Two-Layer Negative Electrode for Silicon Battery Cycle Stability
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with Si-containing compounds as negative electrode active materials face degradation in charge-discharge cycle characteristics due to volume changes, leading to increased resistance and poor input characteristics, as the coating formed during initial charging and discharging processes cannot conform to these changes.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a negative electrode with a two-layer structure, where the first layer includes a carbon material A and a Si-containing compound, and the second layer includes a carbon material B with higher tap density, along with lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte salt, which forms a stable, ionic conductive coating preferentially on the second layer, reducing the impact of volume changes and maintaining bond integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Si-containing compound is used as a negative electrode active material to increase lithium ion storage capacity, then the battery capacity is improved, but the charge-discharge cycle characteristics are degraded due to volume changes causing coating instability
Solution Approach 1:
The negative electrode mixture layer is divided into a first layer containing the Si-containing compound and a second layer containing carbon material without Si-containing compound. This segmentation isolates the volume-changing Si-containing compound from direct contact with the electrolyte, while the carbon-based second layer provides a stable outer surface that maintains coating integrity during charge-discharge cycles.
Solution Approach 2:
The invention uses a composite structure combining Si-containing compound (for high capacity) with carbon material (for stability). The first layer contains the high-capacity Si-containing compound, while the second layer uses stable carbon material to form a protective outer layer. This composite approach allows the battery to achieve both high lithium ion storage capacity and good cycle characteristics.
2Reliability
If a coating is formed on the Si-containing compound during initial charging and discharging to prevent continuous side reactions, then charge-discharge cycle characteristics are improved, but the coating cannot conform to volume changes during subsequent cycles, leading to continuous coating formation and degradation
Solution Approach 1:
The negative electrode is segmented into two functional layers: the first layer with Si-containing compound that undergoes volume changes, and the second layer with carbon material that provides a stable, conformal coating surface. This segmentation allows the coating to form on the stable carbon layer rather than directly on the volume-changing Si-containing compound.
Solution Approach 2:
The carbon material in the second layer acts as an intermediary between the Si-containing compound and the electrolyte. It provides a stable surface that forms a consistent coating, mediating the interaction between the volume-changing Si-containing compound and the electrolyte to prevent continuous side reactions.
3Reliability
If the amount of coating formed on the Si-containing compound is increased during initial charging and discharging to prevent continuous contact with electrolyte, then charge-discharge cycle characteristics are improved, but the resistance of the negative electrode increases, degrading input characteristics
Solution Approach 1:
The negative electrode is segmented into a first layer with Si-containing compound and a second layer with carbon material. This segmentation allows the coating to form on the carbon-based second layer, which has better electrical conductivity and lower resistance, thereby maintaining good input characteristics while still providing protection against continuous side reactions.
Solution Approach 2:
The composite structure combines Si-containing compound for capacity with carbon material for conductivity and coating stability. The carbon-based second layer provides a conductive pathway that reduces resistance while the stable coating prevents continuous side reactions, achieving both improved reliability and maintained power characteristics.
4Ease of manufacture
If a single-layer negative electrode structure is used to simplify manufacturing, then ease of manufacture is improved, but the ability to accommodate volume changes while maintaining coating stability is reduced
Solution Approach 1:
The negative electrode mixture layer is divided into two layers with distinct functions: the first layer accommodates volume changes through Si-containing compound, while the second layer provides stable coating formation through carbon material. This segmentation allows each layer to optimize its specific function, improving adaptability to volume changes while maintaining reasonable manufacturing complexity.
Solution Approach 2:
Different regions of the negative electrode are given different compositions and properties. The first layer has Si-containing compound for high capacity and volume accommodation, while the second layer has carbon material for stable coating formation. This local differentiation of quality allows the electrode to simultaneously handle volume changes and maintain coating stability.
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 the battery's input characteristics and charge-discharge cycle characteristics by maintaining the stability of the coating and preventing isolation of negative electrode active material particles from conductive paths, thereby improving overall performance.
Implementation Method 1
lithium bis(fluorosulfonyl)imide (LiFSI), which forms a stable, ionic conductive coating preferentially on the second layer
Implementation Method 2
the Si-containing compound undergoes a significant volume change in association with charging and discharging
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes a negative electrode mixture layer formed on a negative electrode current collector. The negative electrode mixture layer 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 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.