An in-situ spectroscopy investigation of alkali metal interaction mechanism with the imide functional group
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partment of Chemistry, National University of Singapore, Singapore 117543, Singapore Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore 3 School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore 4 National University of Singapore (Suzhou) Research Institute, Suzhou 215123, China 5 Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Fuzhou 350207, China 6 National Synchrotron Radiation Laboratory, Department of Chemical Physics, University of Science and Technology of China, Hefei 230029, China 7 Department of Physics, National University of Singapore, Singapore 117542, Singapore 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 23 May 2020 / Revised: 26 June 2020 / Accepted: 19 July 2020
ABSTRACT Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups. However, the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically. Here, a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI. The interaction at the alkali/PTCDI interface was probed by in-situ X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations. Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI. Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface. It was found that Na shows a stronger electron transfer effect than Li. Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications.
KEYWORDS perylene-3,4,9,10-tetracarboxylic diimide (PTCDI), lithium storage, organic anode, imide, electron transfer
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Introduction
The current lithium-ion batteries (LIBs) based on graphite anode and inorganic cathode are facing a significant challenge to meet the ever-growing demands for high energy density electricity storage applications due to the limited theoretical capacity and potential resource scarcity [1–4]. To address this challenge, researchers focus their studies on other promising battery systems such as sodium-ion batteries (SIBs) [5], potassiumion batteries (PIBs) [6], lithium metal batteries (LMBs) [7, 8], Li–S and Li–O2 batteries [9] and high-performance electrode materials for next-generation energy storage systems [10–13]. Recently, intensive research efforts have been
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