University of Kentucky UKnowledge Theses and Dissertations--Biosystems and Agricultural Engineering Biosystems and Agricultural Engineering 2019 LIGNIN-DERIVED CARBON AND NANOCOMPOSITE MATERIALS FOR ENERGY STORAGE APPLICATIONS Wenqi Li University of Kentucky, [email protected] Digital Object Identifier: https://doi.org/10.13023/etd.2020.002 Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Li, Wenqi, "LIGNIN-DERIVED CARBON AND NANOCOMPOSITE MATERIALS FOR ENERGY STORAGE APPLICATIONS" (2019). Theses and Dissertations--Biosystems and Agricultural Engineering. 68. https://uknowledge.uky.edu/bae_etds/68 This Doctoral Dissertation is brought to you for free and open access by the Biosystems and Agricultural Engineering at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Biosystems and Agricultural Engineering by an authorized administrator of UKnowledge. 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Wenqi Li, Student Dr. Jian Shi, Major Professor Dr. Donald Colliver, Director of Graduate Studies LIGNIN-DERIVED CARBON AND NANOCOMPOSITE MATERIALS FOR ENERGY STORAGE APPLICATIONS ________________________________________ DISSERTATION ________________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Colleges of Agriculture and Engineering at the University of Kentucky By Wenqi Li Lexington, Kentucky Advisor: Dr. Jian Shi, Assistant Professor of Biosystems and Agricultural Engineering Lexington, Kentucky 2019 Copyright © Wenqi Li 2019 ABSTRACT OF DISSERTATION LIGNIN-DERIVED CARBON AND NANOCOMPOSITE MATERIALS FOR ENERGY STORAGE APPLICATIONS With a growing demand for electrical energy storage materials, lignin-derived carbon materials have received increasing attention in recent years. As a highly abundant renewable carbon source, lignin can be converted to a variety of advanced carbon materials with tailorable chemical, structural, mechanical and electrochemical properties through thermochemical conversion (e.g. pyrolysis). However, the non-uniformity in lignin structure, composition, inter-unit linkages and reactivity of diverse lignin sources greatly influence lignin fractionation from plant biomass, the pyrolysis chemistry, and property of the resulting carbon materials. To introduce a better use of lignocellulosic biomass to biofuels and co-products, it is necessary to find novel ways to fractionate lignin and cellulose from the feedstock at high efficacy and low cost. Deep eutectic solvent (DES) was used to extract lignin from high lignin-content walnut and peach endocarps. Over 90% sugar yields were achieved during enzymatic hydrolysis of DES pretreated peach and walnut endocarps while lignins were extracted at high yields and purity. The molecular weights of the extracted lignin from DES pretreated endocarp biomass were significantly reduced. The native endocarp lignins were SGH type lignins with dominant G-unit. DES pretreatment decreased the S and H- unit which led to an increase in condensed G-units, which may contribute to a higher thermal stability of the isolated lignin. Lignin slow pyrolysis was investigated using a commercial pyrolysis–GC/MS system for the first time to link pyrolysis chemistry and carbon material properties. The overall product distributions, including volatiles and solid product were tracked at different heating rates (2, 20, 40 ℃/min) and different temperature regions (100-200, 200-300 and 300-600 ℃). Results demonstrate that changes in reaction chemistry as a factor of pyrolysis conditions led to changes in yield and properties of the resulting carbon materials. Physical and chemical properties of the resulting carbon material, such as porosity, chemical composition and surface functional groups were greatly affected by lignin slow pyrolysis temperature and heating rate. Lignin-derived activated carbons (AC) were synthesized from three different lignin sources: poplar, pine derived alkaline lignin and commercial kraft lignin under identical conditions. The poplar lignin-derived ACs exhibited a larger surface area and total mesopore volume than softwood lignin-derived AC, which contribute to a larger electrochemical capacitance over a range of scan rates. The presence of oxygen-containing functional groups in all lignin-derived ACs, which participated in redox reaction and thus contributed to an additional pseudo-capacitance. By delineating the carbonization and activation parameters, results from this study suggest that lignin structure and composition are important factors determining the pore structure and electrochemical properties of the derived carbon materials. A 3-dimensional, interconnected carbon/silicon nanoparticles composite synthesized from kraft lignin (KL) and silicon nanoparticles (Si NPs) is shown to have a high starting specific capacity of 2932 mAh/g and a retaining capacity of 1760 mAh/g after 100 cycles at 0.72 A/g as negative electrode in a half-cell lithium-ion battery (LIB) test. It was found the elemental Si and C of the C/Si NPs were most likely linked via Si-O-C rather than direct Si-C bond, a feature that helps to alleviate the mechanical degradation from Si volume change and assure a sound electronic and ionic conductivity for enhanced electrochemical performance. EGA-MS and HC-GC/MS analyses suggest that the interaction of the Si, O and C can be tailored by controlling pyrolysis conditions. This study systematically investigated the interconnecting aspects among lignin source, pyrolysis chemistry, characteristics of the derived carbon materials and electrochemical performance. Such knowledge on the processing-structure-function relationships serves as a basis for designing lignin-based carbon materials for electrochemical energy storage applications. KEYWORDS: Lignin, pyrolysis, energy storage materials, supercapacitor, biorefinery, lithium-ion battery Wenqi Li (Name of Student) 12/08/2019 Date LIGNIN-DERIVED CARBON AND NANOCOMPOSITE MATERIALS FOR ENERGY STORAGE APPLICATIONS By Wenqi Li Jian Shi Director of Dissertation Donald Colliver Director of Graduate Studies 12/08/2019 Date DEDICATION I dedicate this dissertation in memory of my maternal grandmother, Shuhua Gao, my father, Xinping Xue and my paternal grandfather, Renzong Xue. ACKNOWLEDGMENTS I would like to express the deepest appreciation to my advisor Dr. Jian Shi, not only for his excellent guidance, endless support and help to me and my family, and providing me with open-minded, free atmosphere to do research, but more importantly, giving me confidence. I will never forget the words he encouraged me, which makes me believe I am not worse than anyone else on doing research. Without the confidence, I would never be able to finish my PhD work. I would also like to thank Dr. Yang-Tse Cheng and Dr. Doo Young Kim for their generous authorizing me to access their lab, immediate guidance and help whenever I need. Also, I would like to thank my committee members, Dr. Sue Nokes and Dr. Michael Montross and Dr. Conners as outside examiner for their valuable and constructive advices that help me to initial research proposal and enrich it with practical details. I would also like to thank my former and current group members, Dr. Lalitendu Das, Enshi Liu, Nguyen Truc, Siquan Xu, Luke Dodge, Ryan Kalinoski, Joseph Stevens, Makua Vin-Nnajiofor, Can Liu, Dr. Binling Ai and Yuxuan, Zhang, and student from Dr. Yang-Tse Cheng’s lab, Dr. Tao Chen, Dr. Yikai Wang, Dr. Jiazhi Hu, Ming Wang, Dingying Dang and student from Dr. Doo Young Kim’s lab, Dr. Yan Zhang, Namal Wanninayake, Rosemary Lynn Calabro for their valuable help, assistance and each enjoy moment we spent together. I would also like to thank all the faculty, staff and graduate students and those undergraduates that once worked in Shi lab. Everyone in this department is so nice to me, which make me never feel lonely, although far away from home. iii Finally, I would like to my lovely