NIMH versus Lithium batteries in PHEV

I wouldn't buy the first year of a new (that is, new to that maker or specific application) battery technology. Also, upgrading is an expensive hobby.

 

Re: NIMH versus Lithium batteries in PRIUS 2012 !!

Don't know but see http://priuschat.com/forums/prius-h...-prius-v-prius-c-prius-phv-3.html#post1244222.

 

Li-Ion batteries hold charge better than Ni-MH. However, Li-Ion requires tighter control than Ni-MH. The Ni-MH batteries are more robust and will take more abuse without the sometimes catastrophic results that have been experienced with Li-Ion.
Here is a link to some info:
http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

Be careful what you wish for.

 

LiFePO4 batteries are pretty safe. Just take a look at Jack Rickards videos on the batteries he has destroyed. They can melt down but they dont do what was in that LiPo fire video.

 

One of the main problems with LiFePO4 is the low charging rate. Maximum charging rate is generally a function of amp-hour capacity. NiMH is great because it will take 15C, i.e. 15 times amp-hour capacity on charge and discharge. This is ideal for regenerative braking, as a small amp-hour NiMH pack can efficiently store and release energy. We see 100 amps of boost and regen in the Prius. The downside of NiMH is weight and bulk, which makes NiMH less practical for EV and PHEV use. With LiFePO4, having max charge rates of 4C or less, it is necessary to have a pack with high amp-hour rating, at least 25 ah, in order to support max regen. Such a battery in Gen II or III would be in the neighborhood of 5 kWh.

 

Li-Ion and Li-Po covers a lot more chemistry variations, with significantly different safety and energy density levels, and even voltage levels, than is mentioned in this article.

 

No, it will happen with gen 4 in 2014. (2015 MY)

 

LiFePO4 may have a lower constant charge rate than NiMh but for PHEV use LiFePO4 would be better since you would have a higher capacity to work with. NiMh is perfect for the regular hybrid where all its used for is to capture regen or energy that would otherwise be burned off as heat. You dont need a big battery to that.

 

Link?

 

Nobody knows the cost. All I've read is that one exec said it won't be more than $10k over the current price.

The test models had PHEV operation on 2 Li packs and HEV operation on a regular Prius NiMH pack.

I don't see Toyota rushing away from NiMH since they've proven reliable it's relatively cheap for them to make due to their patents and interest in the manufacturer. Right now they're going to increase manufacturing to 1 million packs per year and are going to do their own recycling so they have easier access to the materials.

As TheForce wrote there's little advantage for Li over NiMH in HEVs. For ease of manufacturing I'd expect Toyota to stick with the 1-2 set-up in the production Prius PHVs and NiMH in their hybrids for a long time.

I hope I'm wrong because that'd mean cheap and reliable Li batteries available.

 

NiMh has been very dependable, as proven by 2 million Prii buzzing around with very few battery problems and no fire/safety issues I've seen.

I'm sure Toyota has tested Lithium technology. If they think it's an advantage you will see Lithium on future models.

I personally don't think Lithium is very durable. Under heavy loads they swell up and become unusable. Storing them at low charge and full charge decrease the lifespan. My experience with Lithium batteries in my cell phones and laptops hasn't been great. They usually die within a year or two, and that's not even under a heavy load.

 

Lithium used for cell phone and laptop batteries can be different than what is used for EV use. For small devices you want a more energy dense Lithium battery which only last a few hundred cycles.

Batteries used for EV are of a different chemistry and can last 1000-3000 cycles or more. They have a lower energy density but are safer and since they will be used in a car you have more room to work with. More energy dense is desirable for more range but I think people would choose cycle life over energy density. The LiFePO4 batteries from CALB and Thundersky are looking pretty good for cycle life as well as shelf life.

 

No, just a guess. if one of the lithium packs in the PHEV can be used as the hybrid traction battery then why have double inventory etc for the new model and PHV.

 

- They are majority owners of the company that manufactures their batteries. If they abandon NiMH, they abandon the company.
- The test Prius PHV is manufactured in the same plant as the Prius and sharing as much of the platform as possible makes sense. Some of the other components are beefed but essentially it's a Prius with 2 extra Li packs, a plug and recharging hardware. Keeping NiMH for the HEV pack means they don't have to match a Li design to the NiMH.
- The Li packs are deliberately used much less than the NiMH packs. In the test models at least, running in EV mode the packs are normally just discharging unless there is regen. The car alternates between Li packs. Once a Li pack is fully discharged it is no longer used. This design keep discharge cycles low and therefore reduces the risk of the new technology.

 

Well from the technical descriptions Toyota published and some comments made on this forum, it seems the 3 Lithium battery packs in the PHV are about 1.7 KWh each. This serves 2 purposes: make exactly the same battery pack over and over to get economy of scale and helps with the design. For the 1st 20,000 PHVs to be sold they'll need 60,000 lithium battery packs. As a direct replacement for the NiMH battery the Lithium battery already is 32% better capacity. This means it can store 32% more regen power as well as deliver 32% more power over time.

Based on this assumption, it is not necessary to put extra regen power back into the sub battery packs (I like to call them SBPs and the main battery pack, the MBP). Making a 1-way connection between the active SBP and the MBP simplifies design as well as makes the design much safer. Also the size of the MBP is probably the reason for it maintaining 50mpg acting as a regular hybrid. It would have to, lugging around an extra 200lbs of drained SBPs. Now before everyone bemoans this as a "game-stopper" or takes them off the list of buyers, think about it this way. Regen/gliding will become extremely important as a way to keep the sub-packs from discharging. Also this enhances the idea of micro cycling the SBPs. Whenever you can, after you stop, start a recharge even if you know you're going back out after the grocery list is done or if you are just stopping long enough for a bite to eat before going out again. Make it a habit. It'll be far easier than doing this with the Volt, which would require 10 hours to recharge its battery pack. You'd be surprised how often you say to yourself, I'll only be 10 minutes only to come out a half hour later. As much as you'd like to tell yourself, there is nothing ordinary about this car.

 

The rumor is gen IV is a '16 my due sometime in 2015. I agree it is doubtful toyota will stick to nimh.

One key here is CARB that has toyota giving a 10 year warenty. Toyotas costs are overblown, but we don't really even know how many of the Nimh will last 10 years and keep their capactity. With nimh they are only using 40% of the capacity, so I suppose if it loses half capacity it will be hard to prove.

The benefits of Li are easy to see. They weigh less and take up less space for the came energy and more power. The differences are significant. The question really is will they last 10 years? I don't think Toyota even thinks their Nimh will, otherwise they would warrant them the same in non-carb states. 8 years seems safe on both technologies and the warranty that nissan and chevy give their lithium batteries.

The company bought sanyo for better lithium technology. It needs to shift. The writing is on the wall. Just like for lap top and cell phones, the best batteries are lithium.