Novel micronano thin film based on Li-B-P-O target incorporating nitrogen as electrolyte: How does local structure influence chemical and electrochemical performances?

A novel electrolyte thin film has been prepared by radio-frequency magnetron sputtering using a Li-B-P-O target in a pure N₂ atmosphere at various temperatures. The results indicate that the thin film deposited at room temperature is amorphous and its surface is smooth, dense, and uniform with the average thickness <1 μm, whereas that deposited at 400 C shows the mixture of crystal and amorphous structure, which is more beneficial to the improvement on lithium ion motility in the network. The thin films exhibit an ionic conductivity of 3.5 × 10^-6 S cm^-1 and a electrochemical stability window of 7.8 V as well as outstanding chemical durability. Structural analyses suggest that their excellent chemical and electrochemical performances can be attributed to the combination of "mixed former" and "nitrogen incorporation" effects. The former produces nonbridging oxygen groups that provide vacant sites for lithium ions to move in or out of as well as expand the lithium ion conduction pathway. The latter leads to a more complicated cross-linked structure containing -N< and -N bonds instead of -O- and O, which brings about more lithium ion transport channels in the network.