Advanced Investigation of the Electrolyte-Mg Anode Interphase for the Development of Mg-Ion Batteries

When and Where

Nov 29, 2022
2:30pm - 2:45pm

Hynes, Level 3, Ballroom C

Presenter

Martina Romio

Yuri Surace

Nicolas Eshraghi

Benedikt Herzog

Bruno Eckmann

Damian Cupid

Johannes Hoffmann

Marcus Jahn

Co-Author(s)

Martina Romio¹,Yuri Surace¹,Nicolas Eshraghi¹,Benedikt Herzog²,Bruno Eckmann²,Damian Cupid¹,Johannes Hoffmann²,Marcus Jahn¹

Austrian Institute of Technology¹,Federal Institute of Metrology METAS²

Abstract

Martina Romio¹,Yuri Surace¹,Nicolas Eshraghi¹,Benedikt Herzog²,Bruno Eckmann²,Damian Cupid¹,Johannes Hoffmann²,Marcus Jahn¹

Austrian Institute of Technology¹,Federal Institute of Metrology METAS²

Magnesium-ion batteries (MIBs) represent a promising chemistry to potentially substitute Li-ion technologies in the e-mobility and stationary energy storage applications. This is due to the favourable properties of metallic Mg, such as: abundancy, non-toxic nature, high recycling rate1, low redox potential (-2.37 vs SHE), safety (smooth Mg2+ electrodeposition), as well as divalent character of Mg2+ cations which leads to higher theoretical volumetric capacity (3833 mAh/cm3) than Li (2046 mAh/cm3) and commercial graphite (760 mAh/cm3).2 However, the major obstacle in the development of MIBs is the incompatibility of Mg anode with electrolyte formed by mixing simple Mg-based salts (e.g Mg(TFSI)2, etc.) and polar aprotic solvents (e.g. acetonitrile, etc.). These solutions decompose at the Mg surface forming an electronic and ionic insulating layer, which blocks the electrochemical activity of Mg anode. Conversely, organoborate (Mg-tetrakis(hexafluorosisopropyloxy)borate in monoglyme, MgBOR)3 or organoaluminate (1:2 AlCl3:PhMgCl in THF, APC)4 ethereal solutions are known to prevent the passivation of the Mg metal anode, allowing the reversible Mg2+ electrodeposition. Despite a great effort has been done in the development of MIB,5 very little is known about the formation, evolution and degradation of the solid electrolyte interphase (SEI) formed at the interface between metallic Mg and electrolyte. This work, therefore, aims to investigate the interactions between Mg metal and passivating (Mg(TFSI)2 in monoglyme:diglyme, Mg(TFSI)2 in M:D) and non-passivating (MgBOR and APC) electrolytes combining ex-situ and in-situ spectroscopic and microscopic techniques with electrochemical testing (cyclic voltammetry, galvanostatic cycling with potential and electrochemical impedance spectroscopy). As the first step, a successful polishing method was developed to remove the native oxide layer form the surface of Mg discs allowing to expose a bare Mg metal to the electrolyte solutions. The polishing method also enabled to perform scanning microwave microscopy imaging6,7 of the Mg metal since a roughness between 1-2.5 µm was achieved. This method was applied to MIB technologies for the first time in this work. The Mg discs were then immersed in the electrolyte solutions and an initial deposition of interfacial species (few nm thickness) was observed by SEM when Mg(TFSI)2 in M:D was used, whereas a smooth surface was detected with MgBOR and APC electrolytes. This resulted in different electrochemical behaviours. In fact, symmetric cells (Mg|Mg) with MgBOR electrolyte showed a significantly higher cycling stability (> 250 h) than those with Mg(TFSI)2 in M:D solution. In addition, when the latter electrolyte was used, fluorinated by-products were identified by X-ray photoelectron spectroscopy. To study the SEI formation and growth further, in-situ Raman and was employed to establish a correlation between the chemical composition of the electrolyte, the voltage range of the electrochemical tests and cycling time. References 1. I. R. P. United Nations Environment Programme, (available at https://wedocs.unep.org/20.500.11822/8702); 2. J. Niu, Z. Zhang, D. Aurbach, Adv. Energy Mater., 2020, 10, 2000697; 3. Z. Zhao-Karger, M. E. Gil Bardaji, O. Fuhr, M. Fichtner, J. Mater. Chem. A, 2017, 5, 10815–10820; 4. D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature, 2000, 407, 724; 5. R. Dominko, J. Bitenc, R. Berthelot, M. Gauthier, G. Pagot, V. Di Noto, J. Power Sources, 2020, 478, 229027; 6. A. Buchter, J. Hoffmann, A. Delvallée, E. Brinciotti, D. Hapiuk, C. Licitra, K. Louarn, A. Arnoult, G. Almuneau, F. Piquemal, M. Zeier, F. Kienberger, Rev. Sci. Instrum., 2018, 89, 23704; 7. J. Hoffmann, M. Wollensack, M. Zeier, J. Niegemann, H. Huber, F. Kienberger, in 2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), pp. 1–4.