Core-shell structure nanofibers-ceramic nanowires based composite electrolytes with high Li transference number for high-performance all-solid-state lithium metal batteries

Abstract

Using all-solid-state electrolytes to replace flammable liquid electrolytes can effectively improve the energy density and safety of lithium metal batteries. However, low room temperature ionic conductivity and small Li transference number of these electrolytes have caused the increase in the growth of lithium dendrites and battery internal resistance. In this work, a novel polyvinylidene fluoride (PVDF)-poly(ethylene oxide) (PEO) composite lithium ions conductor nanofiber membrane with core-shell structure and the low-cost Gd-doped CeO2 (GDC) ceramic nanowires with oxygen vacancies are simultaneously introduced into the polymer electrolyte to obtain composite electrolytes. The core layer PVDF and the shell layer PEO in the composite nanofibers can enhance the mechanical strength and provide a three-dimensional (3D) ordered transmission channel for lithium ions, respectively. Moreover, the GDC nanowires can further provide long-range and orderly transport channels for Li-ions. The optimized composite electrolyte has a high ionic conductivity of 2.3 × 10−4 S cm−1 at 30 °C, a fast Li+ transference number of 0.64 and a high mechanical strength up to 10.8 MPa. In addition, the composite electrolyte shows excellent compatibility with lithium metal anode, LiFePO4 cathode and high-voltage LiNi0.8Mn0.1Co0.1O2 (NMC) cathode. The assembled lithium symmetric battery can be cycled stably under large current densities at different capacities of 0.1, 0.2, and 0.4 mAh cm−2, and the Coulombic efficiency of the Li/NMC battery can always be maintained at around 99.2% during 250 cycles at 0.5 C. This work demonstrates that the novel electrolyte has excellent application prospects in the next generation all-solid-state lithium metal cells.