Rechargeable nonaqueous lithium-O-2 batteries are considered as the most promising energy storage system for electric vehicles due to their extremely high energy density. However, the inefficient O-2 diffusion, large overpotential and unwanted side reaction still restrict their specific capacity and cycle performance. This work presents a facile method to prepare a novel 3D binder-free N-doped carbon nanonet by using an economical, green and sustainable biomass-silkworm cocoon as the precursor. Li-O-2 batteries with this N-doped carbon nanonet as the cathode delivered a superior specific capacity and excellent cycling stability, which attributable to the 3D porous and through structure, high specific surface area, the enhanced catalytic activity of ORR/OER arising from the incorporation of N, and the absence of binders in the electrode. Therefore, by taking advantages of the unique structure and morphology of biomass, the low-cost and green 3D binder-free N-doped carbon materials are a feasible approach for the preparation of high-performance cathode for Li-O-2 battery.