High-Performance All-Solid-State Cells Fabricated With Silicon Electrodes

All solid-state thin-film lithium microbatteries are a promising component able to fulfill most of the specific requirements to power autonomous microsystems. Nevertheless, metallic lithium, which is commonly used as the negative electrode in microbatteries, has a very low melting temperature (Tm = 181 degrees C) that appears to be incompatible with the solder-reflow operation (maximum temperature Tmax 260 degrees C) usually used to connect electronic components. Silicon is a promising candidate to replace lithium in solder-reflowable lithium-ion cells due to its high volumetric capacity (834 mu Ah cm-2 mu m-1 for Li15Si4) and its ability to reversibly insert lithium at a low potential. Nevertheless, it suffers from a large volumetric expansion during lithium insertion (280%), which is partly responsible for a rapid capacity fading when cycled in liquid electrolyte. In this study, all-solid-state Li/LiPONB/Si cells are prepared using physical vapor deposition (PVD) techniques. The cycle life and the coulombic efficiency are found to be excellent in these solid-state cells with almost no loss during 1500 cycles. Despite the large volume expansion due to lithium insertion confirmed by scanning electron microscopy, no evidence of cracks is found in the film or at the electrode/electrolyte interface, even after 1500 cycles.