Molecular tailoring of MnO2 by bismuth doping to achieve aqueous zinc-ion battery with capacitor-level durability

The poor structural stability and sluggish reaction kinetic leading to rapid capacity fading are still major obstacles for MnO2 as aqueous zinc-ion batteries (ZIBs) cathode materials. Herein, to address this issue, a bismuth (Bi) doping technology is proposed for α-MnO2. A comprehensive study suggests that the Bi stabilizes the tunnel structure by Bi-O bond, enhance the electrical conductivity and weaken the chemical bond strength between the Zn2+ and O via distorting the electron cloud of O. The reaction mechanism analysis further confirms the highly stable phase structure of the Bi-doped α-MnO2 (BMO-6) during the Zn2+/H+ co-insertion/extraction. As result, the BMO-6 cathode manifests an amazing cycle life over 10000 cycles with a capacity retention of 93%, which surpasses the reported Mn-based cathodes in aqueous ZIBs as far as known. Meanwhile, the BMO-6 ZIB displays good rate performance and outstanding energy density of 486 Wh kg−1. Furthermore, the assembled flexible ZIB based on BMO-6 also exhibits excellent mechanical stability at different deformations. This work has proved that Bi doping can boost the electrochemical performance of MnO2 and open new horizons for exploiting other potential cathodes in aqueous ZIBs.