In the two papers I have by these men they are using LiFEPO4 cells.If you want
a copy let me know.
The latest is dated October 2015 Here is the abstract.
ABSTRACT
This study investigates the effects of elevated temperature on
commercially available high power graphite/LiFePO4 cells using
a temperature dependent, electrolyte enhanced, single particle
model (ESPM-T) coupled with a Solid Electrolyte Interphase
(SEI) layer growth aging model. The ESPM-T is capable of simulating
up to 25C and 10 sec charge-discharge pulses within a 35-
65% SOC window and 25oC to 40oC temperature range with less
than 1% voltage error, so it is suitable for hybrid electric vehicle
(HEV) applications. The aging model is experimentally validated
with an aggressive HEV cycle running for 4 months with
less than 1% error. Instead of defining battery End of Life (EOL)
as an arbitrary percent of capacity loss, we use the cycle number
when the battery voltage hits 3.6V/2V (maximum/minimum)
voltage limits. This is the practical limit of operation without
reduced performance. Simulations show that operating cells at
35oC increases their life by 45% compared to room temperature
operation. If the cell temperature is increased stepwise, then battery
life is increased 85% more with a 50oC cell temperature at
EOL. Battery initial size can be reduced by 24% using this temperature
set-point strategy.
From: tomw via EV <ev@lists.evdl.org>
To: ev@lists.evdl.org
Sent: Wednesday, November 18, 2015 8:25 AM
Subject: Re: [EVDL] A math formula can model li-ion pack aging, Pyrite pack
/"According to the researchers, this new simple aging formula takes into
account only the factors shown to most influence lithium-ion battery aging
by affecting growth of the SEI layer, which include state of charge, how
often the battery charges/discharges completely, operating temperature, and
current."/
The battery companies have for years understood that electrolyte additives
make a huge difference in reactions at the SEI layer, strongly effecting
lifecyles, especially at higher temperatures and voltages (remember the Dahn
video where he showed data on this, with best performers being from battery
companies using propreietary additives).
Impossible to tell from the article if this "formula" explains much of
anything. It may simply describe behaviour in terms of some external
variables such as temperature and current as the article seems to indicate.
This could be based on a fit to data on a particular chemistry, or they may
have derived it from more basic principles. In the former case it would not
say anything about the molecular mechanisms that give rise to such effects,
and would only be fairly predictive of performance for the cell chemistry
data to which it was fit. Different additives would give different results,
and it would have no power in predicting these. Would be nice to know how
the equations were derived.
--
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