Silicon Negative Electrode Aluminum Layer Volume Control
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Solution Overview
Problem
Silicon-based active materials for negative electrodes in lithium secondary batteries suffer from poor service life and swelling characteristics due to side reactions with the electrolytic solution, limiting their high-capacity potential.
Innovation Solution
A three-layered structure for the negative electrode, comprising a carbon-based first layer, a silicon-based second layer, and an aluminum or aluminum-containing compound third layer, with the third layer's thickness controlled to improve stability and suppress volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase capacity, then battery capacity is improved, but service life and swelling characteristics deteriorate due to side reactions with electrolyte
Solution Approach 1:
The negative electrode active material layer is divided into two separate layers: a first layer containing carbon-based active material and a second layer containing silicon-based active material. This segmentation allows the silicon-based material to provide high capacity while the carbon-based layer provides structural stability, preventing the swelling and service life issues that would occur if silicon-based material alone was used.
Solution Approach 2:
The invention uses a composite structure combining carbon-based active material and silicon-based active material in a layered configuration. The carbon-based material acts as a stable foundation that mitigates the swelling characteristics of silicon-based material, while the silicon-based material contributes high capacity. This composite approach resolves the contradiction between capacity improvement and reliability maintenance.
2Reliability
If third layer thickness is increased to improve stability, then service life is improved, but electrode thickness increases reducing productivity
Solution Approach 1:
The invention optimizes the thickness parameter of the third layer (aluminum-containing compound layer) to be within a specific range: greater than 0 μm and equal to or less than 1/20 of the sum of the thicknesses of the first and second layers. This parameter optimization ensures sufficient protective function for service life while maintaining thin overall electrode thickness for high productivity.
Solution Approach 2:
The third layer is applied selectively with specific thickness characteristics - it provides localized protection where needed (at the electrode surface facing the separator) while maintaining thin overall dimensions. The local quality of the third layer is optimized to provide maximum service life improvement with minimum thickness increase.
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
The layered structure enhances cycle life, service life, and swelling characteristics by stabilizing the silicon-based active material, allowing for higher capacity and thinner electrode design.
Implementation Method 1
an inorganic layer containing relatively hard aluminum can suppress changes in volume of an active material layer containing a silicon-based active material with high swelling
Data Source
AI summary
The present invention relates to a negative electrode for lithium secondary batteries and a lithium secondary battery, the negative electrode comprising: a current collector; a first layer provided on the current collector and including a carbon-based active material; a second layer provided on the first layer and including a silicon-based active material; and a third layer provided on the second layer and including aluminum or an aluminum-containing compound, wherein the thickness of the third layer is greater than 0 but not exceeding 1/20 of the combined thickness of the first and second layers.