Silicon-Graphite Anode Composite for Volume Expansion Control
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Solution Overview
Problem
Existing negative electrode materials for lithium ion secondary batteries, particularly those using silicon, face challenges with volume expansion and low cycle characteristics due to the conversion of silicon compounds to silicon carbide during mechanochemical treatment, leading to decreased capacity and efficiency.
Innovation Solution
A composite material comprising nanosilicon particles, graphite, and amorphous carbon, with specific particle size distributions and BET surface areas, is used, along with a manufacturing method involving heat treatment in an inert gas atmosphere to enhance Si dispersibility and compounding, resulting in improved initial discharge capacity, Coulomb efficiency, and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mechanochemical treatment is applied to carbon and silicon compounds, then composite material is formed, but silicon compound converts to silicon carbide causing capacity decrease
Solution Approach 1:
The invention changes the treatment parameter from mechanochemical treatment to heat treatment at 600-1000°C, which prevents the conversion of silicon compounds to silicon carbide while still forming a composite material structure, thereby maintaining high capacity
Solution Approach 2:
The invention replaces the mechanical mechanochemical treatment system with a thermal processing system, using heat treatment instead of mechanical energy to form the composite material, thus avoiding unwanted chemical conversions
2Quantity of substance
If silicon is used as negative electrode active material, then theoretical capacity is higher than graphite, but volume expansion causes self-destruction and low cycle characteristics
Solution Approach 1:
The invention creates a composite material containing silicon particles, carbon particles, and silicon carbide particles in specific proportions, where the carbon and silicon carbide components provide structural support to accommodate silicon's volume expansion, preventing self-destruction and improving cycle characteristics while maintaining high capacity
Solution Approach 2:
The invention creates a heterogeneous composite structure where different materials (silicon, carbon, silicon carbide) are distributed in specific proportions and arrangements, with each component serving a specific function: silicon for capacity, carbon for flexibility and conductivity, and silicon carbide for structural stability
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 composite material achieves high initial discharge capacity, high initial Coulomb efficiency, and improved cycle characteristics by ensuring uniform dispersion and compounding of silicon and carbon, preventing excessive volume expansion and maintaining battery performance over cycles.
Implementation Method 1
a manufacturing method involving heat treatment in an inert gas atmosphere to enhance Si dispersibility and compounding
Data Source
AI summary
A negative electrode material for lithium ion secondary batteries, including composite material particles containing nanosilicon particles having a 50% particle diameter (Dn50) of 5 to 100 nm in a number-based cumulative particle size distribution of primary particles, graphite particles and an amorphous carbon material; the composite material particles containing the nanosilicon particles at a content of 30 to 60 mass % or less, and the amorphous carbon material at a content of 30 to 60 mass % or less; the composite material particles having a 90% particle diameter (DV90) in the volume-based cumulative particle size distribution of 10.0 to 40.0 μm, a BET specific surface area of 1.0 to 5.0 m2/g, and an exothermic peak temperature in DTA measurement of 830° C. to 950° C. Also disclosed is a paste for negative electrodes, a negative electrode sheet, a lithium ion secondary battery and a method for manufacturing the negative electrode material.