Negative Electrode Graphite Blend for Cycle-Stable Power Output
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Solution Overview
Problem
Solid graphite in energy storage devices has lower input/output performance due to fewer reaction active sites and durability issues, while reducing particle size to improve performance can lead to decreased discharge capacity and degrading charge-discharge cycle performance when mixed with hollow graphite and subjected to press working.
Innovation Solution
An energy storage device with a negative electrode comprising solid graphite particles of a specific median diameter, hollow graphite particles with a larger median diameter, and a conductive agent of fibrous carbon, which reduces resistance differences and maintains electron conductivity over charge-discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If solid graphite particle size is reduced to improve input/output performance, then power performance is improved, but discharge capacity may be decreased
Solution Approach 1:
The invention uses a mixture of solid graphite particles and hollow graphite particles with different size characteristics. The hollow graphite particles have larger particle sizes that maintain discharge capacity, while solid graphite particles provide reaction active sites. This segmentation of particle types resolves the contradiction between power performance and discharge capacity.
Solution Approach 2:
Different regions of the negative active material layer contain different proportions of solid and hollow graphite particles. The fibrous conductive agent creates local conductive networks that preferentially connect hollow graphite particles, ensuring that larger particles contribute to capacity while maintaining overall power performance.
2Ease of manufacture
If solid graphite and hollow graphite are mixed and subjected to press working, then manufacturing is facilitated, but charge-discharge cycle performance degrades
Solution Approach 1:
The fibrous conductive agent acts as an intermediary between solid and hollow graphite particles during press working. It maintains electrical contact and mechanical integrity between particles of different sizes, preventing the degradation of charge-discharge cycle performance that would otherwise occur during manufacturing press working.
Solution Approach 2:
The negative active material layer is designed as a composite material system combining solid graphite, hollow graphite, and fibrous conductive agent. This composite structure maintains charge-discharge cycle performance while allowing press working for manufacturing.
3Power
If hollow graphite particles are used to increase reaction active sites, then input/output performance is improved, but resistance difference between particle types increases
Solution Approach 1:
The fibrous conductive agent serves as an intermediary that equalizes electrical resistance between hollow and solid graphite particles. It creates conductive pathways that compensate for the inherent resistance differences, allowing both particle types to contribute effectively to input/output performance.
Solution Approach 2:
The invention changes the electrical resistance parameter by introducing the fibrous conductive agent, which modifies the overall resistance characteristics of the negative active material layer. This allows hollow graphite particles to contribute to input/output performance without creating excessive resistance differences.
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 energy storage device exhibits improved charge-discharge cycle performance and power performance by reducing current distribution and progressive deterioration between solid and hollow graphite particles, while maintaining favorable electron conductivity.
Implementation Method 1
the conductive agent is fibrous carbon
Data Source
AI summary
An aspect of the present invention is an energy storage device including a negative electrode including a negative substrate and a negative active material layer layered directly or indirectly on at least one surface of the negative substrate, where the negative active material layer contains: solid graphite particles that have a median diameter D1; hollow graphite particles that have a larger median diameter D2 than the solid graphite particles; and a conductive agent, and the conductive agent is fibrous carbon.