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

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 of N -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. References 1. Gao, Z. et al. Promises, Challenges, and Recent Progress of Inorganic Solid-State Electrolytes for All-Solid-State Lithium Batteries. Adv. Mater. 30 , 1705702 (2018). 2. Famprikis, T., Canepa, P., Dawson, J. A., Islam, M. S. & Masquelier, C. Fundamentals of inorganic solid-state electrolytes for batteries. Nat. Mater. 18 , 1278–1291 (2019). 3. Fan, L., Wei, S., Li, S., Li, Q. & Lu, Y. Recent Progress of the Solid-State Electrolytes for High-Energy Metal-Based Batteries. Adv. Energy Mater. 8 , 1702657 (2018). 4. Bachman, J. C. et al. Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction. Chem. Rev. 116 , 140–62 (2016). 5. Hartmann, P. et al. Degradation of NASICON-Type Materials in Contact with Lithium Metal: Formation of Mixed Conducting Interphases (MCI) on Solid Electrolytes. J. Phys. Chem. C 117 , 21064–21074 (2013). 6. Wang, C. et al. Suppression of Lithium Dendrite Formation by Using LAGP-PEO (LiTFSI) Composite Solid Electrolyte and Lithium Metal Anode Modified by PEO (LiTFSI) in All-Solid-State Lithium Batteries. ACS Appl. Mater. Interfaces 9 , 13694–13702 (2017). 7. Bosubabu, D., Sivaraj, J., Sampathkumar, R. & Ramesha, K. LAGP|Li Interface Modification through a Wetted Polypropylene Interlayer for Solid State Li-Ion and Li–S batteries. ACS Appl. Energy Mater. 2 , 4118–4125 (2019). 8. Wang, L., Liu, D., Huang, T., Geng, Z. & Yu, A. Reducing interfacial resistance of a Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte/electrode interface by polymer interlayer protection. RSC Adv. 10 , 10038–10045 (2020).