Boosting pseudocapacitive sodium storage while restraining the shuttle effect of polysulfides in holey nickel disulfide nanoplatelets by a polypyrrole-coating strategy

The application of transition metal sulfide-based anodes in sodium-ion batteries (SIBs) is held back by the poor rate capability and the knotty shuttle effect of polysulfides. Herein, a facile and scalable polypyrrole coating strategy is proposed to address the aforementioned issues. In-situ polymerization of pyrrole on porous NiS2 nanoplatelets produces a polypyrrole-coated NiS2 composite (NiS2@PPy). The holey structure of NiS2 enhances ion transport while increasing contact area with polypyrrole shells. When used as the anode for SIBs, the conductive polypyrrole coating of NiS2@PPy can significantly accelerate the electrode kinetics by boosting fast interfacial pseudocapacitive charge storage, which accounts for ∼90 % of total capacity even at a low sweep rate of 0.1 mV s−1. Meanwhile, the conformal coating can accommodate the volume expansion of NiS2 during cycling, enhancing the long-term durability of NiS2@PPy. More importantly, the intermediate polysulfides are efficiently adsorbed by the nitrogen atoms on the polypyrrole framework, thereby alleviating the under-voltage failure caused by the shuttle effect. Consequently, the as-prepared NiS2@PPy achieves high capacities of 393 and 373 mAh/g at 2.0 and 5.0 A/g over 1700 cycles. Motivated by the encouraging results in SIBs, we also explored the potentiality of NiS2@PPy for the potassium-ion batteries.