Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes by implementing the anionic redox process that has recently boosted the capacity of Li-rich layered oxides.Here, we report the first anionic-redox active O3-NaLi1/3Mn2/3O2 phase obtained through a ceramic process by carefully controlling the delicate balance between synthesis conditions and stoichiometry. It shows a sustained reversible capacity of 190 mAh g −1 by redox processes on oxygen and manganese ions as deduced by combined HAXPES and mRIXS spectroscopy techniques. Remarkably, unlike any other anionic-redox layered oxides so far reported, O3-NaLi1/3Mn2/3O2 electrodes do not show voltage fade upon cycling. This finding is due to switching from the interlayer to intralayer migration of the Mn cations promoted by Li + displacement towards the alkali layer upon first Na + de-insertion. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Besides providing insightful fundamental findings pertaining to anion redox, this work offers future directions towards designing high energy density electrodes for advanced Na-ion batteries.

In 2D magnets, interlayer exchange coupling is generally weak due to the van der Waals layered structure but it still plays a vital role in stabilizing the long‐range magnetic ordering and determining the magnetic properties. Using complementary neutron diffraction, magnetic, and torque measurements, the complete magnetic phase diagram of CrPS4 crystals is determined. CrPS4 shows an antiferromagnetic ground state (A‐type) formed by out‐of‐plane ferromagnetic monolayers with interlayer antiferromagnetic coupling along the c axis below TN = 38 K. Due to small magnetic anisotropy energy and weak interlayer coupling, the low‐field metamagnetic transitions in CrPS4, that is, a spin‐flop transition at ≈0.7 T and a spin‐flip transition from antiferromagnetic to ferromagnetic under a relatively low field of 8 T, can be realized for H∥c. Intriguingly, with an inherent in‐plane lattice anisotropy, spin‐flop‐induced moment realignment in CrPS4 for H∥c is parallel to the quasi‐1D chains of CrS6 octahedra. The peculiar metamagnetic transitions and in‐plane anisotropy make few‐layer CrPS4 flakes a fascinating platform for studying 2D magnetism and for exploring prototype device applications in spintronics and optoelectronics.

Rhombohedral NaZr2(PO4)3 is the prototype of all the NASICON‐type materials. The ionic diffusion in these rhombohedral NASICON materials is highly influenced by the ionic migration channels and the bottlenecks in the channels which have been extensively studied. However, no consensus is reached as to which one is the preferential ionic migration channel. Moreover, the relationships between the Na+ distribution over the multiple available sites, concerted migration, and diffusion properties remain elusive. Using ab initio molecular dynamics simulations, here it is shown that the Na+ ions tend to migrate through the Na1–Na3–Na2–Na3–Na1 channels rather than through the Na2–Na3–Na3–Na2 channels. There are two types of concerted migration mechanisms: two Na+ ions located at the adjacent Na1 and Na2 sites can migrate either in the same direction or at an angle. Both mechanisms exhibit relatively low migration barriers owing to the potential energy conversion during the Na+ ions migration process. Redistribution of Na+ ions from the most stable Na1 sites to Na2 on increasing Na+ total content further facilitates the concerted migration and promotes the Na+ ion mobility. The work establishes a connection between the Na+ concentration in rhombohedral NASICON materials and their diffusion properties.