College of Chemistry and Molecular Engineering , Qingdao University of Science and Technology , Qingdao 266042 , P. R. China.
Qingdao Industrial Energy Storage Research Institute, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences , Qingdao 266101 , P. R. China.
ACS Appl Mater Interfaces. 2018 Jul 18;10(28):23757-23765. doi: 10.1021/acsami.8b04674. Epub 2018 Jul 9.
Highly reductive magnesium borohydride [Mg(BH)] is compatible with metallic Mg, making it a promising Mg-ion electrolyte for rechargeable Mg batteries. However, pure Mg(BH) in ether-based solutions displays very limited solubility (0.01 M), low oxidative stability (<1.8 V vs Mg), and nucleophilic characteristic, all of which preclude its practical utilization for any battery applications. Herein, we present a multifunctional additive of tris(2 H-hexafluoroisopropyl)borate (THFPB) for preparing Mg(BH)-based electrolytes. By virtue of the strong electron-acceptor ability of the THFPB molecule, a transparent and high-concentration Mg(BH)/THFPB-diglyme (DGM) electrolyte (0.5 M, almost 50 times higher than that of the pristine Mg(BH)-DGM electrolyte) is first obtained, which shows dramatic performance improvements, including high ionic conductivity (3.72 mS cm at 25 °C) and high Mg plating/stripping Coulombic efficiency (>99%). The newly-generated active cation and anion species revealed by Raman, NMR and MS spectra, increase the electrochemical potential window from 1.8 V to 2.8 V vs Mg on stainless steel electrode, rendering electrolytes the ability to examine high voltage cathodes. More importantly, on account of the non-nucleophilicity of active electrolyte species, we present the first example of magnesium-sulfur (Mg-S) batteries using Mg(BH)-based electrolytes, which exhibit a high discharge capacity of 955.9 and 526.5 mA h g at the initial and 30th charge/discharge cycles, respectively. These achievements not only provide an efficient and specific strategy to eliminate the major roadblocks facing Mg(BH)-based electrolytes but also highlight the profound effect of functional additives on the electrochemical performances of unsatisfied Mg-ion electrolytes.
高度还原的硼氢化镁[Mg(BH)]与金属 Mg 相容，使其成为一种很有前途的可再充电 Mg 电池的 Mg 离子电解质。然而，纯 Mg(BH)在醚基溶液中的溶解度非常有限（0.01 M），氧化稳定性低（<1.8 V 相对于 Mg），亲核特性，所有这些都排除了其在任何电池应用中的实际利用。在此，我们提出了一种三（2 H-六氟异丙基）硼酸酯（THFPB）的多功能添加剂，用于制备基于 Mg(BH)的电解质。由于 THFPB 分子具有很强的电子受体能力，首次获得了透明且高浓度的 Mg(BH)/THFPB-二甘醇（DGM）电解质（0.5 M，几乎比原始 Mg(BH)-DGM 电解质高 50 倍），其表现出显著的性能改善，包括高离子电导率（25°C 时为 3.72 mS cm）和高 Mg 电镀/剥离库仑效率（>99%）。拉曼、NMR 和 MS 光谱揭示的新生成的活性阳离子和阴离子种类，将不锈钢电极的电化学电势窗口从 1.8 V 提高到 2.8 V 相对于 Mg，使电解质能够检验高压阴极。更重要的是，由于活性电解质物质的非亲核性，我们首次提出了使用基于 Mg(BH)的电解质的镁-硫（Mg-S）电池，其在初始和第 30 次充放电循环时分别表现出 955.9 和 526.5 mA h g 的高放电容量。这些成就不仅提供了一种有效和特定的策略来消除基于 Mg(BH)的电解质面临的主要障碍，而且还突出了功能添加剂对不满意的 Mg 离子电解质电化学性能的深远影响。
