Iron oxide encapsulated in nitrogen-rich carbon enabling high-performance lithium-ion capacitor
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Published online 30 July 2020 | https://doi.org/10.1007/s40843-020-1414-0
Iron oxide encapsulated in nitrogen-rich carbon enabling high-performance lithium-ion capacitor 1†
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Jinhua Zhou , Shuchi Xu , Qi Kang , Lu Ni , Ningna Chen , Xiaoge Li , Chunliang Lu , 1 1 1 1 1* Xizhang Wang , Luming Peng , Xuefeng Guo , Weiping Ding and Wenhua Hou ABSTRACT Lithium-ion capacitors (LICs) could combine the virtues of high power capability of conventional supercapacitors and high energy density of lithium-ion batteries. However, the lack of high-performance electrode materials and the kinetic imbalance between the positive and negative electrodes are the major challenge. In this study, Fe3O4 nanoparticles encapsulated in nitrogen-rich carbon (Fe3O4@NC) were prepared through a self-assembly of the colloidal FeOOH with polyaniline (PANI) followed by pyrolysis. Due to the well-designed nanostructure, conductive nitrogen-rich carbon shells, abundant micropores and high specific surface area, Fe3O4@NC-700 delivers a high capacity, high rate capability and long cycling stability. Kinetic analyses of the redox reactions reveal the pseudocapacitive mechanism and the feasibility as negative material in LIC devices. A novel LIC was constructed with Fe3O4@NC-700 as the negative electrode and expanded graphene (EGN) as the positive electrode. The wellmatched two electrodes effectively alleviate the kinetic imbalance between the positive and negative electrodes. As a result, Fe3O4@NC-700//EGN LIC exhibits a wide operating voltage window, and thus achieves an ultrahigh energy density −1 of 137.5 W h kg . These results provide fundamental insights into the design of pseudocapacitive electrode and show future research directions towards the next generation energy storage devices. Keywords: Fe3O4, carbon, N doping, expanded graphene, lithium-ion capacitor
INTRODUCTION Electrochemical energy storage systems play a crucial role in consumer electronics, automotive, aerospace and sta-
tionary markets. Lithium-ion batteries (LIBs) and supercapacitors (SCs) are currently recognized as two primary promising energy storage systems [1–3]. LIBs can provide −1 a high energy density (100–200 W h kg ) as a result of Faradaic reactions derived from the intercalation of large numbers of Li ions into the active electrode materials. However, the sluggish insertion/extraction of Li ions in the bulk and the accompanied volumetric strain limit −1 their power density (
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