Metal doping and vacancy synergistic induced electron/ion engineering to optimize the redox kinetics of sodium storage: A case study Mo1-xWxSe2

Transition metal dichalcogenides have emerged as potential anodes for sodium-ion batteries (SIBs) and dual-ion batteries (DIBs), but their sodium storage properties require further improvement due to their ubiquitous shortcomings including inherently poor electronic conductivity, considerable volume variations and severe structural collapse of electrodes during electrochemical reactions. Here, we report a Se vacancy-tunable Mo1-xWxSe2 embedded N-doped porous carbon superstructure (Mo1-xWxSe2/N-PC, x = 0-1) via a controllable self -assembly approach and subsequent selenization process. Varying the relative metal cation doping concentra-tion can in situ adjust the anion Se vacancy concentration without requiring additional post-treatments. As a result, the most optimized Mo0.5W0.5Se2/N-PC for SIBs presents high capacities of 688 mAh g-1 at 0.1 A g-1 after 300 cycles. Electrochemical kinetic analysis and density functional theory calculations verify that abundant Se vacancies and metallic W doping have significant effects on improving ionic and electron diffusion kinetics. Furthermore, the DIB full cell assembled using Mo0.5W0.5Se2/N-PC anode combined with the expanded graphite cathode exhibit durable cycling stability (104 mAh g-1 at 1.0 A g-1 over 700 cycles) and outstanding rate performance (142 mAh g-1 at 4.0 A g-1). The proposed approach for fabricating tunable vacancy-modulated TMD superstructures provides an effective method for constructing advanced electrode materials for energy storage systems.