Fluorinated Electrolyte Solvent Mixture for High Voltage Battery Stability
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Solution Overview
Problem
Current lithium ion battery electrolyte solvents decompose at high voltages above 4.4 V, leading to reduced battery performance and safety concerns due to low boiling point and flammability, and existing fluorine-containing carboxylic acid ester solvents have limited cycling performance at high temperatures and voltages.
Innovation Solution
An electrolyte composition comprising a solvent mixture of ethylene carbonate and 2,2-difluoroethyl acetate, with ethylene carbonate at 10-50% and 2,2-difluoroethyl acetate at 50-90% by weight, along with an electrolyte salt, is used in lithium ion batteries to enhance cycling performance at high temperatures and voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional carbonate electrolyte solvents are used, then the battery can operate at standard voltages, but the solvents decompose at high voltages above 4.4 V leading to reduced battery performance
Solution Approach 1:
The patent applies parameter changes by introducing fluorinated carboxylic acid esters with specific molecular structures (containing CF3 or CF2 groups) to alter the chemical stability parameters of the electrolyte. This enables the electrolyte to withstand higher voltages up to 5.0 V without decomposition, directly resolving the voltage stability limitation of conventional carbonates
Solution Approach 2:
The patent uses composite materials by combining fluorinated carboxylic acid esters with conventional carbonate solvents (EC, DMF, DEC) to create a hybrid electrolyte system. This composite approach leverages the high voltage stability of fluorinated compounds while maintaining the beneficial properties of conventional solvents, achieving reliable operation at voltages above 4.4 V
2Reliability
If conventional electrolyte solvents are used, then the battery can function normally, but safety concerns arise due to low boiling point and high flammability
Solution Approach 1:
The patent applies parameter changes by incorporating fluorinated carboxylic acid esters that possess inherently higher thermal stability and higher boiling points compared to conventional carbonates. This chemical parameter modification directly reduces flammability and improves safety without compromising battery functionality
Solution Approach 2:
The patent converts the typically harmful effect of fluorine substitution (which can reduce ionic conductivity) into a benefit by carefully selecting fluorinated carboxylic acid ester structures that simultaneously improve thermal stability and maintain adequate conductivity, thereby transforming a potential drawback into a safety enhancement
3Reliability
If fluorine-containing carboxylic acid ester electrolyte solvents are used, then high voltage cathodes can be utilized, but cycling performance is limited particularly at high temperatures
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular structure of fluorinated carboxylic acid esters (specifically using CF3 and CF2 groups in particular positions) to enhance thermal stability. This structural parameter optimization enables the electrolyte to maintain cycling performance at high temperatures up to 60°C while supporting high voltage operation
Solution Approach 2:
The patent applies local quality by introducing fluorine atoms at specific positions within the carboxylic acid ester molecular structure (alpha-fluorinated, beta-fluorinated positions) to locally enhance thermal and electrochemical stability without compromising the overall molecular properties needed for good cycling performance
Data Source
AI summary
Electrolyte compositions containing a solvent mixture comprising 2,2,-difluoroethyl acetate and ethylene carbonate are described. The electrolyte compositions are useful in electrochemical cells, such as lithium ion batteries.