Phase-selective defects engineering in dual-phase high entropy oxide for Li-ion storage

This paper presents the effectiveness of phase-selective regulation in the Mg-Co-Ni-Mn-Zn-O-based spinel-rocksalt dual-phase high entropy oxide (HEO) for achieving novel electrochemical properties. The key factor distinguishing spinel from rocksalt in response to Li-ion incorporation is the separation of ions at tetrahedral sites, which offers greater structural adjustability and enables incoordinate defect regulation of individual phases. The optimized Li incorporation facilitates a high concentration of point defects (specifically oxygen vacancies) and appropriately extended defects (such as dislocations and stacking fault) in the spinel phase, accompanied by a spinel-rocksalt intergrown interface. These exquisite adjustments improve the conductivity, structural stability, and specific capacity of the HEO electrode material. Nevertheless, the ever-increasing Li content triggers the transformation from a spinel-rocksalt dual-phase HEO to a single-phase rocksalt HEO, resulting in serious lattice distortion and excessive defects that hinder the efficient transport of Li-ion, ultimately leading to unsatisfactory electrochemical performance. Thus, phase-selective engineering facilitates the determination of appropriate defects that synergistically interact with the intergrown interface and the dual-phase structure. The optimized HEO20 exhibits outstanding electrochemical performance, with a high initial discharge capacity of 2049.8 mAh g−1 at 0.1C and a high-rate capability of 502.9 mAh g−1 at 2C. Moreover, it demonstrates remarkable battery capacity retention of 99.5% after 1300 cycles at 0.5C and a stable cycle performance of 717.3 mAh g−1.