Correlating Local Structure and Electrochemical Performance in Metal-Substituted Vanadium Ferrite Aerogel Electrodes for Lithium-Ion Batteries

Abstract

Disordered vanadium ferrite (VFe2Ox) materials exhibit promising performance for electrochemical energy-storage applications such as rechargeable lithium-ion batteries.1,2 We employ an epoxide-promoted sol–gel reaction of iron chloride and vanadium isopropoxide to form nanostructured vanadium ferrite gels. Subsequent supercritical-CO2 extraction of the pore fluid yields high surface–area aerogels. Heat treatment under either O2-containing or inert atmosphere yields disordered or nanocrystalline variants, respectively. Electroinactive metal cations such as aluminum, zinc, and zirconium are substituted during the initial sol–gel synthesis to alter the local electronic environment of VFe2Ox. The resulting series of native and substituted VFe2Ox materials are evaluated as powder-composite cathodes versus lithium metal in coin cells with conventional nonaqueous lithium-ion electrolyte. We correlate such critical battery-performance parameters as total specific capacity, high-rate capability, and cycle life as a function of MVFe2Ox composition and its degree of structural order/disorder. In-lab X-ray absorption spectroscopy also provides important information on metal oxidation state and element-specific coordination for these VFe2Ox aerogels, including during operando electrochemical lithiation/delithiation. In parallel with experimental advancements, calculations on VFe2Ox reveal that V incorporation into the defect-induced spinel structure occurs at tetrahedral sites. Further, both disorder of vacancies and Fe/V tetrahedral occupation lower the overall energy, opening an electronic energy gap that establishes the redox sequence during lithiation. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3, 12059 (2015). C. N. Chervin, R.H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11, 14495 (2021).