Sandwich-like MnO2/Mn/MnO2 nanotube array shows high supercapacitive performance
28 June 2012
|
|
| Nanotube array architecture, triple-layered structure, and high conductivity in electrodes provide ion and electron “superhighways”. Credit: ACS, Li et al. Click to enlarge. |
Researchers at Sun Yat-sen University in Guangzhou, China designed and synthesized novel MnO2/Mn/MnO2 sandwich-like nanotube arrays for supercapacitors. In testing reported in the ACS journal Nano Letters, the hybrid MnO2/Mn/MnO2 sandwich-like nanotube arrays exhibited an excellent rate capability with a high specific energy of 45 Wh/kg and specific power of 23 kW/kg and excellent long-term cycling stability (less 5% loss of the maximum specific capacitance after 3,000 cycles).
The high specific capacitance and charge−discharge rates offered by the sandwich-like nanotube arrays make them promising candidates for supercapacitor electrodes, combining high-energy densities with high levels of power delivery, the researchers suggest.
Supercapacitors—also called ultracapacitors or electrochemical capacitors (ECs)—offer high power density, fast charging−discharging rate, and excellent cycle stability. Various materials, including carbon materials, transition-metal oxides, conducting polymers, and hybrid composites have been widely studied as electrodes for these devices, the team notes.
|
|
| Left. Ragone plots (energy density vs power density): (1) MnO2/Mn/MnO2 SNTAs and (2) MnO2 NTAs. Right. Comparison of cycling performance of (1) and (2) for 3000 cycles at 1.5 A/g. (The specific mass loading is 0.32 mg/cm2). Credit: ACS, Li et al.Click to enlarge. |
There has been extensive interest in developing the inexpensive transition-metal oxide electrodes, such as MnO2, Co3O4, NiO, VOx, and TiO2 for supercapacitors. MnO2 is an attractive electrode material owing to its high theoretical specific capacitance, low cost, natural abundance, and environmental friendliness. However, poor electrical conductivity (10−5∼10−6 S/cm) remains a major challenge and limits rate capability for high power performance.
Recent work has explored possible solutions such as hybrid composite nanostructures in which thin MnO2 layers were loaded on highly conductive materials such as metal, conducting polymer, carbon nanotube, or graphene for enhanced performance.
The enhanced performance was also obtained by coating MnO2 onto SnO2 nanowires, ZnO nanorods, and Zn2SnO4 nanowires. In all of the above cases, MnO2 is of relatively low weight fraction and usually has excellent rate and cycling performance; however, the energy and power densities of electrodes are sacrificed.
To realize the practical applications for high-performance ECs that needs large capacitance and high energy storage, here we design and synthesize novel MnO2/Mn/MnO2 sandwich-structured nanotube arrays (SNTAs) with high MnO2 weight fraction...The aligned SNTAs represent a new prime example of materials with a well-defined pore structure.
—Li et al.
The team outlined four primary reasons for taking this approach:
The middle crystalline metal Mn layer in the sandwich provides electron “superhighways”—highly conductive cores—for charge storage and delivery, which overcomes the key weakness (the limited electric conductivity) of MnO2.
The MnO2/Mn/MnO2 SNTAs relax the transport of ions because of the hollow nanostructures. In addition, the double thin layers of MnO2 in SNTAs would enable fast, reversible Faradaic reactions and provide short ion diffusion paths.
The SNTAs with double MnO2 shells would obviously enhance the utilization rate of MnO2 material because of anisotropic morphology, large specific surface area, and hollow nanostructures.
The SNTAs directly growing on conductive substrate have an excellent electrical contact with current collectors, and this would let each MnO2/Mn/MnO2 nanotube effectively participate in electrochemical reactions with almost no “dead” volume.
The maximum specific capacitances of 937 F/g at a scan rate of 5 mV/s by cyclic voltammetry (CV) and 955 F/g at a current density of 1.5 A/g by chronopotentiometry were achieved for the MnO2/Mn/MnO2 sandwich-like nanotube arrays in solution of 1.0 M Na2SO4.
Resources
Qi Li, Zi-Long Wang, Gao-Ren Li, Rui Guo, Liang-Xin Ding, and Ye-Xiang Tong (2012) Design and Synthesis of MnO2/Mn/MnO2 Sandwich-Structured Nanotube Arrays with High Supercapacitive Performance for Electrochemical Energy Storage. Nano Letters doi: 10.1021/nl301748m
This sounds like a marriage made in heaven with fuel cells.
2-3 kgs of these and the surge in energy needed for braking is covered, as is regenerative braking.
Posted by: Davemart | 28 June 2012 at 04:39 AM
S/be 'energy needed for acceleration'
Posted by: Davemart | 28 June 2012 at 04:43 AM
As with other supercapacitors we've been reading about lately, the performance is there and now it is just a question of cost.
Posted by: Engineer-Poet | 28 June 2012 at 06:22 AM
I have no idea what the final costs will be, but the materials at least are cheap enough.
Posted by: Davemart | 28 June 2012 at 06:26 AM
Wait, asides of the beauty of the results that makes these supercapacitors battery like, how do they grow the nanotube ? with some CVD or epitaxy then this won't be used for anything else than powering a cell phone at very best. Nanotube are extensively studied but there is still no manufacturing tool to make them in volume as far as I am informed
Posted by: Treehugger | 28 June 2012 at 07:03 AM
Yes DM ... it would be an ideal companion for FC equipped vehicles or for BEVs equipped with very high energy density batteries.
Cost, like for most new technologies, will come down with mass production in the right place.
Posted by: HarveyD | 28 June 2012 at 07:23 AM
Harvey
Your simplistic view of things is just incredible, so mass production is the solution to lower cost of all goods ? the reality is that most of lab discoveries don't pass this barrier of being mass produce-able. Growing array of nanotube, do you have any idea of what it looks like ? it requires CVD machines the size of a truck to grow a substrate of a few inches size and at a snail pace.
Posted by: Treehugger | 28 June 2012 at 08:27 AM
Remember 300 baud internet phone modems? A few resources, including mass production, improved performance by factors of thousands - and reduced costs in a few years.
Posted by: kelly | 28 June 2012 at 09:09 AM
The same phone pairs which could support an alarm circuit could also support a T1 line; the long stagnation in data rates was more due to Bell obstruction than technological backwardness.
Thank goodness neither autos nor capacitors are a regulated monopoly!
Posted by: Engineer-Poet | 28 June 2012 at 10:01 AM
yes kelly
and also laserdisc, 8track, betamax
for everything mass producable and usefull there are dozens that go nowhere
Posted by: danschl | 28 June 2012 at 12:35 PM
You can't really compare information with power.
Information is subject to Moore's law (at present), power isn't.
That is why we have 256 GB SSDs and 900 M transistor processors, but still have aircraft which fly at 600 mph, as they have done since 1960.
Posted by: mahonj | 28 June 2012 at 02:35 PM
Treehugger, I prefer to think of Harvey as a "glass half full" kind of guy :-)
Posted by: DaveD | 28 June 2012 at 03:19 PM
Technically, the glass is always "fully" full: A glass with water in one half still has air in the other half. One half of this + one half of that = a full glass. ;-)
Posted by: ai_vin | 28 June 2012 at 09:26 PM
LOL Now that is one I have never heard before. Thanks ai_vin
Posted by: DaveD | 29 June 2012 at 03:29 AM
Tree....you know very well that mass production (in the right place) is the ONLY way to cut cost by 10x or even more. That's what has already happened with small Li-On batteries and will no doubt happen with most, if not ALL, new battery technologies. EV batteries cost is going from 2,000/Kwh to as low as $150/Kwh (by 2020?) while performance will probably go up 3X to 4X or even more.
Look at the latest $500 iPad. Almost equivalent units are currently being produced at under $50 in India and China. By 2020, expensive Desktops and Laptops will find their way to the museum and will be replaced by lower cost, higher performance 7, 10, 11.6, 13.3 ++ inch tablets
$5000 large flat LCD TVs of 10 years ago are now available at under $500 with improved performance.
That is not simplifying, it is historical.
A big question remains, are we the right place to do it? Probably not.
Posted by: HarveyD | 29 June 2012 at 11:00 AM
Tree....I recently bought a bunch of GU10, 12-Watt Dimmable, LED bulb made with 4X - 3W excellent CREE modules @ $3.12 each from China. They are Warm White type and work like a charm with a Leviton 6633 LED Preset Dimmer. Equivalent LEDs sell for $32+ each in the local HomeDepot and other local HW Stores. That's a bit more than a 10X reduction in price.
Than same will soon happen with EV batteries.
Posted by: HarveyD | 29 June 2012 at 12:04 PM
A pessimist thinks the glass is half empty.
An optimist thinks the glass is half full.
A mechanical engineer thinks the glass is twice as large as it needs to be.
Posted by: sheckyvegas | 29 June 2012 at 01:59 PM
A successful investor/speculator would use a shrinkable imported paper cup to always look full and fool the users?
Posted by: HarveyD | 29 June 2012 at 02:27 PM
In practice, the world may not need to mass produce more than 5% of the inventions. Producers can pick which one will sell with a reasonable profit? The good inventions to be mass produced (at a relative low cost in the right places) in the next ten years could be:
1. Improved (from 100 lm/watt to 250+ ml/watt) very low cost LED lights. Coming very soon.
2. Improved lower cost ($50) tablets with educational apps.
3. Improved (from 150 to 450+ Wh/Kg) lower cost EV batteries
4. Very light in-wheel e-motors.
5. Electronic drivers assistance every where.
6. Ultra light weight car bodies.
7. Ultra high speed (fixed and wireless) EV battery chargers.
8. Ultra high efficiency (40+ %) lower cost solar panels.
9. Improved Heat-Pumps for homes and vehicles.
10. Improved window panes for homes and vehicles.
11. Many more....
Posted by: HarveyD | 29 June 2012 at 02:45 PM
Harvey, can't you even pretend that this post is about supercapacitors?
Posted by: Engineer-Poet | 29 June 2012 at 03:49 PM
I find infinite techno optimism as boring as the doomers chants......
Posted by: Davemart | 30 June 2012 at 04:20 AM
Hummm......
Seems to me that someone said "As with other supercapacitors we've been reading about lately, the performance is there and now it is just a question of cost."
And following that post the conversation moved to how the cost of other technologies had improved.
Why supercapacitors, and batteries, wouldn't follow that same track eludes me. I'm sure that right now some very bright folks are busting their butts working on how to get prices down and capture market share.
Posted by: Bob Wallace | 30 June 2012 at 10:32 PM