Electrochemical properties of niobium and phosphate doped spherical Li-rich spinel LiMn2O4 synthesized by ion implantation method

Spherical Li-rich lithium manganese oxide (LMO) spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously. The material was characterized by scanning electron microscopy, X-ray diffraction and BET specific surface area analysis. The electrochemical performances were investigated with galvanostatic techniques and cyclic voltammetry. The synthesis process was investigated with TG/DSC. The results show that the lithium ion can be immersed into the pore of manganese dioxide at a low temperature with the ion implanted method. The prepared materials have a higher discharge capacity and better crystallization than those prepared by solid phase method. The doped Nb can improve the capacity of the Li-rich LMO spinel and reinforce the crystal growth along (111) and (400) planes. The crystal grains show circular and smooth morphology, which makes the specific surface area greatly decreased. Phosphate-doped LMO spinel exhibits good high-rate capacity and structure stability. The prepared Li_1.09Mn_1.87Nb_0.031O_3.99(PO₄)_0.021 delivers a discharge capacity of 119 mAh g^-1 at 0.2 C (1 C=148 mA g^-1) and 112.8 mAh g^-1 at 10 C, the discharge capacity retention reaches 98% at 1 ℃ after 50 cycles at 25 ℃ and 94% at 55 ℃.