The Study Of PTC Electrode Based On PAN And PPY In The Positive Electrode Of Lithium Ion Battery

With the gradual increase in energy density and power density of lithium-ion batteries,their sudden safety problems have also attracted more attention.The survey found that the most important cause of lithium-ion battery safety accidents is thermal runaway.Using the positive temperature coefficient?PTC?electrode is an effective measure to improve its safety performance.The principle of action is to increase the ohmic polarization of the electrode at high temperature to turn off the battery reaction and suppress the thermal runaway of the battery.In this paper,three ultra-thin polymer positive temperature coefficient?PPTC?conductive material layers were prepared on the positive current collector by coating and electrodeposition,and the PPTC safety electrode was prepared by coating the ternary material LiNi_0.5Co_0.2Mn_0.3?NCM523?.The PPTC electrode material and its structure were characterized,and the effects of PPTC safety electrode on the electrochemical performance of lithium ion battery at room temperature and thermal safety performance at high temperature were investigated.The main research contents and conclusions are as follows:?1?Three sets of polyaniline and carbon nanotubes prepared by cast coating method are PAN-CNTs composite PPTC electrodes with a ratio of 8:1,7:2 and 6:3,respectively,and the coating thickness is about 3-5?m.Infrared absorption spectroscopy indicated that the conductive polyaniline was in the intermediate oxidation state;with the increase of CNTs content,the R_ct value in the EIS curve decreased gradually;when the ratio of 7:2 was selected,the PPTC electrode exhibited better electrochemical performance.The high temperature impedance test found that the R_ct value increased by 5.4 times.The results show that the PPTC coated electrode can show good electrochemical stability in the lithium ion battery and excellent thermal safety performance relative to the reference electrode.?2?In order to further reduce the thickness of the PPTC material layer thus increasing the energy density of the battery,three sets of electrodeposited polyaniline PPTC electrodes with different thicknesses were prepared by three-electrode cyclic voltammetry to control the number of scanning turns n,and the deposition thickness was about 1-3?m.Conductive polyaniline prepared by electrodeposition is in an intermediate oxidation state with sulfate doping;with the increase of the number of scanning n of synthetic polyaniline,the R_ct value in the impedance spectrum is gradually increased,and the overall electrochemical performance of the battery is affected.However,the small-rate cyclic charge and discharge is basically stable;the charge transfer impedances of the high-temperature impedance test electrodes PAN/n=8,PAN/n=9,and PAN/n=10 are increased by 6.68 times,4.14 times,and 6.76,respectively,and the safety performance is improved.?3?In order to further reduce the thickness of the PPTC material layer thus improving the electrochemical performance of the battery,three sets of electrodeposited polypyrrole PPTC electrodes with different thicknesses were prepared by three-electrode cyclic voltammetry to control the number of scanning turns,and the deposition thickness was less than 1?m.Infrared absorption spectroscopy indicated that the electrodeposited material was sulfate-doped conductive polypyrrole;when the number of scanning turns was small,the cycle performance and rate performance of the electrodeposited polypyrrole PPTC electrode were slightly improved compared with the reference electrode.When the number of turns n is increased,the cycle stability and rate performance are reduced.The charge transfer impedance of the high temperature impedance test electrodes PPy/n=7,PPy/n=9 and PPy/n=12 is increased by 12.23 times,respectively.13.92times and 7.02 times,the security performance has been further improved.