Charge limit to 80% vs 90%. Will 90% significantly degard battery capacity?

[Zoomit]

Something else to consider is that pack degradation as a function of state of charge (SoC) tends to show up much later in life.

There will likely be minimal differences in capacity/lifespan between a battery charged to 60% and a battery charged to 90% up until there isn't, at which point the pack charged to a higher SoC will degrade significantly and the pack charged to a lower SoC will continue to see modest degradation for a longer period of time.

https://www.nrel.gov/docs/fy13osti/58550.pdf (page 7)

At this point where don't know where that difference is. Odds are it's north of 200k miles like it is with the S/X, but we don't have enough data yet to say for certain.

Thanks for the link to that presentation.

The degradation data shown isn't about the upper limit for the charge, but rather depth of discharge (DoD). It indicates that a deep DoD is worse than a shallow DoD. It doesn't say anything about a difference in degradation due to routine charging between, for example, 60 and 90% verses 50 and 80%, both of which have a 30% delta DoD.

 

[omgwtfbyobbq]

Thanks for the link to that presentation.

The degradation data shown isn't about the upper limit for the charge, but rather depth of discharge (DoD). It indicates that a deep DoD is worse than a shallow DoD. It doesn't say anything about a difference in degradation due to routine charging between, for example, 60 and 90% verses 50 and 80%, both of which have a 30% delta DoD.

Doh! It should have been this pdf. All things being equal, larger SOCs are harder on batteries, but SOC(average) tends to be more detrimental, to the point where losses from it can be much greater than losses from larger SOCs. (page 8)

https://www.nrel.gov/docs/fy16osti/66708.pdf

 

[Zoomit]

Doh! It should have been this pdf. All things being equal, larger SOCs are harder on batteries, but SOC(average) tends to be more detrimental, to the point where losses from it can be much greater than losses from larger SOCs. (page 8)

https://www.nrel.gov/docs/fy16osti/66708.pdf

Interesting slide.

I agree with the conclusion, but I don't like how they presented the data. The 90%DOD battery is putting out 3x the energy on each day. So 10 years at 30% DOD is equivalent to 3.3 years at 90% DOD in terms of energy output. Here the 30% DOD NCA battery degrades to about 0.79 relative capacity at 10 years, whereas the 90% DOD NCA battery only degrades to 0.92 relatively capacity at 3.3 years.

So with the chemistry modeled, a battery experiencing 10-100% charge cycles has less than half the degradation of a battery doing 3x more 70-100% cycles. I would love to see how Tesla's various formulations compare to these models, but acknowledge the trend is the same across the five Li-ion technologies they plotted.

 

[omgwtfbyobbq]

Interesting slide.

I agree with the conclusion, but I don't like how they presented the data. The 90%DOD battery is putting out 3x the energy on each day. So 10 years at 30% DOD is equivalent to 3.3 years at 90% DOD in terms of energy output. Here the 30% DOD NCA battery degrades to about 0.79 relative capacity at 10 years, whereas the 90% DOD NCA battery only degrades to 0.92 relatively capacity at 3.3 years.

So with the chemistry modeled, a battery experiencing 10-100% charge cycles has less than half the degradation of a battery doing 3x more 70-100% cycles. I would love to see how Tesla's various formulations compare to these models, but acknowledge the trend is the same across the five Li-ion technologies they plotted.

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Where does it say the 100-70% cycles are done 3x more than the 100-10%? I think both had a 2 hour charge, a 10 hour rest, a 2 hour discharge, and another 10 hour rest, and the higher SOC(average) is what's really hurting capacity of the 100-70% category (at 28C).

 

[Zoomit]

Where does it say the 100-70% cycles are done 3x more than the 100-10%? I think both had a 2 hour charge, a 10 hour rest, a 2 hour discharge, and another 10 hour rest, and the higher SOC(average) is what's really hurting capacity of the 100-70% category (at 28C).

Sorry I wasn't clear. I agree with the conclusion that this data shows the higher average SOC yields more degradation.

I take issue with the plots because it underplays this effect, because it focuses on the calendar aging instead of the energy usage aging. The 24-hr cycle for 90% DOD case discharges and recharges 3x the energy of the 30% DOC case. Said another way, the 90% DOD battery is discharging 3x the energy over the 10 years. Basically, I would rather the x-axis be discharge energy instead of time to make a more equal comparison of battery degradation.