Toyota Research team reports significant advance in electrolytes for high-energy Mg batteries
01 June 2015
A team at Toyota Research Institute of North America (TRINA) reports a critical advance in the the development of electrolytes for magnesium (Mg) batteries in the journal Angewandte Chemie. The researchers, led by Dr. Rana Mohtadi, Principal Scientist at TRINA, developed an electrolyte based on a simple-type magnesium monocarborane salt (MMC) that is compatible with Mg metal (> 99 % coulombic efficiency); possesses high anodic stability (3.8 V vs. Mg); and is non-corrosive. By contrast, state-of-the-art Mg electrolyte systems are complex, halogen-based, and corrosive.
The properties of the new electrolyte, coupled with its “inert and benign character”, make MMC-based electrolytes well-suited for future Mg batteries, the scientists said. The development of this non-corrosive electrolyte enabled the first demonstration of a high voltage coin cell battery, previously prohibited using all known systems. “This achievement is a turning point in the research and development of Mg electrolytes that has deep implications on realizing practical rechargeable Mg batteries,” the scientists wrote.
TRINA researchers have been investigating magnesium batteries for a number of years (e.g., earlier post). Because magnesium is divalent, it can displace double the charge per ion (i.e., Mg2+ rather than Li+). As an element, magnesium is much more abundant than lithium, and more stable. Magnesium-ion batteries theoretically could offer good electrochemical performance, while being safer and less expensive than Li-ion batteries. However, Mg-ion batteries have suffered from a number of limitations, among them being anode/electrolyte incompatibility.
Currently, the prospect of attaining energy densities beyond those offered by current lithium-ion batteries is driving interest in rechargeable magnesium batteries. Mg metal offers high volumetric capacity (3833 mAh cm-3 vs. 2036 mAh cm-3 for Li metal) while being non-dendritic and abundant in the earth crust (fifth most abundant element). Since Aurbach et al. demonstrated the first and only rechargeable Mg battery prototype, challenges toward realizing Mg batteries still remain. These stem from the absence of practical electrolytes and high capacity/high voltage cathodes. For instance, the field demands electrolytes capable of operating at high voltages whilst being compatible with Mg metal and all other battery components.—Tutusaus et al.
Early work suggested that salts uses in Li-ion batteries would fail in Mg system because they passivate the Mg metal surface. Alternative strategies that successfully resulted in complex solutions with high anodic stability; however these corrosive solutions had reduced compatibility with other battery components such as steel casings and current collectors.
In 2014, Mohtadi and her TRINA colleagues demonstrated that Mg(BH4)2 was a highly competent electrolyte for magnesium-battery applications. This electrolyte was the first non-organomagnesium electrolyte compatible with Mg metal and provided excellent electro-chemical performance.
In tandem with further research into this system, the TRINA team sought to pursue potential routes to materials with enhanced oxidative stability as compared to Mg(BH4)2’s observed oxidation onset potential of 1.7 V (vs. Mg on Pt).
High oxidative stability is crucial for the development of Mg batteries for operation with future high-voltage cathodes. Although organomagnesium compounds with oxidative stability above 3 V (vs. Mg) have been reported, most have significantly reduced oxidation onset potentials when deposition and stripping occurs on non-noble-metal surfaces. This reduced stability has been linked to corrosion of the metal by the electrolyte solution and constitutes a major hurdle to the utilization of current high-voltage electrolytes, as non-noble metals are the most appropriate materials for the construction of battery-casing and current-collector materials. Notably, Mg(BH402 displayed enhanced stability on these metals, as corrosion of the electrode material did not occur. We therefore sought to identify an electrolyte candidate which would retain the attractive properties of Mg(BH4)2 but offer enhanced oxidative stability. The identification of such an electrolyte would effectively overcome a major hurdle towards the development of Mg batteries with high energy densities.—Tutusaus et al.
Pursuing a new design concept involving boron cluster anions, they found that monocarborane CB11H12- produced the first halogen-free, simple-type Mg salt that is compatible with Mg metal and displays an oxidative stability surpassing that of ether solvents.
In the short term, tangible impact of MMC electrolyte on accelerating the research and development of high-voltage cathodes is expected by enabling the examination of a variety of cathodes in coin cells. Finally, as the anodic stability of MMC surpasses that of ethers, discovering new Mg-compatible and oxidatively stable solvents emerges as one of the new avenues for electrolyte research that can widen the portfolio of accessible high-voltage Mg cathodes.—Tutusaus et al.
Oscar Tutusaus, Rana Mohtadi, Timothy S. Arthur, Fuminori Mizuno, Emily G. Nelson, and Yulia V. Sevryugina (2015) “An Efficient Halogen-Free Electrolyte for Use in Rechargeable Magnesium Batteries”Angewandte Chemie International Edition doi: 10.1002/anie.201412202
Tyler J. Carter, Rana Mohtadi, Timothy S. Arthur, Fuminori Mizuno, Ruigang Zhang, Soichi Shirai, and Jeff W. Kamp (2014) “Boron Clusters as Highly Stable Magnesium-Battery Electrolytes” Angewandte Chemie International Edition Volume 53, Issue 12 Pages: 3173–3177 doi: 10.1002/anie.201310317
Is this a major breakthrough or one of hundreds of research announcements we see every year on GCC?
And if it is a major breakthrough, how long before we can buy the cells (or cars with the cells in them ?)
Posted by: mahonj | 01 June 2015 at 05:42 AM
@mahonj This is one of many breakthroughs needed to make Mg-ion batteries a commercial reality. As the article says, now it's time to move on to finding a suitable cathode that is compatible with this electrolyte. Likely still 5-10 years before we see a commercial Mg-ion battery and that one will likely not outperform the Li-ion batteries of the time in terms of energy density.
Posted by: Sublime | 01 June 2015 at 06:02 AM
Ten years to find a low cost suitable cathode seems to be a very long time. It would compare with the time used to develop a practical A-bomb and put a man on the moon.
That time could be reduced by 3X if enough resources were used in 20 to 30 different places?
Posted by: HarveyD | 01 June 2015 at 07:39 AM
These comparisons made very often here and there are very misleading. First because there is no point of comparison between making a battery and putting a guy on the moon (some challenges that could appear way "easier", because less fancy ?, than getting on the moon have been unsolved for decades).
But also because, industrial work is not comparable with very specialized work. Put one man on the moon, at any cost, is something. Develop an industrially viable device - especially for mass production - is something totally different.
Posted by: toitoimontoi | 01 June 2015 at 07:55 AM
Toyota could have it in production in five years, but that is just a guess. It depends on resources, budgets and talent. Pelion in the U.S. is working on magnesium, they have computers working on the combinations that are compatible.
Posted by: SJC | 01 June 2015 at 08:06 AM
With the concentration of efforts in battery research and the wide variety of materials being studied I believe it will not be long before we see dramatic improvements commercially available.
Posted by: Paroway | 01 June 2015 at 08:27 AM
A 'man on the moon' and 'A-bomb' were mentioned to illustrate what can be done in a short time when essential resources and the will to do it are there. It could have been the 'Jet engine' or Jumbo-Jets' or 'rockets' or various 'vaccines' or 'high speed e-trains in Europe and China' etc.
For Toyota to use the same low performance battery technology in their HEVs for 18+ years while higher performance units exist is questionable?
Let's hope that the TESLA-PANASONIC mega-factory will be more progressive and use more recent technologies..
Posted by: HarveyD | 01 June 2015 at 09:10 AM
Toyota has skin in the hydrogen game so they are somewhat conflicted about BEVs and FCVs; but, the good news is they are actually active in traction battery research.
I think the Tesla factory and the DOE JCESR project are the best bets for bringing the 'better battery' to market anytime soon.
Posted by: Lad | 01 June 2015 at 12:07 PM
Every so often,we get massive leaps forward, as exemplified by
the moonshot, antibiotics, A and H bombs, and the 50 years of Moore's law in microelectronics.
But not everything is as dramatic as those and are subject to more incremental changes.
Batteries are one of these evolutionary technologies.
You have to balance so many parameters:
Energy, power, safety, weight, cost, cycles.
Companies make advances in one, but not in all; in many ways it is like a game of snakes and ladders where you go up a few, but back some other parameters.
A lot of money is being spent by a lot of people to make progress, but it is slow (but steady). So things are getting better (vis Tesla and Panasonic), but it is not dramatic, (not like PCs in the 1990s and 2000s) or smartphones since 2007.
You can see progress: alcaline batteries are way better than zinc carbon, LiIon is better than NiMh, but we are waiting for safer LiIon and newer technologies which could change everything. maybe we will have to go from rechargeable to "factory rechargeable" (LiAir for instance), or maybe it will be something out of the blue like this.
"people" want improved batteries so much, and so much is being spent on research, that we can expect improvements, possibly even breakthroughs in the future, but who knows when or where or what technology.
It would be a brave man* that would bet on a single technology.
* or woman.
Posted by: mahonj | 01 June 2015 at 04:11 PM
Research bothers the private sector, there is no guarantee of return in the time frame they want. This is why so much of it is done at public institutions. Yet another way the private sector benefits from public dollars.
Posted by: SJC | 01 June 2015 at 06:09 PM
Regarding battery research, a lot is funded by private companies such as car manufacturers or chemical producer. I have never been more free to do research than when I was funded by a private company actually, so it is not that easy.
I still believe that comparison with moore's law, a-bomb or other technologies are very misleading. One has to look at into details to anticipate what will be the leading technology in the battery market. Oversimplifying is not always that good.
Posted by: toitoimontoi | 01 June 2015 at 11:29 PM
This chemistry uses significative quantities of Boron.
Interesting technology, but does not fit traction battery requirements.
Boron is scarce, VERY expensive.
Posted by: peskanov | 02 June 2015 at 03:13 AM
Toyota is one of the few car companies doing battery research. They want it for themselves and they want to advance beyond present methods. This is the difference, public research can be available to ALL car makers.
Posted by: SJC | 02 June 2015 at 07:30 AM