Development of new hybrid silica-epoxy electrolytes for application in lithium-ion microbatteries

RAÚL A. PROCACCINI

Buenos Aires

Simposio; International Symposium - Challenges on lithium oxygen rechargeable batteries; 2012

INQUIMAE

Rechargeable lithium-ion batteries play a key role as efficient energy storage devices for electronic, computing, telecommunication equipment, and cellular phones, because of its high energy density. Besides, lithium batteries contribute to achieve important goals such as energy renewal and environmental control. This research field is expected to influence the storage of intermittent energy sources, e.g., solar or wind, as well as the powering of controlled emission, electric or hybrid vehicles. However to achieve these important goals, lithium ion batteries still require improvements especially in terms of reliability, safety and cost. Regarding this, a promising approach deals with variations in the configuration of the conventional liquid electrolyte. Traditionally, a liquid electrolyte including a lithium salt (most commonly LiPF6) and organic solvents is used in Li-ion batteries, either with a separator or as a component in a polymer gel. However, it is difficult to obtain conformal coatings of either the separator or the inert polymer gel component onto complex substrates, both at the nano- and micro-scale. To find a suitable, solid-state electrolyte is therefore crucial in many of the currently studied 3D-microbatteries approaches. Polymeric and inorganic solid electrolytes have been extensively investigated, but their major disadvantage is that the conductivity values achieved are too low compared to those of lithium salts in organic solutions. The suitable combination of inorganic and organic materials into hybrid nanostructured thin film electrolytes could result in an interesting combination of properties able to substitute the liquid electrolyte. Among the most important advantages are: amorphous at room temperature (causes comparatively higher conductivities, and provide higher mechanical and thermal stability than pure organic matrices), solid (no risk of leakage of electrolyte; increased safety), no separators needed, high-capacity, long-life, possibility of miniaturization. The main weakness still is the low ionic conductivity at room T: ~ 10-5 S/cm compared to that of a liquid electrolyte: ~ 10-2 S/cm. The present project involves the preparation and properties of a new silica-epoxy hybrid ionic conductor, using a sol-gel approach. Tetraethyl orthosilicate (TEOS), 3-glycidoxypropyl-trimethosysilane (GPTMS) and lithium acetate have been used as precursors. Optimization of the processing parameters leads to homogeneous coatings of several microns of thickness. No evidence of lithium agglomeration was observed through small angle X-ray spectroscopy (SAXS) performed with synchrotron light on coatings, while FT-IR characterization shows interactions between OH groups and Li-ion as shifts in ν O-H wavelength. Electrochemical impedance spectroscopy shows an increase in the ionic conductivity, reaching 10-5 S/cm at 120ºC. Also, additional characterization techniques, as microprobe Raman confocal analysis and grazing incidence X-ray diffraction spectroscopy were used to study the coatings as solid functional electrolytes.