Sandwich-type composited solid polymer electrolytes to strengthen the interfacial ionic transportation and bulk conductivity for all-solid-state lithium batteries from room temperature to 120 °C

The insurmountable charge transfer impedance at the Li metal/ solid polymer electrolytes (SPEs) interface at room temperature as well as the ascending risk of short circuits at the operating temperature higher than the melting point, dominantly limits their applications in solid-state batteries (SSBs). Although the inorganic filler such as CeO₂ nanoparticle content of composite solid polymer electrolytes (CSPEs) can significantly reduce the enormous charge transfer impedance at the Li metal/SPEs interface, we found that the required content of CeO₂ nanoparticles in SPEs varies for achieving a decent interfacial charge transfer impedance and the bulk ionic conductivity in CSPEs. In this regard, a sandwich-type composited solid polymer electrolyte with a 10% CeO₂ CSPEs interlayer sandwiched between two 50% CeO₂ CSPEs thin layers (sandwiched CSPEs) is constructed to simultaneously achieve low charge transfer impedance and superior ionic conductivity at 30 °C. The sandwiched CSPEs allow for stable cycling of Li plating and stripping for 1000 h with 129 mV polarized voltage at 0.1 mA cm⁻² and 30 °C. In addition, the LiFePO₄/Sandwiched CSPEs /Li cell also exhibits exceptional cycle performance at 30 °C and even elevated 120 °C without short circuits. Constructing multi-layered CSPEs with optimized contents of the inorganic fillers can be an efficient method for developing all solid-state PEO-based batteries with high performance at a wide range of temperatures.