Phosphite as Polyanion-Based Cathode for Li-Ion Battery: Synthesis, Structure, and Electrochemistry of LiFe(HPO₃)₂

Abstract

A new lithium containing iron(III) phosphite, LiFe(HPO3)2, has been synthesized via a solvent-free, low temperature, solid-state synthesis route. The crystal structure of this material has been determined employing single-crystal X-ray diffraction, which indicates that the compound has a three-dimensional structure formed by isolated FeO6 octahedral units joined together via bridging HPO3 pseudopyramidal moieties. This arrangement leads to the formation of channels along all the three crystallographic directions, where channels along the a- and b-axes host Li(+) ions. The compound was further characterized by TGA, IR, and Mössbauer spectroscopic techniques. Additionally, it has been demonstrated that this phase is electrochemically active toward reversible intercalation of Li(+) ions and thus can be used as a cathode material in Li-ion cells. An average discharge potential of 2.8 V and a practical capacity of 70 mAh·g(-1) has been achieved as indicated by the results of cyclic voltammetry and galvanostatic charge-discharge tests.

Mössbauer Spectral Study of the Low-Temperature Electronic and Magnetic Properties of α-FePO4 and the Mixed Valence Iron(II/III) Phosphate SrFe3(PO4)3

“…Many related alkali and alkaline iron phosphate compounds also have valuable practical applications, such as cathodes in lithium ion batteries, as heterogeneous catalysts, or as a medium for ion exchange. − Indeed, over the past few years several new strontium iron phosphate compounds have been prepared and characterized, including SrFe 2 (PO 4 ) 2 , SrFe 3 (PO 4 ) 3 , SrFe 3 (PO 4 ) 3 O, SrFe 3 (P 2 O 7 ) 2 , SrFe 5 (PO 4 )­(OH)­H 2 O, Sr 9 Fe 1.5 (PO 4 ) 7 , SrFe­(PO 4 ) 2 (HPO 4 ), and Sr 2 Fe­(PO 4 ) 2 (H 2 PO 4 ) . Further, several additional alkali or alkaline cation containing complexes with interesting, often unexpected, properties, including LiFePO 4 , Li 1.43 Fe 5 (HPO 3 ) 6 ·1.5H 2 O, K 0.75 Fe 5 (HPO 3 ) 6 ·0.5H 2 O, Mg 2.88 Fe 4.12 (PO 4 ) 6 , and LiFe­(HPO 3 ) 2 , have been reported. Of special interest are some of the above and related iron cation containing compounds, namely RbNa 3 Fe 7 (PO 4 ) 6 , Li 1.43 Fe 5 (HPO 3 ) 6 ·1.5H 2 O, Na 3 Fe 3 (PO 4 ) 4 , Ba 2 Fe 3 (PO 4 ) 4 ·2H 2 O, BaFe 3 (PO 4 ) 3 , and α-Fe 2 (PO 4 )­O, all of which exhibit interesting magnetic properties.…”

Iron Borophosphate as a Potential Cathode for Lithium- and Sodium-Ion Batteries

“…Subsequent realization that iono-covalency of the metal–ligand bond caused by the inductive effect of the central atoms of the polyanion moiety can tune the redox potential, with respect to Li + /Li, has fueled chemists to look out for polyanions beyond phosphates. , Thus, a large number of polyanionic materials in phosphates, , silicates, , sulfates, − and borates , are being investigated as viable cathodes for Li-ion batteries. We have recently shown that phosphite (HPO 3 2– ) can also act as cathode for Li-ion batteries. , The focus is also shifting toward Na-ion batteries as well, because limited global Li abundance may cause Li-ion batteries to become cost-prohibitive in the future. − Similarly, our focus from monopolyanionic material is shifting to mixed polyanionic materials. It was recently predicted from high-throughput computation that mixed polyanionic compounds of transition metals could be attractive cathode materials for Li-ion batteries, both in terms of average voltage and specific capacity .…”

Sustainable Production of Reduced Phosphorus Compounds: Mechanochemical Hydride Phosphorylation Using Condensed Phosphates as a Route to Phosphite

“…Phosphorous acid (H 3 PO 3 ) and its conjugate base, phosphite (HPO 3 2– ), have found applications as reducing agents, as cathode materials for lithium- and sodium-ion batteries, 1 − 3 as well as the starting material for other commercially important reduced phosphorus compounds, such as glyphosate. 4 Phosphite and related H -phosphonate esters are a family of key intermediates to organophosphorus compounds via elaboration of the P–H function into P–C bonds.…”

“…Phosphorous acid (H 3 PO 3 ) and its conjugate base, phosphite (HPO 3 2– ), have found applications as reducing agents, as cathode materials for lithium- and sodium-ion batteries, − as well as the starting material for other commercially important reduced phosphorus compounds, such as glyphosate . Phosphite and related H -phosphonate esters are a family of key intermediates to organophosphorus compounds via elaboration of the P–H function into P–C bonds. − Recent advances in biotechnology have also cleared out a path for phosphite to act as an environmentally friendly herbicide, biostimulant, and biocide in modern agriculture owing to its minimal toxicity to humans and animals, biodegradability in soil, and inability to trigger eutrophication of natural water bodies through agricultural runoff .…”