<p>As the future of energy looks increasingly electrified, the development of safe and sustainable battery technologies has never been more relevant. This is particularly critical for applications in stationary energy storage and transportation, where batteries must be produced and stored at large scale. Sustainability is necessary to meet the volume of demand at reasonable cost without straining resources. Safety is also paramount since fires can easily spread from one cell to the next and result in catastrophe when batteries are stored in proximity for large power banks or EVs. The focus of this thesis is thus to design and engineer materials for rechargeable batteries, which improve safety and sustainability while still enhancing the electrochemical performance. Towards this end, polymers play a central role throughout this thesis work due to their tunable chemical and physical properties.</p>

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While Li-ion batteries (LIBs) are the prevailing electrochemical energy storage technology, development of batteries using earth abundant alkali metals (e.g., Na and K) is necessary to alleviate LIB supply chain concerns. K-ion batteries (KIBs) offer a compelling advantage over Na via their compatibility with commercialized graphite anodes, and therefore may be more readily adopted within existing battery production lines. K-ions present some inherent advantages as well, such as rapid diffusion and low energy barriers to desolvation in the battery electrolyte that may enable fast charging. Presently, research on KIBs is in early stages and it is unclear if the same battery design principles produced by decades of study on LIBs apply to KIBs. Here, I examine structure-performance relationships in KIB anodes and electrolytes to propose broad design rules. In the first chapter, I summarize the motivations and prominent advancements in materials used for KIBs, providing commentary on the direction of the field. I begin by summarizing present concerns over materials criticality facing LIBs and how KIBs address these concerns but do not necessarily achieve lower costs. I continue with a summary of popular materials choices for KIB anodes, cathodes, and electrolytes. I place particular emphasis on the discovery and development of graphite anodes and the advantages of using a weak Lewis acid such as K-ions in batteries. Finally, I discuss the challenges presented by using highly reactive K metal anodes in research. In the second chapter, I examine the mechanisms of potassiation/depotassiation of two high-capacity tin phosphide anodes, Sn₄P₃ and SnP₃, and discuss possible failure modes. Ex situ 31P and 119Sn solid-state nuclear magnetic resonance (NMR) analyses reveal that both Sn₄P₃ and SnP₃ exhibit phase separation of elemental P and the formation of KSnP-type environments (which are predicted to be stable based on DFT calculations) during potassiation, while only Sn₄P₃ produces metallic Sn as a byproduct. In both anode materials, K reacts with elemental P to form K-rich compounds containing isolated P sites that resemble K₃P, but K does not alloy with Sn during potassiation of Sn₄P₃. During charge, K is only fully removed from the K3P-type structures, suggesting that the formation of ternary regions in the anode and phase separation contribute to capacity loss upon reaction of K with tin phosphides. The third chapter addresses the use of fluorinated electrolyte additives in KIBs. Fluoroethylene carbonate (FEC) is a well-known additive used in Li-ion electrolytes, because the products of its sacrificial decomposition aid in forming a stable solid electrolyte interphase (SEI) on the anode surface. Here, we show that FEC addition to KIBs containing hard carbon anodes results in a dramatic decrease in capacity and cell failure. Using a combination of 19F solid-state NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), we show that FEC decomposes during galvanostatic cycling to form insoluble KF and K₂CO₃ on the anode surface, which correlates with increased interfacial resistance in the cell. Our results strongly suggest KIB performance is sensitive to accumulation of an inorganic SEI, likely due to poor K transport in these compounds. The fourth chapter presents a nonflammable electrolyte mixture for use in KIBs. In this report, we show that a low-concentration (1 M) KPF6 electrolyte combining ethylene carbonate (EC), propylene carbonate (PC), and triethyl phosphate (TEP) is nonflammable, retains high ionic conductivity, and is compatible with graphite. Notably, we then show that this electrolyte is only usable in KIBs; the analogous Li electrolyte fails immediately due to the incompatibility of Li, PC, and graphite. We continue the study by characterizing the impact of TEP on the graphite interphase using a combination of EIS, XPS, and 1D and 2D NMR spectroscopy. We show that, compared to using EC/PC alone, the addition of TEP reduces resistance of the SEI layer, lessens reductive decomposition of carbonates to soluble organic species, and produces inorganic phosphate salts (that we posit contribute to passivation in lieu of fluorination in the SEI). The fifth chapter concludes by summarizing the design strategies learned in each of the preceding three chapters and makes recommendations for future studies. The proposed research emphasizes the need for fundamental studies on materials properties in KIBs, contradicting the current push towards optimizing capacity and longevity of KIBs to prove their relevance. Doing so will not only inform how to design high-performance batteries, but potentially uncover distinct advantages of KIBs that complement existing LIB technologies.

Computational methods, including homology modelling, in-silico dockings, and molecular dynamics simulations have been used to study the functional dynamics and interactions of K⁺ channels. Molecular models were built of the inwardly rectifying K⁺ channel Kir2.2, the bacterial homolog K⁺ channel KirBac3.1, and the twin pore (K2P) K⁺ channels TREK-1 and TRESK. To investigate the electrostatic energy profile of K⁺ permeating through these homology models, continuum electrostatic calculations were performed. The primary mechanism of KirBac3.1 gating is believed to involve an opening at the helix bundle crossing (HBC). However, simulations of Kir channels have not yet revealed opening at the HBC. Here, in simulations of the new KirBac3.1-S129R X-ray crystal structure, in which the HBC was trapped open by the S129R mutation in the inner pore-lining helix (TM2), the HBC was found to exhibit considerable mobility. In a simulation of the new KirBac3.1-S129R-S205L double mutant structure, if the S129R and the S205L mutations were converted back to the wild-type serine, the HBC would close faster than in the simulations of the KirBac3.1-S129R single mutant structure. The double mutant structure KirBac3.1-S129R-S205L therefore likely represents a higher-energy state than the single mutant KirBac3.1-S129R structure, and these simulations indicate a staged pathway of gating in KirBac channels. Molecular modelling and MD simulations of the Kir2.2 channel structure demonstrated that the HBC would tend to open if the C-linker between the transmembrane and cytoplasmic domain was modelled helical. The electrostatic energy barrier for K⁺ permeation at the helix bundle crossing was found to be sensitive to subtle structural changes in the C-linker. Charge neutralization or charge reversal of the PIP2-binding residue R186 on the C-linker decreased the electrostatic barrier for K⁺ permeation through the HBC, suggesting an electrostatic contribution to the PIP2-dependent gating mechanism. Multi-scale simulations determined the PIP2 binding site in Kir2.2, in good agreement with crystallographic predictions. A TREK-1 homology model was built, based on the TRAAK structure. Two PIP2 binding sites were found in this TREK-1 model, at the C-terminal end, in line with existing functional data, and between transmembrane helices TM2 and TM3. The TM2-TM3 site is in reasonably good agreement with electron density attributed to an acyl tail in a recently deposited TREK-2 structure.

Over the last few decades, computer simulation techniques have been established as an essential tool for understanding biochemical processes. This thesis deals mainly with the application of free energy calculations to ribosomal complexes and a cardiac ion channel. The linear interaction energy (LIE) method is used to explore the energetic properties of the essential process of codon–anticodon recognition on the ribosome. The calculations show the structural and energetic consequences and effects of first, second, and third position mismatches in the ribosomal decoding center. Recognition of stop codons by ribosomal termination complexes is fundamentally different from sense codon recognition. Free energy perturbation simulations are used to study the detailed energetics of stop codon recognition by the bacterial ribosomal release factors RF1 and RF2. The calculations explain the vastly different responses to third codon position A to G substitutions by RF1 and RF2. Also, previously unknown highly specific water interactions are identified. The GGQ loop of ribosomal RFs is essential for its hydrolytic activity and contains a universally methylated glutamine residue. The structural effect of this methylation is investigated. The results strongly suggest that the methylation has no effect on the intrinsic conformation of the GGQ loop, and, thus, that its sole purpose is to enhance interactions in the ribosomal termination complex. A first microscopic, atomic level, analysis of blocker binding to the pharmaceutically interesting potassium ion channel Kv1.5 is presented. A previously unknown uniform binding mode is identified, and experimental binding data is accurately reproduced. Furthermore, problems associated with pharmacophore models based on minimized gas phase ligand conformations are highlighted. Generalized Born and Poisson–Boltzmann continuum models are incorporated into the LIE method to enable implicit treatment of solvent, in an effort to improve speed and convergence. The methods are evaluated and validated using a set of plasmepsin II inhibitors.

Constructing dual-ion energy storage devices using anion-intercalation graphite cathodes offers the unique opportunity to simultaneously achieve high energy density and output power density. However, a critical challenge remains in the lack of proper anodes that match with graphite cathodes, particularly in sustainable electrolyte systems using abundant potassium. Here, a surface grafting approach utilizing multifunctional azobenzene sulfonic acid is reported, which transforms V2C MXene into a high-kinetics K+-intercalation anode (denoted ASA-V2C) for dual-ion energy storage devices. Importantly, the grafted azobenzene sulfonic acid offers extra K+-storage centers and fast K+-hopping sites, while concurrently acting as a buffer between V2C layers to mitigate the structural distortion during K+ intercalation/de-intercalation. These functionalities enable the V2C electrode with significantly enhanced specific capacity (173.9 mAh g−1 vs 121.5 mAh g−1 at 0.05 A g−1), rate capability (43.1% vs 12.0% at 20 A g−1), and cycling stability (80.3% vs 45.2% after 900 cycles at 0.05 A g−1). When coupled with an anion-intercalation graphite cathode, the ASA-V2C anode demonstrates its potential in a dual-ion energy storage device. Notably, the device depicts a maximum energy density of 175 Wh kg−1 and a supercapacitor-comparable power density of 6.5 kW kg−1, outperforming recently reported Li+-, Na+-, and K+-based dual-ion devices.