Regulating Cathode−Electrolyte Interphases in Single-Crystalline Ni-Rich Cathodes by Gd ₂ O ₃ -Integrated Protective Layers

Recently, single-crystalline high-nickel cathode materials (SC-NCM) have received considerable attention owing to their energy density and structural stability; however, interfacial instability in SC-NCM remains the most challenging issue for long-term cycling. To address this, herein, we report gadolinium oxide (Gd 2 O 3 )-coated SC-NCM cathode materials that effectively regulate undesired interfacial reactions at the SC-NCM cathode. In particular, Gd 2 O 3 physically protects the surface based on hard and soft acids and bases theory; Gd chemically traps F − via a chemical reaction, thereby enhancing interfacial stability and suppressing degradation. Furthermore, incorporating Gd 2 O 3 into SC-NCM is expected to suppress parasitic interfacial reactions during cycling. In terms of cycling performance, 2.0 Gd exhibits higher capacity retention than the standard SC-NCM even after 100 charge/discharge cycles−post-cycling analyses, including SEM, XRD, EIS, XPS, and ToF-SIMS, further show that the Gd 2 O 3 -based coating layer effectively protects the surface and suppresses electrolyte decomposition. Therefore, the formation of the Gd 2 O 3 -derived surface layer is an effective strategy for achieving improved, prolonged cycling performance.