RESUMEN
Rechargeable lithium batteries have ushered the wireless revolution over last two decades and are now matured to enable green automobiles. However, the growing concern on scarcity and large-scale applications of lithium resources have steered effort to realize sustainable sodium-ion batteries, Na and Fe being abundant and low-cost charge carrier and redox centre, respectively. However, their performance is limited owing to low operating voltage and sluggish kinetics. Here we report a hitherto-unknown material with entirely new composition and structure with the first alluaudite-type sulphate framework, Na2Fe2(SO4)3, registering the highest-ever Fe(3+)/Fe(2+) redox potential at 3.8 V (versus Na, and hence 4.1 V versus Li) along with fast rate kinetics. Rare-metal-free Na-ion rechargeable battery system compatible with the present Li-ion battery is now in realistic scope without sacrificing high energy density and high power, and paves way for discovery of new earth-abundant sustainable cathodes for large-scale batteries.
RESUMEN
The particle-size effects on the thermodynamic properties and kinetic behavior of a Li(x)FePO(4) electrode have a direct influence on the electrode properties. Thus, the development of high-performance Li-ion batteries containing a Li(x)FePO(4) cathode requires a complete understanding of the reaction mechanism at the atomic/nano/meso scale. In this work, we report electrochemical calorimetric and potentiometric studies on Li(x)FePO(4) electrodes with different particle sizes and clarify the particle-size effect on the reaction mechanism based on the entropy change of (de)lithiation. Electrochemical calorimetry results show that a reduction in particle size shrinks the miscibility gap of Li(x)FePO(4) while potentiometric measurements demonstrate that the Li(x)FePO(4) particles equilibrate into either a kinetically metastable state or a thermodynamically stable state depending on the particle size.
RESUMEN
The magnetic structure and properties of sodium iron fluorophosphate Na2FePO4F (space group Pbcn), a cathode material for rechargeable batteries, were studied using magnetometry and neutron powder diffraction. The material, which can be described as a quasi-layered structure with zigzag Fe-octahedral chains, develops a long-range antiferromagnetic order below â¼3.4 K. The magnetic structure is rationalized as a super-exchange-driven ferromagnetic ordering of chains running along the a-axis, coupled antiferromagnetically by super-super-exchange via phosphate groups along the c-axis, with ordering along the b-axis likely due to the contribution of dipole-dipole interactions.
RESUMEN
The crystal structure of the NaMnSO4F fluorosulfate phase prepared by low-temperature solid-state synthesis has been solved and refined by the Rietveld analysis of synchrotron X-ray powder diffraction data. Isostructural to the naturally occurring triplite family of minerals, this compound crystallizes in monoclinic C2/c symmetry (No. 15) with unit-cell parameters of a = 13.77027â (17), b = 6.63687â (8), c = 10.35113â (14)â Å, ß = 121.4795â (3)° and V = 806.78â (2)â Å(3). Its structure is built of edge-sharing chains of distorted MO4F2 octahedra, which are interconnected by constituent SO4 tetrahedra to form a robust three-dimensional polyanionic framework. MO4F2 octahedra are randomly occupied by Na and Mn with close to 1:1 occupancy. This random mixing of cations among polyhedral building blocks means that there are no channels for Na-ion conduction, rendering it electrochemically inactive. The structure is discussed and compared with other known alkali metal fluorosulfates as well as to naturally occurring triplite-type minerals.