Core-shell NiS₂@C encased by thin carbon layer as high-rate and durable electrode for aqueous rechargeable battery

Nickel sulfides, as promising candidate for aqueous rechargeable battery, have aroused broad attention on account of abundant natural resources, rich phases, moderate price and high theoretical capacity. Nevertheless, tremendous volume expansion during repeated charging-discharging procedure leads to the poor rate capability and cycling stability of nickel sulfide electrodes. Therefore, in this work, core-shell NiS₂@C encapsulated by thin hydrothermal carbon (HC) layer (NiS₂@C/HC) has been designed and prepared without any surfactants or templates assistance, which avoid tedious process and shorten preparation cycle greatly. When matched with the treated iron powder (TIP) electrode to form NiS₂@C/HC//TIP aqueous rechargeable battery, the NiS₂@C/HC//TIP battery exhibits a high discharge capacity of 205.1 mAh g^-1 at 1 A g^-1, remarkable rate ability (176.4 mAh g^-1 at 5 A g^-1, about 86% capacity conversation) and superiorly durable stability (80.8 % capacity retention after 10,000 cycles at ultra-high current density of 15 A g^-1). The outstanding high-rate capability and cycling stability for aqueous rechargeable battery can be ascribed to the distinct cowpea-like architecture and intrinsic properties of NiS₂@C/HC. Specifically, the interior porous carbon provides a space to tolerate the volume expansion of the NiS₂ nanoparticles and prevent NiS₂ nanoparticles from aggregation, guaranteeing its high-rate capability. Meanwhile, the exterior HC layer is conducive to improve the electric conductivity to facilitate the electrons transfer and promote the mechanical strength of the whole active materials, ensuring its robust cycling stability.