KF-Enriched Solid Electrolyte Interface Films Enable ZnSe Nanowires with Enhanced Capacity and Stability for K-Ion Batteries

Solid electrolyte interphase (SEI) films exert a profound impact on the electrochemical performance of metal selenide anodes for potassium-ion batteries (PIBs). However, severe electrolyte decomposition caused by metallic potassium at the discharge state and substantial mechanical stress induced by the large K+ radius limit the stability of the SEI films. In this study, we design Ag-doped ZnSe nanowires using an ion exchange technique, which exhibit a stable interfacial film with superior reaction kinetics. The doped Ag facilitates the decomposition of KPF6 inside the electrolyte, promoting the formation of a KF-enriched SEI layer on the ZnSe surface. A fluoride-rich SEI layer significantly enhances interfacial stability while mitigating the continual loss of electrolyte throughout battery operation. Besides, the incorporation of larger Ag atoms can expand the lattice spacing within ZnSe, thereby augmenting both ionic and electronic conductivity. Therefore, the Ag-doped ZnSe nanowires deliver a high reversible capacity of 435 mAh g–1 at 0.1 A g–1 and 152 mAh g–1 at 5.0 A g–1, and they demonstrate remarkable cycling durability without attenuation even after 800 cycles at 1.0 and 5.0 A g–1.