NASICON-type air-stable and all-climate cathode for sodium-ion batteries with low cost and high-power density.
ABSTRACT: The development of low-cost and long-lasting all-climate cathode materials for the sodium ion battery has been one of the key issues for the success of large-scale energy storage. One option is the utilization of earth-abundant elements such as iron. Here, we synthesize a NASICON-type tuneable Na4Fe3(PO4)2(P2O7)/C nanocomposite which shows both excellent rate performance and outstanding cycling stability over more than 4400 cycles. Its air stability and all-climate properties are investigated, and its potential as the sodium host in full cells has been studied. A remarkably low volume change of 4.0% is observed. Its high sodium diffusion coefficient has been measured and analysed via first-principles calculations, and its three-dimensional sodium ion diffusion pathways are identified. Our results indicate that this low-cost and environmentally friendly Na4Fe3(PO4)2(P2O7)/C nanocomposite could be a competitive candidate material for sodium ion batteries.
Project description:The solid solution, sodium [iron(III)/manganese(II)] tris-(orthophosphate), Na?.?Mn?.?Fe?.?(PO?)?, was obtained using a flux method. Its crystal structure is related to that of NASICON-type compounds. The [(Mn/Fe)?(PO?)?] framework is built up from an (Mn/Fe)O?octa-hedron (site symmetry 3.), with a mixed Mn/Fe occupancy, and a PO? tetra-hedron (site symmetry .2). The Na? cations are distributed over two partially occupied sites in the cavities of the framework. One Na? cation (site symmetry -3.) is surrounded by six O atoms, whereas the other Na? cation (site symmetry .2) is surrounded by eight O atoms.
Project description:This paper reports the crystal structure of tetra-sodium diiron tris(phosphate), Na(4)Fe(2+)Fe(3+)(PO(4))(3), which has been synthesized hydro-thermally at 773?K and 0.1?GPa. The crystal structure has been refined in the space group Rc and is identical to that of ?-NASICON. The heteropolyhedral framework is based on a regular alternation, in three dimensions, of corner-sharing PO(4) tetra-hedra and FeO(6) octa-hedra, constituting so-called 'lantern units' stacked along the c axis. The Na(+) cations are distributed over two crystallographic sites: the six-coordinated Na1 site which lies between two 'lantern units', and the eight-coordinated Na2 site which lies at the same z value as the P site.
Project description:Single crystals of the title compound, tris-odium divanadium(III) tris-(orthophosphate), were grown from a self-flux in the system Na(4)P(2)O(7)-NaVP(2)O(7). Na(3)V(2)(PO(4))(3) belongs to the family of NASICON-related structures and is built up from isolated [VO(6)] octa-hedra (3. symmetry) and [PO(4)] tetra-hedra (.2 symmetry) inter-linked via corners to establish the framework anion [V(2)(PO(4))(3)](3-). The two independent Na(+) cations are partially occupied [site-occupancy factors = 0.805?(18) and 0.731?(7)] and are located in channels with two different oxygen environments, viz sixfold coordination for the first (. symmetry) and eightfold for the second (.2 symmetry) Na(+) cation.
Project description:The title compound, rubidium ditin(IV) tris-(phosphate), RbSn(2)(PO(4))(3), belongs to the NASICON-type family of phosphates and crystallizes in the space group R[Formula: see text]. The structure is composed of PO(4) tetra-hedra (1 symmetry) and two slightly distorted SnO(6) octa-hedra, both with 3. symmetry, which are inter-linked through corner-sharing O atoms to form a (3) (?)[Sn(2)(PO(4))(3)](-) framework. The Rb(+) cations are located on threefold inversion axes in the voids of this framework and exhibit a coordination number of 12. The crystal studied was twinned by merohedry with a component ratio of 0.503:0.497.
Project description:The title compound, sodium chromium/aluminium molybdenum/aluminium dodeca-oxide, Na0.72Cr0.48Al1.74Mo2.77O12, was prepared by solid-state reaction. Its crystal structure is related to NaSICON-type compounds. The framework is built up from M1O6 (M1 = Cr/Al) octa-hedra and M2O4 (M2 = Mo/Al) tetra-hedra inter-connected by corners. The three-dimensional framework contains cavities in which sodium cations are located. Two validation models (BVS and CHARDI) were used to confirm the proposed structural model. The mobility of Na+ ions in the structure has been investigated by theoretical means.
Project description:Carbonate (CO<sub>3</sub>) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate-phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO<sub>3</sub> and PO<sub>4</sub> concentrations. The surface speciation of CO<sub>3</sub> has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO<sub>3</sub> occurs predominately via formation of bidentate inner-sphere complexes, either (?FeO)<sub>2</sub>CO or (?FeO)<sub>2</sub>CO··Na<sup>+</sup>. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO<sub>4</sub>. Additionally, a minor complex is present at high CO<sub>3</sub> loadings. The CD model, solely parametrized by measuring the pH-dependent PO<sub>4</sub> adsorption as a function of the CO<sub>3</sub> concentration, successfully predicts the CO<sub>3</sub> adsorption to Fh in single-ion systems. The adsorption affinity of CO<sub>3</sub> to Fh is higher than to goethite, particularly at high pH and CO<sub>3</sub> loadings due to the enhanced formation (?FeO)<sub>2</sub>CO··Na<sup>+</sup>. The PO<sub>4</sub> adsorption isotherm in 0.5 M NaHCO<sub>3</sub> can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO<sub>3</sub> complex formation and resolved a new species (Fe(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub> <sup>3-</sup>(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.
Project description:The new compounds NaMV<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> (M = Fe, Co, Ni) were synthesized via a sol-gel synthesis route, and their crystal structures were refined using the Rietveld method from X-ray powder diffraction data. NaCoV<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> was also characterized by TGA, cyclic voltammetry, and galvanostatic cycling. The three phases crystallize with the orthorhombic symmetry and the space group <i>Imma</i>. The structures are isotypic to the stuffed ?-CrPO<sub>4</sub>-type structure and contain two vacant sites in which two sodium atoms can be intercalated. When NaCoV<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> is cycled at a 1C rate in the voltage ranges of 0.1-3 and 0.7-3 V vs Na<sup>+</sup>/Na, it delivers specific capacities of 190 and 75 mA h/g, respectively, with an average operation potential of ?1.4 V. This attests to the electrochemical activity of this compound and indicates that the ?-CrPO<sub>4</sub>-type compounds could be suitable for hosting other guest ions.
Project description:Sodium-ion batteries are widely regarded as a promising supplement for lithium-ion battery technology. However, it still suffers from some challenges, including low energy/power density and unsatisfactory cycling stability. Here, a cross-linked graphene-caged Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>F<sub>3</sub> microcubes (NVPF@rGO) composite via a one-pot hydrothermal strategy followed by freeze drying and heat treatment is reported. As a cathode for a sodium-ion half-cell, the NVPF@rGO delivers excellent cycling stability and rate capability, as well as good low temperature adaptability. The structural evolution during the repeated Na<sup>+</sup> extraction/insertion and Na ions diffusion kinetics in the NVPF@rGO electrode are investigated. Importantly, a practicable sodium-ion full-cell is constructed using a NVPF@rGO cathode and a N-doped carbon anode, which delivers outstanding cycling stability (95.1% capacity retention over 400 cycles at 10 C), as well as an exceptionally high energy density (291 Wh kg<sup>-1</sup> at power density of 192 W kg<sup>-1</sup>). Such micro-/nanoscale design and engineering strategies, as well as deeper understanding of the ion diffusion kinetics, may also be used to explore other micro-/nanostructure materials to boost the performance of energy storage devices.
Project description:Emerging sodium-ion batteries (SIBs) devices hold the promise to leapfrog over existing lithium-ion batteries technologies with respect to desirable power/energy densities and the abundant sodium sources on the earth. To this end, the discoveries on novel cathode materials with outstanding rate capabilities are being given high priority in the quest to achieve high power density SIBs devices, and the multi-dimensional Na+ migration pathways with low diffusion energy barriers are crucial. In light of this, the recent development of Prussian blue analogs and sodium superionic conductor (NASICON)-type materials with 3D Na+ diffusion pathways for building high power density NIBs are provided in this perspective. Ultimately, the future research directions to realize them for real applications are also discussed.
Project description:The structure of the title compound tris-odium aluminium bis-(arsenate), Na(3)Al(AsO(4))(2), is built up from AlO(4) and AsO(4) corner-sharing tetra-hedra, forming an undulating two-dimensional framework parallel to (100). The layers are constituted of large Al(6)As(6)O(36) rings made up from six AlO(4) and AsO(4) tetra-hedra in which two sodium cations are situated, the third sodium cation being located in the inter-layer space. The structural relationships between the title compound and Na(3)Fe(PO(4))(2), NaAlCo(PO(4))(2) and Al(5)Co(3)(PO(4))(8) are discussed.