Silicon-Carbon Negative Active Material for Cycle-Life and Ion Transport
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Solution Overview
Problem
Existing rechargeable lithium batteries face challenges in achieving high capacity, efficient charge and discharge, and long cycle-life due to limitations in negative active materials, particularly with silicon-based materials that experience significant volume expansion during charging and discharging.
Innovation Solution
A composite negative active material comprising a silicon core coated with a carbon layer, combined with crystalline and amorphous carbon materials, including a rod-type crystalline carbon as a second active material to enhance ionic conductivity and a spherical crystalline carbon as a third active material to improve initial cycle-life, along with specific weight ratios to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based materials are used as negative active material to achieve high capacity, then energy density is improved, but volume expansion during charging and discharging causes poor cycle-life
Solution Approach 1:
The silicon core is nested within a carbon coating layer, which is in turn embedded in a composite structure with rod-type crystalline carbon and spherical crystalline carbon. This nested architecture allows the silicon to expand and contract during lithium insertion/extraction while being constrained and protected by the surrounding carbon structures, preventing volume expansion damage and improving cycle-life while maintaining high capacity
Solution Approach 2:
The invention uses a composite negative active material consisting of silicon core, carbon coating layer, rod-type crystalline carbon, and spherical crystalline carbon. This composite structure combines the high capacity of silicon with the structural stability and ionic conductivity of carbon materials, achieving both high energy density and long cycle-life by leveraging the complementary properties of each component
2Reliability
If conventional carbon coating is applied to silicon to reduce volume expansion, then cycle-life is improved, but ionic conductivity decreases
Solution Approach 1:
The invention introduces rod-type crystalline carbon with high aspect ratio (4-100) that creates localized high-ion-conductivity pathways within the carbon coating layer. The rod-shaped structures provide preferential channels for lithium ion transport, ensuring efficient ionic conductivity in critical regions while the overall carbon coating maintains its protective function against volume expansion
Solution Approach 2:
The invention changes the morphological parameters of the carbon coating by incorporating rod-type crystalline carbon with specific aspect ratios (4-100) and controlled lengths (20-100 μm). This parameter optimization creates a balance between the coating's protective function and its ionic conductivity, allowing lithium ions to efficiently transport through the carbon matrix while still constraining silicon expansion
Data Source
AI summary
A negative active material, including a first active material including a silicon core and a carbon coating layer on the core, a carbon second active material having an aspect ratio of about 4 to about 100, and a crystalline carbon third active material.