Equilibrium Lithiation Dynamics Induced Strain Partitioning Design Minimizing Volume Change of Bulk Alloy Type Anode for Lithium Ion Battery

ABSTRACT Alloy‐type anodes possess ultrahigh theoretical capacities but suffer from severe volume expansion and mechanical degradation during cycling, impeding their practical application in lithium‐ion batteries (LIBs). Here, this work proposes an equilibrium lithiation dynamics strategy to design an indium (In)‐tin (Sn) alloy‐type foil anode that effectively mitigates bulk strain through intrinsic strain partitioning. The incorporation of In regulates the lithiation pathway of Sn by forming a LiInSn intermediate phase with high Li + diffusivity, which promotes a balanced and homogeneous phase transition. This kinetically optimized lithiation process significantly reduces localized stress accumulation and enables uniform strain distribution throughout the electrode. Benefiting from this synergistic mechanism, the InSn foil exhibits only 27.2% volumetric expansion under practically relevant conditions (2 mAh cm −2 , 100 cycles), setting a benchmark in strain management for alloy anodes. Its interlocking structure forms a stable solid‐solid interface that dissipates stress efficiently, ensuring mechanical robustness and fast Li + transport. The anode delivers high Coulombic efficiency (>99.5%) and excellent cycling stability. Full cells (InSn‐E||LFP, InSn‐E||NCM811) achieve 96.9% capacity retention after 500 cycles and over 1300 Wh L −1 . This work establishes a paradigm of equilibrium‐driven strain partitioning for alloy‐type anodes, offering both mechanistic insight and a practical pathway toward high‐energy‐density LIBs.