Due to a significantly increasing demand for large-scale energy storage units especially for the power grid and sustainable vehicles, systems that are beyond lithium chemistry have gained much attention in recent years. New secondary battery chemistries based on multivalent cation charge carriers, such as Mg²⁺ and Zn²⁺, which involve more than one electron transfer, may lead to higher specific capacity and energy density. They are also relatively abundant, inexpensive, and offer superior safety compared to lithium when exposed to air. Despite the advantages of these systems over lithium chemistry, the development of multivalent-ion rechargeable batteries has been hampered by a variety of intrinsic problems related to the design and synthesis of multivalent intercalation cathodes. An approach to developing electrode materials that can reversibly insert multivalent cations is to chemically intercalate ions such as Mg²⁺ and Zn²⁺ into a host structure with a highly open framework or large interlayer distance, thus allowing facile multivalent-ion transport. As a result, the inserted Mg²⁺ or Zn²⁺ cations inside the host structure can serve as charge carriers in energy storage systems.

Traditionally, chemical intercalation is done by using organometallic reagents in heptane or hexane, such as di-n-butylmagnesium for Mg²⁺ and dimethylzinc or diethylzinc for Zn²⁺ by constant stirring the solution for 1‒2 weeks. These organometallic compounds are, however, known to be moisture-sensitive and react violently with water, thus raising safety concerns. We present here a new microwave-assisted chemical insertion technique, using the corresponding metal acetate as a metal ion source and diethylene glycol (DEG) as a reducing agent. This approach has been successfully demonstrated in microporous Mo_2.5+yVO_9+z host framework with large open channels. Mo_2.5+yVO_9+z with tunnels constructed by three-, six-, and seven-membered ring units of MO₆ octahedra (M = Mo^5+/6+ or V^4+/5+) belongs to the family of isostructural MoVNbTeO compounds, which are very active oxidation catalysts for light alkanes due to the redox activities of Mo and V. With this microwave-assisted technique, divalent-ion-inserted compounds A_xMo_2.5+yVO_9+z (A = Mg, Zn, 0 < x ≤ 3) can be prepared in as little as 30 min at 160‒200 ºC. The Mg-inserted compounds Mg_xMo_2.5+yVO_9+z (0 < x ≤ 3) thus obtained have been investigated as cathode materials in Mg-ion batteries. Our preliminary results suggest that the inserted Mg²⁺ ions can be removed electrochemically from the framework and reinserted for many cycles. This novel process offers a fast, inexpensive, easily scalable method to insert multivalent metal ions using relatively much safer chemicals which can be carried out in ambient atmosphere.