The Study On The Properties Of Cathode

In the experiment, we used LiNi0.8Co0.2O2 / LiCoO2 as active materials to make electrodes by casting respectively. The emphasis of this article is to discuss the influences of species of the carbon black and the content of PVDF and carbon black on the performances of cathode. And the compatibility of cathode to electrolyte was studied. At last, the electrochemical properties of the 18650 cell discharged at different rate were discussed.The results showed: the PVDF has similar influences on the electrochemical performances of LiNi0.8Co0.2O2 and LiCoO2 compounds respectively. The lithium-ion cell has the best cycling performance contents 4% PVDF, when the LiNi0.8Co0.2O2 compounds exhibited a good performance whose first discharge capacity is 190 mAh/g, first coulomb efficiency is 91% and Ac impedance plots is 32Ω,and the LiCoO2 compounds obtained first discharge capacity which is 190mAh/g, first coulomb efficiency which is 91% and Ac impedance plots which is 30Ω.Comparisons of the acetylene black and conductive carbon black and scale graphite added acetylene black(1:2), the conductive carbon black is the best conductive material which was used to improve the electrochemical properties of the cathode. The influence of cathode conductive agent content to the battery's performance and AC impedance were investigated. The results suggested that the influence on LiNi0.8Co0.2O2 and LiCoO2 compounds were similar. When the composition of carb- on black is 3% the lithium ion cell has the best performance. Cyclic voltammograms of LiNi0.8Co0.2O2 and LiCoO2 compounds showed good cycling performance. The determination result of AC impedance spectrum of lithium ion battery shows that the variation value of cathode charge transfer impedance is relative to the conductive agent content in the cathode. AC impedance spectrum of the cathodes after the twen- tieth cycle were much more to increase by twice than the AC impedance spectrum of the cathodes after the first cycle, the other that have more weight ratio of carbon black increased by one time. The high rate discharge ability was improved by adding the carbon black to the cathode.The investigations to the interfacial reactions between cathode to electrolyte show that the compatibility of cathode to electrolyte (1mol/L LiPF6/ (EC+DEC +DMC)) is best when the ratio of mixed solvent (EC:DEC:DMC) is 1:1:1.When the 18650 cell discharged at different rate, it had the different performances. During electrochemical charge/discharge cycling, it exhibited litter capacity fade rate and voltage plateaus, which discharge at 0.5C below. When the battery was discharged at high rate, its discharge capacity was decreased with the increase of current.