Lithium-assisted surface transformation for high-efficiency silicon anodes

Abstract

Silicon is a leading high-capacity anode for lithium-ion batteries, yet severe initial lithium loss and unstable interfaces undermine first-cycle Coulombic efficiency and long-term durability. Conventional prelithiation mitigates these issues but faces constraints in reactivity, safety, and scalability. This study demonstrates a lithium-assisted surface transformation using lithium acetate dihydrate that, upon controlled lithium acetate thermolytic reduction (LATR) process, generates conformal LixSiy (Zintl-type silicide)/ LixSiyOz hybrid shells on nano-Si. Structural analyses reveal a LixSiy-rich crystalline inner shell capped by an ultrathin, discontinuous LixSiyOz overlayer, forming a robust core-shell heterostructure that suppresses formation-stage Li consumption. Leveraging Zintl Si-based phases where electropositive Li donates electrons to the Si sublattice to form covalently bonded polyanionic motifs provides localized Li reservoirs and Li-permissive interphases that stabilize cycling. As a result, early Li loss is mitigated, first-cycle efficiency increases, and long-term stability improves. Electrochemical testing delivers a first-cycle Coulombic efficiency of 81% and 85% capacity retention after 100 cycles at 0.2C. First-principles calculations indicate highly exergonic Li adsorption on Si(111) (−1.38 eV per Li) and the thermodynamic preference for Li-lean Zintl phase alloys under Li-deficient, carbon-present conditions, rationalizing the predominant formation of Li7Si3 with minor Li2SiO3. This simple, low-cost, and scalable surface-engineering strategy harnesses Zintl-type interphases to advance practical, high-efficiency, durable silicon anodes for next-generation lithium-ion batteries.