You are correct it is a form of accelerated life testing, but very
different from traditional testing for Li ion batteries. Almost
unrecognisable in comparison. I spoke with Dahn about setting up a
commercial lab to do this as verification testing. Because they are a
research group, and working for particular customers (Medco for example),
they are interested in tracking more closely the changes. So to gain
detail they did cycle at a very reduced rate. It is not necessary to cycle
however. It just depends on how granular a look at capacity degradation
you want to get. The testing I wanted to do would have reduced the cycle
rate and overall test time to a greater degree. For QA purposes, or
comparison between prospective suppliers, not research and development, for
example, you could possibly do one long cycle, or very few cycles.
The capacity loss does track linearly with cycles (or more properly with
the time spent at higher SOC%), but it is not linear with respect to
temperature, and C rate (related to temperature). Bottom line: It is not
the number of test cycles that is important.
I think you could predict performance given a particular operating routine
(or non-routine) without being concerned with the number of test cycles,
but instead looking at how the combination of C, temperature, time of dwell
at high SOC%, and whatever other significant inputs that may be
discovered. Maybe they are working this out, I have not been keeping up
with the research for a couple years now.
Their original intent was to improve the state of testing and to get
funding. That is probably still where they stand regarding motivation.
I don't know about the AABC meeting. Do you know if there is a video or
For anyone in the battery industry, manufacturing or use, Dr. Dahn seems to
be very responsive. It is his stated goal to improve the industry, and he
seemed willing to connect directly.
On Fri, Oct 14, 2016 at 1:30 PM, Roger Stockton via EV <firstname.lastname@example.org>
> Michael Ross wrote:
> > Even though marketing likes accelerated life testing, and it
> > gives a higher comfort level to everyone, accelerated life
> > testing can just take resources away from more serious
> > investigation;
> > This is where the work at Dalhousie got its motivation.
> > Their approach was to jump up the accuracy of testing by orders of
> > magnitude. In a nutshell they built top of the line test
> > equipment using very high quality current sources, they performed testing
> > in thermal chambers maintaining extremely steady, elevated temperatures,
> > and so on, all to reduce environmental and measurement noise and
> > uncertainty. Through these means they were able to detect very small
> > levels of cell deterioration and malfunction, while NOT cycling the
> > cells; instead simply maintaining the damaging conditions and
> > stopping occasionally to examine cell function (capacity, resistance,
> > etc.), the test periods were drastically reduced from accelerated life
> > testing protocols.
> First of all, what you describe *is* accelerated life testing, whether the
> cells are being cycled or not.
> Secondly, you are mistaken about the not cycling part; the presentation
> that Dr. Dahn gave at AABC a few years ago describing the high precision
> test equipment they had designed and how it was being used specifically
> stated that the purpose of the high precision equipment was to allow the
> measurement of the (hopefully ;^) very small amounts of capacity loss that
> results each time the cell is *cycled*. Since the capacity loss is
> (supposedly) linear with the number of cycles, the higher precision test
> equipment allowed them to determine the rate of capacity loss while
> performing much fewer cycles than had traditionally been required, and it
> was then possible to extrapolate from the measured capacity loss per cycle
> to predict the cell cycle life to whatever residual capacity level one
> He may certainly have moved to the test regime you describe in more recent
> times, however this was not the original intent behind the development of
> the high precision test equipment.
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Michael E. Ross
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