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Alumina powders have been widely used in lithium-ion batteries such as separator coating, electrode surface modification and electrolyte fillers. Rod-like alumina with its special aspect ratio is expected to open up a new application direction. In this work, alumina nanorods were prepared by a facile hydrothermal method. The aspect ratio and morphology of alumina nanorods were optimized by adjusting the hydrothermal temperature, hydrothermal synthesis time, volume ratio, directing agent, and sintering temperature. γ-Al2O3 nanorods with a diameter of 200–300 nm and a mean length of 5 μm and α-Al2O3 with a diameter of 100–200 nm and mean length of 5 μm were obtained by calcining the alumina precursor (AACH) at 800 °C and 1200 °C, respectively. The prepared alumina nanorods were added into polymer solid electrolyte, which promoted the dissociation of the lithium salt and stabilized the propylene polycarbonate (PPC) polymer, resulting in an improved potential window (4.5 V) and ionic conductivity (3.7 × 10−4 S/cm) of the PPC-based polymer solid electrolyte (SE). An NCM622/SE/Li solid-state battery showed enhanced electrochemical performance at ambient temperature with an initial discharge capacity of 188.5 mAh/g and a retention capacity of 158.1 mAh/g after 200 cycles at a current density of 0.5 C. These alumina nanorods have potential to be widely used in high-performance solid electrolytes.

Low ionic conductivity at room temperature and poor interfacial compatibility are the main obstacles to restrain the practical application of polymer solid electrolytes. In this work, lanthanum zirconate (LZO) fibers were prepared by electrospinning method and used for the first time as fillers in sandwich polypropylene carbonate (PPC)-based solid electrolyte. Meanwhile, a graphite coating was applied on one surface of the composite solid electrolyte (CSE) membrane. The results show that the LZO fibers significantly increases the room-temperature electrochemical performance of the CSE, and the graphite coating enhances the interfacial compatibility between electrolyte and lithium anode. Furthermore, an ultra-thin PPC-LZO CSE with a total thickness of 22 μm was prepared and used in NCM622/CSE/Li solid-state cell, which shows an initial discharge capacity of 165.6 mAh/g at the current density of 0.5C and a remaining capacity of 113.0 mAh/g after 250 cycles at room temperature. Rise to 1C, the cell shows an initial discharge capacity of 154.2 mAh/g with a remaining capacity of 95.6 mAh/g after 250 cycles. This ultra-thin CSE is expected to be widely applied in high energy-density solid-state battery with excellent room-temperature electrochemical performances.