Zn-Iodine Flow Battery Electrolyte and Membrane for Iodine Cross-Over
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Solution Overview
Problem
Aqueous zinc-iodine flow batteries (Zn—I FBs) face challenges such as low operating current density, inferior power density, and significant cross-over issues of iodine active materials, leading to capacity loss and reduced coulombic efficiency.
Innovation Solution
The introduction of a rechargeable aqueous Zn∥IS flow battery system utilizing a starch-based colloidal chemistry approach, which regulates the size of iodine species in the catholyte to prevent cross-over, combined with low-cost porous polypropylene membranes for enhanced ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Nafion-membrane systems are used, then ion selectivity is improved, but power density decreases due to limited ionic conductivity and significant overpotentials
Solution Approach 1:
The patent changes the membrane material from Nafion to low-cost polyolefin-based porous membranes (LPPM), fundamentally altering the membrane's physical and chemical parameters including porosity, hydrophobicity, and pore size distribution. This parameter change enables high ionic conductivity while maintaining adequate ion selectivity, resolving the contradiction between selectivity and power density
Solution Approach 2:
The patent replaces expensive Nafion membranes with low-cost polyolefin-based porous membranes, significantly reducing material cost while maintaining functional performance. This substitution allows for broader deployment and improves overall system economics without sacrificing essential ion selectivity
2Reliability
If dense Nafion-based membrane is used, then coulombic efficiency is improved, but voltage efficiency and energy efficiency decrease due to increased membrane resistance
Solution Approach 1:
The patent optimizes the porosity parameter of the LPPM to achieve a balance between ion selectivity and ionic conductivity. The specific pore size and porosity distribution are tuned to allow sufficient ion transport (maintaining voltage efficiency) while preventing iodine crossover (maintaining coulombic efficiency)
3Power
If low-cost polyolefin-based porous membranes are used, then ionic conductivity is improved, but cross-over issues of iodine active materials increase leading to capacity loss
Solution Approach 1:
The patent introduces a size-sieving mechanism as an intermediary filtering approach, where the porous membrane structure acts as a physical sieve that allows small ions to pass while blocking larger iodine species based on size exclusion, thus preventing cross-over while maintaining ionic conductivity
Solution Approach 2:
The patent utilizes the porous structure of LPPM with specific pore size and distribution to achieve size-based separation. The porous morphology is optimized to create a sieving effect that permits ion transport while preventing iodine molecule passage, resolving the contradiction between conductivity and cross-over prevention
4Reliability
If membrane coatings are introduced, then cross-over prevention is improved, but inner resistance increases and energy efficiency decreases
Solution Approach 1:
The patent extracts and eliminates the problematic membrane coating layer entirely, using the intrinsic properties of LPPM (porosity, hydrophobicity, pore size) to achieve cross-over prevention without adding external coating layers that would increase resistance and reduce energy efficiency
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 solution achieves high coulombic efficiency, voltage efficiency, and energy efficiency, with a power density of at least 40 mW cm−2 and stable cycling performance for 350 cycles, while significantly reducing the installed cost of the flow battery system.
Implementation Method 1
a separator positioned between the cathode and anode
Implementation Method 2
utilizing a starch-based colloidal chemistry approach, which regulates the size of iodine species in the catholyte to prevent cross-over
Implementation Method 3
low-cost porous polyolefin-based porous membranes (LPPM) have emerged as promising separators to enhance working currents due to their high ionic permeability and low ionic resistance
Implementation Method 4
The anolyte and the catholyte flow between the cathode and the anode by a peristaltic pump
Implementation Method 5
the electrode material on the cathode side absorbs and stores one or more ions from the catholyte, and the electrode material on the anode side absorbs and stores one or more ions from the anolyte
Data Source
AI summary
The present invention relates to a rechargeable aqueous Zn∥IS flow battery system. The system includes a cathode side comprising an electrode material and a first storage tank providing a catholyte, wherein the catholyte comprises zinc iodide and a soluble starch, forming an electrolyte having aggregated colloidal nanoparticles; an anode side comprising the electrode material and a second storage tank providing an anolyte; and a separator positioned between the cathode and anode. The anolyte and the catholyte flow between the cathode and the anode by a peristaltic pump. The present invention provides a system to further exploit colloidal electrolyte chemistries for the LPPM-based flow battery systems towards power cost-effectiveness and high-temperature large-scale energy storage.