LAGP|Li Interface Modification through a Wetted Polypropylene Interlayer for Solid State Li-Ion and Li–S batteries

The development of solid state batteries is constrained by imperative factors like the high reactivity of lithium with solid electrolytes, high grain boundary resistance of the solid electrolyte, and interfacial resistance between the solid electrolyte and electrodes. In the present work we exploited Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) as a solid electrolyte and noticed a spontaneous reactivity of lithium with LAGP. Further, we observed that  introduction of a wetted polypropylene (PP) layer between LAGP and lithium successfully prevented the undesirable reaction between lithium and the surface of the solid electrolyte. Aside from that, it also considerably decreased the interfacial resistance and polarization. This strategy has been applied to both Li-ion and Li–S battery systems, and we observed considerable improvement in the electrochemical performance of these solid state devices. The lithium ion battery retained 100% capacity and Coulombic efficiency after 50 cycles with an observed capacity of 190 mAhg^–1. After 200 cycles with varying C-rates, 98.5% capacity retention is observed. Similarly, in the Li–S battery, LAGP effectively restricted the polysulfide shuttle and maintained 78% of the initial capacity after 200 cycles. Such high capacity retention is the outcome of the PP layer which functions as an interlayer that protects the LAGP surface against reacting with the lithium metal anode as inferred by post-mortem analysis.