Study On The Preparation And Electrochemical Performance Of Lignin Based Activated Carbon Microsphere

Lignin,the second most abundant biopolymer after cellulose,is a high carbon content renewable resource in nature.It is a polyphenol with a three dimensional structure consisting of randomly cross-linked phenyl propane building blocks,making it a potential polymer for the carbon material.The objective of this study was to prepare lignin based microsphere via reverse phase polymerization from commercial lignin,combined modification and molding,examine the physical and chemical changes of lignin precursor during the reverse phase polymerization,and explore the influence of preparation conditions and reaction mechanism on the lignin based sphere.And then the application of lignin based microsphere on activated carbon for supercapacitors was explored preliminarily.This work is very practical meaningful to accelerate the the utilization of industrial lignin resource.Different regions,types of industrial alkali lignin,sulfonated lignin and high purity lignin were selected as raw materials.The refined alkali lignin（JL）and high purity lignin（GL）have the phenyl propane building blocks and elementary composition.The average molecular weight of GL is larger,M_n 3500,M_w 8700,and the molecular weight distribution is more concentrated,so its thermal stability is better than that of alkali lignin.What is more,GL is rich in more phenolic hydroxyl group,carboxyl group active functional groups.Therefore,GL was selected for the next application study.Two different methods were used to prepare lignin based activated carbon.One is directly activation.The other way is carbonization and activation.The lignin based activated carbon GLAC-T improved pore structure,surface chemical structure,maintaining morphology and increasing graphitization degree.As a result the GLAC-T showed much more excellent electrochemical performance.And the gravimetric capacitance of GLAC-T is 312 F g^-1,and even after 10,000 cycles at 1 A g^-1 a specific capacity of 261 F g^-1 remains,higher than GLAC-D 70 F g^-1.The obtained lignin based microsphere GLS,thermosetting ball with both controllable diameter distribution and smooth surface through the reverse phase polymerization process.It played a key role of modifying the morphology,surface appearance and size distribution of lignin based microsphere by coordinating the ratio of solid content and dispersed phase content.The phenolic reaction and mannich reaction happened among the Lignin molecular formaldehyde and HMTA during reverse phase polymerization process at the attendance of ammonium hydroxide.Lignin benefited a cross-linking carbon structure and some oxygen/nitrogen functional groups were introduced.GLS was superior to GL on thermal stability and surface chemical stability.And GLS got more ordered microstructure and more reasonable pore structure.Thus,better electrochemical performance of lignin based activated carbon microsphere is obtained.And the gravimetric capacitance of GLACS is as high as 334 F g^-1,and even after 10,000 cycles at 1 A g^-1 a specific capacity of286 F g^-1 remains,higher than GLAC-T 25 F g^-1.The lignin/sucrose based microsphere GLZS was obtained by the reverse phase polymerization process at the attendance of sucrose.Sucrose molecular depressed the phenolic reaction and mannich reaction among lignin,formaldehyde and HMTA by reacting with lignin molecular.So the property of GLZS is different from GLS.GLZACS also got good electrochemical performance.And the gravimetric capacitance of GLZACS is 307 F g^-1,and even after 10,000 cycles at 1 A g^-1 a specific capacity of 237 F g^-1 remains.