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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]

Herein, a modified solid state synthesis of Na0.67Mn0.5Fe0.5O2 and the results of a detailed investigation of the structural and magnetic properties via Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), X‐ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), and energy dispersive X‐ray (EDX) analysis are reported. The magnetic properties of Na0.67Mn0.5Fe0.5O2 do not fit the Curie–Weiss law and a model regarding the spin configuration of the Mn and Fe ions and a possible ferrimagnetic order is suggested. Electrochemical measurements and ex situ structural analysis of the cathode material confirm the reversible structural transitions for the cells charged up to 4.0 V. Environmental temperature–dependent electrochemical measurements reveal a strong temperature dependence of both, the initial capacity and the capacity retention. Ex situ SEM, FTIR, and XRD studies on the battery membrane verify the formation of a Na2CO3 phase on the membrane, which blocks the Na ion diffusion through membrane pores and is responsible for the capacity fade for this compound. [ABSTRACT FROM AUTHOR]

Na-ion batteries represent a promising complementary alternative to Li-ion batteries due to their high energy density and natural abundancy of Na. However, these batteries have short cycle life and extensive research activities on these batteries are required to understand the mechanism of such drawbacks. In this report, we investigate the capacity fading mechanism of Na0.44MnO2via ex situ X-ray diffraction, X-ray absorption spectroscopy, Fourier transform infrared spectroscopy and magnetization measurements. Our results show that the unit cell volume, the effective mass of Mn–O bonds, the number of Mn4+ ions and the effective magnetic moment decrease upon repeated cycling. We propose that some Mn4+ ions in the octahedral environment become Mn3+ ions in a square pyramidal environment, causing oxygen release upon cycling. Any free oxygen in the battery is expected to react with the electrolyte and cause capacity fade. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) are the most promising alternative to lithium-ion batteries (LIBs) due to their low cost and environmental friendliness; therefore, enhancing the performance of SIBs' components is crucial. Although most of the studies have focused on single-phase cathode electrodes, these materials have difficulty in meeting the requirements in practice. At this point, composite materials show superior performance due to balancing different structures and are offered as an alternative to single-phase cathodes. In this study, we synthesized a Na 0.44 MnO 2 /Na 0.7 MnO 2.05 composite material in a single step with cobalt substitution. Changes in the crystal structure and the physical and electrochemical properties of the composite and bare structures were studied. We report that even if the initial capacity is slightly lower, the rate and cyclic performance of the 1% Co-substituted composite sample (CO10) are superior to the undoped Na 0.44 MnO 2 (NMO) and 5% Co-substituted (CO50) samples after 100 cycles. The results show that with the composite cathode phase transformations are suppressed, structural degradation is prevented, and better battery performance is achieved., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Na-ion batteries represent a promising complementary alternative to Li-ion batteries due to their high energy density and natural abundancy of Na. However, these batteries have short cycle life and extensive research activities on these batteries are required to understand the mechanism of such drawbacks. In this report, we investigate the capacity fading mechanism of Na 0.44 MnO 2 via ex situ X-ray diffraction, X-ray absorption spectroscopy, Fourier transform infrared spectroscopy and magnetization measurements. Our results show that the unit cell volume, the effective mass of Mn-O bonds, the number of Mn 4+ ions and the effective magnetic moment decrease upon repeated cycling. We propose that some Mn 4+ ions in the octahedral environment become Mn 3+ ions in a square pyramidal environment, causing oxygen release upon cycling. Any free oxygen in the battery is expected to react with the electrolyte and cause capacity fade.