01 Feb Will Silicon Ever Be as Ubiquitous as Graphite in Li-Ion Batteries?
Chelsea, MI, February 1, 2017– Silicon is an appealing anode material because its capacity is 3,575 mAh/g is ten times that of graphite. Therefore, it can reduce cell weight in applications where weight is critical. Not only that, 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-Silicon™ become as ubiquitous as graphite in Li-ion batteries? Stay tuned!
Paraclete Energy manufactures nanoparticle 3,575 mAh/g silicon metal for the graphite and Li-ion battery industry. Paraclete can manufacture tons of many types of nanoparticle silicon metal, our premier silicon product is SM-Silicon™. The SM stands for Surface Modified. This surface modifier functions as an artificial SEI that diminishes the negative effects of electrolyte interaction and thereby enables both cycle stability and very high loadings of silicon well beyond the ~5% limit of silicon oxide. The cycle stability of SM-Silicon™ acts to compound the benefits to customers given now they can replace many times as much graphite with silicon metal that has over double the capacity of silicon oxide. Paraclete’s SM-Silicon™ can be priced from a $/kWh perspective at less than graphite. The surface modifier is also what makes Paraclete’s silicon safe to handle in a battery manufacturing facility. Paraclete Energy’s air and water stable prelithiated SM-Silicon/PL™ can be seamlessly integrated into customers’ standard aqueous slurry techniques and thereby enable 100% first cycle efficiency and much lower cost and time for production while increasing the manufacturing plant’s capacity by 15-20% with no new investment in CAPex. The surface modifier also acts as an artificial SEI for cycle stability but, with SM-Silicon/PL™, also acts as a protective shell from air and moisture.
Paraclete Energy also offers Rapid Prototyping Services for custom designing and making cycle-stable, high-capacity SM-Silicon™ based batteries so that customers can test and prototype their next generation products. Paraclete’s SM-Silicon™, when combined with these services, enables customers’ next generation products and batteries to be prototyped and brought to market sooner.
SM-Silicon™: The Capacity of Silicon, the Price of Graphite.