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Author Topic: Why do lithium-ion batteries have three terminals?  (Read 41356 times)

Offline Geezer

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Rechargeable Li-ion batteries usually have three terminals. I think one must let electrons in and one must let electrons out, so is the third terminal allowing some other type of particle to nip around?
« Last Edit: 01/09/2011 21:26:44 by chris »


 

Offline MikeS

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Re: Why do lithium-ion batteries have three terminals?
« Reply #1 on: 01/09/2011 09:50:29 »
Rechargeable Li-ion batteries usually have three terminals. I think one must let electrons in and one must let electrons out, so is the third terminal allowing some other type of particle to nip around?

It's a thermistor terminal to monitor the temperature of the battery.  You don't want your electrons nipping about too energetically do you.
 

Offline Geezer

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Re: Why do lithium-ion batteries have three terminals?
« Reply #2 on: 01/09/2011 18:36:37 »
Rechargeable Li-ion batteries usually have three terminals. I think one must let electrons in and one must let electrons out, so is the third terminal allowing some other type of particle to nip around?

It's a thermistor terminal to monitor the temperature of the battery.  You don't want your electrons nipping about too energetically do you.

Thanks! I wondered if "T" stood for "Telectrons", but "Thermistor" makes a lot more sense  :D
 

Offline chris

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Why do lithium-ion batteries have three terminals?
« Reply #3 on: 01/09/2011 21:28:16 »
Yes, the batteries are "intelligent" and have various monitoring functions built-in to prevent over-discharge and over-temperature; nothing, sadly, to prevent over-price, however...
 

Offline SeanB

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Why do lithium-ion batteries have three terminals?
« Reply #4 on: 01/09/2011 22:43:40 »
On basic batteries this is a connection to a thermistor, used to prevent overcharging the cell, by allowing the rise in temperature to be accurately measured, as the voltage of the cell is dependent on temperature. In more sophisticated packs the terminal is connected to a charge controller inside the unit, that uses this connection to control the charger that is providing the power to charge, as well as info about cell charge percent, an well as other information like a serial number, max capacity, number of charge cycles and other info.
 

Offline Geezer

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Why do lithium-ion batteries have three terminals?
« Reply #5 on: 02/09/2011 01:05:38 »

On basic batteries this is a connection to a thermistor, used to prevent overcharging the cell, by allowing the rise in temperature to be accurately measured, as the voltage of the cell is dependent on temperature.


If the voltage iof the cell is dependent on the temperature, why would you need a thermistor? You could just measure the voltage.
 

Offline Bored chemist

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Why do lithium-ion batteries have three terminals?
« Reply #6 on: 02/09/2011 07:13:51 »
Because that's not the only thing it depends on.
 

Offline Geezer

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Why do lithium-ion batteries have three terminals?
« Reply #7 on: 02/09/2011 19:11:35 »
Because that's not the only thing it depends on.

Gosh! Well, I'm impressed BC. That certainly clears things up a lot  ::)
 

Offline Geezer

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Why do lithium-ion batteries have three terminals?
« Reply #8 on: 02/09/2011 19:59:22 »
BTW, nickel-cadmium rechargeable batteries can get pretty toasty too, but I don't think they have T terminals.
 

Offline FuzzyUK

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Why do lithium-ion batteries have three terminals?
« Reply #9 on: 03/09/2011 02:14:47 »
BTW, nickel-cadmium rechargeable batteries can get pretty toasty too, but I don't think they have T terminals.
 

Offline FuzzyUK

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Why do lithium-ion batteries have three terminals?
« Reply #10 on: 03/09/2011 02:33:07 »
A NiCad can reach 800 atmospheres internal pressure before the vent blows. Fast charging at 10C rate is a risk and hence the need to monitor the charge.

In earlier days a battery was fast charged by cycling for 900ms with an off charge period of 100ms. The voltage was monitored during the latter sequence. Batteries are usually switched to trickle charge once they reach 80% of full charge. The thermistor was really a last resort cut out device and would rarely kick in unless the battery was faulty.

I used to design battery chargers. One day a NiCad battery pack literally exploded in the laboratories so we chucked the smoldering wreck out of the window and the whole factory had to be evacuated. Scary.
« Last Edit: 03/09/2011 02:36:58 by FuzzyUK »
 

Offline SeanB

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Why do lithium-ion batteries have three terminals?
« Reply #11 on: 03/09/2011 12:16:11 »
Lithium cells have a terminal voltage dependent on charge state and temperature. If the cell is too hot or too cold it will not charge properly. If charged to a point over 100% of capacity it will heat up, and generates gas that causes the cell to swell up, and eventually burst. The problem with these cells is the gas generated is flammable, and the materials that make the cell are both flammable and react with moisture. Thus you get the all too common laptop flaming battery.
 

Offline Geezer

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Why do lithium-ion batteries have three terminals?
« Reply #12 on: 03/09/2011 18:12:04 »
Lithium cells have a terminal voltage dependent on charge state and temperature. If the cell is too hot or too cold it will not charge properly. If charged to a point over 100% of capacity it will heat up, and generates gas that causes the cell to swell up, and eventually burst. The problem with these cells is the gas generated is flammable, and the materials that make the cell are both flammable and react with moisture. Thus you get the all too common laptop flaming battery.

Ah! That makes sense.

So, to properly charge a Li-ion cell I would need to take account of voltage, temperature and (presumably) current?
 

Offline Bored chemist

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Why do lithium-ion batteries have three terminals?
« Reply #13 on: 04/09/2011 09:55:16 »
And time, they commonly measure rate of change of temperature as an indicator of the state of the battery.
 

Offline Geezer

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Why do lithium-ion batteries have three terminals?
« Reply #14 on: 04/09/2011 17:21:49 »
And time, they commonly measure rate of change of temperature as an indicator of the state of the battery.

Good point BC.
 

Offline Davidwh000

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Re: Why do lithium-ion batteries have three terminals?
« Reply #15 on: 17/04/2016 14:50:16 »
If I have a battery with 3 terminals and do not wish to monitor the thermal pin do I need to pull it low or high. When I measure the battery from white to red I see positive volts as do I between black and red. I assume therefore that I should either leave the white wire unconnected or connect it to the black (negative) connection. Please can someone either confirm or explain what should be done.
David
 

Offline chris

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Re: Why do lithium-ion batteries have three terminals?
« Reply #16 on: 17/04/2016 16:15:18 »
David, you'll need to check the spec of the battery you are dealing with, because the connector configuration and colour-coding are potentially different for every cell type.
 

Offline evan_au

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Re: Why do lithium-ion batteries have three terminals?
« Reply #17 on: 18/04/2016 11:58:06 »
Sometimes there is a chip inside the battery case that expects an external computer to communicate with it using some data transfer protocol. You may be able to find some details on this protocol if you google the battery model and "protocol" or "interface".

This communication provides important information about the state of charge of the battery. Ignore it, and the battery could catch fire.

On the news I have seen several homes burnt down this year due to poorly designed chargers for the lithium-ion batteries in so-called "hoverboard" toys. The consumer protection organization in my country has mandated a recall on these products.
 

Offline Robcat

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Re: Why do lithium-ion batteries have three terminals?
« Reply #18 on: 18/04/2016 15:53:30 »
One anode, one cathode and one electrolyte or that is what we were doing at SAFT in the 1970,s
 

Offline Robcat

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Re: Why do lithium-ion batteries have three terminals?
« Reply #19 on: 18/04/2016 17:20:59 »
Sorry about the photo of us in 1975 making lithium batteries Hampton Middlesex  but
If you want to keep updated Google.  ChargedEVs magazine and sign up
It's a good viewer to see what is going on from solid state Lithium batteries to new forms that don,t need
Thermal runaway sensors as a third sensor terminal.

I,m Still a lithium Battery consultant 41 years on... Rob
 

Offline chris

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Re: Why do lithium-ion batteries have three terminals?
« Reply #20 on: 18/04/2016 19:13:42 »
So what's actually going on in the hood, Rob?
 

Offline Robcat

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Re: Why do lithium-ion batteries have three terminals?
« Reply #21 on: 03/05/2016 23:07:13 »
Lithium likes a dry atmosphere so we used glove boxes
Primaries were lithium silver chromate,  lithium copper oxide, lithium manganese dioxide , lithium iron sulphide
Lithium thionyl chloride, lithium sulphur dioxide. Etc

Rechargeable In the 1970s were secret research helped via specialist precious metal company but no lithium
iron phosphate  etc

All history prior to nanochemistry and solid electrolyte ... Lithium sulphur and lithium air  a la 2016
 

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Re: Why do lithium-ion batteries have three terminals?
« Reply #21 on: 03/05/2016 23:07:13 »

 

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