Crystal Growth and Neutron Diffraction Studies of LiCoO2 Bulk Single Crystals

Uthayakumar Sivaperumal 1Manoj S. Pandiyan 1Daniel Porter 1Matthias J. Gutmann 2Jon Goff 1

1. Royal Holloway University of London (RHUL), Egham Hill, Egham TW200EX, United Kingdom
2. Science and technology facilities council, Rutherford Appleton laboratory, Didcot OX110QX, United Kingdom

Abstract

There has been a renaissance of research on alternative energy sources to decrease global warming and environmental pollution. Hence energy generation and energy storage are two of the biggest challenges facing modern science. Lithium ion batteries are considered to be one of the most attractive technologies in recent years due to its high energy density and long service life. Such high performance batteries based on the movement of Li+ ions in layered transition metal oxides such as LiCoO2 have made a revolution possible in the technology industry in products from iPods to mobile phones. These materials are already used extensively in commercial applications, but until now it has not been possible to study their basic properties using single crystal neutron scattering. To develop this pollution free system further, it is imperative to understand the growth-structure interrelationship to shed light on material properties such as the electro chemical properties, capacity loss and cyclability.

Material synthesis is a key component in the discovery and design of energy related research. The most common method of preparing LixCoO2 is by solid state reaction method. However the results obtained from polycrystalline samples lead to scattered results due to irregular morphology, grain boundaries or impurities. An alternative, the slow cooling technique, leads to particle coarsening and evaporation of lithium species. This in turn significantly hampers the electrochemical properties. To solve these issues we employed the optical floating-zone technique (FZ-T-10000-H-VI-VPO-PC, Crystal System) and found that this favours improved morphological and chemical reactivity compared to slow cooling and the solid state reaction techniques.

The as-grown crystals were subjected to various characterizations. Fundamental understanding with regard to melt processing is essential for optimizing processing conditions. Hence, DTA–TGA analysis was made to optimize the thermal profile for the growth. The surface morphology was analysed by scanning electron microscope. Using a SQUID, magnetic measurements were performed in a field of 1Tesla in both the H || C and H ⊥ C configurations. A transition was observed at 10K. Analysis of small (<0.5mm) crystals using single crystal x-ray diffraction at RHUL indicate the high crystalline quality of the growth. A much larger boule was screened using neutron diffraction in SXD at ISIS. SXD combines the white beam Laue technique with area detectors covering a solid-angle of 2π steradians, allowing comprehensive surveys of 3D volumes of reciprocal space. We were able to cleave large samples (>1 cm) with sharp Bragg reflections from a single grain. The structure refined in the space group R3- m with an Rw-factor of 7.96 %. It was possible to accurately determine the Li concentration.  This is the first time that it has been possible to grow a large high quality single crystal of LixCoO2, allowing further measurements that require large single crystals, such as studies of diffusion using neutron scattering. The results and growth procedures will be presented in detail.

 

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Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Uthayakumar Sivaperumal
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-03-28 15:18
Revised:   2013-07-19 00:38