Densification and charge transport characterization of composite cathodes with single-crystalline LiNi_0.8Co_0.15Al_0.05O₂ for solid-state batteries

Solid-state batteries (SSBs) hold great promise for high-performance and safe energy storage solutions. Several challenges, however, including the standardization of cell/electrode formats and interface instabilities between electrode components, remain to be overcome. Here, the densification effect of composite cathodes on the electrochemical properties in SSBs was studied. By varying the pressure during uniaxial pressing, composite cathode pellets consisting of single-crystalline LiNi_0.8Co_0.15Al_0.05O₂ and Li₆PS₅Cl particles are fabricated without conductive agents, and the microstructural evolution, charge transport kinetics, and electrochemical performance are examined. The densification process results in a close connection between the component particles while reducing the pore spaces within the composite cathodes. The cathode compacted with a nominal pressure of 1500 MPa shows excellent capacity retention (≥ 99%) with discharge capacities of ∼160 mAh g⁻¹ (areal capacity of ∼3.68 mAh cm⁻²) at 0.1 C (∼0.46 mA cm⁻²) over 100 cycles and improved rate capability. These improvements are attributed to the enhanced effective conductivities and diffusion coefficients of Li⁺ ion and electron, based on impedance and DC polarization measurements. These findings will enhance an understanding of the correlation between the microstructure and charge carrier transport properties of composite cathodes for SSBs based on sulfide-based SEs.