Study On The Effect Of Some Factors On The Cathode Performance Of Lithium-ion Batteries

In lithium-ion battery, cathode is a key electrode to control battery performance. Cathode controls the charging-discharging characteristics, including discharging platform. Cathode impedance mainly contributes to battery impedance in different temperature environment; Cathode impedance increase is also the main cause of battery cycle fading. But till now, a great deal of research focus on single electrode behavior, while seldom research focuses on cathode behavior of actual battery system. There is little relative basic research of battery technics. However, the research on actual cathode performance is more necessary and practical.In this paper, the relationship among fabricating technics, electrochemical parameter and lithium ion battery performance were discussed, after the review of advance of lithium-ion battery performance and fabricating technics. A good many factors affecting the performance of practical lithium ion battery system were investigated with many physical, chemical and electrochemical detecting means.Stable technical platform is very important for research of fabricating technics, electrochemical parameter and battery performance. We have built a fabricating anddetecting technical platform upon a pilot manufacture line, and it guarantees that we can acquire stable and credible volume data of practical battery performance for basic research of technics.Several means were provided to evaluate cathode material of lithium ion battery. With these means, some lithium cobalt oxide (cathode material) samples were investigated by comparing their common physical and chemical parameter, SEM appearance, particle size distribution etc. According to the result, we point outthat we should consider more about the microstructure and shape of cathode material besides its capacity when we select a cathode material.Cathode of lithium ion battery is a complex porous electrode which is composed of solid powder material and polymer binder; there are many macro holes and micro holes in the electrode. These holes affect the impedance and other electrochemical parameter of cathode, and influence the battery performance. Apart from the intrinsic characteristics of cathode material, the fabricating technical parameters will also affect the cathode and battery performance. After weinvestigate the effect of treating cathode material in different temperature and preparing cathode slurry with different ingredient adding sequence, we find that thecathode material treated in relatively high temperature has suitable particle size, stable crystal structure and compatibility to other materials. Cathode made of this kind of materials will have stable structure and better cycle life. We also find that cathode slurry prepared with slowly and evenly adding process will form cathode with high electrochemical activity, low electrochemical reactivity impedance, better charging-discharging performance and cycle life. When we prepare slurry we should we should disperse every material well, while avoiding micro agglomerate of material powder in slurry.The results of conductive regent experiment show that high performance electrode is the electrode in which the conductive agent is distributed symmetrically. In this cathode, the cathode material will be utilized fully, the electrode density is suitable, and the surface electrochemical reactivity impedance is small and stable. The battery fabricated with this cathode will show good 1C discharge performance and cycle life. We find in experiment that we can detect the inflexion point of impedance cure to judge whether the conductive agent is enough. Using this characteristic of impedance curve, we present a way to determine the best content of conductive agent in an electrode.Different laminating temperature and gap between two rolls of the laminationmachine will affect the cathode performance distinctively in its structure and aggregating status. We present that we should laminate the cathode according to thetemperature between the softening point and melting point of...