Lithium-ion batteries are one of the most common batteries technologies used in the world today. However, despite their improved functionality over older systems (e.g. lead-acid car batteries), inherent limited storage capacities do not meet emerging energy demands. The storage capacity of a lithium-ion battery is intrinsically limited to its cathode material; which houses lithium upon battery discharge. An emerging field of cathode development looks at using multivalent cations (Ca2+, Mg2+, Zn2+); where the number of moving electronic charges correlates to the oxidation state of the mobile cation. In theory, the insertion of these ions into solid-state host structures (intercalation) resembles that of lithium-ion systems. In general, the energetic stability of oxides qualifies them as favorable hosts for ion intercalation. Specifically, Mn2O4 spinel cathodes are stable at high temperatures only decomposing at about 342°C and so, act as superior host structures for multivalent ions. In addition to its stability, Mn2O4 tends to have an optimal discharge voltage of about 2.9 V vs. Mg+/Mg. In 2015, the Cabana group at the University of Illinois at Chicago experimentally confirmed magnesium intercalation into Mn2O4 host in an aqueous electrolytic environment. However, these electrochemical experiments were completed on de-lithiated LiMn2O4 electrode materials supplied by a commercial manufacturer. Synthetic routes to achieve MgMn2O4 spinel cathodes directly must be developed to have a practical Mg-ion battery prototype. Colloidal synthesis reactions are known to produce nanoparticles with uniform size distribution and morphological characteristics. In a simple direct colloidal reaction, precursor materials are heated in a solvent/ligand; whereupon reaching a critical temperature, nanoparticles nucleate and grow. Preliminary results from our group show that direct synthesis of MgMn2O4 yields nanocrystals with incorrect stoichiometry (Mg0.5Mn2.5O4) and site mixing between Mg2+ and Mn3+ cations. Therefore, the goal of this research project is to optimize synthetic routes to produce nano-sized spinel-type MgMn2O4 cathode materials. Based on our findings, we hope to optimize other colloidal synthetic routes to obtain spinel-type ZnMn2O4 and CaMn2O4.

Colloidal synthesis: A route towards nanometric cathode material for mutivalent batteries

253rd National Meeting (2017)

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