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

Na-rich cathodes with anionic redox activities are considered as one of the breakthroughs in solving the low capacity of sodium-ion batteries. However, these cathodes still facing many challenges, such as sluggish kinetics, irreversible evolution and poor cyclic property, etc. This work adopted a heteroatomic doping strategy with cobalt to develop high-performance Na-rich Na 2 RuO 3 cathode material with facilitation of both anionic and cationic redox processes. • Na-rich layered cathodes were synthesized via typical solid-state reaction method. • Co-doping facilitated both anionic and cationic redox processes in SIBs cathodes. • Co-doped cathodes exhibited high capacity and excellent rate performance. • Structure-activity relationship of cathodes was clarified by various experiments. 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 Na 2 RuO 3 cathode. As a result, cobalt-doped layered cathode can exhibit not only high capacity of 177 mAh g -1 at 0.2 C within 1.5-4.3 V, but also excellent rate performance with initial capacity of 127 mAh g -1 at high rate of 5 C. Moreover, the fabulous capacity retention of 74% is also obtained after 300 cycles, representing prominent electrochemical reversibility as well as enhanced ionic redox of Na 2 RuO 3 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.