Preparation of highly ionic conductive lithium phosphorus oxynitride electrolyte particles using the polygonal barrel-plasma treatment method

Herein, lithium phosphorus oxynitride (LiPON) electrolyte particles with high ionic conductivity were prepared using the polygonal barrel-plasma treatment method. Results showed that the ionic conductivity of Li₃PO₄ (particle size: 77 nm) was improved via the N₂-plasma treatment (treatment time: 60–180 min). The maximum ionic conductivity (8.8 × 10^–6 S cm^–1 at room temperature) was obtained for a treatment time of 90 min, and it approximates that of amorphous LiPON films in literature. X-ray photoelectron spectroscopy of the treated samples (particle size: 29 µm) revealed the formation of LiPON: the area ratio of triply coordinated nitrogen (P–N<P₂) versus doubly coordinated nitrogen (P–NP) [dbnd]bonds, which compose LiPON, increased as the treatment time increased to 90 min, and then decreased. The particle surface morphology hardly changed during treatment, whereas the cross-sectional observation showed that at least 320-nm amorphous LiPON layer was formed near the particle surfaces. Based on the LiPON layer thickness, it was found that amorphous LiPON particles can be obtained through N₂-plasma treatment of 77 nm Li₃PO₄ particles. However, the formed LiPON was partially crystallized under the 120 and 180 min treatments. Thus, a variation in the formation of P–N<P₂ and P–NP[dbnd] bonds and partial crystallization of the formed amorphous LiPON cause the treatment time dependence of ionic conductivity of the treated samples.