Earlier this fall, after months of rumors suggesting it would do so, Nissan announced it would bring the 2016 LEAF electric car to market with an optional 30 kilowatt-hour battery pack, extending the range of the popular plug-in car from the 84-miles of EPA-approved range of last year’s model to 107 miles per charge.
The new battery pack, more energy dense and thus capable of storing more energy per unit mass than its predecessor, catapulted the Nissan LEAF to the top of the range charts for sub $40,000 electric cars, beating cars like the BMW i3 and Kia Soul EV to the top space.
Now, it seems like BMW could be preparing to follow in Nissan’s tire tracks, with the news from UK magazine Autocar that BMW is readying a new, next-generation battery pack which could extend the range of the i3 to “well over 124 miles” per charge in real-world conditions.
It’s not the first we’ve heard of this particular rumor. Indeed, just last month, German language newspaper Zeit said BMW CEO Harald Krüger had confirmed BMW would extend the range of the i3 electric car upwards from its current 81 miles of EPA-approved range for the 2017 model year. At the time, Krüger didn’t discuss specifics, but talking to Automotive News Europe earlier this year, the BMW CEO had promised the brand would improve the energy density (and thus range) of the BMW i3 electric car and BMW i8 plug-in hybrid sports car battery packs by a minimum of 20 percent every three years.
So far, so good. But while the rumor from Autocar does seem to back up similar rumors we’ve already heard, there’s something in the reporting which has already got some enthusiasts a little confused.
You see, while Autocar reports anonymous sources within the automakers claiming BMW has a brand-new, next-generation battery pack in development, it also reports no change in battery pack capacity — the usual way in which automakers increase electric car range.
“The i3 will receive a new lithium ion battery with the same 22kWh (18.7kWh usable) capacity as that used today but a higher power density for a longer range,” the publication states. But while it uses the term ‘power density,’ we think it means energy density instead.
That’s because power density is the measurement of how much instantaneous power a battery can provide per unit mass (or volume). A battery with a high power density is capable of moving energy into and out of the battery more quickly than a battery with a low power density. Energy density meanwhile is the measurement for how much energy can be stored per unit mass (or unit volume).
Capacity meanwhile, is how much electrical energy a battery is capable of storing, measured in kilowatt-hours. A high energy density battery can store more electrical charge per unit volume than a low energy density battery pack.
Here’s where we think it might get confusing.
In the world of electric cars, we’ve got used to the idea that improvements in battery chemistry mean that automakers automatically increase an electric car battery pack’s range by using a more energy-dense battery cell chemistry in the same physical battery pack space as its predecessor. So far, we’ve seen just that happen with the Nissan LEAF, the Tesla Model S (multiple times) and both the Chevrolet Volt and Chevrolet Spark EV.
In each case, range has been increased slightly, with the higher-capacity battery pack taking up the same physical space inside the vehicle as previous-generation packs.
But battery pack capacity isn’t the only way to increase range. Saving weight can help, too. And if a next-generation battery pack is lighter than its predecessor, it will save energy.
That’s something that BMW knows only too well. Indeed, both the BMW i3 and BMW i8 have class-leading efficiencies, thanks to the use of lightweight carbon-fiber reinforced plastic (CFRP) for body panels and lightweight aluminum chassis replacing traditional steel ones. Thanks to the wonderful laws of physics, the less weight there is to push down the road, the less energy you need to move it.
Which brings us nicely to our theory. While we think the Autocar report may have confused the terms power density and energy density, we certainly wouldn’t be surprised to see the BMW i3 gain extra range from a more energy-dense, more lightweight pack. Given BMW’s focus on efficiency rather than simply building an electric vehicle with zero tailpipe emissions, this rumor (taken in the context above) does make sense.
There are advantages to this method over simply using a larger pack, too. With an identical battery pack capacity but far more energy-efficient drivetrain, BMW ensures running costs stay the same for customers, as well as charging times for standard Level 2 charging. Combine a more energy dense pack with a more power dense pack — in other words a pack which can store more energy per unit volume than its predecessors but also transfer energy more easily than its predecessors — and you have a double-whammy: a battery which offers fast recharge times and low running costs.
While we can’t say for sure that’s what BMW is planning, that explanation fits better than anything else we’ve thought of. Do you agree? Leave your thoughts in the Comments below.
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