Abstract
Solid boosters are an emerging concept for improving the performance and especially the energy storage density of the redox flow batteries, but thermodynamical and practical considerations of these systems are missing, scarce or scattered in the literature. In this paper we will formulate how these systems work from the point of view of thermodynamics. We describe possible pathways for charge transfer, estimate the overpotentials required for these reactions in realistic conditions, and illustrate the range of energy storage densities achievable considering different redox electrolyte concentrations, solid volume fractions and solid charge storage densities. Approximately 80% of charge storage capacity of the solid can be accessed if redox electrolyte and redox solid have matching redox potentials. 100 times higher active areas are required from the solid boosters in the tank to reach overpotentials of <10 mV.
Highlights
Substituting conventional carbon-based energy resources with renewables, intermittent energy resources such as solar and wind, requires effective storage policies to ensure the balance between the energy production and the energy consumption [1,2].Redox flow batteries (RFBs), as a technology in which electricity and chemical energy are interconverted by using redox-active species dissolved in electrolyte solutions stored in tanks, are proposed as a promising alternative for stationary energy storage and present advantages such as high safety, stability, flexibility, and scalability [3]
RFBs are able to decouple the power from the capacity so that by increasing the tank size and the amount of electrolyte, the storage capacity would increase with obtaining the same power output
Thermodynamical treatment allows for evaluation of the requirements for solid boosted redox flow batteries. 80% capacity utilization of the solid materials can be reached if the redox potentials of the redox electrolyte and the redox solid match well
Summary
Substituting conventional carbon-based energy resources with renewables, intermittent energy resources such as solar and wind, requires effective storage policies to ensure the balance between the energy production and the energy consumption [1,2]. While the amount of electrolyte is the same, the storage capacity of the battery will be increased and will no longer be determined solely by the solubility of the dissolved redox species This translates to a higher energy density than that of the conventional redox flow batteries. Electrode materials of Li-ion batteries have a high effective concentration of charges, e.g., 22.8 M for LiFePO4 and 22.5 M for TiO2 , resulting in a superior capacity The addition of these materials in the tanks will enhance the capacity compared with the classical vanadium redox flow battery where the concentration of vanadium species is between 1.5 M and 2 M [5,6,7].
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