An FeF₃·0.5H₂O Polytype: A Microporous Framework Compound with Intersecting Tunnels for Li and Na Batteries

Abstract

To improve the energy/power density of energy storage materials, numerous efforts have focused on the exploration of new structure prototypes, in particular metal-organic fameworks, Prussian blue analogues, open-framework oxides, and polyanion salts. Here we report a novel pyrochlore phase that appears to be useful as a high-capacity cathode for Li and Na batteries. It is an iron fluoride polymorph characterized by an intersecting tunnel structure, providing the space for accommodation and transport of Li and Na ions. It is prepared using hydrolyzable ionic liquids, which serve as reaction educts and structure-directing agents not only as far as the chemical structure is concerned but also in terms of morphology (shape, defect structure, electrode network structure). A capacity higher than 220 mA h g(-1) (for Li and Na storage) and a lifetime of at least 300 cycles (for Li storage) are demonstrated.

Enhanced electrochemical activity of rechargeable carbon fluorides–sodium battery with catalysts

“…This is consistent with the result from XRD. Previous studies on the electrochemical reaction of FeF 3 with sodium had suggested that the initial discharge capacity of the FeF 3 electrode is more than 130 mAh/g when the cell was cycled between 1.5 and 4.0 V [3,4]. However, the first discharge capacity is less than 50 mAh/g for the composite electrode consisting of FeF 3 and GNS without CF x (Fig.…”

“…Notably, FeF 3 sodium capacity of 250 mAh/g over a voltage range of 0. .0 V [3,4]. Recently, we have firstly indicated the reversibility of the CF x as a cathode material for SIBs and a highly reversible capacity of 1061 mAh/g with the discharge voltage plateau at 2.4 V [5], which is much higher than that of any other advanced Na storage materials reported previously.…”

Graphene Quantum Dots Coated VO2 Arrays for Highly Durable Electrodes for Li and Na Ion Batteries

“…8 There are recent reports available on a number of new materials such as layered transition metal oxides P2-Na x CoO 2 , 9 Na x [Fe 1/2 Mn 1/2 ]O 2 , 10 cubic Na x MnFe(CN) 6 , 11 NASICONtype Na 3 V 2 (PO 4 ) 3 , 12 and fluoride-based ReO 3 -type FeF 3 . 13 These pioneering work in NIBs opened a new window, albeit the fact that the reported capacities are still very low (less than 200 mAh/g) compared to LIBs.…”

Mechano-chemical synthesis of nanostructured FePO4/MWCNTs composites as cathode materials for lithium-ion batteries

“…The MWCNTs are dispersed into the ionic liquid mixture of bmimFeCl 4 and bmimCl via "cation-p" interaction between the imidazolium cations and the p-electrons of the MWCNTs surface, resulting in the formation of a Bucky-gel. 30,31 The composition of the as-obtained material was identied by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). 28,29 Equilibrium between FeCl 4 À and Fe 3+ , allows the precipitation of FePO 4 from the mixture, where the nano-grains are well separated due to the interfacial tension.…”