|
Professor Sandi has been at Argonne National Laboratory for over eight years and previously worked in industry. Her current interests focus on energy systems such as fuel cells and rechargeable batteries. Her recent research projects include:
Synthesis and Characterization of Carbon Anodes for Rechargeable Lithium Batteries
Carbon has shown to be an excellent candidate for negative electrodes because it can take the form of lithium intercalation compounds. Two important attributes of carbon compared to lithium metal are its stability to electrolyte decomposition and an increase in lithium diffusivity. The risk of dendrite penetration of the separators present in the lithium metal batteries is then eliminated.
One of the main objectives of our project is to design carbon electrodes with predictable porosity and surface area characteristics. The crystal structure of the carbon influences the intercalation of lithium within it, both in how much can be intercalated and at what voltage. Inorganic templates have been used for the synthesis of the carbons from polymeric precursors. After elimination of the matrix via pyrolysis and demineralization, the layered structured carbons showed holes due to the pillars where lithium diffusion can occur.
In Situ Small Angle Neutron and X-Ray Scattering Studies
In order to understand the structure-function relationship in carbons and polymer electrolytes, we have applied small angle neutron and X-ray scattering (SANS and SAXS) to obtain information on their microstructure in terms of the pore size, the geometric arrangement of the pores in the carbonaceous matrix, their accessibility to the solvent, and the structure-conductivity relationship in polymer. Small-angle scattering from either x-rays or neutrons arises due to the presence of discontinuities in the density in a material. Thus, the particles and pores in the carbons can produce strong small angle scattering signals from x-rays (SAXS) or neutrons (SANS) in a wide momentum-transfer (q = 4p sinq/l where 2q is the scattering angle and l is the wavelength of radiation) range. The small angle scattering data can be modeled to obtain information on the microstructure of the porous network.
Polymer Nanocomposites for Lithium Batteries and Fuel Cells
Improved safety over conventional liquid electrolytes provides a compelling rationale for use of polymer electrolytes in rechargeable lithium batteries, but these polymers often show insufficient conductivity or poor mechanical properties. The dual ion-conducting nature of most polymer electrolytes also poses problems. Cationic transference numbers are non-unity or even negative, indicating substantial transport by anionic complexes, particularly at high salt concentration. Concentration gradients caused by the mobility of both cations and anions in the electrolyte arise during cell operation, resulting in premature cell failure. This is a more severe problem than in liquid electrolytes because of the lower salt diffusion coefficients and the relative immobility of the polymer hosts.
The conductivities of lithium-containing polymer-clay nanocomposites are greatly enhanced over synthetic polymer single-ion conductors because only cations are mobile in these materials. Preparation is simpler, the films are self-supporting, and generally have excellent mechanical properties.
In our laboratories, we have prepared a series of nanocomposites containing PEO intercalated in the layers of synthetic lithium hectorite (SLH) clays. Isomorphous substitutions in the lattice of Li(I) for Mg (II) in the octahedral layers of hectorite cause an overall negative charge that is compensated by the presence of interlayer, or gallery, cations. | 