The Role of Sodium in LiNi_0.8Co_0.15Al_0.05O₂ Cathode Material and Its Electrochemical Behaviors

Abstract

Sodium is first introduced to modify Ni-rich LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode material in this work, and Li 1– x Na x Ni 0.8 Co 0.15 Al 0.05 O 2 ( x = 0, 0.01, 0.02, 0.05) is successfully synthesized by using Na 2 CO 3 as sodium resource through coprecipitation and solid state calcination route. The morphology of the samples analyzed with SEM, EDS. and TEM show that all the samples maintain sphere-like morphology and the main elements are uniformly distributed. X-ray diffraction (XRD) results show that all the synthesized materials have typical hexagonal structure without impurities. The lattice parameters calculated from the XRD data are also refined by Rietveld refinement methods, confirming that the position of Na in the NCA is occupying the Li slab as designed. Despite a slight decrease in the initial discharge capacities, the sodium doped materials display improved capacity retention as well as superior performance at high rates. The Li 0.99 Na 0.01 Ni 0.8 Co 0.15 Al 0.05 O 2 exhibits an initial discharge specific capacity of 184.6 mAh g –1 at 0.1 C and a capacity retention of 90.71% after 200 cycles when cycled at 1 C between 2.8 and 4.3 V, which is greatly superior to the pristine one, owing to the enlarged Li layer spacing, decreased Li + migration activation energy, the low cation mixing, and enhanced structural stability brought by sodium treatment.