Designing Metal Phosphide Solid-Electrolyte Interphase for Stable Lithium Metal Batteries Through Electrified Interface Optimization and Synergistic Conversion

Regulating the nucleation and growth of Li metal is crucial for achieving stable high-energy-density Li metal batteries (LMBs) without dendritic Li growth, severe volume expansion, and "dead Li" accumulation. Herein, we present a modulation layer composed of porous SnP_0.94/CoP p-n heterojunction particles (SCP), synthesized applying the Kirkendall effect. The unique heterointerfaces in the SCP induce a fully ionized depletion region and built-in electric field. This provides strong Li affinity, additional adsorption sites, and facilitated electron transfer, thereby guiding dendrite-free Li nucleation/growth with a low Li deposition overpotential. Moreover, the strategic design of the SCP, accounting for its reaction with Li, yields electronically conductive Co, lithiophilic Li-Sn alloy, and ionic conductive Li₃P during progressive cycles. The mixed electronic and ionic conductor (MEIC) ensure the long-term stability of the SCP modulation layer. With this layer, the SCP@Li symmetric cell maintains a low overpotential for 750 cycles even at a high current density of 5 mA cm^-2. Additionally, the LiFePO₄//SCP@Li full cell achieves an imperceptible capacity decay of 0.03% per cycle for 800 cycles at 0.5 C. This study provides insight into MEIC heterostructures for high-performance LMBs.