Regulating Phase Transition and Oxygen Redox to Achieve Stable High-Voltage O3-Type Cathode Materials for Sodium-Ion Batteries

O3-type layered oxides are promising cathode materials for sodium-ion batteries. However, unsatisfying cyclic stability hinders its practical application, mainly resulting from harmful phase transition and irreversible oxygen redox, especially in high-voltage regions. Herein, a co-doped strategy by incorporating Li+, Mg2+, Ca2+, and Sb5+ into the O3-Na0.8Ni0.4Fe0.2Mn0.4O2 cathode materials is proposed. Both suppressing the undesired phase transition over 4.1 V (vs Na/Na+) and reducing the anisotropic strain are achieved with the novel Na0.8Ni0.3Fe0.2Mn0.3Li0.1Mg0.02Ca0.05Sb0.03O2 (LMCS NFM). Moreover, restricted but highly reversible oxygen redox is observed due to strong attraction from Sb5+ and special "Li-O-vacancy" and "Mg-O-vacancy" configurations. The strategy brings about excellent high-voltage cyclic stability with a reversible capacity of 130 mAh g-1 and a capacity retention of 85% after 250 cycles at 4.2 V, and less thermal runaway risk and moisture sensitivity, increasing the probability of O3-type oxide cathode practical applications. The O3-type cathode materials always deliver an unsatisfying cyclic performance for the sodium-ion batteries (SIBs), especially with a high cut-off voltage. The new configuration in this research exhibits much-enhanced structure stability and practical application possibility via regulating the phase transition and oxygen redox at 4.2 V.image