Developing the Polarizable Force Field: Focus on Amino Acid Residues

Polarizable force field has been successfully used in molecular modeling for years, especially in biological and protein simulations. In this research thesis, development of a new polarizable force field ―POSSIM (POlarizable Simulations with Second order Interaction Model) involving electrostatic polarization is described and parameters for several protein residues were produced. In this research thesis, the POSSIM force field was extended to the side chains of the following residues: lysine, glutamic acid, prontonated hisidine, phenylalanine and tryptophan. This work involved producing parameters for methyl ammonium, acetate ion, imidazolium cation, benzene and pyrrole molecules. The parameters fitting procedure starts from the molecular complex with dipolar electrostatic probes of a many-body system to produce polarizabilities, compute the energies, then charges and Lennard-Jones parameters are produced by fitting to gas-phase dimerization calculations, followed by the torsional parameters fitting and end up with the pure liquid simulations. In all the cases, three-body energies, dimerization energies and distances agree well to the accurate quantum mechanical results. The final parameters obtained assured the error of less than 2% in the heat of vaporization and average volume results compared with the available experimental data. Unlike the quantum mechanical calculations, the polarizable force field computations require a relatively small amount of computational resources. Moreover, compared to fixed-charges empirical force fields, polarizable force fields are much more accurate in a number of energy calculations. In the following chapters, the results obtained with this particular polarizable force field are discussed

Synthesis and Impurity Study of High Performance LiNixMnyCozO2 Cathode Materials from Lithium Ion Battery Recovery Stream

A ¡°mixed cathodes¡± LIB recycling process was first proposed and developed in the CR3 center at Worcester Polytechnic Institute. This process can efficiently and economically recover all the valuable metal elements in LIB waste. In the end of the recovery process, lithium, nickel, manganese, and cobalt ions will be recovered in the leaching solution. The objective of this work is to utilize the leaching solution to synthesis NixMnyCoz(OH)2 precursors and their corresponding LiNixMnyCozO2 cathode materials. The synthesized cathode materials can be used to build new LIBs, allowing the overall process to be a ¡°closed loop¡±

Porous TiO₂/C Nanocomposite Shells As a High-Performance Anode Material for Lithium-Ion Batteries

Porous TiO₂/C nanocomposite shells with high capacity, excellent cycle stability, and rate performance have been prepared. The synthesis involves coating colloidal TiO₂ nanoshells with a resorcinol-formaldehyde (RF) layer with controllable thickness through a sol–gel-like process, and calcining the composites at 700 °C in an inert atmosphere to induce crystallization from amorphous TiO₂ to anatase and simultaneous carbonization from RF to carbon. The cross-linked RF polymer contributes to the high stability of the shell morphology and the porous nature of the shells. A strong dependence of the capacity on the amount of incorporated carbon has been revealed, allowing the optimization of the electrode structure for high-rate cell performance