Since thermal safety is a significant topic in Li-ion batteries (LIBs), monitoring the internal temperature can offer valuable information to clarify the mechanism of heat accumulation. However, it is a challenge to measure the internal temperature of LIBs due to the harsh electrochemical environment and unexpected impacts on the battery performance. For addressing such issue, a novel internal temperature measurement technique with a minimized influence on the electrochemical performance is developed for in situ measuring the internal temperature of the LIB. In the specific design, one end of the LIB is sealed with a BaF₂ optical glass, through which the infrared camera is allowed for real-time monitoring the internal temperature during charging and discharging processes. In addition to a stable electrochemical performance in such the visualized LIB, the observation results indicate that the temperatures are different during the charging and discharging processes. A maximum temperature difference 2.0°C between internal and surface of the visualized LIB is observed at the end of discharge process under 2C rate condition. It indicates that internal temperature is more important to analyze the effects of temperature on the thermal safety of the high capacity LIBs. The proposed internal temperature measurement technique could be widely used for analyzing the effects of temperature on the thermal safety of LIBs in further work.

由于热安全性是锂离子电池（LIB）的重要主题，因此监视内部温度可以提供宝贵的信息，以阐明热量积聚的机理。但是，由于恶劣的电化学环境和对电池性能的意外影响，测量LIB的内部温度是一项挑战。为了解决这个问题，开发了一种对电化学性能影响最小的新型内部温度测量技术，用于原位测量LIB的内部温度。在特定设计中，LIB的一端用BaF ₂密封光学玻璃，红外摄像头可通过该玻璃实时监视充电和放电过程中的内部温度。除了在这种可视化的LIB中具有稳定的电化学性能外，观察结果还表明在充电和放电过程中温度是不同的。在2C速率条件下放电过程结束时，观察到的可视化LIB内部和表面之间的最大温差为2.0°C。这表明内部温度对于分析温度对高容量LIB的热安全性的影响更为重要。所提出的内部温度测量技术可被广泛用于分析温度对LIBs热安全性的影响。