Tuerxun Feilure, Yamamoto Kentaro, Hattori Masashi, Mandai Toshihiko, Nakanishi Koji, Choudhary Ashu, Tateyama Yoshitaka, Sodeyama Keitaro, Nakao Aiko, Uchiyama Tomoki, Matsui Masaki, Tsuruta Kazuki, Tamenori Yusuke, Kanamura Kiyoshi, Uchimoto Yoshiharu
Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsucho, Sakyo-ku, Kyoto 606-8316, Japan.
Center for Green Research on Energy and Environmental Materials and International Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan.
ACS Appl Mater Interfaces. 2020 Jun 10;12(23):25775-25785. doi: 10.1021/acsami.0c03696. Epub 2020 May 27.
To clarify the origin of the polarization of magnesium deposition/dissolution reactions, we combined electrochemical measurement, soft X-ray absorption spectroscopy ( SXAS), Raman, and density functional theory (DFT) techniques to three different electrolytes: magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA))/triglyme, magnesium borohydride (Mg(BH))/tetrahydrofuran (THF), and Mg(TFSA)/2-methyltetrahydrofuran (2-MeTHF). Cyclic voltammetry revealed that magnesium deposition/dissolution reactions occur in Mg(TFSA)/triglyme and Mg(BH)/THF, while the reactions do not occur in Mg(TFSA)/2-MeTHF. Raman spectroscopy shows that the [TFSA] in the Mg(TFSA)/triglyme electrolyte largely does not coordinate to the magnesium ions, while all of the [TFSA] in Mg(TFSA)/2-MeTHF and [BH] in Mg(BH)/THF coordinate to the magnesium ions. In SXAS measurements, the intermediate, such as the Mg ion, was not observed at potentials above the magnesium deposition potential, and the local structure distortion around the magnesium ions increases in all of the electrolytes at the magnesium electrode|electrolyte interface during the cathodic polarization. Our DFT calculation and X-ray photoelectron spectroscopy results indicate that the [TFSA], strongly bound to the magnesium ion in the Mg(TFSA)/2-MeTHF electrolyte, undergoes reduction decomposition easily, instead of deposition of magnesium metal, which makes the electrolyte inactive electrochemically. In the Mg(BH)/THF electrolyte, because the [BH] coordinated to the magnesium ions is stable even under the potential of the magnesium deposition, the magnesium deposition is not inhibited by the decomposition of [BH]. Conversely, because [TFSA] is weakly bound to the magnesium ion in Mg(TFSA)/triglyme, the reduction decomposition occurs relatively slowly, which allows the magnesium deposition in the electrolyte.
为了阐明镁沉积/溶解反应极化的起源，我们将电化学测量、软X射线吸收光谱（SXAS）、拉曼光谱和密度泛函理论（DFT）技术应用于三种不同的电解质：双（三氟甲磺酰）亚胺镁（Mg(TFSA)）/三甘醇二甲醚、硼氢化镁（Mg(BH)）/四氢呋喃（THF）和Mg(TFSA)/2-甲基四氢呋喃（2-MeTHF）。循环伏安法表明，镁沉积/溶解反应在Mg(TFSA)/三甘醇二甲醚和Mg(BH)/THF中发生，而在Mg(TFSA)/2-MeTHF中不发生。拉曼光谱表明，Mg(TFSA)/三甘醇二甲醚电解质中的[TFSA]在很大程度上不与镁离子配位，而Mg(TFSA)/2-MeTHF中的所有[TFSA]和Mg(BH)/THF中的[BH]都与镁离子配位。在SXAS测量中，在高于镁沉积电位的电位下未观察到诸如镁离子之类的中间体，并且在阴极极化期间，镁电极|电解质界面处所有电解质中镁离子周围的局部结构畸变都会增加。我们的DFT计算和X射线光电子能谱结果表明，在Mg(TFSA)/2-MeTHF电解质中与镁离子强烈结合的[TFSA]容易发生还原分解，而不是镁金属沉积，这使得电解质在电化学上不活泼。在Mg(BH)/THF电解质中，由于与镁离子配位的[BH]即使在镁沉积电位下也很稳定，因此镁沉积不会受到[BH]分解的抑制。相反，由于[TFSA]在Mg(TFSA)/三甘醇二甲醚中与镁离子的结合较弱，还原分解相对较慢，这使得电解质中能够发生镁沉积。
