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

Owing to the slight volume expansion after potassiation, hard carbon is regarded as a promising anode material for 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 with a sulfur content of 25.8 wt % is prepared by calcining glucose in molten salt (K₂SO₄@LiCl/KCl). It exhibits high specific capacities of 361.4 mA h g^-1 during the 1st cycle and 317.7 mA h 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 the cyclic voltammetry test and galvanostatic intermittent titration technique. This work is an effective application of the molten salt method for PIBs, furnishing an understanding to K-storage behaviors of hard carbon- with high sulfur content.