OCV curve principles
See :
- Papers :
- Charge and discharge characteristics of a commercial LiCoO(2)-based 18650 Li-ion battery.pdf
- https://res.mdpi.com/d_attachment/batteries/batteries-06-00032/article_deploy/batteries-06-00032-v2.pdf
Do we need to measure the curve at different temperatures? How significan are the differences?
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
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
The programming software looks like this:
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: