Structure and properties analysis of yttrium doped high-voltage LiNi0.5Mn1.5O4 cathode materials for Li-ion batteries

High voltage cathode spinel material of LiNi_0.5Mn_1.5O₄ was doped by yttrium (Y) element in the form of LiNi_0.5Mn_1.5−x Y _x O₄ (x = 0, 0.05, 0.1) for Li-ion batteries. Structure and properties analysis was conducted to study the effect of Y addition on the crystal structure and the electrochemical performances of LiNi_0.5Mn_1.5−x Y _x O₄. The results show that undoped LiNi_0.5-Mn_1.5O₄ (x = 0) fit to cubic spinel structure with space group Fd-3m with some Li_xNi_1-xO detected as impurities. The addition of Y with x = 0.05 and 0.1 resulted in the change of LiNi_0.5Mn_1.5−x Y _x O₄ structure to space group P4 ₃32. The Y addition was confirmed to enter 4b site co-existed with Mn and this result is closely related to the increase in lattice parameters a from 8.1384(1) Å to 8.1496(5) Å and 8.1627(1) for x = 0, 0.05 and 0.1, respectively. The cubic unit volume of LiNi_0.5Mn_1.5−x Y _x O₄ also increased with increasing Y addition. The addition of Y is liable to the formation of more stable [Mn,Y]O₆ and MnO₆ octahedra and whole crystal structure. The result from charge/discharge analysis shows that the addition of Y resulted in decreasing discharge capacity from 123.56 mAh g⁻¹ to 105.175 mAh g⁻¹ and 104.369 for x = 0.05 and 0.1, respectively. However, capacity retention after the 25th cycle increased constantly from 77% to 88% and 92% with increasing Y addition. Doped Y, in general, improves the electrochemical performance of LiNi_0.5Mn_1.5−x Y _x O₄ as cathode material for LIBs.