Gradient-integrated bilayer solid polymer electrolyte enabling enhanced room-temperature cyclability for rechargeable lithium metal batteries

Simultaneous maintenance of interfacial stability of solid polymer electrolytes (SPEs) towards both high-potential cathodes and highly active Li anodes is still a significant challenge in rechargeable lithium metal batteries (LMBs). In this study, a bilayer SPE was prepared via a facile two-step coating strategy, in which an oxidation-resistant poly(vinylidene fluoride) (PVDF) layer incorporating ionic liquid (IL) and LiODFB additive was used for stabilizing the cathode surface, and a reduction-friendly polyethylene oxide (PEO) layer combined with a suitable amount of succinonitrile (SN) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) was fabricated for maintaining the anode compatibility. The resultant bilayer SPE possessed a unique architecture of gradient concentration integration with negligible Li+ migration discontinuity across the additional electrolyte interface, providing favorable overall properties in terms of ionic conductivity, Li+ transference number, mechanical strength and thermal stability. Furthermore, the combination effect of the two polymer layers greatly improved the interface properties of the cathode/anode, enabling the LMBs to operate at room temperature with extended cycle life and good rate capability. A novel bilayer solid polymer electrolyte was developed for room-temperature Li metal batteries, consisting of an oxidation-stable PVDF composite layer and a reduction-friendly PEO composite layer, characterized by gradient concentration integration.