Lithium-metal battery breakthrough: 400 Wh/kg

Sion Power of Phoenix announced last week that its Licerion® (EV) cell has achieved a significant battery breakthrough, with an energy density measuring 400 Wh/kg in a pouch cell.

That energy density is right up there with the announced results for the Volkswagen/Bill Gates-backed QuantumScape solid state battery (380 – 500 Wh/kg) and the 380 Wh/kg that Tesla is aiming for in the next generation battery it announced last August. Current Tesla packs have an energy density of about 260 Wh/kg.

What is energy density?

To put it simply, energy density is a measurement of how much energy a battery can store. It is generally measured by weight or by volume: Watt hours (or kilowatt hours) per kilogram of storage material, or Watt hours or kilowatt hours per Litre of storage material. To be more correct, the volume measurement is called energy density and the measure by weight (actually mass) is called specific energy or gravimetric density.

Lead acid batteries have densities of 35–40 Wh/kg and 80-90 Wh/L and lithium-ion batteries generally have anywhere from about three to six times that density: 100–265 Wh/kg  250–700 Wh/L. Think of it as a lithium-ion battery will take your electric boat 3 to 6 times as far as a lead acid battery that weighs the same amount or takes up the same space.

With an energy density of 400 Wh/kg, a Sion Licerion® product could take you even further –  10 times as far as lead acid.

The weight and size of things are obviously of major concern on a boat, so it’s obvious that a battery storing more energy in a smaller/lighter unit is preferable. What is not so obvious is how to achieve that.

Worldwide hunts for battery breakthrough

There are different companies and researchers working on adjusting different chemical compositions of batteries, on coating the chemicals with other chemicals, on building batteries in different ways like 3D printing…and lots of other techniques that are being tested every day.

Probably the most common avenue being pursued is the solid state battery in which a solid electrolyte replaces the liquid or gel electrolyte material that is in almost all batteries today. (The electrolyte is the material that allows the flow of electrical charge between the two electrodes – the anode (negative) and cathode (positive).

For lots of reasons, a solid state electrolyte makes for a higher energy density than a liquid or gel version, but there are other things that need to be worked out beyond density, like how quickly the battery can be charged, how many times it can be charged, safety, cost…and you can imagine working on this chemistry isn’t simple.

Sion began in 1989 as a spin-off from the U.S. Department of Energy’s Brookhaven National Laboratory and concentrated on one of the lesser known chemistries – Lithium Sulfur (Li-S) batteries. They produced the highest energy density and specific energy Li-S cell in the world and in 2014 set a world’s record for continuous flight on the Airbus Defence and Space Zephyr® 7 HAPS flight (High-Altitude Pseudo-Satellite).

While great for one continuous flight, what that cell wasn’t great for was being recharged hundreds of times like an electric vehicle owner would demand. So in 2015 Sion started looking at an old technology from the 1980s – lithium metal anodes –  in part because of a ‘serendipitous’ experiment, as Sion COO Dr. Jeff Britt told the Tucson News.

Britt relates how researchers were experimenting with different materials to substitute for the carbon in the battery anodes. When they kept the cathode materials the same but used lithium metal in the anode he says “We found that we could also use the same types of cathodes that are used with lithium ion cells, and we got much better results than we get with sulfur, so the company transitioned to this new technology.”

Solving the dendrite dilemma

The problem for lithium metal 25 years ago was dendrites – microscopic filaments that build up on the anodes like a cave floor of jagged sharp stalactites and reduce the efficiency of the charging and can also initiate dangerous fires.When lithium-ion batteries came along and became the energy source of choice for computers and cellphones, the metallic lithium option fell out of favour with researchers.

On revisiting the lithium metal technology, Sion successfully overcame the dendrite problem by developing a thin, chemically stable ceramic barrier on the anode. The Licerion® cells also have additives in the proprietary electrolyte system which is technically liquid, but a “negligible amount compared to traditional Li-ion cells”. All of that means more power storage in less weight.

For those who want to delve more deeply into the technology, there is lots of information available on the Sion website. For those of us who are more concerned about what the technology does rather than how it does it, here is what company’s battery breakthrough means.

First of all, it needs to always be stressed that this battery pack is not coming to your local marina next week. For one thing, Sion’s goal is the EV market, and for another thing, it takes a while for these things to get to market.

Cells being produced in commercial sizes

Having said that, there has been an incredible amount of progress even since last February, when successful tests were announced on much smaller Licerion® cells.

The company notes in the latest release that “Scaling to useful cell sizes is a challenge for high-energy battery technologies. Sion Power has successfully accomplished that scaling process.  Both 17 Ah and 6 Ah Licerion®-EV cells are routinely produced on the Sion Power pilot line and are undergoing third-party validation tests.

Dr. Urs Schoop, Chief Technology Officer for Sion Power, said “Less than a year ago, Sion Power had demonstrated this technology on a 1.8 Ah cell. Today we have proven the results on large format cells. Although we have seen many high-energy battery companies in the news, few of them claim to produce cells in high-capacity commercial sizes.”

So when will you see a Licerion® battery in the hull of your electric boat? Well, that may take time, because there is a lot more opportunity in the EV market right now than there is in electric boats. But the website says they are developing battery packs to include a 1 kWh, 12 V and 24V battery packs, a 2 kWh, 24 V battery pack and ‘custom battery packs are also available‘.