Graphite Negative Electrode Coating for Lithium Deposition Control
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Solution Overview
Problem
Non-aqueous electrolyte secondary cells with graphite negative electrodes experience a decrease in cycle characteristics due to lithium deposition and volume changes during charge-discharge cycles, leading to heterogeneous charge-discharge reactions and reduced capacity retention.
Innovation Solution
A negative electrode active material comprising scaly graphite particles and coated graphite particles with an amorphous carbon coating layer, which reduces lithium deposition and maintains capacity while minimizing internal resistance through the combination of high electron conductivity and volume absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If graphite negative electrode is used for high-rate charge-discharge operations, then power and charge-discharge rate are improved, but lithium deposition occurs on the surface resulting in decreased capacity retention
Solution Approach 1:
The negative electrode uses a composite structure combining scaly graphite particles with coated graphite particles. The coated graphite particles have a core-shell structure with graphite core and amorphous carbon coating layer, creating a composite material system that balances high-rate performance and capacity retention
Solution Approach 2:
The amorphous carbon coating layer is applied locally on the surface of graphite particles, creating different functional zones: the inner graphite core provides high capacity while the outer amorphous carbon layer provides lithium ion acceptance and prevents deposition. This local differentiation resolves the contradiction between power and reliability
2Use of energy by moving object
If graphite negative electrode undergoes charge-discharge cycles, then capacity is utilized, but volume changes cause wrinkling and heterogeneous reactions leading to decreased cycle characteristics
Solution Approach 1:
The invention changes the physical parameters of graphite particles by controlling particle shape (scaly vs. coated spherical), size distribution, and coating thickness. These parameter changes allow the negative electrode to accommodate volume expansion/contraction during cycling while maintaining structural integrity and homogeneous reactions
Solution Approach 2:
The amorphous carbon coating layer acts as an intermediary between the graphite core and the electrolyte. It mediates the volume changes during charge-discharge cycles, absorbing stress and preventing direct contact between the expanding graphite and the electrolyte, thereby maintaining cycle stability
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 solution achieves excellent high-rate charge-discharge cycle characteristics and improved capacity retention by balancing conductivity and volume stability, enhancing the performance of non-aqueous electrolyte secondary cells.
Implementation Method 1
The coating layer contains amorphous carbon particles and an amorphous carbon layer... amorphous carbon having a smaller capacity than graphite, amorphous carbon has a high performance to accept lithium ions
Implementation Method 2
amorphous carbon having a smaller capacity than graphite... balancing conductivity and volume stability
Data Source
AI summary
Disclosed is a non-aqueous electrolyte secondary cell excellent in capacity retention rate and I-V characteristics after repeated cycles. The secondary cell contains a negative electrode active material containing scaly graphite particles and coated graphite particles. The coated graphite particles contain graphite particles and a coating layer coating the surfaces of the graphite particles. The coating layer contains amorphous carbon particles and an amorphous carbon layer. It is preferable that the negative electrode active material contain 1 to 6% by mass of the scaly graphite particles and that the graphite particles, the amorphous carbon particles, and the amorphous carbon layer be in a mass ratio of 100:α:β where 1≦α≦10, 1≦β≦10, and α≦1.34β.