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Na 3 V 2 (PO 4 ) 2 F 3 (NVPF), a typical sodium superionic conductor (NASICON) type structure, has attracted much interest as a potential positive electrode in sodium-ion battery. However, the inherently poor electronic conductivity of phosphates compromises the electrochemical properties of this material. Here, we develop a general strategy to improve the electrochemical performance by preparing a new composite material "polyaniline (PANI)@NVPF" using a Pickering emulsion method. The X-ray diffraction and Raman results indicated a successful PANI coating without affecting the NASICON-type structure of NVPF, and they enhanced the interfacial bonding between the two components. Also, thermogravimetric analysis and scanning electron microscopy analyses revealed that the PANI content influenced the thermal stability and morphology of the nanocomposites. As a result, the sodium test cells exhibited multielectron reactions and a better rate performance for PANI@NVPF nanocomposites as compared to NVPF. Specifically, 2%PANI@NVPF maintained 70% of its initial capacity at 5C. Ex-situ electron paramagnetic resonance revealed the existence of mixed valence states of vanadium (V 4+ /V 3+ ) in both discharge and charge processes. Consequently, the successful PANI coating into the sodium superionic conductor framework improved the sodium diffusion channels with a measurable increase of diffusion coefficients with cycling (ca. 3.25 × 10 -11 cm 2 s -1 ). Therefore, PANI@NVPF nanocomposites are promising cathode candidates for high-rate sodium-ion battery applications.

A Mg-cell with P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 layered oxide cathode provides novel reaction mechanism not observed in Na-cells. The sodium/vacancy ordering and Jahn-Teller effects are suppressed with the insertion of magnesium ion. The Mg-cell exhibits different features when operating between 4.5 and 0.15 V and 3.9 and 0.15 V versus Mg 2+ /Mg. To analyze the structural and chemical changes during Mg insertion, the cathode is first charged to obtain the Na 1/3 Ni 1/3 Mn 2/3 O 2 compound, which is formally accompanied by an oxidation from Ni 2+ to Ni 3+ . As structure models Mg 1/6 Na 1/3 Ni 1/3 Mn 2/3 O 2 and Mg 1/12 Na 1/2 Ni 1/3 Mn 2/3 O 2 are utilized with a large 2 3 a $2\sqrt 3 a$ × 2 3 a $2\sqrt 3 a$ supercell. On discharge, the Mg-cell exhibits a multistep profile which reaches ≈100 mA h g -1 with the valence change from Ni 3+ to Ni 2+ . Such profile is quite different from its sodium counterpart (230 mA h g -1 ) which exhibits the sodium/vacancy ordering and deleterious presence of Mn 3+ . Depending on how the two interlayer spacings are filled by Na and Mg the "staged," "intermediated," and "average" models are analyzed for Mg y Na 8 Ni 8 Mn 16 O 48 supercell. This fact suggests differences in the cell performance when Mg is used as counter electrode providing some tips to improve the structure engineering on cathode materials., (© 2023 Wiley-VCH GmbH.)