Lithium electronic environments in rechargeable battery electrodes

Materials Science

Hightower, Adrian ; Fultz, Brent T.

University:California Institute of Technology

Department:Engineering and Applied Science

关键词: Materials Science;   

Others  :  https://thesis.library.caltech.edu/6183/1/Hightower_a_2001.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

This work investigates the electronic environments of lithium in the electrodes of rechargeable batteries. The use of electron energy-loss spectroscopy (EELS) in conjunction with transmission electron microscopy (TEM) is a novel approach, which when coupled with conventional electrochemical experiments, yield a thorough picture ofthe electrode interior.Relatively few EELS experiments have been preformed on lithium compounds owing to their reactivity. Experimental techniques were established to minimize sample contamination and control electron beam damage to studied compounds. Lithium hydroxide was found to be the most common product of beam damaged lithium alloys. Under an intense electron beam, halogen atoms desorbed by radiolysis in lithium halides. EELS spectra from a number of standard lithium compounds were obtained in order to identify the variety of spectra encountered in lithium rechargeable battery electrodes. Lithium alloys all displayed characteristically broad Li K-edge spectra, consistent withtransitions to continuum states. Transitions to bound states were observed in the Li K and oxygen K-edge spectra of lithium oxides. Lithium halides were distinguished bytheir systematic chemical shift proportional to the anion electronegativity. Good agreement was found with measured lithium halide spectra and electron structure calculations using a selfconsistant multiscattering code.The specific electrode environments of LiC_6, LiCoO_2, and Li-SnO were investigated. Contrary to published XPS predictions, lithium in intercalated graphite was determined to be in more metallic than ionic. We present the first experimental evidence of charge compensation by oxygen ions in deintercalated LiCoO_2. Mossbauer studies on cycled Li-SnO reveal severely defective structures on an atomic scale.Metal hydride systems are presented in the appendices of this thesis. The mechanical alloying of immiscible Fe and Mg powders resulted in single-phase bcc alloys of less than 20 at% Mg. Kinetic studies on LaNi_(5-x)Sn_x alloys proved that the mass transfer of hydrogen through these alloys was not hindered with increasing Sn substitutions for Ni. Collaborations with Energizer© found LanNi_(4.7)Sn_(0.3) alloys to possess limited utility in rechargeable nickel-metal-hydride sealed-cell batteries.