Now the MIT group has adapted these methods to make battery electrodes

For the negative electrode, or anode, the electrolyte also works with lithium metal films, which are lighter than current anode materials. That means the battery can provide more energy for the same weight. Based on the battery’s single cell, Seeo has calculated that it would have an energy density of up to 300 watt-hours per kilogram, which is 50 percent greater than lithium-ion batteries that are on the market today.

Indeed, when subjected to an open flame, the safer electrolytes do not catch fire. As an added bonus, says 3M’s battery-research technical manager, Doug Magnuson, the new chemistries work better at extremely cold temperatures, such as minus 40 degrees Celsius, at which other electrolytes block ion flow and effectively reduce battery capacity by 80 to 90 percent.

Those driving Tesla cars won’t immediately see the added range from the new high-energy battery cells, Straubel says, since there is a lengthy process for validating the performance of new cells. What’s more, the actual range increases can vary. (For example, electronic controls keep a battery from completely discharging to help improve safety and reliability–complete discharges can harm some battery materials. The way the battery is controlled depends upon its chemistry and other details of the cell design.)

Thin-film cells also can be stored for decades and retain almost all their charge, developers say–and deliver a powerful burst of energy when finally needed. And, in many applications, they can be actively used for decades, since they can be charged and discharged tens of thousands of times.

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 company has developed additives for existing electrolytes, as well as new electrolytes that will not react with the electrodes.

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.

Some issues likely remain. For one thing, the batteries may be costly–lithium metal is the most expensive form of lithium. Also, firm data isn’t yet available on how many recharge cycles the batteries can undergo and how they respond to safety tests. Still, Nazar says, the technology has “certainly come a long way. Our developments and those of a couple of other companies are certainly enabling it to be much closer to reality.”

The new battery still has significant issues, particularly in maintaining capacity. After just five discharge and recharge cycles, the cells lost one-third of their initial energy storage capacity and ceased to function after 40 to 50 cycles. The loss is likely due to polysulfides, chemicals that form during normal discharging and recharging.

In the new lithium-ion batteries, cobalt oxide is replaced with iron phosphate, a much more stable material. Indeed, a traditional lithium-ion battery will burst into flames in abuse tests, such as being pierced by a nail (see this A123 and this Valence video). But the new materials show little reaction at all.

Earlier this year GM had picked A123 Systems as a potential supplier of lithium-ion batteries for a new version of its Saturn Vue hybrid that can be recharged by plugging it in, giving it a 10 mile all-electric range. It could be on the roads as early as 2009.

What’s more, reducing the amount of active, energy-storing material has the counterintuitive effect of increasing the composite’s storage capacity. If too much lithium is removed from conventional cobalt oxide materials, the material degrades and quickly loses its ability to fully charge and discharge. The inactive material makes it possible to use much more of the lithium without damaging the material.

The advantages of polymer materials have warranted research on polymer electrolytes for more than three decades. In fact, lithium polymer batteries are already found in radio-controlled cars and MP3 players. But they use a polymer gel containing solvents, so, like liquid electrolytes they carry the risks of fire or explosion and do not have a very long life.

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