Why does Li-Ion cell have different charging and discharging current

[lefile]

Hello,

So, why does the maximum charging current (or power) of lithium-ion battery packs differs from discharging one if the internal resistances are almost the same for charging and discharging (hysteresis is also neglible)? For example, Saft superphosphate cell could be discharged with as much as 1500 A, but charging is restricted to only about 150 A.

Thank you!

 

[IRstuff]

Probably a question of heat, and for certain chemistries, the generation of explosive gases

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[lefile]

But generated heat is due to equivalent resistance, which is more or less the same for dis/charging. I'm not chemist so don't know about explosive gases but I don't think gases are created during discharging any more than during charging.

 

[itsmoked]

I bet Shaft could tell you precisely why the charge and discharge are differently spec'd.

A cell could have the same dis/charging resistance but the electromechanical aspects of replating Li back onto it's matrix may take physically longer than ripping it off during discharge. Consider that discharging may rip atoms off of a plate and into a fluid whereas pulling things out of fluid and putting them onto a plate takes mechanical lattice building which probably takes longer or if done too fast causes lots of distortion.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

NO! These are CHEMICAL batteries. It takes WORK to put the energy back into the chemistry. That generates heat.

High charging voltages, which are needed for rapid charging results in electrolysis in water-based chemistries, which generates molecular hydrogen and oxygen, which is combustible.

Most of this stuff is available on the web.

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