Simulating the Impact of Glassy Carbon Foam Electrodes on the Performance of Sodium Iodine Batteries

This publication examines the influences of glassy carbon foam electrodes on the overall battery performance of secondary sodium iodine batteries. The battery combines a molten sodium anode and an iodine-based cathode with NaSICON serving as a ceramic separator. The battery system works at 100 °C and is suitable for stationary energy storage. A long cycle life and good resource utilization are major concerns for establishing the proposed battery system. This paper employs a spatially resolved simulation approach to investigate the effects of foam electrodes of different porosities and cell sizes on the charging and discharging behavior. The spatially resolved model reflects species and mass transport as well as electrochemical processes and reactions in the positive half cell. An open-pored glassy carbon foam cathode structure shows an improved utilizable capacity compared to a simpler two-dimensional electrode. Parameter studies of foam porosity and specific surface area indicate that porosity is the crucial parameter for achievable depth of discharge. We conclude that glassy carbon open-pored foam of preferably high porosity is a suitable material for cathode electrodes in sodium iodine batteries

Methodical selection of thermal conductivity models for porous silica-based media with variation of gas type and pressure

If the effective thermal conductivity of a silica powder in any gas atmosphere is to be calculated analytically, one is faced with a whole series of decisions. There are a lot of different models for the gas thermal conductivity in the pores, the thermal accommodation coefficient or the effective thermal conductivity itself in the literature. Furthermore, it has to be decided which input parameters should be used. This paper gives an overview and recommendations as to which calculation methods are best suited for the material classes of precipitated silica, fumed silica, silica gel and glass spheres. All combinations of the described methods result in a total of 2800 calculation models which are compared with pressure-dependent thermal conductivity measurements of 15 powdery materials with 7 different gases using Matlab computations. The results show that with a model based on a spherical unit cell, which considers local Knudsen numbers, the measuring points of all powder-gas combinations can be determined best with an average variance of about 18.5%. If the material class is known beforehand, the result can be predicted with an average accuracy of about 10% with the correspondingly determined methods