This documentation is still very early and not complete nor well written.
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OCV curve principles

See :
Do we need to measure the curve at different temperatures? How significan are the differences?
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Relaxing time

  • 90min seems to be standard
  • 60min seems to be precise enough most of the time
  • 15min can lead to about 5% imprecision vs 60min
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β‡’ We will use 90min relaxing times to maximize accuracy of our curves

OCV curve measurement

We will use an 8-ch cycling machine to measure OCV on cells
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The programming software looks like this:
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OCV measurement using successive discharges + relax periods

OCV in discharge steps

First, make sure the cell has been fully charged according to the instructions below:
Step
Mode
Set1
Set2
Cutoff
Comment
1
C-CV
1
4.2
0.1
Fully charge the cell before measurement
2
Wait
0
0
90
Then, after a relax time > 90min, follow:
Step
Mode
Set1
Set2
Cutoff
Comment
1
D-CC
1
2.5
360
Discharge for 6 min = 100 mAh @ 1A. Cut at 2.5V (depends on cell, see datasheet)
2
Wait
0
0
90
Relaxing time
3
Cycle
0
0
36
For a 3500mAh cell, 35 * 100mAh β‡’ At least 36 cycles to ensure complete discharge

OCV in charge steps

Due to the hysteresis effect, the curve is slightly different when in charge vs in discharge
See
Make sure the cell has been completely discharged according to the instructions below:
Step
Mode
Set1
Set2
Cutoff
Comment
1
D-CC
1
2.5
0
Fully discharge
2
Wait
0
0
90
Then, after a relax time > 90min, follow:
Step
Mode
Set1
Set2
Cutoff
Comment
1
C-CV
1
4.2
0.1
IMPOSSIBLE TO CHARGE FOR 100MAH ON THE ZKE TESTER?
2
Wait
0
0
3
Cycle
0
0

OCV measurement using average chg+dsg curves

See procedure here:
On a relaxed cell, with a cut-off of 2.65V (such as Samsung 35E):
Step
Mode
Set1
Set2
Cutoff
Comment
1
C-CV
0.1
4.2
0.1
Charge to 100% at 0.1A
2
Wait
0
0
90
Relaxing time
3
D-CC
0.1
2.65
0
Discharge to 0% at 0.1A
4
Wait
0
0
90
Relaxing time
5
C-CV
0.1
4.2
0.1
Charge to 100% at 0.1A
6
Wait
0
0
90
Relaxing time
7
D-CC
0.1
2.65
90
Discharge to 0% at 0.1A (2nd time, should be more precise, compare with 1st)
8
C-CV
1
3.6
0.1
Charge to ~30% SOC for storage
Compare 2nd discharge with 1st discharge. Same curve? If so, delete 2nd discharge in the procedure
See tests here: