Development of calcium metal batteries has been historically frustrated by a lack of electrolytes capable of supporting reversible calcium electrodeposition. In this paper, we report the study of an electrolyte consisting of Ca(BH₄)₂ in tetrahydrofuran (THF) to gain important insight into the role of the liquid solvation environment in facilitating the reversible electrodeposition of this highly reactive, divalent metal. Through interrogation of the Ca²⁺ solvation environment and comparison with Mg²⁺ analogs, we show that an ability to reversibly electrodeposit metal at reasonable rates is strongly regulated by dication charge density and polarizability. Our results indicate that the greater polarizability of Ca²⁺ over Mg²⁺ confers greater configurational flexibility, enabling ionic cluster formation via neutral multimer intermediates. Increased concentration of the proposed electroactive species, CaBH₄⁺, enables rapid and stable delivery of Ca²⁺ to the electrode interface. This work helps set the stage for future progress in the development of electrolytes for calcium and other divalent metal batteries.

中文翻译：

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组态灵活性在促进硼氢化物溶液中可逆反应性金属沉积中的关键作用

过去，由于缺乏能够支持可逆钙电沉积的电解质，钙金属电池的开发一直受挫。在本文中，我们报告了在四氢呋喃（THF）中由Ca（BH ₄）₂组成的电解质的研究，以深入了解液体溶剂化环境在促进这种高反应性二价金属的可逆电沉积中的作用。通过对Ca ²⁺溶剂化环境的询问并与Mg ²⁺类似物进行比较，我们表明以指示速率可逆地电沉积金属的能力受到指示电荷密度和极化率的强烈调节。我们的结果表明，Ca ²⁺具有更大的极化率超过Mg ²⁺具有更大的构型灵活性，可通过中性多聚体中间体形成离子簇。所提出的电活性物质CaBH ₄ ^+的浓度增加，可以将Ca ²⁺快速稳定地传递到电极界面。这项工作有助于为钙和其他二价金属电池电解液的开发奠定未来的舞台。