Amorphous Iron Oxyhydroxide Nanosheets: Synthesis, Li Storage Property and New Model in Electrochemical Impedance Analysis Chen Xu, a,b Yi Zeng, a Xianhong Rui, a Jixin Zhu, b Huiteng Tan, a, Antonio Guerrero Castillejo, c juan toribio bueso, c Juan Bisquer, c Germà Garcia Belmonte, c, * and Qingyu Yan a,b, * a School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore b TUM CREATE Research Centre@NTU, Nanyang Technological University, Singapore 637459, Singapore c Departament de Física, Universitat Jaume I, 12071 Castelló, Spain Corresponding Authors * Qingyu Yan E-mail: alexyan@ntu.edu.sg * Germà Garcia Belmonte E-mail: garciag@uji.es Abstract We present a facile approach to synthesize amorphous iron oxyhydroxide nanosheet from the surfactant-assisted oxidation of iron sulphide nanosheet. The amorphous iron oxyhydroxide nanosheet is porous and has a high surface area of 223 m 2 g -1 . The lithium storage properties of the amorphous iron oxyhydroxide are tested: it is a conversion-reaction electrode material, and it demonstrates superior rate capabilities (e.g. discharge capacities as high as 642 mAhg -1 is delivered at a current density of 2C). In the EIS analysis, a RC subcircuit is set up to model the conversion reaction process. And, the time constant of the RC subcircuit reproduces the hysteresis in the discharge/charge voltage profile, indicating that the conversion reaction has a thermodynamic origin rather than a kinetic limitation. Keywords: amorphous; nanosheet; conversion reaction; EIS analysis.