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surfingslovak
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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 8:23 am

JeffN wrote:Where do these Volt chemistry estimates come from? I recall someone writing at a GM-Volt.com forum that GM engineers at a Detroit event with Volt owners unofficially said Volt packs would likely last around 14-15 years in mild temperature areas and 10-13 in hot climates like the Southwest (when reasonable care is taken like parking in shade or leaving connected to an EVSE for TMS).
I believe Stoaty was referring to this PDF file posted by Charles Whalen on the Volt forum.Image

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 9:03 am

surfingslovak wrote:I believe Stoaty was referring to this PDF file posted by Charles Whalen on the Volt forum.Image
That's correct, and it doesn't conflict with the Volt life stats you quoted. End of Life is considered 70%, I think. Since the Volt uses a smaller portion of the battery (10.3 of 16 kWh, I believe), they can use the same 10.3 kWh and gradually shrink the unused portion until the total battery capacity decreases to 10.3 kWh. So end of life for Volt battery would be 10.3/16 = 64%. Even then, the Volt can still drive electric, it will just have decreasing electric range.
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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 9:38 am

surfingslovak wrote:
JeffN wrote:Where do these Volt chemistry estimates come from? I recall someone writing at a GM-Volt.com forum that GM engineers at a Detroit event with Volt owners unofficially said Volt packs would likely last around 14-15 years in mild temperature areas and 10-13 in hot climates like the Southwest (when reasonable care is taken like parking in shade or leaving connected to an EVSE for TMS).
I believe Stoaty was referring to this PDF file posted by Charles Whalen on the Volt forum.Image
Okay, thanks. Presumably that is based on a generic LiMnO2 battery and not the actual Volt battery which has tweaks to its cathode, anode, and perhaps electrolyte that would tend to extend the cell life significantly beyond a generic cell.

LG Chem (CPI) has gotten Energy Dept. battery research grants in recent years along with many others. Their status reports, which seem to describe cells very similar to the ones used in the Volt, claim to meet research targets for 15 calendar years of life and 5,000 recharge cycles (I think), although they have been a bit vague on the evidence for meeting the calendar goal.

I agree with Stoaty that Volt can also effectively hide battery degradation in early years due to the reduced battery SOC range that is usable.

Also, I went looking for my sources on this. The post I was thinking of for the mild climate scenario was specifically a claim of around 16 years for the Michigan area. The post was by Bob Livonia who was apparently quoting Andrew Farah or some other senior Volt engineer from a private discussion at the Woodward (Michigan) Dream Cruise auto event in August 2011. I'm not sure where I picked up the Southwest battery lifetime range estimate although I recall Farrah being quoted elsewhere that the Southwest temperatures were a challenge for the Volt designers as well.
Last edited by JeffN on Fri Jun 22, 2012 11:19 am, edited 1 time in total.

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 10:33 am

JeffN wrote:Okay, thanks. Presumably that is based on a generic LiMnO2 battery and not the actual Volt battery which has tweaks to its cathode, anode, and perhaps electrolyte that would tend to extend the cell life significantly beyond a generic cell.
Yes, presumably, and thank you for your post. It would be great if we could get Charles Whalen clarify the source for this chart. I believe that several people have contacted him or are about to. Scott Fauque referred to an interesting post on the Volt forum, where an owner described his experience with preconditioning on a hot day. I believe that it's been established that the chemistries in the Volt and the Leaf are pretty similar? I remember looking at an older data sheet from LG Chem last year, but it was quite old, and I couldn't find comparable information on the cells used in the Volt.Image

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 10:49 am

JeffN wrote:Where do these Volt chemistry estimates come from? I recall someone writing at a GM-Volt.com forum that GM engineers at a Detroit event with Volt owners unofficially said Volt packs would likely last around 14-15 years in mild temperature areas and 10-13 in hot climates like the Southwest (when reasonable care is taken like parking in shade or leaving connected to an EVSE for TMS).
This one? http://gm-volt.com/forum/archive/index.php/t-10464.html" onclick="window.open(this.href);return false; Obviously the chief engineer would know and he's talking about the cells used in the Volt not generic cells:

I had dinner sitting next to Andrew Farah. He is the chief engineer for the Volt. One of my many questions was about the useful battery life. He answered with the question of "where". He explained that there is a difference depending on whether you use your Volt in Detroit or Phoenix. These batteries don't like heat. In Detroit's climate he said that we can expect a minimum of 15 years, 12 in Phoenix.

So a minimum of 12 years in AZ. That's consistent with the slightly increased range for the Volt, achieved in part by using slightly more of the SOC.

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 11:32 am

surfingslovak wrote:I believe that it's been established that the chemistries in the Volt and the Leaf are pretty similar? I remember looking at an older data sheet from LG Chem last year, but it was quite old, and I couldn't find comparable information on the cells used in the Volt.Image
I believe the Volt and LEAF batteries are roughly comparable in many ways although obviously not identical. Nissan's battery company publishes some basic data sheets. I can't find anything from LG Chem or GM that is directly attributable to the specific cells used in the Volt however I have found various material that seems to describe cells that are either the same or very similar.

Here is a writeup I posted awhile ago elsewhere:

------------------------------------------------------

The LG Chem cell used in the Volt appears to have struck a happy medium with Manganese Spinel plus some Nickel and Cobalt for the Cathode and a mixed graphite and amorphous (hard) carbon anode giving good energy density, high power, 5,000 cycle life and 10-15 year calendar life. The cells are each 383g and have a 15 Ah capacity at an average discharge voltage of around 3.7V for around 55 Wh. The Volt pack uses 288 of them for 16 kWh of nominal capacity. The data sheet for them reportedly rates them as 150 Wh / kg and 300 Wh / L which would put them near the top of the energy density bar chart of battery chemistries you posted recently. They are also specified for greater than 10C continuous discharge and show low and evenly spread heat dissipation.

The above cell specs are gathered from multiple sources (DOE, NASA, and battery conference presentations) but I believe them to be correct and to approximately represent the cell used in the Volt although to my knowledge GM and LG Chem have not published the data sheet online.

The battery supplier for Nissan publishes data sheets for the LEAF cell and also another cell intended for use in non-plug hybrids. The energy density of the LEAF cell works out to around 160 Wh / kg but the power dense hybrid cell is only around 80 Wh / kg. In addition, the LEAF cell looks to be just slightly less energy dense by volume than the apparent Volt cell.

Like the cells used in the Nissan LEAF, these LG Chem cells are state of the art for plugin automotive use and actually appear to have roughly similar characteristics.

Sources:
http://www.eco-aesc-lb.com/en/product.html" onclick="window.open(this.href);return false;
http://ntrs.nasa.gov/archive/nasa/casi. ... 010830.pdf" onclick="window.open(this.href);return false;
http://ntrs.nasa.gov/archive/nasa/casi. ... 025423.pdf" onclick="window.open(this.href);return false;
http://www1.eere.energy.gov/vehiclesand ... torage.pdf" onclick="window.open(this.href);return false; (see pages 75-77 & 190-194)

Update: fixed AESC battery energy density typos (Wh, not kW per kg)
Last edited by JeffN on Fri Jun 22, 2012 1:56 pm, edited 1 time in total.

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 1:41 pm

Apparently someone in California has dropped a bar also.

http://www.plugincars.com/replacing-ev- ... 22261.html

From the article:
Some owners have already put 30,000 to 40,000 miles on their LEAFs, and we’re getting the first reports of battery power loss. The LEAF has a 12-bar indicator and Nissan says it’s seen the loss of a bar in “a few cases.” Mike Ferry, the transportation programs manager at the California Center for Sustainable Energy, says he’s seen it in exactly one LEAF (with 40,000 miles on it).
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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 2:43 pm

Well, not that this is a surprise, but Nissan service says the loss is "normal," and I got 5/5 stars on the battery report (although I don't think that's showing up in the scan, but it is indeed 5/5 on all measures). So I'm doing everything they tell me to do in order to take care of my battery, and we lose 15% in the first 10-1/2 months.

I showed the tech the information about lost capacity in the service manual and the expected 20% remaining capacity after 5 years in the disclosure statement. He shook his head and said his information says this is normal. He added that he's seen a lot of cars coming in like that. He also commented, "You can call Nissan," but he again indicated this rate of loss is considered "normal."

Note that even in the Battery Information Sheet, it indicates the car is down to 11 bars (I added the arrow).

Image

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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 3:28 pm

Here's another data point for what I would consider "normal" aging of the battery pack:

Code: Select all

Date	  100% Charge	Differential 	Differential Annual	Cumulative Loss 	Cumulative Annual	Comments
	          Percent	        Loss	           Loss Rate		                        Loss Rate

06/12/11	100.0%					                                                                    Assumed, not measured
10/15/11	96.8%	            3.2%	                9.4%              3.2%	              9.4%	Date approximate, Gid meter installed
02/15/12	95.7%	            1.1%	                3.2%              4.3%	              6.3%	Date approximate, battery balanced
06/22/12	94.7%	            1.1%	                3.0%              5.3%	              5.2%	Battery not balanced
Notes:

1) My Leaf spends about 8% of its life in the San Fernando valley when it is hot, the rest of the time it is in parking garage with temperatures between 50 and 75 degrees. (Edit: actually, it also spends another 16% of its life in San Fernando Valley in cooler weather with 5 temperature bars always showing)
2) I don't know if my Leaf suffered a more rapid loss the first 4 months (? from hot summer weather or steeper part of loss curve), or if I never had 281 Gids (meter purchased after 4 months ownership)
3) While the battery might show a few more Gids if balanced, two balancings in a row in February had no effect on the Gid count at 100% charge
4) Differential loss is the loss from one measuring date to the next
5) Annual loss rates were calculated by extrapolation, e.g., a 2% loss over 4 months would be a 6% annual loss rate
6) The annual loss rate is slowing, but factors such as assumed Gid charge when new and hot weather during first measuring period make this questionable without another year of data
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Re: Lost a "high-voltage battery status" bar, down to 11

Fri Jun 22, 2012 6:35 pm

Stoaty wrote:
JPWhite wrote:I see you have 7 temp bars, I've had 6 or less all year. Only saw 7 temp bars once last year after driving fast in heat and charging soon after.
I think that 7 temperature bars (= 98.2 degree F. or above) means that your Leaf has a fever. If the fever persists or goes higher, your Leaf is going to have some degree of brain (battery pack) damage. I have never seen 7 bars on my Leaf, it is usually at 5 bars, but spends significant time at 6 bars in the Valley during the summer; my pack appears to be in good shape (around 95-96% on a full charge by Gid-o-meter last I checked). I propose that time spent at 7 bars or above may be a good indication of who is going to have premature aging of the pack (assuming Leaf is not left at high SOC for significant periods of time). This fits well with the information on the Volt chemistry that 90 degrees is a lot worse for the pack (5 year life expectancy if) than 72 degrees (8 year life expectancy). My guess is that higher spikes are even worse, even if few and short-lived.
I agree with this.
My experience is only slightly worse:
7 bars - once after QC.
6 bars common during the day in both spring and summer.
5 bars almost always by morning from night-time garage temperatures in low 60s.
Currently showing a Gid loss of about 5.5% at 100% charge (based upon recent 80% charges).

However I seem somewhat more concerned about gradual loss than you, because I am not confident that the rate of loss is going to slow down before Fall.

I would suggest one additional rule-of-thumb for modest rate of capacity loss: how much time the car spends at 5 bars. Even though right now, before the worse summer heat, the pack returns to 5 bars at night, I suspect my car spends much less time at 5 bars than yours in your coastal home climate.

Of course time at 4 bars each day would be even better.

If above rule proves out, my loss rate may accelerate somewhat when the battery pack rarely gets back to 5 bars (72 F reported).

I have another basic concern that may well have been voiced by others. As the pack capacity shrinks, I will need to charge closer to the "new" 100% more often to do the same trips without charge in-route. This additional stress will tend to cancel the decline in the t^.5 loss rate.
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