PEO-Based Polymer Membranes As Lithium Protective Interlayers to Improve the Interfacial Compatibility with Sulfide Solid Electrolytes

Abstract

While the last century was unquestionably dominated by energy generation from fossil fuels, the 21st century seems devoted to the energy transition towards more sustainable sources. Because of their high energy density, efficiency and flexibility, Li-ion batteries (LIBs) are currently dominating the electrochemical energy storage market share. However, driven by the continuous technological progresses resulting in more powerful portable devices as well as the rapid growth of EVs, the rapidly increasing market is demanding for batteries with higher energy densities and longer lifespan. The integration of a high specific capacity and low redox potential material like lithium metal in lithium metal batteries (LMBs) may help to achieve these goals. Nevertheless, its integration in commercial systems requires to address key issues such as users’ safety and environmental risks related to the thermal runaway phenomenon. All-solid-state lithium batteries (ASSLBs) are considered one of the most promising alternatives to state-of-the-art lithium-ion batteries because of their improved safety. Among the several solid electrolytes (SE) proposed, the sulfide-based ones, e.g., Li6PS5Cl (LPSCl), are considered promising candidate materials because of their comparatively high ionic conductivity.[1] Despite these advantages they suffer of some interfacial challenges on both the cathode and the anode side.[2] In this regard, we focused on the SE/lithium interface investigating the use of Li+ ion conductive polymer interlayers with the aim of (i) separate the two interphases suppressing the side reactions and (ii) improve the physical contact between the interphases, to eventually achieve homogeneous lithium stripping-plating improving the compatibility of the sulfide solid electrolyte with lithium metal.Polyethylene oxide (PEO) is a well-known polymer used in electrochemical applications thanks to its ability of conducting lithium ions. Using it as polymer matrix, several PEO-based polymer interlayers were prepared differing in the salt composition. Starting from a PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) membrane (EO:Li = 10:1), a partially substitution (10 and 20 %wt.) of this last were made with lithium bis(fluorosulfonyl)imide (LiFSI) and lithium tricyanomethanide (LiTCM).[3] The polymer interlayers were prepared by a UV-induced (co)polymerization to interlink the polymer matrix with the tetraglyme plasticizer.[4] The as-obtained sticky membranes were physical-chemically characterized and their interfacial behavior electrochemical investigated.