Microscopically Heterogeneous Electrolyte Enables Li+ Enrichment for Stable Lithium Metal Batteries

Abstract

Efficient charge transfer and uniform lithium deposition in lithium metal batteries critically depend on both the solid electrolyte interphase (SEI) composition and the local Li⁺ availability at the anode surface. Herein, we report a microscopically heterogeneous colloid electrolyte containing Li₃P and Li₃Ag nanoparticles (∼30 nm), which modulates the interfacial microenvironment to achieve a Li⁺-sufficient zone and promote the formation of a multiphase inorganic-rich SEI. Finite-element simulations and molecular dynamics confirm localized enrichment of Li⁺, PF₆^–, and fluoroethylene carbonate (FEC) around the lithium metal surface. XPS and cryo-TEM reveal a uniform SEI composed of amorphous LiF/Li₂CO₃, crystalline Li₂O and N, P-rich inorganics, and a Li–Ag alloy interface. The heterogeneous grain boundaries act as space charge accumulation sites, significantly enhancing the Li⁺ transport. Kinetic analysis using temperature-dependent EIS and relaxation time distribution shows a 68.8% reduction in charge-transfer activation energy, indicating accelerated interfacial kinetics. The resulting Li∥NCM811 full cell (3.3 mAh cm^–2, 50 μm Li) achieves 80% capacity retention over 290 cycles. This work demonstrates an interfacial engineering strategy that couples ionic enrichment with grain-boundary-enhanced transport to realize long-life LMBs under practical conditions.