Synergism of Cu and Al co-doping on improvements of structural integrity and electrochemical performance for LiNi0.5Mn1.5O4

Abstract Cu and Al co-doped LiNi0.5-xCuxMn1.49Al0.01O4 (x = 0.01, 0.03, 0.05) cathode materials, are synthesized by the alcohol-colloidal method combined with high temperature calcination. The effect of Cu and Al doping on LiNi0.5Mn1.5O4 and their optimum content is investigated. Structural analyses indicate that co-doped LiNi0.5Mn1.5O4 materials remain spinel structure with an octahedral morphology, Fd-3m space group. Furthermore, Cu and Al doping enhances the degree of cation disorder. The most highlight result is that LiNi0.47Cu0.03Mn1.49Al0.01O4 has the optimal both rate and cycling performances. The capacity retention of LiNi0.47Cu0.03Mn1.49Al0.01O4 remains 96.55% after 100 cycles at 0.25 C and its specific capacities maintains up to 103.4 mAh g−1 even at 5 C. The excellent electrochemical properties can be attributed to the synergistic effect of Cu and Al. Al enriched on the surface serves as a protective layer to suppress side reactions and compensate the adverse effect of more Mn3+, enhancing thermodynamic stability. Simultaneously, Cu in the bulk offers larger diffusion tunnel, accelerating transition kinetics of Li+. Co-doping of metal ions with different valence is a prospective approach to promoting properties of 5 V LiNi0.5Mn1.5O4 cathode materials.