Local electronic structure constructing of layer-structured oxide cathode material for high-voltage sodium-ion batteries

Abstract

As the cyclable sodium ions' primary suppliers, O3-type layer-structured manganese-based oxides are recognized as one of the most competitive cathode candidates for sodium-ion batteries. Suffering from complex structural transformations and transition metal migration during the sodium intercalation/deintercalation process, particularly at high voltage, the energy density and lifespan cannot satisfy the increasing demand. The orbital and electronic structure of the octahedral center metal element plays an important role in maintaining the octahedral structural integrity and improving the Na⁺ diffusivity by the introduced heterogeneous [Me–O] (Me: transition metals) chemical bonding. Herein, inspired by the 4f and 5d orbital bonding possibility from the abundant configuration of extranuclear electrons and large ion radius, O3-type Na[La_0.01Ni_0.3Mn_0.54Cu_0.1Ti_0.05]O₂ was synthesized with a nearly single crystal structure. Based on the experimental and computational results, the introduced heterogeneous [La–O] chemical bond with larger bond strength can not only ensure the stability of the lattice oxygen framework and the reversibility of oxygen redox but also optimize the oxygen local electronic structure resulting from La 5d and O 2p orbital mixing due to O 2p → La 5d charge transfer. It delivers an optimal electrochemical performance with a high energy density and cycling lifespan.