Preparation And Capacitance Performance Of Carbonized Bacterial Cellulose Nano-hybrid Materials

Supercapacitor,which has the characteristics of fast charge-discharge capacity,ultra-high power transmission capacity and ultra-long cycle life,is one of the most promising energy storage devices and has been widely concerned in the field of materials and energy.In recent years,nano-carbon electrode materials play a more and more important role in these energy storage devices.However,nano-carbon electrode materials such as graphene and carbon nanotubes,which are the most studied at present,have some defects,such as high requirement of raw materials,tedious process,unenvironmental protection,high price and so on.The research on nano-carbon electrode materials with rich renewable raw materials,simple green process and high performance-price ratio has become an important direction in academia and industry.In this paper,bacterial cellulose?BC?,a cheap and easily available biomass environmental protection material,was used as carbon precursor to prepare carbonized bacterial cellulose?CBC?basic material with three-dimensional nanofiber structure by programmed pyrolysis method,and then doping and composite modification were carried out.N/P atom doped CBC negative material?N/P-CBC?,CBC and Polyaniline composite positive material?CBC/PANI?and CBC and nickel molybdate composite cathode material?CBC/NiMoO₄?were prepared.The composition,structure,microstructure and electrochemical properties of these materials were analyzed in detail and structural design optimization,Finally,two kinds of asymmetric supercapacitors,?CBC/PANI//N/P-CBC and CBC/NiMoO₄//N/P-CBC?,were assembled with the optimized electrode materials,and their specific capacitance,rate performance and cycle life were studied and compared.The results are as follows:Firstly,using BC as carbon precursor,CBC basic materials with three-dimensional network structure were prepared by programmed pyrolysis at 600^oC,700 ^oC and 800 ^oC,respectively.the carbon materials still maintained the original nanofiber network structure of BC and were amorphous after pyrolysis.The specific capacitance of the carbonized product prepared at 800^oC is the highest?100.70 F/g?.Secondly,the heteroatom doped CBC supercapacitor negative materials were further prepared by doping N and P atoms or diatoms into CBC by one-step pyrolysis.The results show that heteroatom doping can increase the specific capacity of CBC,and the effect of N and P diatomic co-doping on capacitance is more obvious than that of single atom doping,when the concentration of diatomic dopant?NH₄?₂HPO₄ is 0.025 M,The capacitance performance of the prepared N/P-CBC-0.025 electrode material is the best.when the current density is 1 A/g,the specific capacity reaches 232.10 F/g,and the specific capacity retention rate is still 97.78%after4 A/g cycle charge and discharge for 2000 times.Then the composite positive material of CBC/PANI supercapacitor was synthesized by in-situ oxidative polymerization,and the type and concentration of doped acid were adjusted to optimize the composite material with the best capacitance performance.It is assembled with N/P-CBC-0.025 as positive to form asymmetric supercapacitor.The results show that the specific capacitance of CBC/PANI composite is higher than that of CBC base material.The electrochemical properties of CBC/PANI-T composites prepared with p-toluenesulfonic acid as doped acid were better than those of CBC/PANI-P composites prepared with phosphoric acid as doped acid.When the concentration of p-toluenesulfonic acid is 0.5 M,The capacitance properties of CBC/PANI-T-0.5 composites are the best?324.81 F/g?.The specific capacity of the assembled CBC/PANI-T-0.5//N/P-CBC-0.025 asymmetric supercapacitor is 53.65 F/g,The energy density and power density are 6.92 Wh/kg and 483.73 W/kg in 1.0 V potential window,respectively.After 2000 cycles,the capacity is still 66.61%,which show good electrochemical performance.Finally,the composite cathode material of CBC/NiMoO₄ supercapacitor was prepared by hydrothermal method.the composite with the best capacitance performance was selected by controlling the reaction time,and it was assembled with N/P-CBC-0.025 as cathode to form asymmetric supercapacitor.The results showed that with the prolongation of reaction time,the crystallinity of NiMoO₄,composites began to grow on the surface of CBC,and when the reaction time was 4 h,the electrochemical properties of the prepared CBC/NiMoO₄-4 electrode materials were the best,and the current density was 1 A/g,and the electrochemical properties of CBC/NiMoO₄-4 electrode materials were the best when the reaction time was 4 h.The specific capacity is 726.24 F/g,which is higher than that of CBC basic material.Compared with CBC/PANI-T-0.5//N/P-CBC-0.025,the assembled CBC/NiMoO₄-4//N/P-CBC-0.025 asymmetric supercapacitor has larger specific capacity?102.69 F/g?and higher energy density?38.08 Wh/kg?and power density?816.97 W/kg?,as well as good cycle stability.After 2000 cycles of charge and discharge,the specific capacity retention rate is still 72.69%.Therefore,CBC and its nano-hybrid materials,as green environmental protection materials with high performance-price ratio,have great application potential in the field of electrochemical energy storage.