Effects of Particle Size and Stack Pressure on the Electrochemical Cycling of Solid-State Batteries Composed of Single-Crystalline LiNi 0.6 Mn 0.2 Co 0.2 O 2

Solid-state Li-ion batteries are considered as a major contender to satisfy the requirements for new energy applications due to offering higher safety and energy densities compared to their liquid counterparts. Despite its promising future from theoretical studies, several challenges remain, mainly originating from the chemo-mechanical changes during continuous cycling. In this project, we synthesized single-crystalline LiNi 0.6 Mn 0.2 Co 0.2 O 2 (SC-NMC) cathode active materials (CAM) of particle sizes (D 50 = 0.91, 2.3, 4.6 and 6.5 µm) using well-known coprecipitation and subsequent solid-state synthesis. These CAMs were tested by fabricating solid-state composite cathodes using Li 6 PS 5 Cl (LPSC) as the solid electrolyte and Li 4 Ti 5 O 12 (LTO) as the anode. The rate capability of the full cells (SC-NMC|LPSC|LTO) was evaluated under different stack pressures of 1, 7, and 17 MPa. At low current, all particle sizes deliver comparable discharge capacities due to alleviating transport limitations. However, as current increases, strong particle-size-dependent behavior emerges. The 4.6 µm particles exhibit the highest discharge capacity, followed by 6.5 µm and 2.3 µm materials, while the smallest particles (0.91 µm) show negligible capacity at 2.0 C current. (see the uploaded images). With increasing the applied stack pressure, the discharge capacity increases, ascribed to well-maintained contact at the SC-NMC/LPSC interface. Galvanostatic intermittent titration technique (GITT) measurements and polarization analysis from dQ/dV profiles reveal that the optimal rate capability of intermediate-sized particles originates from a balance between ionic-transport pathways, reduced tortuosity, and minimized interfacial degradation. In contrast, sub-micron NMC particles exhibit severe polarization and limited Li-ion transport, likely due to poor particle-to-particle percolation and increased interfacial side reactions with LPSC. A macro-homogeneous model will be developed to elucidate the influence of stack pressure and microstructural evolution as a function of particle size within the composite cathode and its implications on the cathode chemo-mechanical dynamics. Figure 1