A hydrostable cathode material based on the layered P2@P3 composite with revealed redox behavior of Cu for high-rate and long cycling sodium-ion batteries

Viewing from the perspective of sustainable development, the low‐cost layered oxides without Ni or Co are considered to be the most promising type of cathode materials for future sodium‐ion batteries. The atmospheric and electrochemical corrosion occurring at the interfaces of layered cathodes, however, results in serious degradation of both the capacity and cycle life. A P2@P3 layered oxide composite induced by Zn doping, which only consists of cheap transition metals with high rate and long cycling performance represents a promising cathode for sodium‐ion batteries. The P2@P3 biphase synergetic property in this composite is well revealed not only in electrochemical performance but also its humidity resistance. The results indicate partial Zn substitutes in Na0.78Cu0.33‐xZnxMn0.67O2 composite can effectively promote and control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with Electron‐Energy‐Loss spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray absorption near‐edge spectroscopy, a possible way of Cu2+/3+ redox reaction has been revealed in this material, and the mechanism of Na0.78Cu0.33‐xZnxMn0.67O2 composite is proposed to be a solid solution and two‐phase mechanism.