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

Abstract

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) 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 bonds and partial crystallization of the formed amorphous LiPON cause the treatment time dependence of ionic conductivity of the treated samples.