Silicon-Carbide-Coated Anode Material for Stable Li-Ion Cycling
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in maintaining cycle characteristics due to volume expansion of silicon-based negative electrode active materials, leading to damage, disrupted conductive paths, and irreversible reactions with the electrolyte.
Innovation Solution
A negative electrode material comprising composite particles with amorphous carbonaceous and silicon particles, a silicon carbide layer, and a coating layer of magnesium or fluorine compounds is developed, which enhances the stability and conductivity of the electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative electrode active material to increase capacity, then battery capacity is improved, but volume expansion during charging causes damage to electrode material and decreases cycle characteristics
Solution Approach 1:
The patent applies nested structure by placing silicon particles inside carbonaceous particles, forming a core-shell composite structure. The silicon core provides high capacity while the carbon shell constrains volume expansion and prevents direct contact with electrolyte, resolving the contradiction between capacity and cycle stability
Solution Approach 2:
The patent uses composite materials by combining silicon particles with carbonaceous particles to form a composite negative electrode active material. This composite structure leverages the high capacity of silicon while the carbon component provides structural stability and conductivity, addressing both capacity and reliability requirements
2Quantity of substance
If silicon particles are used as negative electrode active material, then battery capacity is improved, but conductive path between particles is cut due to volume expansion
Solution Approach 1:
By nesting silicon particles within carbonaceous particles, the carbon shell maintains continuous conductive pathways around the silicon core even during volume expansion, preventing isolation of silicon particles and maintaining electrical conductivity throughout the electrode structure
Solution Approach 2:
The carbonaceous particle shell acts as a flexible constraint that can accommodate silicon volume expansion while maintaining structural integrity and continuous conductive pathways, preventing the cutting of conductive paths during charging cycles
3Quantity of substance
If silicon-based negative electrode active material undergoes volume expansion, then capacity is improved, but peeling occurs at interface between active material layer and current collector
Solution Approach 1:
The composite structure of silicon particles embedded in carbonaceous particles creates a more mechanically stable negative electrode active material layer with reduced overall volume expansion, maintaining better adhesion to the current collector interface
Solution Approach 2:
The patent changes the physical and chemical parameters of the negative electrode material by using amorphous carbonaceous particles with specific size ranges (1-50 nm) and controlling the silicon content (5-50 mass%), creating a material with optimized mechanical properties that resist peeling while maintaining high capacity
4Quantity of substance
If silicon-based negative electrode active material is used, then battery capacity is improved, but cracks occur in SEI coating film due to volume expansion
Solution Approach 1:
The nested structure confines silicon volume expansion within the carbonaceous particle shell, preventing direct transmission of expansion stress to the SEI coating film on the electrode surface, thereby maintaining SEI film integrity
Solution Approach 2:
The carbonaceous particle shell acts as a pre-established cushioning layer that absorbs and distributes the mechanical stress from silicon volume expansion before it can reach and crack the SEI coating film, protecting the film integrity throughout cycling
Data Source
AI summary
This negative electrode material for a lithium ion secondary battery may include a composite particle, a silicon carbide layer, and a coating layer. The composite particle may include amorphous carbonaceous particles and amorphous silicon particles having an average primary particle size of 1 nm or more and 50 nm or less. The silicon carbide layer may be located between the composite particle and the coating layer. A film thickness of the silicon carbide layer may be 1 nm or more and 100 nm or less. The coating layer may include a compound of magnesium or fluorine.