Single-Crystalline LiNiO2 as High-Capacity Cathode Active Material for Solid-State Lithium-Ion Batteries

Abstract

To increase the specific capacity of LiNi1-x-y Co x Mn y O2 (NCM) cathode active materials, academia and industry are aiming at a higher nickel content. The end member of this family, LiNiO2 (LNO), offers the highest practical specific capacity, but suffers from morphological and structural instabilities during electrochemical cycling. Especially for the successful implementation in solid-state batteries, coarse-grain powders of single-crystalline LNO need to be synthesized to achieve high performance cells. While NCM-type solid solutions with Co and Mn show sufficient structural stability during synthesis, LNO rapidly decomposes under the conventional conditions for the preparation of single crystals. We address this issue by presenting an alternative route towards single-crystalline LNO based on a flux-assisted synthesis. First, LNO is prepared from NiO and LiOH precursors, which yields agglomerated crystals of LNO with notable Li deficiency. Secondly, this raw LNO is transferred into a Li2CO3 melt, which induces crystal growth and separation, and further offers a high chemical potential of Li2O for defect healing. With this method, well-separated and near-stoichiometric, large-grain LNO single crystals are obtained. When tested in solid-state battery cells, this material yields specific discharge capacities q dis >200 mAh g−1 at room temperature and clearly outperforms the state-of-the-art polycrystalline LNO.