There is a growing interest in all-solid-state lithium batteries(ASLBs) for their safety and high energy density. However, the power density for ASLBs is still far away from satisfactory on the account of high interfacial resistance at electrode / solid electrolyte interface.

For example, Garnet-type solid-state electrolytes (SSEs) are considered as a good choice for solid-state batteries, yet the interfacial issues with metallic Li limit their applications. In my group, we propose an ultra-simple and effective strategy to enhance the interfacial connection between garnet SSEs and Li metal just by drawing a graphite-based soft interface with a pencil[1]. Both experimental analysis and theoretical calculations confirm that the reaction between graphite-based interfacial layer and metallic lithium forms a lithiated connection interface with good lithium-ionic and electronic conductivity. Compared to the reported interfacial materials, the graphite material provides a soft interface with better ductility and compressibility. With the improvement by this soft interface, the impedance of symmetric Li cells significantly decreases from 1350 to 105Ωcm² and the cell can cycle for over 1000hoursat a current density of 300 μA/cm² at room temperature. Moreover, a solid-state battery with Li-metal anode, ternary cathode NCM523 and graphite-based interface modified garnet SSEs is fabricated and displays excellent rate capability and long cycling performance.

In addition, LGPS-type materials show extremely high Li⁺ conductivity. But when in contact to Li metal, they can be reduced to produce Li₂S, Li₃P and Li-M alloy and form a mixed ionic and electronic conducting layer at the interface, which hinders the application of Li metal in such solid electrolyte system. We report on a simple approach for the modification of the interface between Li and Li₁₀SnP₂S₁₂ sulfide solid electrolyte by utilizing ionic liquid[2]. Our study shows that the addition of 1.5M LiTFSI/Pyr₁₃TFSI ionic liquid can not only promote intimate contact but can in-situ form a stable SEI layer at the interface between Li and solid electrolyte as well. A stable SEI layer instead of mixed conducting layer can prevent sulfide solid electrolyte from further decomposition and improve the cycle performance of batteries.

References:

1) Y.J. Shao, H.C.Wang, et al ; ACS Energy Lett.; 2018, 3, 1212-1218

2) B.Z. Zheng; J.P.Zhu, et al; ACS Applied Mater. & Interfaces; 2018, 10, 25473-25482