High Sulfur-Doped Hard Carbon with Advanced Potassium Storage Capacity via a Molten Salt Method.

Owning to the slight volume expansion after potassiation, hard carbon is regarded as a promising anode material of potassium-ion batteries (PIBs). Heteroatom doping (such as sulfur or nitrogen) is a common method to modify hard carbon for high K-storage capacity and long cycling performance. High sulfur-doped hard carbon (HS-HC) with a sulfur content of 25.8 wt% is prepared by calcining glucose among molten salt (K2SO4@LiCl/KCl). It exhibits high specific capacities of 361.4 mAh g-1 during the 1st cycle and 317.7 mAh g-1 during the 100th cycle at 0.05 A g-1. The high capacity arises from the K-S reaction behavior, which is demonstrated by cyclic voltammetry test and galvanostatic intermittent titration technique. This work is an effective application of molten salt method for PIBs, furnishing an understanding to K-storage behaviors of hard carbon with high sulfur content.