| Lithium ion batteries demonstrated many advantages,so it has been used more and more widely,especially in the field of digital electronic products and electric vehicles.However,the safety of lithium-ion batteries has been plagued by the further development of lithium-ion batteries.Numerous studies have shown that a large amount of heat cannot be effectively dissipated,which can easily lead to unsafe behaviors such as rupture,burning and explosion.In response to this problem,this paper explores a self-blocking polypyrrole(PPy)-based new temperature-sensitive electrode for lithium-ion batteries,which can effectively prevent the battery from thermal runaway.This improves the safety performance of the battery and lays a theoretical foundation for building a safer lithium-ion battery.The specific research work of this paper is as follows:(1)After doping the intrinsic conductive polymer(ICP),the room temperature conductivity is greatly improved,and some of them will drop sharply after thermal dedoping,showing a good positive temperature coefficient resistance(PTC-R)effect.In this paper,PPy doped with dodecylbenzenesulfonate ion(DBS-),p-toluenesulfonate ion(TOS-)and chloride ion(Cl-)was prepared by chemical methods.And studied the structure,morphology,thermal stability and PTC-R characteristics of PPy/DBS',PPy/TOS' and PPy/Cl-.SEM results show that PPy/DBS-has a bulk structure and a large size,while PPy/TOS-and PPy/Cl-have a spherical structure and a relatively small size.TG test results show that there is obvious weightlessness around 90?.On the one hand,it may be related to the loss of water absorbed in PPy at 90?.On the other hand,it may be related to the dedoping of doped ions,while PPy/Cl-has the most weight loss and the degree of dedoping may be the largest.The resistance-temperature(R-T)test results show that the resistance of PPy/DBS-,PPy/TOS-and PPy/Cl-all rise sharply to about 104? due to dedoping and have a significant PTC effect.It shows that PPy has the possibility of being a temperature-sensitive electrode.(2)PPy powder doped with three different ions(PPy/DBS-,PPy/TOS-,PPy/Cl-)were mixed with polyvinylidene fluoride(PVDF)at a mass ratio of 9:1 and an appropriate amount of N-methyl-2-pyrrolidone(NMP)was added dropwise to mix well.A PPy coating with a thickness of 5 ?m was coated on the aluminum foil.After drying,LiNi0.6Co0.2Mn0.2O2(622)active material was coated on it to prepare a composite electrode with Al/PPy/622(622-PPy)sandwich structure.The electrochemical performances of the 622-PPy/DBS-,622-PPy/TOS-and 622-PPy/Cl-composite electrodes at room temperature and high temperature were tested respectively.The test results at room temperature show that the three composite electrodes 622-PPy/DBS-,622-PPy/TOS-and 622-PPy/Cl-are very similar to the pure 622 electrode without PPy coating.The lower composite electrode and the pure 622 electrode showed similar charge and discharge performance.At a current density of 50 mA/g,the difference in discharge specific capacity of the three composite electrodes and the pure 622 electrode was less than 4%.However,when the battery was heated to about 90?,the three composite electrodes all exhibited obvious PTC behavior.The rapid rise of the battery's resistance caused a large ohmic instant and the specific capacity of the battery was greatly reduced.In particular,the voltage of the 622-PPy/Cl-composite electrode immediately fell to the cut-off voltage at 90?,that is,the electrode reaction was turned off.The specific capacity of the 622-PPy/Cl-composite electrode dropped sharply to 0.04 mAh/g,accounting for only 0.2%of the initial specific capacity at room temperature.The pure 622 electrode can still exert a specific discharge capacity of 161.8 mAh/g,which is only 1.7%lower than that at room temperature.This shows that the three composite electrodes have excellent high-temperature safety performance,which is expected to protect the battery from thermal runaway and also provides a great possibility for building a safer lithium-ion battery. |
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