Study of Mechanical and Thermal Damage of Lithium Ion Battery Separators Advanced Manufacturing and Design Laboratory (AMDL) Douglas Wicker, Mason Pingel, Alex Francis, and Dr. Ilya Avdeev

Objective Courtesy of tesla.com

Experiments Compression of separator

Experiments (cont.) Heating of separator Heat for 1 minute on hot plate One sample at 110°C and second at 135°C Temperature verified with thermal imaging camera

SEM Images of Separator 15kN 30kN 33.0 MPa 66.0 MPa Undamaged 45kN 60kN 100.0 MPa 133.0 MPa 110°C 135°C

Coin Cell Cycling Procedure (After Formation) Building Batteries Coin Cell Cycling Procedure (After Formation) Charge: 1C charge using 1.475 mA to 4.1 V Constant Voltage: hold 4.1 V until current is 0 A Rest: allow the cell to rest for 1 minute Discharge: 5C discharge using -1.151 mA to 2.7 V Repeat x 200 2023 coin cell (1.475 mAh)

Determining 2D Porosity SEM Image Processed Image

Determining 2D Porosity (cont.)

Determining True (3D) Porosity

Cycle Life

Conclusions Porosity decreases rapidly at a threshold of damage then continues to decrease slowly with increasing damage Cycle life and capacity are reduced with decreasing porosity Porosity of 110°C sample similar to low stress level compressed samples *mercury intrusion tests were not conclusive Porosity of 135°C sample similar to high stress level compressed samples

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