Nonaqueous Battery Electrolyte Ratio for Si Anode Cycle Retention
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with Si-containing materials in the negative electrode do not achieve sufficient cycle characteristics, such as capacity retention rate, when using a nonaqueous electrolyte containing only fluoroethylene carbonate or lithium difluorophosphate.
Innovation Solution
A nonaqueous electrolyte secondary battery with a positive electrode containing a lithium transition metal complex oxide, a negative electrode with graphite particles and a Si-containing material, and a nonaqueous electrolyte comprising fluoroethylene carbonate and difluorophosphate, where the ratio of fluoroethylene carbonate to Si-containing material is 0.2 or more, effectively protecting the electrode surfaces and improving capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-containing material is used in the negative electrode to achieve higher capacity, then the capacity increases, but cracking occurs during charging/discharging leading to poor cycle characteristics
Solution Approach 1:
The fluoroethylene carbonate in the electrolyte performs preliminary protective action by adsorbing onto the Si-containing material surface before cracking occurs. This forms a protective film that suppresses side reactions and reduces the harmful effects of cracking during subsequent charging/discharging cycles, thereby improving capacity retention.
2Device complexity
If the ratio of fluoroethylene carbonate to Si-containing material is insufficient, then the electrolyte composition is simpler, but the protective effect on the negative electrode surface is inadequate
Solution Approach 1:
The patent specifies that the ratio of fluoroethylene carbonate to Si-containing material should be 0.05 or more to ensure adequate protective effect. This parameter optimization ensures sufficient fluoroethylene carbonate is present to form effective protective films on the Si-containing material surface without requiring excessive amounts that would complicate the electrolyte composition.
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 enhances the capacity retention rate and suppresses cracking of the Si-containing material during charging/discharging, leading to improved cycle characteristics and reduced gas production.
Implementation Method 1
Fluoroethylene carbonate adsorbs onto a surface of the negative electrode to protect a surface of the Si-containing material and suppresses side reactions with the electrolyte
Implementation Method 2
The lithium difluorophosphate can adsorb onto a surface of the positive electrode to protect the surface of the positive electrode active material and can suppress an increase in internal resistance thereof
Data Source
AI summary
The present disclosure provides a nonaqueous electrolyte secondary battery including: an electrode body having a positive electrode and a negative electrode; and a nonaqueous electrolyte. The positive electrode includes a lithium transition metal complex oxide, the negative electrode includes graphite particles and a Si-containing material, and the nonaqueous electrolyte includes fluoroethylene carbonate and a difluorophosphate. The ratio of the mass of the fluoroethylene carbonate to the mass of the Si-containing material is 0.2 or more.