Kinetics Of Waste Seed-based Biomass Pyrolysis And Applications Of Pyrolyzed Products For Lithium Batteries

Energy from different renewable resources is crucial to address the future needs of energy in numerous energy consumption regions.Biomass is one of the largest and most abundant sources for the production of renewable energy,functional carbon materials,biochemicals and fuels.It is a reliable and persistent source of energy,and functional carbon materials as compared to other available renewable sources.Several biomass conversion technologies are available and some are still under development.Thermochemical conversion approaches are advantageous among them,which offer higher conversion efficiency along with product versatility and selectivity.Hydrothermal conversion technologies such as steam hydrogasification,and hydrothermal conversion are still under development.These approaches have many striking aspects for utilization in inexpensive decentralized applications without applying any pretreatment.Several mature thermochemical conversion options are also available which include pyrolysis,gasification,and combustion.New promising approaches for example the biorefinery routes,which combine with different conversion methods synergistically and produce multiple range of products.These synergistic combination is expected a key component in addressing the technical and economic obstacles for current biomass conversion techniques.Herein,we choose two waste seed-based biomass as the research object,trying to reveal the thermal decomposition behavior of biomass through systematic research and explore new ways for its efficient utilization.The main research content of this thesis includes three aspects:Firstly,thermal degradation kinetics of two different waste seed-based biomasses（jujube pits,and Himalayan horse chestnuts（HHCNs））were systematically studied to understand the effect of biomass components on degradation mechanism and pyrolysis products.Different model free,and model fitting methods were employed,which describe the whole devolatilization process.The residual carbon was further characterized by elemental analysis,SEM,Raman,XRD,and XPS.The kinetic results revealed that jujube pits have low activation energies(80.70,82.28,and 86.19 k J mol^-1)as compared to HHCN(119.45,140.11,and 145.76 k J mol^-1)by KAS,FWO,and FRL methods,respectively which indicated that jujube pits require low energy barrier as compared to HHCNs.Furthermore,higher degree of graphitization,higher porosity,presence of microspheres,higher conductivity and abundant oxygen functional groups make jujube pits carbon a suitable material for energy conversion and storage applications.Therefore,jujube pits derived carbon was further utilized as an anode material in lithium ion batteries（LIBs）and it shows excellent performance as an anode material.The obtained oxygen-rich renewable graphitic carbon from jujube pits based anode delivers high specific capacity(166m Ah g^-1)and ultra-stable cycling performance by retaining almost 100%columbic efficiency over 2000 cycles at 2 A g^-1.Cyclic voltammetry（CV）reveals the kinetic mechanism of charge storages and shows an oxidation peak indicating stable lithium ion intercalation.The research results revealed that by regulating the thermal pyrolysis process of biomasses,high energy utilization value can be achieved and new functional carbon materials can be provided for lithium ion batteries.Secondly,the utilization of raw biomass has certain limitations such as low energy density,less HHV value and poor fuel properties,which can be enhanced by thermochemical conversion approaches such as microwave-assisted hydrothermal Carbonization（HTC）.The microwave-assisted HTC improves the fuel and physicochemical properties of waste seed-based biomass and produces functional carbon materials and renewable fuels.The kinetics of microwave-assisted HTC of Himalayan horse chestnuts were systematically studied.The composition of biomass and its variation during hydrothermal carbonization were explored by thermogravimetric analysis,SEM,XRD,Raman spectroscopy and infrared spectroscopy.Microwave assistance has a significant impact on the hydrothermal carbonization reaction process,reducing the temperature at which the aromatic structure of organic molecules in biomass is formed.Hydrothermal carbonization reaction at 200°C can produce carbon-containing products with relatively high aromatic structure content in molecules and also changes in their yield.The composition of the obtained product was explored and its HHV value,O/C,H/C and other related parameters were calculated in order to prove the energy recovery efficiency of the process for the utilization of this type of biomass energy.Lastly,Fabrication of functional carbon materials from Himalayan horse chestnut waste was achieved via microwave-assisted HTC method at very low temperatures of 120～200℃and high yields of 62～46 wt.%.The reaction mechanism,energy properties,chemical and molecular structure of the hydrochar were carefully investigated.The as-prepared hydrochar has abundant negatively charged oxygen functional groups,which are tunable by controlling the degree of graphitization.These negatively charged oxygen containing hydrochars can be utilized in lithium-sulfur（Li-S）batteries to effectively suppress polysulfide shuttling with electrostatic repulsive forces and simultaneously ensure uniform lithium-ion transportation,leading to substantially improved battery performance.The effect of hydrochar on the positive electrode active material during the charging and discharging process of the lithium-sulfur battery was analyzed;the cycle performance of the battery with the modified separator and the structural change of the electrode were explored under different rate conditions and investigated the EIS impedance in the cycle process.Furthermore,the electrochemical properties were also measured by multilayer pouch cell,which is more vital for applied application of Li-S batteries.The pouch cell assembled with hydrochar shows high specific capacity of 1123 m Ah g^-1 and maintains 80%retention.This research provides an efficient method to produce negatively charged carbon products from biowaste,which improves the biomass feedstock utilization and promotes the commercialization of Li-S batteries.