KF-Containing Interphase Formation Enables Better Potassium Ion Storage Capability

Rechargeable potassium ion batteries have long been regarded as one alternative to conventional lithium ion batteries because of their resource sustainability and cost advantages. However, the compatibility between anodes and electrolytes remains to be resolved, impeding their commercial adoption. In this work, the K-ion storage properties of Bi nanoparticles encapsulated in N-doped carbon nanocomposites have been examined in two typical electrolyte solutions, which show a significant effect on potassium insertion/removal processes. In a KFSI-based electrolyte, the N-C@Bi nanocomposites exhibit a high specific capacity of 255.2 mAh g^-1 at 0.5 A g^-1, which remains at 245.6 mAh g^-1 after 50 cycles, corresponding to a high capacity retention rate of 96.24%. In a KPF₆-based electrolyte, the N-C@Bi nanocomposites show a specific capacity of 209.0 mAh g^-1, which remains at 71.5 mAh g^-1 after 50 cycles, corresponding to an inferior capacity retention rate of only 34.21%. Post-investigations reveal the formation of a KF interphase derived from salt decomposition and an intact rod-like morphology after cycling in K2 electrolytes, which are responsible for better K-ion storage properties.