Analysis of Crossover-Induced Capacity Fade in Redox Flow Batteries with Non-Selective Separators

Abstract

Redox flow batteries (RFBs) are candidates for grid-scale energy storage. For RFBs mechanistic understanding of redox-active species crossover is needed to optimize electrolyte composition (both of inert salt ions and redox-active species) especially when low-cost separators are used instead of ion-selective membranes. We simulate these effects using a multi-component porous electrode model with Nernst-Planck fluxes and Marcus-Hush-Chidsey kinetics to predict capacity utilization and fade. The molar ratio of inert salt to redox species and the ratio of their diffusivities are used to parameterize different electrolytes in RFBs with non-selective separators. Irrespective of whether redox couples use a common charge-balancing counterion (rocking chair configuration) or not (salt splitting configuration) the molar ratio of inert salt to redox species must exceed 50% to cycle with substantial capacity. Using Damköhler numbers (characteristic scales of reaction rates to transport rates) for both inert salt Da salt and redox-active species Da redox we classify three RFB operating regimes: redox shuttle limited, ohmic polarized, and sufficient supporting electrolyte. In the sufficient supporting electrolyte regime capacity fade is found to scale inversely with Da redox , resulting in capacity fade per cycle less than 0.01% for Da redox larger than 10 5 and capacity utilization of approximately 80% for Da salt smaller than 12.

Side by Side Battery Technologies with Lithium‐Ion Based Batteries

“…The separators also play a crucial role on the performance of RFBs. [95][96][97][98] Generally, four different type of separators are reported: a) ion-exchange membrane, b) porous separator, c) hybrid membranes, and d) solid ionic conductors. [99] Depending on the cell chemistry, one of these separators can be utilized in the RFB.…”

Quinones for Aqueous Organic Redox Flow Battery: A Prospective on Redox Potential, Solubility, and Stability

“…As the RFB charges and the state of charge (SoC) increases, the composition of the electrolyte changes, which can affect its properties including viscosity. [128,129] It is crucial to maintain a low viscosity regardless of the level of energy storage to ensure optimal performance throughout the charge/discharge cycles .Viscosity is directly linked to mass transfer processes within the RFB. Geoffroy et al discovered a relationship between the activation energy of viscous flow and ionic conductivity, with their product The ionic conductivity of eutectic quinone supporting electrolyte mixtures is compared in different compositions.…”

A High Potential, Low Capacity Fade Rate Iron Complex Posolyte for Aqueous Organic Flow Batteries

“…In the pursuit of a high-performing and long-lasting flow battery, understanding the capacity fade mechanism is of great importance. [39,40] Irreversible capacity fade in ARFBs can be attributed to active species crossover through the membrane [41,42] or their decomposition. [39] In this study, several post-mortem analysis techniques including electrochemical methods, NMR, and mass spectrometry are deployed to unravel the capacity decay mechanisms.…”