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BQ40Z50-R2: ChemID and FCC accuracy

Chen Jia
Intellectual 850 points
Part Number: BQ40Z50-R2

To whom it may concern:

In a new design, we use MOLI INR18650M35A cell in 2S1P configuration. The spec is attached. It is a pretty new cell, so no ChemID is available at this point, which is understandable. So we use the online tool to choose a ChemID close to this cell, and the recommends are 2141 and 2144, 3000mAh and 3400mAh. We tried both ChemID, and generate the ROM/SREC file based on the use case, 25W CP discharge.

After the battery fully discharged, the FCC is about 3250mAh, as expected; however, when the battery is charged to 30% and idle for a while, the FCC RemCap and RSOC will all shrink down, as attached. If the battery if fully charged and discharge again, the FCC will increase to 3250mAh range again. Do you have any suggestions to correct this?

 We are trying to generate the SREC file with 0.2C discharge now, but afraid after 25W CP discharge, the problem will still exist. Do you think this may be caused by the ChemID?

Thank you!

Chen

  • 0
    TI__Mastermind 42535 points
    Hi Chen,

    Can you please attach the file you are talking about here? Can you please also include your gg file and srec along with the chem ID match result. This will allow me to help you.
  • 0 in reply to Batt
    Intellectual 850 points

    Hello Batt.:

    Here is the gg file and cell chemistry file. 

    We did some more test, and the problem is still exist. If the battery is charged to 26% RSOC in normal charge-discharge cycle, it will change to 18% RSOC after 5 hours rest.

    Please help to review the files. Thank you very much!

    Chen

    Fullscreen 7028.GPC_report.txt Download 
    Chemistry ID selection tool, rev=2.46		
		
Configuration used in present fit:		
ProcessingType=2		
NumCellSeries=1		
ElapsedTimeColumn=0		
VoltageColumn=1		
CurrentColumn=2		
TemperatureColumn=3		
		
Best chemical ID : 2141	Best chemical ID max. deviation, % : 3.28	
		
		
		
Summary of all IDs with max. DOD deviation below 3%		
		
Chem ID	max DOD error, %	Max R deviation, ratio
0	0	0
		
Warning: Deviation is above recommended level. New chem ID needs to be released for this cell. Please contact your TI representative to send the cell to Dallas for characterization		
		
		
Selection of best generic ID for ROM based devices like bq274xx		
		
		
Device / Family #1		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
3142	bq27421-G1D: 4.4V LiCoO2	21.38
354	bq27411-G1C: 4.35V LiCoO2	23.84
128	bq27421-G1A: 4.2V LiCoO2	28.46
312	bq27421-G1B: 4.3V LiCoO2	34.94
Best generic ID 3142		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule		
		
		
Device / Family #2		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
1210	bq27621:  (ALT_CHEM1) 4.3V LiCoO2	23.39
1202	bq27621: (default) 4.2V LiCoO2	23.47
354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	23.84
Best generic ID 1210		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule		
		
		
Device / Family #3		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
3142	bq27426: (ALT-CHEM2) 4.4V LiCoO2	21.38
1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	23.47
3230	bq27426: (default) 4.35V LiCoO2	24.04
Best generic ID 3142		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule

  • 0 in reply to Chen Jia
    Intellectual 845 points

     Hi Chen!

     Have you resolved your issue?

     We encountered similar jump in RSOC after loading ChemId for different cells than are used.

     What ChemId matching error was reported after you finished Best Chemistry Match procedure by dedicated TI tool ?

     Thanks for advice!

  • 0 in reply to Chen Jia
    TI__Mastermind 42535 points

    Hi Chen,

    We believe this is related to chem ID. A general analysis is that once you are in relax, the RSOC depends on the OCV voltage. It may be that with a 26% RSOC your terminal voltage is dropping quickly to what would be an OCV at 18%. Typically at 26% RSOC with a new cell you would expect an OCV around 3462mV to 3492mV. At 18%, it would be around 3377mV to 3400mV.

  • 0 in reply to Batt
    Intellectual 850 points

    Hello Batt:

    Thanks for your reply. So is there a way to solve this problem? Is it possible to get the accurate Chem ID?

    THanks.

    Chen

  • 0 in reply to Chen Jia
    TI__Mastermind 42535 points

    Unfortunately we have a chem ID queue and this process takes a month or two in the best case scenario. Your alternative for a quicker resolution is to pick from the list of batteries we have already characterized with IDs.

  • 0 in reply to Batt
    Intellectual 850 points

    Hello Batt.:

    Thank you.

    We already use the chem ID from the auto selection tool. However, both results were not accurate, and the cells are 3200mAh and 3000mAh. The cell we want to use is 3400mAh.

    We may need to send you some samples for the chem ID. How many samples you need? Totally understand this will take some time.

    Thank you!

    Chen

  • 0 in reply to Chen Jia
    TI__Mastermind 42535 points

    Hi Chen,

    I'll talk to the chemistry engineers and get back to you on this by Monday.

  • 0 in reply to Batt
    TI__Mastermind 42535 points

    Hi Chen,

    The char queue is 3 months long, we need 7 samples if you still want to proceed.