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Effects of processing conditions and microstructure development on multifunctionality of lithium titanate - nickel composites

Huddleston, William
http://orcid.org/0000-0001-7537-3029
http://rave.ohiolink.edu/etdc/view?acc_num=case1619531582582196

Abstract Details

2021, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Electrified aircraft propulsion systems are sought for increased efficiency, reduced emissions, and noise abatement in next-generation aerospace concepts. For hybrid-electric and all-electric systems, the operational range is limited by the energy density of state-of-the-art electrochemical energy storage devices. Specifically, lithium-ion batteries have too low of a theoretical energy density, and higher energy density devices based on lithium-metal anodes introduce safety concerns with the formation of lithium dendrites leading to cell shorting and thermal runaway. To overcome these limitations, multifunctional energy storage devices provide simultaneous energy storage and load-bearing performance to achieve systems-level mass savings by minimizing parasitic weight of the structure. Recent development of structural batteries has leveraged carbon fiber composites as active anodes and structural materials. However, few investigations have explored the load-bearing capabilities of sintered lithium-ion battery active materials. In this work, processing-microstructure-property relationships were investigated to improve multifunctional performance of a strain-free anode composite based on Li4Ti5O12 containing nickel current collector particles. The influence of processing controls of nickel volume fraction, sintering temperature, and dwell time were analyzed with respect to bulk electrical conductivity and current collector particle size coarsening. Conductivity was modeled by power law percolation theory and increased as a function of nickel volume fraction and sample densification. Conductivities greater than 1 S/cm were achieved at relatively low volume fractions with tuning of sintering conditions. Analysis of particle size distributions revealed the impact of nickel fraction on particle interaction, and sintering temperature and dwell time on increase in average particle size. Coarsening was modeled according to Ostwald ripening theories and an activation energy of 1.04 eV was measured, indicating transport through matrix grain boundaries. In addition to bulk conductivity, the fracture stresses of samples were analyzed as a function of processing controls. Fracture stress was significantly improved at higher nickel fractions, up to 200 MPa, and fracture stress was strongly dependent on sample densification. Samples processed for long dwell times that showed very large average particle sizes showed toughening in the load-displacement curves, and crack bridging and plastic deformation of nickel was observed at fracture surfaces. To more clearly capture trends in microstructural development controlling variation in multifunctional properties, additional microstructural descriptors were analyzed including counts per area, relative particle spacing, and particle shape. Comparing trends in each descriptor allowed for the deconvolution of particle network formation from particle coarsening that would be impossible through analysis of particle size evolution alone. Finally, the compilation of microstructural descriptors was leveraged to train machine learning regression models. Random forest regression models allowed for the prediction of conductivity and fracture stress from observations of the microstructure with high accuracy, with up to 0.98 adjusted R2. Model analysis indicated the relative importance of each descriptor, with the nickel area coverage, nickel particle size, bulk density, and nickel particle network complexity metrics the most important for predicting properties. These studies of processing-microstructure-property relationships inform future design of load-bearing lithium-ion electrodes. This work correlated relationships between processing conditions and conductivity and strength, and developed methods to characterize and identify the relative importance of microstructural parameters to design for multifunctionality. Future research on composites that incorporate additional phases and alternative processing routes can build upon the findings of this study.
Alp Sehirlioglu (Advisor)
Mark De Guire (Committee Member)
David Matthiesen (Committee Member)
Burcu Gurkan (Committee Member)
134 p.
Materials Science
processing; anode; ceramics; cermet; composite; machine learning; conductivity; fracture; Lithium Titanate; nickel;

Recommended Citations

Citations

  • Huddleston, W. (2021). Effects of processing conditions and microstructure development on multifunctionality of lithium titanate - nickel composites [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1619531582582196

    APA Style (7th edition)

  • Huddleston, William. Effects of processing conditions and microstructure development on multifunctionality of lithium titanate - nickel composites. 2021. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1619531582582196.

    MLA Style (8th edition)

  • Huddleston, William. "Effects of processing conditions and microstructure development on multifunctionality of lithium titanate - nickel composites." Doctoral dissertation, Case Western Reserve University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619531582582196

    Chicago Manual of Style (17th edition)

case1619531582582196
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© 2021, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.