Faculty of Production Engineering, Innovative Sensor- and Functional Materials Research Group , University of Bremen , Badgasteiner Str. 1 , 28359 Bremen , Germany.
Fraunhofer Institute for Manufacturing Technology and Advanced Materials - IFAM , Wiener Str. 12 , 28359 Bremen , Germany.
ACS Appl Mater Interfaces. 2018 Oct 31;10(43):37188-37197. doi: 10.1021/acsami.8b09789. Epub 2018 Oct 17.
LiLaZrO (LLZO) and related compounds are considered as promising candidates for future all-solid-state Li-ion battery applications. Still, the processing of those materials into thin membranes with the right stoichiometry and crystal structure is difficult and laborious. The sensitivity of the Li-ion conductive garnets against moisture and the associated Li/H cation exchange makes their processing even more difficult. Formulation of suitable polymer/ceramic hybrid solid state electrolytes could be a prosperous way to reach the future large scale production of solid state Li-ion batteries. In fact, solvent mediated and/or slurry based wet-processing of the LLZO, e.g., tape-casting, could result in irreversible Li-ion loss of the pristine material due to Li/H cation exchange. The concomitant structural changes and loss in functionality in terms of Li-ion conductivity are the results of the above process. Therefore, in the present work a systematic study on the chemical stability and structural retention of Al-substituted LLZO in different solvents is reported. It was found that Li/H exchange in LLZO occurs upon solvent immersion, and its magnitude is dependent on the availability of -OH functional groups of the solvent molecules. As a result, a larger degree of Li/H exchange causes higher increase of the lattice parameter of the LLZO, determined by synchrotron diffraction analyses. The expansion of the cubic unit cell was ascertained, when Li was replaced by H in the host lattice, by ab initio computational studies. The application of the most common solvent as dispersion medium, i.e., high purity water, causes the most significant Li/H exchange and, therefore, structural change, while acetonitrile was proven to be the best suitable solvent for wet postprocessing of LLZO. Finally, computational calculations suggested that the Li/H exchange could result in diminished ionic, i.e., mixed Li-H, conductivity due to the insertion of protons with lower mobility than that of Li-ions.
镧锆锂氧化物（LLZO）和相关化合物被认为是未来全固态锂离子电池应用的有前途的候选材料。然而，将这些材料加工成具有正确化学计量比和晶体结构的薄膜仍然具有挑战性。锂离子导电石榴石对水分的敏感性以及相关的 Li/H 阳离子交换使得它们的加工更加困难。合适的聚合物/陶瓷混合固态电解质的配方可能是实现未来大规模生产固态锂离子电池的一种有前途的方法。事实上，溶剂介导和/或基于浆料的湿处理（例如，带铸法）可能会导致原始材料不可逆的锂离子损失，原因是 Li/H 阳离子交换。结构变化和锂离子电导率功能丧失是上述过程的结果。因此，在目前的工作中，对不同溶剂中 Al 取代 LLZO 的化学稳定性和结构保持进行了系统研究。研究发现，LLZO 中的 Li/H 交换会在溶剂浸入时发生，其程度取决于溶剂分子中 -OH 官能团的可用性。因此，较大程度的 Li/H 交换会导致 LLZO 的晶格参数增加更多，这是通过同步辐射衍射分析确定的。通过从头计算研究证实，当 Li 被 H 取代时，立方晶胞会发生膨胀。应用最常见的溶剂（即高纯水）作为分散介质会导致最显著的 Li/H 交换和结构变化，而乙腈被证明是 LLZO 湿后处理的最佳溶剂。最后，计算计算表明，Li/H 交换可能会导致离子导电性（即混合 Li-H）降低，这是由于质子的插入导致其迁移率低于锂离子。
