Study On Sodium Storage Properties Of Bacterial Cellulose-derived Carbon And Composites Materials

As a new-type energy storage device,Na hybrid capacitors?NHCs?both have the advantages of Na ion batteries and supercapacitors,which showed extensive application prospect in the field of electrochemical energy storage.To improve the energy and power density of NHCs,the anode materials of beacrial cellulose derived carbon aerogel nanofibers,SnS₂ nanosheets and their nanocomposites have been synthesized and their Na storage performance have been investigated in detail.By carbonization combined with chemical activation,the cathode material based on BCCFs has been prepared.By structure design and optimization of electrode materials,NHC based on BCCFs anode and cathode have been constructurd and its supercapactivie performance have been investigated by electrochemical tests.The main research contents are as follows:?1?Preparation and electrochemical properties of Bacterial Cellulose Derived Carbon Aerogel:BCCA at different temperatures is prepared by calcining in an inert atmosphere using bacterial cellulose as a carbon source.After high temperature pyrolysis,BCCA hard carbon maintains the three-dimensional poros network structure of bacterial cellulose precursor,shortens the transmission path of electrons and sodium ions,and exhibits excellent cycle performance and rate performance.Among them,BCCA-10 obtained at 1000°C has the best cycling performance and rate capability.BCCA-10 delivers still 235 mAh g^-1 capacity after 300 cycles at current density of 0.05 A g^-1,and126.3 mAh g^-1 at 2 A g^-1 current density,showing excellent cycling performance and rate capability.?2?Synthesis and sodium storage performance of SnS₂/BCCA composites:Metal disulfide SnS₂has proven to be a potential negative electrode material for sodium ion batteries?SIB?due to its high theoretical specific capacity and large interlayer spacing.However,the large volume change during the electrochemical sodiation/desodiation results in poor cycle performance and rate performance.We used tin source and sulfur source are SnCl₄·H₂O and thioacetamide?TAA?,respectively.The SnS₂nanosheets and bacterial cellulose-derived carbon aerogels were synthesized by simple hydrothermal reaction?SnS₂/BCCA?composites.Three-dimensional nanofiber network structure not only significantly improves the stacking of SnS₂ nanosheets and increases more active sites,but also promotes electron transport and alleviates the large volume changes during charge/discharge.The composite electrode of SnS₂/BCCA-5(specific surface area is 144.7 m² g^-1)deliveres high specific capacity of 408 mAh g^-1 at 50 mA g^-1 current density after 100 cycles and 196.4 mAh g^-1 at 2 A g^-1current density with improved rate performance.?3?Study on sodium storage performance bacterial cellulose-derived carbon aerogel for hybrid sodium ion capacitor:We constructed a hybrid sodium ion capacitor,utilizing complex multi-walled carbon nanotube and co-doped N O heteroatoms BCCA-10 as the anode?NO CT/CA?,and a BCCA activated by KOH as the cathode electrode?a-BCCA-4?.The anode conductivity of the mixture multi-wall carbon nanotubes and N O heteroatom co-doping is improved obviously,and has excellent rate performance.KOH-activated a-BCCA-4 exhibits excellent cycle performance.The resulting NO CT/CA//a-BCCA-4 hybrid sodium ion capacitor deliver an exception high density(51.67 Wh kg^-1)and high power density(6006.9 W kg^-1).NO CT/CA//a-BCCA-4 hybrid sodium ion capacitor at a current density of 0.5 A g^-1 at a voltage window of 2.0-4.0 V,which capacity retention rate was 60.4%after 3000 cycles.In addition,we also studied the NO CT/CA//a-BCCA-4 at a current density of 0.5A g^-1 at a current window of 1.5-4.2 V,which capacity retention rate after cycling was 14.6%.It can be seen that the selection of the voltage window plays a crucial role in the hybrid sodium ion capacitor.