| China is a big agricultural country with great achievements in agricultural development.However,there are still a lot of agricultural waste are not effectively utilized,which not only cause a huge waste of resources,but also bring serious environmental pollution.At the same time,with the rapid development of China’s economy,the development of new electrochemical energy storage devices is of great significance for the growing demand for electronic products and new energy vehicles.Hybrid supercapacitors have become a research hotspot in recent years because they combine the advantages of high energy density of batteries and high power density of capacitors.Zinc-ion hybrid supercapacitors（ZHSCs）as one of hybrid supercapacitors,the advantages of high performance,low cost,high safety,green and environmentally friendly make it a relatively ideal energy storage devices.Typically,ZHSCs use zinc metal as the negative electrode and carbon material as the positive electrode,where energy storage comes from the redox reaction of the negative electrode and the capacitive behavior of the positive electrode.Biomass carbon materials are considered as candidate materials for positive electrodes of ZHSCs due to their advantages such as abundant resources,low price,and green.Therefore,combining the advantages of agriculture and new energy materials disciplines,agricultural waste is converted into biochar as an electrode material for electrochemical energy storage devices,while solving the problems of ecological environment pollution and energy shortage.In this paper,biomass as carbon source,using carbonization,activation processing to obtain the controlled heteroatom-doped,high specific surface area,porous structure of porous carbon materials.A series of ZHSCs with high energy density,high power density and long cycle life are assembled by using biomass-based electrode material as capacitive material and metal zinc foil as battery material.Relevant research contents and results are as follows:（1）In this Chapter,by utilizing biomass pine needles,as carbon source,we developed a novel all-in-one method to prepare microporous and nitrogen-doped carbon materials with high specific surface area（PNMNC）with high specific surface area.The precursor was obtained by precarbonizing pine needles at low temperature,and was evenly mixed with KOH activator by freeze-drying,so as to improve the activation and self-doping effect in the carbonization process.The effects of the amount of activator on the micro-morphology,specific surface area,elemental composition and electrochemical performance of pine needle derived porous carbon were systematically investigated,and the optimal activation ratio was determined.When the mass ratio of activator to precursor is 2,PNMNC-2 has a specific surface area of up to 2493.4 m2 g-1 and rich pore structure.The ZHSCs assembled with PNMNC-2 as the cathode have a high specific capacitiance of 472.5 F g-1 at the current densities 0.1 A g-1 and excellent rate capability.Even after10000 cycles at the current densities of 5 A g-1,the capacitance is still retained 97.1%.This excellent electrochemical performance indicates that the low-cost and controllable PNMNCs have great potential in the application of novel energy storage devices.（2）Taking wheat straw as a biomass carbon source,due to its inherent characteristics and low nitrogen content compared to pine needles,similar to the synthesis method in work 1,urea and KCl were added to achieve N doping and auxiliary KOH activation during the synthesis process.After pre-carbonization and activation of wheat straw,wheat straw derived carbon N-WSK is obtained,the ZHSCs assembled with N-WSK as the cathode have a specific capacity of 274.1 F g-1 at a current density of 0.1 A g-1.Even at a current density of 20 A g-1,they still have a specific capacity of 104.1 F g-1.At the same time,at the current density of 5 A g-1,the capacity retention rate after 10000 cycles reached 98.3%,showing excellent cycle stability.In addition,the maximum energy density of ZHSCs assembled based on N-WSK is 90.1 Wh kg-1.（3）On the basis of N-WSK,nitrogen doped Mn O2 and carbon based composite material（0.2）Mn O2/N-WSK were synthesized through a simple hydrothermal reaction.It was demonstrated through SEM characterization that Mn O2 was successfully loaded onto the surface of carbon materials and the ZHSC assembled with（0.2）Mn O2/N-WSK as the cathode has better rate performance and long cycle stability compared to Mn O2,with a high capacity of 280 m Ah g-1 at a current density of 0.2 A g-1.Even at a current density of 1 A g-1,it still has a high capacity of 220m Ah g-1,and there is no significant capacity degradation after 1000 cycles.The results indicate that（0.2）Mn O2/N-WSK successfully combines the good conductivity of carbon materials and the high capacity of Mn O2,making it a promising material for application in ZHSCs. |
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