Three-Dimensional Carbon Material Prepared By Carbonizing Sponge For Electrochemical Energy Storage

Melamine sponge can be obtained by special foaming process with melamine formaldehyde resin as the raw material,which is widely used in electronic products,automobiles,aerospace,construction,electromechanical,textile and daily cleaning products and other practical fields.Nitrogen-doped porous three-dimensional carbon materials are obtained by carbonizing melamine sponges,which can be used in energy storage and energy conversion.In this study,we explored the application of melamine sponge in lithium metal batteries and supercapacitors through self-growing carbon nanotubes and KOH activation.The main results are described as follows:Although with an extremely high theoretical capacity(3860 mA h g-1),the large volume variation and unstable solid electrolyte interphase,and thus the deterioration of Coulombic efficiency and the formation of dendrites have caused significant problems related to cycle life and safety when the lithium metal is used as an anode.Although considerable effort has been devoted to overcoming these problems,Li metal anodes reported so far typically possess capacities of?5 mA h crm-2 and cyclable at currents of?5 mA cm-2.In this work,a hierarchal carbon scaffold is designed with the self-growth of carbon nanotubes(CNTs)in nickel-decorated melamine sponges via thermal annealing.It is found that the nitrogen-doped carbon obtained from the melamine sponge,coupled with CNTs,provides an overall strong yet internally flexible host which enables an areal capacity of up to 15 mA h cm-2 cyclable at a charging/discharging current of 15 mA cm-2 as Li metal anodes.Characterizations show that the highly-conductive yet uniformly-distributed CNTs effectively suppress the local current density,leading to more uniform Li nucleation in Li plating.The flexible CNTs in the stiff scaffold enhance the tolerance to the stress caused by the intrinsic volume variation in Li plating/striping,resulting in the stable cycling performance at high currents.Three-dimensional carbon materials,named as MF or aMF,were prepared by carbonization,followed by potassium hydrioxide(KOH)activation.After activation,the capacitance of optimized aMF sample is 200 F/g,196 F/g and 188 F/g at the current density of 1 A/g,2 A/g and 5 A/g,respectively.The activation temperature,duration time and the concentration of loaded KOH are main factors affecting the supercapacitance.We should keep balance between keeping the three-dimensional structure of sponge and activation.Under the same other conditions,the supercapacitance of aMF obtained by activation is better than that obtained by direct carbonization,which indicates that activation is benefitial to improving the supercapacitance of carbon materials.