LiFSI-LiTDI Electrolyte Mixture for Aluminum Corrosion and HF Formation

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Solution Overview

Problem

Lithium-ion batteries face challenges with the degradation of LiPF6, which forms hydrofluoric acid and affects battery longevity and safety, while alternative salts like LiTFSI are corrosive to aluminum current collectors, and there is a need for improved performance, cycling stability, and capacity retention across a wide temperature range.

Innovation Solution

A mixture of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI) is used as a battery electrolyte, with a composition ranging from 85% to 99.9% LiFSI and 0.1% to 15% LiTDI, providing improved stability and performance without corrosiveness to aluminum.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If LiPF6 is used as the lithium salt in the electrolyte, then the electrolyte shows good ionic conductivity and electrochemical stability, but LiPF6 degrades to form hydrofluoric acid which causes dissolution of the cathode material and affects battery longevity and safety

Engineering Contradiction:

Improvebattery longevity and safetyVSAvoidhydrofluoric acid formation

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The invention extracts LiPF6 from the electrolyte composition to eliminate the source of hydrofluoric acid formation. By removing the harmful component (LiPF6) while retaining alternative salts (LiFSI and LiTDI) that do not produce HF, the patent eliminates the harmful effect while maintaining electrolyte functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the stable but harmful LiPF6 with a combination of salts that offer improved stability profiles. LiFSI provides long-term hydrolytic stability while LiTDI contributes to overall electrochemical stability, creating a more durable electrolyte system that prioritizes longevity over initial conductivity performance.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Stability of the object's composition

If LiTFSI is used as the lithium salt in the electrolyte, then the salt shows little or no spontaneous decomposition and is more stable to hydrolysis than LiPF6, but LiTFSI is corrosive to aluminum current collectors

Engineering Contradiction:

Improvehydrolysis stabilityVSAvoidcorrosiveness to aluminum

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The invention merges LiFSI and LiTDI into a combined electrolyte system where LiFSI provides hydrolytic stability without the severe aluminum corrosion issues of LiTFSI, while LiTDI enhances overall electrochemical stability. The synergistic combination achieves improved hydrolysis stability while reducing harmful corrosiveness to current collectors.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the chemical composition parameters of the electrolyte by selecting specific salt ratios (85-99.9% LiFSI and 0.1-15% LiTDI). This parameter optimization adjusts the balance between hydrolytic stability and aluminum corrosion resistance, achieving a profile that exceeds LiTFSI in stability while minimizing corrosiveness through the milder LiFSI structure.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If the battery operates over a wide temperature range from -25°C to 60°C, then the battery must maintain adequate power performance and capacity retention, but extreme temperatures accelerate electrolyte degradation and reduce battery lifespan

Engineering Contradiction:

Improvetemperature range performanceVSAvoidbattery lifespan

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent optimizes the electrolyte composition parameters by selecting LiFSI and LiTDI in specific proportions (85-99.9% LiFSI and 0.1-15% LiTDI). This parameter optimization enhances the electrolyte's thermal stability and low-temperature fluidity, enabling the battery to maintain adequate power performance and capacity retention across the -25°C to 60°C range while minimizing degradation acceleration at extreme temperatures.

Inventive Principle:

Principle #35Parameter changes

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 LiFSI/LiTDI mixture enhances battery power performance and stability over a wide temperature range, improving charging speed and capacity retention, while being non-corrosive to aluminum current collectors, thus addressing safety and longevity issues.

Implementation Method 1

The electrolyte generally consists of a lithium salt dissolved in a solvent which is generally a mixture of organic carbonates

Methodology Applied

Scientific EffectDissolution: Solvation

Implementation Method 2

Among the most used salts we find LiPF6 (lithium hexafluorophosphate)... LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide)

Methodology Applied

Scientific EffectIonic conduction: Conduction (electrical)

Data Source

PatentEP3607601B1Lithium salt mixture and uses thereof as a battery electrolyte

Publication Date: 2023.05.03 ARKEMA FRANCE SA

AI summary

The invention relates to a lithium salt mixture comprising: from 85% to 99.9 mol % of lithium bis(fluorosulfonyl)imidide; and from 0.1% to 15 mol % of lithium 2-trifluoromethyl-4,5-dicyano-imidazolate. The invention also relates to an electrolyte composition containing same and to the uses thereof.