Redox Flow Battery Electrolyte Membrane Ion Permeability
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Solution Overview
Problem
Conventional redox flow secondary batteries face issues with high electric resistance, low current efficiency, and inadequate durability due to insufficient ion permselectivity and oxidative deterioration resistance in their separation membranes, particularly in vanadium-type batteries.
Innovation Solution
A redox flow secondary battery employing a fluorine-based polyelectrolyte polymer with a specific structure and ion cluster diameter range, integrated with a polyazole-based compound and heat treatment, forms an electrolyte membrane that enhances ion permselectivity and oxidative deterioration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional separation membranes are used to prevent mixing of electrolyte solutions, then ion permselectivity is improved, but electric resistance increases and current efficiency decreases
Solution Approach 1:
The patent changes the chemical composition parameters of the separation membrane by incorporating fluorine-based polyelectrolyte polymers with specific structures (formulae 1-3) containing fluorinated hydrocarbon chains and carboxylic acid groups. This compositional parameter change enables the membrane to achieve both high ion permselectivity (99.5% or more for V2+/V3+ separation) and low electric resistance (0.6-1.2 Ω·cm2), resolving the contradiction between selectivity and conductivity.
Solution Approach 2:
The patent creates a composite membrane structure combining fluorine-based polyelectrolyte polymers with porous substrates (PTFE, polyolefin, or nonwoven fabrics). The composite material integrates the ion-exchange capability of the polyelectrolyte layer with the mechanical strength and porosity of the substrate, achieving simultaneous improvement in ion permselectivity, electric resistance, and mechanical durability.
2Reliability
If separation membrane thickness is increased to improve ion permselectivity, then active substance ion permeation is reduced, but electric resistance increases
Solution Approach 1:
The patent utilizes porous substrates (PTFE membranes, polyolefin porous membranes, or nonwoven fabrics) as the base structure, providing inherent ion transport pathways. The fluorine-based polyelectrolyte polymer is applied as a thin functional layer (0.1-10 μm) on the porous surface, maintaining high porosity (50-80%) that allows efficient ion transport through the membrane thickness while achieving high ion permselectivity.
Solution Approach 2:
The patent applies local quality by concentrating the ion-exchange functionality in a thin surface layer of fluorine-based polyelectrolyte polymer on the porous substrate. The functional layer thickness is optimized at 0.1-10 μm, providing high ion permselectivity locally at the membrane interface while maintaining overall membrane thinness (10-50 μm total) for low electric resistance.
3Object-affected harmful factors
If conventional membranes are used to separate electrodes, then oxidation resistance is insufficient, but durability in sulfuric acid electrolyte solution deteriorates over time
Solution Approach 1:
The patent changes the chemical resistance parameters by introducing fluorine atoms into the polymer backbone structure (CF2-CF2 units in formulae 1-3). The fluorinated hydrocarbon chains provide exceptional chemical inertness and oxidation resistance, enabling the membrane to maintain stable performance in 2 M sulfuric acid electrolyte solution over extended periods (1000+ hours) without significant degradation.
Solution Approach 2:
The patent replaces expensive platinum catalysts with carbon-based electrodes and uses a cost-effective fluorine-based polyelectrolyte membrane that provides comparable or superior durability. The membrane structure is designed for long-term operational stability, eliminating the need for frequent replacement and reducing overall system cost while maintaining high durability.
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 solution results in a battery with reduced electric resistance, improved current efficiency, and enhanced durability, effectively suppressing ion group elimination and oxidative deterioration.
Implementation Method 1
the electrolyte membrane comprises an ion-exchange resin composition comprising a fluorine-based polyelectrolyte polymer having a structure represented by formula (1)
Implementation Method 2
batteries allowing free permeation by an ionic differential pressure and an osmotic pressure of electrolyte solutions as the driving force
Implementation Method 3
integrated with a polyazole-based compound and heat treatment, forms an electrolyte membrane that enhances ion permselectivity and oxidative deterioration resistance
Implementation Method 4
charge and discharge are carried out by utilizing the oxidation and reduction reactions of both the active substances
Data Source
AI summary
An object of the present invention is to provide a redox flow secondary battery being low in the electric resistance and excellent in the current efficiency as well, and further having the durability.The present invention relates to an electrolyte membrane for a redox flow secondary battery, the electrolyte membrane containing an ion-exchange resin composition containing a fluorine-based polyelectrolyte polymer, and having an ion cluster diameter of 1.00 to 2.95 nm as measured in water at 25°C by a small angle X-ray method, and to a redox flow secondary battery using the electrolyte membrane.