High-Energy Density Redox Flow Lithium Battery with Unprecedented Voltage Efficiency

A redox flow lithium battery (RFLB) has decoupled energy storage and power generation units like a conventional redox flow battery, while it stores energy in solid materials by virtue of the unique redox targeting concept. Hence, it presents superior energy density and represents a promising approach for large-scale energy storage. In a RFLB, the potential difference between the redox shuttle molecules used in the same electrolyte normally brings about an intrinsic voltage hysteresis, resulting in a compromised voltage efficiency of the battery. Here we report a novel redox shuttle molecule pair to minimize the voltage hysteresis: anatase TiO 2 is reduced by bis(pentamethylcyclopentadienyl)chromium (CrCp* 2 ), while Li x TiO 2 is oxidized by cobaltocene (CoCp 2 ). The potential difference between CoCp 2 and CrCp* 2 is only 0.15 V. A redox flow lithium battery is successfully demonstrated with an unprecedented voltage efficiency of 84%. The RFLB shows good cycling stability, and >90% Coulombic efficiency was demonstrated in the first 50 cycles.