Define battery capacity

[wigging]

I'm trying to simulate a constant current discharge for three different battery capacities (see example code below). I set the battery capacity using the 'Nominal cell capacity [A.h]' parameter. However, based on the generated plots, the capacity value given to the model parameters seems to be ignored. Am I setting the wrong parameter value or is there another way to set the battery capacity for the model?

import matplotlib.pyplot as plt
import pybamm

plt.style.use('default')

# Parameters
# ----------------------------------------------------------------------------

discharge = 1.8
capacities = [0.60, 0.70, 0.80]

# Simulations
# ----------------------------------------------------------------------------

t = []
capacity = []
current = []
voltage = []

for i in range(len(capacities)):
    model = pybamm.lithium_ion.SPMe()

    param = model.default_parameter_values
    param['Nominal cell capacity [A.h]'] = capacities[i]
    param['Current function [A]'] = '[input]'

    sim = pybamm.Simulation(model, parameter_values=param)
    sim.solve([0, 4000], inputs={'Current function [A]': discharge})

    t.append(sim.solution['Time [s]'].entries)
    capacity.append(sim.solution['Discharge capacity [A.h]'].entries)
    current.append(sim.solution['Current [A]'].entries)
    voltage.append(sim.solution["Terminal voltage [V]"].entries)

# Plot
# ----------------------------------------------------------------------------

_, ax = plt.subplots(tight_layout=True)
for i in range(len(capacities)):
    ax.plot(t[i], voltage[i], label=f'{capacities[i]} Ah')
ax.set_xlabel('Time [s]')
ax.set_ylabel('Terminal voltage [V]')
ax.legend(loc='best')

_, ax = plt.subplots(tight_layout=True)
for i in range(len(capacities)):
    ax.plot(t[i], capacity[i], label=f'{capacities[i]} Ah')
ax.set_xlabel('Time [s]')
ax.set_ylabel('Capacity [Ah]')
ax.legend(loc='best')

_, ax = plt.subplots(tight_layout=True)
for i in range(len(capacities)):
    ax.plot(capacity[i], voltage[i], label=f'{capacities[i]} Ah')
ax.set_xlabel('Capacity [Ah]')
ax.set_ylabel('Voltage [V]')
ax.legend(loc='best')

plt.show()

[valentinsulzer]

Nominal capacity is just nominal, used to convert between "C-rate" and "current". The easiest way to just change capacity is to change the area of the cell (electrode height or width). If you want to change the areal capacity (Ah/m2) you can change the thickness of either electrode or the active material volume fraction. Then see this notebook for calculating the theoretical capacity between voltage limits

[wigging]

To make sure I'm adjusting the relevant parameters, are these the parameters you are referring to:

• 'Electrode height [m]'
• 'Electrode width [m]'
• 'Negative electrode thickness [m]'
• 'Positive electrode thickness [m]'
• 'Negative electrode active material volume fraction'
• 'Positive electrode active material volume fraction'

[valentinsulzer]

Yep

[PippaVossen]

Thanks for posting this question & answer - could you repost the link to 'this notebook' for calculating the theoretical capacity between voltage limits @tinosulzer ? The page is not found...