轻度过放模式下钛酸锂电池性能及热安全性

Thermal behavior of lithium titanate based Li ion batteries under slight over-discharging condition

钛酸锂(LTO)电池因其优良的循环寿命、倍率性能和热安全性而备受青睐,然而关于电滥用和热滥用等对其电化学性能和热安全性的影响报道较少。本文以某商用圆柱形18650钛酸锂电池为实验对象,利用电化学工作站和加速量热仪(ARC)研究了以不同倍率的电流对钛酸锂电池进行轻度过度放电的工况(0.5 C、1 C、2 C、5 C、1 C 100圈循环)下其电学性能和热安全性特征。此外还进一步采用了“top-down”方式将上述电池拆解并分离出正负极材料,并利用X射线衍射(XRD)和扫描电子显微镜(SEM)从微观角度剖析电极材料结构的变化。实验结果表明:①5 C及以下倍率单次过度放电对钛酸锂电池内阻的影响可忽略,而多次过放循环会大大加速电池的老化,表现为能量保持率快速下降和内阻增加,然而其热安全性未现明显下降;②大倍率(5 C)过度放电会显著降低钛酸锂电池的热安全性,表现为自产热起始温度(T_(1))降低,同时热失控过程中最高温度(T_(3))升高。负极钛酸锂材料颗粒的部分破碎粉化,以及负极表面生成不均匀的SEI膜是导致电池过度放电后热稳定性下降的主要因素。本研究揭示了过度放电对钛酸锂电池性能和安全性的潜在危害,对其安全应用具有科学指导意义。

Lithium titanate(LTO)batteries are well-known for their long cycle life,good rate performance,and thermal safety.However,few studies reported the effects of electric and thermal abuse on the electrochemical performance and thermal safety of LTO batteries.In this study,the electrical and thermal safety properties,as well as the microstructure of electrode materials of certain types of commercial cylindrical 18650 LTO batteries were studied under a series of slight over-discharging conditions at various current rates(0.5 C,1 C,2 C,5 C,and 1 C 100 cycles)with the aid of an electrochemical workstation and accelerating rate calorimeter.Moreover,we then adopted a"top-down"strategy to disassemble the LTO batteries to obtain their anode and cathode materials.We also examined the structure of such electrode materials via an X-ray diffractometer and scanning electron microscope from a microscopic point of view.Related results have illustrated that(1)the internal resistances of LTO batteries changed little after the first cycle of over-discharging with current rates of no more than 5 C.While manifold cycles of over-discharging dramatically accelerated the aging of LTO batteries,reflected by the quick drop in their energy retention rate and the rise in internal resistance.However,the thermal safety character of the batteries with manifold cycles of over-discharging has shown no significant change.(2)The thermal safety of LTO batteries can be significantly reduced after over-discharging treatment at a large current rate(5 C),with the onset temperature of self-heating(T_(1))decreasing and the maximum temperature(T_(3))in the thermal runaway process rising simultaneously.The partial cracking and pulverizing of LTO particles and the uneven SEI generated on the anode material are the leading causes for the deterioration of the thermal safety character of LTO batteries under over-discharging conditions.This research has illustrated the potential risk of over-discharging on the electrochemical performance and thermal safety of LTO batteries.We hope this work could bring attention to the safe application of LTO batteries.