Conversion/alloying anode materials exhibiting high K storage capacities suffer from large volume variations and unstable electrode/electrolyte interfaces upon cycling. Herein, taking SnS/reduced graphene oxide (SnS/rGO) anodes as an example, the electrochemical performance of SnS/rGO could significantly be improved via employing potassium bis(fluorosulfonyl)imide (KFSI) salt in electrolytes and ultrathin TiO2 coating. KF-rich inorganic layer was demonstrated to help form robust SEI layer, which could suppress the side reactions to increase the Coulombic efficiency. The formed potassiated KxTiO2 coating layer was constructed to boost charge transfer capability and K-ion diffusion kinetics. The as-prepared SnS/rGO@TiO2-20 electrode in KFSI electrolyte delivers the high CE of 99.1% and 424 mAh·g−1 after 200 cycles with an ultrahigh capacity retention of 98.5%. [Figure not available: see fulltext.].