Plasma Design of Alloy‐Based Gradient Solid Electrolyte Interphase on Lithium Metal Anodes for Energy Storage

Design and optimization of the solid electrolyte interphase (SEI) is extremely important for the construction of advanced lithium metal anodes. Herein, we pioneer a novel SnCl₄/trifluorotoluene hybrid plasma technology to construct a Li-Sn alloy-based gradient SEI on lithium metal anodes to synergistically regulate reaction kinetics, structure, and crystal orientation of lithium deposition. Notably, the designed SEI displays a gradient layered structure, with a Li-Sn alloy constituting the bottom layer, LiF occupying the middle layer, and a composite layer of LiCl and organic lithium compounds forming the top layer. The formation mechanism is primarily attributed to the differential acceleration effects exerted by the plasma shell's electric field on different plasma ions. The gradient SEI exhibits multifunctionality, featuring not only high Young's modulus (13.9 GPa) and enhanced interfacial structural stability, but also enabling the Li-Sn alloy component within the SEI to facilitate the preferential growth of the (110) crystal plane with a low migration barrier, thereby achieving the uniform deposition of Li without dendrite growth. Consequently, the modified Li anode exhibits a low overpotential and high coulombic efficiency, and the corresponding pouch cell shows improved cycling stability. This research provides a pioneering interfacial modification strategy for the fabrication of high-performance lithium metal anodes.