Easily water-synthesisable iron-chloranilate frameworks as high energy and high-power cathodes for sustainable alkali-ion batteries

Abstract

Achieving high battery performance from low-cost, easily synthesisable electrode materials is crucial for advancing energy storage technologies. Metal–organic frameworks (MOFs) combining inexpensive transition metals and organic ligands are promising candidates for high-capacity cathodes. Iron-chloranilate-water frameworks are herein reported to be produced in aqueous media under mild conditions. Removal of reticular water from known [Fe2(CAN)3(H2O)4] ⋅ 4H2O yields a new supramolecular metal–organic framework (SMOF), [Fe2(CAN)3(H2O)4]. Removing coordination water, a new 2D honeycomb-like MOF forms, Fe2(CAN)3, stable without counterions and solvent. This MOF adopts the unusual ABC layer-stacking, as determined using a combination of ab initio random structure searching, electron diffraction, and Rietveld refinement of powder XRD data. Magnetometry, Mossbauer and Raman spectroscopy confirm that all three [Fe2(CAN)3(H2O)x]⋅yH2O phases contain HS-Fe3+ and CAN2−, with magnetic ordering temperatures increasing (5→20 K) as the Fe−CAN connectivity increases. The SMOF and MOF show reversible (de)insertion of >4Li+/f.u. at average 2,59 V and 2,76 V vs Li+/Li, respectively. [Fe2(CAN)3] achieves 146 mAh/g at 1 C, thus specific energy (563 Wh/kg) and power (446 W/kg) in Li half-cells competitive with conventional LiFePO4 (~580 Wh/kg and ~450 W/kg). Beyond Li, [Fe2(CAN)3] delivers 394 Wh/kg and 421 Wh/kg, for Na and K half-cells respectively, becoming a competitive cathode for sustainable batteries.