Composite Ion-Selective Membranes for Flow Battery Crossover Control
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Solution Overview
Problem
Existing ion-selective membranes for flow batteries face challenges with mechanical properties, especially when wet, and high costs due to expensive materials like Nafion®, which also complicates surface bonding, leading to issues with cross-over contamination and reduced cycle life.
Innovation Solution
A composite membrane is developed using a microporous polyolefin substrate with a high surface area, hydrophilic filler and an ion-selective polymer coating that is non-porous on one or both sides, providing enhanced mechanical strength and chemical stability, while minimizing residual process oil and using cost-effective ion-selective polymers like Kraton Nexar™, and crosslinking agents to prevent ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expensive ion-selective polymers like Nafion are used, then ion-selective performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive Nafion polymer with cheaper alternative ion-selective polymers that can achieve comparable performance when combined with hydrophilic fillers and proper composite structure design
Solution Approach 2:
The patent creates a composite membrane structure combining polyolefin substrate with ion-selective polymer coating and hydrophilic fillers, achieving cost-effective ion selectivity through material synergies rather than relying on expensive single-material solutions
2Ease of operation
If porous substrate is used, then wettability and ion transport are improved, but mechanical strength deteriorates
Solution Approach 1:
The patent combines porous polyolefin substrate with ion-selective polymer coating and hydrophilic fillers to create a composite structure where the substrate provides porosity and wettability while the coating and fillers contribute to mechanical reinforcement
Solution Approach 2:
The patent applies ion-selective polymer coating selectively on the substrate surface, creating regions with different properties: the porous substrate provides wettability and ion transport pathways, while the coated regions provide mechanical reinforcement and ion selectivity
3Reliability
If ion-selective polymer coating is applied, then ion selectivity is improved, but ion migration increases
Solution Approach 1:
The patent modifies the coating properties by incorporating hydrophilic fillers and adjusting coating thickness and crosslinking degree, optimizing the balance between ion selectivity and preventing ion migration
Solution Approach 2:
The patent creates a composite coating structure combining ion-selective polymer with hydrophilic fillers, where the composite morphology provides selective ion transport pathways while restricting unwanted ion migration
4Reliability
If non-porous coating is applied, then cross-over contamination is reduced, but ion transport resistance increases
Solution Approach 1:
The patent uses a porous polyolefin substrate as the base layer to provide ion transport pathways, then applies a non-porous ion-selective coating that prevents cross-over while allowing selective ion transport through the porous substrate structure
Solution Approach 2:
The patent divides the membrane into functional layers: the porous substrate handles ion transport, while the non-porous coating handles cross-over prevention, allowing each layer to optimize its specific function without compromising the other
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 composite membrane exhibits improved durability, reduced ion migration, and lower electrical resistance, enhancing the efficiency and longevity of flow batteries by maintaining integrity and preventing cross-over contamination.
Implementation Method 1
The ion-selective, polymer-rich, non-porous layer can also be crosslinked
Implementation Method 2
ion transport can still take place through wetting of available pores and swelling of the ion-selective polymer coating
Implementation Method 3
ion transport can still take place through wetting of available pores and swelling of the ion-selective polymer coating
Implementation Method 4
microporous polyolefin substrate with a high surface area, hydrophilic filler
Data Source
AI summary
This disclosure relates to free-standing, composite membranes that include an ion-selective polymer coating that covers at least one surface and partially penetrates into the pore structure of a polyolefin substrate. While the composite membranes do not have open, interconnected pores that connect each major surface, ion transport can take place through wetting of available pores and swelling of the ion-selective polymer coating accompanied by ion migration from one membrane surface to the opposite surface. Such composite membranes are useful for separating the anolyte and catholyte in a flow battery.