Materials for suspension (semi-solid) electrodes for energy and water technologies

Abstract

Suspension or semi-solid electrodes have recently gained increased attention for large-scale applications such as grid energy storage, capacitive water deionization, and wastewater treatment. A suspension electrode is a multiphase material system comprised of an active (charge storing) material suspended in ionic solution (electrolyte). Gravimetrically, the electrolyte is the majority component and aids in physical transport of the active material. This principle enables, for the first time, scalability of electrochemical energy storage devices (supercapacitors and batteries) previously limited to small and medium scale applications. This critical review describes the ongoing material challenges encompassing suspension-based systems. The research described here combines classical aspects of electrochemistry, colloidal science, material science, fluid mechanics, and rheology to describe ion and charge percolation, adsorption of ions, and redox charge storage processes in suspension electrodes. This review summarizes the growing inventory of material systems, methods and practices used to characterize suspension electrodes, and describes universal material system properties (rheological, electrical, and electrochemical) that are pivotal in the design of high performing systems. A discussion of the primary challenges and future research directions is included.

Review Article: Flow battery systems with solid electroactive materials

“…27,148,208 Second, four suspension storage tanks are needed for intermittent flow operation because one tank is required for charged suspensions and one for discharged suspensions for each electrode. 104 Such a system must then account for the additional cost, space, and complexity requirements of four tanks as opposed to two per system. In addition, a stable method to switch active material batches is needed to avoid power interruptions between batches of electrolyte suspension being pumped into the electrochemical reaction cell intermittently.…”

“…More details and discussions on capacitive water deionization and electrochemical flow electrodes can be found in recent reviews. 104,106,108,[111][112][113] Research on electrochemical flow capacitors and water capacitive deionization has demonstrated the applicability of solid suspensions for capacitive and electrochemical devices. Recently, progress has also been made in using solid suspensions in RFBs-where the move to solid particles provides a route to increase the battery energy density by overcoming the solubility limitation of active species.…”

“…42,44,92,[99][100][101][102] More detailed discussion on the current status and research perspectives for supercapacitors and EFCs can be found in these recent reviews. 29,40,45,46,103,104 Capacitive water deionization is another application where solid suspensions have been coupled into a system with electrodes and electrical potential driving forces. [104][105][106][107] In a conventional capacitive deionization system, a potential is applied between the two electrodes which forms electric double layers and drives ions toward the two electrode surfaces [shown in Fig.…”

“…27 There is a tradeoff between conductivity and viscosity with varied carbon additive loading, with multiple groups previously reporting on this phenomena in the literature. 104,339 Particle size, morphology, and salt concentration have previously been reported to have significant influence on the rheological properties of solid suspensions, 138,208,338,[340][341][342] and hence provide potential directions to decrease the fluid viscosity. There are a few reports in the literature aimed at decreasing the fluid viscosities of battery material solid suspensions in particular.…”

Carbons, Ionic Liquids, and Quinones for Electrochemical Capacitors

“…Along with the idea that electrochemical capacitor power density can be significantly enhanced with the introduction of redox-active electrolytes, the possibility of creating flow capacitors (Hatzell et al, 2015) has emerged.…”