Ni‐Rich Layered Cathode Materials with Electrochemo‐Mechanically Compliant Microstructures for All‐Solid‐State Li Batteries

Abstract While Ni‐rich cathode materials combined with highly conductive and mechanically sinterable sulfide solid electrolytes are imperative for practical all‐solid‐state Li batteries (ASLBs), they suffer from poor performance. Moreover, the prevailing wisdom regarding the use of Li[Ni,Co,Mn]O 2 in conventional liquid electrolyte cells, that is, increased capacity upon increased Ni content, at the expense of degraded cycling stability, has not been applied in ASLBs. In this work, the effect of overlooked but dominant electrochemo‐mechanical on the performance of Ni‐rich cathodes in ASLBs are elucidated by complementary analysis. While conventional Li[Ni 0.80 Co 0.16 Al 0.04 ]O 2 (NCA80) with randomly oriented grains is prone to severe particle disintegration even at the initial cycle, the radially oriented rod‐shaped grains in full‐concentration gradient Li[Ni 0.75 Co 0.10 Mn 0.15 ]O 2 (FCG75) accommodate volume changes, maintaining mechanical integrity. This accounts for their different performance in terms of reversible capacity (156 vs 196 mA h g −1 ), initial Coulombic efficiency (71.2 vs 84.9%), and capacity retention (46.9 vs 79.1% after 200 cycles) at 30 °C. The superior interfacial stability for FCG75/Li 6 PS 5 Cl to for NCA80/Li 6 PS 5 Cl is also probed. Finally, the reversible operation of FCG75/Li ASLBs is demonstrated. The excellent performance of FCG75 ranks at the highest level in the ASLB field.