Preparation Of Lignin Derived Hard Carbon Composite Electrodes And Its Sodium Storage Performance

As a new type of energy storage device,Sodium Ion Capacitors（SICs）combine the high energy density of Sodium Ion Batteries and the high-power density of Supercapacitors,and SICs are expected to be widely used in the field of energy storage.The development of high-performance anode materials is the key and difficult point to improve the electrochemical performance of SICs.Biomass is good precursors for anode materials.Lignin is the second largest biomass resource in nature and it has abundant aromatic carbon rings and intrinsic three-dimensional network structure.Lignin is widely used in energy storage devices because of its abundant reserves and high carbon content.In this study,lignin from black liquor is used as the original material.And the electrochemical sodium ion storage performance of lignin-derived hard carbon materials is studied.Here,we develop sodium ion capacitors based on lignin derived hard carbon.The project is of great significance for promoting the research and development of lignin-based functional materials and improving the technical level of forestry industry.（1）Hard carbon materials are prepared from papermaking black liquor by lignin purification,pre-carbonization and high temperature pyrolysis.The variation of graphite interlayer spacing and microcrystalline structure of hard carbon materials with pyrolysis temperature and their effects on sodium storage performance of hard carbon electrode are analyzed.The results show that with the increase of pyrolysis temperature from 800°C to 1600°C,the graphite layer spacing of hard carbon materials decreases from 0.406 nm to 0.378 nm.And the proportion of pseudo-graphite area increases from 52.69%to 77.60%.Therefore,more Na⁺is intercalated and deintercalated between the graphite layers during the charge and discharge process of the hard carbon electrode.The plateau capacity of the electrode is increased from56.8 m Ah·g^-1 to 236.0 m Ah·g^-1 so that reversible capacity up to 333.7m Ah·g^-1.The SIC assembled with HC-1600 hard carbon electrode as anode and commercial activated carbon electrode as cathode exhibits a high energy density of 42.1 Wh·kg^-1 at a power density of 439 W·kg^-1.（2）On the basis of high plateau capacity of hard carbon electrode,the overall sodium storage capacity is improved by increasing the slope capacity.Layered molybdenum disulfide is synthesized in situ on the surface of HC-1600 hard carbon material by hydrothermal reaction to prepare hard carbon/molybdenum disulfide composites.The stacking of molybdenum disulfide forms the interconnected porous structure,which promotes the storage of electrolyte on the surface of electrode materials and the diffusion of electrolyte ions.The results show that when the molar ratio of reactants（sodium molybdate dihydrate and thioacetamide）is 1:2,the electrochemical performance of the composite electrode is best.For the HMS-12 composite electrode,the reversible capacity of it is367.5 m Ah·g^-1,and the slope capacity of it is 144.6 m Ah·g^-1.Compared with HC-1600 hard carbon electrode,the reversible capacity increased by61.7 m Ah·g^-1.The SIC assembled with HMS-12 composite electrode as anode and lignin-derived activated carbon electrode as cathode exhibits a high energy density of 109.2 Wh·kg^-1 at a power density of 200 W·kg^-1.（3）In view of the lack of sodium storage platform for hard carbon electrode in high voltage region（>0.1 V）,reactive cobalt sulfide was introduced with HC-1600（optimized hard carbon material）as the main body.The conversion reaction between cobalt sulfide and sodium ion can introduce a sodium storage platform in the high voltage region,thereby increasing the overall sodium ion storage capacity of the electrode and realizing multi-voltage platform sodium ion storage of the composite electrode.Cobalt sulfide containing two phases（Co S and Co₉S₈）is synthesized on the surface of HC-1600 hard carbon material by hydrothermal reaction to prepare hard carbon/cobalt sulfide composites.The results show that when the molar ratio of reactants（cobalt chloride hexahydrate and thioacetamide）is 1:3,the electrochemical performance of the prepared composite electrode is best.For the HCS-13 composite electrode,its reversible capacity is 481.1 m Ah·g^-1.The capacity is 147.6m Ah·g^-1 when the voltage is less than 0.1 V and 333.5 m Ah·g^-1 when the voltage is greater than 0.1 V.The introduction of cobalt sulfide reduces the sodium ion storage capacity in low-voltage of HC-1600 hard carbon electrode.And the conversion reaction greatly increases the capacity in the high-voltage.The SIC assembled with HCS-13 composite electrode as anode and lignin-derived activated carbon electrode as cathode exhibits a high energy density of 85.7 Wh·kg^-1 at a power density of 200 W·kg^-1.