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 TiO2 is reduced by bis(pentamethylcyclopentadienyl)chromium (CrCp*2), while LixTiO2 is oxidized by cobaltocene (CoCp2). The potential difference between CoCp2 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.