Preparation Of Polyaniline Compositesand Application In Lithium Secondary Battery

Polyaniline has been attracted attention widely used in lithium secondary batteries because of its unique advantages such as easy synthesis, low cost, environmentally friendly and excellent electrochemical properties. But the capacity of battery which pure polyaniline used as the cathode was dacay rapidly, and power density was too low, which were important factors that l imited its development. Therefore, polyaniline composites has become a hot topic in rencent years.In this paper, the synthesis conditions were optimized. The study found that polyaniline has the highest yield, doped rate, conductivity and low internal resistance when aniline concentration was 0.7 mol/L, n [(NH4)2SO4] / n(An) = 1.25, hydrochloric acid concentration was 1.5 mol/L. in addition, an two-oxidant system(Mn O2+APS) was also established.The two kinds of PANi/C composites which included emeraldine base and leucoemeraldine base were prepared according to the above-mentioned optimum technology. The FT-IR spectrum show that the absorption peak of quinone structure in leucoemeraldine base had weakened significantly, which indicate had got a better reduction. XRD and SEM test also showed the effect of the compound is ideal. The lithium secondary batteries which the PANi/C composites used as positive electrode were assembled. EIS show that PANi had doped Li Cl O4 in the battery, and had a lower internal res isitance compared with pure PANi. The discharge capacity of batteries used composites as positive electrode had reached as high as 146.9 m Ah/g and 170.9 m Ah/g at 0.2 C rate in the first cycle. After 100 charge-discharge cycles, the capacity of those batteries were still more than the pure PANi whose capacity only reached 73.7 m Ah/g. Besides, the coulombic efficiency of batteries were maintained more than 98%. At the 5 C rate,the discharge capacity were as high as 115.6 m Ah/g and 143.2 m Ah/g respectively in the first cycle. The capacity decay ratio was only 23.4% and 11.0% afer 100 charge-discharge cycles. The results indicate that batteries had a good cycle life and rate performance.PANi/RGO composites were prepared by five kinds of methods. PANi with GO co-reduction and leucoemeraldine reacted with GO were the two of the five methods. In the FT-IR spectrum, the absorption peaks of the oxygen-containing functional group in GO and the quinoid structure in PANi were weakened obviously or disappeared, which indicated that GO and PANi had been got a better reduction. The XRD and SEM tests show that they had higher degree of crystallinity and better compound effect compared with other methods. a series of lithium secondary batteries were fabricated with the composites prepared by the five kinds of methods used as positive electrodes respectively. The EIS and tafel tests show that the two kinds of methods mentioned above had lowest internal resistance, and the electrode reactions were more easy. At the 0.2 C rate, the discharge capacity of the two kinds of batteries were as high as 162.5 m Ah/g and 190.6 m Ah/g respectively in the first cycle. The capacity of batteries were still far surpassed the pure PANi afer 100 charge-discharge cycles. Besides, coulombic efficiency of the batteries were over 98%. At the 5 C rate, charge-discharge tests show the discharge capacity of batteries were reached 127.8 m Ah/g and 143.2 m Ah/g respectively in the first cy cle. After 100 charge-discharge cycles, The capacity decay ratio was only 11% and 16%. The results above show that PANi/RGO composites prepared by two of the five kinds of methods had an excellent cycle life and rate performance.