Uncovering the role of atmosphere on thermal stability of NASICON type solid electrolytes and oxide-based cathode materials via high temperature X-ray diffraction

Thermal stability of NASICON type solid electrolytes, Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) and Li 1.25 Al 0.25 Ge 1.75 (PO 4 ) 3 (LAGP), were studied against LiCoO 2 (LCO), Al-doped LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NCM), LiMn 2 O 4 (LMO) and LiCoPO 4 (LCP) in both air and inert gas. An in-situ high temperature X-ray diffractometer was employed to monitor phase changes during the co-sintering of the electrolytes-cathode composites. The effect of atmosphere on the thermal stability of LATP/LAGP is closely related to the stability of cathode material in the composite. LATP and LAGP are less stable in air than in inert gas when in contact with NCM and LCO. However, their thermal stabilities are similar in both air and inert gas when mixed with LMO and LCP. In the composite samples of LATP/LAGP+LMO, only traces of the impurities were detected at 700 °C due to the decomposition of LATP/LAGP. The initial lithium rich LMO loses approximately 5 % of its lithium but retains the same crystal structure. Therefore, the LATP/LAGP + LMO could be promising composite cathodes.