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I recently learned that the 2021 Sienna Hybrid battery is a NiMh one and not the LION one like that of Tesla. Can anyone think of a possibility in future that Toyota might allow an option to have this battery be replaced with a Lion thus providing us with greater battery density that translates into greater range in EV mode?
 

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Sure, they'll just make you buy a new car to go with it ;-)

I'm also a bit surprised they keep at it, but I have to admit Toyota's NiMH chemistry is battle tested and proven over nearly two decades in the Prius. I don't know how they do it with NiMH's notorious memory effect compared to Li-ion, but it obviously works pretty well for many service years per pack. I also like that it's less resource intensive to make and easier to recycle.
 

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Sure, they'll just make you buy a new car to go with it ;-)

I'm also a bit surprised they keep at it, but I have to admit Toyota's NiMH chemistry is battle tested and proven over nearly two decades in the Prius. I don't know how they do it with NiMH's notorious memory effect compared to Li-ion, but it obviously works pretty well for many service years per pack. I also like that it's less resource intensive to make and easier to recycle.
And it doesn't tend to spontaneously combust like the Tesla's ;)
 

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I recently learned that the 2021 Sienna Hybrid battery is a NiMh one and not the LION one like that of Tesla. Can anyone think of a possibility in future that Toyota might allow an option to have this battery be replaced with a Lion thus providing us with greater battery density that translates into greater range in EV mode?
Going back to your original quesion. I do not think Toyota will "allow" the NiMH to be replaced by aftermarket Li-Ion (and still be under the same warranty). Some third party companies already producing Li-Ion specifically for the Prius and Lexus Hybrid cars (see link below). Its possible - that same company might make one for the Sienna, Highlander, etc in the future. At this time, I dont see any incentive for Toyota to replace NiMH to Li-Ion on used Hybirds unless:

1) There is a global shortage for producing Nickel (NiMH).
2) Li-Ion or any other new battery becomes so cheap to make that it does not make sense to produce NiMH as replacement parts for old Toyotas/Lexus Hybrids.
3) Govt/Environmental regulations require us to switch from one type of battery to another.

 
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Toyota - rightfully so - considers the current lithium ion battery tech "Work in progress", while the Ni-MH is an older and more predictable tech that Toyota has been perfecting for 25 years.

Here is an interesting simile: Through my other interests I know that it's easier to find a 60-year old vinyl record in a well-used, but still great condition than a functioning used CD half the age.

Apart from general reliability I believe Ni-MH isn't as temperature-sensitive as lithium ion. I briefly had a CRV Hybrid, which had a lithium-ion battery. The thing could barely cling to 30 mpg in winter - about as much as its gas-only version, whereas I never saw less than 35 mpg on the Sienna, which is two sizes bulkier than the CRV.

Toyota does have a so called bipolar Ni-MH battery, used e.g. in the new Aqua aka Prius C, which is unfortunately not available in the US. This battery is said to have twice the energy density of the regular Ni-MH. I wouldn't mind if the Sienna hadg a 4kWh battery to better capture the energy of going downhill, but I don't think I am going to get it any time soon.
 

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NiMH batteries are generally more reliable. With the vehicles charge controller, there shouldn't be any memory issues. Still, better than losing one cell on a Lithium pack which would render that battery bank useless till its physically replaced or repaired. I'd take reliability over higher discharge potential. Since the Sienna is only a mild Hybrid with no plug-in option. It makes no sense to swap to Lithium.
 

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NiMH batteries are generally more reliable. With the vehicles charge controller, there shouldn't be any memory issues. Still, better than losing one cell on a Lithium pack which would render that battery bank useless till its physically replaced or repaired. I'd take reliability over higher discharge potential. Since the Sienna is only a mild Hybrid with no plug-in option. It makes no sense to swap to Lithium.
I dont know if you saw the link I sent earlier but the Lithium battery packs are the same modular design & voltage voltage as NiMH. If a pack is bad - just replace that pack. Its the same for Lithium or NIMH.

The advantage of Toyota Hybrids is the availability of aftermarket choices of battery options. We are not stuck with OEM products. It is that competition that drives most people to consider the cheaper, lighter Lithium-ion, Lithium-Poly, or whatever battery tech is out there in the future. Just for comparison, The Sienna oem NIMH battery pack costs $5k without tax and labor.
 

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so, its also a weight consideration too. Just an FYI, but during the extreme shortages, some of the RAV4 hybrids got either NiMH or LiFePO packs depending on what was available, and the LIpo packs are significantly heavier because they have to be a lot more fire rated. They are also way more expensive, and will not do as well for the charge/discharge that the NiMH can do. Weight is also the reason we don't have a PHEV sienna or highlander yet. the necessary battery weight to get even a 50kWh pack in there without killing cargo/carrying capacity is really not possible right now.


I dont know if you saw the link I sent earlier but the Lithium battery packs are the same modular design & voltage voltage as NiMH. If a pack is bad - just replace that pack. Its the same for Lithium or NIMH.

The advantage of Toyota Hybrids is the availability of aftermarket choices of battery options. We are not stuck with OEM products. It is that competition that drives most people to consider the cheaper, lighter Lithium-ion, Lithium-Poly, or whatever battery tech is out there in the future. Just for comparison, The Sienna oem NIMH battery pack costs $5k without tax and labor.
automotive applications are not using Lithium battery chemistry like your phones battery, those would never withstand the charge/discharge cycles that are necessary for a cars operation. they use LithiumIronPhosphate, also called LiFePO(as opposed to LiPO). they are more expensive, less energy dense, and heavier, but will last a lot longer. they can handle faster charges, harder discharges, and more cycles, but come at a cost in both price and complexity.
 

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NiMH batteries are generally more reliable. With the vehicles charge controller, there shouldn't be any memory issues. Still, better than losing one cell on a Lithium pack which would render that battery bank useless till its physically replaced or repaired. I'd take reliability over higher discharge potential. Since the Sienna is only a mild Hybrid with no plug-in option. It makes no sense to swap to Lithium.
A small correction: Sienna is a full hybrid, whereas mild hybrid is something like the hybrid versions of the last generation Tundra or F-150, where the electric motor only assists the gas engine and cannot move the vehicle on its own.
Otherwise, I agree with your assessment.
 

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What is interesting to note is that if you go to toyota.com and build specs for a 2022 Toyota Prius and compare a XLE (Li-Ion) vs the XLE AWD-e (NiMH) you will see some differences in mpg and other details. That will give us a better comparison because besides one being AWD - the ICE is the same. The FWD version seems to have a 3mpg advantage - but I dont think its because of the battery type. Its more because of the added weight-resistance of having another motor/drivetrain in the back. Overall, the AWD is 150 lbs heavier.

Most importantly - the Hybrid battery warranty is the same for both Lithium and NiMH. That is how committed toyota is to both these technologies.
 

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What is interesting to note is that if you go to toyota.com and build specs for a 2022 Toyota Prius and compare a XLE (Li-Ion) vs the XLE AWD-e (NiMH) you will see some differences in mpg and other details. That will give us a better comparison because besides one being AWD - the ICE is the same. The FWD version seems to have a 3mpg advantage - but I dont think its because of the battery type. Its more because of the added weight-resistance of having another motor/drivetrain in the back. Overall, the AWD is 150 lbs heavier.

Most importantly - the Hybrid battery warranty is the same for both Lithium and NiMH. That is how committed toyota is to both these technologies.
If I remember correctly, the AWD Prius has a miniscule rear motor, something like 7 hp, and along with the differential it's kind of nested among the elements of the rear suspension .... would this itsy-bitsy assembly explain the loss of 3 mpg? As a comparison, Sienna's rear motor is 54 hp, but the mpg loss is only 1 (city) or even zero (highway).
 

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If I remember correctly, the AWD Prius has a miniscule rear motor, something like 7 hp, and along with the differential it's kind of nested among the elements of the rear suspension .... would this itsy-bitsy assembly explain the loss of 3 mpg? As a comparison, Sienna's rear motor is 54 hp, but the mpg loss is only 1 (city) or even zero (highway).
If you put it in perspective -- 3 mpg loss from 54 mpg in a Prius is 5%. 1 mpg loss from 36 mpg in Sienna is almost 3%.

Going back to O/P - I really do not know right now how much advantage there is between NiMH and Li-Ion other than Li-Ion being lighter and thus can offer a higher power to weight ratio. Weight is a very big factor especially in smaller vehicles.
 

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If you put it in perspective -- 3 mpg loss from 54 mpg in a Prius is 5%. 1 mpg loss from 36 mpg in Sienna is almost 3%.

Going back to O/P - I really do not know right now how much advantage there is between NiMH and Li-Ion other than Li-Ion being lighter and thus can offer a higher power to weight ratio. Weight is a very big factor especially in smaller vehicles.
Well, looking at 3% to 5% is one prospective; another one would be to compare the relative fuel efficiency loss due to AWD. For the Prius, it's twice as high as the for Sienna. But the real surprise here is that in the Prius this higher loss occurs despite the fact that the rear motor is much smaller .... in fact, one might even question its utility.

From what I understand, Toyota is very fond of the Ni-MH batteries because they are more resilient, present a lower fire risk, tolerate low temperatures better, and probably have lower manufacturing costs than comparable Li-ion batteries. I may have mentioned earlier that Toyota now has a "bipolar" Ni-MH battery as well, with much higher (2x I think) energy density than the "regular" Ni-MH. I do not know if this battery will make it to the North American market, though.

I know the Rav hybrids come with both Nimh and Li-ion batteries. The weight difference between the 2 is about 40 pounds.
Do you mean globally, as in for example Li-Ion in Europe and Ni-MH in the Americas?
 
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From Toyota USA Web site:

Prius Hybrid XLE AWD-e (NiMH) 201.6 volts 51/47/49
Prius Hybrid XLE FWD (Li-Ion) 207.2 volts 54/50/52

RAV4 Hybrid XLE AWD (NiMH) - 244.8 volts 41/38/40
RAV4 Hybrid XLE Premium AWD (Li-Ion) - 259.0 volts 41/38/40

Just to reiterate this is really not a fair apples to apples comparison. Prius 5% (3mpg loss) comparing AWD (NiMH) with FWD (Li-Ion). Siennas 2.7 % (1mpg loss) AWD vs FWD (both NiMH).
 

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Well, looking at 3% to 5% is one prospective; another one would be to compare the relative fuel efficiency loss due to AWD. For the Prius, it's twice as high as the for Sienna. But the real surprise here is that in the Prius this higher loss occurs despite the fact that the rear motor is much smaller .... in fact, one might even question its utility.

From what I understand, Toyota is very fond of the Ni-MH batteries because they are more resilient, present a lower fire risk, tolerate low temperatures better, and probably have lower manufacturing costs than comparable Li-ion batteries. I may have mentioned earlier that Toyota now has a "bipolar" Ni-MH battery as well, with much higher (2x I think) energy density than the "regular" Ni-MH. I do not know if this battery will make it to the North American market, though.



Do you mean globally, as in for example Li-Ion in Europe and Ni-MH in the Americas?
The North American Ravs get can get either.
 
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