In Situ Ions Induced Formation of K_xF-Rich SEI Layers toward Ultrastable Life of Potassium-Ion Batteries

Engineering F-rich solid electrolyte interphase (SEI) layers is regarded as an effective strategy to enable the long-term cycling stability of potassium-ion batteries (KIBs). However, in the conventional KPF₆ carbonate electrolytes, it is challenging to form F-containing SEI layers due to the inability of KPF₆ to decompose into K_xF. Herein, AlCl₃ is employed as a novel additive to change the chemical environment of the KPF₆ carbonate electrolyte. First, due to the large charge-to-radius ratio of Al³⁺, the Al-containing groups in the electrolyte can easily capture F from PF₆ ^- and accelerate the formation of K_xF in SEI layer. In addition, AlCl₃ also reacts with trace H₂O or solvents in the electrolytes to form Al₂O₃, which can further act as a HF scavenger. Upon incorporating AlCl₃ into conventional KPF₆ carbonate electrolyte, the hard carbon (HC) anode exhibits an ultra-long lifespan of 10000 cycles with a high coulombic efficiency of ≈100%. When coupled with perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), the full cell exhibits a high capacity retention of 81% after 360 cycles-significantly outperforming cells using conventional electrolytes. This research paves new avenues for advancing electrolyte engineering towards developing durable batteries tailored for large-scale energy storage applications.