Sodium Iron Pyrophosphate Research Articles

Off-Stoichiometry of Sodium Iron Pyrophosphate as Cathode Materials for Sodium-Ion Batteries with Superior Cycling Stability.

As one of the important devices for large-scale electrochemical energy storage, sodium-ion batteries have received much attention due to the abundant resources of raw materials. However, whether it is a base station power source, an energy storage power station, or a start-stop power supply, long energy cycle life (more than 5000 cycles), high stability, and safety performance are application prerequisites. Regrettably, currently, few sodium-ion batteries can meet this requirement, mainly due to shortcomings in positive electrode performance. We report a sufficiently stable sodium-ion battery cathode material, Na2Fe0.95P2O7, that retains 97.5% capacity after 5000 charge/discharge cycles. The use of nonstoichiometry in the lattice enables simultaneous modification of the crystal and electronic structure, promoting Na2Fe0.95P2O7 to be extremely stable while still being able to achieve a capacity of 92 mAh g-1 and stable cycling at high temperatures up to 60 °C. Our results confirm the positive effect of nonstoichiometric ratios on the performance of Na2Fe0.95P2O7 and provide a reliable idea to promote the practical application of sodium-ion batteries.

Stable High-Temperature Cycling of Na Metal Batteries on Na3V2(PO4)3 and Na2FeP2O7 Cathodes in NaFSI-Rich Organic Ionic Plastic Crystal Electrolytes.

Sodium batteries have emerged as a promising alternative for large-scale energy storage applications due to the low cost and high abundance of sodium. Sodium batteries require safe, high-voltage, and cost-effective electrolytes and cathode materials for their practical applications to be realized. In the present study, Na metal cells with a mixed-phase electrolyte comprising a high concentration of Na salt in an organic ionic plastic crystal (OIPC), namely, triisobutylmethylphosphonium bis(fluorosulfonyl)imide, are investigated-coupled with either a sodium vanadium phosphate-carbon composite (NVP/C) or a sodium iron pyrophosphate (NFpP) cathode. The performance of the Na/NVP/C and Na/NFpP cells are evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic cycling at 60 °C and room temperature. The results reported herein indicate the performance improvement in terms of cycling stability, with high Coulombic efficiency at 60 °C granted by the OIPC and ionic liquid mixtures, compared to a conventional organic solvent electrolyte.

Seaweed-derived synthesis of Na3.12Fe2.44(P2O7)2/r-GO aerogels as air stable cathode materials for sodium-ion batteries

Due to the high theoretical capacity and open frameworks, the low-cost sodium iron pyrophosphate Na3.12Fe2.44(P2O7)2 has become a promising candidate for cathode materials of the sodium ion batteries (SIBs). However, NFPO is very sensitive to moisture and CO2, which causes serious surface oxidation reaction and results in degraded high-rate charge/discharge performance and cyclic stability. Herein, we developed a seaweed-derived synthesis strategy to prepare air stable NFPO/r-GO aerogels by using sodium alginate (SA) and reduced graphene oxide (r-GO) as precursors. X-ray photoelectron spectroscopy (XPS) proved that there were no residual Na species on the surface of prepared NFPO/r-GO aerogels and no any oxidized impurities after exposing in air for 100 days. When evaluating the NFPO/r-GO aerogels as cathode materials for SIBs, the sample exhibits excellent reversible capacity of 116.1 mAh g−1 at 0.1 C, 88.82% capacity retention after 5000 cycles and superior rate capacity of 72.3 mAh g−1 at 20 C. The superior electrochemical performances are mainly attributed the delicate structure, which can not only increase the electronic conductivity, but also improve air stability of NFPO by suppressing surface side reactions with moisture and CO2.

Electrochemical and Chemical Na+/Li+ Ion Exchange in Na-Based Cathode Materials: Na1.56Fe1.22P2O7 and Na3V2(PO4)2F3

In this work, XRD, EDX, Mössbauer and NMR spectroscopy were used to study chemical and electrochemical Na+/Li+ ion exchange in the sodium iron pyrophosphate Na1.56Fe1.22P2O7 with a triclinic symmetry, S. G. P-1, and sodium vanadium fluorophosphate Na3V2(PO4)2F3 with a tetragonal symmetry, S. G. P42/mnm, cathode materials. Electrochemical Na+/Li+ ion exchange was performed in hybrid-ion cells with Li metal anode and LiPF6-based electrolyte, while chemical ion exchange was realized in the solution of LiBr in acetonitrile. A facile electrochemical and chemical Na+/Li+ ion exchange was observed for both cathode materials, resulting in the formation of the mixed Na-Li compositions: ∼Na1.2Li0.36Fe1.22P2O7 and ∼Na2.47Li0.53V2(PO4)2F3, respectively. Partial Na+/Li+ ion exchange did not cause noticeable structural changes to the pristine sodium-based materials. Both materials showed an excellent electrochemical performance in hybrid-ion cells. It was suggested that during cycling, a mixed Na+/Li+ cathode reactions occurred.

Electrochemical and Chemical Na+/Li+ Ion Exchange in Na-Based Cathode Materials

Na2FeP2O7 sodium iron pyrophosphate with a triclinic symmetry (the space group P-1) has been prepared by mechanochemically assisted solid state synthesis. Electrochemical performance of the pristine Na2FeP2O7, NaFeP2O7 prepared by chemical oxidation with NO2BF4 and NaLiFeP2O7 obtained by non-oxidative Na+/Li+ ion exchange with LiBr were studied by galvanostatic cycling in a Li cell with Li as an anode and LiPF6 dissolved in EC+DMC as an electrolyte. XRD, EDX, Mössbauer and NMR spectroscopy studies showed that all the samples were active upon cycling in Li cells which resulted in exchange of one ~Na+ for one Li+ per f.u. to produce a new mixed phase NaLiFeP2O7 with the same triclinic structure as Na2FeP2O7 and good electrochemical performance.

Pyro-synthesis of Na2FeP2O7 Nano-plates as Cathode for Sodium-ion Batteries with Long Cycle Stability

Carbon-coated sodium iron pyrophosphate (Na₂FeP₂O 7 ) was prepared by a simple and low-cost pyro-synthesis route for further use as the cathode for Na-ion batteries. The X-ray diffraction (XRD) pattern of the sample annealed at 650℃ confirmed the pure triclinic phase of Na₂FeP₂O 7 . Electron microscopy studies revealed a cross linked plate shape morphology of the Na₂FeP₂O 7 sample. When tested for application in Na-ion battery, the Na₂FeP₂O 7 cathode showed two redox pairs in the potential window of 2.0-4.0 V. The cathode registered initial discharge and charge capacities of 80.85 and 90 mAh/g, respectively, with good cycling performance.

Electrochemical and Chemical Na+/Li+ Ion Exchange in Na-Based Cathode Materials

Sodium-based insertion materials are of interest for low-cost and large-scale Na- and Li-ion batteries. Substantial research effort has been invested during the previous years to produce electrode materials for sodium batteries that will allow for facile intercalation of Na-ions at suitable potentials. Amongst the cathode materials investigated, a variety of layered oxides (e.g. NaxCoO2, NaCrO2, NaVO2, Nax[Fe0.5Mn0.5]O2) and polyanionic compounds (e.g. NaFePO4, Na3V2(PO4)3, Na2FePO4F, NaFeSO4F) have been reported. The ability of these materials for facile Na+/Li+ ion exchange has been also revealed [1]. Recently, sodium vanadium fluorophosphates [2-5] and sodium iron pyrophosphate [6,7] have been examined and showed good electrochemical properties in Na-cells. The aim of the present work was to investigate electrochemical and chemical Na+/Li+ ion exchange in these materials. Sodium vanadium fluorophosphates Na1+yVPO4F1+y (0≤y≤0.5) and sodium iron pyrophosphate Na2FeP2O7 were prepared by mechanochemically assisted solid state synthesis using high-energy AGO-2 planetary mill. The activated mixtures were subsequently heat treated at 600-700 °C in Ar flow. Structure and morphology of the as-prepared materials were analyzed by XRD with Rietveld refinement using GSAS and TOPAS software packages, SEM, FTIR, Mössbauer, 23Na and 31P MAS NMR spectroscopy. Electrochemical Na+/Li+ ion exchange was studied by galvanostatic cycling in Li+ cells with Li as an anode and LiPF6 dissolved in EC+DMC as an electrolyte. Non-oxidative chemical ion exchange was carried out in the solution of LiBr in acetonitrile for 24 h. Ex situ XRD, EDX, Mössbauer and NMR spectroscopy studies were carried out to control the phase and structural transformations. Structure of the as-obtained mixed Na/Li compositions was compared with that of the correspondent lithium compounds [8]. [1] N.V. Kosova, V.R. Podugolnikov, E.T. Devyatkina, A.B. Slobodyuk, Mater. Res. Bull. 60 (2014) 849. [2] J. Barker, M.Y. Saidi, J.L. Swoyer, Electrochem. Solid-State Lett. 6 (2003) A1-A4. [3] J.M. Le Meins, M.P. Crosnier-Lopez, A. Hemon-Ribaud, G. Courbion, J. Solid State Chem. 148 (1999) 260. [4] J. Barker, R.K.B. Gover, P. Burns, A.J. Bryan, Electrochem. Solid-State Letters 9 (2006) A190. [5] M. Bianchini, N. Brisset, F. Fauth, F. Weill, E. Elkaim, E. Suard, C. Masquelier, L. Croguennec, Chem. Mater. 26 (2014) 4238. [6] P. Barpanda, T. Ye, S. Nishimura, S. Chung, Y. Yamada, M. Okubo, H. Zhou, A. Yamada, Electrochem. Commun. 24 (2012) 116. [7] T. Honma, A. Sato, N. Ito, T. Togashi, K. Shinozaki, T. Komatsu, J. Non-Cryst. Solids 404 (2014) 26. [8] N.V. Kosova, A.M. Tsapina, A.B. Slobodyuk, S.A. Petrov, Electrochim. Acta 174 (2015) 1278.

Na2FeP2O7 as a Novel Material for Hybrid Capacitive Deionization

Capacitive deionization (CDI) which removes ionic species from solution by applying electric energy to carbon based electrodes is one of excellent convergence technologies combined with energy storage technology and environmental systems. In recent decades, the technology for synthesizing new carbon materials has advanced, the electrical double layer capacitance in porous structures has become better understood, and novel deionization systems have been developed. Nevertheless, achieving a higher deionization performance is required for CDI to compete with reverse osmosis for deionization. The recently introduced Hybrid CDI (HCDI), which utilizes sodium manganese oxide (Na4Mn9O18) and carbon material, successfully demonstrated its superior deionization performance over conventional CDI systems. Despite the great promise of the HCDI system, the limited availability of aqueous based intercalation materials and the lack of information regarding the characteristics of the HCDI system operations are obstacles to the advancement of HCDI. Thus, we report a new HCDI system with sodium iron pyrophosphate (Na2FeP2O7), which is a promising material for sodium ion batteries due to its high capacity, low cost and environmentally benign nature. The major results of the HCDI system with Na2FeP2O7 showed a superior maximum deionization rate performance (0.081mgg−1s−1) with a comparable deionization capacity (30.2mgg−1) compared to the previous HCDI system with Na4Mn9O18. Furthermore, the analysis of the CDI Ragone plot revealed the hybrid behavior characteristics of this HCDI system and that the high deionization capacity originated from the high capacity of Na2FeP2O7 at a low current density, whereas the fast deionization rate originated from the supercapacitor system at a high current density. Consequently, this study on a new HCDI system with Na2FeP2O7 contributes to expanding the understanding of the kinetic properties of the HCDI system with respect to its diverse operations.

Sodium iron pyrophosphate: A novel 3.0 V iron-based cathode for sodium-ion batteries

Extending the pyrophosphate chemistry for rechargeable Na-ion batteries, here we report the synthesis and electrochemical characterization of Na2FeP2O7, a novel Fe-based cathode material for sodium batteries. Prepared by conventional solid-state as well as solution-combustion synthesis (at 600°C), the Na2FeP2O7 adopts a triclinic structure (space group: P-1) with three-dimensional channels running along [100], [−110] and [01-1] directions. With no further optimization, the as-synthesized Na2FeP2O7 cathode was found to be electrochemically active, delivering a reversible capacity of 82mAh·g−1 with the Fe3+/Fe2+ redox potential centered around 3V (vs. Na/Na+). With its theoretical capacity of ~100mAh·g−1 and potential high rate-capability, Na2FeP2O7 forms a promising novel cathode material, with the distinction of being the first ever pyrophosphate-class of cathode for sodium-ion batteries.

Bioavailability of Zinc in Infant Cereals

The bioabailability of zinc in three cereals was determined by a rat assay, using total femur zinc as the indicator. The basal diet contained 25% egg white solids and 0.6 microgram zinc per gram. The infant cereals were included in the diets at three graded levels to supply 3--12 microgram zinc per gram. Zinc sulphate was used as a standard source, with and without supplemental iron (185, 370, 555 microgram/g, respectively) at 3, 6 and 9 microgram zinc per gram with a view to determine the effect of excess iron on zinc availability. Added iron from sodium iron pyrophosphate was not found to have any effect on the bioavailability of zinc from zinc sulphate. The responses for the three cereals were linear but the regression lines representing them and the standard source did not have a common intercept. However, the ratio of the slope of the regression line for the test source to that of the standard indicated that the cereal containing soy protein was a better source of zinc (ratio = 0.49) than the barley cereal (9.10) or the rice cereal (0.32). These ratios did not show any correlation with the actual iron-precipitable phytate phosphorus content or the reported crude fibre content.

Biological Availability of Iron Supplements for Rats, Chicks and Humans

Fourteen experiments were concluded on the effect of protein and carbohydrate sources in the assay diets on the relative biological values (RBV) of food grade sodium iron pyrophosphate (NaFePP) and ferric orthophosphate (FePO4) vs. ferrous sulfate (FeSO4) for rats and chicks, using the response in blood hemoglobin to graded levels of supplemental iron as the assay criterion. Two trials were made with volunteers to estimate the RBV of NaFePP and FePO4 for humans, based on the increase in plasma iron 2 hours after ingestion of 100 mg of iron of a test dose following an overnight fast. The RBV of iron from NaFePP and FePO4 for rats were consistently lower when the basal diet contained nonfat dried milk (9 to 16 and 28, respectively, vs. FeSO4=100) than when casein was used (25 to 28 and 49, respectively). The addition of 22% beta-lactose, replacing sucrose in a diet containing casein fed to rats, significantly reduced the RBV of iron from NaFePP from 25 to 15; the addition of 22% alpha-lactose or 40% glucose in place of sucrose had no effect on the RBV of this iron source. The RBV of iron from NaFePP and FePO4 for chicks were 4 to 6 and 4, respectively, with the source of dietary protein having no effect. Very low RBV of iron from NaFePP and FePO4 (4.3 and 5.9, respectively, vs. FeSO4=100) were also obtained with human subjects.

The Absorption of Iron as Supplements in Infant Cereal and Infant Formulas

The absorption of iron was measured from isotopically tagged salts used in supplementing infant cereals and as the iron supplement in cow's milk and soy-based formulas. Iron as sodium iron pryophosphate and ferric orthophosphate were poorly absorbed from infant cereal (mean, smaller than 1.0%) and thus are not dependable sources of iron to meet the nutritional needs of infants. Reduced iron of very small particle size and ferrous sulfate when added to cereal was absorbed to a greater extent (mean, 4.0% and 2.7% respectively). For technical reasons, these two forms of iron had not been added to commercial cereal products because of discoloration, distribution problems of the iron in the product, and shortened shelf life. Therefore, at the present time, iron supplementation of infant cereals with sodium iron pyrophosphate, ferric orthophosphate, and reduced iron of large particle size does not provide a predictable and available source of iron to meet the needs of infants. Supplemental iron as ferrous sulfate in milk- and soy-based formulas gave a mean absorption of 3.4% and 5.4%. The iron supplements in these formulas can essentially meet the needs for dietary iron of healthy infants.

Bioassay for Iron Source Additives

Modifications of the assay of Pla and Fritz (1971) for the determination of bioavailability of iron have been suggested. The basal diet contained 20% casein and vitamins and minerals (except Fe) were added to meet the requirements of rats according to N.R.C. recommendations. After feeding the basal diet to male weanling Wistar rats for 5 weeks, supplements of standard (FeSO4)and test sources were added (reduced iron and sodium iron pyrophosphate) and feeding continued for 3 weeks. Food intake, body weight and hemoglobin were measured weekly. Two week response measured as hemoglobin (g %) had a linear relationship with the logarithm of ppm of (FeSO4) iron added to the diet. The response of test sources was found to be parallel to that for FeSO4. The 95% fiducial limits of the relative biological value obtained were 20% below and 25% above the centre. Other parameters tested viz product of hemoglobin (g %) and body weight (g) at 2 and 3 weeks, hemoglobin at 3 weeks gave comparable results but did not improve the precision of the determination.

Iron absorption in Indians studied by whole body counting: a comparison of iron compounds used in salt fortification.

SummaryFortification of common salt (NaCl) with iron has been suggested, for preventing iron deficiency anaemia in India. From a technological point of view three insoluble iron compounds: sodium iron pyrophosphate, ferric orthophosphate and ferric pyrophosphate have been considered suitable for this purpose. Absorption of iron from these compounds and ferrous sulphate was studied in 45 healthy male adult subjects employing 59Fe labelled salts and whole body counting. “When given alone, mean absorption of iron from ferric orthophosphate, sodium iron pryophos‐phate and ferric pyrophosphate were 8.3%, 6.3% and 0% respectively, while absorption from ferrous ascorbate was 30.6%. However, when administered with a meal of the type normally consumed in India, iron absorption from sodium iron pyrophosphate was unacceptably low, while that from ferrous sulphate was only 3.7%. It is concluded that these insoluble iron compounds are not acceptable for fortification of common salt from the point of view of availability of iron.

Iron Status of Anemic Rats Fed Iron-Fortified Cereal-Milk Diets

Regeneration of hemoglobin was studied in anemic rats fed a cereal-milk diet unfortified with iron or fortified with sodium iron pyrophosphate, reduced iron or ferrous sulfate. At the end of the 28-day period of iron repletion, mean body weight and mean concentration of hemoglobin were significantly greater for rats fed the diet fortified with ferrous sulfate than for rats in the other feeding groups. Rats fed the basal diet with no added iron (15 mg/kg of naturally occurring iron) had significantly lower hematocrits but not significantly different concentrations of hemoglobin than did the rats fed sodium iron pyrophosphate or reduced iron. Approximately 9% of the reduced iron, 10% of the sodium iron pyrophosphate, and 65% of the ferrous sulfate in the diet were incorporated into hemoglobin.

Iron and Associated Trace Mineral Problems in Man and Animals

There is a high incidence of iron-deficiency anemia in the United States and throughout the world. The prevalence is high in adult women and infants because of their greater needs for iron. The typical human diet furnishes less than 6 mg iron per 1,000 kcal and does not meet the current recommended dietary allowances for critical groups because so much of the iron in whole, raw foodstuffs is removed in processing. Farm animals fare better because they receive fractions removed from human foods. A few livestock groups, notably baby pigs, do need supplemental iron. The cereal enrichment program failed to alleviate human anemia because of reduced consumption of cereals and because poorly utilized sources of supplemental iron were employed. Ferric orthophosphate and sodium iron pyrophosphate were poorly utilized by chicks, rats, and humans. Ferrous sulfate was well utilized by each of the three species, while reduced iron was intermediate. The source of supplemental iron had more influence on bioavailability than did other diet components. It is recommended that the level of iron be increased in enriched cereals, that milk and other foods be fortified with iron, and that iron sources with good bioavailability be used in the fortification program.

A Study of the Availability of the Iron in Enriched Bread: Two Figures

Sodium iron pyrophosphate, administered to rats maintained on a diet of whole milk, has been found to have an availability of considerably less than 50% as compared to the utilization of ferrous or ferric sulfate. Likewise, when enriched bread containing sodium iron pyrophosphate or ferrous sulfate was fed to anemic rats, the availability of the former compound was less than 50% of that of the ferrous sulfate. After this paper was submitted, an article appeared by Nakamura and Mitchell (’43), which calls for comment. These workers reported that the utilization of iron as sodium iron pyrophosphate or ferric chloride is equally satisfactory as tested in anemic rats. It is difficult to reconcile these findings with those reported here. Mitchell (’43) has pointed out that in their experiments the iron compounds were administered daily, in contrast to the thrice-weekly administration of the iron salts in the present study. However, while this might account in part for the difference observed when the iron salts were administered as such, it would not explain the poor utilization of sodium iron pyrophosphate when fed in enriched bread ad libitum. It should also be pointed out that while the preparations of sodium iron pyrophosphate were obtained from the same manufacturer, they were, of course, different samples, and this might to some extent account for variation in degree of utilization. No doubt further work will clarify this matter.