Chevrel phases such as Mo6S8 are the cathode materials with good cycles for rechargeable magnesium battery which Prof. Aurbach announced in 20001. In case of sulfide and selenide compounds, the discharge voltage is around 1 V (see figure 1 below) which is much lower than those (above 3V) for Li ion battery cases. It is expected that Mg2+ is difficult to diffuse in cathode materials due to the
higher charge than Li+. Oxides could be a good candidate for higher (> 2V) voltage materials, but the Mg-O bond is also stronger than Li-O. Thus, once Mg-O bond is formed, it could be more difficult to break-and-form for diffusion. A new cathode candidates with above 2V discharge voltage is required.
Figure - Cyclic Voltammogram of Mo6S8 vs. Mg/Mg2+. Discharge voltage is about 1 volt. The Chevrel phases could be represented as a formula of M2Mo6X8 where X= S, Se, Te, and M= Cu, Ag, Li, Mg, Ca, Pb, some lanthanides, Sn, Tl, In, , Sb, Bi etc. Many kinds of atoms can be incorporated into the Chevrel phases. M2Mo6X8 is prepared easily, but it is difficult to directly synthesize Mo6X8. Cu2Mo6X8 is prepared first, and later the Cu is removed using FeCl3 solution or electrochemically, resulting in Mo6X8 only.
Any proposed solution should address the following Technical Requirements:
higher charge than Li+. Oxides could be a good candidate for higher (> 2V) voltage materials, but the Mg-O bond is also stronger than Li-O. Thus, once Mg-O bond is formed, it could be more difficult to break-and-form for diffusion. A new cathode candidates with above 2V discharge voltage is required.
Figure - Cyclic Voltammogram of Mo6S8 vs. Mg/Mg2+. Discharge voltage is about 1 volt. The Chevrel phases could be represented as a formula of M2Mo6X8 where X= S, Se, Te, and M= Cu, Ag, Li, Mg, Ca, Pb, some lanthanides, Sn, Tl, In, , Sb, Bi etc. Many kinds of atoms can be incorporated into the Chevrel phases. M2Mo6X8 is prepared easily, but it is difficult to directly synthesize Mo6X8. Cu2Mo6X8 is prepared first, and later the Cu is removed using FeCl3 solution or electrochemically, resulting in Mo6X8 only.
Any proposed solution should address the following Technical Requirements:
The cathode material must have an average discharge voltage greater than 2V vs. Mg/Mg2+ as measured by cyclic voltammetry.
The material’s electric conductivity must be comparable to Li-ion cathode materials and be greater than 1 x 10-7 S/cm.
Mg2+ must de/intercalates reversibly in the material2 as measured by cyclic voltammetryor charge/discharge measurements, followed by X-ray diffraction measurements to confirm.
The material must be stable under an ambient atmosphere.
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