An asymmetric double-layer poly(ethylene oxide)/inorganic composite electrolyte for stable and dendrite-suppressing all-solid-state Li metal battery

Poly (ethylene oxide) (PEO)-based electrolytes are promising in all-solid-state Li metal batteries on account of their distinct merits of cost-effectiveness, good chemical stability against Li metal and facile large-scale membrane fabrication. However, the application of PEO-based electrolytes is mainly hindered by their low ionic conductivity and the risk of short circuit derived from lithium dendrite growth. In this study, we report an asymmetric composite PEO-based solid electrolyte with a bilayer structure, i.e. Li6PS5Cl-PEO-LiTFSI/Li1.3Al0.3Ti1.7(PO4)3-PEO-LiTFSI (LPSCl-PEO/LATP-PEO) composite electrolyte, in which the LATP-PEO layer as the main part of electrolyte faces toward the LiFePO4 cathode and the LPSCl-PEO layer contacts with Li metal. The ionic conductivity of LPSCl-PEO/LATP-PEO based on 2 % of LPSCl nanoparticles and containing 15 % of LATP nanoparticles reaches up to 3.37 × 10−4 S cm−1, comparable to that of other modified PEO-base electrolyte. Benefiting from the excellent ionic transport capacity and interfacial stability, the Li/Li batteries based on the optimal LPSCl-PEO/LATP-PEO stably cycles over 2000 h with no short-circuit at a current density of 0.2 mA cm−2, which is significantly better than pure PEO and unmodified LATP-PEO single-layer electrolyte. Moreover, Li/LiFePO4 all-solid-state battery with the LPSCl-PEO/LATP-PEO electrolyte has a highest capacity of 156.3 mAh g−1 with a capacity decay rate of 0.0375 % per cycle after 400 cycles at 0.5C, and its coulombic efficiency approaching 100 %. This asymmetric double-layer structure electrolyte prepared by a simple and scalable solution casting method provides a feasible solution for the application in stable and dendrite-suppressing all-solid-state Li metal battery.