Improved electrochemical performance of LiCoO 2 electrodes for high-voltage operations by Ag thin film coating via magne
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.517
Improved electrochemical performance of LiCoO2 electrodes for high-voltage operations by Ag thin film coating via magnetron sputtering Taner Zerrin1, Mihri Ozkan2, Cengiz S. Ozkan1 1
Materials Science and Engineering Program, Department of Mechanical Engineering, University of California, Riverside, CA 92521, USA 2
Department of Electrical Engineering, University of California, Riverside, CA 92521, USA
ABSTRACT
Increasing the operation voltage of LiCoO2 (LCO) is a direct way to enhance the energy density of the Li-ion batteries. However, at high voltages, the cycling stability degrades very fast due to the irreversible changes in the electrode structure, and formation of an unstable solid electrolyte interface layer. In this work, Ag thin film was prepared on commercial LCO cathode by using magnetron sputtering technique. Ag coated electrode enabled an improved electrochemical performance with a better cycling capability. After 100 cycles, Ag coated LCO delivers a discharge capacity of 106.3 mAh g-1 within 3 – 4.5 V at C/5, which is increased by 45 % compared to that of the uncoated LCO. Coating the electrode surface with Ag thin film also delivered an improved Coulombic efficiency, which is believed to be an indication of suppressed parasitic reactions at the electrode interface. This work may lead to new methods on surface modifications of LCO and other cathode materials to achieve high-capacity Li-ion batteries for high-voltage operations.
INTRODUCTION LiCoO2 (LCO) is the dominating cathode material used in commercial lithiumion batteries (LIBs) in portable electronic devices due to its high energy density, cycling stability and ease of production [1]. To meet the growing demand of large-scale applications of LIBs with higher storage capacities, such as electric vehicles, the research on further improvement of LCO electrodes by exploring its high-voltage limit has been gradually increasing [2]. Although it is theoretically possible to increase the capacity of
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LCO by charging it e.g. to 4.5 V, which is above the normal value of 4.2 V vs. Li/Li+, its cycling performance suffers a fast degradation due to the irreversible structural changes of the active materials and formation of an unfavorable solid electrolyte interface (SEI) layer [3,4]. Many researchers have focused on surface coatings to alter the electrochemistry between the electrolyte and cathode [5,6]. Majority of the efforts used cost-efficient chemical ways [7,8] or very controllable but expensive atomic layer depositon method [9]. Herein, we proposed the deposition of Ag thin film on LCO cathodes, using magnetron sputtering (MS), a technique that has been intensively used in industry for thin film fabrication. MS is a lower-cost and m
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