The Aftermarket Traction Battery Thread

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Currently own a Tesla Model S 85kWhr model. Been eyeing a 2nd electric car for awhile and used Leafs are pretty cheap. But battery degradation is obviously a concern. I'm in engineering and an avid DIYer on auto maintenance so have been learning about EVs.

First, I'd like to explain a little of what I learned about battery degradation. There are major 2 factors (capacity and heat) but most people only talk about heat which is probably the secondary problem.

1. Capacity.

A rechargeable battery life chart shows lifecycle is a lot longer if only cycling with low amount of charge and discharge. Large charge and discharge cycles degrades battery life in any technology including our trusty old 12V lead acid batteries. Here is some info

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

So a 24kWhr battery used frequently in say 40-50 mile range charge/discharge cycles will loose capacity really fast regardless of thermal control. Using the LiPO4 discharge table from the above link, we can see 80% discharge/charge cycles provides about 1000 cycles before losing 30% of the original capacity. So 50 miles x 1000 cycles = 50k miles. And 4/12 bars loss = 33%. This pretty much matches the data we see from <= 24kWhr battery electric cars.

Cooling is not as much of an issue at this capacity level because high depth of discharge will pretty much guarantee high capacity loss at 50k miles. Other ~24kWhr EVs like Focus Electric also have active battery thermal heating+cooling and all show the same range loss pattern at 50k miles. I think Nissan recognized this and decided to just leave out the expense of active thermal control for a 24kWhr design.

Compared to a Tesla 85kWhr driven 50 miles per day. 20% DOD (50mi/250 range) 2 yields 500,000 miles before 30% degradation. So I hear about high mileage 85kWhr Teslas lose about 10% at 200k miles.

2. Thermal Control

The reason rechargeable battery degrades faster in heat is due to basic chemistry. From high school chem class, we learned every chemical reaction has parasitic reaction. Parasitic reaction basically produces unwanted products and use up some of the reagents. With increased heat (say a bunsen burner in the chem class), reaction (and parasitic reaction) goes faster.

Thermal control also isn't just cool the battery cell. It is about how to cool every corner and interior of the chemical reaction surface. Large cells like Nissan and LG Chem surely have difficulty to cool the center interior.

So what would be an ideal aftermarket LEAF battery look like?

1. Leverage energy density increase to get say 2X capacity for the same space. An aftermarket design using newer battery chemistry should gain the energy density improvements since 2001. Not sure if 2X has been reached but certainly soak up the improvements. This helps with DOD discussed above. If replacement capacity stays at 24kWhr, it will suffer the same fate at 50k miles.

2. Cooling. Tesla battery design is very different from Nissan and LG Chem and I'm guessing there is huge benefit. Teslas uses small cells (little bigger than AAs) and submerge them in coolant for thermal control. Nissan and LG Chem makes big battery cells (size of a shirt box). Bigger cells have better density but smaller cells have better cooling (can't cool the center of the big cells). The key is probably to find the good balance between these 2 factors. Tesla's cell design is evolving from the original Panasonic battery cell to now slightly bigger to provide 2X capacity. Likely a design trade off after gathering statistics on the original design. Cell size can grow a little while maintain thorough cooling to the cell center.

Self contained thermal control would need air scoops on the bottom and internal heat exchangers + pumps + coolant bath) to provide a plug+play solution. Tesla's a battery have 2 coolant ports because they mount the heat exchangers mounted in the front of the car to collect cool air. Leaf have no such coolant port so would need to self source air and internal thermal control components.

Last, I can see Tesla also does 3 other things

1. Limit charging rate when battery is cold or full. Regen is limited under these conditions
2. Limit discharge rate when battery is cold. Can't do rocket take offs.
3. Cooling system goes into overdrive at the Superchargers (basically faster version of Nissan Quick Charge). DC fast chargig is the fastest chemical reaction so it generate the most heat so the cooling system needs to to offer max performance here.

With a few sensors accelerometer and temp sensors, maybe its possible to build in these controls directly into the battery pack.

In summary, following Tesla's world class battery design, a good aftermarket pack would need to

1 Source a good cell design. This is probably the most challenging. Tesla+Panasonic factories probably produce the best cell right now at the right size for density+cooling. They are probably not available for anyone else.

2. Build a good thermal+smart architecture with the good cells. Incorporating active thermal control (heater for cold and cool air for heat). Limit charge/discharge when cold etc..

Probably not going to get this level of replacement battery design but I thought I share with what I learned from Tesla's design.
 
howardc64 said:
In summary, following Tesla's world class battery design, a good aftermarket pack would need to

1 Source a good cell design. This is probably the hardest part. Tesla+Panasonic factories probably produce the best right now at the right size for density+cooling. They are probably not available...
Much of your post is well reasoned, but neither Nissan nor any reputable replacement pack manufacturer is ever likely to use current Tesla+Panasonic cells in their packs, due to their flammability and the resulting liability.

IMO, LEAF packs offer superior performance because they do not require ATM.

But even if there were net benefits to ATM, adding it to an aftermarket pack design is highly impractical.
 
edatoakrun said:
neither Nissan nor any reputable replacement pack manufacturer is ever likely to use current Tesla+Panasonic cells in their packs, due to their flammability and the resulting liability.
I would agree, unlikely these cells can be sourced.

In terms of flammability. All lithium ion batteries are highly flammable if punctured. Tesla's issue were mainly self leveling suspension cars that auto lowered at highway speeds. Early model's well documented cases where car burned up was due to road debris damaged the front end of the pack at highway speeds. They retrofitted the cars with a titanium shield in the front of the battery pack and issue is pretty much gone. Really not a battery cell design issue as much as low road clearance and physical protection issue. Here is a video of shield vs concrete follow by a video of where and how the shield was installed.

https://www.youtube.com/watch?v=_5OurZx1ihI
https://www.youtube.com/watch?v=AHdxakaGrkw

edatoakrun said:
IMO, LEAF packs offer superior performance because they do not require ATM.
I do think all EV LiON battery packs will be both higher capacity and ATM going forward. Low capacity battery cars depreciate too much to be competitive in the future and ATM will be needed to increase the life cycle of a even higher priced high capacity battery pack.

edatoakrun said:
But even if there were net benefits to ATM, adding it to an aftermarket pack design is highly impractical.
Haha yeah, I agree, quite a bit of engineering involved :) So I guess best anyone can do is source high cap cells. This would beef up overall range and lifecycle but of course also cost more. So perhaps same 24kWhr capacity at lower end of the cost is all that is practical. All of this is only possible if someone figures out any computer interlinks between the pack and the car.
 
So I wonder if an aftermarket pack can be created with the guts of the new 40kwh pack being made for the 2018 Leaf. As I understand it, the pack has the same footprint as the original. Perhaps then if the form factor is close enough, something could be done...
 
kWh battery cost is around $300 for cells itself. Nissan giving replacement for around $6k which is about $5000/24=$250. This is below cost of cells and third party cannot compete, and you should get your battery from Nissan.
 
I think it will happen, and if it doesn't I will do it.

I own multiple Toyota/Lexus hybrids as well, and I was hoping for aftermarket cells for the Prius at least since it is so popular. Some of the first that came on the market were crap. Some were OK but didn't play nicely with the OE cells. Now I make a pack that is brand new based of an existing style of kit using my battery factory contacts and they are being installed in cars now. Got them in my Gen-2 Prius and a couple in China that people at the factory own.

I figure when the Leaf's battery degrades enough that I can't drive 20-25 miles on a sunny day, I'll need a replacement. And if there aren't any new cells available, then I'll be making my own. Batteries aren't that hard. Making them physically fit an existing mold is more difficult. But not impossible.
 
Panasonic 2170 cells are rated at 20w capacity. So you would need 1500 for 30KWH capacity. Arrange the cells as 16 cells in parallel by 2 sets in series to match one of Nissan's modules. 48 modules to make up a pack. 1536 cells total. 26.5 in by 40 in. by 2.8 in. thick. Reuse the BMS from the old battery since the cell voltages and currents should be similar. Flood the batteries with mineral oil and circulate it through a radiator for cooling. There should be plenty of room in the under the seat hump for a radiator and pump. You would have to modify the shell for venting for the radiator and fans but it shouldn't be too hard. If you want a bigger battery, just add more 2170 cells to each module. You could actually cram 60KWH into the existing shell but I don't know if the BMS would like it and you would need an external radiator.

As far flammability and liability goes, every 18v cordless device (drills, saws, sanders, etc.) uses the same chemistry and I don't hear any reports of exploding tools or tools catching on fire. The biggest problem with this idea is getting a hold of the 2170 cells in the first place. I understand that Samsung is going to produce a 2170 cell also so that might be an alternative source.
 
I dont know russian, but from what I've understood, the 24KWh battery works with erasing only some DTC error codes on the 30KWh Leaf, but the 30KWh battery works on 24KWh Leaf only after they changed some module(s) too.
 
bzalex said:
I dont know russian, but from what I've understood, the 24KWh battery works with erasing only some DTC error codes on the 30KWh Leaf, but the 30KWh battery works on 24KWh Leaf only after they changed some module(s) too.

I have asked the guys in a different video. See comments from Jostein Sand: https://www.youtube.com/watch?v=XHLddeIxxig&lc=z22uwha5rqq1xddxd04t1aokgrnp5y4kw0yjp1a0werwbk0h00410.1515217125752645

They confirmed that if you buy VCM and battery from same it should work.
I have actually just bought this combination myself and is waiting for delivery. It's gonna be a garage project DIY-style so it could take some time but I will report back to this thread when there is progress.
 
jsa061 said:
...They confirmed that if you buy VCM and battery from same it should work.
I have actually just bought this combination myself and is waiting for delivery. It's gonna be a garage project DIY-style so it could take some time but I will report back to this thread when there is progress.
Looking forward to it.
 
jsa061 said:
bzalex said:
I dont know russian, but from what I've understood, the 24KWh battery works with erasing only some DTC error codes on the 30KWh Leaf, but the 30KWh battery works on 24KWh Leaf only after they changed some module(s) too.

I have asked the guys in a different video. See comments from Jostein Sand: https://www.youtube.com/watch?v=XHLddeIxxig&lc=z22uwha5rqq1xddxd04t1aokgrnp5y4kw0yjp1a0werwbk0h00410.1515217125752645

They confirmed that if you buy VCM and battery from same it should work.
I have actually just bought this combination myself and is waiting for delivery. It's gonna be a garage project DIY-style so it could take some time but I will report back to this thread when there is progress.

Please report back when you can. Thanks!
 
Allright, so I'm finally done. It was a little more work then I expected but that's what you get when you are an optimist. I changed the battery in my own garage and in hindsight I wish I had invested in better, taller jack stands. The car needs about 70 cm ground clearance, at least if you are going to take out the battery from the back of the car.

After the car had the proper height it was actually not to difficult getting the battery out. I used a lifting table on wheels that I borrowed from a friend. ( Minimum height of table was 34 cm, battery pack is about 26 cm. And some extra cm penalty for taking the battery out from the back of the car) .Then it's easy to support the battery as you unscrew the bolts. Of course, you need to unload the old battery and get the new one on the table - there is some logistic there that took some time as well.

Another issue I had that took a long time figuring out was how to remove the main battery cable. Nissan has made some crazy patent that involves first pressing really hard on one side of the cable-release-mechanism , pull a little and then press another place. Why?

Swapping out the VCM was one of the easier parts of the operation. You just have to remove all the screws you can find on the inside and outside of the glove department and take the hole thing out. Than it's straight forward.

After swapping the battery and the VCM I of course wanted to test the car only to find out I got a lot of error messages. It all boiled down to that the keys need to be registered in the VCM. It's a straight forward procedure that has to do with Nissan immobilizer system. I got no error regarding incorrect battery ID or anything in that regards ( Leaf Spy pro). The range and everything was displaying correctly but it was not possible to get the car out of Park. This is where my part of the job ended. I had to tow the car ( front wheels were locked so I just called the professionals) to Nissan and they actually were quite helpful. They registered the keys with the VCM and now everything is working properly except the app. I'm not able to preheat the car or read out the battery information using the Nissan app. Interestingly, I can see my driving history on the app.

Some pictures:
 
https://1drv.ms/i/s!AjT0AFfFvlhXkKR6zzWmc6zCssmXwQ
https://1drv.ms/i/s!AjT0AFfFvlhXkKUANHoTm0v1XLt93g
https://1drv.ms/i/s!AjT0AFfFvlhXkKR_wPj3goFiF3RJ-w
https://1drv.ms/i/s!AjT0AFfFvlhXkKR-FlIW-lvydF0XTg
https://1drv.ms/i/s!AjT0AFfFvlhXkKR8c51xZ7F_6dcBQQ
https://1drv.ms/i/s!AjT0AFfFvlhXkKR7uQyCYOpLgUPyXQ
https://1drv.ms/i/s!AjT0AFfFvlhXkKVZhqNNN-5YjdHElA
 
That's great news. Pity you had the troubles with the keys.
I wonder if it would be possible to buy the VCM together with the paired keys ?
 
I actually got hold of keys from the same donor car as the battery and the vcm. You still have a problem because now you have some units, BCM for instance, that's using the old keys and VCM that's using the new. So unless you are planning to change all boxes related to Nissan immobilizer you need to program the boxes. I got a tip that you can use unofficial tools for this job. This one:

https://www.aliexpress.com/item/OBDSTAR-X-100-ProS-OBD2-Auto-Key-programmer-C-model-eeprom-security-code-reader-same-x200/32687310187.html

In any case. Registering you keys with the VCM is a 5 min job for Nissan. It shouldn't be a problem .
 
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