Ultralong‐Cycling Lithium Storage of SrGe ₂ O ₄ S Anode Enabled by In Situ Formed Oxysulfide Matrix

High-energy lithium-ion batteries (LIBs) demand next-generation alloying-type anodes with high capacity and low voltage. While silicon-based anodes are in industrial use, commercial alloying-type anodes still suffer from excessive volume expansion and inadequate cycle life. Even incorporating silicon-carbon composites within graphite (typically <20% in commercial products) fails to resolve these limitations. Herein, we report a novel SrGe₂O₄S anode for ultralong-cycling lithium storage. An oxysulfide matrix (Li₂O/SrS) was in situ formed around Ge nanodomains. Enabled by the strong covalency of soft S²⁻ anions and the pinning effect of large Sr²⁺ ions, this synergistic matrix has demonstrated capabilities to enhance interfacial compatibility with Ge, facilitate efficient Li⁺ transport, suppress agglomeration of Ge nanoparticles and buffer volume expansion, as evidenced by in/ex situ characterizations, density functional theory calculations, and finite element analysis simulations. The anode harvests a low charging medium voltage of 0.42 V and reversible capacity of 587 mA h g^-1 at 0.1 A g^-1 after 800 cycles (8300 h) with 93.2% capacity retention. The LiCoO₂||SrGe₂O₄S full cell delivers a high capacity of 142 mA h g^-1 and energy density of 482 Wh kg^-1. This work sheds light on constructing functional matrix to relieve volume expansion and particle agglomeration of high-capacity ultralong-cycling alloying-type anodes.