Solution processing approaches for solid electrolytes and electrode materials
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Solution processing approaches for solid electrolytes and electrode materials Steven P. Simner, Pu-Wei Wu, and Bruce Dunn Department of Materials Science and Engineering, University of California – Los Angeles, Los Angeles, California 90095-1595 (Received 18 September 1997; accepted 5 January 1998)
Solution processing methods have been used to prepare a solid electrolyte, copper-doped bismuth vanadate, and several different lithium transition metal oxide cathode materials. Dense thin films of the bismuth vanadate were prepared by pyrolysis of metal organic precursors deposited on various oxide substrates. A high degree of crystal orientation was obtained using single crystal MgO substrates. The Pechini process was used to prepare powders of the different materials and a variety of results were obtained. The bismuth vanadate exhibited a second phase of BiVO4 while LiNiO2 and the LiCox Ni12x O2 solid solution require further efforts at obtaining the proper phase and stoichiometry. The LiCoO2 system formed readily and exhibited good electrochemical performance.
I. INTRODUCTION
Solution processing of inorganic materials has grown increasingly important because of the advantages offered for the synthesis and fabrication of advanced materials. Solution processing, often called “soft chemistry” or “chimie douce,” generally refers to several different approaches including co-precipitation, sol-gel processing, metal organic precursors, emulsions, citrate gel (or Pechini) methods, and hydrothermal techniques which enable one to prepare inorganic materials at substantially lower temperatures than traditional solid state reactions, often using aqueous-based, environmentally benign conditions.1,2 One reason for the increased interest in these synthetic methods is the recognition that solution processing provides a means of directly fabricating inorganic films, coatings, fibers, and even monolithic shapes without the need to use powders.3 The solution nature of the process offers molecular level mixing of constituents leading to excellent chemical homogeneity and composition control, particularly important features for multicomponent systems. Shorter diffusion distances for reactants lead to lower reaction temperatures for crystallization which, in turn, alleviate stoichiometry problems associated with volatilization of high vapor pressure components. The present paper concerns the application of solution processing methods to the electrochemical materials used as solid electrolytes and electrodes in fuel cells and batteries. While solution processing approaches have been well investigated for ceramic superconductors4 and ferroelectric materials,2 electrochemical materials have received far less attention. In some instances, the advantages of solution processing methods have been recognized; co-precipitation of Y2 O3 -stabilized ZrO2 is commercially available (Tosoh Corp.) and the Na1 ion 866
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 4, Apr 1998
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