Masaki Matsui

Electrolyte roadblocks to a magnesium rechargeable battery

Low cost, non-dendritic magnesium metal is an ideal anode for a post lithium ion battery. Currently, development of magnesium electrolytes governs the rate of progress in this field, because electrolyte properties determine the class of cathodes utilized. A review of the latest progress in the area of magnesium battery electrolyte and a perspective on mitigating present challenges is presented herein. Firstly, density functional theory has been shown to predict the potential window of magnesium electrolytes on inert electrodes. Secondly, we report initial efforts aimed to overcome the corrosive property of these magnesium organohaloaluminates towards less noble metals such as stainless steel. This is a major challenge in developing high voltage magnesium electrolytes essential for batteries which operate above 3V. We lastly touch on cathode candidates including the insertion and conversion classes. One conversion cathode we pay particular attention to is electrophilic sulfur which can be married with magnesium metal anodes by utilizing non-nucleophilic electrolytes obtained by simple crystallization of in situ generated magnesium organohaloaluminates. Effectively, non-nucleophilic electrolytes open the door to research on magnesium/sulfur batteries.

Magnesium borohydride: from hydrogen storage to magnesium battery.

Beyond hydrogen storage: The first example of reversible magnesium deposition/stripping onto/from an inorganic salt was seen for a magnesium borohydride electrolyte. High coulombic efficiency of up to 94 % was achieved in dimethoxyethane solvent. This Mg(BH(4))(2) electrolyte was utilized in a rechargeable magnesium battery.

Surface Layer Formation and Stripping Process on LiMn2O4 and LiNi1 ∕ 2Mn3 ∕ 2O4 Thin Film Electrodes

Surface layer formation and stripping processes on LiMn 2 O 4 and LiNi 1/2 Mn 3/2 O 4 thin film electrodes were analyzed by using in situ Fourier transform infrared (FTIR) spectroscopy. For LiMn 2 O 4 , the peak intensity of in situ FTIR gradually increased up to 4.2 V vs Li/Li + during anodic polarization and decreased more anodic electrode potential. In situ FTIR spectra of LiNi 1/2 Mn 3/2 O 4 showed a strong peak intensity at a two electrode potential, 4.2 V vs Li/Li + and 4.8 V vs Li/Li + These observations indicated that a surface layer formation process is accelerated by a redox couple of transition metals (Mn 3+ /Mn 4+ or Ni 2+ /Ni 4+ ) in active materials. In addition, in situ FTIR spectra for a 3 V plateau area of LiMn 2 O 4 were also investigated to confirm the surface layer formation and stripping by redox couple of transition metals at low electrode potential. The surface layer stripping was observed at 2.9 V vs Li/Li + , and the lower electrode potential and formation process was also observed from 2.9 to 3.2 V vs Li/Li + . It can be explained that the surface layer was formed by immersing the cathode materials into the electrolyte solution.

First-principles study of the magnesiation of olivines: redox reaction mechanism, electrochemical and thermodynamic properties

Development of Mg batteries relies heavily on the thermodynamics and kinetics of the magnesiation of cathode materials that favor the high mobility of Mg ions in the host lattice and energy densities at least comparable to Li ion batteries. In this paper, we performed Density Functional Theory studies to understand the thermodynamics of the magnesiation of olivine compounds. The redox reaction mechanism was revealed in the magnesiation process of MnSiO4. Mn4+ in the host structure was first reduced to Mn3+ resulting in the formation of Mg0.5MnSiO4. Further reduction of Mn3+ to Mn2+ took place to form MgMnSiO4. We also investigated the electrochemical and thermodynamical properties of the magnesiation of olivine compounds. Except for Fe2+/Fe3+, the redox potential of magnesiation–demagnesiation for olivine compounds showed TM2+/TM3+ redox couples at 3–4 V vs. Mg/Mg2+ and TM3+/TM4+ redox couples about 4 V with TM = Mn, Fe, Co and Ni. Full magnesiation of MnSiO4 to MgMnSiO4 showed the largest volume expansion of approx. 20%. We concluded that magnesiation process of olivine compounds showed high thermodynamic similarities with lithiation and Mg0.5FePO4 could be the preferred compound for reversible Mg battery cathodes.