Thermodynamic and kinetic properties of conversion reactions in new, sodium based battery systems

• Applicant: Professor Dr. Philipp Adelhelm
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257682551

The development of safe and low cost electrochemical energy storage devices with high energy densities is one of the key challenges for current battery research. Current lithium-ion battery technology is mostly based on the reversible formation of intercalation compounds with layered structure. Higher capacities can be achieved by compounds that undergo so-called conversion reactions with lithium. The general reaction can be written as MaXb + (bc)Li = aM + b LicX with M being a transition metal (Fe, Co, Ni, Cu, etc.), X being a non-metal (F, O, N, P, S, etc.), and Li being lithium. Despite the intensive research in this field, no suitable electrode material could be identified so far that exhibits suitable cell characteristics for application at room temperature. Aim of the present research proposal is to investigate the largely unknown cell chemistry of sodium based conversion reactions for their use in room temperature sodium-ion batteries. The second important aim is to compare the cell chemistry of sodium based conversion reactions with the analogue lithium system. Similarities and differences between both reactions will be used to deepen the fundamental understanding of the underlying mechanisms of conversion reactions. As a result, general guidelines for the improvement of conversion systems towards application might be formulated. In both cases, experiments using thin film model electrodes allow the most accurate and exact investigations. Here, an important advantage of sodium over lithium is the easier analytical access due to the higher atomic weight of Na compared to Li. Objective of the subproject bulk phase is the systematic investigation of the general cell chemistry of conversion reactions and their structural characterization with standard methods (XRD, SEM, TEM, XPS, galvanostatic cycling, cyclic voltammetry, mass spectrometry). Important aim of the subproject is, to identify the most promising compounds MaXb for the comparison between sodium and the analogue lithium systems. Objective of the subproject model systems is the preparation of highly defined model electrodes and cells from selected compounds by means of pulsed laser deposition with the aim to develop suitable in situ experiments.

• DFG Programme: Research Grants