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The Role of Fe(IV)-O Anion Redox Centers in the Electrochemical Behavior of Al- and Ga-Doped T-LiFeO2

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide The high natural abundance and low toxicity of iron oxides provide a strong motivation to develop iron-based lithium-ion battery cathode materials. T-LiFeO 2 adopts a cation-ordered wurtzite structure consisting of apex-linked LiO 4 and FeO 4 tetrahedra. Chemical or electrochemical lithium extraction rapidly converts T-LiFeO 2 to the spinel LiFe 5 O 8 and leads to poor energy storage performance. We have investigated the role of Al and Ga substitution on the stability of T-LiFeO 2 . Partial substitution of Fe by Al leads to the formation of cation-disordered solid solutions. In contrast, neutron diffraction data reveal that the Ga-substituted phase LiFe 0.5 Ga 0.5 O 2 adopts an Fe/Ga cation-ordered structure. Chemical delithiation of LiFe 1– x M x O 2 phases reveals that 25% Al or 50% Ga substitution stabilizes the T-LiFe 1– x M x O 2 phases with respect to spinel conversion. The delithiated phases show no evidence of cation migration or oxygen loss. However, Fe-XANES, O-XAS, and O-RIXS data indicate that lithium extraction does not proceed via simple oxidation of Fe 3+ to Fe 4+ but rather via an anion redox process involving the formation of localized “Fe IV –O” centers. Electrochemical data indicate that the formation of Fe IV –O centers is irreversible, and so these oxidized species accumulate with continued electrochemical cycling, leading to a rapid decline in energy storage capacity. The electrochemical behavior of LiFe 0.5 Al 0.5 O 2 and LiFe 0.5 Ga 0.5 O 2 is discussed in terms of their crystal chemistry to account for the differing electrochemical performance of the Al- and Ga-substituted materials.

Source: Chemistry of Materials

DOI: 10.1021/acs.chemmater.4c03322