Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.

Manganese substituted sodium cobaltate, Na(2/3)Co(2/3)Mn(1/3)O(2), with a layered hexagonal structure (P2-type) was obtained by a co-precipitation method followed by a heat treatment at 950 °C. Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space. The oxidation states of the transition metal ions were studied by magnetic susceptibility measurements, electron paramagnetic resonance (ESR) and (23)Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The charge compensation is achieved by the stabilization of low-spin Co(3+) and Mn(4+) ions. The capability of Na(2/3)Co(2/3)Mn(1/3)O(2) to intercalate and deintercalate Na(+) reversibly was tested in electrochemical sodium cells. It appears that the P2 structure is maintained during cycling, the cell parameter evolution versus the sodium amount is given. From the features of the cycling curve the formation of an ordered phase for the Na(0.5)Co(2/3)Mn(1/3)O(2) composition is expected.

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The abundance of Ca, its low redox potential and high specific capacity make Ca metal batteries an attractive energy storage system for the future. A recent demonstration of room temperature calcium plating/stripping opened a new avenue of the development, but the performance of cathode materials is lagging far behind. Due to the nature of divalent cations, conversion and coordination electrochemical reactions show better performance compared to insertion. Herein, we demonstrate the use of the anthraquinone‐based polymer as a cathode material for the Ca metal‐organic battery. Electrochemical mechanism investigation confirms the reversible reduction of the carbonyl bond and coordination with Ca2+ cations in the discharged state, opening a pathway toward high energy density battery. Continued performance of a 2‐electrode cell is strongly hampered by the overpotential increase caused by the Ca stripping process on the Ca metal anode stating the need for further development of Ca electrolytes. Ca metal‐organic battery promises to achieve cells with gravimetric energy density on the practical level compared to the state‐of‐the‐art Li‐ion batteries.

For a long time p-block elements such as Sb and Bi have stimulated the battery research community due to their interesting alloying/ dealloying processes in Li-ion as well as in Na-ion batteries. In fact, high capacity and good cyclability can be reached provided that an adapted electrode formulation is applied. Can we extend such electrochemical behavior and performance to potassium? K with a bigger atomic radius was ignored for a long time in spite of its low standard potential in conventional electrolyte and its low cost, which would make K-ion batteries excellent systems. The present study explores the potentiality of Sb and Bi electrodes in K-ion batteries and investigates the electrochemical mechanism occurring through operando XRD. The mechanism in Sb/K and Bi/K systems is then compared to those previously proposed for Li-and Na-ion batteries.

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The new layered compound Li(3)Ni(2)BiO(6) has been prepared by a solid-state reaction. It crystallizes in the monoclinic C2/m space group; its lamellar structure is characterized by a honeycomb ordering between Ni(2+) and Bi(5+) within the slabs, while Li(+) ions occupy octahedral sites in the interslab space. Stacking defects weakly alter the XRD pattern. By substitution of half of the nickel ions, the new phases Li(3)NiM'BiO(6) (M' = Mg, Cu, Zn) isostructural with Li(3)Ni(2)BiO(6) have been synthesized under similar conditions. All these compounds demonstrate paramagnetic behavior at high temperature, and Li(3)Ni(2)BiO(6) exhibits an antiferromagnetic ordering at 5.5 K. By topotactic molten salt ionic exchange, the new delafossite compound Ag(3)Ni(2)BiO(6) has been also obtained and characterized.