Oxidative-Stability Enhancement and Charge Transport Mechanism in Glyme-Lithium Salt Equimolar Complexes
Oxidative-Stability Enhancement and Charge Transport Mechanism in Glyme-Lithium Salt Equimolar Complexes
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DOI：
10.1021/ja203983r
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发表时间：
2011-08-24
影响因子：
15
通讯作者：
Watanabe, Masayoshi
中科院分区：
文献类型：
--
作者：
Yoshida, Kazuki;Nakamura, Megumi;Watanabe, Masayoshi
分子的氧化稳定性通过与碱金属阳离子的复合物形成增强。可以通过将Glyme（Triglyme或Tetraglyme）与lithium bis（三氟甲基磺酰基）-Amide（Li [tfsa]）混合，以1：1的形式将透明液体获得。等摩尔复合物[li（Triglyme或tetraglyme）（1）] [TFSA]在较宽的温度范围内保持稳定的液态状态，可以被视为由[li（glyme）（1）]组成的室温离子液体（+）复合阳离子和[TFSA]（ - ）阴离子，在室温下表现出高自我分离（离子性）。 [li（glyme）（1）] [tfsa]的电化学氧化发生在与5 v vs li/li+相似的电极电位上，而含有过量glyme分子的溶液的氧化（[li（glyme）（x）（x）） ] - [TFSA]，x> 1）在4 V vs li/li+处发生。氧化稳定性的这种增强是由于向Li+阳离子捐赠了单个以太氧原子对，从而导致glyme分子的最高占用分子轨道（HOMO）能级降低，这是由AB Initio Mitio Mitio Solecular oblecular oblecular Orbital Carcurets证实的。 [Li（Glyme）（X）] [TFSA]溶液中Li+阳离子和离子传导机制的溶剂化态通过核磁共振（NMR）和电化学方法阐明。实验结果强烈表明，等摩尔复合物中的li+阳离子传导是通过[li（glyme）（1）]（+）阳离子的迁移而发生的，而当[li（glyme）的界面电化学反应时，配体交换机制是重叠的（1）]（+）阳离子发生。配体交换传导模式通常在锂电池中看到，当liCoo2阴极的放电反应（即，即，fertical bar [li（li（glyme）（glyme）（glyme）（glyme）（1）））的配置，即[li（glyme）（1）]]（+）的脱溶剂，并将结果的li+插入阴极中，发生在电极 - 电解质界面。无论使用基于醚的电解液，电池都可以在3.0-4.2 V的电池电压中以200多个电荷释放循环操作，因为配体汇率速度远高于电极反应速率。
The oxidative stability of molecules is enhanced by the complex formation with alkali metal cations. Clear liquid can be obtained by simply mixing glyme (triglyme or tetraglyme) with lithium bis (trifluoromethylsulfonyl)-amide (Li[TFSA]) in a molar ration of 1:1. The equimolar complex [Li(triglyme or tetraglyme)(1)][TFSA] maintains a stable liquid state over a wide temperature range and can be regarded as a room-temperature ionic liquid consisting of a [Li(glyme)(1)](+) complex cation and a [TFSA](-) anion, exhibiting high self-dissociativity (ionicity) at room temperature. The electrochemical oxidation of [Li(glyme)(1)][TFSA] takes place at the electrode potential of similar to 5 v vs Li/Li+, while the oxidation of solutions containing excess glyme molecules ([Li(glyme)(x)]-[TFSA], x > 1) occurs at around 4 v vs Li/Li+. This enhancement of oxidative stability is due to the donation of lone pairs of ether oxygen atoms to the Li+ cation, resulting in the highest occupied molecular orbital (HOMO) energy level lowering of a glyme molecule, which is confirmed by ab initio molecular orbital calculations. The solvation state of a Li+ cation and ion conduction mechanism in the [Li(glyme)(x)][TFSA] solutions is elucidated by means of nuclear magnetic resonance (NMR) and electrochemical methods. The experimental results strongly suggest that Li+ cation conduction in the equimolar complex takes place by the migration of [Li(glyme)(1)](+) cations, whereas the ligands exchange mechanism is overlapped when interfacial electrochemical reactions of [Li(glyme)(1)](+) cations occur. The ligand exchange conduction mode is typically seen in a lithium battery with a configuration of [Li anode vertical bar[Li(glyme)(1)][TFSA]vertical bar LiCoO2 cathode] when the discharge reaction of a LiCoO2 cathode, that is, desolvation of [Li(glyme)(1)](+) and insertion of the resultant Li+ into the cathode, occurs at the electrode-electrolyte interface. The battery can be operated for more than 200 charge-discharge cycles in the cell voltage of 3.0-4.2 V, regardless of the use of ether-based electrolyte, because the ligand exchange rate is much faster than the electrode reaction rate.