Porous flexible nitrogen-rich carbon membranes derived from chitosan as free-standing anodes for potassium-ion and sodium-ion batteries

Abstract

Large-size flexible biomass carbon membranes have been prepared by using inexhaustible chitosan (CS) as carbon source. The microstructure of carbon membranes depends on the pyrolysis temperature, and the resulting membrane has a porous honeycomb-like architecture with N-doping content of 6.3% after the pyrolysis at 1000 °C. The flexible carbon membranes can be directly used as self-standing electrodes for various batteries, that is, with no current collectors, organic binders, or additional conductive agents. The carbon membranes as anodes for potassium-ion batteries exhibit excellent rate performance and a stable reversible capacity of 146 mAh g−1 at 2 A g−1 after 500 cycles, and its sodium-ion storage remains 236 mAh g−1 after 70 cycles. The kinetic analysis of carbon membranes in batteries shows that the surface-controlled mechanism plays a decisive role in the potassium/sodium storage because the honeycomb structure and high proportion of pyridine N-doping can improve the adsorption of K+/Na+ ions and the conductivity. In addition, the main reasons for the capacity degradation of the carbon membrane under long cycle and different current densities are discussed. The CS-derived flexible carbon membranes show a promising application as cost-effective, binder-free electrodes in flexible batteries.