Metal-Containing Ionic Liquid Electrolyte for Redox Flow Battery Energy Density
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Solution Overview
Problem
Redox flow batteries face limitations in energy density and footprint due to the typical energy density range of 20-25 Wh/L, necessitating improvements in chemistry and cost reduction to enhance competitiveness in energy storage.
Innovation Solution
The use of metal-containing ionic liquids as both catholyte and anolyte in redox flow batteries, which serve as solvent, redox-active material, and supporting electrolyte, with specific formulations like 1-Butyl-3-methylimidazolium (BMIM) iron chloride, offering high charge density and stability, thereby increasing energy density and reducing the battery footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional aqueous electrolytes are used in redox flow batteries, then the system achieves good stability and long cycle life, but the energy density is limited to 20-25 Wh/L resulting in large footprint
Solution Approach 1:
The patent changes the fundamental parameter of electrolyte composition from traditional aqueous solutions to metal-containing ionic liquids. This parameter change enables simultaneous achievement of high energy density (up to 50 Wh/L or higher) and good stability, as the ionic liquids provide both high charge density and electrochemical stability required for long cycle life
Solution Approach 2:
The patent employs composite electrolyte formulations combining metal-containing ionic liquids with traditional aqueous electrolytes or other components. This composite approach allows optimization of both energy density and stability by leveraging the high charge density of ionic liquids while maintaining the proven stability characteristics of established aqueous redox flow battery systems
2Quantity of substance
If the concentration of redox-active species is increased to improve energy density, then the charge density increases, but the viscosity increases and mass transport becomes slower
Solution Approach 1:
The patent changes the solvent parameter from water to metal-containing ionic liquids, which have inherently different viscosity characteristics and solvation properties. This enables achieving high concentrations of redox-active species (high charge density) while maintaining acceptable mass transport rates due to the unique properties of ionic liquids
Solution Approach 2:
The patent optimizes the local composition of the electrolyte by selecting specific metal-containing ionic liquids with tailored properties for different regions of the battery. The ionic liquid formulation can be optimized locally to balance charge density and mass transport requirements in different operational conditions
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 implementation of these ionic liquids results in a significant increase in energy density, with charge densities up to twice that of traditional vanadium redox flow batteries, improved stability over thousands of cycles, and reduced footprint, making the batteries more competitive in energy storage applications.
Implementation Method 1
The liquid electrolytes are formulated to have molecular species with multiple states of oxidation which are stable over long time periods within a foreseeable temperature range. The cycling of these species through their accessible oxidation states during battery charge and discharge is referred to as a reduction/oxidation process, or a redox process for short.
Implementation Method 2
An ion transfer membrane typically separates the anolyte from the catholyte, only allowing specific ions to cross from one liquid electrolyte to the other to maintain charge neutrality during charging and discharging of the anolyte and catholyte.
Data Source
AI summary
Redox flow battery performance may be improved with a metal containing ionic liquid as a liquid electrolyte. Metal containing ionic liquids are liquids at all temperatures of interest and therefore do not need dilution. As such, voltage separation between the anolyte and catholyte may exceed 0.5 V and therefor rival current state-of-the-art energy storage technologies and with higher voltage separation may attain energy densities above 100 Wh/L.