I am currently manufacturing a graphite||LiFePO4 battery using a LiPF6 electrolyte. Both are coated on copper and aluminum foils respectively. I assembled them in a split test cell in inert conditions. As assembled OCV is 0.4 volts. At a charging rate of 0.008 mA, the voltage rises upto 3.6 volts, however, as soon the charging is stopped, voltage falls back to 0.4 volts again.
It would really help if the respective experts guide in this regard.
So what is your issue?
I would like to know the C-rate corresponding to 0.008 mA and the cut-off voltage. And please also provide the charging time and the (specific) charge capacity.
the voltage of the battery rises to 3.6 volts during charging but then falls back to 0.4 volts when charging is stopped, could be due to a number of factors. Some possibilities include:
- Insufficient charge transfer at the electrode/electrolyte interface: This could be caused by poor contact between the electrodes and the electrolyte, or by poor conductivity of the electrolyte itself. This would prevent the lithium ions from effectively moving between the electrodes during charging and discharging.
- Inadequate ion transport in the electrolyte: The lithium hexafluorophosphate (LiPF6) electrolyte you are using is known to have poor ionic conductivity, which can limit the rate at which lithium ions can move through the electrolyte. This can also lead to a poor charge transfer at the electrode/electrolyte interface.
- Inadequate surface area of the electrodes: The surface area of the electrodes plays a crucial role in the performance of a battery. If the surface area of the electrodes is too small, it can limit the rate at which lithium ions can move in and out of the electrodes during charging and discharging, which can lead to poor battery performance.
- Issues with the separator: The separator is a porous material that is placed between the anode and cathode to prevent the electrodes from coming into direct contact with each other. If the separator is not functioning properly, it can lead to poor charge transfer and poor battery performance.
It's worth noting that this is a complex issue and it would be beneficial if you could provide more information about your setup, such as the thickness of the electrodes, the composition of the electrodes, and the conditions under which the batteries were tested. I would also recommend seeking the help of experts in the field to troubleshoot the problem.
It's important to verify that all the parameters of the manufacturing process and the conditions of the test cell are correct, if you can provide more information about the manufacturing process and the test cell, it would help to have a better understanding of the problem.
Hey, hmm is there any voltage plateau that appears ? sometimes we just tend to put the order of electrodes so that the voltage is initially positive, which is not always correct, so keep an eye on which electrod is the LFP and which is Graphite and make sure to put the positive as LFP and then charge.
Also, sometimes it's because there is a low first columbic efficiency of Graphite and that it's not prelithiated, so the LFP will loose Lithium and it will all be lost in forming the SEI. So for this, try to make half cells (with lithium metal as anode) for each material alone and see how it behaves, in order to choose the right ratio of Anode capacity/ Cathode capacity. Then you can try to make three electrodes cell with Lithium as the third electrode, so you can see is it the LFP that does not loose Lithium and does the lithium ion intercallate propery in the anode.
An-Giang Nguyen .. I did not record the weight of the cathode material used ergo I could not calculate the theoretical charge capacity. I have noted your questions as suggestions for future working guidelines.. Thanks alot for your kind help..
Ponniah Vajeeston ... much thanks for your suggestions sir, really appreciate it.
We are currently assembling in a SS seperable two cell electrode split test cell that is assembled using Allen bolts. We use PP seperator soaked in LiPF6.
Your suggestions and questions have provided me insight about the parameters to be controlled. Much thanks, really appreciate it.
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