Improved static membrane-free zinc‑bromine batteries by an efficient bromine complexing agent

Zinc‑bromine batteries (ZBBs) are very promising in distributed and household energy storage due to their high energy density and long lifetime. However, the disadvantages of existing zinc‑bromine flow batteries, including complicated structure, high cost for manufacturing and maintenance, limited their large-scale applications seriously. Additionally, polybromide anions during the charging process of ZBBs will result in the problem of self-discharge. Here, a static membrane-free ZBB (SMF-ZBB) structure has been proposed, in which the phenyl trimethyl ammonium bromide (PTMAB) works as a bromine complexing agent (BCA). Because PTMAB has a feature of strong polarity, it can be combined well with polybromide anions to reduce the self-discharge effectively. Furthermore, it can also reduce the internal resistance of electrolytes and improve the energy density of SMF-ZBB. Compared with the blank electrolyte, the coulombic efficiency (CE) of the battery with PTMAB addition was increased by 10 % at 20 mA/cm2. The CE with a value of 93.1 % can be well maintained even after >5000 cycles at 10 mA/cm2. The results show that the introduction of PTMAB into the electrolytes can improve the CE and energy efficiency (EE) effectively.