Amprius, a start-up company from Menlo Park, CA, has invented an innovative type of anode for Li-Ion batteries. The material that they intend to use is made of silicon nanowires, that are said to store 10 times more electricity than graphite, that’s been widely used for decades in batteries, including in the latest Li-Ion versions (you know that if you ever opened up a battery).
For example, the company says that the electric vehicles equipped with batteries benefiting their silicon nanowire anode could go 380 miles on a charge, compared to 200 miles if using normal Li-Ions.
In a normal charging process, lithium ions move from the cathode to the anode. In the discharge phase, the process is reversed. So far, silicon has been targeted to make a better storage than graphite (10 times more – theoretically), but it has one deficiency: it swells and cracks after just one charge cycle.
Yi Cui, Amprius founder and assistant professor of materials science and engineering at Stanford, has demonstrated that silicon nanowires meet the pure silicon’s theoretical charge storage capacity and that they do not break like silicon does (they’re flexible). Additionally, being pliable, the nanowires have a very high surface area, thus interacting better with lithium.
The nanowires are grown from a gas on a metal substrate coated with a catalyst. The company would not detail how the anodes are made, but it has developed a process that uses a more conductive substrate and a cheaper catalyst. “The anodes can be grown on a large scale at a fast speed in large areas on foil and with lower materials costs,” says Cui.
The theory is always better than the reality, though. The cathodes used nowadays in lithium ion batteries don’t match the qualities of the new silicon nanowire anodes Amprius is developing, and so they can’t yet build a real battery with their optimistic specifications of 10 times the capacity of a normal Li-Ion. Still, to compensate that, they built a model battery made of a thin anode and a thick cathode which gives only 40% improvement over today’s standard graphite-based rechargeable batteries.