Vehicular lithium-ion batteries (LIBs) may suffer from minor damage or defects owing to external mechanical abuse, such as deformation and scratches, during cycling. This study uses non-destructive testing methods to analyze the effects of minor mechanical deformation on the lifetime and performance of commercial 21700 lIBs. Firstly, incremental capacity analysis (ICA) is performed to quantify the charge/discharge performance and cycle aging behavior of LIBs under different deformations. Secondly, X-ray computed tomography (XCT) technology is utilized to qualitatively analyze the internal structure variations of LIBs caused by minor mechanical deformation. Results show that with an increase in mechanical deformation, the internal resistances of LIBs increase, charging curves move to high voltage areas, and peak points of the incremental capacity (IC) curves decrease and move to high voltage areas. Cyclic charge/discharge of LIBs with different deformations show that with an increase in cycles, the capacity and state-of-health (SOH) of mechanically deformed LIBs decrease significantly due to the changes in the internal structure of batteries. Furthermore, the tomographic images of LIBs demonstrate that the increased internal gaps within the electrodes result in the increase of internal resistance, and the mechanism for capacity loss of batteries in the cyclic is revealed.

Dynamic impact safety of lithium-ion batteries (LIBs) is a hot subject. The mechanical-electrical behavior of LIBs under dynamic loading was studied in this study. Drop-weight tests of two types of indenter, namely, round and flat heads, were conducted. Strain rate and state of charge (SOC) effects on the mechanical properties of LIBs under different indenters were fully discussed. The interaction between mechanical performance and electrical behavior was studied. Experiments show that the structural stiffness of batteries increases with strain rate increase but exhibits little effect from SOC. Different indenters have a significant influence on the mechanical behavior of the prismatic LIBs. Under the same impact rate and SOC, the peak load of a flat head is considerably larger than that of a round head. The battery exhibits a hard short-circuit under the impact of a round head and a soft short-circuit under the impact of a flat head. This result shows that the larger the contact area between the indenter and the battery is, the larger the impact load under the same drop-weight and impact rate will be, although the impact safety of the battery does not decrease. The results provide useful insights into the basic understanding of the electromechanical coupling integrity of LIBs.

Lithium-ion batteries (LIBs) inevitably encounter abusive mechanical loading during engineering applications and result in mechanical deformation, internal short circuit, and even thermal runaway. A 18650 LIB under minor mechanical deformation is subjected to cyclic charge/discharge experiments in this study to analyze its aging behavior. Aging mechanism of the battery with minor deformation is qualitatively investigated through the incremental capacity analysis (ICA). ICA, a commonly used method for exploring degradation mechanism of LIBs, can transform flat voltage plateaus into peaks in the capacity increase curve (IC curve). Experimental data during the battery charging/discharging cycle can be used to calculate the IC curve, which can reflect the characteristics of electrochemical changes inside the battery. Results showed that the LIB suffers from deterioration in the state of health (SOH) in the entire charge/discharge cycle upon minor mechanical deformation. Possible explanations for the slight decrease in SOH with the increasing number of cycles in the early stages and the rapid decrease in the charge/discharge capacity in the late stages were provided. However, precise mechanisms for these phenomena require further detailed research. Moreover, damaged cells demonstrate considerably higher temperature increments than original ones. This temperature difference will increase if additional charging/discharging cycles are conducted. This research infers that additional metallic lithium deposits in damaged cells compared with the original ones cause serious exothermic reactions and lead to enhanced heat accumulation.