13 December 2010

from NatureAsia Website

 

 

Author affiliation
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Institute of New Energy, Fudan University,

Shanghai 200433, China

 

 

 

An aqueous lithium-ion battery can be recharged a thousand times with marginal capacity loss.

Lithium-ion batteries in which lithium ions are transported between the positive and negative electrodes through an aqueous solution could be used to power electric vehicles.

The lead-acid batteries used to start conventional cars use water rather than organic solvents as the electrolyte. Frequent recharging of such aqueous batteries degrades their electrodes, lowering their performance and making them unsuitable as a primary power source.

 

In contrast, the lithium-ion batteries typically found in laptops and mobile phones can pack a large amount of energy into a small space, and continue to work well after thousands of recharging cycles.

 

 

Lithium-ion batteries in which lithium ions are transported

between the positive and negative electrodes

through an aqueous solution could be used to power electric vehicles.

 

 

This recharge capacity comes at a cost, however, because the flammable organic solvent used in lithium-ion batteries to carry electrical current between electrodes makes the batteries relatively expensive and somewhat explosive - factors that have prevented larger lithium-ion batteries from being used in vehicular applications.

Yong-Yao Xia and colleagues at Fudan University in Shanghai, China, have now developed a lithium-ion battery that relies on water rather than a flammable solvent.1

 

This technology could enable much larger lithium-ion batteries to be used safely in electric vehicles.

 

As the battery charges, lithium ions are added to the negative electrode, which is made from lithium titanium phosphate. On discharging, lithium ions leave this electrode and travel through the electrolyte - in this case an aqueous solution of lithium sulfate - before inserting into the positive electrode, which is made from carbon-coated lithium iron phosphate.

In its discharged state, the negative electrode tends to react with oxygen, reducing its capacity. To circumvent this issue, the battery was fabricated in an oxygen-free environment and then sealed to prevent air leaking in. The scientists also realized that the negative electrode could react with water unless they excluded acidic hydrogen ions, a problem they solved by making the electrolyte highly alkaline.

 

Operating at 1.4 V, the battery could be completely charged and discharged a thousand times with only 10% loss in capacity.

Aqueous lithium-ion batteries have a lower energy density than organic-based batteries, but their lower price and greater safety are major advantages for larger-scale energy storage, says Xia.

 

The scientists are now developing ways to prevent the generation of oxygen in the battery when it is overcharged by limiting the maximum voltage of the positive electrode.
 

 

 

Reference

1. Luo, J.-Y., Cui, W.-J., He, P. & Xia, Y.-Y.* Raising the cycling stability of aqueous lithium-ion batteries by eliminating oxygen in the electrolyte. Nat. Chem. 2, 760 (2010) - (article)