LiFSI-THF Electrolyte Composition for Subzero Lithium Cell Cycling
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Solution Overview
Problem
Conventional lithium-ion batteries face performance issues at low temperatures due to low ionic conductivity, salt precipitation, and high charge transfer resistance, primarily attributed to the electrolyte, which limits their application in extreme conditions like submarines and space exploration.
Innovation Solution
An electrolyte composition featuring lithium bis(fluorosulfonyl) imide (LiFSI) dissolved in tetrahydrofuran (THF) with high salt concentrations, forming a thin, inorganic-rich interfacial layer that enhances ion transport and stability, allowing for improved performance at subzero temperatures without relying on carbonate solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional carbonate-based electrolytes are used, then the electrolyte can form stable SEI layers, but the ionic conductivity becomes too low and salt precipitation occurs at subzero temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing carbonate solvents with ether-based solvents (TEGDME, DGBL) and adjusting the lithium salt concentration to 1.0-2.0 M LiFSI. This parameter change enables the electrolyte to maintain liquid state at subzero temperatures while forming stable SEI layers, resolving the contradiction between SEI stability and ionic conductivity at low temperatures.
Solution Approach 2:
The patent creates a composite electrolyte system combining ether-based solvents (TEGDME and DGBL) with lithium bis(fluorosulfonyl)imide (LiFSI) salt. This composite material approach leverages the low-temperature fluidity of ethers and the stable SEI-forming capability of LiFSI, achieving both improved ionic conductivity and SEI stability at subzero temperatures.
2Temperature
If conventional electrolytes are used, then the electrolyte maintains liquid state at room temperature, but the charge transfer resistance becomes too high at low temperatures
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrolyte by using ether-based solvents with lower freezing points and higher dielectric constants than conventional carbonates. This enables the electrolyte to remain liquid at subzero temperatures while reducing charge transfer resistance through improved ion solvation and mobility, as evidenced by the lower Rct values observed in electrochemical measurements.
3Temperature
If alternative solvents like ethers are used, then the electrolyte can operate at low temperatures, but the SEI layer stability becomes insufficient
Solution Approach 1:
The patent combines ether-based solvents (TEGDME, DGBL) with lithium bis(fluorosulfonyl)imide (LiFSI) to create a composite electrolyte system. The LiFSI salt provides superior SEI-forming capability compared to traditional lithium salts, while the ether solvents ensure low-temperature fluidity. This composite approach achieves both low-temperature operation and stable SEI layers, as confirmed by electrochemical testing.
Solution Approach 2:
The LiFSI salt acts as an intermediary that mediates between the ether solvent and the electrode surface. It facilitates the formation of a stable, low-resistance SEI layer that prevents direct contact between the reactive ether solvent and the electrode, thereby ensuring SEI stability while maintaining low-temperature ionic conductivity.
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
The electrolyte composition enables extended subzero temperature operation with enhanced cycling performance, maintaining 80% capacity at -20°C and 43% at -40°C, compared to room temperature, by creating a kinetically favorable solvation and solid electrolyte interphase structure.
Implementation Method 1
the electrolyte composition has ion-aggregates dominant solvation structures by introducing larger amounts of FSI anions than found with conventional solid electrolytes, resulting in a thin, inorganic-rich, interfacial layer between anode and electrolyte
Data Source
AI summary
An electrolyte composition for use is in an electrochemical cell. The electrolyte contains 5 M lithium bis(fluorosulfonyl) imide (LiFSI) dissolved in tetrahydrofuran (THF), wherein the electrolyte composition has ion-aggregates dominant solvation structures by introducing larger amounts of FSI anions than found with conventional solid electrolytes, resulting in an interfacial layer between anode and electrolyte of an electrochemical cell utilizing the electrolyte composition, less resistive than an interfacial layer between an anode and a conventional solid electrolyte in an electrochemical cell. Also disclosed is an electrolyte containing Lithium bis(fluorosulfonyl) imide (LiFSI) salt dissolved in tetrahydrofuran (THF), fluoroethylene carbonate (FEC), 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether wherein the electrolyte is capable of being used in an electrochemical cell at −80° C. and lower. Electrochemical cells containing these electrolytes, with cathode-electrolyte and capable of combination is rechargeable up to −80° C. and lower.