Back at the start of Autumn, after a summer full of rumors and speculation, Nissan confirmed that its 2016 Nissan LEAF electric car would be offered with a choice of two different battery packs: a 24 kilowatt-hour, next-generation pack offering the same range but improved longevity over previous model-year LEAFs; and a longer-range 30 kWh next-generation pack capable of an EPA-approved 107 miles per charge.
While there was no official U.S. launch event for the longer-range 2016 LEAF, we were able to get to the European launch event, where Nissan told us that the next-generation, higher-capacity cell technology and reduced internal resistance within the new 30 kWh battery meant that CHAdeMO DC quick charging would result in a higher charge rate for longer.
Now we’ve got data to back that up, courtesy of our friends at the FastNed charging network in the Netherlands, who took their recently-obtained 30 kWH 2016 Nissan LEAF to a FastNed rapid charging station in order to see just how much faster the 30 kWh LEAF was to refill.
The charging provider tweeted about its experiences a few weeks ago — and we’ve been in contact with the company to find out a little more.
How much faster does the 30 kWh LEAF charge compared to the 24 kWh LEAF? As the image on the right shows, a fair bit.
“We drove a brand new Nissan LEAF with 30 kWh battery from Amsterdam to our station [in] Lageveen, which is a 153 km (95.07 miles) drive,” said Roland van der Put, Networks Operations Manager for FastNed, in an email to Transport Evolved last week. “There was only 7 km (4.35 miles) on the odometer when we started. We arrived (almost) empty and charged to 90 percent in just 33 minutes. This was one of the fastest fast charge sessions we have seen.”
Why the difference? It’s all down to internal cell resistance and the way in which batteries accept charge. When a battery is nearly empty, its internal cell resistance is reasonably low, meaning it’s easy for electrical energy to pass through the battery and be converted through electrochemical reactions into stored chemical energy. As the battery’s state of charge increases (or the amount of energy stored within it as chemical energy increases) the cell’s internal resistance rises. And that means it’s harder for electrical energy to pass into the battery and be converted into chemical energy.
As the internal resistance increases, the process of transferring energy from electrical to chemical energy becomes more inefficient as more of the electrical current being fed into the battery is lost as heat. Apply too much current at this point, and the battery overheats, causing irreversible damage to the cell structure and reducing the amount of energy the battery can ultimately store.
If you’d prefer, you can also think about a battery like an empty metro train in the morning rush hour. As it starts its journey with few passengers on the train, it’s easy at first for passengers to jump on at the nearest door and find a space to sit in the car of their choice. As the cars fill up along the line however, it becomes harder and harder for passengers to get on the train. People shove, tempers rise, and the temperature goes up.
Regardless of which analogy you prefer however, the internal cell resistance and increased capacity in the new 30 kWh Nissan LEAF battery pack means that 2016 Nissan LEAFs fitted with the larger pack can charge at 50 kilowatts (maximum power) for longer before the car is forced to turn down the CHAdeMO power.
In the graph above, captured by FastNed during testing, you’ll note that the charging station delivers a full 50 kilowatts of power for the best part of twenty-eight minutes before it ramps down the current as the battery nears full.
In an earlier Nissan LEAF with previous-generation battery technology in it, the car would use the full 50 kilowatts available from the charging station for the first fifteen minutes or so, ramping down power shortly afterwards to protect the battery pack.
At this point we should note a couple of important things governing the speed at which a Nissan LEAF rapid charges using a CHAdeMO DC charging station. Firstly, not all charging stations are capable of providing the 50 kilowatts of power, meaning charging will take longer overall. Also, the age of the battery pack and the temperature of the battery pack come also play a part. With only a handful of miles on the battery pack when it was driven to its first rapid charging station, the 30 kWh LEAF used by FastNed to test charging speed was performing at its optimum. A car with tens of thousands of miles on the odometer would have a battery pack with reduced capacity and increased internal cell resistance, meaning that overall charging times will take longer.
Indeed, as the battery ages, the state of charge at which the car (which controls the charge rate of the external charging station via the CHAdeMO port) reduces the charging current to protect the battery will gradually reduce, resulting in ever-increasing recharge times. According to Nissan however, the effects of battery aging should be less severe with this new chemistry compared to previous battery pack chemistries used by Nissan.
What does this mean? If you’re about to buy a brand-new Nissan LEAF with larger 30 kWh battery pack, you’ll find it charges far more quickly than a comparable 24 kWh LEAF. As time takes its toll on your battery, it will start to take longer to charge than it did when new from a DC CHAdeMO quick charging station, but the effects won’t be anywhere near as marked as they would be for a 24 kWh LEAF.
Our advice then? If you can afford it, opt for the larger 30 kWh LEAF wherever possible.
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