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Updated: Aug 23, 2025
09:49
A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery
Published on: February 13, 2017
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High Energy Density, Asymmetric, Nonaqueous Redox Flow Batteries without a Supporting Electrolyte
Yichao Yan1,2, Paban Sitaula3,2, Susan A Odom3,2
1Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
ACS Applied Materials & Interfaces
|October 31, 2022
Summary
Researchers developed high-solubility organic molecules for nonaqueous redox flow batteries (RFBs). These molecules enable asymmetric designs, overcoming solubility and crossover limitations for higher energy density.
Area of Science:
- Electrochemistry
- Materials Science
- Energy Storage
Background:
- Nonaqueous redox flow batteries (RFBs) face energy density limitations due to low solubility of redox-active organic molecules (ROMs).
- Symmetric RFBs require 1:1 ROM mixtures, further restricting concentrations and performance.
- Separator limitations exacerbate ROM crossover issues between battery compartments.
Purpose of the Study:
- To develop novel ROMs with high solubility and low membrane crossover for enhanced nonaqueous RFB performance.
- To enable the creation of asymmetric RFBs by utilizing ROMs with negligible crossover.
- To demonstrate a high energy density nonaqueous RFB system without supporting electrolytes.
Main Methods:
- Synthesis of permanently cationic oligomers of viologen, tris(dialkylamino)cyclopropenium, and phenothiazine.
- Evaluation of ROM solubility in acetonitrile.
- Assessment of ROM crossover rates across an anion exchange membrane.
- Assembly and testing of an asymmetric RFB comprising oligomeric viologen and cyclopropenium ROMs.
Main Results:
- Synthesized oligomeric ROMs exhibit high solubility in acetonitrile.
- Oligomeric ROMs demonstrate slow to undetectable crossover rates through an anion exchange membrane.
- An asymmetric RFB achieved a voltage of 1.66 V and a theoretical energy density of 22.2 Wh/L at 1.0 M concentration.
- The system operates without added supporting electrolyte, relying only on counteranions for conductivity.
Conclusions:
- Permanently cationic oligomeric ROMs effectively address solubility and crossover challenges in nonaqueous RFBs.
- Asymmetric RFB designs utilizing these oligomers offer a pathway to significantly higher energy densities.
- This approach represents a promising advancement for high-performance nonaqueous energy storage systems.
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