Sol-Gel Non-hydrolytic Synthesis of a Nanocomposite Electrolyte for Application in Lithium-ion Devices
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Sol-Gel Non-hydrolytic Synthesis of a Nanocomposite Electrolyte for Application in Lithium-ion Devices Flávio L. Souza 1* , Paulo R. Bueno 3 , Ronaldo C. Faria3 , Elson Longo 2 , and Edson R. Leite1,2 1
PPGCEM - Department of Materials Science and Engineering,
2
CMDMC - Department of Chemistry, Federal University of São Carlos,
C. Postal 676, 13565-905 - São Carlos, SP, Brazil. 3
FFCLRP - Department of Physics, University of São Paulo,
Av. Bandeirantes, 14.040-901 - Ribeirão Preto, SP, Brazil. ABSTRACT A new nanocomposite electrolyte was synthesized using a simple non-hydrolytic sol-gel route without specific treatment of the reagents. The nanocomposite ion conductor was prepared with citric acid, tetraethyl orthosilicate and ethylene glycol, forming polyester chains. The timeconsuming drying step that is a necessary part of most chemical syntheses was not required in the preparation of the present nanocomposite electrolyte of the polyelectrolyte class, because only Li+ is mobile in the polymeric chain. The effects of the concentration of Li, SiO 2 and SnO 2 nanoparticles were investigated in terms of Li+ ionic conductivity. Conductivity measurements as a function of the metal oxide nanocrystal content in the nanocomposite revealed a significant increase in conductivity at approximately 5 and 10 wt % of nanoparticles. The new nanocomposite conductor proved to be fully amorphous at room temperature, with a vitreous transition temperature of approximately 228K (-45°C). The material is solid and transparent, displaying an ionic conductivity of 10-
4
to 10-
5
(O.cm)-1 at room temperature presenting
excellent reproducibility of all these characteristics. Cyclic voltammetry measurements indicate that the hybrid electrolyte possesses outstanding electrochemical stability. INTRODUCTION Polymer electrolytes are expected to play an important role in the development of improved energy sources, which are required pursuant to the rapid development of cellular
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phones, book-type computers, and many personal digital assistants [1, 2, 3]. The classic polymer electrolytes are based on organic macromolecules mostly containing, in the backbone, poly(ethylene oxide) units that are doped with inorganic salts. It is well-established that conductivity in pure polymer electrolyte occurs in the amorphous phase, above the glass transition temperature, via a liquid-like motion of the cations associated with segmental reorientations of the neighboring chains [1, 4]. Because these electrolytes often contain crystalline regions, leading to low ionic conductivity at room temperature, much effort has focused on increasing the volume fraction of the amorphous domains to enhance conductivity. In this respect, considerable advance has been gained recently by designing new polymer electrolytes based on organic-inorganic hybrids or nanocomposite systems, among which silicabased materials hold a prominent place. These systems are called ORMOLYTEs (organically modified electrolytes) or ORMOCERs (organically modified ceramics)
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