Fabrication of composite probe electrode used for localized impedance analysis of solid-state electrolyte LATP

A composite probe combining manganese-based active material with a tipless probe has been developed using a simplified dip-pen process for the localized impedance measurement (LIM) of a solid-state phosphate electrolyte. The active material is found to be composed of a spinel LiMn2O4 crystal phase, while the crystal structure of the solid-state electrolyte is indicated as lithium aluminum titanium phosphate (LATP). Compared with the impedance measurement of the LATP through a platinum/LATP/platinum (Pt/LATP/Pt) metal-insulator-metal (MIM) cell, in which only the overall bulk electrolyte resistance can be recognized, a LIM performed with a tipless probe enables discernment of the grain boundary resistance from the bulk electrolyte. It is seen that ion transport in the bulk electrolyte can be facilitated by applying external DC bias. The composite probe further allows us to detect the charge transfer resistance in the LiMn2O4/LATP interface in addition to the grain boundary resistance. It is also found that the charge transfer and grain boundary resistances increase with a similar trend when a specific high bias voltage (> 1.5 V) is applied. This can be attributed to more ion extraction from LiMn2O4 into the LATP under the bias voltage. Consequently, the excess ions accumulated in the LATP would either inhibit further ion transport into LATP or retard ion transport across the electrolyte grain boundary.