Aqueous Redox Flow Battery Separator Design
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Solution Overview
Problem
Existing flow batteries face challenges with high cell resistance and active material crossover, leading to low performance and short cycle life due to inefficient chemistry and cell design, which have not been effectively addressed despite development efforts.
Innovation Solution
The use of thin, highly conductive ionically charged polymer membranes and aqueous electrolytes with metal ligand coordination compounds having matching ionic charges, along with a separator that allows mobile ions like sodium or potassium to flow while restricting active materials like vanadium or iron, to minimize crossover and maximize efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional membranes and chemistries are used in flow batteries, then cell resistance is reduced, but active material crossover increases
Solution Approach 1:
The patent changes the charge parameter of the ionomer membrane to match the charge of the active materials. By selecting an ionomer with the same charge sign as the active materials (e.g., both negative), the electrostatic repulsion prevents crossover while maintaining ionic conductivity for charge-balancing ions, thus simultaneously reducing cell resistance and preventing active material crossover
Solution Approach 2:
The patent employs a composite approach by combining specifically selected ionomer materials with charged active materials in a coordinated system. The ionomer and active materials are chosen to have complementary charge characteristics that work together to prevent crossover while enabling efficient ion transport, creating a synergistic effect that addresses both contradictions
2Reliability
If separator thickness is increased to reduce active material crossover, then current efficiency is improved, but cell resistance increases
Solution Approach 1:
The patent changes the charge parameter of the separator material to match the active materials, creating electrostatic repulsion that prevents crossover. This allows the use of thinner separators (reducing resistance) while maintaining high current efficiency through the charge-based rejection mechanism rather than relying solely on thickness
3Ease of manufacture
If conventional cell designs are used, then manufacturing is simplified, but performance and cycle life are reduced due to high resistance and crossover
Solution Approach 1:
The patent modifies the charge parameter of the ionomer as a key design variable, selecting ionomers with charges that match the active materials. This parameter change fundamentally improves performance and cycle life by preventing crossover and reducing resistance, while maintaining relative manufacturing simplicity through the use of standard ionomer incorporation processes
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 configuration results in flow batteries with low ion crossover, high voltage efficiency, and improved cycle life, achieving current and voltage efficiencies greater than 90% and energy densities over 30 Wh/L, while maintaining low cell resistance.
Implementation Method 1
The ionic charge of the metal ligand coordination compound is selected so as to be of the same sign as the charge of ionomer. This charge matching is shown to yield flow batteries with low fluxes of ion crossover
Implementation Method 2
The battery is charged or discharged through electrochemical reactions of the active materials inside the electrochemical cell
Implementation Method 3
a separator positioned between said first and second aqueous electrolytes, the separator comprising an ionomer membrane
Data Source
AI summary
This invention is directed to aqueous redox flow batteries comprising ionically charged redox active materials and separators, wherein the separator is less than about 100 microns and the flow battery is capable of operating with high energy densities and voltage efficiencies.