MoS2/Graphene composite materials as high-performance anodes for Li-ion batteries
21 May 2011
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| Left: Rate capability of MoS2/G samples at different current densities:(1) MoS2/G (1:1); (2) MoS2/G (1:2); (3) MoS2/G (1:4). Right: cartoon of the composite. Credit: ACS, Chang and Chen. Click to enlarge. |
A pair of researchers from Zhejiang University (China) have synthesized layered MoS2/graphene (MoS2/G) composites using a facile biomolecular-assisted process for use as high-performance anode materials in Li-ion batteries. The MoS2/G composite with a Mo:C molar ratio of 1:2 exhibited the highest specific capacity of ~1100 mAh/g at a current of 100 mA/g, as well as excellent cycling stability and high-rate capability.
In a paper published in the journal ACS Nano, researchers Kun Chang and Weixiang Chen attributed the electrochemical performances of the MoS2/G composites to their robust composite structure and the synergistic effects between layered MoS2 and graphene.
Graphite, widely used in current commercial Li-ion batteries (LIB), is limited by a small theoretical specific capacity (372 mAh/g). Graphene, a flat, one-atom-thick monolayer exfoliated from graphite, shows excellent electronic behavior and mechanical properties, as well as a large specific surface area, and has attracted considerable research interest for many applications, the authors note.
Graphene nanosheets and their composites thus have been intensively investigated for their electrochemical properties to determine their suitability as anode materials for LIBs, with high capacities from ~600 to 1000 mAh/g having been observed.
To date, numerous studies on metal and metal oxides supported on graphene have been conducted, in which their electrochemical performance as anode materials for LIBs was considerably enhanced. However, research on layered metal sulfides supported on graphene as LIB anode materials has hardly been reported thus far.
As a typical layered transition metal sulfide, MoS2 has the analogous structure of graphene; this structure is composed of three stacked atom layers (S–Mo–S) held together by van der Waals forces. This layered structure enables the convenient intercalation and exfoliation of Li+ ions.
—Chang and Chen
Chang and Chen synthesized their layered MoS2/G composites by an L-cys-assisted solution phase method and subsequent annealing in a H2/N2 atmosphere at 800 °C for 2 h. The layered MoS2 are supported on the graphene surface, which then form the MoS2/G composites.
The MoS2/G composites exhibit a 3D architecture morphology consisting of curved nanosheets, attributed to the self-assembling of graphene hydrogel during the hydrothermal process. In particular, the MoS2/G (1:2) composite delivers a 3D sphere-like architecture.
In addition to the high specific capacity, the composites showed excellent cyclic stabilities. After 100 cycles, the reversible capacities of the MoS2/G (1:1), MoS2/G (1:2), and MoS2/G (1:4) electrodes remained at 734, 1187, and 978 mAh/g, respectively.
Among the different composite materials fabricated, MoS2/G (1:2) also demonstrates better rate performance. Even at a high current density of 1000 mA/g, the specific capacity remains at ~900 mAh/g, which is still higher than that of MoS2 at a low current density of 100 mA/g. Additionally, the extraordinary cycling stabilities of the three electrodes are exhibited at various current densities, the authors found.
The electrochemical evaluations reveal that all the MoS2/G composite electrodes exhibit much higher specific capacities and more cyclic stability than bare MoS2 electrodes...the present results suggest that this novel kind of MoS2/ G composite holds great potential as an anode material for LIBs.
—Chang and Chen
Resources
Kun Chang and Weixiang Chen (2011) L-Cysteine-Assisted Synthesis of Layered MoS2/Graphene Composites with Excellent Electrochemical Performances for Lithium Ion Batteries. ACS Nano doi: 10.1021/nn200659w
This could have excellent future potential. Could it be mass produced. Would a high performance battery. with electrodes made with these materials. be affordable?
Posted by: HarveyD | 21 May 2011 at 09:40 AM
I'm an amateur at calculating the Watt Hour density. My probably imperfect calculations result in 1.6 KWH per pound. 32 KWH for 20 pounds?
Posted by: joewilder | 21 May 2011 at 12:38 PM
I can't wait to see which one of these advances actually makes it into production and brings the price down below $200/kWh and over 500Wh/kg.
When you consider that the average person will spend about $2,500 per year at current US gasoline prices, it doesn't take long for the batteries you buy to pay for themselves.
Posted by: DaveD | 21 May 2011 at 12:49 PM
Nowhere this article gives the voltage used here. AH alone are interesting but we need the WH to asses the real capacity interest for EVs, after multiplying by the voltage, plus we need the instant W of power density to check it can fullfil all purposes including high speeds on motorway and mountain claims, and for the cycles we need to know de % of capacity left after 1K, 3K and/or 5K deep recharges, not just 100.
As DaveD points out 200$/KWH and 500W/KG is a (dream) target that would allow next gen 50KWH battery for $10K and 100KG only, and best dream 500M capable 130KWH battery for $26K and 260KG... Then need check the instant power density and the cycles it will last, and the manageability and safety.
For the cycles I would need to recharge a 50KWH battery 200M range only 2x per week, plus 1x for week-ends 1x per month, plus may be 8 per vacations trips in the summer, means # 124 x deep charges per year, so 10Y would require 1240 x charges with <10% capacity loss. Possible with this ? With 130KWH/500M Battery I could accept less clycles only charging once per week including week-ends plus 4x for vacations, would make 56 x Full charges per year only, so 10Y could work with only 560 x cycles... Can this do it ?
Posted by: CARL75014 | 22 May 2011 at 01:51 AM
Not sure how this compares with Yi Cui’s Silicon nanowire anodes but provides another path to high capacity batteries.
Along with a better anode, a better cathode is required. The most promising cathode is Linda Nazar’s Carbon-Sulfur cathode http://www.nserc-crsng.gc.ca/Media-Media/NewsbulletinStory-ArticleAnterieur_eng.asp?Id=1026 But so far this has proven to be incompatible with silicon nanowires, maybe this would work better with MoS2/G.
Posted by: Roy_H | 22 May 2011 at 07:24 AM
@joewilder,
It is nearly impossible to calculate the energy density of something like this for a number of reasons:
1) As Carl points out, they don't give the Voltage anywhere. The best we can do is assume something like 3.6V which is fairly typical for many Li chemistries
2) This is the anode only, and does not cover the cathode which would have completely different characteristics and would have to be compatible in a number of ways.
3) They don't mention what type of electrolyte is used or even whether it's liquid or if it can work with one of the new solids
4) Even if you knew all these things then you would have to take into account all the packaging and the relative weight of electrolytes and the rest of the packaging to the anode+cathode themselves.
A good guess is that this anode would give you about 900mAh @3.6V = 3,240Wh/kg. The cathodes are usually quite a bit behind this. So let's assume the average of the was ~1,500Wh/kg. Then assume they are taking up half the total weight of the battery pack they would form in the end and you're down to ~750Wh/kg.
Still a great number but even if all these assumptions were true, we have no idea how much they cost or how they react after 1000, 2000 or 3000 cycles. Would they drop off the cliff in capacity somewhere in there? Will they cost $1,000/kWh or $400/kWh? Are they safe? do they operate in a reasonable temperature range? What kind of power density would they have? (Actually, I'm betting they'd be ok on that front..."Even at a high current density of 1000 mA/g, the specific capacity remains at ~900 mAh/g")
Great research at this point, but just that: research. The 2 hour annealing process at 800degrees Celsius certainly doesn't like easy and cheap mass production. We'll see.
Posted by: DaveD | 22 May 2011 at 08:08 AM
The world need more research like this one and specially more applications AND MASS PRODUCTION TO INCREASED PERFORMANCE AND LOWER COST.
Posted by: HarveyD | 22 May 2011 at 04:43 PM
Totally agree Harvey. I'm just getting impatient to see which one(s) will hit production and can work together. There are so many breakthroughs coming and I can't tell which ones are destined for production and which ones are compatible with each other.
Imagine silicon nanowires coated with 3D graphene and using solid state electrolytes...what a great battery...if any of that is even remotely possible together, much less cost effective :-)
Exciting future :-)
Posted by: DaveD | 23 May 2011 at 04:30 AM
Integrating many new technologies into the same battery unit could constitute a major leap forward within two to three years. However, numerous patent protections make this approach almost impossible without strong unpopular government intervention and/or the temporary waving of certain patent rights.
Only two major future markets could try to do it, i.e. China and India. They have a large enough internal market to support strong demand and nobody would dare to attack them.
Of course, we would join together and try to legally stop them from mass producing such superior storage unit in the name of democracy, justice and fairness.
Posted by: HarveyD | 01 June 2011 at 01:30 PM