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.