Silicon Oxide Graphite Negative Electrode Conductive Path Stability
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Solution Overview
Problem
The use of silicon oxide and graphite materials in negative electrode composite layers of non-aqueous electrolyte secondary batteries leads to significant volume changes during charge and discharge, causing conductive path loss and degradation in charge-discharge cycling performance, while excessive conductive materials enhance specific surface area, promoting degradation reactions during high-temperature storage.
Innovation Solution
A negative electrode composite material layer with a BET specific surface area between 3.5 m2/g and 5.0 m2/g, and an elongation at the bending point of 12% or higher, achieved by adjusting the composition and using a higher binder-to-conductive material ratio, along with conductive materials like carbon nanotubes and graphene, to form robust conductive paths that withstand volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon oxide material and graphite material are mixed to increase battery capacity, then specific capacity is improved, but conductive path is lost due to volume change during charge-discharge cycles
Solution Approach 1:
The patent uses a flexible binder material that forms a matrix surrounding the silicon oxide and graphite particles. This binder film flexes with the volume changes of silicon oxide during charge-discharge cycles, maintaining continuous contact between conductive material and active material particles, thereby preventing loss of conductive paths while preserving high capacity
Solution Approach 2:
The patent creates a composite structure where silicon oxide particles, graphite particles, conductive material, and binder are combined in specific ratios. The binder forms a flexible matrix that holds the composite together, allowing the system to maintain both high capacity (from silicon oxide) and good cycling performance (through flexible connectivity)
2Reliability
If a great amount of conductive material is added to form more conductive paths, then charge-discharge cycling performance is improved, but specific surface area increases promoting electrolyte degradation during high-temperature storage
Solution Approach 1:
The patent optimizes the specific surface area parameter to fall within 3.5-5.0 m2/g by carefully controlling the amounts of conductive material and binder. This parameter optimization ensures sufficient conductive paths for good cycling performance while limiting excessive surface area that would promote electrolyte degradation at high temperatures
3Reliability
If conductive material is increased to maintain conductive paths during volume change, then charge-discharge cycling performance is improved, but the negative electrode composite material layer requires more material components increasing complexity
Solution Approach 1:
The binder serves multiple functions simultaneously: it provides structural integrity to the electrode layer, acts as a flexible matrix that accommodates volume changes, and maintains conductive connectivity between particles. This multi-functionality reduces the need for separate dedicated components for each function, simplifying the overall material composition
Data Source
AI summary
A non-aqueous electrolyte secondary battery includes at least a negative electrode composite material layer. The negative electrode composite material layer includes a negative electrode active material, a conductive material, and a binder. The negative electrode active material includes a silicon oxide material and a graphite material. The negative electrode composite material layer has a BET specific surface area not smaller than 3.5 m2/g and not greater than 5.0 m2/g. In an orthogonal coordinate system having an abscissa representing the elongation of the negative electrode composite material layer and an ordinate representing the electrical resistance of the negative electrode composite material layer, an elongation at a bending point (Cp) in the plot is 12% or higher.