NiS2/CoS2@NC@C nanocubes derived from prussian blue analogues as an advanced anode with extraordinary long-cycle performance for sodium ion batteries

Abstract

Transition metal sulfides (TMSs) are regarded as one of the ideal anodes for sodium ion batteries (SIBs) owing to their high theoretical capacity and strong electrochemical activity; nonetheless, it still faces challenges such as large volume variation and low conductivity during chemical reactions for applications. Herein, the nanocubes of carbon-encapsulated NiS2/CoS2 embedded porous nitrogen-doped carbon matrixes (NiS2/CoS2@NC@C) are synthesized as a high-performance anode by in-situ carbonizing and subsequently sulphurating the resorcinol-formaldehyde (RF)-coated Ni-Co-based Prussian blue analogues (PBAs). The RF-derived carbon shell acts as a rigid skeleton to effectively relieve the bulk stress during charging and discharging for ensuring the structure integrity, while the porous nitrogen-doped carbon matrix improves the electronic conductivity, presents rich channels for ion/electron transfer and inhibits the agglomeration of active material during chemical reaction. In addition, the lattice distortion at the heterogeneous interface of the NiS2/CoS2 allows the redistribution of electrons, promoting the chemical reaction kinetics. Consequently, the NiS2/CoS2@NC@C nanocubes exhibit excellent electrochemical properties: a high discharge capacity of 489.9 mA h g−1 after 170 cycles at 1.0 A g−1 (920.6/807.9 mA h g−1 for the initial discharge/charge capacity with the initial coulomb efficiency of 87.7%) and a discharge capacity of 349.7 mA h g−1 with the CE close to 100.0% at 5.0 A g−1 even after 2000 cycles. This study proposes a viable approach for the effective construction of advanced anodes with unique micromorphology and chemical composition based on bimetallic PBAs for SIBs.