Lithium Perfluoroalkylfluorosilicates for Stable High-Concentration Electrolytes
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Solution Overview
Problem
Existing lithium salts used in lithium batteries and electrolytes, such as lithium hexafluorophosphate, have low stability in organic solvents and limited solubility, which affects the performance and longevity of electrochemical cells.
Innovation Solution
The development of lithium perfluoroalkylfluorosilicates, specifically lithium salts of the formula Li[(Rf)nSiF5-n] and Li2[(Rf)nSiF6-n], where Rf is a perfluoroalkyl group with 2 to 12 C atoms, which are synthesized by reacting perfluoroalkylsilanes with lithium fluoride or silicon tetrachloride, offering enhanced solubility and stability in organic solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium hexafluorophosphate is used as conductive salt, then it provides adequate conductivity, but it has low stability toward hydrolysis and limited solubility in organic solvents
Solution Approach 1:
The patent changes the chemical parameters of the lithium salt by replacing the hexafluorophosphate anion with perfluoroalkylfluorosilicate anions. This structural modification alters the solubility and stability characteristics, enabling high solubility in organic solvents while maintaining electrochemical stability.
Solution Approach 2:
The invention creates composite electrolyte systems by combining lithium perfluoroalkylfluorosilicate salts with various organic solvents (cyclic carbonates, chain carbonates, esters, nitriles). This composite approach leverages the complementary properties of the salt and solvent to achieve both high solubility and stability.
2Reliability
If lithium hexafluorosilicate is used to improve stability, then it provides better hydrolysis resistance, but it has very low solubility in organic solvents
Solution Approach 1:
The patent modifies the hexafluorosilicate structure by introducing perfluoroalkyl groups (CF3, C2F5, etc.) in place of simple fluorine atoms. This structural parameter change dramatically increases solubility in organic solvents while preserving the Si-F bond stability that provides hydrolysis resistance.
Solution Approach 2:
The perfluoroalkyl groups are strategically positioned on the silicon center, creating local regions of high electronegativity and steric bulk. This local modification enhances solubility through improved solvent interactions while the central Si-F bonds maintain their stability.
3Ease of manufacture
If conventional lithium salts are used, then the electrolyte can be prepared, but the dissociation capacity into free ions is limited, affecting charge transfer
Solution Approach 1:
The patent changes the ionic parameters by designing salts with asymmetric anions that have optimized charge distribution. The perfluoroalkylfluorosilicate anions facilitate better ion separation and solvation, increasing the concentration of free ions available for charge transfer while maintaining ease of electrolyte preparation.
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
These lithium perfluoroalkylfluorosilicates enable the formation of high-concentration solutions in organic solvents, improving the stability and performance of electrochemical cells, including lithium batteries and capacitors, by enhancing charge transfer and extending their cycle life.
Implementation Method 1
The conductivity of an electrolyte comprising a lithium salt in solution in an organic solvent is determined by the nature of the lithium salt, i.e., by its solubility and the capacity to dissociate into free or solvated cations and anions.
Implementation Method 2
Perfluoroalkylfluorosilanes can be reacted with lithium fluoride in the presence of an organic solvent, and undergo reaction to form lithium perfluoroalkylfluorosilicates.
Data Source
AI summary
The invention relates to lithium perfluoroalkylfluorosilicates, to their preparation, and to their use as conductive salts in electrochemical cells, more particularly in lithium batteries, lithium ion batteries or lithium ion capacitors, and also to electrolytes or electrochemical cells comprising these lithium perfluoroalkylfluorosilicates.