Why does CCCV charging result in more capacity loss than constant current in a single cycle?

General
1

I’m investigating the trade-off between CCCV and constant current (CC) charging strategies by observing the capacity loss due to side reactions over a single charging cycle.

Surprisingly, I found that the capacity loss is lower under constant current charging compared to CCCV, even though both strategies fully charge the battery. The CCCV method introduces additional loss during the CV (constant voltage) phase, where the current is already quite low, yet the side reactions continue to contribute to cumulative capacity loss.

This seems counterintuitive because CCCV is generally regarded as superior to pure constant current charging in practical applications. This result confuses me:

  • Is there something wrong with my interpretation?
  • Or is it that this particular evaluation criterion (capacity loss per cycle) is not sufficient to reflect overall performance?

My ultimate goal is to identify a reasonable and effective metric to evaluate charging strategies, so that I can use it as an objective function for charging optimization.

Below is my test code for reference:
import pybamm

options = {
“thermal”: “lumped”,
“SEI”: “solvent-diffusion limited”,
“lithium plating”: “irreversible”,
}
model = pybamm.lithium_ion.SPMe(options=options)
param = pybamm.ParameterValues(“OKane2022”)
param.update({
“Outer SEI solvent diffusivity [m2.s-1]”: 5e-21,
“SEI kinetic rate constant [m.s-1]”: 2.48e-13,
“Exchange-current density for plating [A.m-2]”: 1e-3
})
experiment = pybamm.Experiment([
(‘Charge at 1 C until 4.2 V’,
‘Hold at 4.2 V until 50 mA’),
], period=“10 seconds”,)
#experiment = pybamm.Experiment([
#(‘Charge at 1 C for 1 hour’,)
#], period=“10 seconds”,)
sim = pybamm.Simulation(model, experiment=experiment, parameter_values=param)
solution = sim.solve(initial_soc=0.0)
cu_loss = solution[“Total capacity lost to side reactions [A.h]”].entries

I’d appreciate any thoughts or clarification on whether this behavior is expected, and whether I should consider a different metric when comparing charging strategies.

2

You can charge to a higher SoC using CCCV than with CC, so it is not a fair comparison.

3

Thank you! That makes sense — I understand now that my current comparison might not be fair, as CCCV may end up charging to a slightly higher SOC than constant current alone.
To follow up on that, what would be a good way to make this comparison fairer?

4

You need to compare two methods that result in the same amount of charge being passed. For example, CCCV vs. multi-step constant current

5

Thanks a lot for your clear explanation and suggestions — really appreciate your time!