Question: Li-ion aging and charging costs

[BarryP]

We have a 16KWHr pack. Say it takes 16.2KWHr to recharge it from 0 to 100%.
Or another way to say it is say we spend (consume) 185 WHrs/mile. (wall to wheel measurement).

But say in 100,000 miles we have an equivalent 13KWHr pack. Will we still spend 185 WHrs/mile?

I’m wondering if charging time will be shorter yet wall to wheel measurement will remain the same? I’m just hoping so.

Thanx,
-Barry

 

[JoeS]

Barry, you're talking about three different parameters, which you have correctly identified.

The first parameter is battery capacity (kWh), which I'm sure will diminish as time goes on. Although presently a nominal 16kWh, I'll be content with a 20% reduction after 100,000 miles to 12.8kWh.

The second parameter is average energy consumption for a distance driven, expressed as Wh/mi, miles/Wh, kWh/100km, etc. This needs to be put into context, as this consumption can be variously expressed as energy sucked out of the battery going into the vehicle (and measured with onboard instrumentation such as CaniOn or a Leaf's dashboard) or, as you and I prefer to express it (and take into consideration the charger inefficiency), Wall-to-Wheels. In my own case, the wall-to-wheels number I carefully measured over 8000 miles was 4.2miles/kWh (0.238kWh/mi, 14.8kWh/100km, etc.), which included the uncontrolled variations due to a mixture of L1 and L2 charging and sporadic heater and aircon use. http://myimiev.com/forum/viewtopic.php?p=5744#p5744

The third parameter is charging rate of energy transfer, kWh/hr or simply power (kW). This is a function of our EVSE settings, up to the maximum ability of our onboard charger which is around 3kW at 240vac.

If I understand you correctly, you are wondering if it will take more energy to charge up our iMiEV after the batteries are partially worn out? I think the numbers will stay the same; i.e., it will not take any more energy to recharge the battery to its (diminished) capacity than it takes to charge to that same capacity level when the battery was new. The wall-to-wheels number should remain unchanged.

 

[Kuuuurija]

Sure, the efficiency drops as battery deteriorates. The ultimate limit is that you can not get out of your garage before the battery is depleted, even if it just finished full charging.

 

[Don]

As the battery ages and it's capacity decreases, so too should the energy necessary to recharge it to 100%

When it was new and it's capacity was 16 Kwh, maybe it took 5% more than that to recharge it fully, so maybe 16.8Kwh. When it's capacity is reduced by 20% to 12.8Kwh, it should still take about 5% more than that to recharge it to 100%, or 13.4 Kwh. Note that a 100% charge is now 12.8 Kwh . . . . the battery just stores 20% less energy than it did when new

Don

 

[Kuuuurija]

You missed the point, that the more the battery is loosing its capacity, the less the car can drive.
Ultimate limit is, that you can charge the battery as much as you wish, but you can not drive even single mile. And even much before, are you ready to go to a 20 miles long trip if your EV-s guess-o-meter lists less than 10 miles?

If to use preheating/cooling, then the efficiency also drops together with capacity loss, because preheating takes the same amount of energy both for long trip with the new battery and for short trip with considerably reduced capacity battery.

 

[Zelenec]

I have the same question these days, Barry. There are two options:

Option 1:
Battery is like a container that is shrinking in time. With less capacity it requires proportionally less energy to be charged to its reduced capacity and reduced range of course.

Option 2:
Battery is degraded in time. The amount of energy used to charge the degraded battery remains the same. The increased difference between the input energy and stored energy is heat that is released due to increased internal resistance of the cells. The increase in internal resistance is the main symptom of degradation of battery capacity.

Some people prefer the first, the others the second option. What's your opinion?

 

[BarryP]

...There are two options:...

That is what I want to find out.
I believe we can find out with those owners who are keeping track of their wall-to-wheels WHrs/mile. What is it brand new? And what is it at 25K, 50K, 75K, and 100K miles?

Of course I’m expecting range to go down.

Thanx,
-Barry

 

[Kuuuurija]

The truth lies between those two options.

 

[Zelenec]

Malm reported that Nissan drivers in Portugal are evidence for option 1. They experienced about 20% battery degradation, they use 20% less energy to recharge the pack as when it was new. They lost 1 bar and about 20% of range. It's important to note that both Mitsubishi and Nissan have the same cells chemistry.

There are some people from the branch of battery technology, claiming that this phenomenon depends on the chemistry of cells. So I made an appointment after the New Year holidays at the local Li'Ion tech "guru" to discuss it and find the truth.