Mn2+Ions Confined by Electrode Microskin for Aqueous Battery beyond Intercalation Capacity

In aqueous rechargeable zinc-manganese dioxide batteries (ZMBs), some irreversible side reactions, such as Mn(2+)dissolution, often lead to capacity fading over cycling. These side reactions play a crucial role in the capacity and cycle performance of the battery. The implementation of a bionic electrode microskin (EMS) composed of collagen hydrolysate to convert the irreversible side reactions into reversible reactions is reported. The proposed EMS effectively adsorbs and confines the Mn(2+)ions around the cathode through van der Waals forces, hydrogen bonds, and/or ionic interactions, which makes the MnO2/Mn(2+)reactions reversible during the charge/discharge process. Such Mn(2+)dissolution reactions, with an ultrahigh theoretical capacity (617 mAh g(-1)), contribute a large amount of capacity, approximate to 44% of the total specific capacity at a low scan rate. Based on these fundamental findings, the assembled ZMBs with an EMS display an unprecedented discharge capacity of 415 mAh g(-1)at 20 mA g(-1), which overcomes the theoretical capacity (308 mAh g(-1)) limitation of the Zn(2+)intercalation mechanism. More significantly, the EMS on all alpha-, beta-, and gamma-MnO(2)cathodes exhibits similar high capacity beyond the theoretical capacity of Zn intercalation and capacity retention enhancement after 3000 cycles.