ABSTRACT
The synthesis of a sustainable material through carbon nitride (C3N4) chemically grafted on waste-derived carbon including carbonizing coals (PM), melamine-urea-formaldehyde resins (MUF-C-1100), and luffa cylindrical sponges (SG), respectively, and its application as sulfur cathode in lithium-sulfur (Li-S) batteries were demonstrated. The Li-S cell assembled by the sulfur (S) cathode with component from C3N4grafted coal-derived carbon (PM-CN) possesses a specific capacity of 1269.8 mA h g-1at 0.05 C. At 1 C, the initial specific capacity of PM cathode is only 380.0 mA h g-1, comparable to the PM-CN5 cathode of 681.9 mA h g-1, and PM-CN10 cathode of 580.7 mA h g-1, respectively. And, PM-CN 5 cathode presents the capacity retention of 75.9% with a coulomb efficiency (C.E.) of 97.3% after 200 cycles. The MUF-CN cathode gives a specific capacity of 1335.6 mA h g-1at 0.05 C, and the capacity retention of 66.7% with a C. E. of 93.6% after 300 cycles at 0.5 C. The SG-CN cathode had a specific capacity of 953.9 mA h g-1at 0.05 C, and capacity retention of 95.1% with a C. E. of 98.2% after 125 cycles at 1 C. The remarkable improved performances were mainly ascribed to the sustainable materials as S host with micro-meso pore and C3N4structure providing the strong affinity N sites to lithium polysulfides (LiPSs). This work provides an attractive approach for the preparation of sustainable materials by rational design of grafting C3N4to waste-derived carbons with functions as S cathode materials for high-performance Li-S batteries.
ABSTRACT
Chemical fabrication of a nanocomposite structure for electrode materials to regulate the ion diffusion channels and charge transfer resistances and Faradaic active sites is a versatile strategy towards building a high-performance supercapacitor. Here, a new ternary flower-sphere-like nanocomposite MnO2-graphite (MG)/reduced graphene oxide (RGO) was designed using the RGO as a coating for the MG. MnO2-graphite (MnO2-4) was obtained by KMnO4 oxidizing the pretreated graphite in an acidic medium (pH = 4). The GO coating was finally reduced by the NaBH4 to prepare the ternary nanocomposite MG. The microstructures and pore sizes were investigated by x-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption/desorption. The electrochemical properties of MG were systematically investigated by the cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy in Na2SO4 solution. The MG as an electrode material for supercapacitor exhibits a specific capacitance of 478.2 and 454.6 F g-1 at a current density of 1.0 and 10.0 A g-1, respectively. In addition, the capacitance retention was 90% after 8,000 cycles. The ternary nanocomposite enhanced electrochemical performance originates from the specific flower-sphere-like morphology and coating architecture bringing higher specific surface area and lower charge transfer resistance (Rct).
