A Modular Standard Operating Procedure for Standardizing Lithium Metal Interfaces

Lithium metal is a promising material for high-energy-density batteries, yet its electrochemical behavior is strongly influenced by the poorly controlled initial surface state of commercial lithium foils. Variations arising from manufacturing, storage, and handling introduce interfacial heterogeneity, leading to performance scatter and limited reproducibility across studies. Herein, we establish a modular standard operating procedure (SOP) to systematically regulate lithium metal interfaces prior to testing. The SOP decomposes lithium pretreatment into three functionally distinct steps: chemical etching (E) to remove native surface layers, mechanical brushing (B) to homogenize surface geometry, and solution soaking (S) to induce a controlled artificial solid electrolyte interphase. Using symmetric Li||Li cells, the integrated E-B-S sequence exhibits improved voltage stability and suppressed interfacial resistance growth compared with partial or no treatments. Structural and interfacial analyses using SEM, lithium-sensitive EDX, AFM, and EIS reveal the formation of a three-dimensionally structured yet chemically uniform lithium surface. Density functional theory calculations and depth-resolved XPS further clarify the chemical origins of controlled etching and interphase formation. The standardized lithium interface is validated in Li||LiFePO₄ full cells, demonstrating enhanced capacity retention, reduced polarization, and improved rate capability. This work provides a transferable and reproducible framework for lithium metal interface standardization.