## UT Austin team identifies promising new cathode material for sodium-ion batteries: eldfellite

##### 24 September 2015

Professor John Goodenough, the inventor of the lithium-ion battery, and his team at the University of Texas at Austin have identified a new cathode material made of the nontoxic and inexpensive mineral eldfellite (NaFe(SO4)2), presenting a significant advancement in the quest for a commercially viable sodium-ion battery. (Edfellite was first found among fumarolic encrustations collected in 1990 on the Eldfell volcano, Heimaey Island, Iceland.) The researchers reported their findings in the RSC journal Energy & Environmental Science.

Sodium-ion intercalation batteries—i.e., using the same process of ion insertion and removal as Li-ion batteries—have emerged as a promising new type of rechargeable battery and a potentially attractive alternative to lithium-ion batteries because sodium is abundant and inexpensive, and the sodium batteries would be safer. (Earlier post.) In contrast, lithium-ion batteries are limited by high production costs and availability of lithium.

However, sodium-ion batteries face issues related to performance, weight and instability of materials. Sodium ion intercalation and storage is challenging because Na ions are about 70% larger in radius than Li ions. This makes it difficult to find a suitable host material to accommodate the Na ions and to allow reversible and rapid ion insertion and extraction.

 Crystal structure of the eldfellite cathode for a sodium-ion battery. Click to enlarge.

The team’s proposed cathode material addresses instability. Its structure consists of fixed sodium and iron layers that allow for sodium to be inserted and removed while retaining the integrity of the structure.

Its 3 V discharge versus sodium for reversible Na+ intercalation has a better capacity, but lower insertion rate than Li+ intercalation, the researchers showed. The theoretical specific capacity for Na+ insertion is 99 mAh g−1. After 80 cycles at 0.1C versus a Na anode, the specific capacity was 78 mA h g−1 with a coulombic efficiency approaching 100%.

At the core of this discovery is a basic structure for the material that we hope will encourage researchers to come up with better materials for the further development of sodium-ion batteries.

—Preetam Singh, a postdoctoral fellow and researcher in Goodenough’s lab

One challenge the team is currently working through is that their cathode would result in a battery that is less energy dense than today’s lithium-ion batteries. The UT Austin cathode achieved a specific capacity that is only about two-thirds of that of commercial lithium-ion batteries.

There are many more possibilities for this material, and we plan to continue our research. We believe our cathode material provides a good baseline structure for the development of new materials that could eventually make the sodium-ion battery a commercial reality.

—Preetam Singh

Resources

• Preetam Singh, Konda Shiva, Hugo Celio and John B. Goodenough (2015) “Eldfellite, NaFe(SO4)2: an intercalation cathode host for low-cost Na-ion batteries” Energy Environ. Sci. doi: 10.1039/C5EE02274F

THis battery does not seem to have high enough energy density for extended range EVs?

Such things may still have their uses.  A cheap, long-lived sodium-ion battery could be a good stationary storage device even at low specific power, or could make surge batteries for e.g. hybrid cars if the specific power can be made high enough.

LMAO! Since when do we have a shortage of Lithium? Have you been reading 2008 oil company press releases again?

Sodium can be had for close to the price of dirt.  Lithium isn't going to be that cheap, ever.

Lithium makes up about 2% of the materials cost in an EV battery, and the materials are about 40% of overall pack costs so, lithium makes up less than one percent of the total cost of an EV pack. If lithium doubles in price, the cost of a pack increases by less that one percent. Sodium is way cheaper than lithium, but if we replace all the lithium in a pack with sodium and then assume all other costs were the same, and they likely are not, then we would save less than one percent. Johnny B. Goodenough knows this. Anyway, energy density is low, but if other components are cheap, this may make a good stationary battery.

Lithium makes up about 2% of the materials cost in an EV battery

What I'm seeing is on the order of $10/kg of Li2CO3, with less than 1/5 being elemental lithium. If a cell requires 1 kg(Li)/kWh there is a price floor of around$100/kWh just for the materials.  Unless the numbers I'm seeing are WAY off, lithium is at least 40% of the cell price (if not much more) and there is less and less room for cost-cutting.

Sodium is way cheaper than lithium

Some distance beneath my chair there is a fossil layer of dozens or hundreds of feet of halite.  The oceans are full of the stuff, and there are lakes which are saturated with it.  There is no possible way that lithium can be as easily obtained.  If you can get the other materials for cheap and you don't care much about mass or bulk, sodium is the way to go.

In a more detailed report from ANL,estimates are presented
varyingv between 113 g and 246 g of Lithium (600g and 1.3
kg LCE) per kWh for various cathode type of batteries
all with a gaphite anode

That's much better than any figures I've seen before.  Did you save the link?

For the near future it doesn't sound promising, certainly for automobile application, but it is pregnant with possibility for other uses.

Is edfellite more available than the article indicates?

Sodium, iron and sulfate are extremely common and cheap.  I would not be surprised if edfellite could be manufactured.

Elemental lithium content in batteries

http://www.transportation.anl.gov/pdfs/B/584.PDF

For the two highest volume:

308 grams per kWh for NCA with graphite.
142 grams per kWh for Lithium Manganese Oxided with graphite.

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