It's the Batteries, Stupid!

[GSP]

UK Researchers at University of St. Andrews demonstrate 100 cycle endurance Li-Air battery. They used gold for the cathode, so even more expensive than Li-Ion cathodes. Sounds promising however, and maybe other cathodes will be found that will work as well or better. The authors sum it up in their last sentence:

"the results presented here encourage further study of the rechargeable non-aqueous Li-O2 cell, although many challenges to practical devices remain."

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GSP

[dsm363]

UK Researchers at University of St. Andrews demonstrate 100 cycle endurance Li-Air battery. They used gold for the cathode, so even more expensive than Li-Ion cathodes. Sounds promising however, and maybe other cathodes will be found that will work as well or better. The authors sum it up in their last sentence:

"the results presented here encourage further study of the rechargeable non-aqueous Li-O2 cell, although many challenges to practical devices remain."

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GSP

Is 100 cycles good? Seems low for automotive purposes.

[WarpedOne]

It is good for Li-Air chemistry.
It is still low for automotive purposes but not that low if it offers > 3 x Li-Ion energy and power density.

[JRP3]

Li air has great specific energy density but low charge/discharge rates, plus some other potential issues.
Why the lithium air battery is over hyped Cleantech News and Analysis

[YoungStranger]

Yeah just read that - Not sure if I would believe GM over IBM. I thought the link for the presentation at IBM which is quite sceptical about Lithium Air in one of the comments was really interesting and useful. i have put it as a link in case anyone wants to check it out (if its not been linked before?)

http://www.almaden.ibm.com/institute...titute2009.pdf

[WarpedOne]

It mentions two problems with LiAir:
- you need a gas pump to deliver fresh air into the battery
- you must dry it - remove all water and steam from it

Now compare these two with a long list of impossible demands that face hydrogen.

It looks to me like a walk in the park.

[Johan]

OK, so I have been reading through most of the threads on battery-tech but there is this one thing I just can't really wrap my head around, and I don't want to start a new thread so I'll ask here:

With the Model S 85 kW battery, what does the 85kW really mean??? First of all, isn't the unit kWh? I'll assume they're just saying kW since it's easier and everyone knows what they mean. So, I understand that the battery is comprised of a lot of small cells, but assuming the pack is functioning and balanced I supposde you could just see it functionally as one hughe cell (electrically) with a lot of Ah. I also understand that SOC (state of charge) is a function of the Voltage, that is "full charge" (in range mode) is the highest voltage that Tesla will allow the cells to be charged to (even so the range mode should not be used more than required and the car should not sit fully charged in range mode for longer periodes since this will degrade the battery). Now my question: as the energy in the battery is used up while driving, the Voltage drops and drops. When the car shows 0% charge, what is the Voltage at that point? We know it wont be zero, because then the battery would be bricked (dead). When Tesla says 85kW(h) do they mean the actual ammount of energy stored in the battery when fully charged, or do they mean the ammount useable (until the car won't let you drive any longer = the gauge shows 0% but there is still some voltage)?

I guess if we knew the average Watts/mile achieved during Tesla's own testing (that resulted in "slightly over 300 miles at constant 55 mpg speed) or the average Watts/mile figure during the EPA test (that resultated in 265 miles) I suppose this could be calculated. (I'm assuming that both tests actually drove the car until it wouldn't go any further?)

[JRP3]

On the Tesla Motors site they use kWh's for size designations, 40kWh-85kWh, which is correct.

[VolkerP]

Johan,

check out the blog entry by Martin Eberhard on the roadster battery: A Bit About Batteries | Blog | Tesla Motors

Tesla uses a reduced voltage window to operate the cells. While the cell voltage is specified as 4.2V, Roadster charging stops at 4.15V (in range mode charge, displayed as 100% SOC) and discharge voltage limit is 3V (=displayed at 0% SOC). The specified battery capacity (e.g. 85kWh) is the usable capacity (= energy to draw between 100%SOC and 0% SOC).

Conclusions:
a) while technically possible, the vehicle won't allow you to put energy into the battery beyond 100% SOC, since that would degrade the cells much faster.
b) you could continue to draw energy from the battery below 0% SOC by letting sit the vehicle unplugged for weeks, but that would destroy the cells so that they cannot be recharged again.

[widodh]

Johan,

check out the blog entry by Martin Eberhard on the roadster battery: A Bit About Batteries | Blog | Tesla Motors

Tesla uses a reduced voltage window to operate the cells. While the cell voltage is specified as 4.2V, Roadster charging stops at 4.15V (in range mode charge, displayed as 100% SOC) and discharge voltage limit is 3V (=displayed at 0% SOC). The specified battery capacity (e.g. 85kWh) is the usable capacity (= energy to draw between 100%SOC and 0% SOC).

Conclusions:
a) while technically possible, the vehicle won't allow you to put energy into the battery beyond 100% SOC, since that would degrade the cells much faster.
b) you could continue to draw energy from the battery below 0% SOC by letting sit the vehicle unplugged for weeks, but that would destroy the cells so that they cannot be recharged again.

My prediction is however that over time they will limit this even further.

Let's say that next-gen cells could go up to 4.5V, they would still stop at 4.2V and never go below 3V

That way you are technically keeping the SOC between 10% and 85%, so a fast/quick/super charge can continue on higher currents for a longer time and drivers don't have to use a "range mode" any longer.

This will also expand the longlivity of the battery which is a win situation for EV's.

A eg 110kWh battery would be limited to 85kWh for example.