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

Carbon-basedthree-dimensional (3D) freestanding electrode materialstypically possess weak mechanical properties such as brittleness,low stress, residual strain, and large energy dissipation during deformationprocesses. Here, we deposit high N-doped carbon layers derived frommelamine-formaldehyde resin in carbon nanotube (CNT) sponge networks,which can not only form the core-shell structure but also knotthe network skeletons by binding interconnected CNTs, thus strengtheningthe 3D structures. The CNT sponges with high N-doped carbon layershave significantly enhanced mechanical properties including high elasticity,compressive stress, and Young's modulus. Meanwhile, compositesponges as lithium-ion capacitor (LIC) anodes can achieve a high specificcapacity of 303 mAh/g, high rate capability, and long cyclic performance.The corresponding LIC cells with amorphous carbon cathodes can delivera high energy density of 153 Wh/kg at 582 W/kg and 49 Wh/kg even ata high power density of 29.1 kW/kg. We provide a method to enhance3D network structures, which have applications in freestanding electrodematerials for flexible energy storage systems and microelectromechanicalsystems.