Er-Doped LiNi_0.5Mn_1.5O₄ Cathode Material with Enhanced Cycling Stability for Lithium-Ion Batteries

The Er-doped LiNi_0.5Mn_1.5O₄ (LiNi_0.495Mn_1.495Er_0.01O₄) sample was successfully prepared by citric acid-assisted sol-gel method with erbium oxide as an erbium source for the first time. Compared with the undoped sample, the Er-doped LiNi_0.5Mn_1.5O₄ sample maintained the basic spinel structure, suggesting that the substitution of Er³⁺ ions for partial nickel and manganese ions did not change the intrinsic structure of LiNi_0.5Mn_1.5O₄. Moreover, the Er-doped LiNi_0.5Mn_1.5O₄ sample showed better size distribution and regular octahedral morphology. Electrochemical measurements indicated that the Er-doping could have a positive impact on the electrochemical properties. When cycled at 0.5 C, the Er-doped LiNi_0.5Mn_1.5O₄ sample exhibited an initial discharge capacity of 120.6 mAh·g^-1, and the capacity retention of this sample reached up to 92.9% after 100 cycles. As the charge/discharge rate restored from 2.0 C to 0.2 C, the discharge capacity of this sample still exhibited 123.7 mAh·g^-1 with excellent recovery rate. Since the bonding energy of Er-O (615 kJ·mol^-1) was higher than that of Mn-O (402 kJ·mol ^-1) and Ni-O (392 kJ·mol^-1), these outstanding performance could be attributed to the increased structure stability as well as the reduced aggregation behavior and small charge transfer resistance of the Er-doped LiNi_0.5Mn_1.5O₄.