Discharging a thin film battery - EFL700A39

[GAbi .1]

Hello,

I'm trying to discharge the solid state thin film lithium battery EFL700A39, with a discharge current of 0.7 mA, in the aim of reaching a state of charge of approximately 20%.

Actually, the problem is the significant difference of voltages when the battery is without load and when the the load is connected.

In other words, for example, the no-load voltage of the battery is 4.152 V. When connected to a load extracting 0.7mA, the initial voltage of the battery changes from 4.152V to 3.85 V. Which is for me is kind of weird.

So should I refer to the voltage with or without load ? any idea ?

Thank you for your help,

Georgina

[Peter BENSCH]

Hi, Georgina,

as you know the EFL700A39 was a rechargable lithium battery which has been obsoleted some years ago. It was based on LiCoO2, which was known for its short life span.

I'm pretty sure your device under test is at least that old and already has increased the internal resistance, hence the voltage drop even at moderate or low currents.

Regards

/Peter

[GAbi .1]

Hi peter,

Thank you for your reply, I appreciate it.

So this might also be the cause of the increase of voltage once I start charging. If the open voltage is 3.9V, when first connected to charge with a current of 0.4 mA, the voltage increases to 4.1. Does it make sense here ?

Plus do you think the increase of the internal resistance lead to a slower charging process ? I'm charging this battery with a current of 0.4 mA, but it takes approximately 50 min to charge from a s.o.c of 10% to 90%. Isn't too much time ?

Thank you for your help,

Georgina

[Peter BENSCH · Accepted solution]

Lithium batteries age even if they have not been used. It doesn't make sense to work on a battery that is almost dead, because its chemistry simply doesn't work anymore.

I'm afraid I can't help you much here.

Regards

/Peter

[GAbi .1]

Thank you Peter.

Kind regards,

Georgina