Fan Shengqi, Cora Saida, Sa Niya
Department of Chemistry, University of Massachusetts Boston, 100 William T. Morrissey Blvd, Boston, Massachusetts02125, United States.
ACS Appl Mater Interfaces. 2022 Oct 19;14(41):46635-46645. doi: 10.1021/acsami.2c13037. Epub 2022 Oct 7.
Formation and evolution of the microscopic solid electrolyte interphase (SEI) at the Mg electrolyte/electrode interface are less reported and need to be completely understood to overcome the compatibility challenges at the Mg anode-electrolyte. In this paper, SEI evolution at the Mg electrolyte/electrode interface is investigated an electrochemical quartz crystal microbalance with dissipation mode (EQCM-D), electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectrometry (FTIR). Results reveal remarkably different interfacial evolutions for the two Mg electrolyte systems that are studied, a non-halogen Mg(TFSI) electrolyte in THF with DMA as a cosolvent (Mg-DMA electrolyte) versus a halogen-containing all-phenyl complex (APC) electrolyte. The Mg-DMA electrolyte reports a minuscule SEI formation along with a significant Coulomb loss at the initial electrochemical cycles owing to an electrolyte reconstruction process. Interestingly, a more complicated SEI growth is observed at the later electrochemical cycles accompanied by an improved reversible Mg deposition attributed to the newly formed coordination environment with Mg and ultimately leads to a more homogeneous morphology for the electrochemically deposited Mg, which maintains a MgF-rich interface. In contrast, the APC electrolyte shows an extensive SEI formation at its initial electrochemical cycles, followed by a SEI dissolution process upon electrochemical cycling accompanied by an improved coulombic efficiency with trace water and chloride species removed. Therefore, it leads to SEI stabilization progression upon further electrochemical cycling, resulting in elevated charge transport kinetics and superior purity of the electrochemically deposited Mg. These outstanding findings augment the understanding of the SEI formation and evolution on the Mg interface and pave a way for a future Mg-ion battery design.
镁电解质/电极界面微观固体电解质界面（SEI）的形成与演化鲜有报道，为克服镁阳极 - 电解质间的兼容性挑战，需要对其进行全面了解。本文采用电化学石英晶体微天平耗散模式（EQCM - D）、电化学阻抗谱（EIS）、场发射扫描电子显微镜（FESEM）、能量色散X射线光谱（EDS）和傅里叶变换红外光谱（FTIR），研究了镁电解质/电极界面的SEI演化。结果显示，所研究的两种镁电解质体系呈现出显著不同的界面演化情况，一种是以DMA作为共溶剂的THF中的非卤化镁（TFSI）电解质（Mg - DMA电解质），另一种是含卤全苯基配合物（APC）电解质。Mg - DMA电解质在初始电化学循环时，由于电解质重构过程，SEI形成极小且伴有显著的库仑损失。有趣的是，在后续电化学循环中观察到更复杂的SEI生长，同时由于新形成的与镁的配位环境，可逆镁沉积得到改善，最终导致电化学沉积镁的形态更均匀，维持富含MgF的界面。相比之下，APC电解质在初始电化学循环时形成广泛的SEI，随后在电化学循环过程中发生SEI溶解过程，同时随着痕量水和氯物种的去除，库仑效率提高。因此，在进一步的电化学循环中导致SEI稳定进展，从而提高电荷传输动力学和电化学沉积镁的纯度。这些突出的发现加深了对镁界面SEI形成与演化的理解，并为未来镁离子电池的设计铺平了道路。
