Wound Li-Ion Battery Anode Gradient for Si Expansion Control
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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 Si active material content varies in the negative electrode mixture layers, with higher content on the surface-facing portions and lower content on the current collector-facing portions, to mitigate volume changes and maintain contact with the 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 negative electrode mixture layer with non-uniform Si active material distribution. The Si active material content is specifically controlled to be lower near the negative electrode current collector and higher toward the separator side, creating different local compositions to address the volume expansion issue at different depths of the electrode structure.
Solution Approach 2:
The patent changes the concentration parameter of Si active material within the negative electrode mixture layer. By controlling the Si active material content to decrease from the separator side toward the current collector side, the patent optimizes the local density and composition parameters to mitigate volume change effects while maintaining overall battery capacity.
2Quantity of substance
If Si active material is used in spirally wound electrode body, then battery capacity increases, but the volume change greatly affects portions with small radius of curvature such as winding start-side edge
Solution Approach 1:
The patent addresses the specific problem at the winding start-side edge by creating a gradient distribution of Si active material. The lower Si content near the current collector in this region reduces local volume expansion, thereby protecting the structural integrity of the electrode at the critical small radius of curvature location while maintaining capacity in other regions.
Solution Approach 2:
The patent applies preliminary anti-action by pre-distributing the Si active material in a gradient pattern before electrode assembly and winding. This pre-planned non-uniform distribution anticipates and counteracts the harmful volume expansion effects that will occur during charging, particularly at the winding start-side edge, before structural degradation can occur.
3Quantity of substance
If Si active material content is increased to enhance battery capacity, then more lithium ions can be occluded, but contact with conduction paths is lost due to volume expansion
Solution Approach 1:
The patent uses local quality by creating regions with different Si active material concentrations. The gradient distribution ensures that areas with higher Si content (better lithium ion occlusion) are compensated by areas with lower Si content (less volume expansion), maintaining overall electrical conduction paths while maximizing lithium ion storage capacity.
Solution Approach 2:
The patent creates a composite structure within the negative electrode mixture layer by combining Si active material with other materials in a gradient distribution. This composite approach allows the electrode to simultaneously achieve high lithium ion occlusion capacity from Si-rich regions and maintained electrical conduction from Si-poor regions, resolving the contradiction between capacity and conduction reliability.
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 materials.
Implementation Method 1
Si and Si-containing materials are capable of occluding a larger amount of lithium ions per unit volume than carbon materials
Implementation Method 2
nonaqueous electrolyte secondary battery including a spirally wound electrode body
Data Source
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AI summary
The purpose of the present disclosure is to improve the cycle characteristics of a nonaqueous electrolyte secondary battery which is provided with a wound electrode body that uses an Si-based active material as a negative electrode active material. With respect to a nonaqueous electrolyte secondary battery according to one embodiment of the present invention, a negative electrode comprises: a negative electrode collector; a first negative electrode mixture layer that is formed on a first surface of the negative electrode collector, said first surface facing the outside of the electrode body; and a second negative electrode mixture layer that is formed on a second surface of the negative electrode collector, said second surface facing the inside of the electrode body. The first negative electrode mixture layer contains a Si-based active material. The content ratio of the Si-based active material based on Si in the negative electrode collector side of the first negative electrode mixture layer is lower than that in the surface side of the first negative electrode mixture layer in the thickness direction of the first negative electrode mixture layer.