Negative Electrode Active Material for Li-Ion Battery
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Solution Overview
Problem
Lithium ion rechargeable batteries face challenges in achieving high electrode density while maintaining electrolyte permeability and cycle characteristics, particularly due to the limitations of flake natural graphite, which results in capacity loss and poor performance at high densities.
Innovation Solution
A mixture of three graphite powders with different hardnesses and shapes is used, comprising 30-60% pulverized artificial graphite, 20-50% coated spherical natural graphite, and 5-30% coated spherical natural graphite, allowing for a balance of electrode density and permeability, with specific relationships between press pressure and electrode density to achieve high performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If flake natural graphite is used to increase electrode density, then electrode density is improved, but charge/discharge efficiency deteriorates and cycle characteristics worsen
Solution Approach 1:
The invention segments the negative electrode material into three distinct graphite powder types with different properties (flake artificial graphite for density, spherical natural graphite for efficiency, and coated spherical graphite for stability). This segmentation allows each component to contribute its strengths while compensating for the weaknesses of others, resolving the contradiction between electrode density and cycle characteristics.
Solution Approach 2:
The invention creates a composite negative electrode material by combining three different graphite powder types in specific proportions. This composite approach integrates the high density of flake artificial graphite with the high charge/discharge efficiency and excellent cycle characteristics of spherical natural graphite, achieving a balance that neither material could provide alone.
2Quantity of substance
If electrode density is increased to enhance battery capacity, then battery capacity is improved, but electrolyte permeability deteriorates due to particle clogging
Solution Approach 1:
The invention incorporates spherical natural graphite particles which, due to their spherical shape, pack more efficiently and create better inter-particle void spaces compared to flake-shaped particles. This spheroidality maintains electrolyte flow paths even at high electrode densities, preventing clogging while maximizing capacity.
Solution Approach 2:
The invention applies different graphite powder types to different extents within the composite material. The spherical graphite components provide local regions with excellent electrolyte accessibility, while the flake artificial graphite provides high density in other regions. This local differentiation ensures both high capacity and maintained permeability throughout the electrode structure.
3Ease of manufacture
If flake natural graphite is used for its low cost and high supply availability, then manufacturing cost is reduced, but charge/discharge efficiency falls below 90%
Solution Approach 1:
The invention creates a composite material system where inexpensive flake artificial graphite is combined with more efficient spherical natural graphite. This composite approach achieves charge/discharge efficiency above 90% while maintaining cost-effectiveness, as the spherical component significantly improves performance without requiring 100% replacement of the cheaper flake material.
Solution Approach 2:
The invention changes the physical and chemical parameters of the graphite material by selecting different graphite types with specific properties (shape, size, coating). By adjusting these parameters—particularly incorporating spherical particles with appropriate size distributions and surface coatings—the charge/discharge efficiency is improved to above 90% while managing manufacturing costs through optimized material selection.
Data Source
AI summary
A negative electrode active material for a lithium ion rechargeable battery having high electrode density, excellent in permeability of an electrolyte, less in capacity loss due to charging/discharging, and excellent in cycle performance is provided at a low cost. The negative electrode active material is a mixture of three kinds of graphite powders having different hardnesses and shapes from one another, with a binder added thereto and is coated onto a metallic current collector to be dried and pressed, thereby rendering an electrode density not lower than 1.7 g/cm3.