Si-M-C Composite Negative Electrode Material for Lithium-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face challenges with cycling stability and volume swelling due to the volume expansion of silicon-based negative electrode materials during lithium ion intercalation and deintercalation, which limits their energy density and safety.
Innovation Solution
A composite negative electrode material comprising a Si-M-C composite with graphene on its surface, where M includes boron, nitrogen, or oxygen, is developed, with specific chemical shifts and peak widths in solid state nuclear magnetic resonance testing, and a controlled graphene content to enhance conductivity and reduce swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used as negative electrode material to increase energy density, then the theoretical gram capacity increases to 4,200 mAh/g, but the volume increases by 120% to 300% during lithium ion intercalation and deintercalation, causing the material to powder and separate from the current collector, degrading cycling performance
Solution Approach 1:
The patent embeds silicon-based particles inside a carbon matrix structure, creating a nested configuration where the silicon is contained within the carbon framework. This nesting approach allows the silicon to expand and contract during lithium ion cycling without compromising the structural integrity of the electrode, thereby maintaining cycling performance while utilizing the high capacity of silicon.
Solution Approach 2:
The patent creates a composite material system combining silicon-based materials with carbon matrix and conductive additives. This composite structure addresses the volume expansion issue by distributing the mechanical stress across different materials with complementary properties, preventing powdering and separation while maintaining electrical conductivity and structural stability during cycling.
2Volume of moving object
If porous silicon-based materials are designed or size is reduced to mitigate swelling, then volume expansion is partially controlled, but side reactions and uncontrollable production of SEI films further limit cycling stability
Solution Approach 1:
The patent optimizes the particle size parameters of silicon-based materials to a specific range that balances volume expansion mitigation with surface reaction control. By carefully controlling the size parameters, the patent reduces excessive SEI formation while maintaining structural stability, thereby improving cycling stability without sacrificing too much capacity.
Solution Approach 2:
The patent applies different material compositions and structures to different regions of the electrode. The carbon matrix provides a stable framework in regions prone to excessive expansion, while silicon particles are strategically positioned and sized to maximize capacity contribution. This local differentiation allows the electrode to handle volume changes more effectively and reduce harmful side reactions.
3Reliability
If graphene is added to improve conductivity, then conductivity of the composite negative electrode material increases, but excessive graphene content may cause excessive swelling and retention of lithium sources
Solution Approach 1:
The patent optimizes the concentration parameter of graphene in the composite material to achieve the desired conductivity while avoiding excessive volume swelling. By precisely controlling the graphene content within a specific range, the patent balances electrical conductivity improvement with volume stability, preventing both insufficient conductivity and excessive swelling that would compromise battery performance.
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 improves cycling stability and reduces volume swelling, maintaining high conductivity and cycling performance while controlling graphene content to prevent excessive swelling and retention of lithium sources.
Implementation Method 1
graphene is present on the surface of the Si-M-C composite material, which improves conductivity of the composite negative electrode material
Implementation Method 2
the Si-M-C composite material has a low swelling rate
Data Source
AI summary
A composite negative electrode material includes a Si-M-C composite material and graphene on a surface of the Si-M-C composite material, where M includes at least one of boron, nitrogen, or oxygen. Solid state nuclear magnetic resonance testing of the Si-M-C composite material shows that chemical shifts of element silicon include −5 ppm±5 ppm, −35 ppm±5 ppm, −75 ppm±5 ppm, and −110 ppm±5 ppm, and a peak width at half height at −5 ppm±5 ppm satisfies 7 ppm<K<28 ppm. The composite negative electrode material and the negative electrode plate and electrochemical apparatus that use the composite negative electrode material have good cycling performance.