Heike Gabrisch Assistant Professor – Materials Chemistry B.S., Technical University of Berlin 1988 Ph.D., Technical University of Berlin 1996 email: hgabrisc@uno.edu phone: (504) 280-1122 office: SC 2003

RA offered to students who are interested in learning about microstructural investigations by Transmission Electron Microscopy.	Postdoctoral position available

Research Interests We are interested in the investigation of intercalation compounds used as active material in rechargeable Li-ion batteries by transmission electron microscopy. Compared to other instruments the TEM provides a localized probe, which enables the correlation between chemistry, structure and morphology. Historically transmission electron microscopy has been successfully applied to the study of alloys used in structural components as well as for characterization of semi conductors. In recent years the advantages of TEM techniques are recognized in the battery field, which is reflected by the number of publications that include information obtained from TEM imaging and electron diffraction. The working principle of rechargeable Li-ion batteries is based on the shuttle of Li ions between both electrodes and the reversible intercalation of Li^+ into the lattice of the active material at both electrodes. During charge discharge cycling of the battery the chemical composition of the active material is constantly changed which is accompanied by crystallographic changes (expansion, change of symmetry) that limit the range of Li-concentrations used. A characteristic feature observed in rechargeable batteries is the decrease of stored capacity after a high number of charge-discharge cycles – usually attributed to the cathode. We aim at understanding the underlying processes that lead to the observed capacity fade by studying the lattice and defect structure of cathode material before and after cycling and aging. An example is the investigation of layered LiCoO2 after electrochemical cycling and ageing. In cycled and aged specimens we found substantial amounts of LiCoO2 with a structure of a cubic spinel, which is electrochemically less active than the starting material. The dark field image below from a specimen after aging in the charged state for 10 days at 70°C shows that the spinel formation starts at the particle surface and progresses inwards. The progressive transformation explains part of the capacity loss that is observed after long cycle life. Other materials studied in our group are compounds currently used (LiMn2O4) as well as materials that are considered for future applications in commercial applications (Li(Co0.33Ni0.33Mn0.33)O2 and LiFePO4). Our work involves collaborations with research groups where batteries are assembled and cycled. Here at UNO we focus on synthesis of model material that is manipulated chemically for systematic studies by TEM, XRD, SEM.

Dark field image of LiCoO2 aged 10 days at 70°C showing spinel formation at the particle surface. Selected Publications "Transmission Electron Microscope Studies of LiNi1/3Mn1/3Co1/3O2 before and after Long-Term Aging at 70^o C" Heike Gabrisch, Tanghong Yi, and Rachid Yazami, Electrochemical and Solid State Letters 11, A119, (2008) [pdf] "TEM Study of Fracturing in Spherical and Plate-like LiFePO4 Particles" Heike Gabrisch, J. Wilcox, and M.M. Doeff, Electrochemical and Solid State Letters 11, A25 (2008)[pdf] "CrystalStructure Studies of Thermally Aged LiCoO2 and LiMnO4 Cathodes" Heike Gabrisch, Yasunori Ozawa, and Rachid Yazami, Electrochimica Acta 52, 4, (2006) [pdf] "Carbon Surface Layers on a High-Rate LiFePO4" Heike Gabrisch, James D. Wilcox, and Marca M. Doeff Electrochemical and Solid-State Letters, 9, A360-363 (2006) [pdf] "Mechanism of electrochemical performance decay in LiCoO2 aged at high voltage" R. Yazami, Y. Ozawa, H.Gabrisch and B. Fultz Electrochimica Acta 50, (2-3), 385-390 (2004) [pdf] "The Hexagonal to Cubic Spinel Transformation in Lithiated Cobalt Oxide" H. Gabrisch, R. Yazami, and B. Fultz Journal of the Electrochemical Society , 151, (6), A891-A897 (2004) [pdf] "A Transmission Electron Microscopy Study of Cycled LiCoO2" H. Gabrisch, R. Yazami, B. Fultz, J. Power Sources, 119-121, 674-679, Sp. Iss. (June 2003) [pdf] "A new method for automated shape measurement of embedded nanoparticles" H. Gabrisch, G. Cong, B. Parvin, U. Dahmen Microscopy and Microanalysis , 90,13-15 (2002) "The Character of dislocations in LiCoO2" H. Gabrisch, R. Yazami, B. Fultz, Electrochemical and Solid State Letters , 5, (6) A111-A114 (2002) [pdf] "Equilibrium Shape and Interface Roughening of Small Liquid Pb Inclusions in Solid Al" H. Gabrisch, L. Kjeldgaard, E. Johnson and U. Dahmen, Acta Mater., 49, 20, 4259-4269 (2001) [pdf]