Organic Multiple Redox Semi‐Solid‐Liquid Suspension for Li‐Based Hybrid Flow Battery

Abstract

Li‐based hybrid flow batteries are very promising in the energy storage market for their high cell voltage and scale‐up flexibility. However, the low volumetric capacity of catholyte has limited their practical application. A novel concept of organic multiple redox semi‐solid‐liquid (MRSSL) suspension was proposed and demonstrated by taking advantage of active materials in both liquid and solid phases in the suspension. In this study, high solubility of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in the liquid phase and high reversibility of 10‐methylphenothiazine (MPT) composite in the solid phase were employed to develop a high‐performance and low‐cost organic MRSSL Li‐based hybrid flow battery. It achieved a small voltage gap (<0.1 V) between liquid and solid phase, high cell voltage (≈3.4 V) and high energy density (260 Wh L−1). Due to the synergistic interactions between the liquid‐phase TEMPO and the solid‐phase MPT, the viscosity of the MRSSL suspension was significantly reduced. An intermittent‐flow‐mode test of TEMPO‐MPT MRSSL suspension was conducted, which proved that the suspension had an applicable cycling performance with high volumetric capacity (50 Ah L−1). The organic MRSSL suspension concept offers a new approach to increase the volumetric capacity and energy density of Li‐based hybrid flow batteries by combining various low‐cost solid and liquid organic active materials.

High-capacity polysulfide–polyiodide nonaqueous redox flow batteries with a ceramic membrane

“…We noticed that the current density applied is lower than that of ARFB, which is mainly limited by the large resistance of ceramic membrane used in our system. The selfmade ceramic membrane has much lower ionic conductivity (4×10 -4 mS cm -1 ) 49 compared with organic electrolyte (9×10 -3 mS cm -1 ) 50 , which leads to large overpotential during cycling process. As shown in Figure S2, EIS results also indicates the large resistance of ceramic membrane in our Li-based half cell tests.…”

Modeling Electrochemical and Rheological Characteristics of Suspension-Based Electrodes for Redox Flow Cells

“…Building on this work, subsequent studies have explored a diverse set of charge storage materials, including, but not limited to, alternative lithium-ion positive and negative electrodes, [20][21][22][23] aqueous metal electrodes, [24][25][26][27][28] redox-active aqueous microgels, 29 and multi-redox organic species. 30 Colloidal, carbon-based suspensions can also be used either as a reactive surface for charge transfer into solution or as a conductive network to transport current to and from appended solid charge storage materials. To date, various classes of FSEs comprising different carbon particles, particle sizes, particle shapes, concentrations, and surface functionalizations have been employed, exhibiting a wide range of electrochemical and rheological properties.…”

“…24-26) along with the boundary conditions (Eqs. [30][31][32][33] were solved using the Chebfun package 61 in MATLAB (R2018a, 64bit). The module uses piecewise polynomial interpolants to construct continuous approximations for the governed quantities within the electrochemical half-cell, achieving roughly machine precision by selecting a suitable order of the polynomials.…”

Strategies to Improve the Energy Density of Non-Aqueous Organic Redox Flow Batteries

“…By applying the semi-solid approach to both anolyte and catholyte, Xing et al 24 reported an all-organic semi-solid flow battery with 10-methylphenothiazine@Ketjen black and thioxanthone@Ketjen black as the active materials for catholyte and anolyte respectively. This proof of concept cell exhibited an open circuit voltage of 2.35 V and an average CE of 83% within the voltage range of 0-3.0 V. To further improve the energy density of the organic semi-solid electrodes, Chen and coworkers 52 proposed an innovative concept of organic multiple redox semi-solid-liquid (MRSSL) catholyte which combined the high soluble TEMPO in the liquid phase and the insoluble MPT in the solid phase suspension. By activating the liquid phase, the proposed Li hybrid MRSSL catholyte exhibited a small voltage gap of 0.1 V between liquid and solid phase, a high cell voltage of 3.4 V, a high volumetric capacity of 75 Ah•L −1 , and a high energy density of 260 Wh•L −1 .…”