LiFSI Electrolyte Composition for High-Temperature Capacity Retention
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Solution Overview
Problem
The instability of LiPF6 in the presence of moisture at elevated temperatures in lithium ion batteries leads to hydrogen fluoride generation and capacity decay.
Innovation Solution
A non-aqueous electrolytic solution comprising lithium bis(fluorosulfonyl)imide (LiFSI) as a primary conducting salt, along with specific additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sultone (PS), which mitigates capacity decay and impedance growth during high-temperature storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as the primary conducting salt, then good ionic conductivity is achieved, but capacity decay and impedance growth occur during high-temperature storage due to instability in the presence of moisture
Solution Approach 1:
The patent changes the chemical composition parameter of the conducting salt from LiPF6 to LiFSI (lithium bis(fluorosulfonyl)imide). This parameter change fundamentally alters the stability characteristics of the electrolyte system, eliminating the moisture-induced decomposition pathway that generates HF from LiPF6, while maintaining adequate ionic conductivity for battery operation
Solution Approach 2:
The electrolyte composition comprises LiFSI as the primary conducting salt at ≥80 mol%, VC at 0.5-5 wt%, FEC at 0.5-5 wt%, PS at 0.5-5 wt%, and ES at 0.5-5 wt%. LiFSI provides inherent moisture stability while the additives collectively form a stable solid electrolyte interface (SEI) layer that prevents further degradation reactions during high-temperature storage
2Reliability
If LiPF6 is used alone, then simple electrolyte composition is maintained, but hydrogen fluoride is generated at elevated temperatures leading to capacity decay
Solution Approach 1:
The patent converts the potential harm of using conducting salts at high temperatures by selecting LiFSI, which has inherently lower reactivity with moisture compared to LiPF6. While LiPF6 generates harmful HF through decomposition, LiFSI remains stable and does not generate significant harmful byproducts, thus converting a potentially harmful scenario into a beneficial one where high-temperature stability is achieved without HF generation
Solution Approach 2:
The patent introduces multiple additives (VC, FEC, PS, ES) as intermediary substances that mediate between the conducting salt and the battery components. These additives form protective intermediate layers (SEI) on the electrode surfaces, preventing direct contact and harmful reactions between LiFSI and moisture or electrode materials, thereby eliminating the HF generation pathway that plagues LiPF6-based systems
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 solution maintains battery performance by reducing capacity decay and impedance growth, enhancing moisture tolerance and improving battery retention under high-temperature conditions.
Implementation Method 1
lithium ions travel back and forth between a cathode and an anode through an electrolytic medium
Implementation Method 2
the instability of LiPF6 in the presence of moisture at elevated temperatures, where hydrogen fluoride (HF) may be generated and decay capacity
Implementation Method 3
The non-aqueous electrolytic solution may be capable of reducing capacity decay and impedance growth of lithium ion batteries during high-temperature storage
Data Source
AI summary
Systems and methods are provided for using electrolytic compositions in lithium ion batteries. In one example, an electrolytic composition may include vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, ethylene sulfite, and a conducting salt including no less than 80 mol % of lithium bis(fluorosulfonyl)imide. In this way, a capacity retention of the lithium ion battery may be maintained, such as during high-temperature storage at 100% state of charge.