Topic: repair of lithium iron phosphate battery

[piersdad]

 explosion of a lithium phosphate battery see below


tags, lithium battery explode,safety of lithium ferric  phosphate battery,li fe po4 battery explode
the batteries  BMS apparently did not work
here is ann explanation of the BMS from a poster on a forum

Thank you very much everyone. I had some contact with battery manufacturers recently and most of them are using Passive Cell Balancing or Active Cell Balancing. Passive uses Resistors and Transistors for each individual cell and when the voltage reach a certain level, the resistor will drain a little current out of the cell . This works better when you recharge the battery and you can let it balance itself for a certain time.

Active Cell Balancing would use Capacitors or Inductance to transfer the excess energy from certain cells to other cell. This way you don't waste the energy in heat like with the Passive Cell Balancing.

Here is an article on that subject:
http://www2.electronicproducts.com/Lithium_cell_balancing_When_is_enough_enough-article-fapo_Panacis_mar2011-html.aspx

[piersdad]

Lithium ferric phosphate battery explosion

Left this battery on charge all night and some thing happened during the  night as in the morning there was the most amazing coverage of lithium and carbon all over the workshop.
The battery box was lying on the floor disassembled
I immediately picked up a small sample of the foil and put it in water and it did not react as say sodium would so the foil was not dangerous to touch.
At least I now know the internals of the battery and know now that the tops are possibly stainless steel and it is safe to put heat on it to solder a substantial wire lead on to the top with out damage to the internals


the collected internals

the casing and top removed

lithium battery case  and exploded cell
Approx weight of the foil was 80 grams
 the recovered carbon was 40 grams
 the  casing was 40 grams
 a complete battery was 260 grams so that leaves 100 grams of some thing about the crannies  of the work shop on the roof and in the spider webs etc



The roof above the battery

I am glad the explosion was not reported as there would have been a major evacuation and boiler suited people and a tremendous fuss all because no one seems to think the lithium was safe, as I found out,  as for the activated carbon  well that goes in the garden.

from this site i found out  li fe po4 compound

Lithium iron phosphate (LiFePO4) is an integral component in Lithium Ion (Li-Ion) batteries. Lithium iron phosphate is a safer and more cost effective alternative to Lithium Cobalt Oxide in the production of battery cathodes.

just found a bit of the copper colored foil in some water and it had corroded to copper sulphate
so the two foils are copper and aluminum


a bvery good site about how this battery works
well worth a visit

http://www.physicscentral.org/explore/action/lithium-1.cfm

In a lithium-ion battery, the lithium ion is the cation that travels from anode to cathode. Lithium (Li) is easily ionized to form Li+ plus one electron. The electrolyte is typically a combination of lithium salts, such as LiPF6, LiBF4, or LiClO4, in an organic solvent, such as ether. Graphite (carbon) is most commonly used for the anode, and lithium cobalt oxide (LiCoO2) is the most common cathode material. This combination gives an overall voltage of 3.6 Volts (V), more than twice that of a standard AA alkaline battery. This gives lithium-ion batteries a much better energy per volume ratio—or energy density—than an ordinary alkaline battery or other common rechargeable battery such as a nickel-metal hydride. This is in part because lithium is the third-smallest element after hydrogen and helium, and thus a lithium ion can carry a positive charge in a very small amount of space. It is important to keep in mind, however, that even lithium-ion batteries are many times less energy dense than substances like motor fuel or food, which store energy in chemical bonds. Increasing the amount of energy that can be packed into a given volume of battery is one of the major challenges facing battery-makers today.

Lithium-ion batteries, unlike standard AA and AAA alkaline batteries, can be recharged by running the anode and cathode reactions in reverse. Typically this is done by a charger that is plugged into a powerful electricity source such as a wall socket or a car cigarette lighter. The ability to be recharged many times over without much loss of capacity is another major advantage of the lithium-ion battery. Imagine if you had to buy a new battery for your cell phone every few days!

[piersdad]

Lithium phosphate battery dismantle and repair
For bicycle type batteries
I was given 5 of these batteries and they all had some sort of fault  so i dismantled the one that was obviously seriously damaged.
it charged ok but voltage a it low
discharge lasted  under a minute.
SO
The 4 screws each end are removed then at the plug end remove the cover from the power plug assembly then the battery can be removed from the case.
There will be 4 grouped at the bottom in a 12v configuration and another above.

The plastic casing has to be cut off and you will find the batteries are glued together with hot glue that is easily removed and replaced later.
 

I numbered the batteries as they are confusing and the one I numbered  (5) had zero volts when the others had 3.3 volts average.
So I charged the battery and initially I got .01 volts indicating no 5 was shorted internally

Tests showed resistance 4.2 ohms one way and 7.3 ohms the reverse way.
The centre negative terminal showed .1 volts across so definitely a dead cell

As I need a 12 volt battery I will now have 3 spare cells for other  repairs.
to remove one crook cell use a sharp knife to cut the interconnecting thin strip of metal as close to the bad cell as possible  carefull not to damage the BMS sensing wire
 
The second type of battery had 3 terminals and there was 12 volts between two and 24v between two
That is  2 /12volt batteries in series.
I removed the bottom  end cap and  this was not needed to be  removed.
So removed the top cap and there were several flat cells running the length of the casing that easily slid out of the casing.
All the batteries had a BMS systems and a little power plug which I think is for a small alarm buzzer which I will be applying to them when I use them later.
the charging plug had a number of small prongs and it appears the charger  charges each individual  cell.
care here trying to measure between each prong with a voltage probe as a short here is nasty
 i will try to get a similar plug so i can check each cell safely as they are charged.

one of the good cells had its positive terminal broken and as its stainless steel could not solder an other one on.
after some thought realized a local battery repair person had the right gear.
he welded the tag on very easily and obviously was a little bit scared of the size etc and asked what it was  and said it was dangerous and would definitely give no guarantee for the job and did not charge me.
he dealt mainly with the straight lithium batteries which are dangerous if damaged

after making a wooden box to fit all the cells side by side  i was able to replace the faulty cell and try it out.
my scooter got a good 6 km on the 10 ah batteries and this is about right for the age and condition of the cells.