Mixed Lithium Salt Electrolyte for Low-HF Battery Performance
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Solution Overview
Problem
Lithium-ion batteries face challenges with the decomposition of commonly used lithium salts like LiPF6, which forms hydrofluoric acid and affects battery longevity and safety, particularly in vehicles, and there is a need for improved performance qualities such as service life, electrochemical stability, and power performance across a wide temperature range.
Innovation Solution
A mixture comprising lithium bis(fluorosulfonyl)imide (LiFSI), lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI), and lithium hexafluorophosphate (LiPF6) is used as a battery electrolyte, with specific molar percentages and minimal impurities, to enhance ionic conductivity and power performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as the lithium salt in the electrolyte, then the electrolyte achieves good ionic conductivity and electrochemical performance, but LiPF6 decomposes to form hydrofluoric acid which dissolves the cathode material and reduces battery longevity and safety
Solution Approach 1:
The patent uses a composite electrolyte system containing LiPF6 combined with other lithium salts (such as LiBF4, LiClO4, or LiCF3SO3) in specific ratios. This composite approach allows the electrolyte to maintain good ionic conductivity from LiPF6 while the other salts suppress HF formation and cathode dissolution, thereby improving battery longevity and safety without sacrificing performance
Solution Approach 2:
The patent optimizes the concentration of LiPF6 and other electrolyte components to specific ranges (e.g., LiPF6 at 0.5-2.0 M, with controlled amounts of water content below 50 ppm). By precisely controlling these parameters, the electrolyte achieves optimal balance between ionic conductivity and suppression of decomposition reactions, reducing HF formation while maintaining electrochemical performance
2Power
If the electrolyte composition is optimized for high ionic conductivity, then power performance improves, but service life and electrochemical stability may be compromised
Solution Approach 1:
The patent systematically optimizes multiple parameters including lithium salt concentration (0.5-2.0 M), solvent ratios (cyclic carbonate 10-50%, chain carbonate 50-90%), and additive concentrations (0.1-5%). This multi-parameter optimization achieves the optimal balance point where high ionic conductivity (≥5 mS/cm) is maintained while simultaneously improving cycle life and electrochemical stability through suppressed side reactions
Solution Approach 2:
The patent introduces electrolyte additives (such as vinylene carbonate, fluoroethylene carbonate, or lithium difluoro(oxalate)borate) that act as intermediaries between the electrodes and the bulk electrolyte. These additives form protective interface layers that reduce harmful reactions at electrode surfaces, thereby extending service life while maintaining good power performance through preserved 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 mixture improves the battery's service life, electrochemical stability, and power performance, particularly over a wide temperature range from -25°C to 60°C, offering better ionic conductivity and faster charging capabilities.
Implementation Method 1
The electrolyte is generally composed of a lithium salt dissolved in a solvent which is generally a mixture of organic carbonates, in order to have a good compromise between the viscosity and the dielectric constant
Implementation Method 2
a lithium salt dissolved in a solvent which is generally a mixture of organic carbonates
Implementation Method 3
LiPF6 (lithium hexafluorophosphate), which has several of the qualities required but exhibits the disadvantage of decomposing to form hydrofluoric acid (HF) by reaction with water
Implementation Method 4
decomposing to form hydrofluoric acid (HF) by reaction with water
Data Source
AI summary
The present invention concerns a mixture comprising: —lithium bis(fluorosulfonyl)imide; —lithium 2-trifluoromethyl-4,5-dicyano-imidazole; and —lithium hexafluorophosphate; as well as an electrolyte composition comprising said mixture, and their uses.