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New Cathode Improves Performance of Li-Ion Batteries with Ionic Fluid Electrolyte

1 September 2006

Seki
Cycle number and discharge capacity for the new cathode (ZrO2-coated) vs. conventional cathode. Click to enlarge.

Nikkei. Researchers at the Central Research Institute of Electric Power Industry (CRIEPI) in Japan have devised a new type of cathode that improves the performance of lithium-ion batteries that use an ionic liquid as the electrolyte.

Unlike the organic solvents usually used as the electrolyte in a li-ion battery, room-temperature ionic liquids (RTIL) are nonflammable and nonvolatile. However, the RTILs lack electrochemical stability up to the reduction potential of lithium.

Batteries designed with the new cathode have around 30% higher charge storage capacity and can be recharged up to three times as often than other lithium-ion batteries with the ionic liquid electrolyte, according to CRIEPI.

The researchers used a mix of ammonium cations and imide anions in the fluid. A separator seeped in this liquid is sandwiched between the cathode and the anode. During charging, lithium ions dissolve off the cathode and migrate to the anode via the separator.

To make the new cathode, the team applied a nanolayer of zirconium oxide (ZrO2) on a lithium cobalt oxide (LiCoO2) cathode. In previous versions of the cathode, the particles of lithium cobalt oxide would release oxygen when subjected to high voltages during recharging, oxidizing and degrading the cations in the ionic liquid.

By coating the particles, the institute improved the stability of the cathode material, thereby allowing the battery to be recharged using a higher voltage.

The result is a battery with higher charge storage capacity and the ability to handle two to three times as many recharges as its predecessors. Even though the newly-developed battery loses 15% of its charge storage capacity after 100 recharges, it represents a step forward in the effort to develop a practical lithium-ion battery based on an ionic fluid electrolyte.

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September 1, 2006 in Batteries | Permalink | Comments (9) | TrackBack (2)

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Comments

"the RTILs lack electrochemical stability up to the reduction potential of lithium" ... anyone able to translate this for a non-chemist?

Neil,

When a lithium ion cell is recharged, lithium ions in the anode receive electrons and are REDUCED to lithium metal. The level of voltage (potential) for this reduction to occur is the reduction potential.

In this particular cell, the voltage neccessary to convert the lithium ion to lithium metal is high enough to cause the electrolyte (ionic liquid in this case) to start undergoing side reactions, ie decomposition most likely.

Judging from the diagram, the discharge capacity is 180 mAh/g, which is an energy density of >500 Wh/kg! Is this correct?

I believe that is correct anne, a typical lithium ion cell is 3.6V...that chart shows a ~430Wh/kg energy capacity after 60 cycles (120mAh/g). Not sure how they average the energy storage of a lithium battery for energy specifications though. Plus the article indicats "30% higher charge storage capacity".

Mike ... good explanation thx.

If energy density is 30% higher than other cells with ionic liquid electrolyte chemistry how does it compare with other Li-poly chemistries? Also currious about charge rate gains (any numbers?) and production costs.

15% over only 100 recharges is rather high. Could the battery be easily reconditioned to reduce costs?

Patrick,

If about 500 Wh/kg is correct, then a 50 kWh battery (like the one in the Tesla) should weigh around 100 kg. A perfectly acceptable 200 kg battery should be enough for an average car to provide a 600+ km radius. Is this the battery technology we're waiting for?

>A perfectly acceptable 200 kg battery should be enough >for an average car to provide a 600+ km radius. Is this >the battery technology we're waiting for?

Is this true?? How long and whats the catch in laymans terms?

Bob

The catch on this chemistry appears to be a very low limit to the number of times this battery can be recharged before it begins to loose capacity. So unless the battery can be cheaply reconditioned the economics won't be there. But it is promising.

Lithium batteries can reach 500 Wh/kg at -100°C.
180 Wh/kg at - 60 / 60 °C. Cooling device for such car must be huge as truck.

"A quick glance at the energy density of batteries reveals that battery technology has a long way to go to catch up with fuels"

Material By Volume By Mass
Diesel Fuel 10,700 Wh/l 12,700 Wh/kg
Heating Oil 10,400 Wh/l 12,800 Wh/kg
Gasoline 9,700 Wh/l 12,200 Wh/kg
Butane 7,800 Wh/l 13,600 Wh/kg
LNG (-160°C) 7,216 Wh/l 12,100 Wh/kg
Propane 6,600 Wh/l 13,900 Wh/kg
Ethanol 6,100 Wh/l 7,850 Wh/kg
Methanol 4,600 Wh/l 6,400 Wh/kg
250 Bar NG 3,100 Wh/l 12,100 Wh/kg
Liquid H2 2,600 Wh/l 39,000 Wh/kg
150 Bar H2 405 Wh/l 39,000 Wh/kg
NiMH Battery 280 Wh/l 100 Wh/kg
Li-Ion Battery 200 Wh/l 150 Wh/kg
Lead-Acid Battery 40 Wh/l 25 Wh/kg
STP Propane 26 Wh/l 13,900 Wh/kg
STP NG 11 Wh/l 12,100 Wh/kg
STP H2 3 Wh/l 39,000 Wh/kg

Material By Volume By Mass
Liquid H2 2,600 Wh/l 39,000 Wh/kg
Propane 6,600 Wh/l 13,900 Wh/kg
Butane 7,800 Wh/l 13,600 Wh/kg
Heating Oil 10,400 Wh/l 12,800 Wh/kg
Diesel Fuel 10,700 Wh/l 12,700 Wh/kg
Gasoline 9,700 Wh/l 12,200 Wh/kg
LNG (-160°C) 7,216 Wh/l 12,100 Wh/kg
Ethanol 6,100 Wh/l 7,850 Wh/kg
Methanol 4,600 Wh/l 6,400 Wh/kg
Li-Ion Battery 200 Wh/l 150 Wh/kg
NiMH Battery 280 Wh/l 100 Wh/kg
Lead-Acid Battery 40 Wh/l 25 Wh/kg
(best volumetric type listed only)

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