A cyano cobalt’‘electron transfer bridge’’boosting the two-electron reaction of a MnO2 cathode with long lifespan in aqueous zinc batteries

摘要

The dissolution/deposition reaction of MnO2 cathode materials in aqueous zinc batteries provides two-electron transfers and delivers high theoretical capacity.However,this process usually requires an acidic environment and pre-added Mn~(2+)salts in electrolytes.Herein,we present an’‘electron transfer bridge’’at the cathode to enhance the two-electron transfer contribution in MnO2 in conventional zinc cells.A composite material with MnO2 and CoOx connected by Mn-N = C-Co interactions was synthesized.Mechanism studies demonstrate that the facile redox center of Co~(3+)/Co~(2+)receives/donates electrons during discharge/charge processes,and electrons effectively transport to the Mn centers thanks to the narrowed band gap and charge delocalization.The dolosse-1ike hollow morphology formed through the inside-out Ostwald ripening process during the discharge further provides abundant reaction sites.These factors largely activate the dissolution/deposition process of MnO2 material.In aqueous zinc cells with the conventional ZnSO4 electrolyte,the composite cathode achieves a high capacity of 425 mA h g~(-1)at 0.1 A g~(-1),and an ultra-1ong life of over 25 000 cycles is realized at 2 A g~(-1)This work presents an effective strategy to promote the high-capacity reaction path of MnO2 in zinc batteries.