Natural Graphite Composite with Non-Graphitized Carbon Coating
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Solution Overview
Problem
Natural graphite anode materials for lithium ion batteries suffer from poor rate performance due to their flaky structure, which reduces electrolyte permeability and results in high electrode expansion rates and poor cycle stability, despite efforts to improve isotropy and surface treatments.
Innovation Solution
A natural graphite-based modified composite material is developed by coating non-graphitizable carbon on the inner and outer surfaces of natural graphite through carbonization treatment, using modifiers like coal pitch or phenolic resin, and subjecting the material to isotropic treatment and carbonization under inert conditions to enhance isotropy and reduce defect sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If flaky natural graphite is pressed parallel to the current collector to improve compacted density, then the compacted density increases, but the electrolyte permeability decreases, resulting in poor rate performance
Solution Approach 1:
The patent applies isotropic pressing to transform the flaky graphite structure into a spherical morphology. This curvature change allows the graphite particles to pack more uniformly while maintaining void spaces for electrolyte penetration, thus improving both compacted density and rate performance simultaneously
Solution Approach 2:
The patent changes the pressing parameters from unidirectional parallel pressing to multi-directional isotropic pressing. This parameter change in the pressing process transforms the particle orientation and morphology, enabling the graphite to achieve high density while maintaining good electrolyte access from all directions
2Stability of the object's composition
If high-pressure treatment is applied to improve isotropy, then the isotropy of the material improves, but the flake graphite breaks and fractures, exposing more defect sites, resulting in poor cycle performance
Solution Approach 1:
The patent performs surface coating treatment before the high-pressure isotropic pressing. This coating layer acts as a cushioning protection during the pressing process, preventing graphite flake fracture and defect formation while still allowing the material to achieve high isotropy
Solution Approach 2:
The patent creates a composite structure by coating the graphite surface with protective material before pressing. This composite approach maintains the graphite's electrochemical activity while the coating layer provides mechanical protection during isotropic treatment, preventing flake breakage and preserving cycle 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 modified composite material achieves improved cycle stability and reduced electrode expansion rates, with a capacity retention rate of over 92% after 300 cycles and an expansion rate of less than 25% after 20 cycles, while maintaining a simple and cost-effective production process.
Implementation Method 1
non-graphitizable carbon covering the inner and outer surfaces of the natural graphite... converted from a modifier through carbonization treatment
Implementation Method 2
applies isotropic pressure to obtain a natural graphite electrode material with high isotropy
Data Source
AI summary
A natural graphite-based modified composite material, a preparation method therefor, and a lithium ion battery comprising the modified composite material. The natural graphite-based modified composite material comprises natural graphite and non-graphitized carbon coated on the inner and outer surfaces of the natural graphite. The preparation method comprises: (1) subjecting spherical natural graphite to isotropic treatment; (2) performing granularity control and shaping treatment; (3) subjecting the inner surface and the outer surface of the material obtained in step (2) to simultaneous modification; and (4) performing carbonization, so as to obtain a natural graphite-based modified composite material.