Two-Layer Silicon Anode Structure for Stable Conduction Paths
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Solution Overview
Problem
Existing nonaqueous electrolyte secondary batteries face challenges in achieving high energy density and excellent output characteristics due to the difficulty of silicon-based active materials' volume change, which can lead to conduction path cut-off and increased resistance.
Innovation Solution
A negative electrode with a two-layer structure, comprising a first layer with a soft carbon-based active material and a second layer with a hard carbon-based active material, where the second layer has a higher compressive strength and lower silicon-based active material content, to mitigate volume changes and maintain favorable output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase energy density, then the energy density of the battery is improved, but the volume change of silicon-based active material causes conduction path cut-off and increases resistance
Solution Approach 1:
The patent changes the physical and chemical parameters of the carbon-based active material by controlling the graphitization degree and amorphous component content. Specifically, it uses carbon-based active material with 10-50 mass% amorphous component and graphitization degree of 10-50%, creating a material with intermediate properties between soft and hard graphite that can accommodate silicon volume changes while maintaining conduction paths
Solution Approach 2:
The patent creates a composite negative electrode active material combining silicon-based active material (5-50 mass%) with carbon-based active material (50-95 mass%). This composite structure allows the carbon matrix to buffer the volume expansion of silicon during lithium insertion, preventing conduction path cut-off while maintaining high energy density
2Power
If hard graphite particles containing large amount of amorphous component are used to improve output characteristics, then the output characteristics are improved, but the graphite particles cannot follow the volume change of silicon-based active material, causing conduction path cut-off
Solution Approach 1:
The patent optimizes the parameters of carbon-based active material by controlling the amorphous component content (10-50 mass%) and graphitization degree (10-50%). This creates a material with intermediate hardness that can follow silicon volume changes better than hard graphite while still improving output characteristics compared to soft graphite
Solution Approach 2:
The patent applies local quality by creating a carbon-based active material with specific local structural characteristics - containing amorphous components that provide flexibility to follow silicon volume changes in the local region, while maintaining sufficient hardness to improve overall output characteristics
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 compatibility between high energy density and long-term output characteristics by suppressing conduction path cut-off and maintaining low resistance values during charging and discharging.
Implementation Method 1
a first carbon-based active material having a 10% compressive strength of 3 MPa or less and a silicon-based active material containing Si, and the second layer contains a second carbon-based active material having a 10% compressive strength of 5 MPa or more
Data Source
AI summary
In a nonaqueous electrolyte secondary battery, a negative electrode mix layer includes a first layer and a second layer disposed successively from a negative electrode collector. The first layer contains a first carbon-based active material having a 10% compressive strength of 3 MPa or less and a silicon-based active material containing Si. The second layer contains a second carbon-based active material having a 10% compressive strength of 5 MPa or more and has a lower content (mass ratio) of the silicon-based active material than the first layer.