NASICON‐type Li conductors (Li‐NASICON) have traditionally been regarded as promising candidates for solid‐state Li‐air battery applications because of their stability in water and ambient air. However, the presence of water in the cathode of a Li‐air battery can induce a highly alkaline environment by modifying the discharge product from Li2O2 to LiOH which can potentially degrade cathode and separator materials. This study investigates the alkaline stability of common Li‐NASICON chemistries through a systematic experimental study of LiTixGe2‐x(PO4)3 (LTGP) with varying x = 0–2.0. Density functional theory calculations are combined to gain a mechanistic understanding of the alkaline instability. It is demonstrated that the instability of LTGP in an alkaline environment is mainly driven by the dissolution of PO43– groups, which subsequently precipitate as Li3PO4. The introduction of Ti facilitates the formation of a Ti‐rich compound on the surface that eventually passivates the material, but only after significant bulk degradation. Consequently, phosphate‐based Li‐NASICON materials exhibit limited alkaline stability, raising concerns about their viability in humid Li‐air batteries.

中文翻译：

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磷酸盐基 Li-NASICON 导体在碱性环境中的降解机制


NASICON 型锂导体 （Li-NASICON） 传统上被认为是固态锂空气电池应用的有前途的候选者，因为它们在水和环境空气中具有稳定性。然而，锂空气电池阴极中存在水会通过将放电产物从 Li2O2 转变为 LiOH 来诱导高碱性环境，这可能会降解阴极和隔膜材料。本研究通过对 x = 0–2.0 变化的 LiTixGe2-x（PO4）3 （LTGP） 的系统实验研究来研究常见 Li-NASICON 化学成分的碱性稳定性。将密度泛函理论计算相结合，以获得对碱性不稳定性的机理理解。结果表明，LTGP 在碱性环境中的不稳定性主要是由 PO43– 基团的溶解驱动的，随后沉淀为 Li3PO4。Ti 的引入有助于在表面形成富含 Ti 的化合物，最终使材料钝化，但前提是在显着的本体降解之后。因此，磷酸盐基 Li-NASICON 材料的碱性稳定性有限，引发了人们对它们在潮湿锂空气电池中的可行性的担忧。