Characterisation of transition metal doped Li+-stabilized Na-beta''-alumina electrolytes

Sodium-based batteries are a promising candidate for large-scale energy storage, because in contrast to lithium, sodium is a low-cost and abundant resource. The key component to a sodium-based battery is the solid electrolyte, which enables Na+-ions to move between the electrodes and also acts as a separator. This electrolyte is usually made from the ceramic Na-v''-alumina and finds application in commercial Na/NiCl2- or Na/S-batteries. It is well known that some metal oxides can promote the conductivity and the fracture strength of Na-v''-alumina. [1-3]Here the effects of Ti, Ni and Mn-doping on Na-v''-alumina were systematically analyzed. Also multi-component doping of had been tested for the very first time. The ceramic electrolyte was synthesized by calcining a mixture of AlO(OH), LiCO3 andNaCO3 and doping amounts of 0; 0.5; 1; 1.5; 2 and 2.5 wt.% and 10 wt.%.Herein after, the powder was granulated, pressed into bars or discs and sintered at 1500, 1600 and 1700 °C. The effects of doping and different sintering temperatures were evaluated by measuring fracture strength, SEM and X-ray diffraction of the disks and ionic conductivity and density of the bars. The X-ray diffraction data were analyzed by Rietveld-analysis to calculate the Na-v''-alumina phase contented and the lattice parameters. The optimal sintering temperature to achieve a high conductivity was only decreased by Ti-doping, while the conductivity was raised by all three dopants. In case of Mn doping-up to 10% and up to 30% in case of Ti-doping. A further increase of the conductivity by multi compound-doping was not observed. While the conductivity increases, a higher temperature does not lead to denser ceramics or a higher fracture strength. In summary, it can be stated that a well-balanced optimum regarding the manufacturing process and the electrolyte performance was achieved by adjusting the degree of doping and sintering temperature. In the future it will be tested whether the doping affects the long-term stability of a Na/NiCl2-battery.