Fluorinated Ester Electrolyte Composition for High-Temperature Li-Ion Cycling
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Solution Overview
Problem
Current lithium ion battery electrolytes decompose at cathode potentials above 4.25 V, leading to reduced battery performance and safety concerns due to low boiling point and high flammability, and they exhibit limited cycling performance, especially at high temperatures when used with high potential cathodes.
Innovation Solution
An electrolyte composition comprising a fluorinated compound, a non-fluorinated carbonate, a lithium/boron compound, and a lithium salt, where the fluorinated compound is represented by R1COOR2 with at least two hydrogen atoms replaced by fluorine, and neither R1 nor R2 contains —CH2F or —CHF— groups, providing improved stability and cycling performance at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional non-aqueous electrolytes (linear carbonates and cyclic carbonates) are used, then the electrolyte can be used in standard lithium ion batteries, but the electrolyte decomposes at cathode potentials above 4.25 V, resulting in loss of battery performance
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte by introducing fluorinated compounds with specific molecular structures (where neither R1 nor R2 contains —CH2F or —CHF— groups) and controlling the carbon atom sum in R1 and R2 to be 2 to 7. This chemical parameter modification enables the electrolyte to maintain stability at high cathode potentials above 4.25 V where conventional electrolytes decompose.
Solution Approach 2:
The patent creates a composite electrolyte system combining fluorinated compounds (R1COOR2 where at least two hydrogen atoms are replaced by fluorine) with conventional carbonate solvents and lithium salts. This composite approach leverages the electrochemical stability of fluorinated compounds while maintaining the beneficial properties of conventional electrolyte components, achieving both high potential stability and good cycling performance.
2Productivity
If conventional non-aqueous electrolytes are used, then the electrolyte provides basic battery operation, but the low boiling point and high flammability create safety concerns
Solution Approach 1:
The patent modifies the physical parameters of the electrolyte by incorporating fluorinated compounds which generally have higher boiling points and lower flammability compared to conventional carbonates. The specific structural constraints (sum of carbon atoms 2 to 7, no —CH2F or —CHF— groups) are designed to optimize both the electrochemical performance and the safety parameters including flammability resistance and thermal stability.
3Reliability
If fluorinated carboxylic acid ester electrolyte solvents are used, then the electrolyte can be used in lithium ion batteries with high potential cathodes (4 V spinel LiMn2O4), but the cycling performance is limited, particularly at high temperatures
Solution Approach 1:
The patent changes the chemical structure parameters of fluorinated esters by imposing specific constraints: the sum of carbon atoms in R1 and R2 must be 2 to 7, and neither R1 nor R2 can contain —CH2F or —CHF— groups. These parameter restrictions are designed to improve high-temperature cycling stability while maintaining compatibility with high potential cathodes, addressing the limitations of previously used fluorinated esters.
Solution Approach 2:
The patent applies local quality modification by specifically targeting the R1 and R2 groups in the fluorinated compound structure. By controlling the fluorine substitution pattern and excluding certain structural motifs (—CH2F and —CHF— groups), the patent optimizes the local chemical environment to enhance thermal stability and cycling performance at high temperatures while maintaining the necessary electrochemical activity.
Data Source
AI summary
The present disclosure is related to an electrolyte composition comprising from 30 to 80% by weight of CH3CO2CH2CF2H, from 10 to 60% by weight of ethylene carbonate or propylene carbonate, from 0.1 to 1.0% by weight of lithium bis(oxalate) borate, from 0.2 to 2.0 moles/L of lithium hexafluorophosphate and from 0.1 to 2% by weight of fluoroethylene carbonate, where the amounts of compounds are based on the total weight of the electrolyte composition, and where when used as an electrolyte in a lithium-ion battery, the composition exhibits an 80% cycle life of at least 250 at a cycling rate is 240 mA/g.