How a Breakthrough Anode Technology Is About to Level-Up Lithium Ion Batteries

By: John A. Lanier

In recent years, multiple companies have made promising progress on replacing graphite with silicon in the anodes of lithium ion batteries. In doing so, they are primed to significantly increase the performance of the battery type that is currently driving the transition to electrified transportation.

Photo courtesy of Amprius

It’s been years since I have written about batteries, and given how quickly things change in that sector, it’s about time I revisited the topic. Often, the buzz around batteries focuses on new types which might be able to topple the king, which is currently lithium ion. That’s not where all the research and innovation is focused, however. Many organizations continue to work on making lithium ion batteries even better than they already are, and in that respect, there has been a recent breakthrough. May I present to you - the silicon anode.

What Is an Anode, and Why is Silicon Better?

As I am wont to do, let’s start with an explainer. An anode is one of the fundamental components of any battery. Take, for instance, the AA batteries that are hanging out in your television remote. On one end of the battery, specifically the side that is flat, you’ll see a “-” sign. This is the anode, with the other side showing a “+” sign for the cathode. Together, anodes and cathodes are the electrodes of a battery, and they serve as the bridge between the energy stored in the battery and the electric circuit to which the battery is designed to connect. In particular, the anode is the side of the battery into which an electric current flows, while the cathode is where the current exits. And in the case of a rechargeable battery, like those in my electric vehicle or this laptop I’m hammering away on, the roles of the anodes and cathodes can reverse depending on if the battery is charging or discharging.

Since rechargeable lithium ion batteries first hit the market in 1991, the anode has primarily been made of carbon in the form of graphite. From the beginning, however, scientists have flirted with the potential of silicon instead. This shouldn’t surprise you, when you consider how silicon has revolutionized electronics. Silicon is an excellent semiconductor, and it’s incredibly abundant, accounting for 27.7% of the Earth’s crust. For much the same reason that we want to use it in computer chips, we also want to use it in batteries. Unfortunately, when historically used as an anode, silicon would swell and shrink when charging and discharging. So it would work really well for a little bit, and then it would physically break the battery. Not ideal.

And so, many different companies have been working on novel fabrication methods of silicon anodes. Turns out that a few of them have broken through. Take OneD Battery Sciences, who has figured out how to put silicon nanowires into a graphite anode to increase how much energy the battery can hold. They’re working with General Motors to deploy improved batteries in electric vehicles. Group14 Technologies out of Washington State recently announced that construction has begun on a one-million-square-foot battery manufacturing facility for silicon battery components. Like OneD, they’ve built a carbon-based scaffolding for the anode into which silicon can be added without breaking the anode upon charge and discharge. They project their components to be in EV batteries by the end of 2024. But there’s another company that has me even more excited for the potential of silicon anode batteries.

The Best Lithium Ion Battery in the World

Allow me to introduce you to Amprius Technologies. What sets them apart is that they have fabricated an anode for lithium ion batteries that is made 100% from silicon. The results, compared to a standard graphite anode lithium battery, are remarkable. First and foremost is energy density, which is the amount of energy a battery holds per unit of weight. I looked up the energy density on the batteries in my 2019 Chevrolet Bolt, and I found an estimated 131 watt-hours per kilogram (Wh/kg). Amprius’s site advertises an energy density of 450 Wh/kg. That’s more than three times! And energy density basically scales linearly, so if you could hypothetically put the same amount of Amprius batteries by weight in my car, it would triple its range. I would have a car that could reliably drive 600 miles per charge.

The next jaw dropping statistic is recharge rates. It turns out that silicon not only helps a battery hold more charge, but it also allows that battery to soak up more energy faster. Whereas a typical graphite anode lithium battery needs about 30 minutes connected to a supercharger to go from empty to 80% charge, Amprius advertises less than 6 minutes on their website. That’s a game changer. If their batteries offer a reasonable range for EVs of at least 500 miles, then we are looking at a 5-minute recharge getting you almost 400 miles of additional range. That’s about how long it takes to fill up an internal combustion engine vehicle at a gas station.

The even better news is that you don’t have to take Amprius’s word for it. Two months ago, an independent third party verified the performance characteristics of their latest battery technology. The latest iteration of Amprius battery clocked in at a whopping 500 Wh/kg.

A Couple of Headwinds That Might Slow the Uptake in Electric Vehicles

There are two bits of bad news, however. First, their batteries have some limitations. For one, the cycle life of the batteries can be as low as 200 cycles, which basically counts how many recharges a battery can handle before it loses performance. This number is lower than the floor for graphite anode batteries, and it likely corresponds to a battery that is primarily charged at high voltages (like a supercharger). In addition, their anode fabrication technique is not “drop-in-ready” with current electric vehicle battery manufacturing, so it’s not likely that their batteries will show up in your next car. They instead are focusing on specialty products, like drones and electric planes.

That leads to the second bit of bad news. At least part of why they are focusing on these markets is because they are military-related, and Amprius is able to command higher profit margins. I lament the fact that the highest margin use for the best mobility battery the world has ever seen is a military application. I’d like to think that maybe, just maybe, solving the climate crisis might be the highest and best use for breakthrough battery technologies. Alas, that’s just me shouting into the wind that is our current economic paradigm.

The news is overwhelmingly good here though. Multiple companies have now cracked the code on utilizing silicon to enhance lithium ion batteries, and it’s only going to get better and cheaper from here. As a result, we have a promising new technological breakthrough that should aid significantly in the decarbonization of transportation globally.