Mechanical Behavior during Electrochemical and Mechanical Deactivation of an Aged Electrode in a Lithium-Ion Pouch Cell

The mechanical behavior of lithium-ion battery electrodes that undergo a severe capacity decrease are investigated by monitoring the out-of-plane displacement on the external surface of a pouch cell. The capacity degradation does not decrease gradually as a function of time but exhibits distinct behaviors with different causes. These are electrochemical aging during cycling and mechanical injury caused by manufacture failure. In the former case, both the permanent evolution and the anomalous distribution of the displacement accompanied with a consistent decrease of the capacity are correlated to the local deterioration of the adhesion of the material layers. The mechanical injury accelerates the capaci-ty decrease by destroying the electrode structure, which results in a sudden decrease of the surface displacement. If the displacement reaches its limit, only a dynamic fluctuation remains, which reflects the remaining electrochemical process at a low level. As a result, we conclude that the loss of electrical connectivity between the active material layer and the current collector is responsible for the severe capacity degradation. This effect is more pronounced on the anode than the cathode. Both electrochemical cycling and mechanical injury can result in the weakening of the adhesion of the anode material on the current collector.