Li Batteries with Porous Sol-Gel Cathodes
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0972-AA06-09
Li Batteries with Porous Sol-Gel Cathodes Antonela Dima1, Maurizio Casalino1, Francesco Della Corte1,2, and Ivo Rendina1 1 Institute for Microelectronics and Microsystems, Neaples, 80131, Italy 2 Università degli studi “Mediterranea”, Reggio Calabria, 89060, Italy ABSTRACT The structure presented is a high-capacity micro-battery, lithium based, consisting of porous cathode, solid electrolyte and silver anode. A spinel LiNi0.4La0.1Mn1.5O4 sol-gel layer was deposited on a porous ceramic substrate to give high specific surface to the chip-like microbatteries. The anode used was thermally evaporated Ag and the electrolyte a sol-gel hybrid Li4SiO4 layer. INTRODUCTION Amine et al. [1,2] report a 5V-cell with consistent high capacity for multiple cycles. The LiNi0.5Mn1.5O4 spinel-oxide used was prepared in sol-gel technology (with the first tests in the mid-1990’s). Lithium-Ion batteries deploy metal oxide materials such as LiCoO2, or tunneled structure materials such as LiMn2O4 as anodes [3] and typically graphitic carbon cathodes. During chargeup/discharge lithium ions are inserted/extracted from the interstitial space between atomic layers within the active material of the battery. During charge-up the positive material is oxidized and the negative material reduced, lithium ions being de-intercalated from the positive material and intercalated into the negative material (reversible removal/insertion into host without significant structural host change). Upon charging Li is oxidized at the cathode [4] Li → Li+ + e- and reduced at the anode Li+ + e- → Li. Sol–gel processing has been applied principally in lithium batteries to the solid electrolyte [4]. The electrolyte is critical for galvanic cells, as it transports ions back and forth between the cathode and anode. The electrolyte is required to have a wide electrochemical potential window and good stability during over/charge and over/discharge. Solid electrolytes are also rigid, holding the components of the cell fixed. Typically thin-film batteries are prepared by sputtering or evaporating cathode / electrolyte / anode films through a physical mask defining the battery components. The size of such components reaches down to 50×50 µm2, with thickness 250 nm and current capacities of 10 µAh/cm2. EXPERIMENTAL RESULTS We report the realization of a lithium micro-cell consisting of: Ag anode, solid electrolyte and a spinel structure cathode. The structure was configured on porous ceramic wafers. Cathode preparation A spinel structure LiNi0.4La0.1Mn1.5O4 sol-gel layer was prepared as cathode. The basic precursors were manganese acetate, nickel ethyl hexanoate, and lithium hydroxide (Sigma
Aldrich). A drying control chemical additive (DCCA) was added in order to reduce the superficial tension and to obtain homogeneous, crack free sol-gel layers. The DCCA used was hexadecyltrimethylammonium bromide. Approximately 20% of the Li+ ions are required to remove the phase impurity and to obtain an ordered spinel structure [5]. La 3+ acts as a dopant, yielding an n-ty
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