Chemistry Department Colloquium

ABSTRACT: Electricity has become a necessity in our technological world, thus the ability to store and dispense it on demand has become of the utmost importance for nearly every sector. Batteries, which convert chemical energy to electrical energy, are key to accomplishing this goal. Lithium-ion batteries (LIBs) have led to a technology revolution since their inception, as they have high energy and power density, excellent cycle life, and reliability. Nevertheless, recent research has focused on how to displace the widely commercialized chemistry used in traditional LIBs due to looming supply chain issues and the demands of new applications. This work begins with the targeted synthesis and electrode development of novel cathode materials that are environmentally friendly, low cost, and have favorable transport properties. In α-MnO2, the substitution of Mn with varying levels of V was investigated to prevent the structural distortion mechanism inherent in this material and enable higher capacity during battery operation. The synthetic substitution was successful and the mechanism for the improved capacity of high V-content materials was ascertained using electrochemical, microscopy, and synchrotron X-ray techniques. Additionally, modulation of electron/ion transport in electrodes was investigated using 3D porous electrodes formed entirely of as-prepared 1D-2D and 2D-2D MoS2+x-carbon heterostructures. The significantly improved capacity retention of the 2D-2D heterostructure system was attributed to the morphology, increased stability of the structure during cycling, and the homogeneous dispersion of the active and carbonaceous materials resulting in good electrical contact. Finally, although graphite remains the dominant anode material in LIBs, research has focused on creating composite electrodes that incorporate higher capacity materials, such as silicon. Implementation has been challenged by the significant Si volume changes during (de)lithiation and associated growth/regrowth of the solid electrolyte interface (SEI). Herein, fluorinated localized high concentration electrolytes (FLHCEs) were designed to stabilize the SEI. Si-graphite/NMC622 full pouch cells using FLHCEs delivered higher capacity and capacity retention compared to control cells with carbonate-based electrolyte after 100 cycles. Post-cycling X-ray photoelectron spectroscopy (XPS) indicated the FLHCEs formed a LiF rich SEI which contributed to stabilizing the Si-graphite electrode over extended cycling.