Thin, Flexible, and High-Performance Solid-State Polymer Electrolyte Membranes for Li–O2 Batteries

A solid-state lithium–oxygen battery (SSLOB) has become more attractive as a next-generation energy storage device, with the expectation of long-term safe and wide applications with superior energy density. However, the development of a thin and flexible solid-state electrolyte having good interfacial and chemical stability toward lithium metal and/or oxygen has been a big challenge. Accordingly, a solid-state composite electrolyte membrane has been prepared by impregnating polyethylene glycol (PEG) and succinonitrile plastic crystals (SNPCs) along with lithium bromide redox mediator into a porous polytetrafluoroethylene (PTFE) substrate for application in a SSLOB. The prepared thin electrolyte membrane (23 μm) displays a high ionic conductivity of 1.03 mS cm–1, a tensile strength of 46.5 MPa, and elongation at a break of 100% with excellent flexibility. It also exhibits a wide electrochemical stability window (∼4.9 V) and low interfacial resistance of 80 Ω cm2. The SSLOB cell assembled with the synthesized XPEG/SNPC@PTFE electrolyte membrane shows excellent electrochemical stability during 277 cycles, maintaining a 1000 mAh g–1 discharge capacity. The low terminal voltage difference between the charge and discharge processes of these polymer electrolyte membranes (∼0.65 V) compared to those of liquid or other polymer electrolytes (∼1.4 V) is also an advantageous characteristic for their application in high-performance SSLOBs.