Modulating Coordination Environment of Cobalt-Based Spinel Octahedral Metal Sites to Boost Metal-Oxygen Bond Covalency for Reversible Lithium-Oxygen Batteries

The intrinsic catalytic activity of conventional spinel electrocatalysts hinders their electrocatalytic outcomes in lithium-oxygen batteries (LOBs), despite their appeal due to compositional variety and structural adaptability. In this work, we reveal that the electrocatalytic activities of these catalysts can be inherently enhanced by modulating metal-oxygen (M-O) bond covalency interactions through the introduction of the Cr element into the MnCo2O4 octahedral sites (MnCr0.5Co1.5O4). The introduction of Cr3+ directly alters the coordination structure of Co octahedral sites, which increases the Co3+-O distance and reduces the lattice symmetry, resulting in enhanced covalency interactions of the M-O bond. Computational analysis supports the effectiveness of Cr in altering the electronic structure of the active site, narrowing the energy gap between Co 3d and O 2p orbitals, evidencing the enhancement of the M-O covalency. In addition, this increased M-O covalency accelerates charge transfer in oxygen-related reactions, thereby facilitating the reversible formation and decomposition of the discharge products in LOBs. As a proof of concept, the MnCr0.5Co1.5O4 catalyzed LOBs exhibit a large discharge capacity of 16 388.3 mAh g(-1) and maintain stability over 329 cycles. This work paves the way for the progression of reversible LOBs by manipulating the coordination structure of the spinel catalysts.