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Tianpeng GAO

Doctor Candidate in Chemical and Biomolecular Engineering

Supervisor: Prof. Ka Ming NG

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Research Topic

LiNixMnyCo1-x-yO2 based cathode material for Li-ion battery

Abstract

LiNixMnyCo1-x-yO2 (NMC) cathode material of Li-ion battery is widely used because of its high specific capacity and superior safety. The widely method to synthesize NMC is first make NixMnyCo1-x-y(OH)2 precursor, then mix the precursor with lithium salts uniformly, finally sinter at certain temperature and duration to obtain final NMC. In my research, three lithium salts, Li2CO3, LiNO3, and LiOH, and Ni0.5Mn0.3Co0.2(OH)2 are used to synthesize NMC cathode material. The corresponding sintering profiles differ using different lithium salts.
It concludes that:
a) when using Li2CO3, the calcination profile with first preheating at 500℃-550℃ for 5h, further heating at 650℃-720℃ for 5h, and finally sintering at 900℃ for 12h could make NMC cathode material with a hexagonal layered structure;
b) when using LiNO3, the calcination profile with first preheating at 265℃-300℃ for 5h, further heating at 550℃-620℃ for 5h, and finally sintering at 900℃ for 12h could make NMC cathode material with a good crystallinity;
c) when using LiOH, the calcination profile with first preheating at 450℃-500℃ for 5h, further heating at 650℃-710℃ for 5h, and finally sintering at 900℃ for 12h could make NMC cathode material with a hexagonal layered structure.
The possible reasons are that:
a) First preheating at lithium salt’s melting point could infiltrate lithium salt into Ni0.5Mn0.3Co0.2(OH)2 precursor, which shortens the diffusion distance between lithium salt and Ni0.5Mn0.3Co0.2(OH)2 precursor.
b) Second heating at reaction temperature to form LiNi0.5Mn0.3Co0.2O2. Because of different bond energy of Li-CO3, Li-NO3, and Li-OH, the reaction temperatures are different. At the second step, LiNi0.5Mn0.3Co0.2O2 are formed, but without a layered hexagonal structure.
c) For finally calcining at 900℃, it’s believed that a layered hexagonal structure is achieved after heating at 900℃. So the third step is also called a crystallization process.
In-situ XRD of calcining lithium salt and Ni0.5Mn0.3Co0.2(OH)2 precursor with the same calcination profile under air atmosphere is a good method to study how crystal structure changes during calcination. Although the in-situ XRD I have tested were under vacuum atmosphere, it clearly showed how crystal structure changes during calcination both when using Li2CO3/Ni0.5Mn0.3Co0.2(OH)2 and LiNO3/Ni0.5Mn0.3Co0.2(OH)2 . Further test at air atmosphere will be performed.