K-doped layered LiNi0.5Co0.2Mn0.3O2 cathode material: towards the superior rate capability and cycling performance
K-doped LiNi0.5Co0.2Mn0.3O2 is successfully synthesized by introducing larger K ions into the Li slabs of the layered material through a substitution of Li source method. Structural and morphological characterizations reveal that the substitution of K ions on the Li site could enlarge the Li layer spacing and decrease the degree of Li+/Ni2+ cation mixing in the hexagonal layered LiNi0.5Co0.2Mn0.3O2. Compared with the LiNi0.5Co0.2Mn0.3O2, the K-doped Li0.97K0.03Ni0.5Co0.2Mn0.3O2 electrode material demonstrates larger reversible discharge capacity (176.5 mAh g−1), higher initial coulombic efficiency (88.45%), and greatly improved rate capability (123.4 mAh g−1, 5 C). The Li0.97K0.03Ni0.5Co0.2Mn0.3O2 electrode also exhibits excellent cycle stability with capacity retention of 93.17% and 86.42% in cell tests at 25 °C and 55 °C after 100 cycles at 1 C. The improved electrochemical performances of Li0.97K0.03Ni0.5Co0.2Mn0.3O2 are attributed to the enlarged interlayer space of O-Li-O, the decreased degree of cation mixing and enhanced structural stability induced by the potassium substitution.