Layered transition-metal (TM) oxides are ideal hosts for Li+ charge carriers largely due to the occurrence of oxygen charge compensation that stabilizes the layered structure at high voltage. Hence, enabling charge compensation in sodium layered oxides is a fascinating task for extending the cycle life of sodium-ion batteries. Herein a Ti/Mg co-doping strategy for a model P2-Na2/3 Ni1/3 Mn2/3 O2 cathode material is put forward to activate charge compensation through highly hybridized O2 p TM3 d covalent bonds. In this way, the interlayer OO electrostatic repulsion is weakened upon deeply charging, which strongly affects the systematic total energy that transforms the striking P2-O2 interlayer contraction into a moderate solid-solution-type evolution. Accordingly, the cycling stability of the codoped cathode material is improved superiorly over the pristine sample. This study starts a perspective way of optimizing the sodium layered cathodes by rational structural design coupling electrochemical reactions, which can be extended to widespread battery researches.
Keywords: high-voltage structural stability; in situ synchrotron characterizations; layered transition-metal oxide cathodes; oxygen charge compensation; sodium-ion battery.
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