High Interfacial-Energy Interphase Promoting Safe Lithium Metal Batteries

Abstract

We report engineering a stable solid electrolyte interphase (SEI) is critical for suppression of lithium dendrites. However, formation of desired SEI by formulating electrolyte composition is very difficult due to complex electrochemical reduction reactions. Here, instead of try-and-error of electrolyte composition, we design a Li-11 wt% Sr alloy anode to form SrF<sub>2</sub>-rich SEI in fluorinated electrolytes. Density functional theory (DFT) calculation and experimental characterization demonstrate that SrF<sub>2</sub>-rich SEI has a large interfacial energy with Li metal and a high mechanical strength, which can effectively suppress the Li dendrite growth by simultaneously promoting the lateral growth of deposited Li metal and the SEI stability. The Li-Sr/Cu cells in 2M LiFSI-DME shows an outstanding Li plating/stripping Coulombic efficiency of 99.42% at 1 mA cm<sup>-2</sup> with a capacity of 1 mAh cm<sup>-2</sup> and 98.95% at 3 mA cm<sup>-2</sup> with a capacity of 2 mAh cm<sup>-2</sup>, respectively. The symmetric Li-Sr/Li-Sr cells also achieve a stable electrochemical performance of 180 cycles at an extremely high current density of 30 mA cm<sup>-2</sup> with a capacity of 1 mAh cm<sup>-2</sup>. When paired with LiFePO<sub>4</sub> (LFP) and LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub> (NCM811) cathodes, Li-Sr/LFP cells in 2M LiFSI-DME electrolytes and Li-Sr/NMC811 cells in 1M LiPF<sub>6</sub> in FEC:FEMC:HFE electrolytes also maintain excellent capacity retention. Designing SEI by regulating Li metal anode composition opens up a new and rational avenue to suppress Li dendrites.