Analysis of 1382 measures of battery State of Health (SoH) from 283 Nissan LEAFS has detected a faster rate of decline for 30 kWh variants than for the original 24-kWh LEAFs.
That's the big takeaway from a recently reported study.
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Of course, there's more to it than just that though. The study states:
"At two years of age, the mean rate of decline of SoH of 30 kWh Leafs was 9.9% per annum (95% uncertainty interval of 8.7% to 11.1%; n = 82). This was around three times the rate of decline of 24 kWh Leafs which at two years averaged 3.1% per annum (95% uncertainty interval of 2.9% to 3.3%; n = 201)."
On the upside, findings suggest that high use of DC fast charging had little impact on battery SoH.
The study concludes by suggesting that the rate of decline in the 24-kWh version of the LEAF is acceptable, but suggests that the 30-kWh pack declines too rapidly to be considered within normal parameters.
The abstract from the work titled "Accelerated Reported Battery Capacity Loss in 30 kWh Variants of the Nissan Leaf" states:
Analysis of 1382 measures of battery State of Health (SoH) from 283 Nissan Leafs (“Leaf/s”), manufactured between 2011 and 2017, has detected a faster rate of decline in this measure of energy-holding capacity for 30 kWh variants.
At two years of age, the mean rate of decline of SoH of 30 kWh Leafs was 9.9% per annum (95% uncertainty interval of 8.7% to 11.1%; n = 82). This was around three times the rate of decline of 24 kWh Leafs which at two years averaged 3.1% per annum (95% uncertainty interval of 2.9% to 3.3%; n = 201).
For both variants there was evidence for an increasing rate of decline as they aged, although this was much more pronounced in the 30 kWh Leafs. Higher use of rapid DC charging was associated with a small decrease in SoH. Additionally, while 24 kWh cars with greater distances travelled showed a higher SoH, in 30 kWh cars there was a reduction in SoH observed in cars that had travelled further.
The 30 kWh Leafs sourced from United Kingdom showed slower initial decline than those from Japan, but the rate of decline was similar at two years of age.
Improvements in the battery health diagnostics, continuous monitoring of battery temperatures and state of charge, and verification of a fundamental model of battery health are needed before causes and remedies for the observed decline can be pinpointed.
If the high rate of decline in battery capacity that we observed in the first 2.3 years of a 30 kWh Leaf’s lifetime were to continue, the financial and environmental benefits of this model may be significantly eroded. Despite 30 kWh Leafs accounting for only 14% of all light battery electric vehicles registered for use on New Zealand roads at the end of February 2018, there is also the potential for the relatively poor performance of this specific model to undermine electric vehicle uptake more generally unless remedies can be found.
Myall, D.; Ivanov, D.; Larason, W.; Nixon, M.; Moller, H. Accelerated Reported Battery Capacity Loss in 30 kWh Variants of the Nissan Leaf. Preprints 2018, 2018030122 (doi: 10.20944/preprints201803.0122.v1)
Let's hope Nissan has rectified this with the new 40-kWh LEAF and then soon the 60-kWh version.
There's a wealth of meaningful discussion on the findings presented in this study at the source link below. You'll find a full PDF version of the study there too.