Here's the paper I'd like to share and discuss: https://www.researchgate.net/publicatio ... _Batteries
. I stumbled upon it while researching the best current to charge my car at to promote the battery's longevity, that's upon purchase of OpenEVSE charger recently. Sorry if it's been covered before.
The results appeared quite surprising and counterintuitive to me, to summarize, they considered three major battery degradation drivers:
charging cycles wear (driving related), and
charge current related aging
they used three temperature levels for the analysis (battery temperature, not ambient one) - 40C, 25C and 5C (104F, 77F, 50F).
To analyze (2)
they used three cycling patterns all with depth of discharge at 25% - up to 50% (low), to 75% (medium) and up to 100% (high) of SOC. No wonder the lowest degradation level was achieved at the low SOC cycling with the temperature effect quite predictable - the higher the temperature - the faster the degradation. What is surprising, the medium and high SOC cycles show significantly higher degradation at lower battery temperature, and this is especially pronounced for high SOC cycling. So, if we charge to 75% and beyond, degradation of the battery will be faster when its temperature is 10C than in case of high 40C temperature. 25С temperature seems to be the sweet spot, providing for the least degradation at any SOC cycling except for the low SOC where it's on par with 10C temperature level.
Considering this, I think that small batteries (like in my i3
) stand no chance in cold climates (like in Ukraine
). They are forced to be charged to 100% every day just to deliver the needed range in most cases, and that's exactly the best way to destroy the battery as fast as possible.
, the results were no less unexpected, from my perspective. Overall, EV storage at high temperature is positively correlated with faster degradation at all times, but, judging by the chart they provide, in case of 25C and 10C battery temperature, the battery capacity decrease seems to peak at 60% SOC and then slightly decrease up to and including 100% SOC. Also, it looks like the lower SOC (and voltage) the battery is stored at, the better it is for its long term health. These results contradict the otherwise well established common wisdom on li-ion battery storage. And this is both true for all manufacturers out there except BMW (store at medium level SOC) and BMW (always be charging - store at 100%).
they say that it's best to avoid lithium metal plating of the anode's surface, because this results in effectively quick death of the battery - accelerated degradation ( (usually occuring at 80% SOH and below). Such plating is driven by high current charging under low battery temperature. They tried charging the cells at 1C, 0.5C and 0.2C rate for a period of 18 months. In case of 1C charging rate the battery dies inevitably, the process is launched immediately. The lower 0.5C charging rate delays the plating development up until about 550-570 cycles, after which we observe accelerated degradation as well, similarly to the 1C test. And the lowest 0.2C rate doesn't seem to trigger any additional degradation aside from normal calendar and charge cycle aging of (1)
, at least for the experiment duration.