Synthetic Strategies Impacting Voltage, Capacity, and Current Capability of Energy Storage Materials

Abstract

Low temperature synthetic strategies for direct control of crystallite size and composition of energy storage materials will be discussed. This ability to synthetically control material properties enabled the systematic exploration of the fundamental properties of the materials, which reveals a dependence of electrochemical reversibility, current capability, and delivered capacity on chemical or physical properties, likely crystallite size. In a more general sense, fundamental studies involving the impact of physical and chemical properties of materials on their electrochemical properties are critical in the rational development of materials, which may address the present and future requirements for stationary and portable power. Results Materials from several structural types could be synthetically controlled to achieve variation in crystallite size. For example, magnetite, Fe3O4, a densely packed structure could be made where the crystallite size is tightly controlled.1,2 Correlation of the electrohemical performance to crystallite size was observed where the cell using the smallest crystallite size, delivered higher capacity under pulse type testing.A second category of materials is represented by AgxMn8O16 (silver hollandite) a tunnel structure.3 Remarkably, as the Ag:Mn ratio was varied via the synthetic approach developed for the system, concomitant changes in the crystallite size were observed.4 This enabled systematic investigation of this variable on the resultant electrochemistry. The delivered capacity, reversibility, and loaded voltage improved significantly for the small crystallite size material.5