Enhancing bismuth-rich SEI on Li anode under high current density through the use of highly conductive additives

The forming of Li-Bi alloy can build a lithiophilic protective layer on the lithium anode, however, it is found that the lithium dendrites trend to grow on the surface of bismuth-rich solid electrolyte interphase (SEI) and there is an exfoliation of SEI from substrate caused by de-alloying process at a large current density. The failure cause of the bismuth-rich SEI is considered as the inadequate Li-ionic conductivity of the passivation layer, which cannot facilitate the lithium deposition on the substrate. Then the components with high Li-ionic conductivities such as Li3N, LiF and Li2S are introduced into the SEI to adjust the characteristic of the bismuth-rich layer by the addition of LiNO3, Bi2S3 and FEC. All of them enhance the SEI's performances effectively and LiNO3 presents the best. With the addition of LiNO3, the SEI thickness is decreased and Li-ionic conductivity is enhanced while Li3N became one of the major components of the layer. Utilizing the improved bismuth-rich protective layer the Li/Li symmetric cell presents an overpotential at ~10 mV in a long cycle over ~1700 hours at 4 mA cm-2, and the LiFePO4/Li cell with the cathode loading of ~10 mg cm-2 exhibits a capacity retention rate 72.1% in 400 cycles. This work provides a new SEI design strategy for lithium metal anode operating at high current density and an inspiration for improving other functional interfacial layers in lithium batteries.