Santhoshkumar Sundaramoorthy, a doctoral candidate in chemistry, will defend their dissertation titled “Design and Synthesis of Complex Chalcogenides as Electrode and Solid-Electrolyte Materials for Energy Storage Applications.” Their advisor, Dr. Dr. Amitava Choudhury, is an associate professor in the chemistry department. The dissertation abstract is provided below.

In this investigation, complex chalcogenides containing transition metals and main group metals were synthesized using a high-temperature building block approach. Their structural and electrochemical properties were evaluated as cathodes and solid electrolytes for lithium and sodium-ion batteries. The primary focus was on rationally designing new cathode materials that leverage both cation and anion redox reactions to enhance cathode capacity and to understand the structural and chemical changes occurring during electrochemical testing. Additionally, new materials were synthesized to achieve efficient solid-state lithium-ion conduction through vacancy creation via aliovalent doping.

In the first part of the investigation, lithium-containing two-dimensional layered structures were discovered, achieving a discharge capacity of 200 mAh/g in Li3.84Cu1.13GaS4 through cation-induced anion redox reactions. A new composition, Li5MSe4 (M = Ga and Al), was synthesized, and aliovalent doping with tin resulted in a fivefold increase in ionic conductivity compared to the parent structure. Cation and anion redox reactions were examined in sodium-containing one-dimensional Na3Fe2S4-xSex (x = 0, 2, and 4), showing a linear reduction in working voltage due to the substitution with selenium, an anion with lower electronegativity.

The second part of the research focused on the synthesis of Li4P2S6 structures with various third-row transition metals using building block approach. This study emphasizes the crystal structures of the compounds and the reversible intercalation of water and ammonia in the structures when exposed to air. These findings were analyzed using single crystal X-ray diffraction, thermodiffractogram, FTIR, and TGA-DSC techniques.