Crash-tests?

[evnow]

I don't know Lithium Manganese (who else is using it ?), but if it's as safe as LiFePo4, then we should be fine.

LG (so Volt, Ford Focus etc) is also Mn. Cobalt is used by Tesla for roadster and also ACP in Mini-E. Infact ACP used Cobalt oxide in Mini-E without any liquid cooling

 

[TRONZ]

That "standard LiIon" cell is lithium cobalt - think Laptop and Tesla here.

The A123 cell is Lithium iron phosphate. The Leaf is a flavor of lithium manganese. These two are the 'safe' lithium chemistries.

That being said, even newer lithium cobalt are much safer. Consider these clips from a few months back with the latest varieties of LiCo and other cells. It took a LOT more than just the nail penetration to get these cells to go off - like taking 4V cells to 15V, then adding heat...

[youtube]http://www.youtube.com/watch?v=dree0rTr1HM[/youtube]

OK, who ever made that video has serious "battery issues"!

 

[garygid]

The job of the BMS (Battery [Cell] Management System) is to keep cells from over-charging (or over-discharging, or over-heating).

When the "pack" (really, any one in-series cell) is full, the Regen energy must be "burnt off" or not generated, not used to over-fill the battery (cells).

So, when Regen is no longer a possibility for braking, that usually leaves just the mechanical disc brakes, for the whole 30-mile downhill trip, possibly getting VERY hot.

 

[AndyH]

That being said, even newer lithium cobalt are much safer. Consider these clips from a few months back with the latest varieties of LiCo and other cells. It took a LOT more than just the nail penetration to get these cells to go off - like taking 4V cells to 15V, then adding heat...

The only trouble, is that lithium chemistries gain a lot of voltage very fast once they reach full charge.

Yes - but the cell's internal resistance also rises as the cell charges above the 85% point - so while the voltage rises, the amount of actual energy entering the cell drops dramatically. Charging slows 'automatically' or 'naturally' as part of the cell design - it's somewhat self-correcting.

The voltage rise isn't a problem for the safe LiFePO4 and LiMN varieties because they don't have any metallic cobalt and don't form any metalic cobalt when overcharged the way LiCo (standard Li-Ion) cells do. The older cells get more unstable when the voltage rises - the safe cells don't.

From a half depleted battery pack, charging at 2A, it will take about 5-6 hours for the cells to go from 3.20V to 3.37V, but then it'll only take a couple minutes to get to 3.75V, knowing that at this point the charger current has dropped from 2A to less than 300mA. If charging current was kept the same, I'd bet than a few minutes (with the right voltage), would bring the cells to 15V really fast.

It's not that slow with larger capacity cells (or lower capacity cells in parallel). I have six 60Ah cells on the bench now each charging at 5A and it takes a long time for them to reach the 85% point (the CC/CV crossover point) and more time for the cell to saturate. [Yep...let's sit here and watch the cells charge, the grass grow and the paint dry...multitasking. ]

I don't know Lithium Manganese (who else is using it ?), but if it's as safe as LiFePo4, then we should be fine.

LiMn is at least as safe as LiFePO4 - and safer in some regards - no worries! Here's some background info. Yes - it's on the Volt pack - but the LG Chem cells used in the Volt pack are LiMn.
http://www.eetimes.com/electronics-...-s-success-hinges-on-its-battery?pageNumber=0

The challenge presented to the interested parties was straightforward: Develop a lithium-ion battery that could be recharged for 4,000 cycles and would last a minimum of 10 years.

From the initial field of 27 entrants, the competition was narrowed to two prospective partners in June 2007. The two finalists were A123Systems, a Michigan-based company with expertise in Li-ion technology, and a coalition team of LG Chem and Compact Power Inc.

I've actually been wondering what happens if you go downhill from a fully charged leaf, if they disable the regen, or if this could lead to overcharge? I can't imagine that the engineers have not thought about it...

The regen down the hill concern is a non-event just as fear of overcharging the cells is not an issue - because the engineers don't allow us drivers to access the top or bottom 10% of capacity. The management system must stop the flow of energy into or out of the battery when we reach either extreme.

When the cells are fully charged, the computer shuts the charger off. When the cells are full and we're regenning down a hill, the regen stops and we rely on the friction brake.

Andy

 

[AndyH]

That "standard LiIon" cell is lithium cobalt - think Laptop and Tesla here.

The A123 cell is Lithium iron phosphate. The Leaf is a flavor of lithium manganese. These two are the 'safe' lithium chemistries.

That being said, even newer lithium cobalt are much safer. Consider these clips from a few months back with the latest varieties of LiCo and other cells. It took a LOT more than just the nail penetration to get these cells to go off - like taking 4V cells to 15V, then adding heat...

OK, who ever made that video has serious "battery issues"!

And his wife is a large-scale laser/plasma scientist. I'm thinking fights around the dinner table look something like a scene from "The Incredibles". :lol:

 

[smkettner]

Yes - but the cell's internal resistance also rises as the cell charges above the 85% point - so while the voltage rises, the amount of actual energy entering the cell drops dramatically. Charging slows 'automatically' or 'naturally' as part of the cell design - it's somewhat self-correcting

I always read as the battery charges the resistance DECREASES and voltage potential increases.
Can Lithium batteries be different?

 

[AndyH]

That's one of the safe aspects of LiFePO4 and LiMn - the higher the voltage rises the more they resist incoming current. The lithium cobalt cells will exotherm and run-away when overcharged - LiFePO4 and LiMn won't.

I just finished bench-testing my LiFePo4 pack from my motorcycle. AC and DC internal resistance was higher on each cell when fully charged - it was lower when the cells were discharged.

Here's a real-world comment from the guy that did the cell destruction videos. He's talking about 10Ah Headway brand cylindrical LiFePo4 cells:

Have you ever tried to make a headways cell do anything exciting? I've overcharged them to +28v then -28v, charged at 150amps to 16v, shorted them with busbars, shot them through with an aluminum crossbow bolt multiple times, smashed them in a vise, cut them in half with a hacksaw, and finally, the only way I got one to do something exciting took 15minutes with a 1800w heatgun blasting on it until the organic solvents boiled and vented a flamable vapor that lit. The steel can of the battery was glowing before the solvent would boil and ignite.


If you know a magic trick to get one to do something exciting, please do tell. I was stabbing things through full charged cells repeatedly, and grinding the layers together with no ill effects.

I would feel comfortable building carseat for my baby out of headways cells.