Silicon-CNT Negative Electrode Composition for Longer Battery Cycle Life
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Solution Overview
Problem
Rechargeable lithium batteries face issues with breakdown due to volume expansion and shrinkage of silicon-based active materials during charging and discharging, leading to reduced energy density and cycle-life characteristics.
Innovation Solution
A negative electrode for lithium batteries is designed with a specific ratio and surface area relationship between silicon-based active material and carbon nanotubes, ensuring a balance of 26 < A * B - (C * D / 10) < 55 and 600 ≤ D ≤ 1000, where A is the weight percentage of silicon-based active material, B is its specific surface area, and C and D are the weight percentage and surface area of carbon nanotubes, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative active material layer is thickly formed to improve energy density, then energy density is improved, but the negative electrode breaks down due to volume expansion and shrinkage of silicon-based active material
Solution Approach 1:
The negative active material layer is segmented into multiple thin layers rather than forming a single thick layer. This segmentation reduces the stress and deformation caused by volume expansion and shrinkage of silicon-based active material during charging and discharging cycles, preventing electrode breakdown while maintaining high energy density through optimized layer thickness and arrangement
Solution Approach 2:
The invention uses a composite structure combining silicon-based active material with other materials in the negative active material layer. This composite approach allows the layer to accommodate volume changes of silicon while maintaining structural integrity and electrical conductivity, thereby improving both energy density and cycle-life characteristics
2Quantity of substance
If silicon-based active material is used to improve energy density, then energy density is improved, but volume expansion and shrinkage cause breakdown of the negative electrode
Solution Approach 1:
The negative active material layer is designed with beforehand cushioning features that accommodate the volume expansion and shrinkage of silicon-based active material during charging and discharging. This pre-designed cushioning structure prevents sudden stress concentration and structural breakdown, maintaining electrode integrity while utilizing the high capacity of silicon-based materials
Solution Approach 2:
The invention employs flexible thin film structures in the negative active material layer that can accommodate volume changes of silicon-based active material. These flexible structures maintain electrical connectivity and structural integrity during expansion and shrinkage cycles, preventing electrode breakdown while preserving high energy density
Data Source
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AI summary
Disclosed is a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same, and the negative electrode includes a current collector and a negative active material layer on the current collector and including a negative active material and a conductive material, the negative active material including a silicon-based active material and the conductive material includes carbon nanotube, wherein the negative active material and the conductive material are included in the negative active material layer in order to satisfy a relationship of Equation 1 and Equation 2. 26<A*B−C*D/10<55 600≤D≤1000 In Equations 1 and 2, A is wt% of the silicon-based active material included in the negative active material layer, B is a specific surface area (m2/g) according to gas adsorption of the silicon-based active material included in the negative active material layer, C is wt% of carbon nanotubes included in the negative active material layer, and D is a specific surface area (m2/g) according to gas adsorption of the carbon nanotubes included in the negative active material layer.