Lithium-ion is the gold standard for chemical energy storage, but a pair of UK companies have been working on alternatives that could knock down the cost of electric vehicles — and knock Li-ion out of the running. The two companies, Oxis Energy and Faradion, caught the eye of the American Chemical Society, which just gave them a huge write-up in its Chemical & Engineering News publication, so let’s take a look and see what’s up.
We were just noticing Oxis Energy, too. Earlier this summer, Oxis announced that it will be ready to bring its lithium-sulfur (Li-S) battery to market next year, and it also entered into a partnership with the home and commercial energy storage installer Anesco.
Writing for Chemical & Engineering News yesterday, Alex Scott brings us up to date. Oxis plans to “double what any lithium-ion [Li-ion] battery can deliver” within about four years, bringing the energy density of its battery cells to 500 Wh per kilogram. The near-term goal, according to the company’s website, is 400.
If Oxis can succeed in using half the material to provide the same performance as Li-ion, that would bring down the cost of an electric vehicle significantly.
The company is aiming for a cost of $125 per kWh (kilowatt-hour) in the near term. Scott does the math and arrives at a cost of $10,000 for an electric vehicle battery with a capacity of 80 kWh.
Comparisons to the much-publicized Tesla EV naturally come to mind. The last time we heard from Tesla Motors cofounder and CEO Elon Musk on the topic of EV battery costs, he was anticipating that the cost of Li-ion batteries (such as those used by Tesla) would drop to around $200 per kWh “in the near future,” while estimates have it at around $250–300/kWh today, so it seems that Oxis’s Li-S solution is looking to really compete.
Sulfur & Energy Storage
In addition to high energy density, Oxis’s Li-S cells get high lifecycle marks. As of 2012, the company was seeing cycles of more than 1,000 before capacity reduces to 80% (as in 80% beginning-of-life capacity). The most recent information on the company’s website describes the expectation of approximately 2,000 cycles to 80%.
According to Oxis, its cells have a 100% available depth-of-discharge, compared to 80% for Li-ion. Unlike Li-ion, the Oxis cell can’t be damaged by over-discharging.
Another advantage is the indefinite shelf life of the Oxis cell, compared to the periodic recharging required of Li-ion. That’s not a particular concern to most drivers, but it’s something to consider if you don’t use your car for months at a time (according to Oxis, Li-ion batteries need to recharge every few months).
Oxis also points out that by using sulfur instead of nickel, cobalt, and other heavy metals, the Li-S cell has a smaller environmental footprint than Li-ion energy storage chemistry. The company also gets Brownie points for sourcing its sulfur by reclaiming oil refinery waste.
And, this is the bottom line for Oxis:
Sulfur represents a natural cathode partner for metallic Li and, in contrast with conventional lithium-ion cells, the chemicals processes include dissolution from the anode surface during discharge and reverse lithium plating to the anode while charging. As a consequence, Lithium-Sulfur allows for a theoretical specific energy in excess of 2700Wh/kg, which is nearly 5 times higher than that of Li-ion.
Faradion also sailed across CleanTechnica’s radar this year, when it demonstrated a sodium-ion battery on an electric bicycle. That’s a big deal because, while sodium-ion energy storage is proven technology, until now it has been considered too bulky for use in electric vehicles.
Scott has this to say about the Faradion sodium-ion battery:
Faradion has made a sodium-ion battery with an energy density—a measure of how much power can be packed into a battery cell—of 140 to 150 watt-hours per kilogram.This compares with about 170 Wh per kg for lithium-ion cells based on cathodes made of lithium cobalt oxide. But the firm is “on track” to hike the density to more than 200 Wh per kg by 2017.
At that level of energy density, sodium-ion would compare very favorably to Li-ion, providing the same performance at a cost of about 30% less.
Among the advantages of sodium-ion technology cited by Faradion, the base material is abundant compared to lithium (not that lithium faces a huge supply issue).
Company sources also claim that the battery can be drained completely for safe storage and shipping.
Scott notes that Faradion comes from the Danish catalysis firm Haldor-Topsøe and global electronics leader Sharp.
Faradion has a ways to go before it can scale up beyond electric bicycles, but the company cites the following advantages to make a good case for more R&D:
Availability and Cost: Na-ion materials have lower material costs than Li-ion materials (e.g. sodium carbonate is < 10 % of the cost of the equivalent lithium salt). Furthermore, cathode and electrolyte costs can be ~ 50 % of cell costs, so the overall cost reduction is substantial.
Na is far more abundant in the earth’s crust than Li (Na ~ 2.6 % vs. Li ~ 0.005 %) making this technology more sustainable.
Drop-in solution: Na-ion materials can be processed in the same way as Li-ion materials at every step, from the synthesis of the active materials to the electrode processing…Existing Li-ion manufacturing lines can be used to make Na-ion batteries
Current collectors in sodium-ion cells can be fabricated from aluminium rather than the more expensive copper necessary in lithium cells.
Faradion also claims an energy density “similar” to that of typical Li-ion materials, and initial tests demonstrate rate capabilities on par with Li-ion.
As for next steps, Faradion has paired up with the company Williams Advanced Engineering in an energy storage project co-funded by the agency Innovate UK, so stay tuned.
Image credits: Top via Oxis Energy, bottom via Faradion.
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