Interfaces, interphases, and other material interactions in lithium ion batteries
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Performance and long-term cycle stability of composite battery electrodes depends on interactions of active materials with electrolyte, binders and conductive additives. This thesis investigates how such interactions affect the performance of Li-ion battery electrodes using state of the art characterization techniques. First, X-ray Photoelectron Spectroscopy (XPS) was used to analyze the solid electrolyte interphase (SEI) layer in commercial and novel Li-ion battery chemistries. Ar+ ion etching was investigated as a method of measuring the thickness of the SEI, and compared with Secondary Ion Mass Spectroscopy (SIMS) and Focus Ion Beam (FIB) etching. The chemistry of the SEI decomposition was also analyzed via the chemical shifts in the detailed XPS spectra. A similar analysis was also performed on a new electrolyte chemistry for Li-S cells. Next, phosphorus-carbon (P-C) composite anodes were synthesized and systematically investigated. In particular, the chemical and mechanical interactions between the conductive carbon additives, binders, P-C composite, and solvents in electrolyte and slurry were investigated. Selected binders showed superior performance on the basis of strength, hardness and adhesion. In addition, complete removal of n-methyl-2-pyrrolidone (NMP) solvent from the electrodes were found to be critical for stability improvements.