Rational engineering of amorphous coating/rock-salt phase dual-coupling for overcoming the capacity–stability conflict in Co-free Ni-rich cathodes

Abstract

The construction of a highly stabilised surface on Co-free Ni-rich cathode materials is a promising method for enhancing their structural stability and cycling performance. In this study, we developed a novel dual-coupling surface engineering strategy whereby we successfully constructed an amorphous Li–Al–O coating layer that synergises with a nanostructured internal rock-salt phase layer on a LiNi_0.95Mn_0.05O₂ (NM95) surface through an in situ modification process. The internal rock-salt phase layer effectively blocks oxygen release and mitigates lattice strain. In addition, the external amorphous coating layer effectively inhibits the interfacial side reactions and enhances the interfacial Li⁺ transport. Benefiting from the dual-coupling synergistic effects, the amorphous Li–Al–O@rock-salt double-layer-coated NM95 cathode exhibited excellent cycling performance, retaining 97.3% of its capacity after 100 cycles at 1 C under 4.3 V, compared to only 66.7% for the pristine sample. Even at a higher cut-off voltage of 4.5 V, the modified cathode still achieved a capacity retention of 91.2% (vs. 44.2% for pristine). This study provides an effective surface engineering strategy that simultaneously stabilises the structure and interface of Co-free Ni-rich NM95 cathode materials and can be applied to the design of other cathode materials.