Enhancing lithium metal batteries with a nano-silicon nitride-based solid electrolyte interface layer

Lithium metal batteries promise high energy density but suffer from unstable solid-electrolyte interphases that promote dendrite growth and premature failure. Here we report a simple drop-casting pretreatment that deposits a uniform layer of nano-sized silicon nitride (Si₃N₄ <50 nm) onto lithium foil, forming a Li₃N-rich artificial interphase. Two loadings, 0.2 and 1 wt%, were evaluated under rinsed and non-rinsed conditions. Structural and chemical characterization results from SEM and X-ray diffraction show that the non-rinsed 1 wt% coating yields a dense, uniform layer dominated by Li₃N. Electrochemical impedance spectroscopy reveals a stable low charge-transfer resistance, and symmetric-cell cycling at 1 mA cm^-2 demonstrates a lifespan of 1375 hours, compared with 950 hours for the rinsed sample and 280 hours for untreated lithium. The improved performance is attributed to the electrochemically stable, ionically conductive, and mechanically robust Li₃N-based interphase that suppresses dendrite formation and preserves interfacial contact. This work highlights nano-Si₃N₄ as an effective additive for enabling safer and longer-lasting high-energy lithium metal batteries.