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.