Fluorinated Ester and Phosphazene Electrolyte for High Fire Point
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Solution Overview
Problem
Nonaqueous electrolyte solutions for lithium ion secondary batteries face challenges in achieving both high flame retardancy and maintaining battery performance due to the high viscosity of fluorinated solvents and the inability of phosphazene compounds to dissolve lithium salts, leading to insufficient flame retardancy and reduced conductivity.
Innovation Solution
A nonaqueous electrolyte solution containing methyl 3,3,3-trifluoropropionate as a fluorinated chain ester compound combined with a phosphazene compound, which significantly improves fire point and maintains battery output characteristics with a small amount of phosphazene, achieving a synergistic high flame-retardant effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phosphazene compound is added at a high concentration to impart sufficient flame-retardant effect, then flame retardancy is improved, but conductivity of the electrolyte solution is reduced due to the phosphazene compound's inability to dissolve lithium salt
Solution Approach 1:
The patent changes the concentration parameter of the phosphazene compound from high to extremely small amount (0.01-5 mass%), and simultaneously changes the solvent composition parameter by introducing methyl 3,3,3-trifluoropropionate. This dual parameter change resolves the contradiction by achieving sufficient flame retardancy with minimal phosphazene while maintaining conductivity through the fluorinated ester solvent's ability to dissolve lithium salts.
2Reliability
If fluorinated solvents are used to provide flame retardancy, then non-flammability is improved, but viscosity increases causing deterioration in battery characteristics
Solution Approach 1:
The patent applies local quality by selectively introducing fluorine atoms at specific positions (the 3-position of the propionate chain) rather than throughout the entire solvent molecule. This localized fluorination provides the desired flame retardancy and non-flammability while minimizing the overall viscosity increase that would occur with more extensive fluorination, thus maintaining battery characteristics.
3Temperature
If a phosphazene compound is added to a lithium salt-containing electrolyte solution including methyl 3,3,3-trifluoropropionate, then fire point is significantly improved with extremely small amount of phosphazene, but the challenge remains to maintain battery performance
Solution Approach 1:
The patent creates a composite electrolyte system combining methyl 3,3,3-trifluoropropionate (fluorinated chain ester) with a phosphazene compound. This composite material approach allows the fluorinated ester to serve as the primary solvent maintaining conductivity and battery performance, while the phosphazene compound acts as a flame-retardant additive. The synergistic interaction between these two components achieves both high fire point and maintained battery performance.
Data Source
AI summary
Disclosed is a nonaqueous electrolyte solution containing a lithium electrolyte, methyl 3,3,3-trifluoropropionate, and a phosphazene compound. Preferably, the phosphazene compound is a cyclic phosphazene compound represented by the disclosed general formula (I).