Preparation And Electrochemical Performances Of LiV₃O₈Composite Cathodes Based On Conduction Polymers

Since the conduction polymers came out in1970s, it has drawn much attention of a largenumber of scientists because of their high electrical conductivity and other novel physical andchemical properties. If the conduction polymers and cathode materials were combined, itwould not only improve the electronic conductivity of the cathode materials, but also adjustthe structure, morphology, distribution and stability of the particles, and therefore the cathodewith high performance would be obtained. Compared with the traditional cathode material ofLiCoO2for lithium-ion battery, LiV₃O₈has the the advantages of high specific capacity, lowcost, environmentally friendly, and easy preparation. Meanwhile, it has some shortcomingsthose limit its practical application in lithium-ion battery, such as poor cycling stability, andmore charge/discharge platforms. In this work, we mainly study the LiV₃O₈cathodecomposites based on the conductive polymer by the techniques of X-ray diffraction （XRD）,scanning electron microscope （SEM）, transmission electron microscope （TEM）, galvanostaticcharge/discharge test, cyclic voltammetry （CV） and electrochemical impedance spectroscopy（EIS）. The structure, morphology and electrochemical performance of the composite materialswere characterized by these test methods. The main content of our study is as follows:First, the blend lithium salt LiNO₃-LiCl, NH₄VO₃as raw materials, the LiV₃O₈powderwith good crystallinity was obtained through a simple low temperature solvent evaporationmethod. Second, the monomers of aniline, pyrrole and3,4-ethylenedioxythiophene dioxidethiophene were dispersed with LiV₃O₈powder in the deionized water under the ultrasonictreatment. Then the oxidative polymerization will be taken place quickly with the aid of addedthe dopant （HCl, SDS and TOSNa） and initiator （APS and FeCl₃）, and the LiV₃O₈/PAn,LiV₃O₈/PPy and LiV₃O₈/PEDOT composites at different composite ratios were obtained.Finally, a series of LiV₃O₈/C composites, referring as LiV₃O₈/C1, LiV₃O₈/C2and LiV₃O₈/C3,were also obtained by using PAn, PPy, and PEDOT as a carbon source after the compositesincluding the conduction polymers underwent the heating treatment at500°C for5h. Weinvestigate the structure, morphology, charge/discharge capacity, electrochemical reversibility,and electrochemical impedance of these composites through a series of test means. Comparewith the bare LiV₃O₈, it is found that LiV₃O₈/conductive polymer composites have lowerdischarge capacities at the former cycles. But the existence of the polymers may inhibit thephase changes in the electrochemical reaction of LiV₃O₈/conduction polymer composites to a certain extent, and the existence of conduction polymers in the composites play a role ofstructure stabilizer, which make the structure of composites maintain stability. Meanwhile, itcan buffer the volume change effect during the process of Li+intercalation/deintercalation,and decrease the stresses of the meaterials during cycling, thereby improving cyclingperformance of the LiV₃O₈/conductive polymer composites with the appropriate content.Similarly, the structure, morphology, and phase transition of LiV₃O₈/C composites in theelectrochemical reaction changed much because of the experience of the high-temperaturesintering and existence of the amorphous carbon. But the cycling stability of LiV₃O₈/Ccomposites is also better than that of the bare LiV₃O₈material owing to its high crystallinityand excellent volume buffering capability.