Ultrasonic Spray Coating of Graphene Oxide for Lithium Metal Battery Separators

The uncontrolled lithium dendrite growth significantly impacts the safety and performance of the polymer separators. This study presents a conformal graphene oxide (GO) coating on polyolefin separators, applied via ultrasonic spray coating to mitigate uncontrolled dendrite growth. The effects of the GO coating layer thickness and single-sided or double-sided coating of the separator on electrochemical performance were investigated. A double-sided GO coating with a total surface density of 30 μg cm^-2 (15 μg cm^-2 per side) yielded the highest electrochemical efficiency. The Li deposition test of the double-sided GO coating on the polyolefin separator can operate for 1600 h without short-circuiting. Additionally, the LiFePO₄∥Li cells with the double-sided GO coating on a polyolefin separator show improved initial discharge capacity (165 mAh g^-1 at 1 C) and superior rate performance (125 mAh g^-1 at 5 C). Moreover, the ultrasonic spray GO coating endows the separator with robust adhesive properties of GO/polyolefin, where GO does not delaminate in operational conditions. When the cathode mass loading was increased from approximately 1 mg cm^-2 to 5 mg cm^-2, similar performance trends were observed, though with an approximate 20% reduction in specific capacity.