Evaluation of electrochemical methods for determination of the seebeck coefficient of redox electrolytes

Recent advances in thermoelectrochemical cells, which are being developed for harvesting low grade waste heat, have shown the promise of cobalt bipyridyl salts as the active redox couple. The Seebeck coefficient, Se, of a redox couple determines the open circuit voltage achievable, for a given temperature gradient, across the thermoelectrochemical cell. Thus, the accurate determination of this thermodynamic parameter is key to the development and study of new redox electrolytes. Further, techniques for accurate determination of Se using only one half of the redox couple reduces the synthetic requirements. Here, we compare three different experimental techniques for measuring Se of a cobalt tris(bipyridyl) redox couple in ionic liquid electrolytes. The use of temperature dependent cyclic voltammetry (CV) in isothermal and non-isothermal cells was investigated in depth, and the Se values compared to those from thermo-electromotive force measurements. Within experimental error, the Se values derived from CV methods were found to be in accordance with those obtained from electromotive force (emf) measurements. The applicability of cyclic voltammetry techniques for determining Se when employing only one part of the redox couple was demonstrated

Electro chemical expansion during cycling monitoring the pressure changes in operating solid state lithium batteries

Solid state lithium ion batteries SSBs are a promising concept for future energy storage applications. Interestingly, the mechanical effects during operation of SSBs, and their correlation to the electrochemical performance, have rarely been investigated. In such systems, the rigid mechanical coupling between the active phases and the solid electrolyte will lead to more complex non local strain effects than in the common liquid electrolyte based lithium ion batteries, where the chemical expansion or compression of the active phases is accommodated by the liquid electrolyte, and only local mechanical strain within the electrode particles exists. In this work we report on the pressure and height changes within typical solid state batteries, which were measured in situ during galvanostatic cycling conditions. The continuous volume changes of both the anode and the cathode during lithiation delithiation are responsible for a highly reproducible cycle of pressure changes during the operation of the solid state battery cell. Bending and cracking of the solid state battery cells are observed with X ray tomography and provide evidence for the critical role of the macroscopic strain generated during cycling. Furthermore, these pressure and dilatometry measurements as well as X ray tomography underline the importance of external confinement and pressure control for SSB