Preparation Of Lignin-based Graphene Ink And Study On Performance Of Its Printing Supercapacitor

Because of considerable power density,rapid charge and discharge,good cycle stability and high safety,supercapacitors made of electrode materials derived from biomass have become a promising sustainable energy storage device.However,biomass-based supercapacitors usually have some problems,such as simple structure,complex preparation process,low electrochemical performance,no mechanical flexibility,unpredictable shape and performance,and inability to be prepared on a large scale with high precision,which makes it difficult to meet the practical application requirements.In order to solve the above problems,this thesis mainly studies the preparation method of porous lignin-based graphene oxide（PLGO）,and explores noncovalent combination strategy between PLGO and natural organic small molecules,thus developing lignin-based porous graphene ink with natural electrochemical active center.Make full use of the flexible designability of the energy-storage green ink screen printing patterned electrode,thus improving the preparation efficiency and electrochemical performance of micro-supercapacitor（MSC）,realizing the electrochemical performance regulation of MSC,exploring the feasibility of flexible integration and scalable production of printed MSC,and developing the flexible energy storage technology of biomass-based supercapacitor.Sodium lignosulfonates with different molecular weights were carbonized and graphitized simultaneously by K₂FeO₄ to prepare porous lignanin-based graphitized carbon（PLGC）.The maximum specific surface area,total pore volume,and conductivity can reach 1882.3 m²/g,1.4 cm³/g,and 6.05 S/cm,respectively.The optimized PLGC was further exfoliated into PLGO by the improved Hummers method,and the obtained PLGO has a hierarchical structure with a micropore ratio as high as 87.2%,an average pore size of only 2.85 nm and a specific surface area of834.2 m²/g.At current densities of 0.5 and 10.0 A/g,PLGO electrode has high specific capacitance of 193.0 and 131.0 F/g,respectively.The interdigital MSC printed with PLGO ink shows good area specific capacitance（7.12 mF/cm²）,energy density（0.99μWh/cm²）,and relatively stable cycle stability（>9000 cycles）.Based on the noncovalent self-assembly mechanism between PLGO and natural mononuclear anthraquinone（MAQ）,a quinone-based electrochemical active center was introduced to prepare MAQ/PLGO colloidal gel with excellent rheological properties and high specific capacitance.Among them,the MAQ/PLGO=1:2 colloidal gel shows nearly linear shear thinning behavior,large shear strain,stable frequency scanning and time scanning modulus,indicating that MAQ/PLGO=1:2 colloidal gel has excellent printability.The ex situ characterization of MAQ electrode shows that the benzoquinone group in MAQ molecule can undergo reversible proton-coupled electron transfer reaction,thus providing high pseudocapacitance.Therefore,the MAQ/PLGO colloidal gel electrode outputs a high specific capacitance of 484.8 F/g at a current density of 1.0 A/g,indicating that MAQ and PLGO in noncovalent self-assembled colloidal gel have a synergistic effect of specific capacitance.In addition,the interdigital MSC printed with MAQ/PLGO gel ink shows good area specific capacitance（43.6 mF/cm²）,energy density（6.1μWh/cm²）,good cycle stability（>10000 cycles）and high mechanical flexibility（keeping capacitance in various bending states）.In order to further improve the specific capacitance and energy density of screen-printed MSC,pteridine derivatives with the electrochemical active center of diazopentadiene(-N₅=C_4a-C_10a=N₁-)was used for noncovalent combination with PLGO.Lumichrome（LC）,alloxazine（ALX）and lumazine（LMZ）with high theoretical specific capacitance will undergo molecular tautomerism under electrochemical induction.N₅ and N₁ are continuously and reversibly oxidized and reduced through the redox center-N₅=C_4a-C_10a=N₁-to promote proton-coupled electron transfer reaction,thus providing pseudocapacitance.The ALX/PLGO=1:2ink prepared by PLGO and ALX with the highest capacity through noncovalent interactions shows remarkable shear thinning behavior,a shear strain of up to 32.25%and excellent mass specific capacitance.This ink can be used to prepare high-precision patterned MSC by screen printing technology,and the electrochemical performance of printed interdigitated MSC can be adjusted and optimized by designing different printing line gap and overprinting passes.The highest specific capacitance and energy density of the MSC can reach 95.3 mF/cm² and 16.3μWh/cm²,respectively,and the capacity retention rate is still higher than 90.5%after 10 000cycles.In this thesis,based on the noncovalent interactions between PLGO and natural organic molecules with electrochemical active centers,a green ink system for energy storage was constructed,and the high-performance MSC can be prepared by efficient and rapid printing.Moreover,the printed MSC has the characteristics of high mechanical flexibility（keeping capacitance in various bending states）,easy integration and large-scale preparation,which confirms the application potential of this green ink in flexible wearable and integrated electronics,and provides a new idea for the scalable production of efficient and sustainable flexible micro energy storage devices in the future.