Vanadium-Mediated High Areal Capacity Zinc–Manganese Redox Flow Battery
Jinpeng Cao, Kaifeng Yu, Jianing Zhang, Biao Lu, Juezhi Yu, Shiqiang Huang, Feifei Zhang
Abstract
Aqueous manganese redox flow batteries (AMRFBs) that rely on the two-electron transfer reaction of Mn 2+ /MnO 2 have garnered significant interest because of their affordability, high voltage, and excellent safety features. Nevertheless, the deposited MnO 2 tends to partially dissolve during discharge, impeding the sustained operation of AMRFBs, particularly at high areal capacities (>5 mA h cm –2 ). Herein, VO 2+ /VO 2 + was introduced into the catholyte as a redox mediator (RM) to facilitate the efficient dissolution/deposition process of MnO 2 . In situ UV–vis spectroscopy and kinetic analysis elucidated the swift reaction mechanism between MnO 2 and VO 2+, which allows for efficient rejuvenation of “dead” MnO 2 with facile amounts of mediator, further achieving a highly reversible MnO 2 cathode. The assembled zinc–manganese redox flow battery with RM demonstrates a high Coulombic efficiency of 99% at 20 mA h cm –2 over 50 cycles. The areal capacity is further increased to 50 mA h cm –2, achieving an exceptional areal energy density exceeding 100 mW h cm –2, surpassing most reported areal capacity in the AMRFB. This work introduces a novel RM to address “dead” MnO 2 and sheds valuable insights into the reaction mechanism between MnO 2 and RM, which will promote the development of other deposition-type batteries.