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Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity and an enhancement of the cycling stability. Thus, the highest capacity is obtained for 2 at.%-MgO-treated Na2/3(Mn1/2Fe1/2)0.9Co0.1O2 (175 mAh/g, with a capacity fade of 28% after 100 cycles). In comparison with Co substituents, the Mg treatment has a crucial role in the improvement of the lattice stability during the cycling process. The best electrode materials, with a chemical formula of 2 at.%-MgO treated Na2/3(Mn1/2Fe1/2)0.9Co0.1O2, were also used for the full cells design, with hard carbon as an anode. In the voltage window of 2–4 V, the capacity of the cells was obtained as 78 mAh/g and 51 mAh/g for applied current densities of 12 mA/g and 60 mA/g, respectively. [ABSTRACT FROM AUTHOR]

To outline the role of dual‐ion intercalation chemistry to reach sustainable energy storage, the present Review aimed to compare two types of batteries: widely accepted dual‐ion batteries based on cationic and anionic co‐intercalation versus newly emerged hybrid metal‐ion batteries using the co‐intercalation of cations only. Among different charge carrier cations, the focus was on the materials able to co‐intercalate monovalent ions (such Li+ and Na+, Li+ and K+, Na+ and K+, etc.) or couples of mono‐ and multivalent ions (Li+ and Mg2+, Na+ and Mg2+, Na+ and Zn2+, H+ and Zn2+, etc.). Furthermore, the Review was directed on co‐intercalation materials composed of environmentally benign and low‐cost transition metals (e. g., Mn, Fe, etc.). The effect of the electrolyte on the co‐intercalation properties was also discussed. The summarized knowledge on dual‐ion energy storage could stimulate further research so that the hybrid metal‐ion batteries become feasible in near future. [ABSTRACT FROM AUTHOR]

This study reports an effective approach to improve dramatically the electrochemical performance of nanosized NaFePO4 with a maricite structure, which is commonly considered as electrochemically inactive due to the absence of structural channels for alkaline ion mobility. The approach is based on the complete oxidation under mild conditions (i.e. at low temperatures around 280 °C and traces of oxygen) of the nanosized maricite phase. It is prepared by the phosphate–formate precursor method and is additionally ball-milled with a carbon additive. The oxidation of Fe2+ proceeds at the nanoscale level within the maricite nanoparticles and causes a massive structural transformation of the maricite phase into a monoclinic NASICON phase Na3Fe2(PO4)3 with the preservation of the crystallinity. The oxidized maricite phase exhibits high specific capacities, cycling stability and rate capability when it is used as an electrode in both Na and Li half-cells. The effect of different sodium and lithium electrolytes on the storage performance is investigated as well. It is found that the highest specific capacity (of about 150 mA h g−1) is achieved in Li half-cells using the LiPF6 electrolyte, while in Na half-cells the electrolyte NaFSI/EC:DMC achieves a specific capacity of around 100 mA h g−1. The rate capability is better in Na half-cells than that in Li half-cells. The mechanism of the reversible intercalation/deintercalation of Na+ and Li+ ions is studied by ex situ XRD and TEM analyses. The results show that the maricite is an electrochemically inactive phase, but through manipulation including oxidation or amorphization it becomes an active electrode material. [ABSTRACT FROM AUTHOR]

This study reports an effective approach to improve dramatically the electrochemical performance of nanosized NaFePO4 with a maricite structure, which is commonly considered as electrochemically inactive due to the absence of structural channels for alkaline ion mobility. The approach is based on the complete oxidation under mild conditions (i.e. at low temperatures around 280 °C and traces of oxygen) of the nanosized maricite phase. It is prepared by the phosphate–formate precursor method and is additionally ball-milled with a carbon additive. The oxidation of Fe2+ proceeds at the nanoscale level within the maricite nanoparticles and causes a massive structural transformation of the maricite phase into a monoclinic NASICON phase Na3Fe2(PO4)3 with the preservation of the crystallinity. The oxidized maricite phase exhibits high specific capacities, cycling stability and rate capability when it is used as an electrode in both Na and Li half-cells. The effect of different sodium and lithium electrolytes on the storage performance is investigated as well. It is found that the highest specific capacity (of about 150 mA h g−1) is achieved in Li half-cells using the LiPF6 electrolyte, while in Na half-cells the electrolyte NaFSI/EC:DMC achieves a specific capacity of around 100 mA h g−1. The rate capability is better in Na half-cells than that in Li half-cells. The mechanism of the reversible intercalation/deintercalation of Na+ and Li+ ions is studied by ex situ XRD and TEM analyses. The results show that the maricite is an electrochemically inactive phase, but through manipulation including oxidation or amorphization it becomes an active electrode material. [ABSTRACT FROM AUTHOR]

The energy storage by redox intercalation reactions is, nowadays, the most effective rechargeable ion battery. When lithium is used as intercalating agents, the high energy density is achieved at an expense of non‐sustainability. The replacement of Li+ with cheaper monovalent ions enables to make greener battery alternatives. The utilization of polyvalent ions instead of Li+ permits to multiplying the battery capacity. Contrary to Li+, the realization of quick and reversible intercalation of bigger monovalent and of polyvalent ions is a scientific challenge due to kinetic constraints, polarizing ion effects and Coulomb interactions. Herein we provide a vision how to make the intercalation of these ions feasible. The idea is to perform dual intercalation of ions having different charges, radii, preferred coordination and diffusion pathway topology. All these features are demonstrated by the recent knowledge on selective and non‐selective intercalation properties of oxides and polyanion compounds with layered and tunnel structures. Based on dual intercalation properties, the fabrication of hybrid metal ion batteries is presented and discussed. This personal account provides a vision for the energy storage by a radical change in the kind of the intercalating ions and intercalation matrices. The idea is to utilize the dual intercalation of monovalent and polyvalent ions in various compounds instead of conventional single Li+ intercalation. This approach will be of significance for elaboration a new type of hybrid metal ion batteries. [ABSTRACT FROM AUTHOR]