Date

2022-9-01

Author

Yıldırım, Mustafa Alp

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The nickel-rich lithium nickel manganese cobalt oxide (NMC) cathode materials are the driving force of Lithium-ion batteries. Despite the high capacity and high energy they offer, their structural stability needs to be improved. The production method and element doping are among prominent research topics in the studies to increase the structural stability of the Ni-rich NMC materials. In this study, Ni-rich LiNixMnyCozO2 (x>0.6) and Ni-rich Li(NMC)1-vNbvO2 (v=0.2, 0.4, 0.8) were produced using the citric acid assisted Pechini sol-gel method. The physical and chemical properties of pure and niobium doped materials with different nickel, manganese, and cobalt ratios were examined and compared. Discharge capacities, discharge energies, and discharge capacity retentions of all materials at 0.1 C were examined, and impedance changes before and after the cycles were compared. Also, the rate capability tests of the materials at 0.3 C and 1 C were examined. In XRD analysis, it was seen that LiNixMnyCozO2 (x>0.6) samples were produced successfully. In XRD analyzes of Li(NMC)1-vNbvO2 (v=0.2, 0.4, 0.8) samples, it was understood that Li3NbO4 phase was formed as a secondary phase besides the LiNixMnyCozO2 phase. In the capacity tests performed at 0.1 C during the electrochemical performance test process, the first discharge capacities increased as the nickel content in the material increased. At the end of 20 cycles, the capacity retention decreased as the nickel content in the structure increased. It was observed that the initial discharge capacities of the niobium doped materials were lower than those of the undoped ones. After 20 cycles at 0.1 C, the capacity retentions of the doped ones were higher than the undoped ones. In the tests carried out at 0.3 C, the niobium doped and undoped materials showed similarity with the tests carried out at 0.1 C. In the capacity tests carried out at 1 C, there was no difference between the capacity retentions of the undoped materials and the capacity retentions of the niobium doped materials. However, in the cycle tests performed at 1 C, the materials showed higher capacity retention as the nickel ratio in the structure increased.

Subject Keywords

Lithium-ion battery, Nickel rich NMC, Niobium doped, Sol-gel method, Cathode active material

URI

https://hdl.handle.net/11511/98765

Collections

Graduate School of Natural and Applied Sciences, Thesis