Improvement of Sinterability in Lithium Ion Conductors Using Spark Plasma Sintering Combined with Coating Technology

Densification enhancement and property improvement must be achieved in tandem, and controlling the dispersion state of sintering aids is crucial for this purpose. In this study, we propose a new addition method in which a sintering-aid component is uniformly coated onto the target particle surfaces at the nanoscale to suppress segregation within the sintered body. LiTa2PO8 (LTPO) was synthesized by a solid-state reaction, and an MgO coating precursor solution was prepared via a metal alkoxide process. LTPO–MgO core–shell particles ([MgO]/[LTPO] = 0.05 and 0.1) were obtained by wet coating process. These powders were sintered by spark plasma sintering (SPS), and after a decarbonization treatment, the microstructure, relative density, and electrochemical properties were evaluated by SEM/elemental mapping, and electrochemical impedance spectroscopy (EIS). The coating-based addition suppressed local Mg segregation and produced a denser microstructure with fewer pores than that obtained by conventional powder mixing, resulting in a marked increase in densification. A maximum relative density of 99.2% was achieved, while the electrochemical performance was optimized at [MgO]/[LTPO] = 0.05, where the grain-boundary resistance was most significantly reduced and the total lithium-ion conductivity reached 4.6 × 10-5 S cm-1. These results demonstrate that combining nano-coating for sintering-aid dispersion control with SPS is an effective approach to simultaneously realize densification and improved grain-boundary ionic transport.