MoSe₂ nanosheets embedded in nitrogen/phosphorus co-doped carbon/graphene composite anodes for ultrafast sodium storage

Sodium-ion batteries have been considered a cost-effective alternative to lithium-ion batteries because of the cheap and abundant sodium reserves. However, the sluggish kinetics arising from the slow ion and electron transport, particularly at high rates, is the main bottleneck of fast sodium storage. Here, few-layer MoSe₂ encapsulated by nitrogen/phosphorus (N/P) co-doped carbon and reduced graphene oxide (MoSe₂@NPC/rGO) composites are fabricated through a simple polymerization reaction followed by selenization. The two-dimensional composite nanosheets effectively shorten the ion diffusion length while the few-layer MoSe₂ exposes a large surface area to the electrolyte. The NPC/rGO sheets intercalated within the composites function as channels for fast electron transfer and surface reactions. First-principles calculations show quick Na transport rates on the surface of MoSe_2, and quantitative kinetics analysis reveals a pseudocapacitance-dominated Na⁺ storage mechanism at high rates. Thanks to the ameliorating functional features and highly reversible conversion reactions, the MoSe₂@NPC/rGO electrode delivers a reversible capacity of ~340 mA h g⁻¹ after 500 cycles at 0.5 A g⁻¹ with a high contribution by surface capacitance. It also possesses a high reversible capacity of ~100 mA h g⁻¹ even at an extremely high current density of 50 A g⁻¹, presenting potential application as anodes for high-power sodium-ion batteries.