Electrochemical properties and kinetics of Li–Cu co-doping LiMn₂O₄ cathode materials

Li_1.05Cu_0.05Mn_1.90O₄ cathode materials were synthesized by liquid phase combustion method at different temperatures from 400 to 700 °C. All samples show good crystallinity and conform to the Fd3m space group of spinel LiMn₂O₄. The Li_1.05Cu_0.05Mn_1.90O₄ sample prepared at 600 °C has a sharp diffraction peak compared to the pristine LiMn₂O₄, while no impurities are detected. Both the Li–Cu co-doping and calcination temperature have effects on the morphology and particle size distribution. The electrochemical properties reveal that initial discharge capacity of the Li_1.05Cu_0.05Mn_1.90O₄ is 102.4 mAh g⁻¹ and pristine LiMn₂O₄ electrode is 105.3 mAh g⁻¹. After 1000 cycles, the capacity retention rate of the pristine LiMn₂O₄ (63.0%) has less than 74.3% of the Li_1.05Cu_0.05Mn_1.90O₄ sample. The lithium-ion diffusion coefficient indicates that the as-prepared Li_1.05Cu_0.05Mn_1.90O₄ electrode (1.58 × 10⁻¹⁰ cm² s⁻¹) at 600 °C displays better Li⁺ diffusion ability when compared with the pristine LiMn₂O₄ (8.06 × 10⁻¹¹ cm² s⁻¹). Simultaneously, the apparent activation energy further demonstrates that the Li_1.05Cu_0.05Mn_1.90O₄ (22.84 kJ/mol) electrode has lower polarization when compared with the LiMn₂O₄ (34.95 kJ/mol) electrode. These results show that synergistic effect of the Li⁺ and Cu²⁺ enhances the cycle reversibility and kinetics properties in cycle of the electrode.