Preparation And Electrochemical Performance Of Carbon-based Composites Derived From Nanocellulose

In order to improve the cycle life,power density,energy density and safety of electrochemical energy storage devices,nano-functional materials have been researched and applied,and cheap and easily available biomass materials have attracted widespread attention.As a natural biomass material,nanocellulose has great potential because it has unique structure and excellent chemical and physical properties.However,poor intrinsic conductivity requires functional design to improve electrochemical performance.For this reason,using nanocellulose as the template precursor,combined with chemical oxidation in-situ polymerization,hydrothermal and carbonization methods,designed and prepared nickel-cobalt layered double hydroxide@mesoporous carbon（NiCo-LDH@MC）and Nickel sulfide/cobalt sulfide@N、S co-doped carbon materials（Ni₃S₄/Co₃S₄@NSCs）,used in supercapacitors and lithium-ion batteries.The specific research content is as follows:（1）Using bacterial cellulose as a template,polymerize aniline in situ by chemical oxidation to obtain polyaniline-coated bacterial cellulose,and obtain mesoporous carbon（MC）by annealing.Further hydrothermal treatment is carried out to grow nickel-cobalt layered double hydroxide on MC to obtain NiCo-LDH@MC composite material.The existence of mesoporous structure is conducive to ion diffusion and electron transfer.The core-shell heterogeneous structure buffers the collapse of the layered NiCo-LDH nanosheets and slows down the irreversible phase change during the charge-discharge process through the synergy between the carbon fiber and the NiCo-LDH nanosheets.Therefore,as a supercapacitor electrode material,the specific capacitance is 2462.75 Fg^-1 at 500 mA g^-1,good energy density(197.02 Wh kg^-1),and excellent power density(720 W kg^-1).As a negative electrode material for lithium-ion batteries,display a high reversible capablity(1003.8 mA h g^-1 at 100 mA g^-1),excellent high rate capacities(238.3 mA h g^-1 at 5000 mA g^-1).（2）Using NiCo-LDH@MC as the precursor and thioacetamide as the sulfur source,the Ni₃S₄/Co₃S₄@NSC composite material was designed and synthesized through hydrothermal technology.It has the advantages of Ni₃S₄/Co₃S₄ heterostructure,mesoporous structure,120°stacked Ni₃S₄/Co₃S₄ nanosheets and the glassy state of Ni₃S₄/Co₃S₄@NSC.The synergy of these structures can effectively enhance the electrochemical reversibility and charge transfer dynamics in the discharge-charge process.Therefore,in the supercapacitor,at 500 mA g^-1,Ni₃S₄/Co₃S₄@NSC shows a specific capacitance of 1725.6 Fg^-1.And at 1000 mA g^-1,it displaying excellent stable cycling life（after 2000 cycles is 67.7%）.When Ni₃S₄/Co₃S₄@NSC is used as a negative electrode material for ion batteries,its exhibits a high discharge capacity of 1619.1 mA h g^-1 at 100 mA g^-1.Discharge capacity maintained at 825.4 mA h g^-1 and the coulombic efficiency is 97.69%at 100 mA g^-1 for over 100 cycles.