RESUMEN
Non-aqueous solvents, in particular N,N-dimethylaniline (NMP), are widely applied for electrode fabrication since most sodium layered oxide cathode materials are readily damaged by water molecules. However, the expensive price and poisonousness of NMP unquestionably increase the cost of preparation and post-processing. Therefore, developing an intrinsically stable cathode material that can implement the water-soluble binder to fabricate an electrode is urgent. Herein, a stable nanosheet-like Mn-based cathode material is synthesized as a prototype to verify its practical applicability in sodium-ion batteries (SIBs). The as-prepared material displays excellent electrochemical performance and remarkable water stability, and it still maintains a satisfactory performance of 79.6% capacity retention after 500 cycles even after water treatment. The in situ X-ray diffraction (XRD) demonstrates that the synthesized material shows an absolute solid-solution reaction mechanism and near-zero-strain. Moreover, the electrochemical performance of the electrode fabricated with a water-soluble binder shows excellent long-cycling stability (67.9% capacity retention after 500 cycles). This work may offer new insights into the rational design of marvelous water stability cathode materials for practical SIBs.
RESUMEN
Ni-rich cathodes with a radial ordered microstructure have been proved to enhance materials' structural stability. However, the construction process of radial structures has not yet been clearly elaborated. Herein, the formation process of radial structures induced by different doped elements has been systematically investigated. The advanced Electron Back Scatter Diffraction (EBSD) characterization reveals that W-doped materials are more likely to form a low-angle arrangement between crystal planes of the primary particles and exhibit twin growth during sintering than a B-doped cathode. The corresponding High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) analysis further proves that the twin growth induced by W doping can promote the migration of Li+. Simultaneously, the W-doped sample reduces the (003) plane surface energy and promotes the retention of the crystal plane, which can effectively alleviate the structural degradation caused by Li+ (de)intercalation. At a cut-off voltage of 4.6 V, the W-doped cathode displays a capacity retention rate of 94.1% after 200 cycles at 1C. This work unveils the influence of different element doping on the structure from the perspective of crystal plane orientation within primary particles and points out the importance of the exposure and orientation of the crystal plane of the particles.
