Browsing by Author "Welty, Connor"

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Divergent Electrically Conductive Pathways in Yttrium-Based 2- and 3-Dimensional Metal–Organic Frameworks
(American Chemical Society, 2024-07) Welty, Connor; Gormley, Eoghan L.; Oppenheim, Julius J.; Dincă, Mircea; Hendon, Christopher H.; Stadie, Nicholas P.
Despite most porous framework solids exhibiting insulating character, some are known to conduct electrical charge. The peak performing conductive metal–organic frameworks are composed of redox-active hexasubstituted triphenylene linkers, but the impact of redox activity on material conductivity remains enigmatic because of limited availability of direct structure–function relationships. Here, we report a hexagonal yttrium-based conductive porous scaffold, comprising hexahydroxytriphenylene connected by Y-chains (YHOTP). In comparison to its known porous cubic counterpart (Y6HOTP2), this material features a 1000-fold increase in peak conductivity in polycrystalline samples (∼10–1 S cm–1). Furthermore, through a comparison of their electronic structures, we rationalize the origin of this difference and highlight the role of charge carrier concentration in dictating bulk electrical conductivity. Together, this work provides a design principle for the development of next-generation conductive porous frameworks.
Exploring the Limits of the Rapid-Charging Performance of Graphite as the Anode in Lithium-Ion Batteries
(The Electrochemical Society, 2022-01) Xu, Wei; Welty, Connor; Peterson, Margaret R.; Read, Jeffrey A.; Stadie, Nicholas P.
Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ∼2 C (∼740 mA g−1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4–20 C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8 C, even with a standard electrolyte and NMC811 cathode and in cells with 1.0 mAh cm−2 loadings. As a rule, capacity and specific energy are inversely proportional to crystallite size at high rates; performance can likely be improved by electrolyte/cathode tuning.
Methodological Studies of the Mechanism of Anion Insertion in Nanometer‐Sized Carbon Micropores
(Wiley, 2022-11) Welty, Connor; Taylor, Erin E.; Posey, Sadie; Vailati, Patric; Kravchyk, Kostiantyn V.; Kovalenko, Maksym V.; Stadie, Nicholas P.
Dual-ion hybrid capacitors (DIHCs) are a promising class of electrochemical energy storage devices intermediate between batteries and supercapacitors, exhibiting both high energy and power density, and generalizable across wide chemistries beyond lithium. In this study, a model carbon framework material with a periodic structure containing exclusively 1.2 nm width pores, zeolite-templated carbon (ZTC), was investigated as the positive electrode for the storage of a range of anions relevant to DIHC chemistries. Screening experiments were carried out across 21 electrolyte compositions within a common stable potential window of 3.0–4.0 V vs. Li/Li+ to determine trends in capacity as a function of anion and solvent properties. To achieve fast rate capability, a binary solvent balancing a high dielectric constant with a low viscosity and small molecular size was used; optimized full-cells based on LiPF6 in binary electrolyte exhibited 146 Wh kg−1 and >4000 W kg−1 energy and power densities, respectively.