Sensing the internal temperature of lithium-ion batteries is particularly useful for reliable battery operation as both electrochemistry and mass transport are dictated by local temperature. In this article, we review in operando techniques to monitor the internal temperature of lithium-ion batteries during charging and discharging. We categorize existing techniques into two groups: invasive and non-invasive approaches. Invasive techniques include optical fibers, thermocouples, and resistance temperature detectors as a thermometer. Non-invasive methods cover the temperature estimation techniques, namely electrochemical impedance spectroscopy as well as X-ray thermometry. For both approaches, we review working principle of thermometry, pros and cons of each thermometry, and recent studies to tackle relevant technical challenges. This review provides useful information for internal temperature measurements, offering chances for thermally reliable battery operation.

This study aimed to characterize the mechanism of thermal runaway phenomenon in lithium-ion batteries, which represent secondary cells among energy storage devices. Thermal runaway reaction was induced by heating 18650 cells with 5%, 40%, and 80% state of charge (SOC). We divided the thermal runaway of the battery into three stages and discussed the physical measurements that distinguish each stage. We also provided a visual comparison and thermal image of the characterized exhaust gases in all stages. The state of charge and the amount of heat generated by thermal runaway were proportional, and in the third stage of thermal runaway, where the highest mass transfer occurred, 40% of SOC released gas for 13 seconds and 80% of SOC emitted gas and flame for 3 seconds. In addition, a temperature and voltage measurement method that can predict the thermal runaway phenomenon of a battery is presented.

Many countries are trying to overcome global warming due to greenhouse gas emissions, such as CO₂. In particular, the regulation on CO₂ emissions of internal combustion engine vehicles has become strictly important. Thus, the automobile companies are putting more effort for improving the manufacturing of the battery, which is the main power supply of electrical vehicles. In the electrode cutting process, laser cutting has been actively discussed to solve problems originating from the conventional electrode cutting processes. However, there is a lack of research considering the effect of thickness of the active material on laser cutting. In this paper, the effect of thickness of the active material on laser cutting of electrodes is analyzed. First, the cut electrodes are observed through a scanning electron microscope (SEM). Next, the kerf width and clearance width of the electrodes are measured and compared at the same laser parameter. The kerf width and clearance width of relatively thick electrodes are narrowly formed. Finally, the cutting quality of the electrode is compared. A uniform cut edge is observed as the scanning speed increases.