As far as explosions go, we hear that a lot with Li-ion batteries. But I feel all kinds of Li batteries overall are just not as forgiving as other types, such as NiMh.
Is it because NiMh is an "older" technology and we understand it very well or is it just more inherently safer chemistry wise?
Thanks
Correct. NiMH technology is much safer as it tolerates charge/discharge abuse and is extremely unlikely to explode. It just doesn't store as much energy per battery weight or volume.
One of the big issues with the Lithium batteries is that when they start a fire, they produce their own oxidizer so you can't just smother them to put the fire out. The people developing the charger for the batteries on the 787 airplane down in Arizona? managed to get one of the big battery packs started and did several million dollars damage to their lab if I remember correctly when they could not get it under control. http://www.seattletimes.com/business/787-battery-blew-up-in-rsquo06-lab-test-burned-down-building/
NiMH batteries have much lower energy density, both volumetrically and by weight. This means there's less energy to start a fire with when things go wrong - and to power your device with when things go right. They are also much less flammable internally - lithium burns real good.
Also, NiMH batteries generally just get degraded (in terms of capacity and general performance) when you abuse them, while lithium batteries often fail catastrophically.
gpsmikey:
One of the big issues with the Lithium batteries is that when they start a fire, they produce their own oxidizer
That is incorrect. They are indeed very difficult to extinguish because they pull oxygen from most extinguishing media (like magnesium fires do, only more) - but they do not carry or produce an oxidizer.
Having worked in an industry reliant on Lithium batteries (non rechargeable) the major thing we found was because of the chemistry involved the risk was amplified if the battery was accidently shorted out
Basically make sure they can't be shorted out, do follow the charging instructions correctly and take care. if a battery feels over hot starts swelling or the housing first thing I would suggest is get it outside and disconnected from any circuits. Mobile phones have used lithium packs for years because they provide more power in a smaller space and hold the charge better.
NiMh cells are better than the older NiCad cells but both types only put out 1.2v which drops as the battery discharges. and generally discharge themselves if not used for a month, A Lithium pack is usually a multiple of 2.4 V and can keep a charge a lot longer. Non rechargeable Lithium batteries are found as internal back up packs,watches,data logggers etc.
Hope this sheds a bit of info.
DrAzzy:
NiMH batteries have much lower energy density, both volumetrically and by weight. This means there's less energy to start a fire with when things go wrong - and to power your device with when things go right. They are also much less flammable internally - lithium burns real good.Also, NiMH batteries generally just get degraded (in terms of capacity and general performance) when you abuse them, while lithium batteries often fail catastrophically.
That is incorrect. They are indeed very difficult to extinguish because they pull oxygen from most extinguishing media (like magnesium fires do, only more) - but they do not carry or produce an oxidizer.
I wish I could find it now, but all I can find is vague references to the fact the electrolyte gets the oxygen stripped out when you get a fire. I do remember either reading or seeing something on this some time ago and at that time they specifically said that the battery could produce oxygen from within when it failed which was part of the reason it was so difficult to put out. Bottom line though - you do NOT want a lithium battery fire !!!
DrAzzy:
NiMH batteries have much lower energy density, both volumetrically and by weight. This means there's less energy to start a fire with when things go wrong - and to power your device with when things go right. They are also much less flammable internally - lithium burns real good.
Nope, there is no metallic lithium in a conventional Lithium Cobalt Oxide battery.
It's the organic electrolyte that burns.
The Lithium Iron Phosphate battery typically used in electric bicycles doesn't have a flammable electrolyte. You can literally drive a nail through a battery and it won't catch fire.
It will get hot and generate smoke, but it won't burn. These typically aren't used in consumer gadgets because they have a lower energy density than Lithium Cobalt Oxide batteries.