University Presents Solution For Fast Charging At Cold Temps

JUL 17 2018 BY DOMENICK YONEY 19

Breakin’ the (Arrhenius) law, breakin’ the law.

Lithium batteries work pretty well at temperatures we humans find pleasant, but when it gets cold, like us, their performance wanes. The drop is basically down to the fact that various chemical reactions within cells follow the Arrhenius law. Now, it appears researchers at Penn State have figured out a way to circumvent this law, allowing fast charging at super cold temperatures.

If you force a lithium-ion battery to fast charge in the cold at what are normal rates for room temperature conditions, you risk “plating” — instead of lithium ions from the cathode parking comfortably within a graphite anode’s structure, they create a traffic jam and permanently block entry into parts of the anode (A more exact description of the interaction can be read here). Plating decreases the amount of energy a cell is able to hold, thus shortening its usable life.

Of course, the obvious solution involves warming the battery before charging, but the approach taken here is a bit more sophisticated. Basically, they’ve added thin nickel foil to the cell which serves double duty as both a sort of internal fast-heating element and a temperature sensor.  In their words:

Two pieces of thin nickel (Ni) foils are inserted into the cell, each located at ¼ cell thickness from cell surfaces. Each Ni foil is coated with thin polyethylene terephthalate for electrical insulation, and sandwiched between 2 single-sided anode layers. One ends of the two Ni foils are welded with tabs of anode layers and connected to the negative terminal; the other ends of the two Ni foils are welded and extend outside to form a third terminal, named activation (ACT) terminal. A switch is added between positive and ACT terminals.

Easy peasy, right? The team found that not only does the new configuration allow cells to be charged to 80 percent in 15 min at −50 °C, it greatly increased the cycle life of cells being charged at 0°C (32°F). Whereas a cell being charged at a medium-high rate of 3.5 C at the freezing point could only do about 50 cycles before losing 20 percent of capacity, the reconfigured cells could do 4,500 cycles, or 90 times.

Source: GreenCarCongress

Image: Nissan/Creative Commons

Categories: Battery Tech, Charging

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19 Comments on "University Presents Solution For Fast Charging At Cold Temps"

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Cool, so 90 times the cycle life at low temperatures. Whats the catch?
Since this functions to heat the cell, will it cause the cell to overheat at room temperature, or worse, on a 110 degree day in Arizona? Also, what about energy density, does the battery retain the same energy density(Wh/kg) as a normal one, or is it less? Power output capability, will the batteries heat up too much under stress of highway driving, or heavy acceleration?
It seems like the article has left a lot of questions un-answered.

There’s a switch that can turn it off if it gets too hot. But I share your concern that this takes up space and correspondingly lower density. Better is to have good TMS that will warm the battery using power from charger.

It should be faster in heating up the cell than an external TMS. Also, in cases where it can be used *instead* of an external TMS, it probably save some space and weight actually.

I think there might be some niche uses where this would be interesting.

You still need TMS for cooling so the extra plate in the cell just for heating is taking up space and not doing anything when cooling is needed. Agree in niche application, but this is not good for general EV solution.

Yes, that’s why I qualified it to cases where TMS is not otherwise needed.

Gotta love these armchair scientists!

“or 90 times boost to life”, as in overall battery life expectancy, from cold weather charging.

The reconfigured cells have an exponentially much better cycle life. This additional Ni foil implementation, hopefully sees the light of day, somewhere down the line, in production cell fabrication and manufacturing.

Hmm. I wonder if this plating phenomenon is what caused my 12 Leaf’s battery to lose 15% of its capacity in 3 years.

Everybody talks about hot-climate Leaf problems, but mine lived in temperate-to-cold Pittsburgh and was Level 2 charged overnight in the garage. Sometimes the garage was barely above freezing, and the 600-lb Leaf battery was certainly not above freezing for many charge cycles after being parked outside all day near 0 F.

If the BMS is any good, it should reduce charging speed to avoid the plating…

And if we’ve learned anything about the Nissan BMS over the years, it’s that it’s nothing if not conservative.

I believe that charging above 80% regularly also affects EV batteries in general, and the Leaf’s in particular, so it might depend on how often you charged over 80%. As well, 15% over 3 years is fairly normal for a Leaf, they’re not great that way.

My 2017 30kwh was showing SOH at 88% after 4 months and 2500km. 🙁

It’s in for the recent battery software update, so we’ll see what it says after I get it back.

I would just take 3.5C charging at any temperature. Makes me wonder the downside, cost, less dense, less capcity?

I’d say they simply used a cell type with a high C-rating to begin with. It’s not like adding a heater would generally increase charging speed at normal temperatures without killing cycle life…

This is good news but I wonder if there are any disimilar metal contact corrosion potential issues. This may also serve as a cold weather version of a propulsion battery pack for an EV.

Sounds useful for EVs without an active TMS — but then again, most people here consider these a very very bad idea anyway… At least for larger batteries. (Two-wheelers generally seem to do fine without active TMS?…)

Two-wheeled EVs are generally not used in sub-freezing temperatures. Obviously there are exceptions, but it’s much less of an issue since they seldom get used in such climates and in such weather.

Good point 🙂

Shouldn’t be, with the Nickel being coated with PTFE. In any case, they probably chose Nickel in part to avoid any electrochemical potential that would cause corrosion.

That’s not breaking the Arrhenius law, just changing conditions to work within its confines… No different in this regard than any old battery heater. It’s just integrated into the cell itself, that’s all.