Nano-meter scaled evaluation for dynamic behavior of lithium ions in a micro secondary battery embedded in silicon substrate

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In this project, we pursued nano-meter scaled evaluation for the dynamic behavior of lithium ions in a micro secondary battery embedded in silicon substrate. For this purpose, surface morphology and charge/discharge characteristic in a 5×5 μm^2 area of an all-solid-state Li secondary battery (Al/Li/SiO_2-15at%P_2O_5/LiMn_2O_4/polycrystalline silicon) embedded in a Si substrate are simultaneously observed by atomic force microscopy (AFM) with a conductive probe. The battery area of 5×5 μm^2 shows charge/discharge behavior corresponding to the movement of 〜2.9×10^<10> Li^+ ions/μm^2, reflecting the cyclic movement of Li^+ ions. The Al electrode consisting of scale-shaped grains of 0.1〜1.5 μm in size rises by 〜30 nm during the first charge operation. The surface of the Al electrode shows a cyclic change from scaly to wrinkled structures with the charge/discharge operations, indicating the drawing of the excess Li in the anode into the glassy electrolyte. These results are promising for th … More e realization of a micrometer-sized battery.Furthermore, we also studied the dynamic behavior of lithium ions in spinel-LiMn_2O_4 cathode. For this purpose, surface morphology in 3.5×x3.5 μm^2 area of spinel LiMn_2O_4, which is a typical cathode,material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Under the negative bias voltage to extract Li^+ ions from LiMn_2O_4, electric current abruptly increases at 5.5 V, indicating Li^+ ionic conduction toward the surface. Corresponding to the increase in current, part of scale shaped grains covering the whole surface expand and flatten, suggesting the Jahn-Teller phase transition induced by the repulsive interaction between the Mn-eg and O-2p electrons in Li accumulated layer. Additionally, optical and electronic properties of a new solid state electrolyte material Li_3AlN_2 and a cathode material LiCoO_2 were studied. In order to fabricate 100×100 μm^2 sized all solid state batteries, isolated holes of 100 μm×100 μm× 2 μm in size were made in Si substrates. In the future, we will try the preparation for the 100×100 μm^2 sized batteries embedded in the mico-meter sized holes. Less