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

Abstract

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 nanospheresmore » 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+}).« less

Authors:
 [1];  [2];  [3];  [1]
  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)
Publication Date:
OSTI Identifier:
22658234
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 248; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Ludwig, Jennifer, Nordlund, Dennis, Doeff, Marca M., and Nilges, Tom, E-mail: tom.nilges@lrz.tum.de. Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres. United States: N. p., 2017. Web. doi:10.1016/J.JSSC.2017.01.015.
Ludwig, Jennifer, Nordlund, Dennis, Doeff, Marca M., & Nilges, Tom, E-mail: tom.nilges@lrz.tum.de. Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres. United States. doi:10.1016/J.JSSC.2017.01.015.
Ludwig, Jennifer, Nordlund, Dennis, Doeff, Marca M., and Nilges, Tom, E-mail: tom.nilges@lrz.tum.de. Sat . "Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres". United States. doi:10.1016/J.JSSC.2017.01.015.
@article{osti_22658234,
title = {Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres},
author = {Ludwig, Jennifer and Nordlund, Dennis and Doeff, Marca M. and Nilges, Tom, E-mail: tom.nilges@lrz.tum.de},
abstractNote = {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+}).},
doi = {10.1016/J.JSSC.2017.01.015},
journal = {Journal of Solid State Chemistry},
number = ,
volume = 248,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2017},
month = {Sat Apr 15 00:00:00 EDT 2017}
}
  • While the majority of research activities on LiCoPO 4 is focussed on the thermodynamically stable olivine-type Pnma polymorph, the metastable Pna2 1 and Cmcm modifications have recently attracted considerable attention due to their interesting material properties. In this study, we present the first Li-deficient structural derivative of the Cmcm modification with the nominal composition Li 0.5–δCoPO 4. As opposed to the substoichiometric olivine ( Pnma) phases Li xCoPO 4 (x = 0; 2/3), which are exclusively accessible by electrochemical or chemical Li extraction techniques, this is also the first time that a direct soft-chemical synthesis route towards a Li xCoPOmore » 4-type material is accomplished. X-ray and neutron diffraction studies indicate that Cmcm-type Li 0.5–δCoPO 4 shows vacancies on both the Li and Co sites, whereas X-ray absorption spectra demonstrate that the structure features heterovalent Co ions (+2/+3) to compensate for the Li deficit. Magnetic measurements reveal a long-range antiferromagnetic order below 10.5 K. A thorough investigation of the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and temperature-dependent in situ X-ray powder diffraction demonstrates that Li 0.5–δCoPO 4 is metastable and exhibits a complex, multi-step thermal decomposition mechanism. In the first step at 394 °C, it decomposes to α-Co 2P 2O 7 ( P2 1/c) and LiCoPO 4 ( Cmcm) upon O 2 release. The LiCoPO 4 ( Cmcm) intermediate is then irreversibly transformed to olivine-type LiCoPO 4 (Pnma) at 686 °C. Furthermore, the material properties of Li 0.5–δCoPO 4 are further compared to the fully lithiated, isostructural LiCoPO 4 ( Cmcm) phase, for which an improved structure solution as well as Co L 2,3-edge X-ray absorption spectra are reported for the first time.« less
  • Highlights: Black-Right-Pointing-Pointer ZnFe{sub 2}O{sub 4}/{alpha}-Fe{sub 2}O{sub 3} composite hollow nanospheres were successfully synthesized via a facile method. Black-Right-Pointing-Pointer Detailed structural, morphology and the phase composition were studied. Black-Right-Pointing-Pointer The incorporation of ZnFe{sub 2}O{sub 4} and {alpha}-Fe{sub 2}O{sub 3} gives an appropriate band gap value to utilize solar energy. -- Abstract: ZnFe{sub 2}O{sub 4}/{alpha}-Fe{sub 2}O{sub 3} composite hollow nanospheres were successfully fabricated via a facile one-pot solvothermal method, utilizing polyethylene glycol as soft template. X-ray diffraction and scanning electron microscopy analysis revealed that the prepared nanospheres with cubic spinel and rhombohedra composite structure had a uniform diameter of about 370 nm,more » and the hollow structure could be further confirmed by transmission electron microscopy. Energy dispersive X-ray, X-ray photoelectron spectroscopy and Fourier transform infrared techniques were also applied to characterize the elemental composition and chemical bonds in the hollow nanospheres. The ZnFe{sub 2}O{sub 4}/{alpha}-Fe{sub 2}O{sub 3} composite hollow nanospheres show attractive light absorption property for potential applications in electronics, optics, and catalysis.« less
  • The chemistry of novel polyhedral borane derivatives has recently attracted new interest because of their potential application in the liposome-mediated boron neutron capture therapy (BNCT) of cancer. The [trans-B{sub 20}H{sub 18}]{sup 2{minus}} polyhedral borane anion has been found to be a versatile source for a variety of these boron-rich derivatives. The synthesis of the stereochemically unprecedented [cis-B{sub 20}H{sub 18}]{sup 2{minus}} and the ammonio-substituted anion [cis-B{sub 20}H{sub 17}NH{sub 3}]{sup {minus}} ([2]{sup {minus}}) has been reported. The two three-center two-electron bonds of [2]{sup {minus}} are electron deficient and susceptible to nucleophilic attack, and the reaction of [2]{sup {minus}} with hydroxide ion producedmore » disubstituted [{alpha}{sup 2}-B{sub 20}H{sub 16}NH{sub 3}(OH)]{sup 3{minus}}. A recent investigation of the reaction of [2]{sup {minus}} with liquid ammonia has led to the discovery of the diammonio-substituted anion, [{alpha}{sup 2}-B{sub 20}H{sub 16}(NH{sub 3}){sub 2}]{sup 2{minus}}. Subsequent aqueous ferric ion oxidation resulted in the neutral derivative, trans-B{sub 20}H{sub 16}(NH{sub 3}){sub 2}. They report here the syntheses and structures of the anion and the neutral compound.« less