LiF-Sn Composite Modification Layer Modified Garnet/Lithium Metal Interface

Wu Yang, College of Energy, Xiamen University, Xiamen 361005, Fujian, China
Xue-Fan Zheng, College of Energy, Xiamen University, Xiamen 361005, Fujian, China
Yu-Qi Wu, College of Energy, Xiamen University, Xiamen 361005, Fujian, China
Shi-Jun Tang, College of Energy, Xiamen University, Xiamen 361005, Fujian, China
Zheng-Liang Gong, College of Energy, Xiamen University, Xiamen 361005, Fujian, China

Abstract

The growing demand for electric vehicles and consumer electronics, as well as the expanding renewable energy storage market, have promoted extensive research on energy storage technologies with low cost, high energy density and safety. Lithium metal and solid-state electrolytes are considered important components for next-generation batteries because of their great potential for improvement in energy density and safety performance. Inorganic garnet-type solid electrolytes with high Li-ion conductivity (about 10-3 S·cm-1) and high shear modulus (55 GPa) are considered ideal solid-state electrolytes, however, the issue of Li dendrite growth still obstructs their practical application. Herein, a simple and efficient strategy is developed to suppress the Li dendrite formation in the garnet solid electrolytes. A composite modification layer composed of 2 nm LiF and 2 nm Sn thin layers is evaporated on the surface of the Li6.5La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte by the high vacuum evaporation. The composite modification layer gives full play to the advantages of LiF and Sn, which effectively improves the interfacial contact between the Li metal and LLZTO electrolyte and promotes uniform Li plating/stripping. LiF-Sn composite modification layer is deposited on the surface of garnet electrolyte to increase the interfacial wettability between the garnet electrolyte and lithium metal and block the injection of electrons into the bulk phase of garnet. The LiF-Sn modification layer effectively enhances the interfacial contact and inhibits the growth of lithium dendrites. Benefiting from the LiF-Sn interfacial modification, cross-sectional SEM image shows intimate contact between the LLZTO-LiF-Sn and the Li metal without any voids and the interfacial impedance of Li/garnet electrolyte interface decreases from 969 Ω·cm2 to 3.5 Ω·cm2. Meanwhile, the critical current density of the lithium symmetric cell increases to 1.3 mA·cm-2, and the lithium symmetric cell can cycle stably for 200 h at a current density of 0.4 mA·cm-2. After disassembling the short-circuited Li/LLZTO/Li cell and reacting the Li metal with alcohol solution, it was found that Li dendrites have grown into the LLZTO pellet.&However, the surface of the LiF-Sn-protected LLZTO remains smooth without dark spots from dendrites.&The excellent electrochemical performance clearly shows that the LiF-Sn composite modification can effectively inhibit the formation of lithium dendrite inside the garnet SSE, proving this interfacial engineering provides a practical solution for addressing the key challenge of Li/LLZTO interface. At the same time, high vacuum evaporation is a mature industrial technology with large-scale application prospects and this method can be widely used to solve solid-state interface problems.