FSI Ionic Liquid Electrolytes for High-Voltage Li-Ion Stability
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Solution Overview
Problem
Existing lithium-ion battery electrolytes face challenges such as oxidative decomposition at high potentials, flammability, and poor solid electrolyte interface (SEI) formation, which limit their energy density and safety in applications like electric vehicles.
Innovation Solution
Development of novel ionic liquids with specific cations, such as those represented by Formula (I), which include functional substituents like fluoro, cyano, and alkenyl groups, to enhance viscosity, SEI formation, and voltage stability, while reducing flammability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional organic carbonate solvent-based electrolytes are used to increase energy density, then the operational potential and voltage can be elevated, but the electrolyte becomes oxidatively decomposed at the cathode surface causing gassing, low Coulombic efficiency, transition metal ion dissolution, and rapid capacity fade
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by introducing ionic liquids with specific cations (containing fluoro, cyano, carbonate ester, alkenyl, or alkynyl groups) and anions, replacing conventional organic carbonate solvents. This parameter change enables the electrolyte to maintain stability at high potentials while supporting elevated operational voltage for energy density improvement
Solution Approach 2:
The patent creates a composite electrolyte system combining ionic liquid components with specific functional groups that work synergistically. The cation contains multiple functional substituents that collectively provide oxidative stability, flame resistance, and SEI formation capability, resolving the contradiction between energy density and reliability
2Use of energy by moving object
If conventional organic carbonate solvent-based electrolytes are used, then energy density can be increased, but the electrolyte becomes extremely flammable due to high vapor pressure and low flashpoint
Solution Approach 1:
The patent fundamentally changes the physical and chemical parameters of the electrolyte by using ionic liquids instead of volatile organic carbonates. The ionic liquid structure with charged species eliminates high vapor pressure and raises flashpoint, achieving non-flammability while maintaining high energy density through elevated operational voltage
Solution Approach 2:
The ionic liquid components create an inherently safer, more inert electrolyte environment. The charged ionic structure and functional groups (especially fluoro and cyano groups) reduce flammability and vapor pressure, eliminating the fire hazards associated with conventional organic carbonate electrolytes
3Object-affected harmful factors
If room-temperature ionic liquids are used as alternatives for conventional carbonate electrolytes, then flammability is reduced and electrochemical window is widened, but the system suffers from high viscosity, poor wettability and poor SEI formation
Solution Approach 1:
The patent applies local quality by introducing specific functional groups (fluoro, cyano, carbonate ester, alkenyl, alkynyl) at specific positions within the cation structure. These localized functional modifications selectively improve SEI formation and wettability without compromising the overall ionic liquid structure's low flammability and high voltage stability
Solution Approach 2:
The patent optimizes the molecular parameters of the ionic liquid cation by controlling the type and position of functional substituents. This parameter optimization reduces viscosity and improves wettability while maintaining the inherent safety advantages of ionic liquids
4Ease of operation
If ionic liquids based on bis(fluorosulfonyl)imide (FSI) anion are used, then viscosity is reduced and conductivity is increased, but SEI formation on graphite anode may still be insufficient compared to other options
Solution Approach 1:
The patent merges the advantages of FSI anion (low viscosity, high conductivity) with cations containing multiple functional groups capable of SEI formation. This combination merges the transport benefits of FSI with the protective benefits of functionalized cations, achieving both good conductivity and reliable SEI formation
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 new ionic liquids demonstrate improved cycling performance, high voltage stability, and reduced flammability, enabling enhanced energy density and safety for lithium-ion batteries, particularly in electric vehicle applications.
Implementation Method 1
capability of forming stable SEI layer on graphite anode
Implementation Method 2
the state-of-the-art (SOA) organic carbonate solvent-based electrolytes tend to be oxidatively decomposed at the cathode surface causing gassing
Data Source
AI summary
Described herein is a method of preparing an ionic liquid comprising a nitrogen or phosphorus cation and a bis(fluorosulfonyl)imidate (FSI) counter anion; the method comprising contacting a precursor selected from the group consisting of a tertiary amine, a tertiary phosphine, and an aromatic nitrogen heterocycle, with an alkyl bis(fluorosulfonyl)imidate in an aprotic solvent to alkylate the nitrogen or phosphorus of the precursor, and directly form a nitrogen or phosphorus cation with an FSI counter anion.