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Sodium iron phosphate-pyrophosphate, Na4Fe3(PO4)2P2O7 (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a simple and unified method for synthesis of composites between NFPP and reduced graphene oxide (rGO) and standard carbon black, designed as electrode materials for both sodium- and lithium-ion batteries. The carbon additives affect only the morphology and textural properties of the composites. The performance of composites in sodium and lithium cells is evaluated at elevated temperatures. It is found that NFPP/rGO outperforms NFPP/C in both Na and Li storage due to its hybrid mechanism of energy storage. In sodium half-cells, NFPP/rGO delivers a reversible capacity of 95 mAh/g at 20 °C and 115 mAh/g at 40 °C with a cycling stability of 95% and 88% at a rate of C/2. In lithium half-cells, the capacity reaches a value of 120 mAh/g at 20 and 40 °C, but the cycling stability becomes worse, especially at 40 °C. The electrochemical performance is discussed on the basis of ex situ XRD and microscopic studies. The good Na storage performance of NFPP/rGO at an elevated temperature represents a first step towards its commercialization. [ABSTRACT FROM AUTHOR]

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]

The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabricated with PVDF and carboxymethyl cellulose (CMC) binders. The Li-storage by nanowires proceeds by a hybrid capacitive-diffusive mechanism between 0.1 and 2.5 V, which enables to achieve a high specific capacity. Sodium titanates accommodate Li+ by formation of mixed lithium-sodium-phase Na2−xLixTi6O13, which is decomposed to the distinct lithium phases Li0.54Ti2.86O6 and Li0.5TiO2. Contrary to lithium, the sodium storage is accomplished mainly by the capacitive reactions, and thus the phase composition is preserved during cycling in sodium ion cells. The isolated nanowires outperform bundled nanowires with respect to rate capability. [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 aims to quantify the synergistic effect of Ni2+ and Mn2+ ions on the capacitive performance of oxide, hydroxide and phosphate electrodes in alkaline electrolytes. Three types of phases containing both nickel and manganese in a ratio of one-to-one were selected due to their stability in alkaline media: oxides with ilmenite and spinel structures (NiMnO3 and Ni1.5Mn1.5O4); hydroxides with layered structures (β-Ni1/2Mn1/2(OH)2); and phosphates with olivine and maricite structures (LiNi1/2Mn1/2PO4 and NaNi1/2Mn1/2PO4). In the mixed hydroxides and phosphates, Ni2+ and Mn2+ ions randomly occupied one crystallographic site, whereas in the ilmenite oxide, a common face was shared by the Ni2+ and Mn4+ ions. The electrochemical parameters of the Ni–Mn compositions were evaluated in asymmetric hybrid supercapacitor cells working with alkaline electrolytes and activated carbon as a negative electrode. A comparative analysis of oxides, hydroxides and phosphates enabled us to differentiate the effects of nickel and manganese ions, structures and morphologies on their capacitive performance. Thus, the best performed electrode was predicted. The electrode composition should simultaneously contain Ni and Mn ions, and their morphologies should comprise spherical aggregates. This was an ilmenite NiMnO3, which delivers high energy and power density (i.e., 65 W h kg−1 at 3200 W kg−1) and exhibits a good cycling stability (i.e., around 96% after 5000 cycles at a current load of 240 mA g−1). [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]

An optimized chemical bath method is applied to obtain well-structured thin films with composition Na 0.33 V 2 O 5 · n H 2 O ( n = 1 and 1.3). The method is based on a controlled precipitation reaction that takes place in the system of sodium metavanadate and diethyl sulfate at 85 °C. The film structure, morphology and the changes occurring during prolonged aging are examined by XRD, IR spectroscopy, TG-DTA, SEM and AFM. The electrochemical and electrochromic properties are studied by cyclic voltammetry and UV–vis spectroscopy. The as-deposited thin films are characterized with high optical transmittance varying between 40 and 70% at the 500 nm visible region in dependence on film thickness. The Na 0.33 V 2 O 5 · n H 2 O thin films exhibit stable electrochemical cycling combined with relatively high electrochromic activity. The reproducibility of the transmittance variance of 55% after 500 cycles in the electrochromic cell is a promising result for the potential application of Na 0.33 V 2 O 5 · n H 2 O thin films in electrochromic devices. [ABSTRACT FROM AUTHOR]

The crystal structure of magnesium potassium arsenate hexahydrate, MgKAsO4 ·6H2O, was refined from powder diffraction data. MgKAsO4 ·6H2O crystallizes in the orthorhombic space group Pmn21 with Z = 2, as the biomineral struvite. Complete dehydration of MgKAsO4 ·6H2O proceeds in a single step, with one endothermic peak at 87.9 °C ( Tonset). The infrared and Raman spectra of protiated and deuterated polycrystalline samples were recorded at room temperature and at the boiling temperature of liquid nitrogen (LNT). The assignments of the observed bands are proposed and spectra-structure correlations are made. [ABSTRACT FROM AUTHOR]

A new and simple chemical method for deposition of thin films of ammonium intercalated V2O5·nH2O xerogels has been designed. The chemical deposition has been performed in aqueous solutions of ammonium metavanadate and acetic acid at temperatures between 50 and 85 °C. Depending on the vanadium concentration and deposition temperature xerogels with different composition have been prepared. The structure, morphology, electrochemical and electrochromic behaviour of the thin films with a composition of (NH4)0.15V2O5·1.3H2O have been examined. The film morphology comprises randomly oriented ribbon-like units (100 nm wide and about 500 nm long) which are composed of aggregated primary smaller particles in the nanoscale region of 50-100 nm. Two relatively stable redox pairs are observed in the cyclic voltammograms which correspond to the two-step electrochromism with colour transformations yellow/green and green/blue. The thin film thickness is found to have strong influence on the transmittance variance as deduced by the optical spectra of the reduced and oxidized states. The best result regarding the transmittance variance of 54% at 400 nm is achieved with thin films with thickness of about 200 nm which makes the prepared films very attractive for application in electrochromic devices. [ABSTRACT FROM AUTHOR]

We have demonstrated the capability of dittmarite-type precursors to act as structure and morphology directed agents for a facile synthesis of electrochemically active lithium manganese phospho-olivine nanostructures which are of interest as positive electrode materials for lithium ion batteries. Two types of compounds from the dittmarite series are considered: potassium and ammonium manganese phosphate monohydrates, M'MnPO4⋅H2O( M' =K ,N H4). Both M'MnPO4⋅H2O( M' =K ,N H4) and NH4MnPO4⋅H2O precursors interact with the eutectic LiCl-LiNO3 composition before its melting, leading to the formation of the target LiMnPO4. The reaction of M'MnPO4⋅H2O( M' =K ,N H4)with LiCl-LiNO3 takes place by a topotactic mechanism including a fast ion exchange of K+ for Li+ and H2O release, as a result of which nanostructured LiMnPO4 is formed. The NH4MnPO4⋅H2O precursor reacts with the lithium salts by massive evolution of H2O, NH3, NO and N2O gasses, resulting in fragmentation of the pristine plate-like aggregates into well-shaped and dispersed particles with nanosizes of about 20-50 nm. [ABSTRACT FROM AUTHOR]

We report precursor-based methods for low-temperature synthesis of two structure modifications of NaMnPO4. The maricite phase is thermodynamically more stable, while the olivine phase is of great interest as a positive-electrode material for lithium and sodium ion batteries. The advantage of synthetic procedures is the formation of defectless NaMnPO4 in the temperature range of 200–400 °C. The structure and morphology characterizations of two modifications are performed by powder XRD, SEM and TEM analyses. The oxidation state of the Mn ions in NaMnPO4 is determined by X-ray photoelectron spectroscopy. The local environment of Na in both structure modifications is assessed by 23Na MAS NMR spectroscopy. The synthesis methods are based on the formation of appropriate precursors that are easily transformed to target NaMnPO4. Thermal decomposition of freeze-dried phosphate–formate precursor yields NaMnPO4 with a maricite structure at 400 °C. KMnPO4·H2O with a dittmarite-type structure acts as a structure-template precursor for the preparation of NaMnPO4 with an olivine structure by an ion exchange reaction. Both olivine and maricite NaMnPO4 do not accommodate any anti-site mixing and Na,Mn deficiency. The morphology of NaMnPO4 consists of nano-sized particles (less than 50 nm) that are closely bound together into aggregates, the shape of the aggregates being dependent on the synthesis procedure used. [ABSTRACT FROM AUTHOR]

Abstract: The compounds M[PO2(OH)2]2·2H2O (M=Mg, Mn, Fe, Co, Ni, Zn, Cd) were prepared from super-saturated aqueous solutions at room temperature. Single-crystal X-ray structure investigations of members with M=Ni, Zn, Cd were performed at 295 and 120K. The space-group symmetry is P21/n, Z=2. The unit-cell parameters are at 295/120K for M=Ni: a=7.240(2)/7.202(2), b=9.794(2)/9.799(2), c=5.313(1)/5.285(1)Å, β=94.81(1)/94.38(1)°, V=375.4/371.9Å3; M=Zn: a=7.263(2)/7.221(2), b=9.893(2)/9.899(3), c=5.328(1)/5.296(2)Å, β=94.79(1)/94.31(2)°, V=381.5/377.5Å3; M=Cd: a=7.356(2)/7.319(2), b=10.416(2)/10.423(3), c=5.407(1)/5.371(2)Å, β=93.85(1)/93.30(2)°, V=413.4/409.1Å3. Layers of corner-shared MO6 octahedra and phosphate tetrahedra are linked by three of the four crystallographically different hydrogen bonds. The fourth hydrogen bond (located within the layer) is worth mentioning because of the short Oh⋯O bond distance of 2.57–2.61Å at room temperature (2.56–2.57Å at 120K); only for M=Mg it is increased to 2.65Å. Any marked temperature-dependent variation of the unit-cell dimension is observed only vertical to the layers. The analysis of the infrared (IR) spectroscopy data evidences that the internal PO4 vibrations are insensitive to the size and the electronic configuration of the M 2+ ions. The slight strengthening of the intra-molecular P–O bonds in the Mg salt is caused by the more ionic character of the Mg–O bonds. All IR spectra exhibit the characteristic “ABC trio” for acidic salts: 2900–3180cm−1 (A band), 2000–2450cm−1 (B band) and 1550–1750cm−1 (C band). Both the frequency and the intensity of the A band provide an evidence that the PO2(OH)2 groups in M[PO2(OH)2]2·2H2O compounds form weaker hydrogen bonds as compared with other acidic salts with comparable O⋯O bond distances of about 2.60Å. The observed shift of the O–H stretching vibrations of the water molecule in the order M=Mg>Mn≈Fe≈Co>Ni>Zn≈Cd has been discussed with respect to the influence of both the character and the strength of M↔H2O interactions. [Copyright &y& Elsevier]

Abstract: The IR and Raman spectra of the isostructural M′M″PO4·H2O compounds (M′=K+, NH4 +; M″=Mn2+, Co2+, Ni2+) are reported and discussed with respect to the normal vibrations of the PO4 3− ions. The vibrational behavior of PO4 3− is in agreement with its low site symmetry Cs in the lattices—the symmetric ν 1 and ν 2 modes are activated in the IR spectra and the degeneration of the asymmetric ν 3 and ν 4 modes is lifted. A relatively large unit-cell group splitting is observed for ν 1 in both the IR and Raman spectra and for ν 3 in Raman spectra. It has been established that the mean wavenumbers of the Pes () are not affected by the M2+ ions present, but they are lower for the NH4-series than for the K-one (predominant influence of both the smaller repulsion potential and the hydrogen bonds in the NH4-lattices over the influence of the M+–O interactions). The extent of the energetic distortion of the PO4 3− ions has been estimated based on the spectroscopic data for the site group splitting of the asymmetric modes (Δν 3 and Δν 4), the separation between the highest and the lowest wavenumbered Pes (Δν max) and the intensity of ν 1 in the IR spectra. The data provide an evidence that the PO4 3− ions in KM″PO4·H2O are more distorted regarding the Pngths than those in NH4M″PO4·H2O, but their angular distortion is the same in both series. The trends for the energetic distortion of the phosphate ions found from the spectroscopic data correspond to the data for their geometric distortion deduced from the values of the distortion indices DI(PO) and DI(OPO). [Copyright &y& Elsevier]

Abstract: The vibrational behavior of the uncoupled νOD modes and of the water librations in dittmarite-type compounds M′M″PO4·H2O (M′=K+, NH4 +; M″=Mn2+, Co2+, Ni2+) is analyzed in terms of the influence of two types of metal−water interactions (M+−H2O and M2+−H2O), the hydrogen bonding and the repulsion potential of the lattices. The M+−H2O interaction is found to be the main factor, which influences ν OD. The strong K+−H2O interaction weakens in a higher degree the intramolecular O−H bonds than the corresponding M2+−H2O interactions (M2+ =Mn, Co, Ni). As a result ν OD is shifted to lower wavenumbers in the potassium series than in ammonium one, irrespective of the synergetic effect of M2+, the hydrogen bond lengths and the repulsion potential of the lattices. The analysis of the spectroscopic data evidences for the dominating influence of the M2+−H2O interaction on the wagging mode. The blue shift of ν wag strictly follows the increasing synergetic effect of M2+, i.e. ν M′/Mn < ν M′/Co < ν M′/Ni, in all cases, irrespective of the strength of the M+−H2O interactions, the hydrogen bond lengths and the higher repulsion potential of the K-lattices. The rocking mode is insensitive to the replacement of the M2+ ions. Some relations between the spectroscopic and structural data are given. [Copyright &y& Elsevier]

The infrared spectra of related compounds with kro¨hnkite-type chains Na2Me(SeO4)2·2H2O (Me=Mn, Co, Ni, Cu, Zn, Cd) containing matrix-isolated SO42− guest ions are reported and discussed with respect to the S&z.sbnd;O stretching modes ν3 and ν1. Due to the low site symmetry C1 of the SO42− guest ions three bands for ν3 and one band for ν1 are seen in all spectra. When SO42− guest ions are incorporated in the triclinic Na2Zn(SeO4)2·2H2O, Na2Co(SeO4)2·2H2O and Na2Ni(SeO4)2·2H2O host lattices the ν3 stretching region resembles a higher local symmetry (A1⊕E) of the SO42− guest ions than the crystallographic one (i.e. Δνab>Δνbc instead of Δνab&ap;Δνbc, a, b and c being three ν3 components). Hence, the ratio between Δνab and Δνbc additionally to Δνmax (the difference between the highest and the lowest wavenumbered S&z.sbnd;O stretching modes) has to be taken into account when the SO42− guest ion distortions are considered (the higher the ratio Δνab/Δνbc is, the weaker the distortion is). Both the site group splittings of the triplet component ν3 (Δνac) and Δνmax values are an adequate measure for the SO42− guest ion distortion when the guest ions are incorporated in the monoclinic Na2Cu(SeO4)2·2H2O, Na2Mn(SeO4)2·2H2O and Na2Cd(SeO4)2·2H2O (i.e. Δνab&ap;Δνbc). In addition to the local potential at the lattice site of the host lattice, the metal environment of the SO42− guest ions reflects on the guest ion distortions. A correlation between the SO42− guest ion distortions and the metal electronic configurations has been found and discussed. Me′2+ guest ions incorporated additionally to the SO42− guest ions in the selenate lattices do not influence practically on the vibrational behavior of the S&z.sbnd;O stretches. [Copyright &y& Elsevier]

The infrared spectra of related compounds with kro¨hnkite-type chains Na2Me(XO4)2·2H2O (Me=Mn, Co, Ni, Cu, Zn, Cd, and X=S, Se) containing matrix-isolated X′O42− guest ions and HDO molecules are presented and discussed in the region of the OD stretching modes. The strength of the hydrogen bonds formed in the compounds under study are discussed in terms of the hydrogen bond acceptor strength of the SO42− and SeO42− ions, the respective Ow⋯O bond lengths, the metal–water interactions (synergetic effect), the repulsion potential of the lattice (reduced unit-cell volume), the hydrogen bond acceptor capability of the oxygen atoms. The frequencies of the uncoupled νOD stretches indicate the formation of stronger hydrogen bonds in the selenate series as compared to the respective compounds of the sulfate one due to the stronger hydrogen bond acceptor capability of the SeO42− ions than that of the SO42− ions. The frequency shifts of νOD corresponding to the guest ions to higher or lower wavenumbers as compared to the parent compounds (i.e. SO42− guest ions in Na2Me(SeO4)2·2H2O and SeO42− guest ions in Na2Me(SO4)2·2H2O, respectively) are due to the translatory and rotatory reorientation of the H2O molecules adjacent to the guest ions. [Copyright &y& Elsevier]

The infrared and Raman spectra of magnesium rubidium phosphate hexahydrate MgRbPO4 ⋅ 6H2O and magnesium thallium phosphate hexahydrate, MgTlPO4 ⋅ 6H2O were recorded at room temperature (RT) and the boiling temperature of liquid nitrogen (LNT). To facilitate their analysis, also recorded were the spectra of partially deuterated analogues with varying content of deuterium. The effects of deuteration and those of lowering the temperature were the basis of the conclusions drawn regarding the origin of the observed bands which were assigned to vibrations which are predominantly localized in the water molecules (four crystallographically different types of such molecules exist in the structures) and those with PO Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. character. It was concluded that in some cases coupling of phosphate and water vibrations is likely to take place. The appearance of the infrared spectra in the O--H stretching regions of the infrared spectra is explained as being the result of an extensive overlap of bands due to components of the fundamental stretching modes of the H2O units with a possible participation of bands due to second-order transitions. A broad band reminiscent of the B band of the well-known ABC trio characteristic of spectra of substances containing strong hydrogen bonds in their structure was found around 2400 cm-1 in the infrared spectra of the two studied compounds. [ABSTRACT FROM AUTHOR]

This study reports an effective approach to improve dramatically the electrochemical performance of nanosized NaFePO 4 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 Fe 2+ proceeds at the nanoscale level within the maricite nanoparticles and causes a massive structural transformation of the maricite phase into a monoclinic NASICON phase Na 3 Fe 2 (PO 4 ) 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 LiPF 6 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.

Sodium manganese phospho-olivine, NaMnPO 4 , is considered to be a higher-voltage alternative to the presently used iron-based electrode material, NaFePO 4 , for sodium ion batteries. Irrespective of this advantage, the electrochemical performance of NaMnPO 4 is still far from what is desired. Herein we provide the first report on the storage performance of NaMnPO 4 having a structure modified by Mg 2+ substitution. The Mg-substituted phospho-olivines are prepared on the basis of ionic exchange reactions involving the participation of Mg-substituted KMnPO 4 ·H 2 O dittmarites as structural template. Furthermore, the phosphate particles were covered with a thin layer (up to 5 nm) of activated carbon through ball-milling. The storage performance of phospho-olivines is analyzed in sodium and lithium half-ion cells, as well as in full-ion cells versus bio-mass derived activated carbon and spinel Li 4 Ti 5 O 12 as anodes. The compatibility of phospho-olivines with electrolytes is assessed by utilization of several types of lithium and sodium carbonate-based solutions. In sodium half-cell, the Mg-substituted phosphate displays a multi-phase mechanism of Na + intercalation in case when NaTFSI-based electrolyte is used. In lithium half-cell, the high specific capacity and rate capability is achieved for phospho-olivine cycled in LiPF 6 -based electrolyte. This is a consequence of the occurrence of dual Li + ,Na + intercalation, which encompass nano-sized domains. The utilization of the Mg-substituted phospho-olivine in the full ion cell is demonstrated., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dittmarite-type compound KMnPO(4)·H(2)O was used as a new precursor for the synthesis of nanostructured LiMnPO(4) phospho-olivines with a plate-like morphology at low temperature (about 200 °C) and a short reaction time (90-180 min). The dehydration of KMnPO(4)·H(2)O was studied by DTA and TG analysis. Structural and morphological characterization of both KMnPO(4)·H(2)O and LiMnPO(4) was performed by powder XRD, SEM and TEM analyses. The formation of nanostructured LiMnPO(4) was examined by electron paramagnetic resonance spectroscopy and TEM. It was found that the reaction between KMnPO(4)·H(2)O with the LiCl-LiNO(3) mixture includes a fast ionic exchange of K(+) with Li(+) in the framework of the dittmarite structure, followed by H(2)O release and the formation of the olivine-type structure. The morphology and texture of the dittmarite-type precursor results in a plate-like morphology of LiMnPO(4) with a preferred orientation along the [100] direction. The plate-like morphology of LiMnPO(4) is stable after annealing at 500 °C. The plates are composed of nanocrystallites, with various sizes in the range 10-20 nm. The EPR signal of LiMnPO(4) is due to the exchange-coupled Mn(2+) ions. It was demonstrated that the EPR line-width correlates with the Scherrer crystallite size., (This journal is © The Royal Society of Chemistry 2011)