LiNi0.5Mn1.5O4−x F x (0≤ x ≤0.1) cathodes, synthesized by ultrasonic spray pyrolysis at 900°C, exhibit superior structural and electrochemical properties. The samples are characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and electrochemical measurements. During Li+ extraction, LiNi0.5Mn1.5O4−x F x has a smaller lattice variation and area-specific impedance than LiNi0.5Mn1.5O4. This enhances the rate capability, especially at high C-rates. LiNi0.5Mn1.5O4−x F x also exhibits better resistance than LiNi0.5Mn1.5O4 to attack by HF.