The Preparation of Carbon Nanotubes/Reduced Graphene Oxide Current Collector by Non-covalent Induction of Ionic Liquid for Sodium Metal Anode

Abstract

Sodium metal batteries have been regarded as promising candidates for next-generation energy storage systems due to their impressive capacity and natural abundance. However, the high reactivity of Na, unstable solid electrolyte interface (SEI) and Na metal dendrite growth with safety hazards inhibit their applications. Various strategies have been proposed to solve the above issues. Designing porous current collectors has been recognized as one of the most promising solutions. Porous carbon/carbon nanotubes/graphene-based materials are widely investigated as host materials for sodium metal anode. However, the sp 2 carbon faces serious issues, such as aggregation or stacking because of their π-π interactions. Herein, we tackle this issue by using ionic liquid as additive during hydrothermal process. The non-covalent interaction between 1-butyl-3-methylimidazolium (Bmim + ) and sp 2 carbon (carbon nanotubes and reduced graphene oxide) helps to inhibit the aggregation of CNTs and the stacking of rGO layers. Also, their interactions induced the CNTs and rGO to form three dimensional (3D) porous carbon (3D-GC) current collector. The ionic liquid 1-butyl-3-methylimidazolium bisulfate ([Bmim][HSO4]) plays great role as a stabilizer and surfactant. The reduced surface tension of the system is also favorable for uniformly interweaving the CNTs and rGO. The prepared 3D-GC exhibit micro-meso-macro porous structure, which provides a large storage space for sodium metal. Meantime, the composite shows a high electrical conductivity, leading to a low deposition overpotential (5.6 mV) of sodium metal. As a result, the 3D-GC@Na anode exhibit an impressive cycling stability for over 1450 cycles (2900 h) at 1 mA•cm −2 with a capacity of 1 mAh•cm −2 . Moreover, when being used in full cells with Na3V2(PO4)2F3 as cathode, they also show well performances.