Uniform Metal Sulfide@N‐doped Carbon Nanospheres for Sodium Storage: Universal Synthesis Strategy and Superior Performance.

Nitrogen‐doped carbon‐coated transition‐metal sulfides (TMS@NCs) have been considered as efficient anodes for sodium‐ion batteries. However, the uncontrollable morphology and weak core–shell binding forces significantly limit the sodium storage performance and life. Herein, based on the reversible ring‐opening reaction of the epoxy group of the tertiary amino group‐rich epoxide cationic polyacrylamide (ECP) at the beginning of hydrothermal process (acidic environment) and the irreversible ring‐opening (cross‐linking reactions) at the late hydrothermal period (alkaline environment), 47 nm‐sized ZnS@NCs were prepared via a one‐pot hydrothermal process. During this process, the covalent bonds formed between the ZnS core and elastic carbon shell significantly improved the mechanical and chemical stabilities of ZnS@NC. Benefiting from the nanosize, fast ion/electron transfer, and high stability, ZnS@NC exhibited a high reversible capacity of 421.9 mAh g−1 at a current density of 0.1 A g−1 after 1000 cycles and a superior rate capability of 273.8 mAh g−1 at a current density of 5 A g−1. Moreover, via this universal synthesis strategy, a series of TMS@NCs, such as MoS2@NC, NiS@NC, and CuS@NC were developed with excellent capacity and cyclability. [ABSTRACT FROM AUTHOR]