Dual interface coupled molybdenum diselenide for high-performance sodium ion batteries and capacitors

Sodium ion capacitors (SICs) can combine the merits of electrochemical capacitors and batteries. The present paper reports a dual-interface composite consisting of few-layer MoSe2 vertically anchored on reduced graphene oxide followed by decoration with metallic MoO2 nanoparticles (MoO2@MoSe2/rGO) as anode material for SICs. Enhanced sodium-ion diffusion and electron transfer could be attributable not only to the metallic MoO2 and graphene, but also to the electronic coupling of MoO2 and MoSe2 at interface, which has been verified and corroborated with DFT simulations and EIS analyses. MoO2@MoSe2/rGO electrode delivers a high sodium-ion storage capacity of 394 mAh g−1 at 3.2 A g−1 and no obvious capacity degradation for over 5000 cycles at 5 A g−1. When paired with an activated carbon cathode, a SIC has been successfully fabricated, manifesting a high energy density of 51 W h kg−1 at 7920 W kg−1 as well as long cyclability (>97% of capacity retention at 10 A g−1 over 4500 cycles). The synergistical dual-interface modification strategy proposed here can pave a way to the rational design and fabrication of a broad array of composite electrodes for next-generation Na-ion batteries and capacitors in clean energy technologies.