CoS/N-doped carbon core/shell nanocrystals as an anode material for potassium-ion storage

Potassium-ion batteries (KIBs) are attracting tremendous attention due to the abundant potassium resources and their low price and high safety. However, the main problem faced by KIBs is the lack of high-capacity and high-stability materials for the intercalation/deintercalation of large-sized K ions. Graphite, alloying-dealloying materials, transition metal chalcogenides, etc. have been reported as KIBs anodes; however, neither the capacity nor the stability is satisfactory. In this work, CoS/N-doped carbon core/shell nanocrystals (CSNCs) were synthesized as a superior anode for boosting the performance in the aspects of capacity, rate performance, and cycling stability. This CSNCs feature with small-sized CoS of 20–30 nm as the core and N-doped amorphous carbon as the shell. The small-sized particles can buffer the volume change due to the reduction of stress in particle dimensions after the intercalation of alkali ions. The flexible carbon shell can overcome the agglomeration of small particles and meanwhile confine the active CoS particles in case of crack and pulverization after large volume expansion. As a consequence, the CSNCs exhibit a high capacity of 303 mAh g−1 at the current density of 0.2 A g−1 after 150 cycles.