Comparative Studies on [B(HFIP)4]-Based Electrolytes with Mono- and Divalent Cations
Comparative Studies on [B(HFIP)4]-Based Electrolytes with Mono- and Divalent Cations
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DOI：
10.1021/acs.jpcc.3c01160
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发表时间：
2023-04
期刊：
影响因子：
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通讯作者：
Toshihiko Mandai;Hiroko Naya;H. Masu
中科院分区：
文献类型：
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作者：
Toshihiko Mandai;Hiroko Naya;H. Masu
开发与还原性金属相容的电解质材料是实现利用金属负极的高能量密度可充电电池的迫切要求。由于金属电极重复循环后形态和新鲜金属的连续变化和再生，电解质应对此类电极具有足够的（电）化学稳定性。弱配位阴离子（WCA）基电解质于1995年首次被提出用于锂基电池应用，由于其在镁和钙金属电池中的成功应用，特别是近年来引起了人们的广泛关注。受这些研究的启发，基于 WCA 的电解质已被重新引入锂离子和钠离子电池化学领域。在本研究中，我们对包含四（六氟异丙氧基）硼酸根（[B（HFIP）4]−）阴离子的代表性WCA电解质作为模型系统进行了全面的比较研究，以了解成对阳离子物质的化合价对传输特性和电化学特性的影响。 X射线晶体学显示，单价锂盐和钠盐以加合物形式获得，其中阴离子与单个溶剂分子一起参与阳离子配位，而二价镁、钙和锌盐形成完全分离的溶剂化物，二价阳离子仅由溶剂配位。这种解离态的化合价依赖性差异会影响溶液性质，因为二价电解质比一价电解质表现出更大的电导率，即使各自溶液中存在相同数量的带电物质。电化学金属沉积/溶解研究与沉积物的形态和随后的元素分析相结合，表明镁阳离子和[B(HFIP)4]-阴离子在醚溶液中具有特定的有利组合。沉积的粗晶镁适度的表面反应性、镁金属适度的还原性以及各组分之间良好平衡的相互作用可能共同促成了如此出色的性能。
The development of electrolyte materials that are compatible with reductive metals is an urgent requirement for realizing high-energy-density rechargeable batteries utilizing metallic negative electrodes. Due to successive changes and regeneration of the morphology and fresh metals, respectively, upon repeated cycling of the metallic electrodes, the electrolytes should possess sufficient (electro)chemical stabilities against such electrodes. Weakly coordinating anion (WCA)-based electrolytes, which were first proposed for lithium-based battery applications in 1995, have attracted significant attention, especially in recent years, owing to their successful application in magnesium and calcium metal batteries. Inspired by these studies, WCA-based electrolytes have been reimported into lithium- and sodium-ion battery chemistry. In this study, we conducted comprehensive comparative studies on the representative WCA-based electrolytes incorporating tetrakis(hexafluoro-iso-propoxyl)borate ([B(HFIP)4]−) anions as a model system to understand the effect of valency of paired cation species on transport properties and electrochemical characteristics. As revealed by X-ray crystallography, the monovalent lithium and sodium salts were obtained as adducts, where the anion participated in cation coordination along with a single solvent molecule, whereas divalent magnesium, calcium, and zinc salts formed fully isolated solvates with the divalent cations being coordinated by solvents alone. Such valency-dependent differences in the dissociation states would affect the solution properties, as the divalent electrolytes exhibited greater conductivities than their monovalent counterparts, even though the same number of charged species was present in the respective solutions. The electrochemical metal deposition/dissolution studies combined with morphological and subsequent elemental analysis on the deposits suggested the specific favorable combination of magnesium cations and [B(HFIP)4]−anion in ethereal solutions. The modest surface reactivity of the deposited macrocrystalline magnesium, moderate reductive nature of the magnesium metal, and well-balanced mutual interactions among the components may have jointly contributed to such outstanding performance.