Is it possible to accurately calculate how long a Li-Ion cell takes to charge?

Question

Since Li-Ion cells are charged using both Constant Current and Constant Voltage modes during their charging cycle, and the transition between these points depends on the cell voltage. Is there an accurate way to work out how long charging for a specific cell would take?

The naive approach of just dividing the capacity by the charging current won't work by my estimation as the CV mode is by far the longest segment of the charging cycle.

Assuming I'm using a single cell (for example LG HG2), how would I calculate the ideal charging time, taking into account CC/CV modes?

Edit: I am specifically asking about how to calculate how long a Li-Ion cell would take to charge given its datasheet parameters. I do not want to apply hardware to this problem yet as I know Gas Gauges can be used to measure SoC

Answer 1

If you want to be precise, you should map the charging cycle of the battery (e.g., the voltage vs. current during the charging cycle). Usually a 2-piece linear approximation of current is adequate, but it will depend on the battery capacity and the charge rate to find the knee. Once that curve is established, the area under the curve represents the A-H delivered to the battery. If you know the capacity and SoC, you can use that to determine the time to full charge.

Answer 2

You can use a gas gauge. STC3100 has an internal coulomb counter so you can know how much mA goes out and how much goes in. Battery efficiency goes down with each complete charge, but you can't know how much easily.

Other gas gauges like BQ27710 tells promising features like "auto calibration" to gives you some stadistics, including remaining battery with current consumption and remaining mAh, but after some messages with TI engineers on TI forum, they told me that "auto calibration" means "you need to have THIS programer and use THIS software to do a particular calibration of THIS BQ27710", so if you plan to do a mass fabrication you need to take into account that factory needs to program each gas gauge. Maybe others gas gauges with real auto calibration works without previous steps.

TI has some cocuments about how "impedance track" algorithm works