In-situ probing phase evolution and electrochemical mechanism of ZnMn2O4 nanoparticles anchored on porous carbon polyhedrons in high-performance aqueous Zn-ion batteries

Inspired by the successful application of spinel LiMn2O4 cathode in Li-ion batteries, analogous spinel ZnMn2O4 (ZMO) is regarded as a promising cathode for rechargeable aqueous Zn-ion batteries (ZIBs). Nevertheless, clear Zn2+ storage mechanism and phase transition of spinel ZMO is still scarce. Herein, in the first time, we report an in-situ Raman study in dynamically probing the phase and structure evolution of a spinel ZMO-based cathode during charging-discharging process, in which spinel ZMO nanoparticles are anchored on porous carbon poly-hedrons (PCPs). By in-situ investigation, it is demonstrated that the electrochemical mechanism can be attributed to the highly reversible phase transformation between spinel ZMO and lambda-type MnO2 upon Zn2+ insertion/extraction, which is driven by stepwise oxidation and reduction reactions of Mn3+/Mn4+ along with efficient charge carriers. Furthermore, the resultant ZMO@PCPs composite as cathode delivers a large reversible capacity of 125.6 mAh g(-1) at a high current density of 1 A g(-1) after 2000 cycles, representing superior long-term cyclic stability (capacity retention of 90.3%) and remarkable rate capability in aqueous ZIBs. As a proof of concept, high-performance flexible aqueous ZIBs are fabricated and represent stable electrochemical performance under various deformation states, indicating their potential applications in portable and wearable electronics.