2017 Chevrolet Volt

2017 Chevrolet Volt

A research team at Carnegie Mellon University (CMU) has pubished an interesting article concerning battery degradation in PHEVs - "Plug-in hybrid electric vehicle LiFePO4 battery life implications of thermal management, driving conditions, and regional climate."

According to the highlights, there are durability disproportions between various scenarios that are fairly large.

For example without battery cooling, aggressive driving can cut battery life (to 80% of initial capacity) by 2/3rds in hot regions.

In general, batteries should last 73–94% longer in mild-weather regions than hot regions, while air cooling can increase life by a factor of 1.5 to 6 - a huge range to be sure.

There is also important factor of battery size/total capacity, as smaller batteries often use more of their capacity to provide all-electric driving, thus reducing their usable lifespan more quickly (fractional discharges produce less strain on the cells).

"Battery degradation strongly depends on temperature, and many plug-in electric vehicle applications employ thermal management strategies to extend battery life. The effectiveness of thermal management depends on the design of the thermal management system as well as the battery chemistry, cell and pack design, vehicle system characteristics, and operating conditions.

We model a plug-in hybrid electric vehicle with an air-cooled battery pack composed of cylindrical LiFePO4/graphite cells and simulate the effect of thermal management, driving conditions, regional climate, and vehicle system design on battery life.

We estimate that in the absence of thermal management, aggressive driving can cut battery life by two thirds; a blended gas/electric-operation control strategy can quadruple battery life relative to an all-electric control strategy; larger battery packs can extend life by an order of magnitude relative to small packs used for all-electric operation; and batteries last 73–94% longer in mild-weather San Francisco than in hot Phoenix. Air cooling can increase battery life by a factor of 1.5–6, depending on regional climate and driving patterns. End of life criteria has a substantial effect on battery life estimates."

Effect of air cooling on capacity fade and battery life when annual miles driven are 14,700 miles. The battery industry traditionally defines end-of-life (EOL) as the point where the battery’s energy storage capacity drops by 20% of its initial value—indicated by the solid horizontal black line on the first two charts. (a) Capacity Fade in Phoenix, comparison of air cooling vs no cooling for two drive cycles. (b) Capacity Fade in Phoenix and San Francisco, using GPS data. The comparison of air-cooling vs. no cooling is provided for two cities (c) Improvement in battery life by air-cooling for different cases simulated. Credit: ACS, Yuksel et al. source: Journal of Power Sources via Green Car Congress

Effect of air cooling on capacity fade and battery life when annual miles driven are 14,700 miles. The battery industry traditionally defines end-of-life (EOL) as the point where the battery’s energy storage capacity drops by 20% of its initial value—indicated by the solid horizontal black line on the first two charts. (a) Capacity Fade in Phoenix, comparison of air cooling vs no cooling for two drive cycles. (b) Capacity Fade in Phoenix and San Francisco, using GPS data. The comparison of air-cooling vs. no cooling is provided for two cities (c) Improvement in battery life by air-cooling for different cases simulated. Credit: ACS, Yuksel et al. source: Journal of Power Sources via Green Car Congress

source: Journal of Power Sources via Green Car Congress