Energy Storage

Improving Lithium-Ion Batteries with Silicon Anode Technology

From the beginning of the electrification evolution, the U.S. has struggled to keep up with the Chinese battery giants, and has also fallen behind Europe in some battery production and adoption areas. Lithium-ion (Li-ion) batteries are not only important for electric vehicles (EVs), but also for energy storage to accommodate intermittent renewables, such as wind and solar, on the power grid.

Concerning EVs, recent reports indicate an overall slowing of EV adoption amongst consumers. Typical anxieties around range, charging time, and battery life still persist. And, added to that, recent news of the inoperability of EVs in extreme cold temperatures is not reassuring to consumers. It is becoming increasingly clear that the path forward to mass adoption will only come from significant technology improvements born out of innovation.

Silicon Anode-Based Batteries

One of the most promising innovations in Li-ion battery technology is the use of silicon-based anodes. To date, most Li-ion battery anodes are made with graphite, a material that is largely controlled and supplied by China. While recent legislation has attempted to effect a change in the U.S.’s reliance on Chinese materials with the removal of certain rebates for EVs made with materials from China and other “foreign entities of concern,” building our own robust battery supply chain will take time and may not happen soon enough to be competitive with other countries. If the U.S. plans to detach itself from dependence on Chinese battery materials, it will need to examine its current reliance on graphite anodes seriously.

Of all the materials on the periodic table, silicon has the most promise as a full or partial replacement for graphite in the anode of lithium-ion batteries. Silicon has a theoretical charge capacity 10 times that of graphite, a property that positively impacts battery performance and efficiency. These improvements will greatly increase EV range, reduce charge times, and lengthen battery life. Another important benefit of using silicon is that it is relatively abundant and low-cost.

Unfortunately, due to a cumbersome combination of pulverization and the buildup of wasteful byproducts, most battery manufacturers can only integrate about 5% to 10% of silicon into their graphite anodes, making the solution of swapping out graphite for silicon less simple than it seems. The battery charging and discharging processes can also result in damage to silicon anode material due to expansion and contraction. This hurts the battery’s fragile solid-electrolyte-interphase (SEI) layer around the surface of the anode. This leads to the accumulation of wasteful byproducts, shortening the battery’s life and hampering its efficiency. If more silicon is going to be integrated into the battery, this problem will need to be addressed.

The Engineered SEI and Nanoparticle Solution

Fundamentally, there are two big issues with the silicon particles that have been used to date in the anodes of lithium-ion batteries. One of these is the nature of the solid electrolyte interphase, and the other is the size and nature of the individual particles. SEI’s that are relatively brittle and don’t have good binding characteristics will break off during cycling, contributing to the wasteful byproducts and degrading battery life. Additionally, silicon particles that are “too large” tend to only contribute to battery performance at their surface, leaving a large portion of the particles non-reactive. The answer to both of these issues is using an engineered SEI on a nano-sized silicon particle.

An engineered SEI can be formed using precise chemical conditions during slurry formation to minimize cracking and byproduct formation. Additionally, reducing the particle size to the nanoscale ensures a significantly higher proportion of the silicon particle can actively participate in battery chemistry. It is worth noting that traditional ball milling processes are generally unable to produce nanoparticles, with a practical limit of about 100 nanometers. Such processes also tend to result in mixes of nonuniform sizes and surface characteristics. A more effective approach to producing uniform nanoparticles is through chemical build-up and modification.

With these nanoparticles and artificial SEI formation processes, there should be more than 10% silicon in graphite anodes. This should make them work better in batteries than anodes made of 100% graphite. While these processes are quite technical, they are grounded in real science and are important to understand. They can have a true impact on the overall performance of Li-ion batteries, which, in turn, could enhance the performance of power grid-connected battery storage systems. It could also make a discernible difference in the current dismal trends occurring in EV production and adoption. If consumers could be more assured that their EV would be equipped with a battery that would take them greater distances, charge quicker, live longer, and not fail them in environments experiencing extreme temperatures, they would be much more likely to consider adopting the technology.

With the greater implementation of silicon nanoparticle-based anode battery technology, the U.S. supply chain for Li-ion battery materials will be at least partly protected from potential global disruptions. Furthermore, the performance of Li-ion batteries will be boosted. This will benefit both the electric power and automotive industries, allowing improved energy storage for the grid and greater adoption rates for EVs.

Michelle Tokarz, PhD is vice president of Partnerships & Innovation at The Coretec Group.

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