Soft chemical routes to electrochemically active iron phosphates

Abstract

New iron phosphates with related structures have been synthesized using hydrothermal and ion-exchange routes, and their electrochemical properties were investigated. First, NaFe(HPO 4 ) 2 was synthesized employing a hydrothermal route and its structure was determined from singlecrystal X-ray diffraction data. Subsequent Na + and partial proton ion exchange with Li + ion produced a known phase, Li 2 Fe(H 0.5 PO 4 ) 2 , and complete deprotonation of Li 2 Fe-(H 0.5 PO 4 ) 2 with Li + by employing a solid-state ion-exchange route produced the new phase Li 3 Fe(PO 4 ) 2 . The structure of the latter was solved from synchrotron powder X-ray data by employing ab initio methods. All of these phases are highly crystalline, built up of similar connectivities between FeO 6 octahedra and PO 4 tetrahedral units. Magnetic susceptibility measurements and room-temperature 57 Fe Mossbauer spectroscopic studies confirm the 3+ oxidation state of the compounds and their antiferromagnetic ordering with Li 2 Fe(H 0.5 PO 4 ) 2 showing some interesting metamagnetic behavior. The compounds are stable up to 400 °C and undergo facile electrochemical lithium/sodium insertion through the reduction of Fe 3+ to Fe 2+ . Galvanostatic charge−discharge studies indicate that up to 0.6 lithium ion and 0.5 sodium ion per formula unit can be inserted at average voltages of 3.0 and 2.75 V for lithium and sodium ion batteries, respectively, for NaFe(HPO 4 ) 2 . The partially Li ion exchanged compound Li 2 Fe(H 0.5 PO 4 ) 2 showed better cycle life and experimentally achievable capacities up to 0.9 Li insertion with strong dependence on particle size. The electrochemical Li insertion in Li 3 Fe(PO 4 ) 2 was also investigated. The electrochemistry of these three related phases were compared with each other, and their mechanism of Li insertion was investigated by ex situ PXRD.

Structural and magnetic characterization of barbosalite Fe3(PO4)2(OH)2

“…The RT SXRPD pattern of the polycrystalline sample can be indexed using the P21/n space group and lattice parameters: a = 7.3231Å, b =7.4687Å, c = 7.4073Å and β = 118.565°, in agreement with the previous reports [5,15]. The barbosalite framework is described as consisting of Fe 3+ -Fe 2+ -Fe 3+ face sharing FeO6 octahedra trimers, oriented along the <110> direction, and connected together by phosphate tetrahedra [15] (Figure 1a and 1b).…”

“…Consequently, the structure was solved in the P21 supercell, using the higher quality data of a chosen small crystal recorded at 175 K, leading to an agreement factor of 5.75% (Table 1). A polar twin was used giving rise to a Flack parameter of 0.55 (5).…”

“…shown to be less performing than LiFePO4 with the possibility to exchange only 0.7 Li at 2.6V [5]. However, barbosalite exhibits the best catalytic properties of the Fe-P-OH-H system [6,7].…”

Synthesis, Structure, and Electrochemical Properties of Some Cobalt Oxalates

“…It is noticeable that both I and III exhibited a large discrepancy of the plateaus between charging and discharging, i.e., a large cell polarization. This is due mainly to the insufficient conductivity of the electrode, analogous to some other cathodes. − Meanwhile, the cycling performances were poor in this study, but this may originate from the decomposition and consumption of electrolytes at high voltages. As previously reported, several Co-based polyanions belong to high-voltage cathodes; , therefore, it is necessary to use high-voltage electrolytes to improve cycling performance and unveil the intrinsic cycling stabilities of the studied electrode materials.…”

Green Synthesis of Iron Oxides and Phosphates via Thermal Treatment of Iron Polyphenols Synthesized by a Camellia sinensis Extract

“…Crystalline and amorphous iron phosphate materials have interesting chemical, thermal, electrical, and magnetic properties and have been investigated for a variety of technological applications, such as industrial coatings, magnetic and optical materials, catalysts, tissue engineering, biosensor fabrication, cathode materials for rechargeable Li ion batteries, and electrode materials in general. − Grattarolaite features a noncentrosymmetric lattice composed of Fe 3+ triangular units that forms a high density of defects within an antiferromagnetic helical phase. This material has been investigated for its insulating properties, magnetization, and specific heat capacity. ,, …”