What makes Li Ion age ?

[Raymund Hofmann]

What determines the lifetime (decrease in capacity) of a Li Ion
accumulator ?

To my current investigation this is determined by the charge / discharge
cycles.

So the function for "age" should be:

age = ac current amplitude * time

This would mean when the accumulator is used where the dc current is
zero, but the ac current amplitude is high (rectagular 1C pp for
example, frequency >1Hz), the user can not determine "charging" or
"discharging", but the accumulator should age quite quickly (300
effective charge cycles in 25 days ).
Obviously the Li Ion should not be fully charged in this example, so I
assume it stays at .5C charge.

Is this assumption correct ?
Does it depend on ac current frequency ?
Is there a model to determine the "age" of a Li Ion accumulator ?
Is there some further information concerning this ?

Raymund Hofmann

 

[James Meyer]

On Sat, 11 Jun 2005 16:24:19 +0200, "Raymund Hofmann"
<filter002@desinformation.de> wroth:

Is this assumption correct ?

It could be easily tested.

Does it depend on ac current frequency ?

That could be part of the test also. My guess is that high frequency AC
currents could be passed through the cell's intrinsic capacitance without having
any direct effect on its internal chemistry.

Is there a model to determine the "age" of a Li Ion accumulator ?

As far as I can determine, the age or lifespan is determined from tests.

Is there some further information concerning this ?

Raymund Hofmann

I have seen detailed information concerning the chemistry involved with
charging and discharging LiIon cells but not any good explanation for aging such
as I have seen for NiCad and lead acid cells.

Jim

 

[DaveC]

On Sat, 11 Jun 2005 07:24:19 -0700, Raymund Hofmann wrote
(in article <d8esaf$otu$1@online.de&gt:

What determines the lifetime (decrease in capacity) of a Li Ion
accumulator ?

To my current investigation this is determined by the charge / discharge
cycles.

So the function for "age" should be:

age = ac current amplitude * time

This would mean when the accumulator is used where the dc current is
zero, but the ac current amplitude is high (rectagular 1C pp for
example, frequency >1Hz), the user can not determine "charging" or
"discharging", but the accumulator should age quite quickly (300
effective charge cycles in 25 days ).
Obviously the Li Ion should not be fully charged in this example, so I
assume it stays at .5C charge.

Is this assumption correct ?
Does it depend on ac current frequency ?
Is there a model to determine the "age" of a Li Ion accumulator ?
Is there some further information concerning this ?

Raymund Hofmann

Cross-posting to sci.chem.electrochem.battery

--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group

 

[Joop]

"Raymund Hofmann" <filter002@desinformation.de> wrote:

What determines the lifetime (decrease in capacity) of a Li Ion
accumulator ?

Not so much usage. More the oxidation of the cells that increase

internal resistance.
To minimize the effect keep the cell's cool and not full (40% ideal).

So if you own a laptop and mostly use it on mains power, then I guess
you could put you battery pack in the fridge when not used. Lift span
may double.

More details at: http://www.buchmann.ca/Chap6-page3.asp

 

[Evgenij Barsukov]

DaveC wrote:

On Sat, 11 Jun 2005 07:24:19 -0700, Raymund Hofmann wrote
(in article <d8esaf$otu$1@online.de&gt:


What determines the lifetime (decrease in capacity) of a Li Ion
accumulator ?

To my current investigation this is determined by the charge / discharge
cycles.

So the function for "age" should be:

age = ac current amplitude * time

This would mean when the accumulator is used where the dc current is
zero, but the ac current amplitude is high (rectagular 1C pp for
example, frequency >1Hz), the user can not determine "charging" or
"discharging", but the accumulator should age quite quickly (300
effective charge cycles in 25 days ).
Obviously the Li Ion should not be fully charged in this example, so I
assume it stays at .5C charge.

Is this assumption correct ?
Does it depend on ac current frequency ?
Is there a model to determine the "age" of a Li Ion accumulator ?
Is there some further information concerning this ?

Aging of Li-ion depends much more on voltage and temperature
where they are stored, and storage time than on actual cycling.

For your exapmle, when storing at 50% charged state (which is
very nice voltage by itself) and cycling at 1Hz with 1C pulses, battery
would has no additional aging compared to just storage without pulses,
if (!) it would not be self-heating (e.g. under assumption of
active cooling). However, it will be substantialy self-heating
under 1C pulses, so temperature increase up to 40-50C will be
main reason why battery will accelerate its aging during this
period.
Good paper on different aging mechanisms in Li-ion is:

Soo Seok Choi, Hong S. Lim, Journal of Power Sources 111 (2002) 130–136

Regards,
Evgenij