Chemical and Biomolecular Engineering Theses and Dissertations

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    TOBACCO MOSAIC VIRUS BASED THREE DIMENSIONAL ANODES FOR LITHIUM ION BATTERIES
    (2011) Chen, Xilin; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Silicon and tin are promising anodic materials with both the high gravimetric and volumetric capacities for the next generation lithium-ion batteries. To prevent silicon or tin electrodes from a structure failure due to the volume change during lithiation and delithiation, a genetically modified Tobacco mosaic virus (TMV1cys) template is used to fabricate a 3D current collector for the silicon or tin electrode. The 3D current collector can effectively enhance the stabilities of the silicon or tin anodes. The TMV1cys particle can vertically self assemble onto the metal (i.e. Au, Ni, Fe) surfaces in a buffer solution ( PH=7 ). The abundant cysteine-derived thiol groups on the outer surface of the TMV1cys particle can react with metals to form near-covalent bonds. Thus it is very simple to form a 3D current collector by reducing metal such as nickel onto the TMV1cys surface by an electroless metal deposition. The 3D structure increases the electrode surface area by 10-fold. In order to investigate the effect of the 3D structure on the silicon anode, a physical vapor deposition methodology is used to deposit silicon onto the 3D current collector to form a nickel-silicon core-shell nano-rod anode. The abundant free spaces in the electrode accommodate the volume change during cycling and thus the cycleability of the silicon anode is greatly enhanced. The retention capacity at 1C is more than 1100 mAh/g after 340 cycles. Furthermore, a simple electrodeposition method is used to replace the complex physical vapor deposition methodology to make a uniform silicon deposition on the 3D current collector. The electrodeposition methodology is also used to prepare a tin anode. The electrodeposited silicon anode has comparable performance to those silicon anodes prepared by the physical vapor deposition technique. In order to enhance the electrochemical kinetics in silicon anode, the phosphorus doped n-type silicon is used to replace the pure silicon for preparing a high-rate-performance 3D silicon anode. Since the electrochemical reactions take place on the interface between the silicon and the electrolyte, the n-type silicon provides a quicker diffusion path for the involved electrons. The rate capability of the silicon anode has been increased and the capacity difference enlarges with the increasing current density.
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    NEW ELECTROLYTE AND ELECTRODE MATERIALS FOR USE IN LITHIUM- ION BATTERIES
    (2010) Basrur, Veidhes; Raghavan, Srinivasa; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Lithium-ion batteries have emerged as the preferred type of rechargeable batteries, but there is a need to improve the performance of the electrolytes and electrodes therein. Here, we report studies on new electrolyte and anode materials for use in such batteries. First, we report a class of gel electrolytes prepared by utilizing the synergistic interactions between a molecular gelator, 1,3:2,4-di-O-methylbenzylidene-D-sorbitol (MDBS), and a nanoscale particulate material, fumed silica (FS). When MDBS and FS are combined in a liquid electrolyte of propylene carbonate and lithium perchlorate, the liquid is converted into a free-standing gel due to the formation of a strong MDBS-FS network. The gel exhibits an elastic shear modulus ~ 1000 kPa and a yield stress around 15 kPa - both values far exceed those obtainable by MDBS or FS alone in the same liquid. The electrolyte also shows high conductivity (~ 5 x 10-3 S/cm), a wide electrochemical stability window (up to 4.5 V), and good interfacial stability with lithium electrode. In the second study, we describe a new polymeric binder [(poly(acrylamide-co-acrylic acid)] for use in conjunction with silicon (Si) anodes. This binder was combined with Si particles to form composite anode materials, which were then subjected to galvanostatic charge-discharge tests. Capacities exceeding 1000 mAh/g after 120 cycles have been obtained depending on the molecular weight of the binder and the concentration of the Si particles. The above binder thus presents a viable alternative to carboxymethyl cellulose (CMC), which is the current benchmark binder material for Si anodes.