Silicon-Graphite Negative Electrode for Capacity and Cycle Retention
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Solution Overview
Problem
The challenge is to maintain the initial capacity and cycling performance of non-aqueous electrolyte secondary batteries, as large silicon domains in negative electrodes tend to crack during charging and discharging, while reducing the silicon domain size with fine carbon domains compromises binding force and conductivity.
Innovation Solution
A negative electrode comprising graphite particles, fibrous carbon, silicon-containing particles with a domain size of 50 nm or less, and a binder containing styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylic acid, where the carbon nanotubes surround the silicon-containing particles, enhancing binding and conductivity, and the oxygen content ratio is kept at 7 wt % or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of silicon domain is made large, then the capacity is improved, but a crack is likely to be formed in the silicon domain due to repeated charging and discharging, with the result that cycling performance is likely to be decreased
Solution Approach 1:
The silicon domain is divided into fine regions by dispersing it in a carbon domain or oxygen domain, creating a segmented structure that prevents crack formation while maintaining high capacity. The silicon is not used as a large continuous domain but as dispersed fine domains within the carbon matrix.
Solution Approach 2:
A composite structure is created where silicon domains are embedded within a carbon matrix, forming a silicon-carbon composite material. This composite structure provides both the high capacity of silicon and the structural stability of carbon, preventing cracks during cycling.
2Manufacturing precision
If the silicon domain is dispersed in a fine carbon domain, then the size of silicon domain is made small, but the force of binding to the silicon-containing particles by a binder is decreased, with the result that it tends to be difficult to secure electric conductivity
Solution Approach 1:
The binder acts as an intermediary substance that bridges the fine carbon domains and silicon particles, providing both binding force and electric conductivity. The binder connects the dispersed fine carbon domains to each other and to the silicon particles, maintaining conductivity despite the fine dispersion.
Solution Approach 2:
The properties of the binder are optimized by selecting specific materials (styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid) and controlling their content ratio, to achieve both sufficient binding force and maintained electric conductivity in the fine-dispersed structure.
3Manufacturing precision
If the oxygen content ratio is increased to attain a small size of silicon domain, then the size of silicon domain is reduced, but the initial capacity is likely to be decreased
Solution Approach 1:
The oxygen content ratio is precisely controlled within the range of 3-7 wt% to achieve the optimal balance between silicon domain size reduction and capacity maintenance. This parameter optimization allows fine silicon domains to be formed without excessive oxygen that would reduce capacity.
Solution Approach 2:
The silicon-containing particles are designed as a composite structure containing silicon, carbon, and oxygen in specific proportions, where the carbon and oxygen components work together to maintain small silicon domain size while the overall composition preserves high capacity.
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
This configuration suppresses the decrease in initial capacity and cycling performance by improving the binding force and conductivity, maintaining the structural integrity of the silicon-containing particles and enhancing the battery's overall performance.
Implementation Method 1
the carbon nanotube exists around the silicon-containing particles
Implementation Method 2
the binder contains styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA)
Data Source
AI summary
The present disclosure relates to a negative electrode for a non-aqueous electrolyte secondary battery, the negative electrode comprising an active material layer, wherein the active material layer contains graphite particles, fibrous carbon, silicon-containing particles, and a binder, a BET specific surface area of the graphite particles is 3.5 m2/g or less, the fibrous carbon includes a carbon nanotube, each of the silicon-containing particles includes a domain composed of carbon and a domain composed of silicon and having a size of 50 nm or less, and an oxygen content ratio in each of the silicon-containing particles is 7 wt % or less. According to the present disclosure, a negative electrode and a non-aqueous electrolyte secondary battery are provided to suppress decrease in initial capacity and cycling performance.