Constructing a magnesium fluoride-rich solid electrolyte interface for high-performance lithium metal anodes

Abstract

The solid electrolyte interface (SEI) layer plays a crucial role in the cycling process of lithium (Li) metal batteries, especially in the process of Li stripping and plating at high current densities. However, the naturally formed SEI is too fragile to prevent the uncontrolled growth of lithium dendrites. In this work, we report the growth of a magnesium fluoride (MgF₂)-rich artificial SEI for Li metal anodes. The dense MgF₂-rich SEI layer can homogenize lithium ion (Li⁺) flux to effectively inhibit the growth of lithium dendrites and reduce the overpotential of Li⁺ nucleation, thus effectively regulating the behavior of Li-plating/Li-stripping. Due to the good mechanical properties of the dense MgF₂-rich SEI layer, the Li||Li@MgF₂ symmetric cell exhibits an overpotential of less than 40 mV (at 3 mA cm⁻² and 1 mA h cm⁻² for 800 h). The LiFePO₄||Li@MgF₂ full cell provides a capacity of around 89.2 mA h g⁻¹ with a capacity retention rate of 70.23% even after 1000 cycles at 2C. This synthesis of a stable SEI layer opens up new prospects for the next generation of highly stable Li metal batteries.