Mesoporous Nickel Sulfide Microsphere Encapsulated in Nitrogen, Sulfur Dual-Doped Carbon with Large Subsurface Region for Enhanced Sodium Storage.

Nickel sulfides are promising anode candidates in sodium ion batteries (SIBs) due to high capacity and abundant reserves. However, their applications are restricted by poor cycling stability and slow reaction kinetics. Thus, mesoporous nickel sulfide microsphere encapsulated in nitrogen, sulfur dual-doped carbon (MNS@NSC) is prepared. The packaged structure and carbon matrix restrain the volume variation together, the N, S dual-doping improves the electronic conductivity and offers extra active sites for sodium storage. Ex-situ X-ray diffraction  appeals copper collector adsorbs polysulfide to inhibit the polysulfide accumulation and enhance conductivity. Moreover, the large subsurface attributed to C-S-S-C bonding further boosts pseudocapacitive capacity, conducive to charge transfer. As a result, MNS@NSC delivers a high reversible capacity of 640.2 mAh g after 100 cycles at 0.1 A g, an excellent rate capability (569.8 mAh g at 5 A g), and a remained capacity of 513.8 mAh g after undergoing 10000 circulations at 10 A g. The MNS@NSC|| NaV(PO) full cell shows a cycling performance of specific capacity of 230.8 mAh g after 100 cycles at 1 A g. This work puts forward a valid strategy of combing structural design and heteroatom doping to synthesize high-performance nickel sulfide materials in SIBs.