Glass-Ceramic Solid Electrolytes for Lithium and Sodium Ion Batteries

Common Lithium and Sodium Batteries have crucial drawbacks in operation caused by the type of separators and electrolytes. Polymeric separators used in Li-batteries show an insufficient stability against rising temperatures and the growth of dendrites. So hot spots, internal shortcuts, and even fire can result. The used solid electrolytes for Na Batteries made of β/β’’-Al₂O₃ work at temperatures around 300 °C what leads to low efficacies by energy consumption for heating of the battery system. Cracks in Al₂O₃ separators can cause severe failure by leakage of molten sodium. For both types of batteries solid glass-ceramic electrolytes can contribute to a higher level in security and safe operation of battery systems by several superior material properties. By high mechanical strength, a precise distance between the electrodes is defined. Due to high thermal stability, thermal runaways are impeded. Glass-ceramic and ion conducting materials can be used as particles or porous solids in combination with liquid electrolytes for common batteries but gastight solid electrolytes even enable new battery concepts like lithium-air batteries. Thin and mechanical stable Na-Ion conducting electrolytes show high conductivities even at ambient temperatures and enable room temperature sodium batteries. Dense galss-ceramic solid electrolytes also enable the use of two different types of liquid electrolytes for anode and cathode compartment.

In the study glasses are molten, quenched and crystallized to obtain ion conductive solid state glass-ceramic electrolytes. The material systems therefore are Li_1+xAl_xTi_2-x(PO₄)₃ for Li-Ion Batteries and Na_3+3x-yRE_1-xP_ySi_3-yO₉ (RE: rare earth) for Na-Ion Batteries respective both are analogues of the NaSiCON-Structure. Glasses with varying ratios of Al/Ti and RE/P/Si are molten and after crystallization by different thermal treatments widely characterized (HTM; DTA; XRD; REM). Impedance spectroscopy measurements are carried out to determine the conductivity with respect to the chemical composition, thermal treatment and microstructure. Room temperature conductivities up to 10^-4 S/cm will be presented and discussed. Promising compositions are processed as slurry for tape casting to gain thin and dense glass-ceramic solid electrolyte tapes for the application in room temperature Batteries.