High-performance and safe lithium-ion battery with precise ultrathin Al2O3-coated polyethylene separator

[Display omitted] •The thin Al2O3 ALD-PE porous separator possesses good electrolyte wettability, high ionic conductivity and low interface impedance.•The 4.5 V high voltage LiCoO2 cell using PE-75 separator exhibits excellent cycling performance and rate capability.•The pouch cell using PE-75 separator has superior safety. Lithium-ion batteries that utilize polyethylene (PE) separators still require improvement. To improve the electrochemical properties and thermal stability of the PE separators, an-ultrathin Al2O3 layer (∼10 nm) was precisely coated onto the surface of a 7 μm thick PE separator via atomic layer deposition. The resulting ultrathin Al2O3 ALD-PE separators exhibited the excellent thermal dimensional stability and flexibility, and the tensile strength was considerably improved. Moreover, the ultrathin Al2O3 ALD-PE separator demonstrated better electrolyte wettability, higher ionic conductivity, and lower interface impedance. The 4.5 V high-voltage LiCoO2/Li coin-cells with the PE-75 separator exhibited better initial specific discharge capacity (184.3 mAh/g) and capacity retention rate (96 % after 300 cycles at 0.5C) compared to the PE separator (176.8 mAh/g; 87.7 % after 300 cycles at 0.5C). Furthermore, the Li/PE-75/Li symmetric cell had stably cycled for 1000 h without significant dendrites generation. Finally, the pouch-cell using the PE-75 separator was less prone to thermal runaway at high temperatures, indicating its improved safety.