Polyaniline Derivatives As Cathode Materials For Lithium Ion Batteries: Preparation And Properties

In this work, polyaniline were modified by introducing of two kinds of redox-active couples electro-active group(ferrocene and 2,2,6,6-tetramethylpiperidin-1-yloxy). Two novel aniline derivatives were synthesized successfully, including aniline-ferrocene(An Fc) and aniline-TEMPO(An T). Then, by designing of molecular structure, a triphenylamine derivative 1-N,1-N,4-N-triphenyl-4-N-[4-(N-[4-(N-phenylanilino)phenyl]anilino)ph enyl]benzene-1,4-diamine was synthesiszed which had a high free radical density. The corresponding homopolymers and copolymers(PAn Fc, P(An-co-An Fc)(2:1), P(An-co-An Fc)(3:1), P(An-co-An Fc)(5:1); P(An-co-An T)(1:1), P(An-co-An T)(3:1), P(An-co-An T)(5:1); PFTP) of these aniline and triphenylamine derivatives were prepared by chemical oxidative polymerization. The electrochemical properties and charge/discharge performance of the as-prepared Li-ion battery cathode materials have been studied.The homopolymer of polyaniline-ferrocene derivatives electrode exhibited an obvious voltage plateau at the voltage of about 3.4 V. By contrast with PAn electrode, P(An-co-An Fc) electrodes improved the discharge plateau in the potential range of about 3.0 ~ 4.0 V. In addition, the discharge capacity increased according with an increase in the proportion of aniline-based moiety in the copolymers. At 20 m A·g-1, the initial discharge capacity of PAn Fc, P(An-co-An Fc)(2:1), P(An-co-An Fc)(3:1), P(An-co-An Fc)(5:1) and PAn electrodes were 35.5, 61.5, 88.2, 104.9 and 108.2 m Ah·g-1, the discharge capacity retention were 92.1 %, 85.6 %, 76.3 %, 67.4 % and 58.5 % after 30 cycles. The results showed that voltage plateau and cycle performance were improved, these excellent electrochemical performances were ascribed to the introducing of the redox reversible and the stable redox-active couples of ferrocene-based moiety into polyaniline skeleton and the improvement of particle morphology was due to the increased distance between polymer chains by molecular structure design.Comparing with PAn electrode, P(An-co-An T) electrodes displayed an improved charge plateau in the potential range of about 3.5 ~ 4.0 V, and the improvement was more apparent with an increase proportion of An T-based moiety in the copolymers. At 20 m A·g-1, the initial discharge capacity of P(An-co-An T)(1:1), P(An-co-An T)(3:1), P(An-co-An T)(5:1) and PAn electrodes were 44.2, 60, 77.3 and 94.3 m Ah·g-1, the discharge capacity retention were 87.1 %, 82.7 %, 78.9 % and 67.1 % after 20 cycles. The results indicted that voltage plateau and cycle performance could be improved by introducing of the redox reversibility and the stable redox-active couples of TEMPO-based moiety into polyaniline skeleton and the agglomeration of PAn was greatly improved which was attritubed to the increased distance between polymer chains by molecular structure design.Poly(1-N,1-N,4-N-triphenyl-4-N-[4-(N-[4-(N-phenylanilino)phenyl]anilino)phenyl]benzene-1,4-diamine)(PFTP) electrode showed three relatively obvious voltage plateau at the voltage of about 3.3, 3.5 and 3.8 V. Comparing with the single voltage plateau of polytriphenylamine(PTPA), multi-plateau could increase the specific capacity. At 20 m A·g-1, the initial discharge capacity of PFTP and PTPA electrodes were 74.2 and 62.3 m Ah·g-1, the discharge capacity retention were 98.25 % and 93.74 % after 50 cycles. SEM measurements demonstrated that PFTP exhibited a more identical, porous and looser morphology in contrast with PTPA. It turned out that PFTP electrode possessed higher initial discharge capacity, more stable capacity retention and smaller particle morphology which were due to polymer’s unique dendritic structure and higher theoretical capacity by molecular structure design.