An ultra-thin composite electrolyte with vertical aligned Li ion transport pathways for all-solid-state lithium metal battery

All-solid-state lithium metal batteries employing composite electrolytes can fundamentally settle the safety issues of commercial liquid electrolytes. However, the thick thickness and low ionic conductivity as well as unregulated ion transport of current composite electrolytes pose great obstacles in further promoting their applicability and compatibility with Li metal anode. Herein, an ultra-thin composite electrolyte with vertical aligned Li ion transport pathways is rationally designed via filling polyethylene glycol-perfluoropolyether polymer electrolyte into the nanochannels of an alumina template via vacuum infusion and in-situ polymerization. The strong Lewis acid-base effect that existed between ions and composite electrolytes can construct numerous fast channels for Li+ transport. A restrained vertical direction of ion immigration can facilitate the uniform deposition of Li+ on metallic Li anode. The shortened Li ion conductive distance and superior electrolyte/electrode interfaces contribute to the improved electrochemical performance of the assembled solid-state batteries. An ionic conductivity of 1.21 × 10−4 S cm−1 and a transference number of 0.37 at room temperature are achieved for the designed composite electrolytes, which is superior to those of the conventional composite electrolytes reinforced with Al2O3 or garnet nanoparticles. The corresponding Li symmetrical cell can stably work for over 1200 h without short-circuit and the LiFePO4 || Li full cell exhibits a high initial discharge capacity of 164.8 mAh g−1 with capacity retention of 93.7 % after 100 cycles with a coulombic efficiency close to 100 %. This work offers an effective tactic to develop ultra-thin composite electrolytes for high-performance all-solid-state lithium metal batteries.