A Hydrostable Cathode Material Based on the Layered P2@P3 Composite that Shows Redox Behavior for Copper in High‐Rate and Long‐Cycling Sodium‐Ion Batteries.

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na0.78Cu0.27Zn0.06Mn0.67O2 obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively 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, a possible Cu2+/3+ redox reaction mechanism has now been revealed. The P2@P3 Na0.78Cu0.33−xZnxMn0.67O2 composite induced by Zn doping with revealed redox behavior of Cu2+/3+ is a promising cathode for Na ion batteries. Zn doping not only induces the formation of a P3 phase, which shows a distinct crystal and atomic arrangement with nanoscale thickness, but also offered a high and flat voltage profile, leading to improvement in both structural/electrochemical stability and humidity resistance. [ABSTRACT FROM AUTHOR]