title: Polythiophene-Wrapped Olivine NaFePO4 as a Cathode for Na-Ion Batteries.
abstract: The surface of olivine NaFePO4 was modified with polythiophene (PTh) to develop a high-performance cathode material for use in Na-ion batteries. The Rietveld refinement results of the prepared material reveal that PTh-coated NaFePO4 belongs to a space group of Pnma with lattice parameters of a = 10.40656 Å, b = 6.22821 Å, and c = 4.94971 Å. Uncoated NaFePO4 delivers a discharge capacity of 108 mAh g(-1) at a current density of 10 mA g(-1) within a voltage range of 2.2-4.0 V. Conversely, the PTh-coated NaFePO4 electrode exhibits significantly improved electrochemical performance, where it exhibits a discharge capacity of 142 mAh g(-1) and a stable cycle life over 100 cycles, with a capacity retention of 94%. The NaFePO4/PTh electrode also exhibits satisfactory performance at high current densities, and reversible capacities of 70 mAh g(-1) at 150 mA g(-1) and 42 mAh g(-1) at 300 mA g(-1) are obtained compared with negligible capacities without coating. The related electrochemical reaction mechanism has been investigated using in situ X-ray absorption spectroscopy (XAS), which revealed a systematic change of Fe valence and reversible contraction/expansion of Fe-O octahedra upon desodiation/sodiation. The ex situ X-ray diffraction (XRD) results suggest that the deintercalation in NaFePO4/PTh electrodes proceeds through a stable intermediate phase and the lattice parameters show a reversible contraction/expansion of unit cell during cycling.
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.|Korea University of Science and Technology , 217 Gajeong-roYuseong-gu, Daejeon 34113, Republic of Korea.
authors.forename: Ghulam
authors.initials: G
authors.lastname: Ali
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.
authors.forename: Ji-Hoon
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.|Korea University of Science and Technology , 217 Gajeong-roYuseong-gu, Daejeon 34113, Republic of Korea.
authors.forename: Dieky
authors.initials: D
authors.lastname: Susanto
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.
authors.forename: Seong-Won
authors.initials: SW
authors.lastname: Choi
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.
authors.forename: Byung Won
authors.initials: BW
authors.lastname: Cho
authors.affiliation: Department of Energy and Materials Engineering, Dongguk University , Seoul 04620, Republic of Korea.
authors.forename: Kyung-Wan
authors.initials: KW
authors.lastname: Nam
authors.affiliation: Center for Energy Convergence Research, Korea Institute of Science and Technology , Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea.|Korea University of Science and Technology , 217 Gajeong-roYuseong-gu, Daejeon 34113, Republic of Korea.
authors.forename: Kyung Yoon
authors.initials: KY
authors.lastname: Chung
keywords: Fe valence; Na-ion batteries; X-ray absorption spectroscopy; olivine NaFePO4; polythiophene