Long term multi-observable measurements for SOC/SOH analysis and crossover modelling

Abstract

The operation of vanadium redox-flow batteries (VRFB) is accompanied by electrolyte crossover through the membrane which can lead to selfdischarge and electrolyte imbalances. These imbalances lead to capacity losses, which decrease the state of health (SOH) of the battery. In commercial VRFB systems the state of charge (SOC) of the battery is typically monitored either by coulomb counting, via an open circuit potential or by a combination of both. With these methods electrolyte imbalances cannot be detected. For a reliable imbalance detection, half-cell specific SOCs are needed. Several SOC/SOH monitoring methods have been developed, which are mostly based on one or two measured quantities. We aim for the development of a stable SOC/SOH monitoring method including crossover effects based on the measurement of several SOC/SOH related observables. To establish a long term data basis for the corresponding analysis we perform correlated and partially redundant in situ measurements in a 500h charge/discharge cycling test. In the next step, a comprehensive SOC and SOH model accompanied by an empiric VRFB crossover model shall be developed.