N-Doped Carbon Knotting Carbon Nanotube Sponge Networks for Lithium-Ion Capacitor Anodes

Carbon-based three-dimensional (3D) freestanding electrode materials typically possess weak mechanical properties such as brittleness, low stress, residual strain, and large energy dissipation during deformation processes. Here, we deposit high N-doped carbon layers derived from melamine-formaldehyde resin in carbon nanotube (CNT) sponge networks, which can not only form the core–shell structure but also knot the network skeletons by binding interconnected CNTs, thus strengthening the 3D structures. The CNT sponges with high N-doped carbon layers have significantly enhanced mechanical properties including high elasticity, compressive stress, and Young’s modulus. Meanwhile, composite sponges as lithium-ion capacitor (LIC) anodes can achieve a high specific capacity of 303 mAh/g, high rate capability, and long cyclic performance. The corresponding LIC cells with amorphous carbon cathodes can deliver a high energy density of 153 Wh/kg at 582 W/kg and 49 Wh/kg even at a high power density of 29.1 kW/kg. We provide a method to enhance 3D network structures, which have applications in freestanding electrode materials for flexible energy storage systems and microelectromechanical systems.