Errors with EIS run with degraded model with experiment

[Akila1993]

Hello All,

I trying to get the EIS for a degraded battery,

1. But when I try to run the full experiment with ["Discharge at 0.1C until 2.5 V"] this part at last EIS run gives me the following error, Without this part EIS run is errorless.

2. Also, when we include the sub-models for Li planting It gives the following error when I increase the cycle number to 500.

Can someone guide me please?

# Initial conditions and parameter update

import pybamm
import matplotlib.pyplot as plt
import pbeis
import numpy as np
import matplotlib.pyplot as plt
import time as timer
from scipy.fft import fft

parameter_values = pybamm.ParameterValues("Chen2020")

pp = pybamm.ParameterValues("OKane2022")

model = pybamm.lithium_ion.DFN(
    {   
        "thermal": "lumped", #lumped thermal submodel 
        "surface form": "differential", #Adding capacitance to the model 
        #"SEI": "solvent-diffusion limited",
        #"SEI porosity change": "true",
        #"lithium plating": "partially reversible",
        #"lithium plating porosity change": "true",  # alias for "SEI porosity change"
        #"particle mechanics":"swelling only",
        #"SEI on cracks": "true",
        #"loss of active material": "stress-driven",
        
    }
)
var_pts = {
    "x_n": 5,  # negative electrode
    "x_s": 5,  # separator
    "x_p": 5,  # positive electrode
    "r_n": 30,  # negative particle
    "r_p": 30,  # positive particle
}


def get_chen2020_parameters():
    parameter_values = pybamm.ParameterValues("Chen2020")
    parameters = parameter_values
    return parameters

def get_okane2022_degradation_parameters():

 degradation_parameters = {
 'Dead lithium decay constant [s-1]': 1e-06,
 'Dead lithium decay rate [s-1]':pp["Dead lithium decay rate [s-1]"],
 'Initial plated lithium concentration [mol.m-3]': 0.0,
 'Lithium metal partial molar volume [m3.mol-1]': 1.3e-05,
 'Lithium plating kinetic rate constant [m.s-1]': 1e-09,
 'Lithium plating transfer coefficient': 0.65,
 'Negative electrode LAM constant exponential term': 2.0,
 'Negative electrode LAM constant proportional term [s-1]': 2.7778e-07,
 "Negative electrode Paris' law constant b": 1.12,
 "Negative electrode Paris' law constant m": 2.2,
 "Negative electrode Poisson's ratio": 0.3,
 "Negative electrode Young's modulus [Pa]": 15000000000.0,
 'Negative electrode cracking rate':pp["Negative electrode cracking rate"],
 'Negative electrode critical stress [Pa]': 60000000.0,
 'Negative electrode initial crack length [m]': 2e-08,
 'Negative electrode initial crack width [m]': 1.5e-08,
 'Negative electrode number of cracks per unit area [m-2]': 3180000000000000.0,
 'Negative electrode partial molar volume [m3.mol-1]': 3.1e-06,
 'Negative electrode reference concentration for free of deformation [mol.m-3]': 0.0,
 'Negative electrode volume change':pp["Negative electrode volume change"],
 'Positive electrode LAM constant exponential term': 2.0,
 'Positive electrode LAM constant proportional term [s-1]': 2.7778e-07,
 'Positive electrode OCP entropic change [V.K-1]': 0.0,
 "Positive electrode Paris' law constant b": 1.12,
 "Positive electrode Paris' law constant m": 2.2,
 "Positive electrode Poisson's ratio": 0.2,
 "Positive electrode Young's modulus [Pa]": 375000000000.0,
 'Positive electrode active material volume fraction': 0.665,
 'Positive electrode cracking rate':pp["Positive electrode cracking rate"],
 'Positive electrode critical stress [Pa]': 375000000.0,
 'Positive electrode initial crack length [m]': 2e-08,
 'Positive electrode initial crack width [m]': 1.5e-08,
 'Positive electrode number of cracks per unit area [m-2]': 3180000000000000.0,
 'Positive electrode partial molar volume [m3.mol-1]': 1.25e-05,
 'Positive electrode reference concentration for free of deformation [mol.m-3]': 0.0,
 'Positive electrode volume change':pp["Positive electrode volume change"],
 'Typical plated lithium concentration [mol.m-3]': 1000.0,
 'Exchange-current density for stripping [A.m-2]':pp["Exchange-current density for stripping [A.m-2]"],
 'Exchange-current density for plating [A.m-2]':pp["Exchange-current density for plating [A.m-2]"],
      
    }
 return degradation_parameters

def update_parameters():
    # Load Chen2020 parameters
    chen2020_params = get_chen2020_parameters()

    # Load OKane2022 degradation parameters
    okane2022_degradation_params = get_okane2022_degradation_parameters()

    # Update Chen2020 parameters with OKane2022 degradation parameters
    chen2020_params.update(okane2022_degradation_params, check_already_exists=False)

    return chen2020_params

updated_parameters = update_parameters()


# Set up experiment

cycle_number = 10

exp = pybamm.Experiment(
["Hold at 4.2 V until C/100",
"Rest for 4 hours",
"Discharge at 0.1C until 2.5 V", # initial capacity check
"Charge at 0.3C until 4.2 V",
"Hold at 4.2 V until C/100",]
+ [("Discharge at 1C until 2.5 V", # ageing cycles
"Charge at 0.3C until 4.2 V",
"Hold at 4.2 V until C/100",)] * cycle_number
+ ["Discharge at 0.1C until 2.5 V"],
)



start_time = timer.time()


sim = pybamm.Simulation(model, parameter_values=updated_parameters,experiment=exp,solver=pybamm.CasadiSolver(mode='safe without grid'),var_pts=var_pts)



solution = sim.solve()


# Set initial conditions of aged_model from the solution and EIS Running 

aged_model = model.set_initial_conditions_from(solution)

#frequency range
frequencies = np.logspace(-4, 2, 30)

#amplitude of the current for EIS 
I = 1 * 1e-3

number_of_periods = 20
samples_per_period = 20

#Current function 
def current_function(t):
    #return I * pybamm.sin(2 * np.pi * F * t)
    return I * pybamm.sin(2 * np.pi * pybamm.InputParameter("Frequency [Hz]") * t)

updated_parameters["Current function [A]"] = current_function

sim_aged = pybamm.Simulation(aged_model, parameter_values=updated_parameters,solver=pybamm.CasadiSolver(mode='safe without grid'),var_pts=var_pts)


impedances_time = []

for frequency in frequencies:
    # Solve
    period = 1 / frequency
    dt = period / samples_per_period
    t_eval = np.array(range(0, 1 + samples_per_period * number_of_periods)) * dt
    sol = sim_aged.solve(t_eval, inputs={"Frequency [Hz]": frequency},initial_soc=0.9)
    # Extract final two periods of the solution
    time = sol["Time [s]"].entries[-3 * samples_per_period - 1 :]
    current = sol["Current [A]"].entries[-3 * samples_per_period - 1 :]
    voltage = sol["Terminal voltage [V]"].entries[-3 * samples_per_period - 1 :]
    # FFT
    current_fft = fft(current)
    voltage_fft = fft(voltage)
    # Get index of first harmonic
    idx = np.argmax(np.abs(current_fft))
    impedance = -voltage_fft[idx] / current_fft[idx]
    impedances_time.append(impedance)`

[Akila1993]

Hi Everyone,

Can anyone support me in this regard?

Thank you.

[brosaplanella]

1. I suspect the issue is that you start with a fully discharged battery and you exceed the voltage limits when performing the EIS cycling. You can change the minimum and maximum cut-off voltages in the parameters to fix that.
2. The output you pasted above is not necessarily an error (it means it failed to converge but the solver tries multiple times before throwing an error message). In any case, it seems a solver issue so you can try changing the solver. Using CasadiSolver in safe mode (and playing with dt_max and/or using the IDAKLUSolver might help.

[Akila1993]

@brosaplanella Thank you. I will get back to you.

[Thiyaga2025]

hi @Akila1993 ,

I am trying degradation modeling with both SEI and Lithium plating modes on but running into convergence issues. were you able to resolve the warnings you mentioned in point 2.
what settings helped to overcome.
thanks for your time.

[Akila1993]

Hi @Thiyaga2025 ,

I have changed the experiment, as mentioned below.

exp = pybamm.Experiment(
    [
        (
            "Discharge at 1C until 2.5 V",  # ageing cycles
            "Charge at 0.6C until 4.2 V (5 minute period)",
            "Hold at 4.2 V until C/100 (5 minute period)",
        )
    ]
    * cycle_number
)

Please see the full code in this discussion

[Thiyaga2025]

hi @Akila1993 , thanks a lot for the reply and sorry for the delayed response. with your suggestions i am able to run degradation model with "SEI", and "Lithium plating" modes on. but the simulation works only with SPM model and i face convergence issues with DFN. the test results show 10% capacity reduction after 1000 cycles. i try to tune,
"Lithium plating kinetic rate constant [m.s-1]' and "SEI kinetic rate constant [m.s-1]". please let me know your thoughts.

thanks and regards

[brosaplanella]

For EIS I would strongly encourage you to use the [PyBaMM EIS](https://github.com/[pybamm-team/pybamm-eis](https://github.com/pybamm-team/pybamm-eis) package, which works directly in the frequency domain and thus it is less likely to encounter solver issues.