Two-Layer Negative Electrode Structure for Si-Anode Input and Cycle Life
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Solution Overview
Problem
The degradation of charge-discharge cycle characteristics in nonaqueous electrolyte secondary batteries using Si-containing compounds as negative electrode active materials is exacerbated by volume changes, leading to increased isolation of active material particles from conductive paths, which degrades battery performance.
Innovation Solution
A negative electrode with a two-layer structure, where the first layer contains a Si-containing compound and carbon material A with polyacrylic acid as a binding agent, and the second layer contains a carbon material B with higher tap density, improving ion acceptance and wetting characteristics, thereby reducing particle isolation and enhancing battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of binding agent is increased to inhibit particle isolation, then charge-discharge cycle characteristics are improved, but resistance of negative electrode mixture layer increases and input characteristics are degraded
Solution Approach 1:
The negative electrode mixture layer is divided into first and second layers with different functions. The first layer (containing Si-containing compound and carbon material A) focuses on maintaining particle contact and reliability, while the second layer (containing carbon material B) focuses on providing conductive paths and improving input characteristics. This segmentation allows optimization of each layer for its specific purpose without compromise.
Solution Approach 2:
Different regions of the negative electrode mixture layer are assigned different compositions and properties. The first layer has higher binding agent content and lower packing density to maintain particle contact, while the second layer has higher carbon content and higher packing density to provide conductive paths. Each local region is optimized for its specific function.
2Quantity of substance
If Si-containing compound is used as negative electrode active material to increase lithium ion storage capacity, then battery capacity is improved, but volume change during charging and discharging causes particle isolation and degrades charge-discharge cycle characteristics
Solution Approach 1:
Carbon material A with lower tap density is placed in the first layer to provide a cushioning effect that absorbs the volume expansion of the Si-containing compound during charging. This cushioning prevents particle isolation and maintains conductive paths throughout charge-discharge cycles, preserving both capacity and reliability.
Solution Approach 2:
The negative electrode uses a composite structure combining Si-containing compound (for high capacity) with carbon materials A and B (for structural stability and conductivity). The multi-material composite approach allows the Si-containing compound to provide lithium ion storage capacity while the carbon materials mitigate its volume change issues.
3Power
If carbon material with higher tap density is used to improve ion acceptance and wetting characteristics, then input characteristics are improved, but particle isolation may increase if not properly balanced with binding agent
Solution Approach 1:
The carbon material is segmented into two types placed in different layers. Carbon material A (lower tap density) is in the first layer where it provides cushioning and maintains particle contact. Carbon material B (higher tap density) is in the second layer where it provides excellent conductive paths and improves input characteristics. This segmentation resolves the contradiction between ion acceptance and particle contact maintenance.
Data Source
AI summary
A negative electrode for a nonaqueous electrolyte with a negative electrode mixture layer that includes a first layer and a second layer. The first layer is formed on the negative electrode current collector and includes a negative electrode active material and a first binding agent. The negative electrode active material in the first layer includes a carbon material A and a Si-containing compound. The first binding agent includes polyacrylic acid or a salt thereof. The second layer is formed on the first layer and includes a negative electrode active material and a second binding agent. The negative electrode active material in the second layer includes a carbon material B. The carbon material B has a tap density higher than a tap density of the carbon material A. A packing density of the second layer is lower than a packing density of the first layer.