Potassium-ion batteries (PIBs) are promising energy storage systems because of the abundance and low cost of potassium. The formidable challenge is to develop suitable electrode materials and electrolytes for accommodating the relatively large size and high activity of potassium. Herein, Bi-based materials are reported as novel anodes for PIBs. Nanostructural design and proper selection of the electrolyte salt have been used to achieve excellent cycling performance. It is found that the potassiation of Bi undergoes a solid-solution reaction, followed by two typical two-phase reactions, corresponding to Bi ↔ Bi(K) and Bi(K) ↔ K 5 Bi 4 ↔ K 3 Bi, respectively. By choosing potassium bis(fluorosulfonyl)imide (KFSI) to replace potassium hexafluorophosphate (KPF 6 ) in carbonate electrolyte, a more stable solid electrolyte interphase layer is achieved and results in notably enhanced electrochemical performance. More importantly, the KFSI salt is very versatile and can significantly promote the electrochemical performance of other alloy-based anode materials, such as Sn and Sb.