A non-nucleophilic gel polymer magnesium electrolyte compatible with sulfur cathode
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A non-nucleophilic gel polymer magnesium electrolyte compatible with sulfur cathode Haiyan Fan1,2, Yuxing Zhao3, Jianhua Xiao3, Jifang Zhang3, Min Wang1,2, and Yuegang Zhang2,3 () 1
School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei 230026, China i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China 3 Department of Physics, Tsinghua University, Beijing 100084, China 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 21 March 2020 / Revised: 1 June 2020 / Accepted: 5 June 2020
ABSTRACT Magnesium/sulfur battery (Mg/S) has recently received wide attention due to its high theoretical energy density (3,260 Wh/L) and low cost. To further improve its safety and flexibility, developing a polymer electrolyte that can be compatible with both electrophilic S and Mg is critical. Here, we report a magnesium chloride-(fluorinated tetraethylene glycolic)borate (MgCl-FTGB) based non-nucleophilic, gel-type polymer electrolyte for Mg/S battery via a facile synthetic method through commercially available reagents. This electrolyte coupled with glass fiber allows reversible Mg deposition/dissolution (100% coulombic efficiency) with low polarization (500 μA/cm2, 300/300 mV), and shows a wide electrochemical window of 4.8 V (vs. Mg/Mg2+). Mg/S battery assembled with this electrolyte can cycle over 50 times with a high specific discharge capacity retention of over 1,100 mAh/g.
KEYWORDS magnesium/sulfur battery, polymer electrolyte, non-nucleophilic electrolyte, safety
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Introduction
As a polyvalent element with a low atomic number, magnesium (Mg) is a promising anode material for high energy density batteries. Compared with Li, Mg has many advantages, such as abundant reserves, low cost, and high specific volume capacity (3,833 mAh/cm3) [1]. A Mg/S battery owns a theoretical energy density of over 3,260 Wh/L, which has attracted widespread attention in recent years [2]. Finding an electrolyte that can match with both electrophilic S and easily-passivated Mg is crucial for implementation of Mg/S batteries. In the past ten years, various non-nucleophilic Mg/S electrolytes have been developed, such as hexamethyldisilazide based electrolytes [2–7], inorganic Mg electrolytes [8–13], boron anion based electrolytes [14–19], magnesium di[bis(trifluoromethanesulfonyl)imide] (Mg(TFSI)2) electrolytes [20–23] and other systems [24–26]. However, all these electrolytes are in liquid phase that is very likely to cause security risks such as electrolyte leakage. To further improve the safety and flexibility of Mg/S battery, developing a polymer electrolyte is critical. There have been some previous reports of polymer magnesium electrolytes [27–34]. Most of them prepared using commercial Mg salts (Mg(TFSI)2, Mg(ClO4)2, et al.) are unable to realize Mg stripping/ plating due to their decomposition on highly reductive Mg foil and the subsequent formation of magnesium ion blocking layers [31]. Only very few p
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