Local electric field effect of montmorillonite in solid polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) with in-built inorganic fillers are very promising for building safe solid-state batteries, owing to their excellent flexibility, prominent interfacial wettability and low costs. However, the morphology and surface state of inorganic fillers greatly affect ionic conductivity of SPEs. Here, we report that ultraviolet (UV) initiates in situ cross-linking of poly(ethylene glycol) methyl ether acrylate (MPEGA), poly(ethylene glycol) diacrylate (PEGDA) and montmorillonite (MMT) between cathodes and anodes of cell, to produce a solid composite electrolyte (CMP/MMT) that is composed of a robust interpenetrating polymer network matrix and layered MMT nanosheets. Surprisingly, the CMP/MMT delivers a high room-temperature ionic conductivity (~1.06 mS cm−1), large lithium-ions transference number (tLi+ = 0.79). The large ionic conductivity enhancement is ascribed to the local electric field effect of montmorillonite (MMT), which accelerates the lithium-ions fast transport in the interlayer of the MMT nanosheets. In addition, the density functional theory (DFT) is conducted to demonstrate the mechanism of improving ionic conductivity. As a result, a solid-state battery with CMP/MMT demonstrates a high capacity of ~140 mAh g−1 and excellent capacity retention of >98% at 0.3 C after 400 cycling.