Multifunctional single-ion conductor-integrated PEO-based solid polymer electrolytes endow highly stable and dendrite-free lithium metal batteries

Poly(ethylene oxide) (PEO) based solid polymer electrolytes (SPEs) hold great promise for circumventing the safety issues caused by liquid electrolytes, which are widely used as one of the leading technical strategies for constructing solid-state lithium metal batteries (LMBs). Unfortunately, developing PEO-based SPEs applicable to high-performance LMBs remains challenging due to the uncontrolled formation of lithium dendrites and sluggish ion migration. In this study, we present the fabrication of highly conductive and mechanically robust composite SPEs (CSPEs) for use in dendrite-proof LMBs by adding a new bis(sulphonyl)imide-based single-ion conductor (LiPEBI) as functional polymer fillers into PEO SPEs network. As expected, the as-prepared CSPEs can simultaneously achieve an excellent mechanical strength of 2.1 MPa, a considerable elongation at a break of 1491.0%, and an optimized degree of crystallization of 37.1%. In addition, introducing the LiPEBI additive promotes the homogeneous distribution of Li-ions and accelerates the ionic transport, resulting in an enhanced ionic conductivity of 4.17 × 10−4 S cm−1 and lithium ion transference number (tLi+) of 0.45 at 60 °C for CSPEs. Such comprehensive physical and electrochemical performances are favorable to suppressing lithium dendrite growth and prolonging the lifespan of LMBs. As a result, the Li||Li symmetrical cells assembled by the CSPEs display a remarkably stable cyclic performance with an extremely low voltage polarization of 60.3 mV over 500 h under 50 μA cm−2 at 60 °C. Also, the CSPEs-based Li||LiFePO4 batteries illustrate superior rate performance up to 1 C and deliver long-term cycling stability with a high discharge capacity of 128.8 mAh g−1 after 100 cycles under 0.4 C at 60 °C. We believe the novel CSPEs have great potential for actual application in the construction of high-safety and dendrite-free solid-state LMBs.