Na+ diffusion mechanism and transition metal substitution in tunnel-type manganese-based oxides for Na-ion rechargeable batteries

Structural, computational and electrochemical investigations are combined to study the intercalation properties of tunnel-type Na0.44MnO2 and Cu-substituted Na0.44MnO2

Physico-Chemical Features of Undoped and Fe/Cu-Doped Na0.67MnO2-Layered Cathodes for Sodium Batteries

Na0.67MnO2 (NMO) stands out among the layered cathode materials used for sodium batteries due to its high-capacity values, low cost, and environmental friendliness. Unfortunately, many drawbacks arise during cycling, but nanostructure tailoring and doping can help to mitigate them. Our aim was to synthesize undoped and Cu- or Fe-doped NMO samples via the sol-gel route, with a different cooling step to room temperature, i.e., in a natural way or via quenching. The formation of a mixture of polymorphs was observed, as well as differences in the external morphology of the powders' grains. The use of spectroscopic techniques, Mössbauer spectroscopy for the Fe-doped samples and Electron paramagnetic resonance, allowed us to gain insights into the oxidation states of transition metals and to make suggestions about the magnetic ordering, as well as on the possible presence of magnetic impurities. Cyclic voltammetry and galvanostatic cycling results were interpreted on the basis of the spectroscopic data: the introduction of substituents, in general, worsens the capacity values, due to the decrease in the P2 amount and the introduction of structural distortions. The structural stability of the samples in air as a function of time was also analyzed via X-ray diffraction, demonstrating the positive effect of Cu presence

Orthorhombic and monoclinic modifications of FeNb11O29, as promising anode materials for lithium batteries: Relationships between pseudocapacitive behaviour and structure

An intriguing and promising anode material for Li ion batteries, FeNb11O29, is emerging in the last few years. Its main strength lies into the possibility to exchange up to 23 electrons per formula unit, thanks to the redox reactions involving Fe3þ and Nb5þ ions, reaching a theoretical capacity value of 400 mAh/g. In this paper, a systematic study to determine the effect of carbon type and polymorph (monoclinic or orthorhombic) used to prepare the anode ink on the electrochemical performances was carried out. The best high rate capacity values (250 mAh/g at 10C after 100 cycles) and structural cycling stability (about 96.4%) were obtained for the orthorhombic polymorph mixed with Super C65 carbon. For the intercalation/ deintercalation process, a prevailing of pseudocapacitive behaviour with respect to the diffusive one was evidenced, especially at higher C rate, that is related to the peculiar structural aspects of FeNb11O29 shear structure

Ca- and Al-doped ZnFe2O4nanoparticles as possible anode materials

Spinel ferrites are an amazing class of materials that can find application in different fields, from sensors and lithium-ion batteries to the intriguing biomedical field. For the use as anode in lithium-ion batteries, ZnFe2O4 is rather competitive due to low price, abundance, environmental benignity, working voltage of ~1.5 V, and, most importantly, a high theoretical specific capacity (~1072 mA h g−1). For its practical application, however, some issues must be overcome, in particular its fast capacity fading and poor rate capability resulting from an inherent low electronic conductivity. Possible strategies are represented by ferrite carbon coating/embedding, peculiar synthesis routes, and doping. In this frame, we synthesized Ca- and Al-doped ZnFe2O4 nanoparticles by using microwave-assisted combustion synthesis, followed by a classical carbon coating (determined as about 5 wt% by thermogravimetry). A good solubility of Ca and Al up to 25 atom% on both Zn and Fe sites was obtained. Cyclic voltammetries evidenced redox reactions involving Zn and Fe ions, but also the Al intervention could be supposed. Galvanostatic charge– discharge cycles proved that particularly Al ions were useful to improve the anode structural stability at high C rate (up to 3C), thanks to the stronger Al–O bonds with respect to Fe–O ones. A further improvement of capacities comes from the use of sodium alginate as binder to substitute polyvinylidene fluoride in the anode preparation

Silicon-doped LiNi0.5Mn1.5O4 as a high-voltage cathode for Li-ion batteries

To improve the electrochemical performance of the LiNi0.5Mn1.5O4 high voltage cathode for Lithium Ion Batteries, silicon-doped LiNi0.5Mn1.5−xSixO4 samples (0.00≤x≤0.35) were prepared by different synthesis routes (solid-state reaction and ball milling) and characterized. The X-ray diffraction investigation and structural and profile Rietveld refinement put into evidence that effective spinel doping is obtained by the ball milling route: a solubility limit is achieved for x=0.10 and silicon preferentially occupies the 8a tetrahedral site of the spinel structure, thus causing lithium to occupy both the tetrahedral and octahedral sites. In contrast, segregation of lithium silicates in the solid-state synthesis is observed. SEM images show that, independent on the synthesis method, silicon controls the particles morphology and grain size. The doped samples show improved electrochemical performances, which can be ascribed to the role of silicon in increasing cations disorder and controlling particles size

Improving the Carprofen Solubility: Synthesis of the Zn2Al-LDH Hybrid Compound

The development of efficient strategies for drug delivery is considerably desired. Indeed, often several issues such as the drug solubility, the control of the drug release rate, the targeted delivery of drugs, the drug bioavailability, and the minimization of secondary effects still present great obstacles. Different methodologies have been proposed, but the use of nano-hybrids compounds that combine organic and inorganic substances seems particularly promising. An interesting inorganic host is the layered double hydroxide (LDH) with a sheets structure and formula [M2þ 1x M3þ x (OH)2](An)x/n yH2O (M2þ ¼ Zn, Mg; M3þ ¼ Al; An ¼ nitrates, carbonates, chlorides). The possibility to exchange these counterions with drug molecules makes these systems ideal candidates for the drug delivery. In this article, we synthesize by co-precipitation method the hybrid compound Carprofen-Zn2Al-LDH. Carprofen, a poorly soluble antiinflammatory drug, could also benefit of the association with a natural antacid such as LDH, to reduce the gastric irritation after its administration. Through X-ray diffraction and Fourier-transformed infrared spectroscopy (FT-IR), we could verify the effective drug intercalation into LDH. The dissolution tests clearly demonstrate a significant improvement of the drug release rate when carprofen is in the form of hybrid compoun

Effect of Mn Substitution on GeFe₂O₄ as an Anode for Sodium Ion Batteries

GeFe2O4 (GFO), with its intriguing intercalation mechanism based on alloying–conversion reactions, was recently proposed as an anode material for sodium ion batteries (SIBs). However, drawbacks related to excessive volume expansion during intercalation/deintercalation and poor electronic conductivity enormously hinder its practical application in batteries. In this regard, some experimental strategies such as cation substitutions and proper architectures/carbon coatings can be adopted. In this paper, pure and Mn-doped GFO samples were prepared by hydrothermal synthesis. The doped samples maintained the spinel cubic structure and the morphology of pure GFO. The electrochemical tests of the samples, performed after proper carbon coating, showed the expected redox processes involving both Ge and Fe ions. The Mn doping had a positive effect on the capacity values at a low current density (about 350 mAh/g at C/5 for the Mn 5% doping in comparison to 300 mAh/g for the pure sample). Concerning the cycling stability, the doped samples were able to provide 129 mAh/g (Mn 10%) and 150 mAh/g (Mn 5%) at C/10 after 60 cycles

Hybrid compounds for improving drugs solubility: Synthesis, physicochemical and pharmaceutical characterization of Nimesulide-LDH

Layered double hydroxides (LDHs) with their sheets structure are undoubtedly interesting inorganic hosts for different applications, in particular for drug delivery. Nimesulide, a poorly soluble anti-inflammatory drug, could benefit of the association with LDH to improve its low dissolution rate and thanks to natural antacid properties of LDH to reduce the gastric irritation after its administration. In this paper, we synthesize by coprecipitation and reconstruction methods the hybrid compound Nimesulide-Mg3Al-LDH, as demonstrated by X-ray powder diffraction (from hydroxide layers expansion with respect to pure LDH), thermal analysis (from the absence of drug melting point in the hybrids) and infrared spectroscopy (from the absence of stretching of NO2 and SO2 in the hybrid, suggesting the loose of its rotational freedom into the LDH). In addition, SEM microscopy/EDS microanalysis supported the formation of new entities. The dissolution tests demonstrate an improvement of two times in terms of percentage of drug dissolved when nimesulide is in the form of a hybrid compound, compared to the drug alone or a reference commercial product

Stability of low-temperature Li7La3Zr2O12 cubic phase: The role of temperature and atmosphere

Rechargeable all solid-state lithium batteries are a promising technology for the next generation of safer batteries. In this context, strict requirements are placed on the electrolytes, among which is emerging the Li7La3Zr2O12 garnet, chiefly for the relationships among synthesis conditions and phase stability. Here, the structural modifications of the low temperature (LT) Li7La3Zr2O12 cubic form were investigated by using in situ X-Rays diffraction analysis. In particular, we studied the role of both temperature and atmosphere (air or argon) on phase stabilization. In argon flow, the LT phase is stable under 750 C, and it transforms into the tetragonal one at lower temperature. In air, it partially decomposes to La2Zr2O7 due to Li loss above 250 C. ICP-OES analysis confirmed that garnet stoichiometry was maintained in argon, whereas in air lithium loss occurred. The structural transformations are driven by the CO2 absorbed in the LT structure that can form Li2CO3 and/or La2(CO3)3 so causing stoichiometry changes responsible of the structural evolutio

From tunnel NMO to layered polymorphs oxides for sodium ion batteries

The search for highly performing cathode materials for sodium batteries is a fascinating topic. Unfortunately, Na0.44MnO2 (NMO), the well-known cathode material with good electrochemical performances, su ers from structural degradation due to reduction of Mn4+ to the Jahn–Teller Mn3+ ion, limiting the long-term cyclability. The cation substitution can be a useful way to mitigate the problem, thanks to the possible stabilization of mixtures of di erent polymorphs. In this paper, NMO was rst substituted with Fe ions, obtaining Na0.44Mn0.5Fe0.5O2, with layered structure, then Al, Si and Cu (10% atom) were substituted on both Mn and Fe ions. Mixtures of P3 type phases, in di erent amount depending on dopant, were obtained and quanti ed by Rietveld re nements, and relationships between chemical composition, polymorph type and morphology were proposed. Cyclic voltammetry showed broad peaks, due to the complex structural transitions consequent to the intercalation/deintercalation of sodium. Charge discharge cycles disclosed the superior performances of Cu doped sample, which also bene ts from improved air stability, a well-known issue of layered compounds. Discharge capacity values of about 63 mAh/g were detected at 1C, obtained, with a capacity retention of 86%