Screening LiMn2O4 Surface Modification Schemes under Theoretical Guidance

Mn dissolution is one of the most important factors for the failure of LiMn2O4 batteries. Doping has been widely adopted in the modification of LiMn2O4 cathodes; however, there is still a lack of theoretical guidance on screening the dopants. Here, through first-principles calculations, we systematically investigated the effects of all 3, 4d transition metals as well as Mg, Ca, Sr, Al, Ga, and In on the surface oxygen stability of LiMn2O4 cathodes, which has been proved to be correlated with the stability of the surface Mn atoms. Six competitive dopants, namely Nb, Ru, Mo, V, Tc, and Ti, were screened out. Besides, for three dopants in low valence states (Mg, Cu, and Zn), their Li-site doping can more effectively stabilize the surface oxygen atoms compared with Mn-site doping. Finally, we synthesized LiMn2O4 samples with Mg, Mo, and Nb surface doping to validate the rationality of the computational results. We found that particle morphology should also be considered in addition to surface oxygen stability for controlling Mn dissolution. Moreover, the electrochemical performance of LiMn2O4 batteries is a more complex issue and cannot be solely regulated by Mn dissolution. During the experiments, we have explored novel efficient binary chromogenic reagents for ultraviolet-visible spectroscopy analysis that can be used for rapid and low-cost Mn dissolution detection. This work provides a paradigm for the systematic design of the surface modification of the LiMn2O4 cathode under theoretical guidance.