Mapping Solid Electrolyte Interphase Evolution and Lithium Deposition at Solid-State Interfaces by Operando Nano-focus WAXS

Abstract Composite solid polymer electrolytes (CSPEs) have emerged as promising candidates for next-generation lithium metal batteries. However, the spatial evolution of the solid electrolyte interphase (SEI) at solid-state interfaces remains poorly understood despite its critical role in lithium metal stability. Herein, the anion-trapping layered double hydroxide (LDH) is introduced to poly(ethylene oxide)-based CSPEs to regulate Li+ transport and stabilize the lithium/electrolyte interface. The LDH-enhanced electrolyte achieves exceptional cycling stability over 950 h with a lithium electrode and 90.1% capacity retention after 250 cycles in LiFePO4||Li full cells. Operando nano-focus wide-angle X-ray scattering maps the spatial distributions of both the SEI and lithium dendrites at the lithium/electrolyte interface across micron-scale lateral and vertical dimensions. The regulated Li+ flux promotes homogeneous lithium deposition and the formation of a robust, multifunctional SEI, thereby suppressing lithium dendrite growth and stabilizing the interface. This study provides direct visualization of SEI evolution in CSPEs and clarifies its role in dendrite-free all-solid-state lithium metal batteries.