All-Solid-State Lithium-Ion Microbatteries with a Silicon Negative Electrode for Microelectronic Systems
This work reports on the development of ‘2 V’ lithium-ion cells, comprising an amorphous silicon film as the negative electrode and amorphous lithium titanium oxysulfide film as the positive electrode, both obtained by sputtering. Silicon thin film electrode was previously found to have excellent cycle life in all-solid-state half-cells . As for TiOySz, these materials exhibit high volumetric capacities, which may vary with composition. Their electrochemical activity involves highly reversible redox processes on both sulfur and titanium around 2V/ Li+/Li [4,5]. In order to obtain Li-ion cells, new lithiated titanium oxysulfide films LixTiOySzwere synthesized and characterized.
The electrochemical behavior of electrode materials, especially the one of new positive electrode materials, and of the complete Li-ion cells was studied (figure 1). The positive material and the cells exhibit excellent cycle life at room temperature when operated up to 130 µA.cm-2(figures 2 & 3).
A higher sulfur content in the positive electrode was found to enhance its specific capacity. EIS measurements showed it also slightly increases the electrode polarization. This polarization was found to sharply increase at the end of the charge for all LixTiOySz compositions. Depending on cycling conditions (voltage window, current density), reversible slow-fading phenomena, as the memory effect related to the LixSi negative electrode, were highlighted .
Finally, no detrimental effect of three successive SR thermal treatments at 260°C on the active core was evidenced.
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