Synergistic effect of interlayered doping and surface modification to improve the performance of Li-rich manganese-based cathode materials

Li-rich manganese-based oxides (LRMOs) with high energy density have been intensively studied, but their practical use as cathode materials for lithium-ion batteries is still impeded by the shortcomings such as low initial coulombic efficiency, voltage decay and poor rate capability. To address these issues, element Nb is selected to bulk dope and simultaneously surface modify the hierarchical Li1.20Mn0.54Co0.13Ni0.13O2 spheres in this work. Synergistic effect of Nb doping and surface modification on the crystalline structure and electrochemical performance of the resultant LRMOs is characterized in detail. The results suggest that Nb5+ ions are doped into the interlayer sites within the crystals while the LiMn2O4 and LiNb3O8 double layers are coated on the primary nanoparticles. The galvanostatic charge-discharge measurements reveal that the optimal LRMO-Nb2 sample can deliver the capacities of 286 and 167 mAh g−1 at the rates of 0.1 C and 5 C, respectively, and retains a capacity of 191 mAh g−1 at 1 C rate after 200 cycles. Ex-situ XRD patterns prove that the layered structure is strongly pillared by the interlayer-doped Nb5+ during the delithiation/lithiation processes. Especially, some lithium vacancies formed around Nb5+ ions can accelerate the diffusion of Li+ ions, which was proved by DFT calculations and experimental results. Our research demonstrates that cooperating of the interlayered doping of Nb5+ with surface coating of LiNb3O8 layer can improve rate capability and cyclability of the resultant LRMOs significantly.