Synergistic Lithiophilic Inner Layer and Nitrogen-Riched Outer Layer in the Gradient Solid Electrolyte Interphase to Achieve Stable Lithium Metal Batteries

Abstract

Lithium metal, heralded as the next-generation anode material for energy storage batteries, faces significant challenges in the application of liquid batteries, including the instability of the solid electrolyte interphase (SEI) layer and the uncontrollable growth of lithium dendrites. In this work, we introduce a dual-strategy involving a lithiophilic Ag nanoparticle layer and a multifunctional electrolyte additive to engineer a durable three-dimensional (3D) porous copper foam anode skeleton (denoted as Ag@CF-me) with gradient SEI. Density functional theory (DFT) calculations reveal that the strong binding energy of Ag facilitates the uniform nucleation and deposition of lithium. The narrow HOMO-LUMO gap in KNO3 promotes its preferential reduction on lithium anodes, enhancing the formation of a stable, highly conductive nitrogen-riched SEI layer which is conductive to rapid Li+ transport. COMSOL simulations confirm that K+ shielding prevents dendrite growth and encourages uniform lithium deposition. Consequently, the sequential structure of lithiophilic, mechanically robust, and fast ion conduction gradient SEI layers can effectually reduce nucleation overpotential, form electrostatic shielding, and regulate uniform lithium deposition. The half-cells with Ag@CF-me achieve a prolong cycle life of 1000 hours at 1 mA cm-2, remarkably low overpotential (~6 mV) and high coulombic efficiency (CE, 99.7% after 600 cycles). The full battery assembled with LiFePO4 (LFP) cathode maintains a capacity retention rate of 90.3% after 600 cycles at 1 C rate. The regulation strategy for constructing gradient SEI layer proposed in this study provides an idea for depositing lithium in a safe location and a facile method for constructing stable lithium metal anode on the 3D skeleton.

Keywords: Gradient solid electrolyte interphase, Cationic shielding effect, DFT calculation, Finite element simulation, 3D lithium anode skeleton