Enhancing the performance of non-flow rechargeable zinc bromine batteries through electrolyte concentration correlation with microporous carbon cathodes

Abstract

The quest for renewable energy storage solutions highlights the need for systems prioritizing safety, cost-effectiveness, and accessibility of materials and compartments. Unlike traditional flow systems requiring frequent upkeep and extensive space, the static setup of rechargeable zinc-bromide batteries (RZBBs) in an aqueous environment emerges as a promising option due to its component abundance, secure setup, and compact storage volume. This study focuses on the interplay between zinc-bromide complexes and the pores of the carbon cathodes' scaffold. We uncover noteworthy insights by meticulously controlling the porous structure of the carbon scaffold and the ZnBr2 concentration in the electrolyte while upholding a high Coulombic efficiency (≥96 %). In materials with small pore volumes, even relatively low concentrations and the highest conductivity (3M) lead to space occupation by the complexes impacting the achieved capacity. This is particularly evident at high concentrations (10M) exhibiting low capacities. Conversely, macro-porous carbon-based cathodes (like CNTs) exhibit a reversal of this trend, showcasing advantages at high electrolyte concentrations. These findings indicate a unique behavior of zinc-bromide aqueous electrolytes in porous carbonaceous media, emphasizing the pivotal role of considering the interplay between cathodes’ surfaces and electrolyte concentration for optimal performance.