Dendrite-free alkali-metal electrodeposition from contact-ion-pair state induced by mixing alkaline earth cation
Dendrite-free alkali-metal electrodeposition from contact-ion-pair state induced by mixing alkaline earth cation
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DOI：
10.26434/chemrxiv-2021-v0rdz
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发表时间：
2021-12
影响因子：
8.9
通讯作者：
Hongyi Li;M. Murayama;T. Ichitsubo
中科院分区：
文献类型：
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作者：
Hongyi Li;M. Murayama;T. Ichitsubo
碱金属，如锂和钠，由于其低电极电势和大容量而有望用于可充电金属阳极电池。然而，电池充电时面临着众所周知的致命问题，即“枝晶生长”导致危险的短路。在这里，通过电化学实验、拉曼和软X射线发射光谱、密度泛函理论计算和分子动力学模拟的综合研究，我们为电解质设计提供了先进的指南，其中碱土金属（Mg、Ca、Ba）盐的混合物用于抑制电沉积过程中碱金属（Li、Na）的枝晶生长。特别是，重点关注CaTFSA2，作为一种突出的示例性碱土阳离子添加剂，我们证明通过改变双阳离子电解质体系中的溶剂化结构，可以成功地获得碱金属电沉积时的无枝晶形态。添加二价Ca2+可促进碱金属阳离子（Li+或Na+）与抗衡阴离子形成接触离子对（CIP），从而取代单阳离子电解液中常见的溶剂分离离子对（SSIP）。这种与碱金属阳离子相关的 CIP 会远远地分离 Ca2+ 离子，以屏蔽二价阳离子之间的强库仑相互作用。 CIP 更强的结合会阻碍碱金属阳离子的去溶剂化动力学，从而在反应受限的过程中实现严格限制的碱金属电沉积，这是无枝晶形态所需的。这项工作为利用单价和多价阳离子之间的协同相互作用构建无枝晶碱金属阳极电池的双阳离子电解质提供了前景。
Alkali metals, such as lithium and sodium, have been expected to be used for rechargeable metal-anode batteries owing to their low electrode potentials and large capacities. However, the well-known fatal problem, “dendritic growth” causing a dangerous short circuit, is faced while charging the batteries. Here, through a comprehensive study with electrochemical experiments, Raman and soft X-ray emission spectroscopies, density-functional-theory calculation, and molecular dynamic simulations, we provide an advanced guideline for electrolyte design in which a mixture of alkaline earth (Mg, Ca, Ba) salts is used to inhibit dendrite growth of alkali metals (Li, Na) during electrodeposition. Especially, focusing on CaTFSA2, as a salient exemplary alkaline-earth-cation additive, we demonstrate that dendrite-free morphology upon alkali-metal electrodeposition can successfully be attained by modifying their solvation structures in the dual-cation electrolyte systems. Adding divalent Ca2+ promotes alkali cation (Li+ or Na+) to form the contact ion pairs (CIPs) with the counter anions, which replaces the solvent-separated ion pairs (SSIPs) commonly existing in single-cation electrolytes. Such CIPs related to alkali cations would separate Ca2+ ions distantly to shield the strong coulomb interaction among the divalent cations. The stronger binding of the CIPs would retard the desolvation kinetics of alkali cations and, consequently, realizes a severely constrained alkali-metal electrodeposition in a reaction-limited process that is required for the dendrite-free morphology. This work provides prospects to construct dual-cation electrolytes for dendrite-free alkali-metal-anode batteries utilizing the concerted interactions between monovalent and multivalent cations.