second region has higher density (providing better energy density). This local quality differentiation allows simultaneous optimization of ion transport and energy storage.
Solution Approach 2:
The first region is designed with lower density corresponding to higher porosity, creating pathways for efficient lithium ion diffusion. This porous structure in the silicon-rich region maintains high ion conductivity despite the high capacity load, while the denser second region provides stable structural support.
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 battery exhibits enhanced discharge rate characteristics and high capacity due to improved lithium ion conductivity and diffusibility, while maintaining cycle stability.
Implementation Method 1
silicon materials, such as silicon (Si) and silicon oxide represented by SiOx, can intercalate more lithium ions per unit volume than carbon materials, such as graphite
Implementation Method 2
The first region has a lower density than the second region... improved lithium ion conductivity and diffusibility
Data Source
AI summary
A non-aqueous electrolyte secondary battery including a silicon material as a negative electrode active material has good discharge rate characteristics. A negative electrode according to an exemplary embodiment includes a negative-electrode current collector and a negative-electrode mixture layer formed on the current collector. The negative-electrode mixture layer contains graphite and a silicon material. A first region that extends from the surface of the mixture layer remote from the negative-electrode current collector in the thickness direction of the negative-electrode mixture layer and has a thickness equal to 40% of the thickness of the mixture layer contains a larger amount of the silicon material than a second region that extends from the surface of the mixture layer adjacent to the negative-electrode current collector and has a thickness equal to 40% of the thickness of the mixture layer. The first region has a lower density than the second region.