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Now the MIT group has adapted these methods to make battery electrodes. Lithium-ion batteries are charged and discharged when lithium ions move from one electrode to the other, driving or being driven by an external current. The more total lithium the battery can store, the greater its total energy storage capacity. The faster the ions can move out of one electrode and into the other, the greater its power. In work published this week in the journal Nature Nanotechnology, the MIT group showed that lithium ions in a battery electrolyte react with oxygen-containing chemical groups on the surface of the carbon nanotubes in the film. Because of the huge surface area and porous structure of the nanotube electrodes, there are many places for the ions to react, and they can travel in and out rapidly, which gives the nanotube battery high energy capacity and power, says Shao-Horn.
"This work has demonstrated once more that the development of methods for careful structural control at the nanoscale leads to major improvements in materials performance," says Nicholas Kotov, professor of chemical engineering at the University of Michigan. "I believe that it's just the beginning of the major improvement of lithium batteries using a materials engineering approach."
The next step, says Hammond, is to "speed things up." Using the dipping method, the group is able to make relatively thick nanotube films, but it takes a week. "If you want to make a car battery, you need to make it thicker, and over large areas," says Hammond. Instead of dipping a substrate in the two nanotube solutions, Hammond's group is now making the electrodes in a few hours by alternately spraying dilute mists of the two nanotube solutions. A major advantage of this misting method is that it's compatible with large-area printing processes that promise speed and compatibility with a wide range of substrates. For example, nanotube batteries might be printed directly onto integrated circuits.
A new method produces dense arrays of carbon nanotubes for digital logic.
The large facility is meant to reflect a change of direction for the bankrupt company.
Wording almost seemed to skirt around issue. Probably reflecting the wording in the press release.
Actually sounds very interesting and has lots of obvious advantages; Rapidity of discharging and perhaps charging being important, especially in hybrid applications, as well as durability.
If one adds increased energy density and high efficiency (most of what goes in comes out) and mass manufacturing and this could be revolutionary. Which is why the wording was so odd. Sounds like they've only got two or three out of four nailed down. Which is OK, a very respectable breakthrough. But if so, say so; adds to "your," whoever "you" is/are, credibility.
Actual power density is not the issue being skirted. The point almost being made is, the large surface area the electrons cross to get in/out of the anode/cathode reduces heat generated to negligible, thus preventing fire. This allows the battery to be filled/emptied quickly without paying the otherwise inevitable price : spontaneous ignition. Thus the unfortunate comparison to ultracapacitor.
The point not being made, and not just here, is the life cycle of SOME SORTS of Lithium Ion Batteries depends not only on how you use it, but also on the simple passage of time. A case of use it, because you are going to lose it. Not a sales point, in spades. You want to be careful about this as it DOES NOT apply to every type of LIon Battery.
The point being omitted intentionally is the manufacturers name. I think it is probably A123. It may be MIT has made a deal with another manufacturer, but they certainly have one with A123. I seem to recall GM does too.
Did I miss where they spoke about cycle life? Energy density and speed of discharge is useless if you can only use it a few times.
Re: No reference to cycle life??
the nature article report exceptional stability. it sounds like studying the stability is less mature than the energy density and power density analysis though. from the article:
The stability of the functional groups on these MWNTs is remarkable when compared to the considerable losses of carbonyl derivative molecules within 50 to 100 cycles reported recently34, 35, 43. We hypothesize that the cycling stability of the LBL-MWNT electrodes can be linked to the strong chemical covalent bonding of the surface functional groups on the MWNTs, in contrast to the gradual separation occurring between the active carbonyl groups and carbon additives in composite electrodes during cycling.
Still thinking in terms of hybrids for nano-tube Li batteries? If these batteries can make it to market with all the capability they claim the car would have sufficient range and quick charging capability to ditch the combustion engine all together.
Thank you to the other commenters for educating me on more of the technical questions. I'd like to add a very non-technical question: when are they projecting availability of this technology? Are they looking at producing these batteries in the next few years or is this yet another "5-10 year" technology that may or may not ever see the light of day?
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tammons
8 Comments
what about energy density
I can see the logic that the carbon tubes can store and release ions faster thus increasing power density but what about energy density of the battery? Comparing it to an ultra capacitor is not very encouraging. Will it help to provide longer running time in a Lap Top or extending range over existing Lion batteries in an electric car?
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yoatmon
30 Comments
Re: what about energy density
The following is a theoretical evaluation of a successful symbiosis of Graphene and CNTs. Practical R&D results from MIT support these theories.
Stacks of several µ-meter thick sheets (approx. the size of a standard sheet of paper) connected in series (strings) and parallel connected strings all stacked to approx. 1mm thick to produce a Ultra-Super Cap could reach an energy density approx. 20 to 25 times higher than present Li-Ion batteries.
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