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BQ25570: How do Li-Ion Batteries age with ultra-shallow (dis)charging

Arndt Zinn
Prodigy 10 points
Part Number: BQ25570

Dears,

i'm a battery scientist and currently using the BQ25570 together with a miniature solar cell (IXYS) for a sensor network node.

During the day, the solar cell constantly charges the Li-Ion battery i use as buffer. Every 5-10 s, the BLE chip polls data and requires more energy than the solar cell provides, therefore discharging the battery.

In my thinking, that means that the battery switches from charging to discharging every 5-10 s. Usually a Li-Ion battery can accommodate 1000 complete cycles over the course of years. But these are very "shallow" cycles. How do batteries age if cycled in such a fashion as the BQ25570 allows? I couldn't find any publications in literature that address this concern. Does TI have experience with it?

Thanks and best,

Arndt

  • 0
    TI__Expert 8230 points

    Hello Arndt,

    When referring to a cycle we typically mean fully charging the cell and discharging it to its cutoff voltage. In the case of shallow discharges/charges, such as charging to full, discharging to 95% for example (or another state of charge), a cycle will be counted when the amount of passed charge is equal to the design capacity of the cell. For example, if the cell is discharged to 95% then charged again to 100% full 20 times, this will be considered one cycle, providing more lifetime cycles. The cell will most likely age more due to cycle aging, cause by mechanical strains in the electrode. However, if the cell is kept at high SOC, it might be affected more by calendar aging.