Publication date: 10th April 2024
Si are promising materials as lithium ion battery anodes for increasing energy densities owing to its low potential (<0.35 V vs. Li+/Li) and extremely large theoretical capacity (3572 mAh g-1 for Li15Si4 vs. 372 mAh g-1 for conventional graphite). However, Si undergoes severe volume changes during cycling, resulting in the loss of electronic and ionic conduction pathways and rapid capacity fading. To accommodate the volume change, nanomaterials such as nanoparticles, nanowires, nanotubes and nanoporous powders have been investigated. However, their high specific surface areas have adverse effect of increasing irreversible capacity owning to the growth of solid electrolyte interface (SEI). To address this challenge, sulfide-based solid electrolytes (SEs) may useful to minimize SEI growth.
We have developed composite anodes with a nanoporous Si fiber, SE and conductive additives.[1] Nanoporous Si fibers were fabricated by electrospinning, followed by magnesiothermic reduction. The total pore volume of the fibers corresponded to the expansion volume to Li12Si7. The anodes exhibited superior performance, achieving an initial coulombic efficiency of 71%, a reversible capacity of 1038 mAh g-1, and capacity retention of 60% after 200 cycles. Compared to pulverized Si fibers, the Si fibers exhibit higher initial charge and discharge capacities, indicating that the electronic and ionic conduction pathways are compensated in the lithiated state; therefore, increasing Si utilization. Compared to non-porous Si powder, the nanoporous Si fibers exhibited superior cycle performance and maintained contact with SE after cycling. Therefore, the outward expansion of the nanoporous Si fibers should be suppressed by pore shrinkage. The proposed approach can reduce the constraint pressure during charging/discharging and may have practical applications in large-area all-solid-state batteries.
This study was supported by JSPS KAKENHI (grant number: JP19K05685). We thank Ms. Yuko Nakao (Rasa Industries, Ltd.) for her assistance with the specific surface analyses and pore size measurements.
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