Amorphous Silicon-Carbon Composite to Limit Anode Volume Expansion
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Solution Overview
Problem
Lithium secondary batteries face issues with volume change and fragmentation during charging/discharging due to silicon-based negative electrode materials, leading to poor cycle characteristics and durability, while carbon-based materials have low energy density and side reactions with electrolytes.
Innovation Solution
An amorphous silicon-carbon composite is formed by mixing silicon and carbon at a molecular level using a pyrolysis method, which reduces volume change and improves electrical conductivity and lifetime characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to achieve high capacity, then the capacity increases, but volume change and fragmentation occur during charging/discharging leading to poor cycle characteristics
Solution Approach 1:
The patent creates a composite material consisting of silicon particles embedded within an amorphous carbon matrix. The carbon matrix provides structural stability and accommodates volume expansion, while silicon provides high capacity. This composite structure prevents fragmentation and maintains cycle characteristics while preserving the high capacity benefit of silicon.
Solution Approach 2:
The patent changes the physical and chemical parameters of the carbon material by creating an amorphous carbon structure through pyrolysis of organic compounds. This amorphous carbon matrix has different mechanical properties compared to crystalline carbon, allowing it to better accommodate silicon's volume changes during charging/discharging cycles.
2Duration of action of stationary object
If carbon-based negative electrode material is used to ensure long lifetime and excellent reversibility, then the lifetime improves, but the energy density per unit volume is low due to low density
Solution Approach 1:
The patent combines carbon (providing long lifetime and excellent reversibility) with silicon (providing high capacity). The resulting composite material achieves energy density superior to pure carbon while maintaining the lifetime and reversibility characteristics of carbon-based materials.
3Quantity of substance
If graphite is used as negative electrode active material to achieve high discharge voltage and energy density, then the energy density improves, but side reactions with organic electrolyte solution occur at high voltage leading to gas generation and capacity reduction
Solution Approach 1:
The silicon-carbon composite provides alternative reaction pathways and surface properties that reduce side reactions with the electrolyte. The amorphous carbon matrix modifies the electrochemical behavior, reducing gas generation while maintaining high energy density.
4Quantity of substance
If SiOx-based negative electrode active material is used to achieve high capacity, then the capacity improves, but the conductive structure is destroyed by volume expansion and contraction leading to deteriorated durability
Solution Approach 1:
The patent uses silicon (or SiOx) particles embedded in an amorphous carbon matrix. The carbon matrix maintains structural integrity during volume expansion and contraction, preserving the conductive structure and electrical connectivity throughout charge-discharge cycles, thereby maintaining durability.
Solution Approach 2:
The amorphous carbon matrix acts as a flexible, accommodating structure that can deform with the silicon particles during volume changes without breaking the overall conductive network. This flexible matrix prevents the destruction of the conductive structure.
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 amorphous silicon-carbon composite minimizes volume expansion, prevents fragmentation, and enhances the electrical conductivity and lifetime of lithium secondary batteries, offering improved performance and manufacturing simplicity.
Implementation Method 1
An amorphous silicon-carbon composite is formed by mixing silicon and carbon at a molecular level using a pyrolysis method
Data Source
AI summary
An amorphous silicon-carbon composite, a method for preparing the amorphous silicon-carbon composite using a pyrolysis method, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the same.