Additive effect on reductive decomposition and binding of carbonate-based solvent toward solid electrolyte interphase formation in lithium-ion battery.
Additive effect on reductive decomposition and binding of carbonate-based solvent toward solid electrolyte interphase formation in lithium-ion battery.
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DOI：
10.1021/ja405079s
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发表时间：
2013-08
影响因子：
15
通讯作者：
Keisuke Ushirogata;Keitaro Sodeyama;Yukihiro Okuno;Y. Tateyama
中科院分区：
文献类型：
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作者：
Keisuke Ushirogata;Keitaro Sodeyama;Yukihiro Okuno;Y. Tateyama
通过溶剂分子还原分解形成的固体电解质界面（SEI）对于锂离子电池（LIB）的稳定性和性能起着至关重要的作用。在这里，我们研究了在碳酸亚乙酯（EC）溶剂（LIB 中的典型电解质）中添加碳酸亚乙烯酯（VC）对还原分解的影响。我们关注可能过程的热力学和动力学，并使用基于密度泛函理论的分子动力学以及显式溶剂和蓝月系综技术来实现自由能变化。我们考虑了仅 EC 溶剂（EC 系统）和含有 VC 添加剂（EC/VC 系统）的 EC 溶剂中的 Li(+)，以阐明添加剂的影响。除了阐明平衡性质之外，我们还评估了单电子 (1e) 还原条件下沿多个 EC 或 VC 分解路径的自由能变化。还检查了双电子 (2e) 还原和阴离子自由基对完整分子的攻击。目前的结果完全再现了实验中观察到的气体产物。我们还发现了一种涉及 VC 添加剂的新机制：VC 添加剂优先与 EC 阴离子自由基反应，抑制 EC 的 2e 还原并增强初始 SEI 的形成，这与 VC 添加剂被牺牲还原及其自由基低聚成为 SEI 来源的传统情况相反。由于我们的机制只需要减少1e，SEI形成处的不可逆容量就会降低，这也与实验观察结果一致。这些结果揭示了 VC 添加剂在 EC 溶剂中的主要作用。
The solid-electrolyte interphase (SEI) formed through the reductive decomposition of solvent molecules plays a crucial role in the stability and capability of a lithium-ion battery (LIB). Here we investigated the effects of adding vinylene carbonate (VC) to ethylene carbonate (EC) solvent, a typical electrolyte in LIBs, on the reductive decomposition. We focused on both thermodynamics and kinetics of the possible processes and used density functional theory-based molecular dynamics with explicit solvent and Blue-moon ensemble technique for the free energy change. We considered Li(+) in only EC solvent (EC system) and in EC solvent with a VC additive (EC/VC system) to elucidate the additive effects. In addition to clarifying the equilibrium properties, we evaluated the free energy changes along several EC or VC decomposition pathways under one-electron (1e) reduction condition. Two-electron (2e) reduction and attacks of anion radicals to intact molecules were also examined. The present results completely reproduce the gaseous products observed in the experiments. We also found a new mechanism involving the VC additive: the VC additive preferentially reacts with the EC anion radical to suppress the 2e reduction of EC and enhance the initial SEI formation, contrary to the conventional scenario in which VC additive is sacrificially reduced and its radical oligomerization becomes the source of SEI. Because our mechanism needs only 1e reduction, the irreversible capacity at the SEI formation will decrease, which is also consistent with the experimental observations. These results reveal the primary role of VC additive in the EC solvent.