β-NaVP2O7 as a Superior Electrode Material for Na-Ion Batteries

Herein, we present a novel β-polymorph of sodium vanadium pyrophosphate NaVP2O7 with the KAlP2O7-type structure obtained via hydrothermal synthesis and further thermal dehydration of a hydrophosphate intermediate. β-NaVP2O7 demonstrates attractive electrochemical behavior as a Na-ion positive electrode (cathode) material with practically achieved reversible capacity of 104 mAh/g at C/10 current density, average operating voltage of 3.9 V vs. Na/Na+ and only 0.5% volume change between the charged and discharged states. Electrode material exhibits excellent C-rate capability and cycling stability, providing the capacity of 90 mAh/g at 20C discharge rate and < 1% capacity loss after 100 charge-discharge cycles. At low voltage region (≈1.5 V vs. Na/Na+), β-NaVP2O7 reversibly intercalates additional sodium cations leading to unprecedented overall Na-ion storage ability exceeding 250 mAh/g within the 1.5 – 4.4 V vs. Na/Na+ voltage region. This material is one of only a few materials that exhibits reversible sodium ion storage capabilities over such a large potential window. </p

“Hydrotriphylites” Li1-xFe1+x(PO4)1-y(OH)4y as Cathode Materials for Li-ion Batteries

Lithium iron phosphate LiFePO4 triphylite is now one of the core positive electrode (cathode) materials enabling the Li-ion battery technology for stationary energy storage applications, which are important for broad implementation of the renewable energy sources. Despite the apparent simplicity of its crystal structure and chemical composition, LiFePO4 is prone to off-stoichiometry and demonstrates rich defect chemistry owing to variations in the cation content and iron oxidation state, and to the redistribution of the cations and vacancies over two crystallographically distinct octahedral sites. The importance of the defects stems from their impact on the electrochemical performance, particularly on limiting the capacity and rate capability through blocking the Li ion diffusion along the channels of the olivine-type LiFePO4 structure. Up to now the polyanionic (i.e. phosphate) sublattice has been considered idle on this playground. Here, we demonstrate that under hydrothermal conditions up to 16% of the phosphate groups can be replaced with hydroxyl groups yielding the Li1-xFe1+x(PO4)1-y(OH)4y solid solutions, which we term “hydrotriphylites”. This substitution has tremendous effect on the chemical composition and crystal structure of the lithium iron phosphate causing abundant population of the Li-ion diffusion channels with the iron cations and off-center Li displacements due to their tighter bonding to oxygens. These perturbations trigger the formation of an acentric structure and increase the activation barriers for the Li-ion diffusion. The “hydrotriphylite”-type substitution also affects the magnetic properties by progressively lowering the Néel temperature. The off-stoichiometry caused by this substitution critically depends on the overall concentration of the precursors and reducing agent in the hydrothermal solutions, placing it among the most important parameters to control the chemical composition and defect concentration of the LiFePO4-based cathodes

A Critical Assessment of the Therapeutic Potential of Resveratrol Supplements for Treating Mitochondrial Disorders

In human cells, mitochondria provide the largest part of cellular energy in the form of adenosine triphosphate generated by the process of oxidative phosphorylation (OXPHOS). Impaired OXPHOS activity leads to a heterogeneous group of inherited diseases for which therapeutic options today remain very limited. Potential innovative strategies aim to ameliorate mitochondrial function by increasing the total mitochondrial load of tissues and/or to scavenge the excess of reactive oxygen species generated by OXPHOS malfunctioning. In this respect, resveratrol, a compound that conveniently combines mitogenetic with antioxidant activities and, as a bonus, possesses anti-apoptotic properties, has come forward as a promising nutraceutical. We review the scientific evidence gathered so far through experiments in both in vitro and in vivo systems, evaluating the therapeutic effect that resveratrol is expected to generate in mitochondrial patients. The obtained results are encouraging, but clearly show that achieving normalization of OXPHOS function with this strategy alone could prove to be an unattainable goal

The Role of Semilabile Oxygen Atoms for Intercalation Chemistry of the Metal-Ion Battery Polyanion Cathodes

Using the orthorhombic layered Na₂FePO₄F cathode material as a model system we identify the bonding of the alkali metal cations to the semilabile oxygen atoms as an important factor affecting electrochemical activity of alkali cations in polyanion structures. The semilabile oxygens, bonded to the P and alkali cations, but not included into the FeO₄F₂ octahedra, experience severe undercoordination upon alkali cation deintercalation, causing an energy penalty for removing the alkali cations located in the proximity of such semilabile oxygens. Desodiation of Na₂FePO₄F proceeds through a two-phase mechanism in the Na-ion cell with a formation of an intermediate monoclinic Na_1.55FePO₄F phase with coupled Na/vacancy and Fe²⁺/Fe³⁺ charge ordering at 50% state of charge. In contrast, desodiation of Na₂FePO₄F in the Li-ion cell demonstrates a sloping charge profile suggesting a solid solution mechanism without formation of a charge-ordered intermediate phase. A combination of a comprehensive crystallographic study and extensive DFT-based calculations demonstrates that the difference in electrochemical behavior of the alkali cation positions is largely related to the different number of the nearest neighbor semilabile oxygen atoms, influencing their desodiation potential and accessibility for the Na/Li chemical exchange, triggering coupled alkali cation–vacancy ordering and Fe²⁺/Fe³⁺ charge ordering, as well as switching between the “solid solution” and “two-phase” charging mechanistic regimes

The Role of Semilabile Oxygen Atoms for Intercalation Chemistry of the Metal-Ion Battery Polyanion Cathodes

Using the orthorhombic layered Na₂FePO₄F cathode material as a model system we identify the bonding of the alkali metal cations to the semilabile oxygen atoms as an important factor affecting electrochemical activity of alkali cations in polyanion structures. The semilabile oxygens, bonded to the P and alkali cations, but not included into the FeO₄F₂ octahedra, experience severe undercoordination upon alkali cation deintercalation, causing an energy penalty for removing the alkali cations located in the proximity of such semilabile oxygens. Desodiation of Na₂FePO₄F proceeds through a two-phase mechanism in the Na-ion cell with a formation of an intermediate monoclinic Na_1.55FePO₄F phase with coupled Na/vacancy and Fe²⁺/Fe³⁺ charge ordering at 50% state of charge. In contrast, desodiation of Na₂FePO₄F in the Li-ion cell demonstrates a sloping charge profile suggesting a solid solution mechanism without formation of a charge-ordered intermediate phase. A combination of a comprehensive crystallographic study and extensive DFT-based calculations demonstrates that the difference in electrochemical behavior of the alkali cation positions is largely related to the different number of the nearest neighbor semilabile oxygen atoms, influencing their desodiation potential and accessibility for the Na/Li chemical exchange, triggering coupled alkali cation–vacancy ordering and Fe²⁺/Fe³⁺ charge ordering, as well as switching between the “solid solution” and “two-phase” charging mechanistic regimes

The Role of Semilabile Oxygen Atoms for Intercalation Chemistry of the Metal-Ion Battery Polyanion Cathodes

Using the orthorhombic layered Na₂FePO₄F cathode material as a model system we identify the bonding of the alkali metal cations to the semilabile oxygen atoms as an important factor affecting electrochemical activity of alkali cations in polyanion structures. The semilabile oxygens, bonded to the P and alkali cations, but not included into the FeO₄F₂ octahedra, experience severe undercoordination upon alkali cation deintercalation, causing an energy penalty for removing the alkali cations located in the proximity of such semilabile oxygens. Desodiation of Na₂FePO₄F proceeds through a two-phase mechanism in the Na-ion cell with a formation of an intermediate monoclinic Na_1.55FePO₄F phase with coupled Na/vacancy and Fe²⁺/Fe³⁺ charge ordering at 50% state of charge. In contrast, desodiation of Na₂FePO₄F in the Li-ion cell demonstrates a sloping charge profile suggesting a solid solution mechanism without formation of a charge-ordered intermediate phase. A combination of a comprehensive crystallographic study and extensive DFT-based calculations demonstrates that the difference in electrochemical behavior of the alkali cation positions is largely related to the different number of the nearest neighbor semilabile oxygen atoms, influencing their desodiation potential and accessibility for the Na/Li chemical exchange, triggering coupled alkali cation–vacancy ordering and Fe²⁺/Fe³⁺ charge ordering, as well as switching between the “solid solution” and “two-phase” charging mechanistic regimes