Figure 9 (a) Schematic representation for improving the contact between garnet and Li metal by engineering the surface of the garnet with a thin Ge layer. The Ge layer, evaporated onto garnet, can alloy with Li metal, which leads to more continuous interfaces between the garnet and Li metal and results in a small interfacial resistance. (b) Schematic of the full cell structure, where a gel membrane was used between garnet and LFP cathode. (c) Cycling performance of the Li/Ge-modified-garnet/LFP cell and Li/liquid-electrolyte/LFP cell at 1 C. (d) Coulombic efficiencies of Li/Ge-modified-garnet/LFP cell and Li/liquid-electrolyte/LFP cell at 1 C. (Reproduced from ref.[126], with permission from Copyright © 2017 Wiley-VCH.)
Since then, the Li-Zn, Li-Sn and Li-Mg alloy modified garnet solid electrolytes have subsequently developed[123-125]. Such a facile surface treatment on garnet electrolyte with forming lithium alloys method offered a simple strategy to solve the interface problem in solid-state lithium metal batteries.

3.5 | Lithium Alloys modified separators

A multifunctional separator through coating a thin electronic conductive film on one side of the conventional polymer separator facing the Li anode could contribute to Li dendrite suppression and cycling stability improvement[127]. Recently, Li and his co-workers developed a multifunctional lithium alloys coating separator by reducing the PbZr0.52Ti0.48O3 (PZT) coating layer on polypropylene (PP) separator[128]. The produced Li-Pb alloy armor between the separator and Li anode, not only uniformed the electric field across the interface but also mitigated the Li metal nucleation, and therefore suppressed the dendrite growth during plating. As a result, the Li/Li symmetric cells and LiFePO4/Li cells with this such PZT-pretreated PP separators exhibit significantly improved Coulombic efficiency and cycling life as shown in Figure 10a and 10b.