For drivers of petrol or diesel cars – that is most drivers – the notion of a 'splash and dash' rapid refill is part of the convenience of internal combustion. EV drivers, on the other hand, have to either plan and if not at home or the workplace then wait for useful range to be re-added to their cars. But a breakthrough by boffins in the US has found a potential solution to the problem using existing technology.
Scientists from Penn State University have worked out a way to enable EVs to be charged in as little as ten minutes – enough time to buy an insipid coffee and get half way through a service station pasty. The study has shown that not only is ultra-fast charging possible with existing battery tech, charging technology is also already up to the task.
Chao-Yang Wang, Director of the Electrochemical Engine Center at Penn State University, said that not only is this charging breakthrough fast, it's also non-detrimental to the battery itself: “We demonstrated that we can charge an electrical vehicle in ten minutes for a 200 to 300 mile range, and we can do this maintaining 2500 charging cycles, or the equivalent of half a million miles of travel.”
This ability to add a potentially full charge in ten minutes or less is made possible by carefully managing battery temperature during charge and discharge. Degradation of lithium-ion batteries is caused by 'lithium plating', where lithium is deposited onto the anode surface. This is typically seen when batteries are rapidly charged at 10 degrees Celsius or less, and even at ambient temperature.
On the flip-side, battery degradation was also observed when charging for long periods at higher temperatures, according to Wang: “At high temperatures battery active materials will react with the electrolyte to form passive surface films, consuming active lithium as well as causing high resistance.”
To avoid this potential degradation, the scientists found a sweet spot in which batteries are heated up for long enough to rapidly charge them, but not long enough for any damage to be done. They are then rapidly returned to ambient temperature. They found that heating to around 60C (via an internal nickel foil structure) for ten minutes gave the best results, enabling 80 per cent charge to be added in that time.
Admittedly the battery that the Penn State scientists used was small at just ten amp hours, but the good news is the technology is scalable to EVs. As long as the charging input is proportional to battery size, the same ultra-fast charging can be achieved; in the case of an EV battery with 150 amp hours, for example, a charger would need to provide a 900 amp current for ten minutes. This is feasible with existing charger technology.
Unfortunately this isn't technology that will be implemented on EVs in the immediate future. Further development is necessary as energy-dense EV batteries require further development, but Wang is positive that the technology could see commercial roll-out in three years. By this time, the Penn State team hopes to have further reduced the time it takes to charge without damaging EV batteries.
In the wider context this research is yet another reassurance that for now, lithium-ion batteries still have a lot of potential for development. Combined with other developments in component technology, such as those we recently reported on by Bosch and others, the next five years could see huge leaps in the day-to-day viability of EVs.
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