Safety Concerns Charging Lithium-Ion and Solid Anode lithium Batteries (Duralite)

[Earl Haury]

Frank

Your points are well taken. 

If I interpret your statement regarding NiMH packs "looses capacity on stand" correctly as self discharging when idle, I haven't found this to be the case. I suspect that all NiMH cells aren't created equal (as with most things) and that the technology may have improved. Specifically, I've found that the Sanyo 1650mah NiMH AA cells retain their charge better than most NiCads I've used. One "test" pack has demonstrated 80%+ capacity after being on the bench for 6 months. 

I agree with your statements regarding NiMH being less tolerant of abusive charging. I've looked at the behavior of a few different "quick" chargers on the bench with instrumentation. A couple of them, even though they offered a NiMH selector, severely overheated packs. I concluded that the Sirius Pro Charger does a nice job without excess heating.

Living in Houston pretty much allows me to dismiss any low temp deficiencies.

Overall, I find NiMH performance to be superior to NiCad for pattern use. Performance defined as reliability, weight vs. capacity, and cost / value. I do prefer to use a 5-cell pack with a regulator to avoid the possibility of low voltage dips during high current demand (NiCads are better here - but I would still use 5 cells). 

Earl
  ----- Original Message ----- 
  From: Frank Bis 
  To: NSRCA Discussion List 
  Sent: Saturday, May 08, 2004 11:01 AM
  Subject: Safety Concerns Charging Lithium-Ion and Solid Anode lithium Batteries (Duralite)


  I have been working in the battery area for 40 + years so let me pass on my knowledge.  When the Duralites first hit the market I went on line and said "Be very careful with these solid lithium anode cells"- they can vent catch on fire etc especially after repeated cycling.  The reason for this is after several charges the lithium forms Dendrites (spikes on the surface) which punch through the separator and short out the cell.  No one paid any attention to this.  Now in the case of the Lithium-Ion these cells DO NOT LIKE TO BE OVERCHARGED.i.e. above 4.2 volts.  They will vent and catch on fire.  I use them in flat packs but each cell has a protective circuit on the cell and can be charged at constant current using a standard charger at 250 mA.  When any cell in the two cell pack reaches 4.2 V the protective circuit on the cell senses this and takes the cell off line, hence the battery of two cells off charge.  Yes these battery packs are a bit lighter and have a higher energy density (Wh/kg).  Let me pose this, Nickel-cadmium cells are a proven technology and can be fast charged safely and work.  Why not stay with they.  The Nickel-metal hydride is a good system.  However, it looses capacity on stand, and requires careful field charging to prevent it from getting too hot and venting.  Also it does not work as well at low temperatures.  My advice stay with Ni-Cd.
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