Silicon Anodes Could Provide Faster EV Charging

Porous silicon anodes could yield fast-charging EV batteries that reach 400km.

(Image courtesy of Enevate.)

(Image courtesy of Enevate.)

Electric vehicle (EV) customers are always concerned with both battery range and charging rate. Today, EV charging still takes much longer than refueling gas-powered vehicles. This is one of the crucial issues that must be addressed.

Battery company Enevate has developed new anode technology that could enable inexpensive lithium-ion batteries to increase EV range by 30 percent. The anodes, which are covered by a porous pure silicon film, could allow the batteries to be charged in only five minutes and deliver 400km of range.

All About the Anode

In standard Li-ion batteries, lithium ions move from the anode to the cathode when discharging. Consequently, during charging, lithium ions are stored in the anode, and the number of stored ions determines the battery capacity.

For years, battery developers have been working to replace graphite anodes with silicon. Lithium ions, when combined with silicon, create Li15Si4, providing a high 15:4 ratio, which means more lithium can be stored in a smaller anode. Thus, silicon anodes could provide higher battery capacity. Furthermore, silicon is a cheaper material than graphite and could be charged up to 75 percent of its capacity in only five minutes.

Designing Silicon Anodes

Making silicon anodes batteries is a real design challenge. Silicon reacts with lithium during charging to expand 300 percent. During discharging, it shrinks again. Over time, silicon anodes disintegrate due to these changes. This leads to a chemical reaction between the anode and electrolyte that damages the battery, which is why silicon anodes have not been able to last long so far.

To overcome this issue, EV battery manufacturers have used a small amount of silicon and combined it with graphite powder using plastic binders. Still, lithium ions react with silicon before graphite, which again leads to the anode disintegration issue.  

Now, Enevate’s researchers have started using an engineered porous pure silicon film. Unlike the commercial approach, it does not use plastic binders but makes a porous thick silicon film (10 to 60µm) directly on a copper foil. It is covered with a protective coating that prevents the silicon from reacting with the electrolyte.

Double-sided finished anode with copper foil in the middle. (Image courtesy of Enevate.)

Double-sided finished anode with copper foil in the middle. (Image courtesy of Enevate.)

As it does not require high-quality silicon, these anodes are more cost-effective than those with graphite elements. In addition, lithium ions slip in and out quicker in the silicon anode, charging the battery to 75 percent of its capacity in five minutes.

Enevate founder and CTO Benjamin Park predicts this will result in EVs with 30 percent more range on one charge. Enevate is now working with multiple EV manufacturers to develop standard-size battery cells for EVs models to be manufactured in 2024 or 2025.