Fast-Charging All-Solid-State Lithium Selenium-Tellurium Batteries Enabled by Se-Te Alloy Cathode.

All-solid-state batteries (ASSBs) are considered as a promising pathway toward high energy density and improved safety. However, achieving fast charging capability in energy-dense ASSBs remains a major challenge, primarily due to sluggish ion transport within solids and poor interfacial compatibility between electrodes and solid electrolytes. These limitations result in inadequate rate capability, low reversible capacity, and shortened cycle life. Here, we report a predominantly amorphous selenium (Se)-tellurium (Te) alloy (a-Se0.8Te0.2) cathode that enables fast-charging all-solid-state lithium Se-Te batteries (ASSLSTBs). Unlike conventional crystalline or single-chalcogen cathodes, this amorphous alloy exhibits synergistic redox activity, triggering a synergistic redox reaction with the argyrodite Li5.4PS4.4Cl1.6 electrolyte during mechanical milling. The reaction generates a surface-enriched Li2TeS3/LiCl layer and bulk intermixing Li2Se species, which facilitates Li+ transport and enhances redox kinetics. The resulting ASSLSTBs deliver high specific capacity of 971.2 mAh g-1 at 0.1C, exceptional fast-charging rate of 5C (7.7 mA cm-2), and stable cycling over 2200 cycles at 2.5 mg cm-2 loading. Even at an ultrahigh loading of 9.68 mg cm-2, areal capacity of 3.03 mAh cm-2 is maintained after 200 cycles at 0.5C. This work shows rationally designed amorphous alloy cathodes can overcome kinetic limits of solid-state conversion reactions, offering a promising strategy for fast-charging.