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Synthesis of a family of lithium iron double aryloxide precursors for production of LiFeO2 nanomaterials

Boyle, Timothy J.; Neville, Michael L.; Apblett, Christopher A.; Pratt, Sarah H.

Lithium iron double aryloxides ([Li2Fe(OAr)4]) were synthesized, characterized, and investigated for use as precursors to LiFeO 2 nanomaterials. From the reaction of iron mesityl, two equivalents of lithium bis(trimethylsilyl) amide, and a series of monosubstituted [HOC 6H4(R)-2 where R = CH3 (oMP), CH(CH 3)2 (oPP), C(CH3)3 (oBP)] or disubstituted [HOC6H3(R)2-2,6 where R = CH 3 (DMP), CH(CH3)2 (DIP), C(CH3) 3 (DBP), C6H5 (DPhP)] aryl alcohols (H-OAr) in tetrahydrofuran (THF) or pyridine (py) were isolated. The mixed-cation Li-Fe precursors that were successfully isolated from this reaction were crystallographically identified as the double aryloxides [Fe((μ-OAr) 2Li(solv)2)2] (OAr = oPP: solv = THF (1), py (2); DMP/THF (3)) and the unusual salt [Li(THF)4][Fe(DBP) 3] (4). For the other OAr/solvent systems investigated, previously published Li or Fe alkoxide compounds or oils were isolated. Compounds 1-4 were further characterized using a variety of analytical methods but the paramagnetic nature of the Fe prevented NMR analyses. The mixed-cation precursors were used for production of nanomaterials following a solvothermal route using dioxane (in place of THF) or pyridine as the solvent. The final materials generated were characterized as the substituted lithium iron oxide structure (LiFeO 2; PDF 01-073-6306). Attempts to cycle the Li in these materials failed to demonstrate appreciable mobile capacity at reasonable potentials; however, a capacity of 87 mAh/g that quickly faded during cycling was observed at very low potentials (start: ∼0.6 V; end: 0.5 V versus Li). © 2013 Elsevier Ltd. All rights reserved.