2D ultrathin carbon nanosheets with rich N/O content constructed by stripping bulk chitin for high-performance sodium ion batteries

Two-dimensional (2D) nanomaterials hold considerable potential in reforming the energy storage performance, and the efficient production of high-performance 2D energy storage materials through facile and sustainable approaches is highly desirable. Herein, for the first time, large-area and ultrathin carbon nanosheets doped with N/O were constructed by stripping bulk chitin via a "top-down" method. On the basis of the specific layered structure composed of nanofibers, chitin samples after removing the protein and CaCO₃ could be efficiently exfoliated into nanosheets (CNs) via the hydrothermal method, which were then carbonized into N/O co-doped porous carbon nanosheets (CCNs). The CCNs with a thickness of about 3.8 nm retained the original nanosheet structure consisting of nanofibers, leading to a 2D structure with hierarchical porosities. When used as anode materials for sodium-ion batteries, the 2D porous nanostructures and abundant N/O doping of CCNs-600 (carbonized at 600 °C) enable a high reversible capacity of 360 mA h g^-1 at 50 mA g^-1, a good rate capability of 102 mA h g^-1 at 10 A g^-1, and an excellent cycling stability of 140 mA h g^-1 after 10 000 cycles at a high density of 5 A g^-1. Full cells consisting of a CCN anode and a Na₃V₂(PO₄)₃/C cathode exhibited favorable rate performance and cycling stability, showing potential application prospects in highly efficient energy storage systems.