Lithium dendrite suppression with Li₃N-rich protection layer formation on 3D anode via ultra-low temperature nitriding

We demonstrate an effective strategy to prohibit lithium dendrite formation in lithium metal batteries (LMBs) by forming a Li₃N-rich protection solid electrolyte interphase (SEI) layer on a three-dimensional (3D) austenitic stainless steel (SS) surface, which maintains the structural stability during Li plating/stripping. The porous SS with 20% Cr is treated by ultra-low temperature ion-nitriding (250 ∼ 350 °C) for energy-saving, resulting in a lithiophilic nitride layer with a chromium nitride (CrN) phase on the surface, evidenced by the X-ray photoelectron spectroscopy (XPS) and further confirmed by Density functional theory (DFT) calculation. Upon cycling, it spontaneously reacts with metallic Li to form a strong and highly ionic conductive Li₃N protection layer, which functionally inhibit continuous side reactions with electrolyte and facilitate the Li-ions transport, consequently leading to a flat Li deposition and ultralong cycling. Additionally, the 3D skeleton of SS reduces the areal current density and provides enough space to relieve volume expansion. The electrochemical results showed that the N-350-SS/Li (porous SS nitrided at 350℃ and composited with Li metal) anode in symmetrical cells exhibited extremely low voltage hysteresis of 14 mV and prolonged excellent cycling for over 2500 h in the normal LiPF₆ electrolyte at 1 mA cm⁻². The half cells retained an excellent Coulombic efficiency (CE) of above 98% and the full cells retained 98.0% of its initial capacity without much degradation after 200 cycles at 3C. This enhancement method is simple and low-cost and the SS can be successfully applied in the real high-energy–density LMBs.