Exploring the effect of lithium halide artificial SEI on the electrochemical performance of lithium metal batteries

•In the solid electrolyte interface, LiF lattice facilitates uniform Li+ transportation.•LiF lattice contributes to the formation of a uniform and dense protective layer.•The protective effect of LiFxClyBrz on Li is enhanced with increasing F component. The urgent need for high-energy–density rechargeable batteries is driving lithium (Li) metal as a promising anode material. However, the conventional solid electrolyte interface (SEI) on lithium metal suffers from elevated interfacial impedance, poor mechanical properties, and non-uniform Li+ flux. Previously, LiF has been proven to be an effective component of the SEI protecting lithium metal. However, this is a rarely reported application of LiCl and LiBr in SEI. Herein, we design SEI containing lithium halide in different ratios (LiF0.8Cl0.1Br0.1, LiF0.33Cl0.33Br0.33, LiCl, LiBr) to investigate the action laws of lithium halide in SEI. It has been shown that the performance of SEI containing lithium halide against lithium anode increases with the LiF content in the SEI. The higher the proportion of LiF in SEI, the better the cycle life and stability of Li-Li symmetric cells, and the higher the initial capacity and the capacity retention of LFP-Li full cells. The symmetric cell with LiF0.8Cl0.1Br0.1@Li has the smallest average polarization voltage (about ± 30 mV) and long cycle life of up to 1000 h. LiFePO4||LiF0.8Cl0.1Br0.1@Li cells have the highest initial capacity (127.4 mAh/g), and still had 83.6 % capacity retention after 1000 cycles at 2C.