Browsing by Author "Palakkathodi Kammampata, Sanoop"

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    Development of Li-based Garnet Electrolytes for All-Solid-State Li Batteries
    (2021-04-26) Palakkathodi Kammampata, Sanoop; Thangadurai, Venkataraman; Marriott, Robert A; Trudel, Simon; Cheng, Yufeng; Kleinke, Holger
    All-solid-state Li batteries employing a ceramic solid electrolyte are considered as the nextgeneration energy storage devices due to their advantages in safety and potentially high energydensity. Garnet-type Li6.5La3-xAxZr1.5-xTax+0.5O12 (A = Ca, Sr, Ba; x = 0, 0.1, 0.3, 0.5) solidelectrolytes were prepared by conventional solid-state synthesis and spark plasma synthesis (SPS).The effect of doping of alkaline earth metals and sintering methods on the structural andelectrochemical properties of the solid electrolytes were investigated in this thesis. Powder X-raydiffraction (PXRD) studies have confirmed the cubic garnet-type structure of the solid electrolytes.Microstructure of the solid electrolytes were analysed by scanning electron microscopy (SEM).The samples prepared by SPS process exhibited higher density than the samples prepared byconventional solid-state route. The AC electrochemical impedance spectroscopy (EIS) was usedto measure the impedance of solid electrolytes. All garnet electrolytes prepared in this thesisshowed bulk conductivity in the range of 10-4 S/cm. Among the alkaline earth metal-doped solidelectrolytes, x = 0.1 (Ca and Sr) members prepared by SPS route showed highest conductivity atroom temperature (4.8 x 10-4 S/cm). Li6.5La2.9Sr0.1Zr1.4Ta0.6O12 prepared by SPS process showedan excellent Li-ion charge transfer resistance of 3.5 ? cm2 at 25 °C and the highest critical currentdensity of 0.6 mA/cm2 among all other samples.X-ray photoelectron spectroscopy (XPS) analyses were conducted on SPS-processedLi6.5La3-xAxZr1.5-xTax+0.5O12 (A = Ca, Sr, Ba; x = 0, 0.1) garnet electrolytes to quantify the impuritylayers on garnet surface. XPS analyses revealed that the surface of these electrolytes is covered byLiOH and Li2CO3-based compounds with a thickness of 4?6 nm within 30 minutes as a result ofthe reaction with traces of H2O and CO2 in an Ar-filled glovebox. Chemical compatibility ofLi7La2.75Ca0.25Zr1.75Ta0.25O12 (LLCZT) with commercial cathode materials and liquid Li-ion electrolytes (LLEs) was investigated using PXRD, SEM and EIS analysis. Hybrid cell consistingof Li metal, LLEs, LLCZT and LiNi0.8Co0.15Al0.05O2 or LiNi0.6Mn0.2Co0.2O2 cathode wereassembled in a coin cell and electrochemical performance was evaluated.
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    ItemOpen Access
    Porous Yttria-Stabilized Zirconia Microstructures for SOFC Anode Fabrication
    (2014-08-05) Palakkathodi Kammampata, Sanoop; Birss, Viola
    Solid oxide fuel cells (SOFCs) are electrochemical devices that convert fuels, such as hydrogen and natural gas, to electricity at high efficiencies, e.g., up to 90 %. SOFCs are emerging as a key technology for energy production that also minimize greenhouse gas emissions compared to conventional thermal power generation. SOFCs, which are normally based on nickel-yttria stabilized zirconia (YSZ) anodes, undergo degradation with time due to their high operating temperatures and their susceptibility to damage due to anode oxidation (redox cycling) and poisoning. Ni infiltration into porous YSZ scaffolds is considered to be a promising approach for overcoming some of these problems and enhancing their redox tolerance. However, long-term instability of the morphology of these types of anodes is an important problem. The focus of this thesis was therefore to develop methods to form porous YSZ scaffolds and attempt to construct stable Ni-YSZ anodes with reasonable electrochemical performance by infiltration. In this work, the issue of long-term instability was considered to originate from both the porous YSZ scaffold microstructure and the Ni infiltration precursor employed. To study this more closely, two different porous YSZ scaffold microstructures were developed by using tape casting, followed by Ni infiltration using a polymeric precursor, known to form a continuous Ni phase, rather than electrically separated Ni particles. Ni infiltration into porous YSZ scaffolds with large grains (0.5 µm) and large pores (two types of pores: ~0.5 µm and 5 µm) resulted in extensive Ni particle growth that resulted in poor stability and poor electrochemical performance (0.5 Ω cm2 per electrode at 800 °C). Ni infiltration into a scaffold having finer grains and pores (~200 nm each) resulted in anodes with a much lower polarization resistance of 0.11 Ω cm2 per electrode at 800 °C, increasing by ~ 5 % after 108 hours at this temperature.