A Computational Study of Multivalent Ion Batteries for Sustainable Energy Storage

• Main Author: Juran, Taylor R
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2020
• Subjects: Physics
• ISBN: 9798662572263

Multivalent ion batteries (MVIBs) provide economical and energy-dense alternatives to Li-ion batteries (LIBs). In the academic pursuit to finding high-performance beyond LIBs, identifying a suitable cathode is a primary issue. More specifically, a cathode that supports high energy density, competitive charge/dis-charge rates, diffusion kinetics, and cyclability is desirable. In this regard, this work computationally investigates several cathodes for the development of MVIBs. Several elements, including Li, Na, Mg, Ca, Zn, and Al, are considered as metal anodes for mono- and MVIBs. While several elements are considered, the emphasis is on Ca ion batteries, due to the increased voltage associated with Ca in comparison with the other di- and trivalent sources considered.Density functional theory (DFT) is used to compute voltage profiles, diffusion energy barriers, and formation energies, as well as to consider the impact of swelling and the electronic properties for the battery chemistries considered within this study. Careful computational benchmarking is performed to balance computational accuracy and cost, ensuring efficient materials studies.The Chevrel phase, Mo6X8 (X = S, Se, Te), is found to produce a voltage ranging from 1.8–2.1 V when used as a cathode intercalated with a Ca ion. The highest voltage occurs when the chalcogen is composed of a S atom. Later, chalcogen tuning is explored as a method of optimizing electrochemical properties to suit MVIBs. Several Chevrel phase hybrids, Mo6S8-ySey, where y = 0–8, are explored in order to identify the composition that will best strike a balance between a high voltage and good diffusion kinetics. Six MnO2 polymorphs are considered as cathodes for MVIBs; a voltage as high as 2.7 V is found when MnO2 is intercalated with a Ca ion. Layered TiSe2 is also considered and found to exhibit a voltage of 1.8 V when intercalated with a Ca ion. Counterintuitive trends for MVIB diffusion kinetics are found for layered TiSe2 cathodes.This work advocates for further materials studies for the advancement of beyond LIB materials. While MVIB research and development is in its infancy, computational materials studies can accelerate next-generation battery research and development.