Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres

Journal Article · Sat Apr 15 00:00:00 EDT 2017 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2017.01.015· OSTI ID:22658234

Ludwig, Jennifer ^[1]; Nordlund, Dennis ^[2]; Doeff, Marca M. ^[3]; Nilges, Tom ^[1]

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1. Technical University of Munich, Department of Chemistry, Synthesis and Characterization of Innovative Materials, Lichtenbergstr. 4, 85747 Garching (Germany)
2. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Rd, Menlo Park, CA 94025 (United States)
3. Lawrence Berkeley National Laboratory, Environmental Energy Technologies Division, 1 Cyclotron Rd, Berkeley, CA 94720 (United States)

The majority of research activities on LiCoPO{sub 4} are focused on the phospho-olivine (space group Pnma), which is a promising high-voltage cathode material for Li-ion batteries. In contrast, comparably little is known about its metastable Pna2{sub 1} modification. Herein, we present a comprehensive study on the structure–property relationships of 15–20 nm Pna2{sub 1}-LiCoPO{sub 4} nanospheres prepared by a simple microwave-assisted solvothermal process. Unlike previous reports, the results indicate that the compound is non-stoichiometric and shows cation-mixing with Co ions on the Li sites, which provides an explanation for the poor electrochemical performance. Co L{sub 2,3}-edge X-ray absorption spectroscopic data confirm the local tetrahedral symmetry of Co{sup 2+}. Comprehensive studies on the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and in situ powder X-ray diffraction show an exothermic phase transition to olivine Pnma-LiCoPO{sub 4} at 527 °C. The influence of the atmosphere and the particle size on the thermal stability is also investigated. - Graphical abstract: Blue nano-sized Pna2{sub 1}-LiCoPO{sub 4,} featuring tetrahedrally-coordinated Co{sup 2+}, was synthesized in a rapid one-step microwave-assisted solvothermal process. The phase relation between this metastable and the stable polymorph was analyzed and electrochemical properties are discussed. - Highlights: • Preparation of uniform 15–20 nm nanospheres of metastable Pna2{sub 1}-LiCoPO{sub 4} polymorph. • Structure redetermination shows cation-mixing (Co blocking Li sites). • In situ investigation of phase transformation to olivine Pnma-LiCoPO{sub 4} at 527 °C. • Pna2{sub 1}-LiCoPO{sub 4} reemerges as a stable high-temperature phase above 800 °C. • X-ray absorption spectroscopy confirms local tetrahedral symmetry (T{sub d} Co{sup 2+}).

• OSTI ID: 22658234
• Journal Information: Journal of Solid State Chemistry, Vol. 248; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
77 NANOSCIENCE AND NANOTECHNOLOGY
ABSORPTION SPECTROSCOPY
COBALT IONS
EXPERIMENTAL DATA
HYDROTHERMAL SYNTHESIS
INFRARED SPECTRA
LITHIUM ION BATTERIES
NANOSTRUCTURES
ORTHORHOMBIC LATTICES
PARTICLE SIZE
TEMPERATURE RANGE 0400-1000 K
THERMAL GRAVIMETRIC ANALYSIS
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY