Cu-substituted Na0.44Mn0.6Ni0.3Cu0.1O2 has been successfully synthesized via a sol-gel method. The effect of Cu-substitution in structure on electrochemical performance, structure and morphology, Na ion diffusion coefficient and battery internal resistance has been studied. Electrochemical testing shows the substitution of Cu has obviously improved the cycle performance of Na0.44Mn0.6Ni0.3Cu0.1O2 electrode. Rietveld refinement results confirm that the introduction of copper retains the P2-type structure and enlarges lattice parameters. The kinetic analysis reveals that Cu-substitution electrode exhibits higher Na+ diffusion coefficients and smaller cell internal resistance as compared to the pristine sample due to the larger atomic radius of Cu2+. In summary, the substitution of copper has a significant effect on increasing the cell and enhancing the migration of sodium ions.