U Waterloo, GM R&D team develops new very high-performance silicon-sulfur-graphene electrode for Li-ion batteries

27 October 2015

Researchers from the University of Waterloo and General Motors Global Research and Development Center have developed a new electrode material for Li-ion batteries that leverages the strong covalent interactions that occur between silicon, sulfur, defects and nitrogen.

In an open-access paper in the journal Nature Communications, they report that the new electrode material shows superior reversible capacity of ~1,033 mAh g−1 for 2,275 cycles at 2 A g−1. The electrode showed a high coulombic efficiency of 99.9%, as well as high aerial capacity of 3.4 mAh cm−2. Professor Zhongwei Chen, leader of the Waterloo team, expects to commercialize this technology and expects to see new batteries on the market within the next year.

Current LIBs [Li-ion battery] systems utilize graphite anodes, where energy is stored by intercalating lithium into the graphite layers. This arrangement, while commercially successful, can only deliver a maximum theoretical capacity of 370 mAh g−1. Incorporating additional components offers the potential to dramatically improve this capacity, whereby silicon can provide up to 4,200 mAh g−1 in theory. While Si-based composites offer immense promise as new generation anode materials, extreme changes in volume during lithiation and delithiation lead to structural degradation and debilitating performance loss over time that impedes their practical application.

Significant efforts have been devoted to tackling these problems by engineering Si-based electrodes at the nanoscale. … We have introduced the concept of using a flash heat treatment that dramatically improved the interfacial properties in the electrode design. However, the limitation in electrode loading and the high cost of high temperatures have led us to think of a new electrode design.

Herein we introduce a new electrode design concept that … involves wrapping SiNP [silicon nanoparticles] with S-doped graphene (SG), and then shielding this composite arrangement with cyclized polyacrylonitrile (PAN). … This provided a robust hierarchical nanoarchitecture that stabilized the solid electrolyte interphase (SEI) and resulted in superior reversible capacity of ~1,033 mAh g−1 for 2,275 cycles at 2 A g−1.

—Hassan et al.

 Schematic of electrode process design. (a) Components mixing under ultrasonic irradiation, (b) an optical image of the as-fabricated electrode made of SiNP, SG and PAN, (c) the electrode after SHT, (d) Schematic of the atomic scale structure of the electrode. Source: Hassan et al. Click to enlarge.

The resulting material consists of micron-scale clusters in which the SiNP are well wrapped by SG and invariably dispersed within the nanosheets matrix.

The SG–Si delivers an initial discharge capacity of 2,865 mAh g−1, based on all masses of SG, c-PAN and Si, with a high first-cycle Coulombic efficiency of 86.2%. (All capacities reported are based on the total mass of SG, c-PAN and Si.) The aerial charge capacity is about 3.35 mAh cm−2—close to the performance targets for next generation high-energy dense LIBs. Stable cyclability up to 100 cycles was obtained with an average capacity of 2,750 mAh g−1.

A similar electrode structure, but prepared with non-doped graphene (i.e., G-Si), yielded an inferior rate capability and cycling stability; the high capacity of the G–Si persists only for 80 cycles, then fades gradually, reaching ~400 mAh g−1 after 800 cycles.

The researchers attributed the capacity fading mainly to the degradation of the Si structure, where the expansion and shrinkage of SiNP during cycling leads to the separation from graphene scaffold, and subsequent loss of conductivity and instability in the SEI structure. They observed that the “significantly different electrochemical performances put a spotlight on the important role of sulfur in binding the SiNP to the surface of SG.

In summary, the novel design of a Si-based electrode through the covalent binding of commercial SiNP and SG along with cyclized PAN offers exceptional potential in the practical utilization of Si anodes for LIB technologies. This covalent synergy enables superior cycling stability along with a high aerial capacity of the electrode, which is close to that of commercial technologies. Such a rational design and scalable fabrication paves the way for the real application of Si anodes in high-performance LIBs. The interaction between S and Si plays a critical role of improving the long-term cycle stability, in addition, the synergistic effect of the covalent bonds between Si–S, the facilitated charge transfer by 3-D graphene network and cyclized PAN and the improved electrode integrity all contributed to the superior cycle performance.

—Hassan et al.

Support for the work came from the Natural Sciences and Engineering Research Council of Canada (NSERC), the University of Waterloo, and the Waterloo Institute for Nanotechnology. Additional support came via the US Department of Energy (DOE) Office of Vehicle Technologies under contract no. DE-AC02-05CH11231, subcontract no. 7056410 under the Batteries for Advanced Transportation Technologies (BATT) Program.

Resources

• Fathy M. Hassan, Rasim Batmaz, Jingde Li, Xiaolei Wang, Xingcheng Xiao, Aiping Yu & Zhongwei Chen (2015) “Evidence of covalent synergy in silicon–sulfur–graphene yielding highly efficient and long-life lithium-ion batteries” Nature Communications 6, Article number: 8597 doi: 10.1038/ncomms9597

This coud become the 3 - 3 - ? EV battery that many have been waiting for?

If so, extended range affordable BEVs may be on the horizon?

Remarkably clear description of the technology and implications. Kudos, Hassan et al.

Harvey

I know the US DOE came up with the 5-5-5 term a few years ago but I've sort of lost track of what that actually means as there is such a wide variety of batteries out there.

I think there is a limit to the energy density required before improvements, no longer have much of an impact. Fifty kwh is probably the standard for a small economic vehicle that meets the normal range requirements when the charging networks become well built out. Doubling the energy density from 165 w/kg to 330 would reduce the weight of the pack from 300 kg to 150 kg, but further doubling to 660 w/kg would only reduce the pack weight by another 75 kg which could probably also be accomplished by light-weighting.

The battery cost seems far more important, and along with the costs, I'm curious about the cycle life. The $100 / kwh battery by 2020 appears to be a generally accepted standard but the number of cycles is never mentioned. If it is 500 or less then the cost per cycle is 20 cents which is not so great even by today's standards. There are some 10,000 cycle batteries and I doubt if they cost$2000/kwh.

@Calgarygary:

5-5-5 batteries will probably not be around as claimed by 2020 but may be marketed by 2025 or so.

By 2020 we may see some 3-3-? batteries.

There are no doubts that total number of possible cycles will eventually go up to close to 10,000 (under restricted conditions) and that the cost per cycle will effectively decrease with mass production and lower cost materials.

The next advanced battery will have to be cheap to manufacture and almost perfect quality over billions of cells.

What would give me some hope for this chemistry is that not only are both the US and Canadian government research groups supporting this but GM R&D is working with the University researchers. This probably means that there is promise of making commercially viable batteries.

This website is depressing.

Previous news, published 2 days ago : http://www.greencarcongress.com/2015/10/20151026-gr%C3%B6ger.html
(open-acess review)
"On the Li-sulfur side, it is difficult to achieve the expected gravimetric energy density from a lithium sulfur battery-system. Along with that, the requirements of the automotive industry have also changed over the years, with increased focus on volumetric energy density rather than only gravimetric energy density. The achievable volumetric energy densities for lithium—sulfur batteries, independent of the anode, will always be substantially lower than that of lithium ion batteries, the authors observe"

And then a news like that is published, only describing a nice scientific work, and people in the comment section are already talking about commercialization, 5-5-5 goals... You really think that this paper does change something ? Use of silicium, sulfur, graphene, the worst materials for volumetric densities, change anything in terms of energy densities ? Warping silicium in polymer increases energy densities ?

And it is like that all the time. It will be the same for the next Si-graphene-ionic-liquid-nano-sulfur-whatever-battery, with excellent cycle life obviously. When are you going to understand that scientific work is only scientific ? They don't even use relevant metrics (mAh/g ?) for pratical applications.
(Don't get me wrong, this is a really good work in terms of material science.)

Then go away.

You can accept substantially lower volumetric performance if you have good enough gravimetric performance, and other things can make up for it.  For instance, going to in-wheel motors or even per-wheel motors mounted on the suspension arms frees up a good deal of volume occupied by differentials, gearcases and driveshafts.  This can be devoted to batteries instead.

Another factor here is charge/discharge rate and cycle life.  2300 cycles at 1/day is in excess of 6 years (probably 15 in normal use), and a 2C charge rate allows charging at 50 kW with a battery as small as 25 kWh.  If the material can be made cheaply at high quality, the performance is good enough to enable a very large expansion in the uses in the market.  If you can design a vehicle around bulky hydrogen tanks, even Li-S doesn't present an insuperable problem.

Suppose you have a Tesla-class vehicle with 100 kWh of batteries capable of 2 C charge and discharge.  That's ~270 horsepower peak output (not supercar, but very good) and a "filling speed" of over 500 MPH assuming 380 Wh/mi.  There are precious few people who need cruising range that long, and many who'd love to be able to pass by the filling station for the rest of their lives and would put up with slightly more pit-stop time on long trips.

"Rational design and scalable fabrication paves the way for the real application of Si anodes in high-performance LIBs".

Interesting that GM R&D is involved in this research. GM's goal would be 'real application of Silicon anodes in high-performance LIBs'.

GM's LIB cell provider, Samsung SDI has a table on its website which lists 2019 as their target date for advanced LIBs with Energy Density of 250Wh/kg:
http://www.samsungsdi.com/automotive-battery/battery-cells

"Silicon makes up 25.7% of the earth's crust by weight, and is the second most abundant element, exceeded only by oxygen. It is found largely as silicon oxides such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper and opal".

I hope that this GM R&D can overcome the serious issues with silicon that cause the battery to be inefficient and quickly degrade.

"While Si-based composites offer immense promise as new generation anode materials, extreme changes in volume during lithiation and delithiation lead to structural degradation and debilitating performance loss over time that impedes their practical application".
"We introduce a new electrode design concept that involves wrapping silicon nanoparticles with Sulpur-doped graphene (SG)".

John Goodenough who developed the cathode that made LIBs possible, is also researching a better anode, using sulphur or lithium metal:
"Goodenough seems most passionate about ending his career with a last, big invention. He is trying, of course, to make a super-battery, one that will make electric cars truly competitive with combustion, and also economically store wind and solar power.
But the path he has chosen involves one of the toughest problems in battery science, which is how to make an anode out of pure lithium or sodium metal. If it can be done, the resulting battery would have 60% more energy than current lithium-ion cells. That would instantly catapult electric cars into a new head-to-head race with combustion. Over the years, numerous scientists have tried and failed—it was lithium metal, for instance, that kept setting Stan Whittingham’s lab on fire at Exxon in the 1970s. Although Goodenough will not spell out his precise new idea, he thinks he is on to something".

http://qz.com/338767/the-man-who-brought-us-the-lithium-ion-battery-at-57-has-an-idea-for-a-new-one-at-92/

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