Asymmetric Membranes Containing Micron-Size Silicon as Anode Material for High Capacity Lithium-Ion Batteries
Lithium-Ion Batteries are widely viewed as a leading candidate for green energy storage in fully electric vehicles, portable electronics, and intermittent power sources such as solar and wind. Currently, graphite is used as the anode material and although it can be cycled many times with minimal capacity loss, it has a relatively low theoretical capacity of 372 mAh g-1. Silicon (Si) is deemed as one of the most promising anode materials due to its high capacity of 4200 mAh g-1, which is nearly eleven times higher than graphite. However, Si suffers from poor stability caused by a massive volume expansion upon lithiation and de-lithiation. As a result of silicon's low mechanical strength, Si particles are cracked and peeled away from current collectors leading to a permanent capacity loss within a few cycles. Although there is exciting advancement in cyclability using silicon nanomaterials (nanowires, nanotubes, nano-thin films, and nanoparticles), the cycling performance of silicon micron powders is most desirable due to their low cost. Herein, we report the synthesis of novel asymmetric sandwich membranes containing micron-sized silicon powders (‰äö1 åµm) to accommodate the large volume expansion (‰äö300%) of silicon during the lithiation and de-lithiation processes. These silicon membranes were systematically characterized using Scanning Electron Microscopy, Transmission Electron Microscopy, Surface Area Analyzer, Thermogravimetric Analyzer, Raman Spectroscopy, and Powder X-Ray Diffraction. Raman spectra shows the characteristic peak of crystalline silicon at a 520 cm-1, as well as broad G and D peaks centered at 1580 cm-1 and 1375 cm-1, respectively. X-Ray Diffraction shows peaks typical of cubic phase silicon. Thermogravimetric analysis confirm that the content of silicon in these sandwich asymmetric membranes is ~35%. Scanning Electron Microscopy clearly shows the asymmetric membrane structures with silicon particles embedded within. The size distribution of silicon micron powders was obtained using Transmission Electron Microscopy. An overall capacity of 610 mAh g-1 can be maintained for 100 cycles with an 88% retention rate, applying a current density of 510 mAh g-1. The Coulombic efficiency is around 99.8% on average. It is notable that such a stable cycling performance has rarely been reported for electrodes made from micron-sized silicon particles. In comparison, the overall capacity of pure Si micron-particles showed an initially high capacity of 970 mAh g-1 and then rapidly degraded to 10 mAh g-1 in as few as 30 Cycles. Carbonaceous asymmetric membranes that don’t contain silicon particles demonstrated a high cycling stability with a 98% retention rate after 100 cycles. However, their specific capacity is quite low (340 mAh g-1). Single-layer silicon membranes without sandwich structures have a high initial capacity of 936 mAh g-1, but suffer from a 38% capacity loss after 100 cycles.
Georgia Southern University Research Symposium
Byrd, Ian, Ji Wu.
"Asymmetric Membranes Containing Micron-Size Silicon as Anode Material for High Capacity Lithium-Ion Batteries."
Chemistry Faculty Presentations.