A Comparative Study of Polycrystal/Single-Crystal LiNi0.8Co0.1Mn0.1O2 in All-Solid-State Li-Ion Batteries with Halide-Based Electrolyte under Low Stacking Pressure

Composite cathodes consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and brittle Li3InCl6 (LIC) solid-state electrolyte (SSE) are assessed for all-solid-state Li-ion battery (ASSLIB) applications under a low stacking pressure (coin-cell configuration: ≈2.0 MPa). Herein, an investigation is conducted to understand how the internal particle morphologies of the polycrystal (PC-)/single-crystal (SC-) NCM cathode materials affect the internal cracking within the composite electrodes and thereby electrode performance. Extensive debonding between NCM and LIC takes place even at a very low current density (0.03C) with high voltage (4.4 V), but substantially narrower/shorter debonding gaps are observed for SC-NCM as compared with PC-NCM (wider/lengthier) due to their different particle sizes. High current rates (e.g., 0.1C) bring about greater strain rates in PC-NCM particles, resulting in widespread microcracking along the grain boundaries between primary particles and consequently creating “dead zones” that are isolated from the ionic and electronic conduction pathways. Although SC-NCM shows microcracking within the agglomerates, individual NCM crystals remain in close contact with the SSEs because of noticeably fewer grains in the agglomerations than in the PC-NCM secondary particles. A low-pressure SC-NCM ASSLIB is demonstrated with good cycle stability comparable with that of a liquid-electrolyte cell even under stressful currents.