New hybrid carbon/sulfur cathode material enables high-energy, high-power Li-sulfur battery; “matching the level of engine-driven systems”
16 May 2014
Researchers at Tsinghua University have combined two types of carbon materials to create a new composite sulfur cathode material for a high-energy and high-power lithium-sulfur battery. In a paper in the journal Advanced Functional Materials, they report the composite cathode (a hierarchical all-carbon nanostructure hybridized with small cyclo-S8 clusters) has a high specific capacity of 1121 mAh g−1 at 0.5 C; a favorable high-rate capability of 809 mAh g−1 at 10 C; a very low capacity decay of 0.12% per cycle; and cycling stability of 877 mAh g−1 after 150 cycles at 1 C.
As sulfur loading in the cathode increases from 50 wt% to 77 wt%, high capacities of 970, 914, and 613 mAh g−1 are available at current densities of 0.5, 1, and 5 C, respectively. Based on the total mass of packaged devices, gravimetric energy density of the cell consisting of the composite cathode and a lithium-metal anode (GSH@APC-S//Li) is expected to be 400 Wh kg−1 at a power density of 10 kW kg−1—“matching the level of engine-driven systems,” according to the team.
| sp2 nanocarbon systems |
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| Carbon atoms have six electrons: two are in 1s states, and four are valence electrons, occupying the 2s and 2p orbitals. sp2 hybridization refers to the mixing of valence electronic states. |
| When carbon atoms bind to each other, their 2s and 2p orbitals can mix with one another in hybridized orbitals. In the sp2 configuration, the 2s and two 2p orbitals mix to form three in-plane covalent bonds; each carbon atom has three nearest neighbors, forming the hexagonal planar network of graphene. |
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| Examples of sp2 carbon materials, including (a) single-layer graphene, (b) triple-layer graphene, (c) a single-wall carbon nanotube, and (d) a C60 fullerene, which includes 12 pentagons and 20 hexagons in its structure. Jorio et al. |
As often noted, the lithium-sulfur battery is one of the most promising candidates for next-generation energy storage because of its very high theoretical energy density of 2,600 Wh kg-1 (based on lithium-sulfur redox couple); wide operating temperature range benefiting from a unique multiple-electron-transfer chemistry; and the abundant reserves and environmental friendliness of sulfur.
However, well-known barriers to commercialization include the ultra-low electrical conductivity of sulfur and its lithiated products; huge volumetric changes during charge and discharge; and the shuttling mechanism of soluble intermediate polysulfides.
The new Tsinghua cathode material combines sp2-hybridized nanocarbon (e.g., carbon nanotubes (CNTs) and graphene) and nanostructured porous carbon. The former exhibits extraordinary mechanical strength and electrical conductivity but limited external accessible surface area and a small amount of pores, while the latter affords a huge surface area and abundant pore structures but very poor electrical conductance.
Combining the two creates a novel carbon nanoarchitecture with the advantages of each. The sp2 graphene/CNT interlinked networks give the composites good electrical conductivity and a robust framework, while the meso-/microporous carbon and the interlamellar compartment between the opposite graphene accommodate sulfur and the lithium polysulfides; provide accessibility for liquid electrolyte to the active material; and suppress the shuttle behavior due to the spacial confinement.
The team will present a paper on their work at the upcoming 17th International Meeting on Lithium Batteries in June in Como, Italy. Future work will explore the increase of sulfur loading, as well as the optimization of the structure of the cell.
Resources
Peng, H.-J., Huang, J.-Q., Zhao, M.-Q., Zhang, Q., Cheng, X.-B., Liu, X.-Y., Qian, W.-Z. and Wei, F. (2014), “Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium-Sulfur Batteries” Adv. Funct. Mater., 24: 2772–2781 doi: 10.1002/adfm.201303296
Peng, H.J. et al. (2014) “Hierarchical Nanostructured Carbon/Sulfur Hybrid Cathode for High-Performance Lithium-Sulfur Battery,” IMLB 17
Jorio, A., Saito, R., Dresselhaus, G. and Dresselhaus, M. S. (2011) “The sp2 Nanocarbons: Prototypes for Nanoscience and Nanotechnology,” in Raman Spectroscopy in Graphene Related Systems, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. doi: 10.1002/9783527632695.ch1
This seems to have the best of both worlds. It may be too good to be true.
However, if it pans out and can be mass produced at an affordable price by 2020 or so, the world may have he first generation of affordable extended range BEVs.
Posted by: HarveyD | 16 May 2014 at 12:32 PM
0.12% fade per cycle is "very low"? As in 74% capacity loss after 100 cycles?
Posted by: Jim McLaughlin | 16 May 2014 at 04:59 PM
@jim, it's a little more than a tenth of a percent loss. How are you getting 74% loss after 100 cycles?
Posted by: electric-car-insider.com | 16 May 2014 at 05:30 PM
0.12% x 100 = 12%
100% - 12% = 88%
88% after 100 cycles is good for a lithium sulfur battery
Posted by: SJC | 16 May 2014 at 06:43 PM
@SJC
You got the math wrong but still got the right answer.
It should be 0.9988 ** 100 = 0.88685 = 88.68%
Sometimes doing the wrong thing still works.
Posted by: sd | 17 May 2014 at 09:05 AM
My approximation was close enough to show magnitude, the more accurate calculation is the sum of the loses in on each charge, which is slightly greater than 88% capacity left after 100 charges.
Posted by: SJC | 17 May 2014 at 06:20 PM
I guess it depends on what a "cycle" is.
Does it mean a full 0-100 (or 0-90)% discharge ?
What if you only discharge to 50% - what does that count as.
My guess is - for best longevity, you should size your batteries such that a typical discharge is 50% of the full capacity.
Thus if you have a leaf and can go 80 miles and have a 40 mile commute - you best be able to charge at work.
(or a 20 mile there and back cycle).
Or can someone correct this.
Posted by: mahonj | 18 May 2014 at 08:52 AM
Fossil Fuels Face the Prospect of $30T in Losses
Assessing the combined impact of climate policy, pollution controls and the declining cost of renewables
http://www.greentechmedia.com/articles/read/fossil-fuels-face-30-trllion-losses-from-climate-renewables
Posted by: SJC | 18 May 2014 at 02:24 PM
@mahonj
I think batteries for BEVs will always be sized for range. When they are cheap and small enough, people will want whatever gives them 300 miles range. But they will drive only 40 miles for 360 days out of the year. Just about every article on new batteries describes capacity lifetime in terms of deep discharge, but practical use will be different.
Posted by: Zhukova | 20 May 2014 at 06:12 PM
So .4 kwh/kg x 4 miles/kwh = 1.6 miles/kg. 300 miles would need about 187 kg. But this gives 10kw/kg x 187 kg = 1870 kw or 2,500 hp, more than matching the power of engine-driven systems.
Posted by: Zhukova | 20 May 2014 at 06:57 PM
What I meant was that people will drive 40 miles each day and recharge at night. So for a 300 mile battery, the discharge is only 13%.
Posted by: Zhukova | 20 May 2014 at 07:17 PM