Phosphazene Ionic Liquid Electrolyte for High-Temperature Battery Stability
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Solution Overview
Problem
Lithium-ion batteries' electrolyte solutions are unstable at high temperatures and high voltages, leading to premature degradation and limiting their deployment in vehicular applications such as hybrid electric vehicles, due to the instability of phosphazene-based ionic liquids with direct phosphorus-fluorine bonds which release aggressive free fluoride ions.
Innovation Solution
Development of phosphazene-based ionic liquids with pendant groups bonded to phosphorus atoms through oxygen, sulfur, or nitrogen atoms, avoiding direct halogen bonds to enhance stability and safety, and incorporating these ionic liquids in electrolyte solutions with solvents like ethylene carbonate and ethyl methyl carbonate for improved performance in energy storage devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphazene-based ionic liquids with direct phosphorus-fluorine bonds are used in electrolyte solutions, then ionic conductivity and liquid state properties are achieved, but stability at high temperatures and voltages deteriorates due to release of free fluoride ions
Solution Approach 1:
The patent removes the harmful direct phosphorus-fluorine bond from the ionic liquid structure. By extracting the fluorine atom from direct bonding to phosphorus, the source of free fluoride ion release is eliminated, resolving the stability problem while maintaining the ionic liquid's functional properties
Solution Approach 2:
The patent introduces an intermediary atom (oxygen, nitrogen, or carbon) between the phosphorus and fluorine atoms. This intermediary prevents direct bonding while allowing the fluorine to remain part of the stable anionic structure, thereby preventing free fluoride release while maintaining ionic conductivity
2Duration of action of stationary object
If conventional electrolyte solutions are used in lithium-ion batteries, then ease of manufacture and initial performance are achieved, but longevity and stability at high temperatures deteriorate leading to tar-like degradation
Solution Approach 1:
The patent creates a composite ionic liquid system combining a phosphazene-based cation with a fluorinated anion (such as BF4-, PF6-, or CF3SO3-). This composite structure leverages the thermal stability of the phosphazene backbone and the electrochemical stability of the fluorinated anion, achieving both high temperature stability and long battery life
3Ease of manufacture
If ionic liquids with halogen atoms directly bonded to phosphorus are used, then synthesis simplicity is achieved, but safety and stability deteriorate due to aggressive fluoride reactants
Solution Approach 1:
The patent introduces an intermediary atom (oxygen, nitrogen, or carbon) between the phosphorus and halogen atoms. This intermediary maintains the structural integrity and simplifies synthesis while preventing the direct release of aggressive fluoride ions, thus resolving both manufacturing ease and safety concerns
Data Source
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AI summary
An ionic liquid including a phosphazene compound that has a plurality of phosphorus-nitrogen units and at least one pendant group bonded to each phosphorus atom of the plurality of phosphorus-nitrogen units. One pendant group of the at least one pendant group comprises a positively charged pendant group. Additional embodiments of ionic liquids are disclosed, as are electrolyte solutions and energy storage devices including the embodiments of the ionic liquid.