Two-Layer Silicon Negative Electrode for Expansion-Stable Cycle Life
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Solution Overview
Problem
Lithium secondary batteries face rapid capacity decrease due to volume expansion and contraction of silicon-based negative electrode active materials, particularly in silicon-based electrodes, which affects their lifespan and performance.
Innovation Solution
A negative electrode structure comprising a first silicon-based active material layer with a low silicon content and a thicker second layer with a higher silicon content, combined with carbon-based materials and conductive components, is applied to a current collector, optimizing the thickness ratio and composition to enhance capacity and cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based negative electrode active material is used to increase capacity, then the energy density is improved, but the volume expansion and contraction during charging and discharging causes rapid capacity decrease and shortens cycle life
Solution Approach 1:
The negative electrode active material layer is divided into two distinct layers: a first layer with low silicon content (5% by weight or less) and a second layer with high silicon content. This segmentation allows each layer to perform different functions - the first layer provides structural stability while the second layer maximizes capacity, resolving the contradiction between high capacity and long cycle life
Solution Approach 2:
Different regions of the negative electrode are given different silicon concentrations tailored to their specific functions. The first layer (closer to current collector) has low silicon content for stability, while the second layer (outer layer) has high silicon content for maximum capacity. This local differentiation of material properties optimizes both cycle life and capacity simultaneously
2Quantity of substance
If the silicon content in the negative electrode is increased to enhance capacity, then the energy density improves, but the volume change during operation becomes more severe
Solution Approach 1:
The negative electrode is segmented into two layers with different silicon contents. The first layer contains 5% by weight or less silicon and serves as a stable base layer that undergoes minimal volume change, while the second layer contains high silicon content for maximum capacity but is positioned where its volume expansion is better managed by the underlying stable first layer
Solution Approach 2:
The volume stability requirement is addressed locally by placing the low-silicon first layer at the interface with the current collector, where it provides a stable foundation. The high-silicon second layer is positioned at the outer region where it can achieve high capacity while its volume changes are accommodated by the flexible structure
Data Source
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AI summary
A negative electrode for secondary batteries according to an embodiment of the present disclosure may include: a negative electrode current collector; a first negative electrode active material layer formed on at least one surface of the negative electrode current collector and including a first silicon-based negative electrode active material; and a second negative electrode active material layer formed on the first negative electrode active material, including a second silicon-based negative electrode active material, and having a greater thickness than that of the first negative electrode active material layer, wherein in the first negative electrode active material layer, the content of the first silicon-based negative electrode active material may be 5% by weight or less based on the total weight of the first negative electrode active material layer, and the weight percentage of the second silicon-based negative electrode active material in the second negative electrode active material layer based on the total weight of the second negative electrode active material layer may be greater than the weight percentage of the first silicon-based negative electrode active material in the first negative electrode active material layer based on the total weight of the first negative electrode active material layer.