A novel embedded method for in-situ measuring internal multi-point temperatures of lithium ion batteries
Graphical abstract
Introduction
Due to the high energy density and long cycle life, Li-ion batteries (LIBs) are regarded as optimal energy storage devices for storing the renewable energy, and they have been widely used in many applications, such as portable electronic equipment, electric and hybrid electric vehicles. However, the explosion and self-ignite occur frequently in many applications [1,2]. Thus, thermal safety has become a critical issue in LIBs.
The self-temperature rise [[3], [4], [5]] can result in the performance degradation of LIBs, even self-ignite and explosion during charging and discharging processes. Therefore, it is important to monitor the temperature to ensure LIBs in the safe operation. Recently, a review paper reports some methods for measuring temperatures of LIBs [6]. The main methods could be used for monitoring temperature variations of LIBs, including thermocouple [[7], [8], [9], [10]], thermo-resistive [[11], [12], [13], [14]], infrared camera [5,[15], [16], [17]] and optical fiber [[18], [19], [20]]. The published temperature measurement methods for LIBs are showed in Table 1. The external or internal temperature variations of LIBs can be obtained. Due to thermal conduction, there is remarkable difference between the external and internal temperatures of LIBs [21,22], especially under high current rate or over-charge/discharge of extreme conditions. Using external temperature measurement, it is a risk if the actual temperature in the LIBs is underestimated [5,8,16,17,19]. Thus, the internal temperature measurement in the LIBs is highly important [[10], [11], [12], [13],18,22,23].
For measuring internal temperature of batteries, it is inevitable that the inserted sensors would have an impact on the battery performance. In order to minimize the impact of the inserted sensors in LIBs, three key requirements should be satisfied for the sensors [6,10]: (I) Minimizing the impact of the inserted sensor on the ionic flow between electrodes; (II) Avoiding the sensor reacting with or dissolving in the electrolytes; (III) Compatible with the battery assembly process. Since the large-size LIBs are applied widely, the thermal safety issue is becoming a critical problem due to the drastic temperature issues and nonuniform temperature distribution. The single-point internal temperature methods [10,12,13] are insufficient to fulfill safe operating temperature range for practical applications. There is an urgent demand for developing multi-point temperature methods. However, the traditional measured methods, including multi-point thermocouples [22,23] and optical fibers [18,19,25], would lead to damage in the electrodes and separators due to the incompatibility with the soft and thin electrodes and separators. Therefore, the thin film sensors [11,12,26] may be an option for internal temperature measurement of LIBs. The inserted thin film sensor was attached to one electrode, which has an impact on the ionic flow between the positive and negative electrodes. Thus, the lithium plating and capacity fade would be observed. Some methods were proposed to minimize the impact of the inserted sensors on the ionic flow. The thin film sensors were located between the electrode and aluminum laminated films [10], so that the ionic flow would not be affected between electrodes. However, the sensors located near the LIB surface could not monitor the actual internal temperature. And, the unexpected effects on the ionic flow between the electrodes have not been well addressed [26].
In the paper, a novel method was developed to integrate multi-point sensor with the electrode, which is compatible with the battery assembly process. The integrated battery was conducted by cyclic test and electrochemical impedance spectroscopy (EIS) test. The results exhibited that the integrated battery presented stable capacity in 100 cyclic tests. The inserted sensor had limited impact on the battery performance. According to the in-situ multi-point internal temperature experiments, the stability of the sensors was also verified. The novel method can offer a platform in analyzing failure mechanism and improving safety of Li-ion battery.
Section snippets
Thin film sensor fabrication and calibration
The resistance temperature detectors (RTDs) consist of temperature sensors, and the resistance increases when temperature rises. The metal platinum was selected due to good stability, high accuracy, a linear behavior and a wide operating temperature range (−260 to 960 °C) [6,27]. The RTD can be fabricated in many ways, and the thin films can be applied to measure the internal temperature of LIBs. The small size of thin films presents faster response and is compatible with the battery assembly
The effect of thin film sensor on the battery
A cyclic test was conducted at the rate of 0.2C between 2.5 V and 4.2 V. As shown in Fig. 3(c), the discharge capacity of the integrated battery could remain stable within 100 cycles. The discharge capacity was equal to 402 mAh approximately, which reached 95.7% of the theoretical capacity (420 mAh). In addition, the Coulombic efficiency also reached 99.91%. Furthermore, the comparison of the voltage-capacity curves between the normal and integrated batteries are displayed in Fig. 3(a). The
Conclusion
In the paper, a novel method for integrating the multi-point sensor with LIBs was proposed. The electrochemical performance of the integrated battery was evaluated by the cyclic test and EIS. The integrated battery had a stable discharge capacity and Coulombic efficiency before 100 cycle tests. And the inserted thin film sensor had limited impact on performance of the LIBs under long-term cyclic test. The thin film sensor can measure the variation of internal temperature in real-time under
CRediT authorship contribution statement
Shengxin Zhu: Writing - original draft, Data curation, Visualization. Jindong Han: Data curation, Visualization. Hong-Yan An: Investigation, Validation. Tai-Song Pan: Resources. Yi-Min Wei: Resources. Wei-Li Song: Conceptualization. Hao-Sen Chen: Conceptualization, Project administration. Daining Fang: Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors gratefully acknowledge the financial support from Beijing Municipal Science and Technology Commission (No. Z191100002719007), National Key Research and Development Program of China (No. 2018YFB0104402) and National Natural Science Foundation of China (Nos. 11672341). This work is also partially supported by the State Key Laboratory of Explosion Science and Technology (No. ZDKT18-03).
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