Si-Gradient Negative Electrode for Better Battery Cycle Life
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Solution Overview
Problem
The cycle characteristics of nonaqueous electrolyte secondary batteries using Si active materials as negative electrode active materials are degraded due to significant volume changes during charging and discharging, particularly affecting spirally wound electrode bodies with small radii of curvature.
Innovation Solution
A spirally wound nonaqueous electrolyte secondary battery design where the content of Si active material varies in a gradient manner within the negative electrode mixture layers, with higher content facing outward and lower content facing the current collector, to mitigate volume changes and maintain contact with electrical conduction paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si active material is used as negative electrode active material to increase battery capacity, then the battery capacity increases, but the cycle characteristics are degraded due to significant volume changes during charging and discharging
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of Si active material content within the negative electrode mixture layer. The Si content is higher in portions facing outward and lower in portions facing the current collector, allowing different regions to have optimized properties: higher Si content regions provide greater capacity while lower Si content regions experience reduced volume change stress, thereby improving cycle characteristics
2Quantity of substance
If Si active material is used to increase battery capacity, then the battery capacity increases, but the volume change during charging and discharging causes degradation of contact with electrical conduction paths
Solution Approach 1:
The gradient distribution of Si active material ensures that regions with higher Si content (which undergo greater volume change) are positioned where they can expand and contract without compromising electrical contact. The lower Si content regions near the current collector provide structural stability and maintain consistent electrical pathways, ensuring reliable contact throughout charge-discharge cycles
3Quantity of substance
If Si active material content is increased in the negative electrode to enhance capacity, then the battery capacity increases, but the portion with small radius of curvature (winding start-side edge) is greatly affected by volume change
Solution Approach 1:
The patent implements local quality by strategically distributing Si active material content throughout the electrode structure. The gradient design ensures that the winding start-side edge and other regions with small radius of curvature have optimized Si content that balances capacity enhancement with structural stability, reducing the detrimental effects of volume change on these critical regions
4Ease of manufacture
If uniform Si active material distribution is used in the negative electrode, then the manufacturing process is simple, but the cycle characteristics are degraded due to uncontrolled volume changes
Solution Approach 1:
The patent applies parameter changes by modifying the spatial distribution parameter of Si active material content within the negative electrode mixture layer. Instead of uniform distribution, the Si content varies continuously or discontinuously, creating a gradient that controls volume change behavior and improves cycle characteristics while remaining manufacturable through conventional coating and drying processes
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 design enhances the cycle characteristics of the battery by limiting degradation and increasing battery capacity while efficiently using Si active material.
Implementation Method 1
Si and Si-containing materials are capable of occluding a larger amount of lithium ions per unit volume than carbon materials
Data Source
AI summary
A nonaqueous electrolyte secondary battery according to an embodiment includes a negative electrode including a negative electrode current collector, a first negative electrode mixture layer disposed on a first surface of the negative electrode current collector, and a second negative electrode mixture layer disposed on a second surface of the negative electrode current collector. The first surface and the second surface face outward and inward of the electrode body, respectively. The first negative electrode mixture layer includes a Si active material. The content of the Si active material in teens of Si is lower in a portion of the first negative electrode mixture layer which faces the negative electrode current collector in a thickness direction of the first negative electrode mixture layer, than in a portion of the first negative electrode mixture layer which faces the surface of the first negative electrode mixture layer in the thickness direction.