Conductivity and interfacial stability of oxynitride alumino-phosphate glasses for solid-state lithium-metal batteries

In this work, we investigated the ionic conductivity and interfacial properties of lithium phosphate oxynitride glasses modified with aluminum and increasing contents of nitrogen. Nitrogen for oxygen substitution was achieved by thermal ammonolysis, where P–N bonds partially replace both bridging and non-bridging oxygens of the phosphate network. Solid-state NMR revealed the formation of P(O,N) 4 groups that give rise to a complex network structure, where lithium ions present higher degree of disorder with nitrogen content. Nitrogen incorporation in the glasses results in a two-fold benefit: the glass network becomes more rigid and compact due to the higher covalent bonds density, which improves the interfacial stability against lithium; and the mobility of lithium ions is enhanced by the reduced electrostatic interaction with non-bridging oxygens, facilitating lithium-ion transport. Cyclic voltammetry measurements demonstrate that the nitrided lithium alumino-phosphate glasses exhibit a stable electrochemical window from 0 to 5 V versus Li/Li + . Nitrogen incorporation significantly enhances interfacial stability, suppresses voltage polarization, and increases the critical current density. As a result, the nitrided samples enable stable cycling for 200 h at current densities of 0.04 mA cm −2 and 0.08 mA cm −2 . This work highlights nitrogen incorporation as a versatile strategy to enhance ion transport and interfacial stability. • N-modified lithium phosphate oxynitride glasses synthesized by thermal ammonolysis. • Nitrogen incorporation enhances Li + mobility and interfacial stability. • Nitrided glasses show a wide electrochemical window (0–5 V vs. Li/Li + ).