Preparation Of Saccharides Derived Carbon-Electrode-Materials And Their Electrochemical Properties

With the development of the“transmission,supply,use and storage”power system,both capacitive-devices and power devices play important roles in the smart grid for energy-peak regulation and frequency modulation,respectively.As the representatives of capacity-based devices and power-based devices,sodium ion batteries and supercapacitors have received extensive attention.Due to the large radius of sodium ion,the capacity and rate performance of carbon anode electrode were highly restricted.Motivated by the portability and miniaturization requirements,the specific volume capacity of porous carbon electrode has become a key factor for the development of supercapacitors.For different energy storage devices,it is of great significance to select appropriate carbon precursors and matched synthesis pathways for the design of the improved carbon electrode materials.Saccharides have attracted wide attention due to their extensive source,diversity,easy extraction and single component.Saccharides contain a large number of hydroxyl groups,carboxyl groups and other active functional groups for the chemical modification,showing great potential in the field of the preparation of carbon materials.However,the mechanism of saccharides pyrolysis is complex,which is not beneficial for the accurate regulation of the morphology,physical and chemical properties and structure of derived carbon materials.In this paper,appropriate saccharides were used as precursors to prepare porous carbons with different structures and properties after rational post-treatments to meet the requirements of capacity-type devices and power-type devices.The specific research results are as follows:1.Using tetramethoxysiloxene（TMOS）modified wood cellulose pulp as precursor,the cellulose-derived carbon material（O-WPC-850）with selectively introduced C=O bond was prepared after carbonization pyrolysis.On one hand,the doping of oxygen heteroatom improves the distance between graphite interlayer.On the other hand,a large number of defects and oxygen-containing functional groups are formed on the surface of the resulting carbons.The preparation process increased the sodium storage capacity,up to 348.9 m Ah g^-1,displayed good rate performance(32.5%capacity remains at 10 A g^-1)and maintain a continuous conductive network of the material at the same time.The important role of C=O in sodium storage process was further explored by kinetic analysis and ex-situ X-ray Photoelectron Spectroscopy.Wood cellulose pulp and TMOS are low cost and easily prepared,which provide a novel idea for synthesis carbon electrode materials,and improving capacity and rate performance of carbon anode electrode for sodium ion batteries.2.Using polypyrrole（PPy）modified cotton nanocelluloses as precursor,the N-doped carbon nanofibers（1/2N-CNF）with cross-linked network structure was prepared after carbonization process.The cotton nanocellulose exhibits crosslinking network structure provided abundant electron transport paths,and the spaces between fibers provide the channels for ion diffusion.Nitrogen doping improves the conductivity of the material,but also introduces a large number of sodium storage active sites on the surface of carbons.Benefiting from the synergistic effect of the cross-linked network structure and nitrogen heteroatom doping,the1/2N-CNF shows an increased sodium storage capacity of 387.0 m Ah g^-1 and excellent rate performance(40.1%capacity remains at 10 A g^-1).This study solves the problem of low capacity and poor rate performance of the carbon anode electrode of sodium ion batteries,providing an idea for the diversity of precursor selection of carbon materials derived from saccharides.3.A porous carbon material（HDAC-25%）with high specific surface area(1139.9 m² g^-1)and high density(0.88 g cm^-3)were prepared using dense di-saccharide system hydrogels as precursors and KOH as activator through a simple inside-out active carbonization strategy.In this process,the specific surface area,pore structure,and packing density of the resulting carbons were regulated by adjusting the proportion of glucose in the hydrogel system and the amount of activator.The optimal HDAC-25%sample displays good supercapacitor performance with a high gravimetric specific capacitance(302.3 F g^-1)and volumetric specific capacitance(265.7 F cm^-3).The assembled supercapacitor device has a high bulk power density(586.6 W L^-1)and bulk energy density(14.7 Wh L^-1).This work proposes an inside-out uniform activation method to achieve both high specific surface area and high density of carbon materials,which provides a new prospect for the miniaturization development of supercapacitors.