Polymeric Active Materials for Redox Flow Battery Application

Abstract

The redox flow battery (RFB) is one of the most promising systems for large scale electrochemical energy storage applications. The development of redox-active materials is an essential part of RFB research. Commercial RFBs utilize redox-active inorganic ions, which have several issues such as expensive and toxic active materials, crossover of redox species, and high cost of the ion exchange membrane. The incorporation of redox-active polymeric materials is an intriguing solution because low-cost polymeric redox-active materials and size-exclusion porous membranes formed by commodity polymers could be applied to replace expensive inorganic redox-active materials and ion exchange membranes, respectively. The development of polymer-based redox-active materials in RFB application (PRFB) has advanced rapidly in the past few years. In this review, the recent progress of PRFB is summarized. Three major categories based on materials are discussed: the aqueous redox-active polymers, the nonaqueous redox-active polymers and oligomers, and polymer suspension systems. This review not only provides comprehensive information on synthetic strategy of polymeric redox-active materials and their properties such as redox potential and solubility in electrolyte but also reports the performance of recent PRFB cells, including cycling stability, cell voltage, and implementation of size-exclusion porous membranes. Finally, a short future perspective of PRFB development is provided.

High-performance all-organic aqueous batteries based on a poly(imide) anode and poly(catechol) cathode

“…4 Aqueous all-polymer batteries (AqPBs) that incorporate redox-active polymers (RAPs) as organic electrode materials (OEMs) and aqueous solutions as safe and cost-effective electrolytes can be promising alternatives for the development of sustainable energy storage systems. [5][6][7] Although a plethora of RAPs have been successfully applied as OEMs in numerous rechargeable battery technologies (mostly, in metal-ion-polymer conguration), [8][9][10][11][12][13][14][15][16][17] examples of AqPBs sporadically appeared in the literature. 18,19 This is partly due to the formidable challenge that requires careful designing of both anode and cathode RAP partners to be not only able to sustain their redox activity in aqueous media, but also deliver a high voltage output within a relatively narrow electrochemical window of aqueous electrolytes ($1.23 and $2 V for pure water and typical salt-in-water electrolytes, respectively).…”

“…[20][21][22][23] Based on the charge storage mechanisms of RAPs, they can be generally classied into: n-type undergoing N4N À , p-type undergoing P4P + , and bipolar exhibiting B À 4B4B + redox reactions, with the simultaneous shuttling of electroneutralizing cations, anions, and dual ions, respectively. [8][9][10][11][12][13][14][15]18,19 Depending on the RAP (n-or p-type) and the chemical nature of the charge carriers, three kinds of AqPBs were realized: (i) n|ntype combination is generally preferred for the capacityoriented design (20-65 mA h g cell À1 , <1 V), [24][25][26] p|p-type combination mostly preferred for the voltage-oriented design (1.1-1.3 V, <45 mA h g cell À1 ), [27][28][29] and n|p-type combination offers a compromise between the capacity and the voltage (10-52 mA h g cell À1 and 0.9-1.3 V) [29][30][31][32][33] ( Fig. S1 and Table S1, see the ESI †).…”

Organic Electroactive Molecule-Based Electrolytes for Redox Flow Batteries: Status and Challenges of Molecular Design

“…One common critical issue in improving the cell performance of RFBs with electrochemical small molecules is the permeability of redox species across the ion-exchange membrane, known as crossover contamination, which leads to Coulombic efficiency fade (Lai et al, 2020). It was believed that larger-sized macromolecules would have difficulty migrating through the membrane, and so electroactive polymers were employed as redox centers in RFBs (Nagarjuna et al, 2014;Burgess et al, 2016Burgess et al, , 2018Iyer et al, 2017).…”

Assessing Capacity Loss Remediation Methods for Asymmetric Redox Flow Battery Chemistries Using Levelized Cost of Storage

“…In working to reduce these key variables, note that electrolyte price and decay rate may not be independent, as functionalization of organic molecules often improves stability [30,72] and, likely, simultaneously complicates the manufacturing process and thus adds to the chemical cost. Relative to those two variables, reactor cost has a lesser effect on LCOS, though it is important to consider as organic molecules are generally larger than their aqueous supporting salts, providing the opportunity to leverage sizeexclusion membranes as opposed to more expensive ion-exchange membranes [33]. There is also the potential to employ lower-cost membranes ill-suited for VRFBs, either via the use of electrolytes with milder pH [37,70] or a less oxidizing active species [9].…”