Li Batteries

We are working on solid block copolymers and glass-polymer composites that selectively transport lithium ions. These materials are used to build all-solid rechargeable lithium batteries. We use characterization techniques such as AC impedance, NMR, electron microscopy, X-ray absorption and scattering, and hard X-ray microtomography. These tools allow us to understand the morphology, ion transport properties, and failure mechanisms of the electrolyte.

Electrolyte Morphology

Block copolymers can be used as electrolytes for next generation batteries due to their ability to decouple material properties. One of the block copolymers we study is polystyrene-block-poly(ethylene oxide) where polystyrene lends mechanical support to the ion conducting abilities of poly(ethylene oxide). In order to make these materials ionically conductive, we dissolve a lithium salt into them. We study the effect of salt on the phase behavior of block copolymer electrolytes. As salt concentration, r, increases, block copolymers microphase separate due to an increase in thermodynamic repulsion, quantified by χeff, between the two polymer constituents. At low values of segregation, the interface between the phases is broad, and this broad interface is depicted by a purple band in the schematics. Interfacial thickness becomes negligible at large values of segregation. We use X-ray scattering techniques to determine the morphology of the microphase separated systems and quantify the thermodynamics by measuring χeff.

Ion Transport Properties

Ion transport in a binary electrolyte is characterized by three transport parameters: conductivity (κ), cation transference number (𝑡+0), and the salt diffusion coefficient (D). When these three parameters are known for an electrolyte as a function of salt concentration, ion transport can be modeled to make useful predictions such as the salt concentration as a function of distance between the electrodes (shown left), the voltage drop across the cell at a particular current density, or the maximum current density that can be passed through the cell. Our lab measures κ, 𝑡+0, and D for a variety of polymer electrolytes in order to develop a complete model of ion transport. In addition, we are interested in using various spectroscopic techniques (FTIR, Raman, NMR, XPS, SAXS/WAXS, etc.) to connect molecular scale interactions to the bulk transport properties we observe.

NMR Characterization

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for elucidating nanoscale molecular environments and properties. We use pulsed-field gradient (PFG) NMR to characterize diffusion within polymer electrolytes. The nuclear specificity of NMR allows the separate determination of diffusion coefficients, and, through electrophoretic NMR, electrochemical mobilities, of the cation, anion, and polymer chain. In addition, due to the sensitivity of peak splitting and chemical shifts to local environments, we can use NMR and solid-state NMR to learn about ion clustering, coordination, and polymer morphology.

Failure Analysis Using X-ray Microtomography

Solid block copolymer electrolytes are promising candidates for batteries with a lithium metal anode: a mechanically reinforcing stiff block is covalently bonded to a softer, ion-conducting block in order to realize an electrolyte that is both ionically conductive and stiff enough to resist the growth of lithium dendrites. We use X-ray microtomography and electrochemical techniques to study cells comprised of solid block copolymer electrolytes and lithium metal electrodes. These studies provide fundamental insight into ion transport through microstructured block copolymer electrolytes, as well as the mechanisms of nucleation, growth, and stripping of lithium metal protrusions.

Drug Capture

This project aims to reduce the side-effects of chemotherapy administration. We are designing and synthesizing polymer membranes for capturing doxorubicin, a drug used in the treatment of liver cancer. The drug is introduced at the artery feeding the liver, and our polymer is placed in the vein that receives blood exiting from the liver. The ideal polymer would capture all of the drug that exits the liver. The drug capturing polymer is introduced in the vein using minimally invasive surgical methods under the supervision of Dr. Steven Hetts (UCSF).

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