Free-Standing N-Doped Nanoporous Graphene/Polypropylene Separator for Robust Lithium Metal Anodes Compatible with High-Loading and High-Voltage Cathodes

Abstract

This study aims to transform the traditional polypropylene (PP) separator from a passive physical barrier into a “functional interfacial layer” to guide lithium deposition. A free-standing nitrogen-doped nanoporous nanotubular graphene (NG) network-based thin film is used to modify the separator (PP@NG) in a binder-free manner. Its open nanoporous/tubular structure and nitrogen-dopants endow the film with excellent electrolyte wettability and electrical/thermal conductivity. Moreover, the nanoporous channel guides the uniform Li+ flux through the film and subsequent deposition. Accordingly, the PP@NG can reduce the lithium nucleation overpotential from 38.0 to 17.7 mV and increase the tLi+ to 0.62. The symmetric Li|PP@NG|Li achieves a better rate performance and stable cycling for 800 h. The Li|PP@NG|LiNi0.8Co0.1Mn0.1O2 full cell shows a capacity retention of 64.8% after 900 cycles at 1.0 C. Even combined with a high cathode mass loading of 6.1 mAh·cm–2 or near 5.0 V high-voltage cathode, clearly enhanced performance can still be achieved.