Metallic Ti4O7 with strong polybromide chemisorption ability as polar host for zinc-bromine batteries

Membraneless and flowless zinc-bromine batteries (MLFL-ZBBs) have emerged as a compelling solution for energy storage due to their cost-effectiveness, high cell voltage, and high safety. However, challenges persist in maintaining long-term stability and efficiency, primarily attributed to the inadequate adsorption of carbon-based host materials in ZBBs to soluble polybromides. Here, we report a highly conductive, inherently polar Ti4O7 as the host material and demonstrate how it improves MLFL-ZBBs stability. Density functional theory calculations suggest the electron densities of Br atoms within polybromides are significantly intertwined with Ti atoms in Ti4O7, resulting in the formation of robust Ti-Br bonding, which are absent as for carbon and bromine interactions. Visual discrimination, UV-Vis, and X-ray photoelectron spectroscopy collectively confirm the substantial adsorption capabilities of Ti4O7 towards polybromides. The Coulombic efficiency of MLFL-ZBBs with Ti4O7 as host materials remain 93.8% after 2,000 cycles, which is more than three times that with traditional carbon-based host.