Chelsea, MI, February 1, 2017 – Silicon is an appealing anode material because its capacity is 3,575 mAh/g – 10 times that of graphite. Therefore, it can reduce cell weight in applications where weight is critical. Not only that, but its volumetric energy density when fully lithiated is 2,194 Ah/L compared to 719 of graphite. Therefore, you can use lower anode loadings, resulting in thinner anodes. Thinner anodes will either increase your cell-specific energy and energy density, or you can pack more capacity in the cell volume. Not only do you get increased performance, but certain mechanical silicon production processes have also been shown to produce active materials at a lower dollar per kilowatt-hour than graphite.
So what's holding this back?
Silicon volume increases nearly three times during full lithiation, resulting in a more rapid capacity fade than graphite for two reasons. First, the large expansion results in fractured solid electrolyte interphase (SEI). Electrolyte containing active lithium is consumed, resulting in a lower coulombic efficiency in graphite, and ultimately to a gradual fade cycle to cycle. Second, the expansion and contraction physically breaks the electrode apart, the silicon becoming inactive due to loss of electrical connection with either the conductive carbon (poor cohesion) or the current collector (poor adhesion). The failure mode is usually seen as a rapid capacity fade.
However, proper material selection and anode design can mitigate these problems. An artificial SEI can be used to decrease electrolyte reactivity, increasing the coulombic efficiency even to that of graphite. Selection of proper binder can improve the cohesion and adhesion of the anode. Finally, proper anode porosity ensures the silicon expands into the anode and does not cause swelling.
Paraclete Energy currently manufactures commercial production quantities of its cycle-stable SM-Silicon, which has the capacity of silicon and the price and the stability of graphite.
The SM in Paraclete Energy’s SM-Silicon stands for surface modification. The SM acts as an artificial SEI, inhibiting electrolyte breakdown on the surface of the SM-Silicon nanoparticles, resulting in improved coulombic efficiency while sustaining the high capacity of the SM-Silicon. Paraclete Energy can further optimize the SM beyond its baseline product dependent on the application for the battery. Additionally, Paraclete Energy works with its customers to design the electrode so that the SM-Silicon expands into the anode, thereby diminishing the typical issues with the swelling that occur during the charging and discharging process.
Unlike the industry standard of using only 5% or less silicon, cells made with Paraclete Energy’s SM-Silicon will sustain cycle stability while containing as high as 25% SM-Silicon. Paraclete Energy is working towards adding as much as 70% SM-Silicon.
So, with the capacity of silicon and the price and stability of graphite, will Paraclete Energy’s SM-Siliconbecome as ubiquitous as graphite in Li-ion batteries? Stay tuned!
Paraclete Energy are Sponsors and Exhibitors of The Battery Show at booth 1805.
View the full exhibitor list here.