Facilitating both anionic and cationic redox processes in Na-rich layered cathode materials by heteroatomic doping

Low energy density was regarded as stumbling block for the commercialization process of sodium-ion batteries (SIBs). In addition to cationic redox process, anionic redox process is considered as supplementary process to contribute extra capacity in cathode materials of SIBs. Nevertheless, to develop high-performance cathodes with joint cationic and anionic redox activities are still facing great challenges, such as sluggish kinetics, irreversible evolution and poor cyclic property, etc. To explore the potential benefits of utilizing both cationic and anionic redox processes, heteroatomic doping strategy with cobalt was adopted to develop high-capacity Na-rich Na2RuO3 cathode. As a result, cobalt-doped layered cathode can exhibit not only high capacity of 177 mAh g-1 at 0.2C within 1.5-4.3 V, but also excellent rate performance with initial capacity of 127 mAh g-1 at high rate of 5C. Moreover, the fabulous capacity retention of 74% is also obtained after 300 cycles, representing prominent electrochemical reversibility as well as enhanced ionic redox of Na2RuO3 system. It is evident that cobalt serves as redox mediator to accelerate anionic kinetics and consequently facilitating anionic redox activity. This work would be of significance for the design of high-capacity cathodes with cationic/anionic redox activity for SIBs.