Ultrathin ZrO₂-coated separators based on surface sol-gel process for advanced lithium ion batteries

Coating inorganic ceramic particles on commercial separators with organic binders attracts significant interest as a facile and effective modification method to enhance the thermal-resistance characteristics of the separators. Nevertheless, this method still suffers from some inherent limitations, involving the desquamation of binders soaked in the electrolytes and a significant thickness increase caused by ceramic coatings. Herein, we introduce self-assembled nano-thick ZrO₂ ceramic coatings onto a polypropylene (PP)/polyethene (PE)/PP separator using a dopamine hydrophilic modification and a subsequent surface sol-gel process. In comparison with the pristine separator, the modified separator exhibits excellent mechanical properties, favorable electrolyte wettability, enhanced thermal-resistance characteristics, elevated ionic conductivity and smaller electrochemical impendence. At high temperature (55 °C), the LiNi_0.8Co_0.15Al_0.05O₂ (NCA)//Li coin cell based on S–10ZrO₂ exhibits the highest specific capacity of 203.7 mAh g⁻¹, which is higher than that of the NCA//Li coin cell using the PP/PE/PP separator. In addition, the reserve experiments at various high temperatures reveal that the cells with S–10ZrO₂ are more stable than the others, holding 4.08 V even for 12 h of storage at a high temperature of 120 °C.