Ternary Potassium‐Bismuth‐Telluride Intermetallic Support Promotes Electrochemical Stability in Potassium Metal Anodes

We employed accumulative roll bonding to fabricate self-standing metallurgical composite of in situ formed alkaline potassium-bismuth-telluride intermetallic K₂(Bi_2/6Te_3/6Vac_1/6) embedded in potassium metal. This newly discovered thermodynamically stable potassiophilic crystal, termed "KBT", is fcc antifluorite with K₂Te archetype. Symmetric cells achieve 880 h of cycling at 0.5 mA cm^-2 and 0.5 mAh cm^-2. Potassium metal battery (KMB) with Prussian blue (PB) cathode in carbonate electrolyte retains 80% capacity after 200 cycles at 1C. In ether-based electrolyte with organic cathode, it achieves 80% retention after 900 cycles at 2C. Combined synchrotron X-ray nano-tomography, cryogenic-focused ion beam microscopy (Cryo-FIB) and sputter-down X-ray photoelectron spectroscopy (XPS) demonstrate uniform electrodeposits, versus baseline of potassium filaments intermixed with pores and coarse SEI. Binary K₃Bi-K and K₂Te-K intermetallic supports also provide improved electrochemical performance, albeit to lesser extent. Multiscale simulation provides insight into role of support structure in adatom energetics, film nucleation, early-stage SEI morphology and interfacial stability.