Like humans, lithium-ion battery packs operate best in temperate climates, where it’s not too hot or too cold. Essentially, they like to be about the same temperature as us for peak energy efficiency, which is why many electric car manufacturers install liquid cooling and heating systems inside their cars’ battery packs to make it easy to heat or cool the pack as required to keep them healthy and happy.
From the time its all-electric LEAF hatchback launched in 2010, Japanese automaker Nissan has maintained that it hasn’t needed to use any form of active liquid thermal management system for its battery packs, opting instead for passive forced-ventilation air cooling from driving the car along in hot weather and simple battery heating pads for extreme cold.
But at yesterday’s international launch event for the Nissan e-NV200 electric van — a vehicle which shares the same 24 kilowatt-hour lithium-ion battery pack and 80 kilowatt electric motor found in the Nissan LEAF — we noticed something rather interesting which makes us think Nissan might be rethinking its policy on battery heating and cooling.
The e-NV200, unlike the Nissan LEAF, has a small air conditioner built into its battery pack.
Although Nissan mentions the fact the e-NV200 has an active battery cooling and heating system in its press release accompanying the e-NV200 launch, it wasn’t until we examined the battery pack more closely in a cut-away model on display that we understood how it worked.
Despite using the same capacity battery pack and identical battery cells to the LEAF, the e-NV200’s battery pack is more tightly packed together under the floor of the e-NV200 than it is in the LEAF.
As with the LEAF, cells are stacked, one on top of another, in an under-floor, sealed battery box — but at the front of the battery compartment just ahead of the first row of cells is a small radiator and large electric fan. And entering the battery pack from the front is a coolant feed from the van’s air conditioning system.
How it works
Nissan wouldn’t go into too many details with us, but it looks as if the e-NV200 can send warm or cold coolant from the van’s main HVAC system to the small integral radiator within the battery box. Air is then drawn through the radiator fins and is then cooled or heated as needed to keep the battery pack and battery box at optimum temperature.
It’s important to note here that unlike some battery packs with liquid thermal battery management, the e-NV200 doesn’t have pipes running in between inside the battery pack. Since the battery itself is sealed in one large battery box, the radiator at the front serves a similar function to the heater matrix inside the van’s cabin: keep everything inside that closed space at a pre-determined, set temperature.
Why is it needed?
Nissan says the addition of the internal radiator is to keep the battery pack’s temperature at optimum operating conditions, since the more tightly-packed battery pack of the e-NV200 has less space for air to circulate around the cells and therefore is more prone to changes in heat than the LEAF battery pack.
There’s also some allusion from Nissan that it expects the e-NV200 to be treated far more roughly than any of its LEAFs would be. As well as the obvious misuse from the hands of delivery drivers or high-milage fleet life, Nissan engineers told us they wanted the e-NV200 to cope with frequent rapid charges in a single day without damaging battery life.
But there’s also the simple fact that with its much larger surface area, heavier weight and 770 kg cargo capabilities, the e-NV200 can’t travel as far per kilowatt-hour as the LEAF. Although NEDC range is set at 170 kilometers, our expectation is a real-world achievable range of 60-70 miles when empty and perhaps less when fully laden. In that situation, the battery packs need to be at optimum temperature to give the best possible range.
What about the LEAF?
When it came to market in late 2010, many criticised Nissan’s all-electric LEAF electric hatchback for not having any form of active battery cooling or heating system fitted as standard. Unlike cars like the contemporaneous Mini E, Tesla Roadster and Chevrolet Volt — all of which used active liquid thermal management to keep their battery packs operating at optimum temperature — the Nissan LEAF simply came with passive, forced-air ventilation.
At the time and even today, Nissan maintains that the LEAF’s battery pack doesn’t need any form of active cooling or heating system to keep its battery pack healthy. To date the only concession Nissan has made to LEAF battery temperatures is to include a cold weather package with simple heating elements to keep the battery pack above -15 degrees Celsius in cold weather environments.
For LEAF owners in ultra-hot climates like Arizona however, a lack of battery cooling in the LEAF has lead to some pretty shocking premature ageing, rapidly decreasing battery pack capacity due to prolonged 50+ degree Celsius temperatures. And while all Nissan electric vehicles come with a battery warranty that covers the effects of premature battery ageing due to extreme heat, Nissan’s experiences in Arizona has led it to develop a more temperature-resistant battery chemistry, a chemistry which Nissan is readying for production later this year.
No one we spoke to at Nissan would confirm or deny the possibility that Nissan is considering active battery cooling or heating for future electric vehicles, nor could we get any indication of the feature making its way into the next generation LEAF, a car we’re expecting to debut some time in 2016/17.
But after seeing first hand how our own LEAF’s battery packs like to heat up in hot weather when rapid charging — not to mention seeing how little the e-NV200 vans appeared bothered about the hot Spanish sun yesterday — we can’t help but think Nissan is about to make a u-turn on its battery cooling policy.
We’re not engineers of course — nor can we tell for sure — but given how alike the LEAF and e-NV200 are, we think it’s highly probable.
What do you think? Leave your thoughts in the Comments below — and we’ll share with you our first impressions of the all-electric e-NV200 van in the coming days.
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