Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO2 particles (O3-LiFeO2) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO2 precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO2. 40-nm LiFeO2 exhibited a higher discharge capacity (115 mAh g−1) than 400-nm LiFeO2 (80 mAh g−1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO2 particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO2 to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe2+/Fe3+ and Fe2+/Fe0 redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO2 were ca. 115, 210, and 390 mAh g−1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.

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► 40-nm-sized O3-LiFeO2 exhibits higher discharge capacities and rate characteristics than 400-nm-sized O3-LiFeO2.
► The cation disorder of Li and Fe ions might have affected the electrochemical activity of the O3-LiFeO2 nanoparticles.
► A phase change from a layered structure to a cubic structure during electrochemical cycling.
► The new cubic phase allowed a stable electrochemical reaction between 4.5 and 1.0 V.