Enabling Superior Lithium Metal Anodes via the In-Situ Construction of a Li–Sn Alloy/Lithium Halide Biphasic Interface Layer

Metallic lithium has been regarded as a perfect anode material for next-generation battery systems with high energy density owing to its ultrahigh theoretical specific capacity and low reduction potential. However, its practical applications face the challenges of inevitable side reactions with liquid electrolytes and uncontrollable lithium dendrite growth. Herein, a facile solution pretreatment followed by a heating method was developed to in situ construct robust biphasic interface layers on the lithium metal anodes (LMAs). The biphasic interface layers consist of lithiophilic Li5Sn2 alloy and LiF phases, which effectively improve Li+ transportation and uniform Li deposition, thus inhibiting the growth of lithium dendrites, as confirmed by DFT theoretical calculations and in situ optical microscopy observations. Consequently, the symmetric cells based on this biphasic interface layer-modified LMA can stably cycle for more than 1800 h with a low voltage hysteresis of 108 mV at 5 mA cm–2. Besides, the Li5Sn2/LiF-Li||LFP full cells exhibit a superior rate capability up to 10 C and outstanding cycling stability for over 800 cycles at both 2 and 5 C. Moreover, the biphasic interface layer can also play a role in the ester electrolyte; the Li5Sn2/LiF-Li||NCM811 full cells with a high cathode loading of 9.2 mg cm–2 deliver a high specific capacity of 120 mAh g–1 after 100 cycles at 0.5 C. Therefore, this work provides a simple and effective approach to achieve highly stable and safe lithium metal batteries.