Glass ceramic separators for room temperature operating sodium batteries

Promising compositions of solid electrolyte materials can be obtained with several compositions by various synthesis routes, like regular melt-quench process or producing NASlCON-type glass ceramic, via sol-gel- or oxide synthesis, followed by calcination and ball milling to fine powders. These powders are transferred into slurries followed by tape casting of thin ceramic foils. Sintering is the most challenging step of the entire process. Cracking, bulging, warping and bloating have to be eliminated to get a plane and dense electrolyte substrate. NASICON-type glass ceramic compositions from the Na2O-REO-SiO2-system (REO-rare earth oxides) with and without additions of P2O5 have been prepared via glass melting, quenching on different materials, grinding to powder with subsequent sintering and crystallization after shaping steps like cold uniaxial pressing and tape casting. The separator materials were characterized by microscopy, XRD, density measurements and electrochemical impedance spectroscopy. Na+ ion conducting ceramics with a relative densities of 95 to 97 %, a thickness about 300 mm and conductivities >1-10-3 S/cm at room temperature were obtained.