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Fast-charging batteries are a concern

There have been several fire-related concerns and cases involving lithium-ion batteries in both laptops and electric-hybrid vehicles. Until recently, the cause of li-ion battery fires and overheating was only speculated, but Cambridge University researchers have found that a growth inside the batteries, called dendrites, are the perpetrators behind this heated mess. 

Dendrites are the growth of metal fibers within the lithium-ion batteries. They grow on carbon anodes due to batteries being charged at a fast rate. As they grow, the fibers can cause short circuits which leads to overheating, fires and in some cases, even explosions

"These dead lithium fibers have been a significant impediment to the commercialization of new generations of higher capacity batteries," said Professor Clare Grey of Cambridge University's chemistry department.

Now that researchers have targeted the fibers as a problem and figured out how they grow, the next step is determining why dendrites form, which, according to Cambridge researchers, could lead to new technologies that could both fix the growth problem and find a way for lithium-ion batteries to still obtain a quicker charge. 

Researchers are now using Nuclear Magnetic Resonance (NMR) spectroscopy, which is a method of identifying elements in molecules, to observe how the dendrites develop. With this sort of development, lithium-ion batteries could be reformed for the next generation of electric cars.

"Fire safety must be solved before we can get to the next generation of lithium-ion batteries and before we can safely use these batteries in a wider range of transport applications," said Grey. "Now that we can monitor dendrite formation inside batteries, we can identify when they are formed and under what conditions."

Fixing the dendrite growth problem could lead to an increase in lithium-ion battery costs, but could also lead to safer driving conditions in electric cars, which is a general concern for new buyers.

"Our new method should allow researchers to identify which conditions lead to dendrite formation and to rapidly screen potential fixes to prevent the problem," said Grey.



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By kilkennycat on 5/21/2010 4:58:33 PM , Rating: 2
Dendrite growth has been a classic problem in 'dry-cell' batteries with thin-separators for many years. Nothing new at all here. The only new element here is the energy-density of the lithium cells, the explosive self-flammability of lithium when exposed to the atmosphere and the high charging currents required for rapid-recharge electric vehicles. A prime cause of long-term loss of capacity in both Ni-Cd and Ni-MH batteries is dendrite growth from the "plates" through the separator causing high internal leakage, and the classic way of clearing such growths to revive a small Ni-CD or Ni-MH battery temporarily (until the dendrites re-grow) is passing a very high 'charging' current (say 5-10amps through a cordless-phone battery) for only A COUPLE of seconds to vaporise the dendrites (NO MORE, unless you want an explosion. Disclaimer: I take no personal responsibilty for any such experiments )

Unfortunately, the very high charging currents to speedily re-charge an auto lithium-cell battery cannot distinguish between charging the battery and vaporizing any dendrites present. In the case of vaporizing dendrites in a lithium-cell battery there is sure a far greater possibility of an unwanted fire/explosion than in either a Ni-Cd or Ni-MH battery.

The above article implies that research into the prevention of dendrite growth has not gone hand-in-hand with the evolution of high-energy-density battery technology. Such an implication astonishes me, considering how long the dendrite-growth issue in thin-separator batteries has been a problem...




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