Electric vehicle batteries charging in two minutes... or not15 Oct 2014
I think it’s great that the gradual rise of electric vehicles (EVs), among other things, means that battery research can get good press, sometimes finding itself in the headlines for the science sections of major news websites. Though I’m always left a little disappointed when the context is inevitably warped and completely fanciful and unrealistic claims become the centrepiece of the article. I get it – you have to spin it to capture the imagination of the reader. But I do worry that continuous hype and over-the-top claims of super performance will ultimately sow distrust towards (and within) the field.
Yes, you can point the finger at journalists asking loaded questions, quoting out of context or applying their own amateur interpretations on the results, but when you give them the ammunition…
"With our nanotechnology, electric cars would be able to increase their range dramatically with just five minutes of charging, which is on par with the time needed to pump petrol for current cars”, said Chen Xiaodong, an associate professor at NTU Singapore, in a press release."
It reminded me a bit of a similar-ish press release from MIT five years ago which ultimately became news articles on the front page of BBC News, for example, claiming that lithium iron phosphate-based batteries could be charged in a matter of seconds, which would pave the way for “lifestyle changes”. The coverage and the journal article that went with it caused something of a row in the battery community (which naturally never made the news) and drew some strongly worded comments and counter-comments in the scientific literature (and at conferences!).
This time, the nanotechnology in question is a new synthetic route for long nanotubes of titanium dioxide as an anode material (paper here). The paper itself is somewhat interesting and, in fairness, makes none of the bold claims of the news articles – but it is a long, long way from enabling the next generation of EV batteries to charge in just a few minutes. Not least for one of the reasons argued five years ago:
“180 kW is needed to charge a 15 kWh battery in 5 min […] the internal resistance of the battery will be of the order of R = 1/4 Ω so that the power dissipated by the Joule effect is RI2 ~ 200 kW, so that the energy lost to Joule effect heating after t = 5 min […] is RI2t = 60 x 106 J. Unfortunately, this is typically what you need to heat a four-story building!”
In other words, it is most likely not feasible or safe to fast charge a battery of that scale even if one can make materials that can store charge at that rate. And not just that…
“it’s not clear that new batteries have a longer charge life, or what is known as gravimetric energy density (the amount of energy stored per unit mass)”
That using titanium dioxide automatically means a cell voltage about ~1.5 V less than for cells using the more conventional graphite or promising high-energy alternative silicon anodes and, in turn, necessarily means a much lower energy density – which is a big problem in terms of driving range.
Not to be too negative about this research though – a smaller, highly rate-capable battery could be very useful for hybrid applications, for example. But full battery-powered EVs that can be charged in minutes are not around the corner, no no…