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Lee, Yongseok,Yoo, Jung-Keun,Oh, Youngseok,Park, Hyunyoung,Go, Wonseok,Myung, Seung-Taek,Kim, Jongsoon The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.36
<P>We report a monoclinic Na2.4V2(PO4)3/poly(3,4-ethylenedioxythiophene) (M-NVP/PEDOT) composite as a novel cathode material for sodium-ion batteries. The active materials were homogenously encapsulated by thin layers of the electro-conductive polymer PEDOT, and X-ray diffraction analysis indicated that the final products were crystallized into a monoclinic structure. The composite exhibited much more outstanding power capability and cyclability than pristine M-NVP. The discharge capacity of the M-NVP/PEDOT electrode was maintained up to ∼109.8 mA h g<SUP>−1</SUP> at 10C (1C = ∼178 mA g<SUP>−1</SUP>), which was ∼9 times higher than that of pristine M-NVP under the same conditions. Moreover, whereas severe capacity degradation was observed for pristine M-NVP, the M-NVP/PEDOT composite delivered ∼81% capacity retention compared with the initial capacity over ∼500 cycles at 1C. In particular, the available capacity of M-NVP/PEDOT was ∼143.3 mA h g<SUP>−1</SUP>, corresponding to ∼2.4 mol Na<SUP>+</SUP> (de)intercalation, which is larger than the reversible capacity of rhombohedral Na3V2(PO4)3, at which only 2 mol Na<SUP>+</SUP> can be (de)intercalated. This unexpectedly high capacity of the M-NVP/PEDOT composite was clearly confirmed through combined studies using several experiments and first-principles calculation.</P>