Unusual Passivation Ability of Superconcentrated Electrolytes toward Hard Carbon Negative Electrodes in Sodium-Ion Batteries
Unusual Passivation Ability of Superconcentrated Electrolytes toward Hard Carbon Negative Electrodes in Sodium-Ion Batteries
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DOI：
10.1021/acsami.7b08414
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发表时间：
2017-10-04
影响因子：
9.5
通讯作者：
Yamada, Atsuo
中科院分区：
文献类型：
--
作者：
Takada, Koji;Yamada, Yuki;Yamada, Atsuo
负极钝化是实现钠离子电池长时间充放电循环的关键。在这里，我们报告了超浓钠盐电解液不寻常的钝化能力。例如，50摩尔%的双(氟磺酸)酰胺钠(NAFSA)/丁二腈(SN)电解液无需任何电解液添加剂、功能粘合剂或电极前处理即可高度可逆地将Na+插入硬碳负极。重要的是，充电时通过优先还原阴离子而形成阴离子衍生的钝化膜，这可以有效地抑制电解液的进一步还原。作为电解液的结构特征，大多数阴离子在高浓度下与多个Na+离子配位，使阴离子的最低未占据分子轨道下移，导致阴离子优先还原。本工作对负离子配位状态下的钝化机理有了新的认识。
The passivation of negative electrodes is key to achieving prolonged charge-discharge cycling with Na-ion batteries. Here, we report the unusual passivation ability of superconcentrated Na-salt electrolytes. For example, a 50 mol % sodium bis(fluorosulfonyl)amide (NaFSA)/succinonitrile (SN) electrolyte enables highly reversible Na+ insertion into a hard carbon negative electrode without any electrolyte additive, functional binder, or electrode pretreatment. Importantly, an anion-derived passivation film is formed via preferential reduction of the anion upon charging, which can effectively suppress further electrolyte reduction. As a structural characteristic of the electrolyte, most anions are coordinated to multiple Na+ cations at high concentration, which shifts the lowest unoccupied molecular orbitals of the anions downward, resulting in preferential anion reduction. The present work provides a new understanding of the passivation mechanism with respect to the coordination state of the anion.