Silicon-Carbon Negative Electrode Structure for Expansion Control
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Solution Overview
Problem
Lithium secondary batteries using silicon-based active materials face challenges such as volume expansion, cracking of active material particles, and reduced lifespan due to charging and discharging, limiting their use in high-energy density and high-voltage applications.
Innovation Solution
A negative electrode structure with a first carbon-containing active material layer and a second silicon-containing active material layer, where the first binder includes styrene-butadiene rubber and the second binder is a copolymer comprising acrylamide, acrylic acid, and acrylonitrile units, enhancing adhesion and controlling thickness expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to achieve high energy density, then capacity increases about 10 times compared to carbon-based material, but volume expansion and cracking occur during charging and discharging
Solution Approach 1:
The patent uses a composite structure consisting of a silicon-based active material core coated with a carbon-containing active material layer. This composite design allows the silicon core to provide high capacity while the carbon coating layer constrains volume expansion and prevents cracking, thereby maintaining structural stability during charging and discharging cycles.
Solution Approach 2:
The patent employs a carbon-containing active material coating layer as a flexible shell around the silicon-based active material. This thin film structure accommodates volume changes through elastic deformation while maintaining integrity, preventing the silicon core from cracking during repeated expansion and contraction cycles.
2Quantity of substance
If silicon-based active material is used at high voltage, then energy density improves, but excessive SEI layer formation and electrolyte depletion occur
Solution Approach 1:
The carbon-containing active material coating layer serves as an intermediary between the silicon-based active material and the electrolyte. This intermediate layer moderates the interaction at high voltages, preventing excessive SEI layer formation and reducing electrolyte depletion while still allowing efficient lithium ion transport.
3Ease of manufacture
If single-layer negative electrode structure is used, then manufacturing is simple, but adhesion and thickness expansion control are insufficient
Solution Approach 1:
The patent divides the negative electrode into multiple functional layers: a silicon-based active material layer and a carbon-containing active material layer. This segmentation allows each layer to perform its specific function - the silicon layer provides high capacity while the carbon layer ensures good adhesion and controls thickness expansion, achieving both reliability and manufacturability.
Data Source
AI summary
A negative electrode including: a negative electrode current collector; a first negative electrode active material layer on the negative electrode current collector, where the first negative electrode active material layer includes a first carbon-containing active material, a first silicon-containing active material, and a first binder; and a second negative electrode active material layer on the first negative electrode active material layer, where the second negative electrode active material layer includes a second carbon-containing active material, a second silicon-containing active material, and a second binder, wherein the first binder includes styrene-butadiene rubber, and the second binder includes a copolymer comprising an acrylamide-derived unit, an acrylic acid-derived unit, and an acrylonitrile-derived unit.