The quest for long range electric cars is heading towards lithium metal batteries, according to two companies who presented at the IDtechEx battery technology conference last week in Santa Clara. The companies, Sion Power and Solid Energy, both claim the lithium-ion battery won’t supply the needed energy density and cost improvements to implement low cost long range electric vehicles. Both claim their lithium-metal approaches have energy density way above lithium-ion, at a lower cost, and with none of the safety problems of other lithium-metal batteries.
Those of us who know lithium battery history will have gulped deeply hearing these claims. Past attempts at lithium metal batteries were, well, the Solid Energy presenter described them as “dangerous”. Dendrite formation on lithium metal inside battery cells caused short circuiting, leading to fires and explosions. That coupled with volatile electrolytes, and the fact that pure lithium metal is highly flammable, made for an explosive combination. In a way it’s a miracle that lithium batteries ever got out of the lab.
Lithium ion battery technology reduces the chance of catastrophic failure – thermal runaway and explosion. The key issue is that pure lithium metal is extremely reactive in typical moist atmosphere, and is one of the metals that burns easily. In nature, as a natural consequence of its reactive nature, lithium is never found as a pure metallic deposit, but is always ionically bound to other materials.
Taking this cue from nature, lithium ion batteries do not use pure lithium metal, but lithium that’s ionically bound to other materials. This enabled the safe battery designs which we have in electronic devices from phones to cars. For the most part they’ve been extremely safe with very few incidents. But there was a trade-off in cost (more materials required in manufacturing), and an energy density low enough to either limit the driving range of affordable electric cars, or make their cost very high.
Lithium battery energy density now and in the future
Solid Energy claims energy density of over 1200 watt-hours/liter, and 400 watt-hours/kilogram, and several hundred charge cycles. For Sion Power, the claim is 1000 watt-hours/liter, and 500 watt-hours/kilogram, and about 500 charge cycles. The number of charge cycles is low, but for a 300 mile range car 500 charge cycles adds up to 150,000 miles of total driving range.
For comparison, it’s typically said lithium ion batteries are at about 200 watt-hours/kilogram.
These figures are important because the watt-hours figure is what delivers total driving range. A 300 mile electric car requires 100 kilowatt-hours or more of energy storage. To enable an effective car, an electric car battery pack must be light enough so the car performs well, small enough to leave interior space for passengers and cargo, and inexpensive enough to compete against incumbent gasoline cars. The automotive and battery industries are working hard to thread their way through these requirements, because the opportunity is enormous for any technology that could unseat fossil fuels as the fuel of choice.
If Lithium metal batteries are one way to implement the required energy density, and lithium metal batteries are dangerous, are these companies proposing to put us in firebomb cars? We currently drive gasoline powered cars with tanks of highly explosive liquids (gasoline) and we don’t seem to mind the occasional car fire that results. But we want our electric cars to be safer.
Sion Power’s Licerion technology
Sion Power has developed what it calls “Licerion Technology” which enables safe lithium-metal batteries at 500 Watt-hours/kilogram and 1000 Watt-hours/liter energy density. Well, Sion Power positioned that energy density as their goal for 2018 rather than what’s being delivered today. They’re targeting multiple formulations for different markets and different energy density characteristics. The presenter gave these four examples:
- UAV applications: can sustain cold temperatures and high altitude, offers 350 Watt-hours/kilogram and 310 Watt-hours/liter energy density
- Electronics: For a “near term product” they are delivering 433 Watt-hours/kilogram and 850 Watt-hours/liter energy density
- Electric Buses: High charge rate, cycleability, and safety considerations, offering 295 Watt-hours/kilogram and 535 Watt-hours/liter energy density
- Electric Cars: Ultra-high energy density, offering 500 Watt-hours/kilogram and 1000 Watt-hours/liter energy density
Concerning alternative technologies, Sion had this to say:
- Silicon Anode: Silicon expands and disforms, and the batteries quickly degrade
- Magnesium Air: “Early science projects” meaning the technology is years away from commercialization
In Sion Power’s Licerion batteries, the lithium-metal anode material is protected. The protective layer was developed in collaboration with BASF. BASF has a $50 million equity investment in Sion Power.
Another partner is Airbus Defence and Space, for the Zephyr 7 UAV. That unmanned aircraft incorporated solar panels and a Sion Power battery system, and flew for over 14 days straight at altitudes around 70,000 feet. The target market for this kind of craft overlaps strongly with communications satellites and weather monitoring (and spy aircraft) with the advantage of being land based.
Sion’s background is in lithium-sulfur batteries, and while they’re continuing that work the Licerion brand name is being applied to both lithium-sulfur and lithium-metal batteries. The technology is suitable for multiple cathode choices including “Metal Oxide, Phosphate and Sulfur.”
Solid Energy is a spinoff from MIT, and is closely tied to A123 Systems. The company has developed a conundrum, namely an anode-less battery – which essentially means there’s so little anode material that there is essentially no anode. Sort of. Their business focus is developing technology which they’ll then get to manufacturing by partnering with larger manufacturing companies.
Their claim is: over 1200 Watt-hours/liter and over 400 Watt-hours/kilogram energy density.
The primary development that Solid Energy claims makes their battery safe is a huge reduction in the size of the lithium-metal anode. (um.. if there’s an anode, then why go to the trouble of calling it an anode-less battery? this is why engineers and marketing don’t get along…) What this means is described by how the company describes the historical development of lithium battery technology:
- Gen 0: Very thick lithium-metal anode, 100-200 Watt-hours/kilogram, 200-300 Watt-hours/liter, and very dangerous. There are scary stories out there of these batteries. We’re much better off without them.
- Gen 1: Carbon anode, lithium-ion, 200-250 Watt-hours/kilogram, 500 Watt-hours/liter,
- Gen 2: Silicon-composite anode, lithium-ion, 250-300 Watt-hours/kilogram, 700 Watt-hours/liter
- Gen 3: Ultra-thin lithium-metal anode, 400-500 Watt-hours/kilogram, 1200 Watt-hours/liter
Safety is not produced just from using an ultra-thin anode, but by coating it with a ceramic.
Solid Energy’s target markets are drones, smart watches, other portable electronics, and electric cars. The picture above is their attempt to demonstrate the advantage of higher energy density.
Neither company are in production with batteries using the technologies they discussed at the conference. Instead they’re both targeting “2018” for delivery in commercialized electric vehicles. It wasn’t entirely clear whether that meant an actual electric car on the market using either of the technologies, or whether they would be in production with automotive grade cells that automakers would start evaluating. Neither presenter was clear on this point, but both did stress the technology could be in vehicles “Real Soon Now.”
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