Spinel-based materials have historically been one of the most promising frameworks for Li-ion cathodes since the discovery of LiMn2O4 in 1983. The material was first proposed due to the diamond network of face-shared unoccupied tetrahedral and octahedral sites in Mn2O4, which offers a three-dimensional pathway for Li-ion transport. Since then, much work has been spent on LiMn2O4 and its Ni-substituted derivative due to their use of Mn, which is more abundant and less expensive than the Co used in the layered-based Li-ion cathodes that dominate the portable electronic and electric vehicle industries. Furthermore, the three-dimensional Li-ion conduction pathway in spinel has made the spinel framework appealing for more applications than just Li-ion cathodes. Various spinel oxides and sulfides have been proposed as potential Mg-ion cathodes, and a low voltage Ti-based spinel has been proposed as a "zero-strain" Li-ion anode. The addition of spinel-like partial order has also been proposed to aid the voltage profile and Li transport in the disordered rock salt materials, which are a more recently-discovered class of high energy density Li-ion cathodes.

In this dissertation, I utilize first-principles techniques based on density functional theory calculations and cluster expansion methods to investigate intercalation in a number of promising spinel-based electrodes. In Chapter 1, I introduce in detail the spinel structure and the possible ways working ions can intercalate in the structure, as well as the techniques that will be used in the following studies.

In Chapter 2, I investigate the barriers to Mg intercalation into the spinel-MgxCr2O4 system. Using first-principles calculations in combination with a cluster expansion model and the nudged elastic band theory, I calculate the voltage curve for Mg insertion at room temperature and the activation barriers for Mg diffusion at varying Mg concentrations in the Cr2O4 structure. Our results identify a potential limitation to Mg intercalation in the form of stable Mg-vacancy orderings in the Cr2O4 lattice, which exhibit high migration barriers for Mg diffusion in addition to a steep voltage change. Additionally, we propose cation substitution as a potential mechanism that can be used to suppress the formation of stable Mg-vacancy orderings, which can eventually enable the practical usage of Cr2O4 as a Mg-ion cathode.

In Chapter 3, I delve into understanding the kinetics of Li transport in spinel Li4Ti5O12, which is a Li-ion anode exhibiting extraordinary rate capability. The rate capability of Li4Ti5O12 is especially surprising given its two-phase reaction and slow diffusion within the endmembers, in contrast to the typical fast-charging battery electrodes that are capable of accommodating lithium continuously via solid-solution transformation. Through real-time tracking of Li+ migration using operando electron energy-loss spectroscopy (EELS) combined with first-principles investigation of the Li configurations, their simulated EELS spectra, and Li migration barriers, it is revealed that the kinetic pathway that enables facile ionic transport in lithium titanate consists of distorted Li polyhedra in metastable intermediate states. This study highlights that the rate capability of fast-charging electrodes may not be controlled solely by the intrinsic ionic diffusivity of macroscopic phases, but also by transport via kinetically accessible low-energy landscapes. These findings may open new avenues for designing fast-charging electrodes.

In Chapter 4, I investigate the thermodynamic effects of disordering the spinel framework of LiMn2O4 towards understanding the partially disordered Li-excess spinels, a promising class of high energy density Li-ion cathodes with good discharge rate capability. To elucidate where in the partially disordered space the optimal materials lie, we investigate the configuration space of spinel with Mn disordered over the 16c and 16d sites. Using a cluster expansion in conjunction with Monte Carlo simulations, we find that disorder shortens the deleterious ~3V plateau between LiMn2O4 and Li2Mn2O4 by raising the energy landscape and stabilizing the motifs found in solid-solution configurations, and the plateau is completely removed with 25% Mn 16c occupancy. We expect partially disordered spinels with this level of disorder to exhibit both solid-solution behavior as well as good rate due to the remaining spinel character. We also identify Ti-doping and Li-excess as potential ways to facilitate 16c/16d disordering.

Audience: This small-group workshop is designed for pre-clinical medical students. The workshop can also be offered to other medical students looking to review first aid in the community setting.

Introduction: First aid training in medical students varies based on each student’s previous experience. Because of this, medical students in their pre-clinical years have expressed a desire for further training in first aid.1 While most bystanders in an emergency situation do not have a medical background, medical students have received additional training that can provide the skillset to process and respond to emergency situations in a different capacity. Most medical schools have not adopted a universal curriculum in teaching medical students first aid.2 Incorporating first aid into a medical school curriculum can enhance medical students’ confidence in emergent situations and lead to better outcomes for patients requiring immediate on-site care.

Educational Objectives: The goal of this workshop was to improve the confidence of medical students in handling emergencies in the community with the use of first aid while also giving them a standard approach to emergencies using an airway, breathing, and circulation approach. The curriculum was evaluated through student-perceived self-efficacy and confidence in handling the provided scenarios, performance on relevant multiple choice questions, and general appeal of the first aid sessions. By the end of this workshop, students will be able to define the goals of “first aid” and first responder actions, describe clinical signs and symptoms suggestive of an airway, breathing, or circulation emergency in the setting of selected medical emergencies, and demonstrate immediate care steps in the setting of selected medical emergencies, specifically the Heimlich maneuver on adults and infants, direct pressure, wound packing, tourniquet application for external bleeding, epinephrine auto-injector administration, and the recovery position for obtunded or unconscious patients.

Educational Methods: Small group activities were performed with a focus on case-based scenarios combined with hands-on instruction. The four scenarios were choking, seizure, anaphylaxis, and bleeding which were taught by an educator who was either faculty, an emergency medicine resident, or an upper-level medical student. Facilitators were provided an educational handout specific to their station to guide them through

the teaching session. A PowerPoint presentation was also provided complete with supporting images and videos to share with the students each session.

Research Methods: Students were asked to complete a pre-test and post-test survey to assess knowledge outcome, self-efficacy in first aid, and overall appeal of the workshop. The multiple-choice knowledge outcome data was scored for percent correct on each question as well as overall performance on questions grouped by content. Students were also asked to provide feedback and comments on their overall experience in the workshop.

Results: Overall, medical students reported increased knowledge and confidence in responding to various first-aid situations. There was overall improvement in pre-test and post-test evaluations. The appeal of the event as a whole and its usefulness was overwhelmingly viewed as positive. Some participants noted they wanted similar workshops with more first-aid topics. Participants also noted they felt better prepared to respond to the various emergencies included in the workshop.

Discussion: A workshop directed at teaching first aid to medical students increased their confidence and knowledge in responding to various emergencies and can successfully be accomplished through a focused large group didactic session and multiple clinically relevant small group teaching sessions.