Redox Active Ionic Liquid Electrolyte for High Energy Density Flow Batteries
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Solution Overview
Problem
Redox flow batteries face limitations in energy density, which affects their footprint and cost, due to the use of traditional liquid electrolytes that require significant storage volumes and are constrained by the electrochemical window of water.
Innovation Solution
The development of redox active ionic liquids with a bipyridinium core and suitable substituents that lower the melting point below 70°C, allowing for a single molecular species to act as both solvent and redox-active material, thereby increasing energy density and reducing the need for bulk solvent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional liquid electrolytes are used in redox flow batteries, then the battery can operate with stable chemistry, but the volumetric energy density remains limited to 20-25 Wh/L requiring large storage volumes
Solution Approach 1:
The patent combines the solvent and redox-active material into a single ionic liquid species. This merging eliminates the need for separate bulk solvent that occupies volume without contributing to energy storage, thereby increasing volumetric energy density while maintaining chemical stability through the inherent properties of ionic liquids.
Solution Approach 2:
The patent changes the physical and chemical parameters of the electrolyte by using ionic liquids with specific melting points below 70°C. This parameter change allows the electrolyte to remain liquid at operating temperatures while achieving higher concentrations of redox-active species, thus improving volumetric energy density without sacrificing operational reliability.
2Volume of stationary object
If high concentration of redox active species is achieved using ionic liquids, then volumetric energy density increases, but the melting point must be controlled below 70°C to maintain liquid state
Solution Approach 1:
The patent systematically adjusts the molecular structure of ionic liquids by selecting specific cations and anions to achieve the optimal balance between melting point and energy density. By changing parameters such as ion size, shape, and interionic interactions, the patent achieves melting points below 70°C while maintaining high concentrations of redox-active species for improved volumetric energy density.
Solution Approach 2:
The patent employs composite ionic liquid systems combining different cation-anion pairs to achieve desirable properties. The composite nature allows tuning of melting point through eutectic effects while maintaining high redox-active species concentration, thus resolving the contradiction between temperature control and energy density enhancement.
3Volume of stationary object
If non-aqueous chemistry is used to improve energy density, then volumetric energy density can be increased, but the system complexity and cost increase
Solution Approach 1:
The patent employs ionic liquids that serve multiple functions simultaneously: as solvent, as supporting electrolyte, and as redox-active material. This multi-functionality eliminates the need for separate components required in traditional aqueous systems, thereby reducing system complexity while achieving high volumetric energy density through non-aqueous chemistry.
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
This approach enhances the volumetric energy density of redox flow batteries, potentially reducing their footprint and operational costs by maximizing the concentration of redox active species and enabling higher voltage operation.
Implementation Method 1
The liquid electrolytes are formulated to have some 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 efficiency and performance may be improved with a high energy density bipyridinium based ionic room-temperature liquid electrolyte. Current electrolytes require solvent to dissolve the redox-active material and a supporting electrolyte to maintain charge balance. A room temperature redox-active electrolyte having intrinsic charge balancing would not need a solvent to form a liquid and would therefore have a higher density of anions and cations involved with charge storage. As such, creating redox-active bipyridinium core ionic materials that are in a liquid form at room temperature or, more particularly, are liquids across the range at which a redox flow battery would operate permit smaller and less costly flow battery design than conventional flow batteries.