Temperature is the key monitoring measurement of lithium-ion battery condition monitoring, and it plays a very important role in battery life prediction, thermal runaway warning, and thermal management decision making. Therefore, this paper mainly summarizes the research status of internal temperature monitoring (ITM) method for lithium-ion batteries. Firstly, the lithium-ion battery ITM methods are divided into three types, namely temperature sensor, battery thermal model, and electrochemical impedance spectroscopy (EIS) types. The measurement principle, implementation difficulty, and measurement effect of the above ITM methods are different. The advantages and disadvantages of these methods are analyzed and pointed out. In particular, the five latest ITM methods based on negative temperature coefficient (NTC) temperature sensor, optical fiber sensor, ultrasonic wireless sensor, electrochemical thermal coupling model, and multi-frequency EIS are introduced. Finally, based on the existing research, the future development trend of the above five methods is discussed.

Lithium-ion batteries (LIBs) are widely used in the fields of consumer electronics, new energy vehicles, and grid energy storage due to their high energy density and long cycle life. However, how to effectively evaluate the State of Charge (SOC), State of Health (SOH), and overcharging behavior of batteries has become a key issue in improving battery safety and lifespan. Acoustic sensing technology, as an advanced non-destructive monitoring method, achieves real-time monitoring of the internal state of batteries and accurate evaluation of key parameters through ultrasonic testing technology and acoustic emission technology. This article systematically reviews the research progress of acoustic sensing technology in SOC, SOH, and overcharge behavior evaluation of LIBs, analyzes its working principle and application advantages, and explores future optimization directions and industrialization prospects. Acoustic sensing technology provides important support for building efficient and safe battery management systems.

The solid-electrolyte-interphase (SEI) plays a critical role in lithium-ion batteries (LIBs) because of its important influence on electrochemical performance, such as cycle stability, coulombic efficiency, etc. Although LiOH has been recognized as a key component of the SEI, its influence on the SEI and electrochemical performance has not been well clarified due to the difficulty in precisely controlling the LiOH content and characterize the detailed interface reactions. Here, a gradual change of LiOH content is realized by different reduction schemes among Co(OH)₂, CoOOH and CoO. With reduced Co nanoparticles as magnetic “probes”, SEI characterization is achieved by operando magnetometry. By combining comprehensive characterization and theoretical calculations, it is verified that LiOH leads to a composition transformation from lithium ethylene di-carbonate (LEDC) to lithium ethylene mono-carbonate (LEMC) in the SEI and ultimately results in capacity decay. This work unfolds the detailed SEI reaction scenario involving LiOH, provides new insights into the influence of SEI composition, and has value for the co-development between the electrode materials and electrolyte.