Single-Particle Electrode Microbatteries Studied
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trol through covalent conjugation of biomolecules, which can be accomplished by applying surface chemical functionality, such as carboxyls or amines, on the silica nanoparticles using well-established silane coupling chemistry.” STEVEN TROHALAKI
Single-Particle Electrode Microbatteries Studied Because the factors limiting the performance of Li-based batteries are not well known, research groups have begun to use micron-sized single-particle electrodes to improve their understanding of the performance of electrode materials relevant to both aqueous and nonaqueous battery systems. A group from the Department of Chemistry at Case Western University has taken these studies a step further by assembling “microbatteries” from singleparticle cathodes and anodes. In the February issue of Electrochemical and Solid-State Letters (p. A122), researchers Q. Shi and D.A. Scherson of Case Western University describe their fabrication of single-particle electrode microbatteries by placing individual microparticles of cathode and anode materials on isolated microelectrodes. They chose LiMn2O4 on Pt as the cathode, and a carbon particle on Ni was used for the anode. Both electrode particles were ~50 µm in diameter and separated by a distance of ~80 µm. The researchers employed 1 M solutions of LiClO4 and LiPF6 as electrolytes, and the entire composite structure was sealed in an electrochemical cell. The researchers focused their first set of experiments on isolated microelectrodes. LiMn2O4 cathodes were charged fully, and thereafter, their discharge or open-circuit potential versus time characteristics were measured. When LiClO4 was chosen as the electrolyte, a rapid stepwise discharge was observed. Plateaus in potential were observed between 0–2 h, then between 2–8 h, after which discharge occurred quickly. A significant improvement was achieved using LiPF6 as the electrode, as the potential quickly stabilized at 4.1 V and remained stable for over 35 h. Importantly, the researchers said, this outcome is consistent with the gain in Li/LiMn2O4 battery performance resulting from the same change in electrodes, indicating that measurements of microcathodes are relevant to battery device performance. Similar electrochemical measurements were recorded using carbon anodes in the LiPF6 electrolyte solution. Spherical mesocarbon microbeads (MCMB) remained at potentials below 0.14 V for 20 h after full charging. 152
Following those measurements, potential versus time curves were recorded for assembled LiMn2O4/MCMB microbattery structures. The device potential dropped from 4.2 V to 3.95 V after just a few minutes, but then remained steady for ~8 h. At that time, the voltage dropped linearly for about 3 h, after which it decreased very rapidly, signaling the end of the battery’s lifetime. According to the researchers, the shortcomings in microbattery performance relative to the individual microelectrodes may occur because the nearby cathode material hastens the discharge of the anode and, consequently, the entire device. Nonetheless, this work
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