Electrode Utilization in a Large Format Lithium-Ion Battery Pouch Cell

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Electrode Utilization in a Large Format Lithium-Ion Battery Pouch Cell

Large lithium-ion batteries are widely employed in electric vehicles and for stationary energy storage applications. In the (stacked) pouch battery cell design, all current exits the cell on the cell “tabs”, and as the cell size and power increases, the voltage gradients in the highly conductive metal foil current collectors may come into play, resulting in a non-uniform current distribution and electrode utilization in the cell.

A non-uniform utilization results in sub-optimal use of the battery electrodes and may also result in non-uniform and accelerated electrode aging.

This tutorial models the current distribution and electrode utilization in a large format lithium-ion battery pouch cell, and how it depends on the cell current.

The model is in 3D. Note that all plots are scaled 100 times in the z direction due to the high aspect ratio of the geometric features.

Model Definition

Figure 1 shows the model geometry. The geometry defines one foil-to-foil unit cell, stacking 5 layers in the z direction:

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Negative metal current collector foil: 10 μm, Cu (due to symmetry, half of this thickness is used in the model geometry)

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Negative electrode: 60 μm, graphite

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Separator: 30 μm

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Positive electrode: 60 μm, LMO

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Positive metal current collector foil: 10 μm, Al (due to symmetry, half of this thickness is used in the model geometry)

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The electrolyte is LiPF6 in 3:7 EC:EMC

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Symmetry is assumed along the center of the cell

The positive and negative current terminals are located opposite to each other (but may easily be placed on the same side by altering the Geometry node in the model).

Figure 1: Model geometry, scaled 100 times in the z direction.

The Lithium-Ion Battery interface is used to set up the physics, using Material data from the Battery Material Library.

The Particle Intercalation subnodes to the Porous Electrode nodes model the solid lithium concentration in an additional particle dimension (extra dimension). The model hence defines a fully coupled “pseudo-4D” model.

The battery is charged from 20% to 80% cell state-of-charge (SOC). The Initial Cell Charge Distribution node is used to set the initial cell state-of-charge.

An Electrode Ground boundary condition is used on the negative tab whereas an Electrode Current boundary condition defines the cell current exiting the cell on the positive tab.

A Parametric Sweep is used to solve for two different charge rates (1C and 4C).

Results and Discussion

Figure 2 and Figure 3 show the potential distribution in the negative and positive metal foils (current collector and tab), respectively, at the beginning of the 4C charge. The potential variation is about 6 mV in the negative current collector and 10 mV in the positive current collector at a 4C charge current.

For a 1C charge current the corresponding potential variation is below 2 mV (results not shown here).

Figure 2: Potential distribution in the negative metal foil (current collector and tab) at the beginning of the 4C charge.

Figure 3: Potential distribution in the positive metal foil (current collector and tab) at the beginning of the 4C charge.

Figure 4 and Figure 5 show the current distribution for a cross section in the middle of the separator at the beginning and end of the 4C charge, respectively. This provides a measure of the instantaneous electrode utilization. The current distribution varies about 6% in the separator plane over time. For 1C, the variation is generally smaller (results not shown here). Initially, the separator current density is higher close to the tabs whereas toward the end of the charge, the current density is higher in the central parts of the cell.

Figure 4: Current distribution in the middle of the separator at the beginning of the 4C charge.

Figure 5: Current distribution in the middle of the separator at the end of the 4C charge.

To get a measure of the utilization over the charge period, General Projection operators are used to integrate the amount of lithium along the electrode depth (the z direction). Dividing the projected change of lithium by the average for the whole electrode gives a measure of the relative utilization (capacity thruput). Figure 6 and Figure 7 show the relative utilization over the whole charge period for the 1C and 4C charges, respectively for the positive electrode. The utilization varies around 2.5% for the 4C charge and 1% for the 1C charge. The cycle-averaged utilization is lower than the instantaneous utilization shown in Figure 4 and Figure 5.

Figure 6: Relative electrode utilization during the 1C charge.

Figure 7: Relative electrode utilization during the 4C charge.

The tutorial demonstrates that the local electrode utilization along the metal foil (current collector and tab) changes over the course of a charge cycle. For this configuration, utilization is fairly uniform during a 1C charge, but a higher charge of 4C results in a slightly non-uniform utilization.

Battery_Design_Module/Batteries,_Lithium-Ion/pouch_cell_utilization

Modeling Instructions

From the menu, choose .

In the window, click

.

1

In the window, click

.

2

In the tree, select .

3

4

5

In the tree, select .

6

Global Definitions

Import the parameter file.

1

In the window, under click .

2

In the window for , locate the section.

3

.

4

Browse to the model’s Application Libraries folder and double-click the file pouch_cell_utilization_parameters.txt.

Set up the model geometry using the following steps.

Work Plane 1 (wp1)

In the toolbar, click

.

Work Plane 1 (wp1)>Plane Geometry

In the window, click .

Work Plane 1 (wp1)>Rectangle 1 (r1)

1

In the toolbar, click

.

2

In the window for , locate the section.

3

In the text field, type W_cell/2.

4

In the text field, type H_cell.

Extrude 1 (ext1)

1

In the window, right-click and choose .

2

In the window for , locate the section.

3

In the table, enter the following settings:


Distances (m)
L_neg_cc/2
L_neg_cc/2+L_neg
L_neg_cc/2+L_neg+L_sep
L_neg_cc/2+L_neg+L_sep+L_pos
L_neg_cc/2+L_neg+L_sep+L_pos+L_pos_cc/2

1

In the toolbar, click

.

2

In the window for , locate the section.

3

In the text field, type W_tab/2.

4

In the text field, type H_tab.

5

In the text field, type L_neg_cc/2.

6

Locate the section. In the text field, type H_cell.

7

.

8

button in the toolbar.

1

In the toolbar, click

.

2

In the window for , locate the section.

3

In the text field, type W_tab/2.

4

In the text field, type H_tab.

5

In the text field, type L_neg_cc/2.

6

Locate the section. In the text field, type -H_tab.

7

In the text field, type L_neg_cc/2+L_neg+L_sep+L_pos.

8

.

Form Union (fin)

In the toolbar, click

.

Scale the geometry in the z direction to make it easier to see the different layers in the model geometry.

In the window, expand the node.

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

From the list, choose .

4

In the text field, type 100.

5

6

button in the toolbar.

The finalized geometry should now look like as follows.

Create named selections of the different battery domains for ease of selection later in the model.

1

In the toolbar, click

.

2

In the window for , type Positive Tab in the text field.

3

Select Domain 1 only.

Positive Current Collector

1

In the toolbar, click

.

2

In the window for , type Positive Current Collector in the text field.

3

Select Domain 6 only.

Positive Electrode

1

In the toolbar, click

.

2

Select Domain 5 only.

3

In the window for , type Positive Electrode in the text field.

1

In the toolbar, click

.

2

Select Domain 7 only.

3

In the window for , type Negative Tab in the text field.

Negative Current Collector

1

In the toolbar, click

.

2

Select Domain 2 only.

3

In the window for , type Negative Current Collector in the text field.

Negative Electrode

1

In the toolbar, click

.

2

Select Domain 3 only.

3

In the window for , type Negative Electrode in the text field.

1

In the toolbar, click

.

2

Select Domain 4 only.

3

In the window for , type Separator in the text field.

Negative Tab End

1

In the toolbar, click

.

2

In the window for , type Negative Tab End in the text field.

3

Locate the section. From the list, choose .

4

.

5

In the dialog box, type 29 in the text field.

6

Positive Tab End

1

In the toolbar, click

.

2

In the window for , locate the section.

3

From the list, choose .

4

.

5

In the dialog box, type 2 in the text field.

6

7

In the window for , type Positive Tab End in the text field.

Negative Current Collector and Tab

1

In the toolbar, click

.

2

In the window for , locate the section.

3

Under , click

.

4

In the dialog box, in the list, choose and .

5

6

In the window for , type Negative Current Collector and Tab in the text field.

Positive Current Collector and Tab

1

In the toolbar, click

.

2

In the window for , locate the section.

3

Under , click

.

4

In the dialog box, in the list, choose and .

5

6

In the window for , type Positive Current Collector and Tab in the text field.

Metal Foil Domains

1

In the toolbar, click

.

2

In the window for , locate the section.

3

Under , click

.

4

In the dialog box, in the list, choose and .

5

6

In the window for , type Metal Foil Domains in the text field.

1

In the toolbar, click

and choose .

2

In the window for , type Cell Voltage in the text field.

3

Locate the section. In the text field, type liion.phis0_ec1.

4

In the field, type V.

5

Select the check box.

6

In the associated text field, type Cell Voltage.

General Projection - Negative

Now add General Projection operators that will be used to integrate the amount of lithium along the electrode depth (the z direction).

1

In the toolbar, click

and choose .

2

In the window for , type General Projection - Negative in the text field.

3

In the text field, type genproj_neg.

4

Locate the section. From the list, choose .

General Projection - Positive

1

Right-click and choose .

2

In the window for , type General Projection - Positive in the text field.

3

In the text field, type genproj_pos.

4

Locate the section. From the list, choose .

Add Copper and Aluminum from the built-in materials.

1

In the toolbar, click

to open the window.

2

Go to the window.

3

In the tree, select and .

4

Click in the window toolbar.

Use the Battery Material Library to set up the material properties for the electrolyte and electrode materials in the pouch cell.

1

Go to the window.

2

In the tree, select and .

3

Click in the window toolbar.

4

In the tree, select .

5

Click in the window toolbar.

6

In the toolbar, click

to close the window.

Aluminum (mat1)

Assign the materials to the corresponding battery domains.

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

Graphite Electrode, LixC6 MCMB (Negative, Li-ion Battery) (mat3)

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

LMO Electrode, LiMn2O4 Spinel (Positive, Li-ion Battery) (mat4)

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

LiPF6 in 3:7 EC:EMC (Liquid electrolyte, Li-ion Battery) (mat5)

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

Lithium-Ion Battery (liion)

Start by adding the separator domain to the battery.

1

In the window, under right-click and choose .

2

In the window for , locate the section.

3

From the list, choose .

Now set up the physics in the porous electrodes and current collectors.

Porous Electrode - Negative

1

In the toolbar, click

and choose .

2

In the window for , type Porous Electrode - Negative in the text field.

3

Locate the section. From the list, choose .

4

Locate the section. From the list, choose .

5

Locate the section. In the εs text field, type epss_neg.

6

In the εl text field, type 1-epss_neg.

Particle Intercalation 1

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

In the rp text field, type rp_neg.

Porous Electrode Reaction 1

1

In the window, click .

2

In the window for , locate the section.

3

In the i0,ref(T) text field, type i0ref_neg.

Porous Electrode - Positive

1

In the toolbar, click

and choose .

2

In the window for , type Porous Electrode - Positive in the text field.

3

Locate the section. From the list, choose .

4

Locate the section. From the list, choose .

5

Locate the section. In the εs text field, type epss_pos.

6

In the εl text field, type 1-epss_pos.

Particle Intercalation 1

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

In the rp text field, type rp_pos.

Porous Electrode Reaction 1

1

In the window, click .

2

In the window for , locate the section.

3

In the i0,ref(T) text field, type i0ref_pos.

1

In the toolbar, click

and choose .

2

In the window for , locate the section.

3

From the list, choose .

Electric Ground 1

1

In the toolbar, click

and choose .

2

In the window for , locate the section.

3

From the list, choose .

Electrode Current 1

1

In the toolbar, click

and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

Locate the section. In the Is,total text field, type I_1C*C_rate.

5

In the φs,bnd,init text field, type 4[V].

Initial Cell Charge Distribution 1

1

In the toolbar, click

and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

In the SOCcell,0 text field, type SOC_start.

5

In the Qcell,0 text field, type Q_cell.

Negative Electrode Selection 1

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

From the list, choose .

Positive Electrode Selection 1

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

Set up the mesh for the model. Use a mapped mesh on boundary and swept mesh for rest of the geometry.

1

In the toolbar, click

and choose .

2

Select Boundary 20 only.

1

In the toolbar, click

.

2

In the window for , locate the section.

3

toggle button.

1

Right-click and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

Locate the section. From the list, choose .

5

In the text field, type 15.

6

In the text field, type 3.

1

In the window, right-click and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

Locate the section. In the text field, type 4.

1

Right-click and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

Locate the section. From the list, choose .

5

In the text field, type 15.

6

In the text field, type 3.

7

Select the check box.

8

.

The finalized mesh should now look as follows.

Parametric Sweep

1

In the toolbar, click

.

2

In the window for , locate the section.

3

4

In the table, enter the following settings:


Parameter name	Parameter value list	Parameter unit
C_rate (C-rate during simulation)	1 4	1

Step 2: Time Dependent

1

In the window, click .

2

In the window for , locate the section.

3

In the text field, type range(0,sim_time/2,sim_time).

4

In the toolbar, click

.

Potential in Negative Current Collector and Tab

The following steps create the plot of the potential at the negative current collector and tab.

1

In the toolbar, click

and choose .

2

In the window for , type Potential in Negative Current Collector and Tab in the text field.

3

Locate the section. From the list, choose .

4

From the list, choose .

5

Locate the section. Select the check box.

6

Click to expand the section. Select the check box.

7

In the text field, type 4.

1

Right-click and choose .

2

In the window for , locate the section.

3

In the text field, type phis.

1

Right-click and choose .

2

In the window for , locate the section.

3

From the list, choose .

4

In the toolbar, click

.

5

button in the toolbar.

Potential in Negative Current Collector and Tab

Duplicate the plot to get the potential at the positive current collector and tab.

Potential in Positive Current Collector and Tab

1

In the window, right-click and choose .

2

In the window for , type Potential in Positive Current Collector and Tab in the text field.

3

In the window, expand the node.

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

From the list, choose .

4

In the toolbar, click

.

5

button in the toolbar.

Relative Current Density Across Separator

Plot the relative current density across the separator using a slice plot.

1

In the toolbar, click

and choose .

2

In the window for , type Relative Current Density Across Separator in the text field.

3

Locate the section. From the list, choose .

4

From the list, choose .

1

Right-click and choose .

2

In the window for , locate the section.

3

In the text field, type liion.IlMag/(I_1C*C_rate/(H_cell*W_cell/2)).

4

Locate the section. From the list, choose .

5

From the list, choose .

6

In the text field, type L_neg_cc/2+L_neg+L_sep/2.

7

In the toolbar, click

.

8

button in the toolbar.

Relative Current Density Across Separator

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

4

In the toolbar, click

.

Utilization (Relative Capacity Thruput)

1

In the toolbar, click

and choose .

2

In the window for , type Utilization (Relative Capacity Thruput) in the text field.

3

Locate the section. From the list, choose .

4

From the list, choose .

5

Locate the section. Select the check box.

1

Right-click and choose .

2

In the window for , locate the section.

3

In the text field, type genproj_pos(at(0,liion.cs_average)-liion.cs_average)*epss_pos*F_const*H_cell*W_cell/2/(I_1C*C_rate*t).

1

Right-click and choose .

2

Select Boundary 16 only.

3

In the toolbar, click

.

4

button in the toolbar.

Utilization (Relative Capacity Thruput)

1

In the window, click .

2

In the window for , locate the section.

3

From the list, choose .

4

In the toolbar, click

.

Battery Voltage Probe Plot

1

In the window, under click .

2

In the window for , type Battery Voltage Probe Plot in the text field.

3

In the toolbar, click

.

4

button in the toolbar.