Lithium Nitride-rich Li Protection Layer via Facile Lewis Acid–Base Reaction for Li Metal Batteries

In this study, we present a scalable approach for forming a lithium nitride (Li3N)-rich protection layer on Li metal, enabling practical applications for high-energy-density lithium metal (Li) batteries. This protection layer is developed through a simple Lewis acid–base reaction involving the direct contact of Li metal with xylylenediamine. This method employs a two-step solution coating process. First, the native oxide layer on the Li surface is removed via chemical polishing. Then, the Li3N protection layer is coated onto the polished Li metal (Li3N@Li). This ensures an effective chemical reaction between Li metal and xylylenediamine, leading to a robust protection layer. The Li nucleation and growth behavior of Li3N@Li shows a dendrite-free morphology with dense and compact properties. Electrochemical evaluations in Li||Li symmetric cells demonstrate dendrite-free Li deposition at 0.5 mA cm–2 for a capacity of 2 mA h cm–2. Additionally, pairing the protected Li anode with a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode achieves an areal capacity of 5 mA h cm–2. The resulting Li||NCM full cells exhibit stable cycling stability with 78.5% capacity retention and an average Coulombic efficiency of 99.8% for over 100 cycles. This work provides insights into the practical realization of high-energy-density Li metal batteries, offering a scalable solution for developing protection layers on Li metal anodes.