Calcium-Modified Graphite for Fast-Charging Li-Ion Anodes
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Solution Overview
Problem
Conventional graphite materials for lithium ion secondary cells, despite surface defects and KOH etching, still have limitations in enhancing the intercalation/deintercalation reaction rate on the basal plane, which affects the high-rate characteristics of the cells.
Innovation Solution
A graphite material with a calcium component supported on the basal plane, where defects enabling lithium ion intercalation/deintercalation are formed, improving the reaction rate by heat treating graphite particles with a calcium-containing substance in a specific temperature range, preferably in a carbon dioxide atmosphere to form calcium carbonate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite material is used as negative electrode active material, then it can occlude a relatively large amount of lithium ions and is inexpensive, but the intercalation/deintercalation reaction rate of lithium ions from the edge surface limits the input/output characteristics of the lithium ion secondary cell
Solution Approach 1:
The graphite particles are divided into smaller particles with a median diameter of 3 μm to 7 μm, increasing the total edge surface area available for lithium ion intercalation/deintercalation reactions, thereby improving input/output characteristics while maintaining high lithium ion capacity
Solution Approach 2:
The invention creates a dual-structure graphite material where spheroidized particles provide overall structural integrity and edge surfaces for rapid lithium ion reaction, while embedded flake graphite structures maintain high lithium ion occlusion capacity, achieving both high capacity and fast reaction rate in different regions of the same material
2Productivity
If the median diameter of graphite particles is reduced to 5 μm to 35 μm, then the diffusion of lithium ions is faster and charge/discharge rate is higher, but the particle size is still not optimized for maximum performance
Solution Approach 1:
The invention optimizes the particle size parameter by setting the median diameter to a specific range of 3 μm to 7 μm, which balances the surface area to volume ratio for maximum lithium ion reaction rate while maintaining sufficient internal volume for high lithium ion capacity, achieving superior performance compared to conventional larger particles
3Area of stationary object
If the surface including the basal plane is etched with potassium hydroxide, then nano-sized pores are formed and the number of intercalation/deintercalation sites is increased, but the intercalation/deintercalation reaction rate on the basal plane is still limited
Solution Approach 1:
The invention spheroidizes the graphite particles, transforming the flat basal planes into curved spherical surfaces. This curvature creates more edge surfaces and defects that are highly active for lithium ion intercalation/deintercalation, significantly improving the reaction rate on what would otherwise be inert basal planes
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 graphite material with calcium support and defects on the basal plane significantly enhances the intercalation/deintercalation reaction rate of lithium ions, leading to improved input/output characteristics of lithium ion secondary cells.
Implementation Method 1
heat treating graphite particles with a calcium-containing substance in a specific temperature range, preferably in a carbon dioxide atmosphere to form calcium carbonate
Implementation Method 2
reversible intercalation and deintercalation of lithium ions occluded between the layers proceed through edge surfaces (laminated surfaces) having exposed edges where the plurality of layers of graphite overlap
Data Source
AI summary
A graphite material for a negative electrode of a lithium ion secondary cell disclosed herein is substantially configured of a graphite particle in which defects enabling intercalation/deintercalation of lithium ions have been formed on a basal plane and which includes a calcium (Ca) component.