Our ability to design new materials with desired electrochemical, thermoelectric or strongly-correlated electron properties is limited by thermodynamic control over reaction products in traditional high-temperature synthetic procedures. On the contrary, topotactic reactions, where extensive parts of the original framework are retained, allow for greater control of the structure of the final products. Therefore, a combination of desired structural\ features, spin and oxidation states can be produced in a final material in a predictable fashion.
Topotactic synthesis and investigation of model compounds for Fe2+/Fe4+ multiple electrons transfer cathodes will be discussed. The transfer of only 1 electron per transition metal during electrochemical cycling limits the total possible cathode specific energy. To further enhance energy density, cathodes with multiple electrons transfer per 3d atom are needed. A cathode material with higher energy density can lead to an overall reduction of Li-ion battery cost. The savings originate since less current collector, electrolyte, separator, and packaging are needed for a battery with the same energy content when higher energy density electrodes are used.
We have prepared a layered ordered rocksalt cobaltate with Co2+/Co3+ oxidation state that shows possible promise as a thermoelectric material. Seebeck coefficient for thermoelectrics with spin-entropy transport depends on ratio of particular spin states. Koshibae's formula predicts the highest possible (of any transitional metal oxide) Seebeck coefficient for this compound. General approaches to soft chemistry synthesis utilized in my group will also be discussed, including the “aliovalent exchange plus intercalation” method and oxygen deintercalation by metal hydrides in an organic solvent under an externally generated pressure.