Silicon-Graphite Negative Electrode for Stable Battery Cycling
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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 crack during charging and discharging, and reducing their 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 contact points and conductivity.
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 granules with a domain size of 50 nm or less, which are dispersed in a carbon domain or oxygen domain. This segmentation prevents crack formation during charging and discharging while maintaining high capacity, thereby improving cycling performance.
2Reliability
If the size of silicon domain is made small by dispersing in fine carbon domain, then cycling performance is improved, but the force of binding to the silicon-containing particles by binder is decreased, with the result that it tends to be difficult to secure electric conductivity
Solution Approach 1:
The invention uses a composite structure where fine silicon granules (50 nm or less) are dispersed in a carbon domain or oxygen domain. This composite approach maintains electric conductivity through the carbon network while preventing silicon domain cracking, thus achieving both improved cycling performance and maintained conductivity.
3Reliability
If an oxygen content ratio is increased to attain a small size of silicon domain, then cycling performance is improved, but an initial capacity tends to be likely to be decreased
Solution Approach 1:
The invention applies local quality by controlling the oxygen content ratio to be 5 wt% or less in the silicon-containing particles. This localized control of oxygen content allows the silicon domains to remain small (50 nm or less) without excessive oxygenation, thereby maintaining both high initial capacity and improved cycling performance.
Data Source
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AI summary
The present disclosure relates to a negative electrode (100) for a non-aqueous electrolyte secondary battery, the negative electrode (100) comprising an active material layer (20), wherein the active material layer (20) contains graphite particles (21), fibrous carbon (22), silicon-containing particles (23), and a binder, a BET specific surface area of the graphite particles (21) is 3.5 m2/g or less, the fibrous carbon (22) includes a carbon nanotube, each of the silicon-containing particles (23) 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 (23) is 7 wt% or less. According to the present disclosure, a negative electrode (100) and a non-aqueous electrolyte secondary battery (200) are provided to suppress decrease in initial capacity and cycling performance.