Impact of LiPON incorporation on the ionic conductivity of mixed oxy-sulfide glassy solid electrolytes

Abstract

Solid-state electrolytes (SSEs) with high ionic conductivity, stability, mechanical strength, and low cost are crucial for next-generation all-solid-state lithium batteries (ASSLBs). These materials could provide better safety, energy density, and lifespan than conventional lithium-ion batteries with liquid electrolytes. Some lithium glassy solid electrolytes (GSEs) stand out for their high ionic conductivity, wide electrochemical stability, and good compatibility with lithium metal anodes. Alkali oxide GSEs offer good chemical stability but suffer from very low ionic conductivity, whereas alkali sulfide GSEs provide much higher conductivity but are unstable with both low-reduction-potential lithium metal and high-oxidation-potential cathodes. Mixed oxy-sulfide (MOS) GSEs combine the benefits of oxides and sulfides, and incorporating nitrogen further enhances their properties, making mixed-oxy-sulfide-nitride GSEs promising candidates for ASSLBs. This study of Li₂S + SiS₂ + LiPO₃ + LiPON mixed glass former MOSN GSEs investigates the influence of LiPON incorporation on the physical properties, electrochemical behavior, and ionic conductivity of the base MOS GSEs. The Christensen–Martin–Anderson–Stuart (CMAS) model was used to model the Li⁺ ionic conductivity activation energy in terms of the coulombic binding and volumetric strain energy components. The binding energy for these GSEs was calculated as a function of the composition and found to be correlated with the concentration of di-coordinated nitrogen in the glass. Further, this study explored the structural, physical, and electrochemical properties of these GSEs and the impact of nitrogen incorporation on density, mechanical moduli, electrochemical stability, and dielectric permittivity. It was observed that the added nitrogen increased the ionic conductivity of these GSEs to 1.1 mS cm⁻¹ at 25 °C and that the addition of nitrogen further improved electrochemical behavior when in contact with lithium metal. These results further show the advantageous role that added nitrogen can have upon the electrochemical properties of GSEs.