A highly crystalline nanosized spinel LiMn₂O₄/3DG composite cathode material for high rate lithium ion batteries was successfully prepared by mixing spinel LiMn₂O₄ particles with reduced graphene oxide (3DG). Spinel LiMn₂O₄ and reduced three-dimensional graphene oxide were synthesized using a hydrothermal method and freeze-drying technology, respectively. The structure, morphology and electrochemical performance of the synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge techniques. The results showed that the LiMn₂O₄/3DG composites exhibited excellent rate capability and stable cycling performance. The discharge capacity was 131 mA h g⁻¹ and the capacity remains at 89.3% after 100 cycles at a 0.5 C rate, while the discharge capacity was 90 mA h g⁻¹ at 10 C. Compared with spinel LiMn₂O₄ materials, the LiMn₂O₄/3DG composites showed obvious improvement in electrochemical performance.