Uncovering ionic conductivity impact towards high power vanadium flow battery design and operation

Abstract

High power output and efficient charge-discharge operation are deemed to be the pivotal for technological development of vanadium flow batteries. Due to large polarizations however, cycling efficiency is still to a great extent limited in high-power commercialized stacks adopting the conventional flow-through design. To facilitate an in-depth understanding of polarizations and realize a high-power and efficient operation, polarization analyses are performed in this study on a flow-through design based vanadium flow cell. Combined experimental and calculated results show that under the investigated testing conditions, the ohmic polarization dominates the cell polarization across 20–250 mA cm−2, while the electrolyte resistance can account for 70% of the cell resistance. To reduce the electrolyte resistance, further experimental results uncover that enhancing the ionic conductivity through adopting a dilute vanadium electrolyte at a high temperature can readily yield an energy efficiency of 80% at 250 mA cm−2. Such an efficiency enhanced operation can aid to reduce the stack cost, and further discussions concerning other electrolyte properties (e.g., viscosity and surface tension) and their associated effects on battery design and operation also manifest that the electrolyte optimization strategy is practically viable and can be considered for certain flow battery application scenarios.