How to extend LIMITED SERVICE LIFE of Prius PHV traction battery.

Can you elaborate more on that?
Cells are connected in series right? so how can 'leadfoot' draw the modest amount of current from each cell because there are many of them?
Also, 'leadfoot' in Prius PHV will evoke the ICE to kick-in so how can it be "lot of current" from 56 cells?

 

This is completely incorrect. First, the Prius Liftback (regular hybrid) uses ~40% of total capacity of its NiMH battery.

Second, there is just one Li-ion battery pack in the Prius Plug-in. Subtracting the capacity of the Liftback battery pack from it is a meaningless calculation. Hybrid mode just uses a small range of the Prius Plug-in battery capacity.

 

This assumes that the Volt and Prius Plug-in both use similar cells that have approximately the same trade-offs in power vs energy density. While there is a volume number for Volt's battery on Wikipedia, I've been unable to find the volume of the Prius Plug-in's battery to determine if they have comparable energy density. It is conceivable that the Prius Plug-in traded energy density for power, so that a cell could supply more power for equal or less stress.

 

Both Leaf and Volt use a mixed parallel + series connection. The Volt's battery contains 288 cells. Groups of three cells are welded together in parallel called cell groups. There are a total of 96 cell groups in the battery assembly. These cell groups are electrically connected in series. Each individual cell group is rated at 3.7 V, for a nominal system voltage of 355 V direct current. The battery cell groups are joined to form 3 distinct sections. The first 30 battery cell groups make up battery section 1. This section is adjacent to the cowl and contains battery cell groups 67 through 96. The next 24 battery cell groups make up battery section 2. This section is located behind section 1 and contains battery cell groups 43 through 66. The transverse battery section is section number 3 and it contains the remaining battery cell groups 1 through 42. The 3 battery sections are individually serviceable components.

So the battery is both in series and in parallel.

High load take advantage of the parallel connections. The series is to ramp up the voltage.


Yes very high loads in the Prius PHV will use the engine.. but sustained travel at 60mph may draw more power for longer time. That cause heating and the heat + high current causes more long-term wear. The Volt's battery is liquid cooled to also help with the issues of high-load heating.

 

That is quite possible and hopefully partially true. It is, however, unlikely the undisclosed battery technology is that much more advanced to make up the difference. The Volt parallel/Series effectively spreads the power demands and reduces stress by a factor of more than 2x.

 

So, in fact, it is 96 'cell groups' against 56 cells not 288/56. And 1 large cell should perform better than 3 smaller in parallel (cell balancing, internal impedance).
The 60 mph stress is also not clear, the Volt can drive EV at higher speeds so the stress will be even higher.

 

It doesn't matter.

Series and parallel give you different voltages. Power is a product of voltage and amperage. So the current draw on each individual cell won't be changed significantly because of the arrangement of the cells. They do it so the voltage is in the range they want for wiring, motors, power electronics etc... if they wanted to run it at 100V they could, but they would need thicker gauge heavier more expensive wire.
It is 288 vs 56, but the cells are not the same anyway so the exact number is irrelevant and silly to compare. The allowable c-rate of 56 18650 cells is going to be higher than 56 pouch cells all other things being equal.

 

There is no "undisclosed battery technology that is much more advanced", rather it is standard battery design. When you design a battery cell, you choose the chemistry to trade off between energy density or power for the particular application. The extremes are a cell that stores a lot of energy but supplies low power or a cell that stores little energy but supplies a lot of power. The Volt has a much larger battery, so may have chosen certain cells with higher energy density and lower power. The Prius Plug-in has a much smaller battery, so may have chosen lower energy density and higher power cells. The Volt also has higher power requirements b/c it is heavier and designed to accelerate more aggressively.

 

It does matter. Series adds voltages. Parallel add currents. Power(P) is the product of voltage (V) and current (I) (P =VI) The series allows them to get to the voltage they want; the parallel allows the power demands with the given cells.

 

Can you point to an article on the Li chemestry in the Prius PHV?
I've not seen one yet. That would answer the density question.
If there is no article, then its undisclosed.

 

No, but by implication, that means you have an article on the Volt's battery chemistry?

Anyhow, as I indicated in my earlier post, it isn't necessary. The Prius Plug-in battery volume is the missing specification that is required to compare the energy density between the batteries of the two cars.

 

Battery costs are continuing to come down. When the Volt first came off the line the battery cost was said to be $500 to $600 per kWh. The Leaf battery pack was reported to be as low as $375 per kWh. Now Tesla's Elon Musk has said that battery cost will drop below $200 / kWh in the "not-too-distant future".

At $200/kWh, the cells in the 4.4 kWh PiP battery will only cost $880.

 

The chemistry is an mix of two technologies. Most of it came from a company called Compact Power (which used to be in Monument Colorado, where I live. I've talked with some of those founders who chose not to move to Mich with the contract for the Volt. CPI was acquired by LG-Chem, giving it the ability to manufacture at the scales needed. The full chemistry is not fully disclosed but there are lots of details known. There were some parallel "discoveries" that required some added licenses, so it was not all public when it started.

Green Car Congress: Profile: Li-ion Provider Compact Power, Inc. Focusing on the Automotive and Vehicle Markets

GM

The Breakthrough Behind the Chevy Volt Battery | U.S. DOE Office of Science (SC)

 

Battery layout doesn't matter, because in the small system of an EV the electrons are essentially moving at the speed of light.

A heavy acceleration event consumers x amount of power. The electrons start flowing in response to this power demand. Even if all the cells were in series, the load on each individual one is the same. This is because as the first cell in the line gives up its electrons, it is replenished by the others down the line. The replenishment is at such a rate that the cell at the front won't suffer any deep discharge issues until x is high enough to deep discharge to entire battery.

 

I think you missed my point completely, probably I was not clear enough:

Say, you have to draw a certain current from 96 cells connected in series. Then, you draw the same current from 56 cells connected in series.
Now, do you believe each cell in the 96 array is subject to lower current than each of the 56 array just because "the total current is distributed among more cells"?
This was drinnovation false reasoning I was referring to.

 

Think about that again with these assumptions.
Lets say you want 100kW from a 10kWhr pack.
Now the batteries are each 50Wh. so you have 200 cells.
If they are at 5V and you put them all in series you get 1000V. So you need to pull 100 amps from the string.

If you have them in parallel to get a 100V operating then you have 10 strings of 20 cells. You need to pull 1000 amps or 100 amps from each of the 10 strings.

Seems similar to me.

 

Have you ever heard of a car manufacturer offering upgrades (other than fixes for design or manufacturing flaws that affect safety) after a car has been sold? I have not. Nissan was saying early on that there would be a bigger battery available for the Leaf in a few years, but I haven't heard anything of this recently. And Nissan was giving out a lot of bad information early on. I think it's a good bet that there will be after-market upgrades to the PiP battery, but not from Toyota itself.

I asked this question and was told that the car is capable of completely filling the battery from regen, assuming you have enough downhill.

The amount of energy available is determined by the mass of the car and the change in elevation. Riding the brakes will not increase the amount of energy you can recover. If the grade is steep, you will need to use the brake pedal to maintain your speed, and if the car can do so, it will use regen for that. But using the braking to go slower will not add to the total energy recovered.

Lithium batteries can safely tolerate a greater range of SoC. Therefore NiMH batteries, if they are to be made to last a long time, must be kept in a narrower range, and yield a smaller percentage of "useful" energy than lithium batteries. Either type can be used to its full range, but if you want to maximize battery life you must, to use your term, baby NiMH batteries more than lithium. (Though some lithium chemistries require more diligent temperature control.)

 

That's how aftermarket providers make money.

They offer enhancements beyond what the car manufacturer chooses too.

It will cost you though. But for the few who choose to mod, it's considered money well spend.
.

 

I see claims of higher energy density without sacrificing power, but unfortunately no numbers quantifying the improvement over unmixed battery chemistries.

It looks like energy density is measured in Wh/kg, so the numbers are:
Prius Plug-in: 4400Wh / 80kg = 55Wh/kg
Volt: 16000Wh / 197kg = 81.2Wh/kg

The batteries must supply:
Prius Plug-in: 38kW
Volt: 111kW

So like I suspected earlier, the energy density on the Volt is higher and the Volt draws more power from its batteries. Unfortunately, I haven't been able to find the layout of the batteries to figure out how much current much be supplied per cell.

Toyota Racing Development does just that. A larger battery would increase the power making the Prius Plug-in accelerate faster. I'm not saying it will happen, but it's not impossible.

 

I believe the question could be getting at this effect: When you go downhill, there may be a maximum amount of regeneration that can happen. I'm sure there has to be as the electronics is designed for some maximum amount of power and current flow. This means that there is some maximum slope (or braking pressure) which when exceeded means the amount of regeneration per unit distance does not increase anymore. By going slower, you can extend the use of that slope by regenerating at the maximum rate the Prius is designed to handle.