Preparation Of Lignin-Based Carbon Fibers By Melt Spinning And Their Energy Storage Application

Lignin is an abundant and renewable natural polymer that occupies an important position in biomass resources.As a rich aromatic polymers on earth,the organic carbon content of lignin is as high as 60%,is deemed to be a high value of biomass carbon resource.At present,most lignin is still burned for energy recovery,and only 5%is utilized to produce bio-based products,which leads to serious underutilization of lignin.Therefore,the study of lignin high-value application can not only improve the economic value of lignin but also effectively maximize biomass resources.Benefiting from the development of electric vehicles,smart grids and mobile power sources,supercapacitors have attracted extensive attention due to their high power density,fast charging and discharging,and long cycle life.Electrode is the main factor affecting the electrical performance of supercapacitor,so the selection and design of electrode material is of great significance.Compared with the carbon materials currently used in commercial supercapacitors,the use of functionalized lignin carbon fiber as electrode materials not only has incomparable advantages in terms of cost,but also can reduce pollution in the production process.However,the actual functional structure requires the carbon fiber to be graphitized at high temperatures.Therefore,the low-cost preparation of lignin carbon fiber（LCF）with conductive graphite structure and the study of its energy storage characteristics are of great significance for the realization of low-cost carbon fiber electrodes.Based on the above background,this study focused on the low-cost preparation method of carbon fiber with graphite structure through melt spinning technology from fusible lignin and non-fusible lignin,and its energy storage application studied.As a fusible lignin,polyethylene glycol lignin（PEGL）was by direct melting spinning to obtain polyethylene glycol lignin fiber（PLF）,and as a precursor was used to prepare lignin carbon fiber（PLCF）surface covered with graphitic carbon.The peroxidation mechanism and catalytic graphitization of the nickel acetylacetone（Ni（acac）2）catalyst were analyzed by combining morphology and thermal characterization.The results showed that Ni（acac）2 played a positive role in the simultaneous carbonization and catalytic graphitization process,and the carbonization graphitization temperature decreased from 582.7℃ to 472.0℃.According to carbon structure test and correlation calculation of PLCF s,compared with PLCF-0,PLCF-0.2 to PLCF-0.6 had graphite structure.Among them,PLCF0.4 had a low specific surface area of 89.92 m²/g and a good surface graphite structure(d₀₀₂=0.35 nm,L_c=0.41 nm and L_a=7.48 nm).Kraft Lignin（KL）is a kind of non-fusible lignin,so KL is blended with thermoplastic polymer to change the melting characteristics,and simultaneously adds catalyst Ni（acac）2 to provide conditions for the subsequent catalytic graphic transformation process.Therefore,KL can form kraft lignin fiber（KLF）by melt spinning technology.After heat treatment,carbonization and catalytic graphic,kraft lignin carbon fiber（KLCF）with conductive structure can be obtained.Based on the morphology characterization and thermal analysis results,the physical blending effectively changed the KL melting characteristics.By summarizing the decomposition temperature,it could be found that Ni（acac）2 effectively reduces the decomposition temperature to 318.6℃,and the mass loss increases to 79.6%.In addition,according to the consequences of carbon structure characterization,graphite structures were present both inside and outside of KLCFs.Compare to other KLCFs,KLCF-3%had a lower surface area of 90.98 m²/g and a better graphite structure(d₀₀₂=0.34 nm,L_c=0.42 nm,and L_a=23.81 nm).Since the electrochemical performance of LCF-based electrode is the decisive factor for its application in the field of energy storage,PLCFs and KLCFs were used as electrode materials to assemble supercapacitors,and the energy storage characteristics of LCF were analyzed by electrochemical test.It was found that the PLCF-0.4 electrode had a maximum specific capacitance of 50.2 F/g,an energy density of 15.7 Wh/kg,and a high power density of 644.9 kW/kg,due to the high conductivity of the graphite structure.And good cycle stability of the PLCF-0.4 electrode,maintaining 100%capacitance after 1500 cycles.Meanwhile,the KLCF-3%had a large specific capacitance of 57.9 F/g,providing a power density of 43.2 kW/kg at 18.1 Wh/kg energy density.Moreover,KLCF-3%had a wide working temperature range,showing that LCF had excellent environmental stability.In this study,based on the melt spinning technology,by studying the melt spinning process of two kinds of lignin,pre-oxidation and catalyst loading process,carbonization and catalytic graphitization process,lignin carbon fiber with graphite structure was prepared and applied to the supercapacitor,which provided important technical support for the development of low-cost lignin carbon fiber applied to the field of energy storage...