Life after the car: Nissan announces second-life project for LEAF battery packs

Nissan Figures Out a Way To Increase Your Electric Car Range: Treat Charging Like a Pint of Beer

Charging a production electric car these days is relatively easy: you pull up at a charging station, open the charge port hatch, and plug a compatible charging lead into your car. It’s a simple action which takes at worst 20 seconds to accomplish if the charging station is free to use, and not much more if you have to first swipe a payment or authentication card before plugging in. While you’re off doing other things, your car — and its on board computer — charge the battery pack until it hits a predetermined charge level, power or time limit, or the battery pack is full.

You probably don't think about charging all that much -- but it's quite complex.

You probably don’t think about charging all that much — but it’s quite a complex process.

Although the act of plugging your car in to charge is a really simple one, the science behind getting energy from the charging station into your car’s battery pack is the complete opposite. As well as the age of the vehicle and its battery pack — something we’re discovering ourselves with our aged Transport Evolved Toyota RAV4 EV staff car — the chemistry of the battery pack, its temperature, and the capabilities of the charging station are all significant factors. Which is why automakers spend a lot of time researching and developing new charging profiles for their electric cars in an attempt to ensure each battery pack lasts for as long as possible.

Nissan has figured out a way to get more energy stored in a battery: treat it like beer.

Nissan has figured out a way to get more energy stored inside a battery: treat it like beer.

Traditionally, automakers have been particularly cautious about the upper and lower charge limits they set for their electric cars in order to facilitate a long battery life. While a battery pack may have a theoretical capacity or 24 kilowatt-hours, for example, the automaker may use just 19 or 20 kilowatt-hours, sacrificing a bit of storage (and thus range) to ensure long life.

As Automotive news (subscription required) detailed on Monday, Japanese automaker Nissan has figured out how to cram extra electrons into the battery pack of its LEAF electric car without changing the upper and lower capacity limits of its battery management system: treat electric car battery packs a little like a pint of beer.

Or rather, to treat the charging of a nearly-full electric car battery pack the same way as you would a nearly-full pint of beer being filled from a tap.

We’ll explain.

As you charge a lithium-ion battery pack, the current flowing through the battery from the charger gives ions at the positive side of the battery enough energy to move to the negative side of the battery, where they stay until discharging takes place. Then the ions make the opposite journey back to the positive electrode, giving up their gained energy in the process and producing an electrical current.

For the charge to be stored however, there need to be tiny microscopic free ‘slots’ at the negative electrode. When the battery is reasonably empty, there are plenty of spaces on the negative electrode for those free energy-filled ions to attach themselves to. Thus, it’s possible to charge at a reasonably high current, moving lots of ions across to the negative electrode rapidly. When the battery nears full, and all of those spaces are taken up, the ions already at the negative electrode push back on any new ions trying to occupy the same space, heating up the battery and making it harder for other ions to pile on. The more ions there are trying to pile onto an already crowded electrode at the same time, the harder the push-back (resistance) becomes.

These micro-charging sessions help squeeze every last ion onto the negative electrode.

These micro-charging sessions help squeeze every last ion onto the negative electrode.

Like a beer glass being filled quickly from the tap and half-full of bubbles, the battery gives the impression of being full even if it there’s still space on the electrode for some extra ions.

Just as a good barkeeper waits for the bubbles to subside before topping off the pint glass, Nissan’s engineers decided to see if giving a nearly-full battery a short break during the final few percent of charging would allow it to encourage more ions to make their way onto the negative electrode. It set up three short micro charges spaced five-minutes apart at the end of the charging cycle, alternating brief low-current charging with short breaks.

Those rest periods — where the battery’s voltage will naturally sag slightly as a small amount of self-discharge and ion realignment happens — makes it easier for fresh ions to find a place on the electrode.

As Nissan explained to journalists earlier this week, its new charging profile allows Nissan’s engineers to squeeze and additional 0.7 percent extra energy into the battery pack without changing cell chemistry or capacity. More stored energy translates to longer range. And while it’s not exactly a huge amount — just 0.75 miles — it all counts, especially on limited-range electric cars like the Nissan LEAF.

At this point we should probably note that Nissan isn’t doing anything particularly new: we’ve seen battery experts advocate just the same kind of behavior over the years with certain types of battery chemistries — but it’s good to see the automaker work hard to squeeze every extra kilowatt-hour out of a battery that it can.

Should you try something similar yourself? It’s probably not a great idea: Nissan’s new charging behavior will be carefully controlled by its battery management system. Trying to replicate it without the proper equipment is likely to do more harm than good.


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  • The beer analogy is a good one, but lost on the vast majority of readers in the US. Ever notice they never try and really fill the glass over here? Nor is it expected by the beer drinking public.

    • Well, there’s a lot of beer consumed directly out of a can around these parts, so….

      • Ha ha .Thanks for reminding me that a glass is more of an oddity 🙂

  • KIMS

    I’m feeling surprised at this, because this is exactly why normal chargers worth their salt since “forever” will switch to trickle/float/maintenance charge at or near the completion of the charge. I’m actually upset that this type of charging hasn’t been standard in ALL the electric cars and car chargers to date?! -This reeks of “lets make them pay for incremental changes that we already have ready to go so that we can maximize profit over time and release ‘new’ things that we’ve had ready on the shelf for years.”

    Anyway, my rant aside, hopefully they will upload these new charging profiles to existing cars free of charge as that is all it is (or all it should be): a change to the onboard charging profile. Failing that, I wonder if unplugging for 5 minutes, then re-plugging a few times would net the same/similar effect? What about the Leaf operator option to charge to (closer to) 100%? Perhaps charge to normal (80%), then rest, then ask car to charge to 100%, but manually (via app or physically at car) stop after a short burst, wait 5 minutes etc. Might be a manual way of doing essentially the same thing..though the batter management may not accurately track or notice this extra capacity.

    • Your passion for the possibility of one extra mile of range is perplexing. I bought my Smart ED knowing it covered my daily driving needs even if the battery pack degraded over time, and even if the manufacturer never improved the car I own with new firmware/hardware/etc. Nissan doesn’t owe you anything more than what you bought, and it might be worthwhile checking your outrage at the door. Then again, we also own a Tesla that has gotten better ever single over the air upgrade since purchase, but that too was factored into our buying decision.

      • KIMS

        If I came across as entitled or used too strong of a language, well, don’t know what to tell you. As an engineer and a consumer, perhaps my expectations is different from other people? -To me, as an electronics and mechanical engineer in particular, my mind is blown that such charging features (that are standard on all but the cheapest battery chargers for home use) was not already implemented. It’s not about the extra miles, its about what amounts to what appears to be a deliberate decision to make a product less than it could be for no apparent reason as a profile change (especially if known since before production) is as close to a zero-cost improvement as you can get.

        On the other hand, I recognize I don’t have all the facts either. Perhaps they already DO the industry standard trickle-charge to top off, and this new research found a way to improve on that by changing the trickle behavior in certain ways.

        At the end of the day, don’t shoot me for expecting ethical and moral behavior from large companies.. you can call me naive for that, but why should I lower my standards just because real world companies often fall short of them?

  • This story seems to have leaked a bit pre-April 1st. 😉

    If there was really a practical benefit to micro-charging sessions near 100% state of charge; Nissan would have designed it into the charging firmware.

    The same effect in range (+/- 1-3%) could be achieved by driving a couple miles slower, or a bit less aggressive driving style.

    An alternative method to gain 0-1 kWh in range capacity would be to strap 1-2 solar panels to the roof of a PEV … this can add 250-600 W per hour … 1-4 kWh of range capacity per day. Just saying … 🙂

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