Solvothermal Synthesis of Electrochemically Active Nanocrystalline Li-Ti-O Spinel
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Solvothermal Synthesis Of Electrochemically Active Nanocrystalline Li-Ti-O Spinel
Dina Fattakhova, Petr Krtil , J. Heyrovsky Institute of Physical Chemistry, Dolejskova 3, 18223 Prague, Czech Republic Valery Petrykin, Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori, 4259 Yokohama, Japan
ABSTRACT Nanocrystalline Li-Ti-O spinel samples were prepared by solvothermal reaction of TiO2 with lithium hydroxide in water and ethanol. The hydrothermal reaction proceeds at temperature higher than 130 °C. The reaction proceeds via dissolution-precipitation mechanism and its course is not sensitive to titanium dioxide polymorph used in the reaction. Product of the reaction in water has cubic rock salt type structure. It converts, however, to spinel if annealed to temperatures exceeding 250 °C. The re-crystallization is accompanied with water removal from the structure. Solvothermal reaction in ethanol leads directly to a product with spinel structure without need for annealing. Both products are active for Li insertion; theelectrochemical activity. The specific capacity ranges between 100 and 160 mAh/g depending on the annealing temperature. INTRODUCTION Nano-crystalline materials play an important role in design of new electrochemical energy related applications namely in development of new rechargeable batteries or photoelectrochemical cells. The use of nano-crystalline materials allows one to improve both the size and quality1,2 of the electrode-electrolyte interface as well as to shorten significantly the characteristic diffusion lengths. Nanocrystalline Ti(IV) based oxides, particularly TiO2 anatase and Li4Ti5O12 spinel make prospective materials for 2V lithium ion batteries. Solvothermal synthsis in Ti oxides chemistry is usually used to prepare large crystals of perovskites 3,4. The potential of the hydrothermal synthesis in preparation of nanocrystals was, on the other hand, also demonstrated on controlled growth of anatase nanocrystals in tetramethylammonium containing solutions at 190-270 °C 5. Li-Ti-O ternary phases are usually prepared by solid-state reaction at elevated temperatures. Hydrothermal synthesis of electrochemically active nanocrystalline Li-Ti-O ternary phases like e.g. Li4Ti5O12 spinel has not been reported. EXPERIMENTAL Nanocrystalline titanium dioxide (Bayer) was used as starting materials in syntheses. Parallel experiments were performed on anatase (PKP 5538) and mixture of anatase and rutile (1:3, P25 Bayer). All other chemicals in all experiments, i.e. LiOH and NaOH were obtained from Fluka. The water used in experiments was of Millipore MilliQ quality, used ethanol was of p.a. grade. V3.26.1
Reactions were carried out in poly(tetrafluoroethylene) (PTFE) - lined stainless steel autoclaves. The molar ratio of TiO2 and LiOH in reaction mixture ranged between 2:1 and 1:5; the pH of the reaction mixture was adjusted to 14 by addition of concentrated NaOH solution. Syntheses were performed at temperatures between 130-200°C for 2 - 24 hours. Products of the reacti
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