The Fabrication And Capacitance Performance Research Derived From Bio-based Cellulose Acetate As Binder-free Carbonaceous Electrode Materials For Supercapacitors

In the past few decades,fossil resources have been widely applied in various fields such as automotive industries,agriculture,electricity and transportation.However,due to the overuse of fuels,the global warming is getting worse and fuel reservoirs reduce urgently.Developing renewable resources based cleaner energy storage and conversion devices like solar cells,lithium ion batteries(LIB)and supercapacitors(SCs),is regarded as an alternative method to avoid excessive consuming of fossil fuels.Supercapacitors with excellent electrochemical performance are considered as potential energy storage devices,which have been widely applied in the field of energy storage.Supercapacitors,also named electrochemical capacitors or ultracapacitors,have caught the intensive attractions,which bridge the gap between conventional dielectric capacitor and LIB.At present,supercapacitors are mainly divided into three categories based on their resources:carbon-based materials,transition metal oxides and conductive polymers.Compared with the others,carbonaceous electrode materials derived from environmentally friendly and widely distributed biomass,have high specific surface area(SSA),developed pores and good electrical conductivity.Therefore,they show advantages in power performance and cycle stability.This work mainly studies the application of carbon materials derived from biomass used in supercapacitors.In order to prepare self-supporting carbon-based supercapacitors with high electrochemical performance,electrospinning technology is used to produce membrane electrodes.Electrospinning is s a facile and continuous approach to fabricate ultrathin nanofibers with uniform diameter distriubution and comtrollable pores.The prepared electrospun nanofiber membranes have three-dimensional(3D)structure,excellent electrical conductivity and abundant pores.After carbonization,activation,heteroatom doping and other post-treatments,the nanofiber membranes can be used directly as self-supporting electrode materials without conductive agents and binders,and thus the electrochemical performance of free-standing electrodes are significantly improved.This paper successfully designs and prepares a series of carbon nanofiber(CNF)membrane electrodes,and their properties are evaluated in detail.The main contents of this work are as follows:1.The hierarchical porous carbon nanofiber membrane was successfully prepared from CA by electrospinning,subsequent de-acetylation and heat treatment processes.And the effects of carbonization temperature on the morphology,structure and electrochemical properties of CA-CNFs electrodes were investigated.Nitrogen adsorption and desorption tests show that specific surface area of CA-CNFs(carbonized at 800 ?)electrode is 720.8 m² g^-1,and the average pore size is 2.42 nm.The maximum specific capacitance of the corresponding electrode material reaches up to 229.4 F g^-1 at the current density of 0.2 A g^-1 in three-electrode system.In addition,the 97.3%initial specific capacitance can be maintained after 40,000 charge-discharge cycles.The CA-CNFs-800 supercapacitor display energy density of 16.4 Wh kg^-1(200 W kg^-1)under two-electrode system.2.Our work further explores and solves the spinnability of SPI and the corresponding electrospinning conditions based on previous researches,and thus CA-SPI composite nanofiber membranes were successfully fabricated.The effects of different carbonization temperature on the morphology and electrochemical performance of CA-SPI carbon nanofiber membrane was studied.The experimental results show that CA-SPI-CNFs possess three-dimensional conductive network,hierarchical pore distribution,fast electron transmission and abundant functional groups.The specific capacitance of CA-SPI-800 electrode is up to 219.3 F g^-1(0.2 A g^-1)in three-electrode configuration.Under two-electrode system,the cycle stability of CA-SPI-800 is significantly improved compared with that of CA-CNFs(10,000 cycles),and the initial specific capacitance of94.1%can still be maintained after 40,000 charge-discharge cycles(20 A g^-1).3.Combination of CA nanofiber membranes and metal salts is investigated to study the feasibility of zinc ion-modified composite nanofiber membranes based on the previous reserches.Besides,we also explore the influence of different soaking time on the electrochemical performance of CA-Zn(OAc)₂ carbon nanofiber membranes.Electrochemical characterizations demonstrate the three-dimensional conductive network structure inside the CA-Zn(OAc)₂membrane electrode.The specific capacitance of CA-Zn(OAc)₂electrode is 71.3 F g-1 under two-electrode system.And CA-Zn(OAc)₂ supecapacitor maintains 90.8%capacitance after 20,000charge-discharge cycles.In summary,this paper aims to fabricate carbonaceous materials based on biomass resource of cellulose acetate by electrospinning technology.To improve electrochemical performance of electrode materials,our works utilize various modified treatments to optimize structrues of the electrodes.It has been confirmed that the prepared CNF membranes have good electrochemical performance.It is expected that these carbonaceous materials will be widely used in the field of energy storage.