Dissertation Defence: Graphitization of Lignocellulosic Bio-mass via Hydrothermal Carbonization and Spark Plasma Sintering
July 31 at 9:00 am - 1:00 pm
Mitchell Ross Barrett, supervised by Dr. Lukas Bichler, will defend their dissertation titled “Graphitization of Lignocellulosic Bio-mass via Hydrothermal Carbonization and Spark Plasma Sintering: Applications in Li-ion Batteries” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering.
An abstract for Mitchell Ross Barrett’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. This examination will be offered in hybrid format. Registration is not required to attend in person, but please email lukas.bichler@ubc.ca to receive the Zoom link for this exam.
Abstract
Graphite is the dominant anode material used in lithium-ion batteries; however, conventional graphite production relies on mining or energy-intensive graphitization processes that exceed 2500 ºC. This dissertation investigates a sustainable alternative through the production of bio-graphite from lignocellulosic biomass using a combination of hydrothermal carbonization (HTC) and spark plasma sintering (SPS).
Multiple biomass feedstocks, including arbutus bark, coffee grounds, seaweed, milfoil, and sawdust, were converted into hydrochar through HTC. The effects of feedstock type and HTC processing conditions on yield, composition, and structural development were evaluated. Increasing HTC temperature and time promoted carbon enrichment and aromatization while reducing oxygen content and solid yield. Among the feedstocks investigated, arbutus bark produced hydrochar with favourable characteristics for subsequent graphitization.
The hydrochars were converted into graphitic carbon using SPS at temperatures between 1200 ºC and 1900 ºC, pressures between 5 MPa and 60 MPa, and hold times of 10 and 30 minutes. Raman spectroscopy, X-ray diffraction, elemental analysis, pycnometry, and thermogravimetric analysis demonstrated that SPS temperature was the dominant parameter controlling graphitic ordering and crystallite development. The optimized condition of 1900 ºC, 40 MPa, and 10 minutes produced the highest degree of graphitic ordering while requiring substantially lower temperatures and shorter processing times than conventional graphitization methods.
The optimized SPS-derived bio-graphite was evaluated as a lithium-ion battery anode material. Following particle size reduction, the material exhibited stable reversible lithium storage with discharge capacities of approximately 140-150 mAh/g and capacity retention of 84-92% after 500 cycles. Extended cycling to 1000 cycles demonstrated continued reversible lithium-storage behaviour, while rate capability testing showed measurable capacity retention at rates up to 9 C.
Overall, this work demonstrated that HTC followed by SPS is a viable route for producing graphitic carbon from renewable biomass feedstocks. Although the electrochemical performance remained below that of highly optimized commercial graphite, the resulting bio-graphite exhibited promising cycling stability, extended cycle life, and reasonable rate capability while being produced using significantly reduced graphitization temperatures and processing times.
