基于光纤布拉格光栅传感的锂电池内部状态原位监测

In-situ Monitoring of the Internal Status of Lithium Batteries Based on Fiber Bragg Grating Sensors

锂电池内部的应力和温度变化难以监测是影响电池安全运行的最大隐患,提出采用光纤布拉格光栅传感技术,在锂电池内部植入光栅对电池阳极的温度和应力变化信息进行实时采集,实现了对锂离子电池阳极的原位监测,建立了电信号与光学传感信号之间的联系。实验结果表明,锂电池工作循环中,锂离子的脱嵌和嵌入会引起温度变化,对应传感器波长偏移达100 pm,温度上升11.1℃;在排除温度因素的影响后,循环电流的跳变会引起阳极收缩,产生的应力使波长漂移达21.96 pm,约为18.3με。此外,研究了不同充放电速率对电池的影响,10 mA电流比2.5 mA电流时温度提高了2.8倍,应力提高了4.4倍。所植入光栅监测系统既可以高精度地测量电化学反应引起的温度、应力变化,同时解调速度快,有利于实时、准确监测锂电池的热失控及形变鼓包故障,研究结果有望为锂电池的安全使用提供有效的实验依据。

As one of the most important energy storage technologies today,the safety and reliability of lithium batteries have always been of great concern.The thermal stability and pressure stability of lithium batteries are important parameters that affect their safe and reliable operation.The internal electrochemical reactions will cause changes in temperature and stress during operation.Abuse of lithium batteries can cause rapid increases in temperature and stress of electrodes,leading to degradation of battery performance and even safety accidents such as combustion or explosion.Therefore,real-time monitoring of internal temperature and stress changes in lithium batteries is crucial for the long-term safe and stable operation of lithium batteries.However,current monitoring methods used for temperature and stress inside lithium batteries just focus on single parameters or external measurements,which have problems such as poor resolution and limited accuracy,making it difficult to monitor the changes inside the battery.In order to improve the healthy level of lithium-ion batteries monitoring,this paper proposes to use fiber Bragg grating sensing technology to monitor the changes.The gratings are implanted to collect real-time temperature and stress changes of the battery anode,realizing an optical channel for in-situ monitoring of the lithium-ion battery anode.Furthermore,combined with the battery test system,the connection between electrical and optical sensing signals is established.In the system,the temperature sensitivity of the FBG sensors is 9.3 pm/℃,and the stress sensitivity is 1.2 pm/με.The FBG sensors are mounted in different ways to achieve accurate measurement of dual parameters.Both ends of FBG1 are fixed for strain measurement.FBG2 fixes single end to monitor temperature and functions as temperature compensation for FBG1 at the same time.FBG3 is outside the battery,which is used to measure the external temperature of working environment.The experimental results show that the FBG sensors can remain good sensing performance at 400℃.The implantation has no effect on pouch cell performance,nor does it affect the sensing performance of FBG sensors.During the working cycles of lithium batteries,the detachment and embedding of lithium ions can cause temperature changes,resulting in a sensor wavelength shift of 100 pm,which means temperature increases by 11.1℃.The coefficient of thermal expansion of anode is 25.5με/℃.After temperature compensation,the stress change of anode can be observed,indicating that the change in stress is influenced by current.In other words,the hop of current can cause the anode to contract and the resulting stress will result in a wavelength drift of 21.96 pm at most,which is approximately 18.3με.According to our research,different charge and discharge rates have different effects.The faster the rate,the greater the variations in temperature and stress.The temperature change is 2.8 times and the stress is 4.4 times higher at 10 mA than at 2.5 mA.If the rate of charge or discharge further increases to 50 mA,the operating temperature will exceed 45℃.After 300 cycles at 45℃,the volume expansion rate of battery is about 10%,and the battery is likely to malfunction.The implantable grating monitoring system in this paper can not only measure the temperature and stress changes caused by electrochemical reaction with high precision,but also has fast demodulation speed,which is conducive to real-time and accurate monitoring of the thermal runaway and deformation bulge failure of lithium batteries.The research results are conducive to quantifying and evaluating the possible thermal runaway and volume expansion problems in the electrochemical process,which is expected to provide an effective experimental reference for the safe use of lithium batteries.