I have found quite a bit of comment about how temperature and state-of-charge (SOC) can affect Lithium-ion battery life. This, together with official Nissan comments that they are avoiding markets like Phoenix for now, suggests to me that prospective Leaf owners need to be aware of these issues when planning how they will drive, park, and charge their vehicles.
For example, parking your car at work all day in an unshaded parking lot might not be advisable in the summer in southern California, because temperatures above 40 degrees C (104 F) can seriously degrade Li-ion battery life. My home garage also gets quite hot during summer afternoons (> 90 F), so I am looking into improving its ventilation.
Apparently the temperature effect can be mitigated by controlling the SOC. A battery at full charge is most vulnerable to hot temperatures, while a battery at 40-60% SOC is least vulnerable. In other words, if you are planning to park in the Sun for part of the day, make sure your charge at that point is no more than 60-70%.
Similarly, if you are going to leave the car parked for more than a day or two, leave its charge at 40-50% until the night before you resume driving.
These references also state that repeated discharges below 20% SOC degrade battery life. This suggests that the best strategy would be to charge your car each night to a level that will leave about 20% when you arrive home the following night after that day's driving.
While Li batteries have no memory effect, their lifetime is affected by the number of charge/discharge cycles. Most sources say a lifetime of 1000 cycles is pretty good, but Nissan may think it can get more from their design. Charging (4 times/week * 50 weeks = 200 cycles/year) * 5 years = 1000 cycles. Perhaps it is best to skip charging some nights of the week if you can. While Nissan has recently announced an 8-yr warranty in response to the Chevy Volt warranty, circumstances suggest that this decision was based more on marketing than engineering judgement.
All this suggests that an occasional trip at up to 90 miles without a charge along the way is OK, but doing this every workday could reduce your batter life by a year or two.
Nissan is using a newer version of Lithium-ion, LiMn2O4, than the older Lithium-cobalt. Lithium-Manganese batteries are safer, and do tolerate higher-temperature operation as shown in this reference table:
http://powerelectronics.com/portable_power_management/battery_charger_ics/804li-ion-battery-life-Table01.jpg
As discussed in another thread, Musk, the Tesla CEO, has criticized the Leaf battery pack for having a "primitive" cooling strategy. Presumably Nissan feels their better battery chemistry makes this simplification feasible. Does anyone have better information as to how much temperature tolerance the LiMn gives ?
If this has already been discussed in another thread, please redirect me.
From Wikipedia (Lithium-ion battery):
A unit that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively.[35][citation needed]
http://www.batteryuniversity.com/parttwo-34.htm
For example, parking your car at work all day in an unshaded parking lot might not be advisable in the summer in southern California, because temperatures above 40 degrees C (104 F) can seriously degrade Li-ion battery life. My home garage also gets quite hot during summer afternoons (> 90 F), so I am looking into improving its ventilation.
Apparently the temperature effect can be mitigated by controlling the SOC. A battery at full charge is most vulnerable to hot temperatures, while a battery at 40-60% SOC is least vulnerable. In other words, if you are planning to park in the Sun for part of the day, make sure your charge at that point is no more than 60-70%.
Similarly, if you are going to leave the car parked for more than a day or two, leave its charge at 40-50% until the night before you resume driving.
These references also state that repeated discharges below 20% SOC degrade battery life. This suggests that the best strategy would be to charge your car each night to a level that will leave about 20% when you arrive home the following night after that day's driving.
While Li batteries have no memory effect, their lifetime is affected by the number of charge/discharge cycles. Most sources say a lifetime of 1000 cycles is pretty good, but Nissan may think it can get more from their design. Charging (4 times/week * 50 weeks = 200 cycles/year) * 5 years = 1000 cycles. Perhaps it is best to skip charging some nights of the week if you can. While Nissan has recently announced an 8-yr warranty in response to the Chevy Volt warranty, circumstances suggest that this decision was based more on marketing than engineering judgement.
All this suggests that an occasional trip at up to 90 miles without a charge along the way is OK, but doing this every workday could reduce your batter life by a year or two.
Nissan is using a newer version of Lithium-ion, LiMn2O4, than the older Lithium-cobalt. Lithium-Manganese batteries are safer, and do tolerate higher-temperature operation as shown in this reference table:
http://powerelectronics.com/portable_power_management/battery_charger_ics/804li-ion-battery-life-Table01.jpg
As discussed in another thread, Musk, the Tesla CEO, has criticized the Leaf battery pack for having a "primitive" cooling strategy. Presumably Nissan feels their better battery chemistry makes this simplification feasible. Does anyone have better information as to how much temperature tolerance the LiMn gives ?
If this has already been discussed in another thread, please redirect me.
From Wikipedia (Lithium-ion battery):
A unit that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively.[35][citation needed]
http://www.batteryuniversity.com/parttwo-34.htm
His comment wasn't about the Leaf specifically, but about EV promises in general. There have been more promises than deliveries across the EV spectrum as I'm sure you'll agree.
