Tailoring shape and exposed crystal facet of single-crystal layered-oxide cathode particles for all-solid-state batteries

The design of composite cathode microstructures is important for improving the performance of all-solid-state batteries (ASSBs). The microstructural properties can provide efficient ionic/electronic percolation, good cathode/solid electrolyte (SE) contact, and minimal void spaces. Although the effects of the size of cathode and SE particles have been extensively investigated, the shape effects of cathode particles remain unexplored. Here, we demonstrate that the shape and exposed crystal facet of cathode particles affect the electrochemical performance of ASSBs using crack-free single-crystalline LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) as the cathode and oxidation-tolerant Li₃YCl₆ as the SE. Systematic studies using five particle shapes (octahedra, plates, rods, spherical single crystals, and spherical polycrystals) reveal the important effects of the shape and exposed facets on the solid–solid contact as well as Li⁺ ion diffusion in composite cathodes. Single-crystalline octahedral NCM particles have a higher rate capability than that of their counterparts because their wide planar surface promoted plane-to-plane contact with the SE and the (0 1 2) facets provided straightforward 3D Li⁺ transfer channels between the surface and the center. These results suggest that single-crystal NCM cathodes with advanced shapes and exposed facets can enable the fabrication of ASSBs with superior performance.