An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery†,Energy & Environmental Science

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An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery†
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2017-11-16 00:00:00 , DOI: 10.1039/c7ee02304a
Aobing Du _{1,

2,

3,

4,

5} , Zhonghua Zhang _{5,

6,

7,

8} , Hongtao Qu _{1,

2,

3,

4,

5} , Zili Cui _{1,

2,

3,

4,

5} , Lixin Qiao _{5,

6,

7,

8} , Longlong Wang _{1,

2,

3,

4,

5} , Jingchao Chai _{1,

2,

3,

4,

5} , Tao Lu _{1,

2,

3,

4,

5} , Shanmu Dong _{1,

2,

3,

4,

5} , Tiantian Dong _{1,

2,

3,

4,

5} , Huimin Xu _{5,

6,

7,

8} , Xinhong Zhou _{5,

6,

7,

8} , Guanglei Cui _{1,

2,

3,

4,

5}

Affiliation

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.

中文翻译：

一种有效的有机硼酸镁基电解质，具有非亲核特性，可用于镁硫电池†

基于地球上丰富的Mg和S的二电子转移化学提供了比目前的锂离子技术更高的能量密度的可能性。可逆和有效地镀覆和剥离Mg的非亲核电解质的开发被认为是实施这种二价电池技术的主要障碍。在这项研究中，我们提出了一种新型的有机硼酸镁基电解质，该电解质主要包含四（六氟异丙基）硼酸根阴离子[B（HFP）₄ ] ^-和溶剂化阳离子[Mg ₄ Cl ₆（DME）₆ ] ²⁺，其中是通过方便的原位合成的硼酸三（六氟异丙基）酯[B（HFP）₃ ]，MgCl ₂和Mg粉末在1,2-二甲氧基乙烷（DME）中的反应。进行了包括NMR，质谱和单晶XRD在内的严格分析，以鉴定上述溶液中的平衡物质。所制备的Mg离子电解质表现出前所未有的Mg电镀/剥离性能，例如高达3.3 V的高阳极稳定性（相对于Mg / Mg 2 ⁺），5.58 mS cm ^-1的高离子电导率，对于电镀工艺而言，低过电位为0.11 V，库仑效率大于98％。依靠这种电解质的非亲核性质，构建了一种完全可逆的Mg / S电池，该电池表现出0.3 V的极低过电势和高达1247 mA hg ^-1的高放电容量，并且产生的比能约为基于活性硫的重量，为1200 W h kg ^-1（比Chevrel基准高10倍）。更重要的是，常用的硫碳纳米管（S-CNTs）阴极的S含量为80 wt％，S负载为1.5 mg cm ^-2被证明可以承受100个以上的循环而不会出现明显的容量衰减，并且能够实现快速转换过程，从而实现了高达500 mA g ^-1的充电电流速率。我们的发现令人信服地证实了新设计的非亲核Mg离子电解质在实际Mg / S电池化学中的关键作用。

更新日期：2017-11-16

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