Tesla Model 3 LFP batteries degrade faster at 100% charge but not enough to really matter

The lithium iron phosphate (LFP) battery chemistry has been a godsend for both the energy storage and electric vehicle industries.

Due to the relative abundance of iron phosphate, LFP cells are much cheaper to produce compared to nickel batteries. Not only that, but they can be charged to 100% more often with less capacity degradation over time.

Tesla even advises charging its vehicles with LFP batteries like the RWD Model 3 and Model Y to 100% at least once a week for properrange estimatecalibration. At one of Tesla's quarterly calls, Elon Musk summed up the presumed charging advantage of LFP batteries very well:

The main differences for you to consider are that the LFP battery has a slightly shorter range, 253 miles, as opposed to the NCA battery, 263 miles. But that slight difference in range is deceptive. The NCA battery probably shouldn't be charged to 100%. Fully charging the battery causes damage to the battery making it likely to deteriorate over the years of ownership. It's perfectly fine to charge the LFP battery to 100% so the driver experience is pretty much the same except for a couple caveats.

A recent study, however, disputes this assumption. "The Operation Window of Lithium Iron Phosphate Cells Affects their Lifetime" university research paper found out that LFP batteries degrade faster at higher states of charge (SoC), just like nickel batteries in long-range or performance electric cars.

The battery scientists put several charging windows to the test, namely the 0%–25%, 0%–60%, 0%–80%, 0%–100%, and 75%–100% ranges at two ambient temperature points.

It comes as a little surprise that charging an LFP battery in hotter weather degrades it faster, but the researchers also found that frequent full charges do the same, contrary to Tesla's advice.

In the best scenario of 0%-25% charge at the lower temperature point, some LFP cells lost just 3% capacity over what would be the realistic equivalent of 10 years of EV charging. In the worst possible circumstance of constant 75%-100% top-up and discharge cycles at the higher ambient temperature, some cells lost 24% capacity. On average, however, the cells degraded less than 10% even in the most tasking scenario.

Moreover, both of the extreme SoC ranges are rather unrealistic, and the study conclusion points out that "cells cycled in the conventional 0%–100% SOC window showed capacity fade rates intermediate to 0%–25% and 75%–100%."

Thus, even if an owner charges their Tesla Model 3 with LFP battery to 100% all the time over the course of a decade, the battery capacity degradation attributed to the state of charge metric would be rather negligible.

In reality, people are clocking hundreds of thousands of miles on their EVs, and calendar aging seems to be the only reliable determinant of a battery capacity loss, with frequent full charges a blip on the battery longevity radar.

Tesla's LFP battery supplier CATL now even has million-mile cells with a 15-year warranty before they degrade to 85% capacity, so Elon Musk's claim that LFP batteries can be charged to 100% still holds water.

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