Phosphate Based Ceramics As Solid Electrolyte for High Temperature Lithium Ion Batteries

Abstract

A Li-ion battery with liquid electrolyte may suffer from security risks such as inflaming or short circuits. A solid electrolyte made of ion conducting glass-ceramic is thermally more stable. If the ion conducting ceramics as combined electrolyte and separator could be used in a battery, the battery will be safer. LAGP (Li1+x AlxGe2-x (PO4)3) was investigated as a candidate for solid electrolytes in Li ion batteries. LAGP glass samples were produced using the melt-quench-method. Samples were fabricated using powder compaction by sintering or by direct heat treatment of the glass. Their ionic conductivities were measured with impedance spectroscopy. Dilatometer measurements, X-ray diffraction and scanning electron microscope analysis were also carried out. The thermal properties like crystallization temperature, heat capacity and thermal conductivity were measured with differential scanning calorimeter and Laser-Flash apparatus. Multiple batches of LAGP with different composition were produced. The ionic conductivity of 3·10-4 S/cm at room temperature and 1·10-2 S/cm at 150°C was achieved. The relationship between the process parameters, the microstructure and ionic conductivity of the solid electrolyte was studied. Also, their influence on the heat capacity and the thermal conductivity was studied. All-solid test cells were fabricated using LAGP ceramic as solid electrolyte. Magnetron sputtering, spark plasma sintering and furnace sintering were used to produce the anode-electrolyte-cathode multilayer tablets. The tablets were assembled in swagelok-cells and tested between 100°C and 200°C.