Silicon Nanowires as a Cost Competitive Replacement to Graphite
While graphite is inexpensive and has a high natural abundance, the future of lithium ion batteries will rely on an alternative anode to increase the energy density required for widespread adoption of electric vehicles (EVs). The EV market is already showing increased share in new vehicle sales but is hampered by the notion of “range anxiety”. Silicon has been suggested to be a leading candidate to replace graphite as the active material in an anode and as the market is highly cost sensitive, it needs to be competitive on a kWh scale. This levelized cost comparison is critical and implicit in this comparison is not only the material costs but also must consider manufacturing costs as well. Thus, a comparison for a battery pack for a fixed capacity is most prudent. That gives a silicon nanowire (Si NW) anode thickness that is a factor of 2.5 less than a corresponding graphite anode. While the Si NW battery pack will have a larger battery capacity, that is normalized by the areal specific resistance of the material (giving the same pack capacity). This still results in a 20% reduction in mass and volume. Making considerations of the bulk price of Si NWs, we find that the cost of materials is roughly 10% less than for a similar graphite battery pack. Additional cost savings can be found with a more simplified electrode processing. Adding the benefits of a smaller mass and volume, Si NWs make a compelling alternative to graphite. One method that has shown promise in large scale synthesis of Si NWs is using cyclohexasilane (CHS). Electrospinning or solution-based synthesis are both possible using CHS to deliver high purity and high yielding processes. CHS provides many advantages over incumbent silicon precursors, including ease of handling and exquisite control over the Si NW size and the ability to simultaneously create coatings.