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Issue 12, 2017
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An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery

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Abstract

Two-electron transfer chemistry based on earth-abundant Mg and S offers great possibilities of delivering higher energy density than current Li-ion technology. The development of non-nucleophilic electrolytes that reversibly and efficiently plate and strip Mg is believed to be a major obstacle to the implementation of this divalent battery technology. In this study, we present a new type of organic magnesium borate-based electrolyte that primarily comprises tetrakis(hexafluoroisopropyl)borate anions [B(HFP)4] and solvated cations [Mg4Cl6(DME)6]2+, which was synthesized via a facile in situ reaction of tris(hexafluoroisopropyl)borate [B(HFP)3], MgCl2 and Mg powder in 1,2-dimethoxyethane (DME). Rigorous analyses including NMR, mass spectroscopy and single-crystal XRD were conducted to identify the equilibrium species in the abovementioned solution. The as-prepared Mg-ion electrolyte exhibited unprecedented Mg plating/stripping performance, such as high anodic stability up to 3.3 V (vs. Mg/Mg2+), high ionic conductivity of 5.58 mS cm−1, a low overpotential of 0.11 V for plating processes and Coulombic efficiencies greater than 98%. By virtue of the non-nucleophilic nature of this electrolyte, a fully reversible Mg/S battery was constructed that displayed an extremely low overpotential of 0.3 V and a high discharge capacity of up to 1247 mA h g−1 and yielded a specific energy of approximately 1200 W h kg−1 (10 times higher that of the Chevrel benchmark) based on the weight of active sulfur. More significantly, commonly used sulfur-carbon nanotube (S-CNTs) cathodes with S contents of 80 wt% and S loadings of 1.5 mg cm−2 were demonstrated to withstand more than 100 cycles without obvious capacity decay and to enable fast conversion processes, which achieved a charging current rate of up to 500 mA g−1. Our findings convincingly validate the pivotal role of the newly designed non-nucleophilic Mg-ion electrolyte for practical Mg/S battery chemistry.

Graphical abstract: An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery

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Publication details

The article was received on 13 Aug 2017, accepted on 16 Nov 2017 and first published on 16 Nov 2017


Article type: Paper
DOI: 10.1039/C7EE02304A
Citation: Energy Environ. Sci., 2017,10, 2616-2625
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    An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery

    A. Du, Z. Zhang, H. Qu, Z. Cui, L. Qiao, L. Wang, J. Chai, T. Lu, S. Dong, T. Dong, H. Xu, X. Zhou and G. Cui, Energy Environ. Sci., 2017, 10, 2616
    DOI: 10.1039/C7EE02304A

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