Electrolyte Interfacial Reactivity Regulates Alloying Anode Pulverization

ABSTRACT Alloying materials are promising anodes for high‐energy alkali‐ion batteries but suffer from rapid capacity fading. Here we demonstrate that tuning electrolyte‐anode interfacial reactivity enables ∼99% capacity retention of high‐loading bismuth anodes over 250 cycles in sodium‐ion batteries, whereas a highly reactive electrolyte results in rapid capacity decay to ∼20% within 10 cycles. Using bulk bismuth as a model system, we show that electrolyte interfacial reactivity critically governs anode pulverization and electrochemical stability by modulating grain refinement and the coupled evolution of particle cracking, electrode architecture, and solid‐electrolyte interphase (SEI) growth. Severe bismuth particle cracking and compositionally similar SEIs are observed in designed electrolytes of differing reactivities. A low‐reactivity electrolyte produces a porous electrode composed of micrometer‐sized bismuth grains coated with a thin SEI. In contrast, a high‐reactivity electrolyte drives pulverization into fine nanoparticles encapsulated by a thick SEI, yielding dense electrodes and fast capacity failure. This mechanism, further validated in Sn anodes for sodium‐ion batteries, is expected to be broadly applicable to large‐volume‐change alloying anodes, offering a general strategy for the development of next‐generation high‐energy alkali‐ion batteries.