2D Co-doped MnCr2O4 nanosheets as efficient bifunctional cathode materials for long-life Li–O2 batteries

Abstract

Lithium–oxygen batteries (LOBs) with ultra-high theoretical energy density have not been commercialized due to shortcomings such as short cyclic lifespan, high charging overpotential, and poor rate capability. Here, Co-doped MnCr₂O₄ (MnCoCrO) with a lamellar structure was successfully prepared by a combination of sol–gel and annealing methods. Thanks to the incorporation of Co, the electron density near the metal ions in the original lattice is strongly affected. Then, the adsorption capacity of the active site for the intermediate LiO₂ is greatly increased, which makes Li₂O₂ more inclined to grow by surface mechanism, and finally contacts with the cathode in a ringlike shape, effectively avoiding the occurrence of complex parasitic reactions, so as to improve the cycle life. LOBs based on the MnCoCrO electrode demonstrate a lower overpotential of 0.89 V, excellent initial discharge capacity (13 600 mA h g⁻¹) at 200 mA g⁻¹, and long-term cycle stability of more than 1000 h under a fixed capacity of 1000 mA h g⁻¹ at 400 mA g⁻¹. This study deeply explains the important role of metal atom doping in improving electrochemical performance and provides a reference for the design of cathode catalysts in LOBs.