PEO-based Interlayers for LAGP-type Solid-State Lithium-Metal Batteries

Abstract

Solid-state electrolytes (SSEs) are expected to play a decisive role for the realization of safer rechargeable batteries and may, additionally, allow for the employment of lithium-metal anodes, thus, paving the way for significantly higher energy densities. 1, 2 There are essentially two main groups of SSEs: (i) polymer and (ii) inorganic solids. The latter can be divided, e.g., into sulfide and oxide based electrolytes. 3 Among the oxides, the so-called NASICON-type electrolytes such as LAGP (lithium aluminum germanium phosphate) are considered as attractive low-cost alternative compared to sulfides. 4 Nonetheless, the incompatibility of LAGP with lithium metal accompanied by the formation of highly resistive interfacial reaction products, detrimentally affecting cycle life and rate capability, remain a great challenge. 5 To overcome this issue, the introduction of polyether (e.g., polyethylene oxide, PEO) as protective interlayer between the lithium-metal anode and the LAGP SSE was proposed. 6, 7, 8 The successful use of such interlayers, however, requires a fast and efficient charge transfer across this interlayer. Herein, we present a comprehensive investigation of PEO-based interlayers comprising varying amounts of ionic liquid-based electrolytes, which consist ofN-butyl-N-methyl pyrrolidinium-based and lithium cations as well as bis(fluorosulfonyl)imide (FSI-) and bis(trifluoromethanesulfonyl)imide (TFSI-) anions. Optimized compositions and the incorporation of selected additives further enhances the charge transfer across this interlayer and the two interfaces with the LAGP electrolyte and lithium metal, enabling long-term stable cycle life and good rate capability of the resulting lithium-metal battery cells.