Novel ZrO₂@Polyimde nano-microspheres-coated polyethylene separators for high energy density and high safety Li-ion battery

Due to the low melting point and non-polarity of polyethylene (PE), the commercially available PE microporous separator intrinsically has poor thermostability above 100 °C and inferior wettability, limiting the development of lithium-ion batteries (LIBs). Herein, a novel PE composite separator coated by high-temperature zirconia@polyimide core–shell nano-microspheres (ZrO₂@PI nano-microspheres) was designed, producing (ZrO₂@PI)/PE separator with thermal stability, wettability, and flame retardancy. On account of the ZrO₂ shell nanoencapsulation, the hydrophilicity of PI nano-microspheres has been dramatically improved, which can enhance the electrolyte wettability of the composite separator, and the prepared (ZrO₂@PI)/PE separator displays enhanced thermal dimensional stability, maintaining its original shape with negligible shrinkage at 150 °C. Furthermore, different from the commercial Al₂O₃ ceramic-coated separators, the (ZrO₂@PI)/PE separators possess lower areal density, which is only half as much as the Al₂O₃/PE separators. Besides, the half-cell assembled with this (ZrO₂@PI)/PE separator shows a comparable capacity of 156.9 mAh·g⁻¹ at 5 C to PE separator (118.4 mAh·g⁻¹). Meanwhile, the cells assembled with (ZrO₂@PI)/PE separator demonstrate enhanced cycle performance and thermal safety performance and can work continuously for 109 min at 140 °C, which has enormous improvement compared with the PE-separator-equipped cell (i.e., 21 min). The above results manifest that the (ZrO₂@PI)/PE separator prepared in this work furnishes LIBs with high safety and electrochemical performance, promising new-generation high energy density and high security LIBs.