Preparation Of Lignin/cellulose-based Carbon Fiber And Its Application In Supercapacitors

With the development and progress of science and technology,the growth trend of energy consumption is already unstoppable while the total amount of non-renewable energy sources on earth is limited.Focusing on the conflict between increasing energy demand and the depletion of fossil resources,it is crucial to develop new technology and shift the energy supply to sustainable renewable sources.Cellulose and lignin,the two most abundant biomass resources in nature,are considered as excellent candidate materials for the preparation of CFs.The biomass-based CFs are firstly prepared by blending cellulose/lignin and the optimum packing ratio was determined by controlling the different lignin/cellulose adding ratio.When adding ratio was 1:1,The resulting precursor fibers exhibit complete fibrous morphology,uniform diameter,large surface area,good flexibility and excellent power storage capacity.The specific capacitance of the biomass-based CNFs supercapacitor reaches 10.9 F/g.In order to imitate this covalent-bond connection in natural trees,an effective strategy is presented to modify lignin and CA as a novel carbon fiber precursor material.Chemical modification methods include isocyanate modification and epoxy modification to solve the phase splitting phenomenon of all biomass-based carbon fiber during spinning and preoxidation respectively.Isophorone diisocyanate(IPDI),containing two functional groups is employed to connect lignin and CA through covalent-bond connection,which is realized by the reaction of isocyanate group and hydroxyl group.By a stable covalent-bond connection,the resulting lignin/CA molecule simultaneously exhibits excellent thermal stability and good spinnability.The covalent-bond connection effectively reduce the phase separation of lignin and cellulose,thus improving the morphology and properties of CFs.When the amount of NCO is 6%,the electrochemical effect of carbon fiber is the best,and its mass ratio capacitance can reach 214.9F/g.However,when the epoxy chloropropane(ECH)was used as a chemical modifier,stable chemical bonds could be formed between lignin and cellulose in the pre-oxidation stage.When the epoxy dosage was 10%,CFs had the best energy storage effect and the mass ratio capacitance was 320.3 F/g.Although,a very long time of pre-oxidation treatment can effectively solve the morphological collapse of the biomass-based CFs,this preparation process leads to extremely high energy consumption and low production efficiency for CFs.In this work,a simple phosphating process was firstly proposed to modify cellulose-acetate(CA)and lignin for a novel energy storage precursor material.Interestingly,the esterification of H₃PO₄ effectively reduced hydrogen bond interaction between lignin molecules,improving the flexibility of the precursor molecular chain and the spinnability of the spinning solution.With the 40%of H₃PO₄ content,the CFs can reach a high specific capacitance of 346.6 F/g.However,the highly branched structure and inherent heterogeneity of lignin remain the key factors limiting the performance of biomass-based CFs.Herein,we develop a simple and efficient method for preparing high-performance green supercapacitor.The fractionated lignin samples exhibit obvious chemical structure differences including the basic structural unit ratio,molecular weight,and intermolecular linkages.Subsequently,the fractionated lignin is phosphatized and mixed with cellulose acetate(CA)for electrospinning.The resulting precursor fibers exhibit good thermal stability of lignin and flexibility of CA.The precursor fibers undergo a short pre-oxidation and carbonization treatment process to obtain the biomass-based CFs with complete fibrous morphology,uniform diameter,large surface area,good flexibility and excellent power storage capacity.These results reveal the effects of the fractionating and phosphating lignin on the manufacture and properties of biomass-based CFs.