Molicel P50B variable charge-rate cycle life test

Test eqiupment:
- NEWARE BTS-4000 test system with T-type thermocoupler module
- The cells are connected to the tester by Micro-TIG welded Cu strips with a cross section of 6 mm2 with separate sense wires for 4W connection
- Tested in room with relatively stable temperature RT: 20 ±3 °C

Test settings:
- The CC-CV method is used for charging, but the charging process is terminated by a time here, for example 4C charging is terminated after 15 min, 3C after 20 min, .., 1C after 60 min. The consequence of using this method is that the cell is never charged to 100% SoC due to the internal resistance of the cell. The higher the charging C-rate the lower the SoC is achieved.
- For discharging, the standard CC method (3C discharge-rate for all tests) is used, with common termination voltage of 2.5 V



Chart below shows dT = Tend - Tstart (The difference between the cell body temperature at the beginning of the charging which is RT: 20 °C with up to 3 °C tolerance and the body temperature reached at the end of the charging). As a Temperature sensor is used NEWARE T-type miniature (0.2 mm) thermocouple, attached with kapton tape.




CC-CV charging: Voltage & Current & Capacity charts

New:



After 1000 cycles:

Small update:

- added Voltage, Current and Capacity charts

Amazing data Pajda. Thank you for taking all the time and effort.

Small update:

- added 1C charge-rate charts

Small update:

- added more cycles

If these get to the $6 range for a hundred cells by next year I'll probably sell the 100 lightly used Samsung 50s I recently bought and swap them into my latest battery pack. Turns out I prefer Molicels- better ebike top end.

Small update:

- added more cycles

Small update:

- added more cycles

Small update:

- added more cycles
- 500 cycles at 4C @ 15min continuous charge-rate with no problem

Small update:

- added more cycles

Wow! Thank you so much for this amazing testing! I have been curious about this for a long time, so really happy to see testing done on this! Cycle life still seems amazing at 20A charging.

I'm curious as to why the charging isn't stopped at say 1A of current instead of with a set timer, is there are technical reason behind this?

Charging with a fixed current is never really optimal, so if the cell can handle being charged at 20A up to ~80% charge with good cycle life it can probably handle much higher currents in the 0-50% charge range. Will you be continuing this with 5C and 6C charging tests as well in the future?

Simon676 said:

I'm curious as to why the charging isn't stopped at say 1A of current instead of with a set timer, is there are technical reason behind this?

Click to expand...

This is more of a commercial reason , where the average user is not interested in the principle of electrochemical cells, but only in the charging time. I called it as “True C-rate” charging test.

Simon676 said:

Charging with a fixed current is never really optimal, so if the cell can handle being charged at 20A up to ~80% charge with good cycle life it can probably handle much higher currents in the 0-50% charge range. Will you be continuing this with 5C and 6C charging tests as well in the future?

Click to expand...

I ended up at 4C with P50B because of the limitation of the current tester to 20A. For higher C-rate I would have to switch back to the ZKE tester, but then we lose the temperature data (I am thinking about 5C which is the maximum continuous charging current by Molicel datasheet) Another thing is that I was more interested in the comparison between modern HP cylindrical cells, where it turns out in my other tests that even 3C charge cycling at >80% DoD is still just too much for most of the competition. So as you suggest, other competitors will need use of the step-charge with high C-rate only up to 50% SoC, ideally combined with preheating the cell to ca 50°C before charging.

Small update:

- added more cycles

Simon676 said:

Wow! Thank you so much for this amazing testing! I have been curious about this for a long time, so really happy to see testing done on this! Cycle life still seems amazing at 20A charging.

I'm curious as to why the charging isn't stopped at say 1A of current instead of with a set timer, is there are technical reason behind this?

Charging with a fixed current is never really optimal, so if the cell can handle being charged at 20A up to ~80% charge with good cycle life it can probably handle much higher currents in the 0-50% charge range. Will you be continuing this with 5C and 6C charging tests as well in the future?

Click to expand...

Outside of what Padja already wrote, stopping charging at max voltage serves as a sort of CC only charging, which does help with battery lifetime and with overpotential, serves as a sort of SOC limiter.

Small update:

- added more cycles