Date

2022-8-22

Author

Coşkun, Elif

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Despite their widespread use in energy storage, high cost and safety are two major concerns for lithium-ion batteries (LIBs). The lack of safe, scalable, robust, and energy-efficient methods enabling high yield synthesis is one of the main reasons for the high cost of electroactive materials. This need has driven an interest in polyol synthesis technique due to simplicity and scalability. As applied in the synthesis of LiFePO4 (LFP) nanoparticles, polyol methods have generally been performed at high temperatures. In this study, a scalable, safe, highly efficient, low temperature polyol process was developed to synthesize hierarchical, dispersible LFP nanoparticles. Unlike previous examples where high chain polyols were common solvents of choice, the use of higher polarity and lower boiling point ethylene glycol was proposed. The relationship between the amount of water in the reaction medium, the boiling point of the polyol and the solubility of the reagents used was revealed. LFP crystallization was observed at temperatures as low as 170 °C and 97% yield was attained after 9 hours of reaction at this temperature. The morphology and size of the LFP particles are critical to enable fast diffusion of lithium ion in structure, to achieve high volumetric energy density and to eliminate the potential processing problems during electrode fabrication. In electroactive particles, while the nano-size offers faster reaction kinetics compared to larger sizes, it increases the suspension viscosity, limits the tap density, and thus decreases the volumetric energy density. The synthesis of hierarchical particles having united structure constructed from nano-units, has recently gained attention. Designing dispersible hierarchical structures leading to low suspension viscosity, high electrochemical behavior and tap density is essential. In this thesis, citric acid and ascorbic acid were used to design hierarchical sub-micrometer sized LFP particles with nano-size primary units via polyol method. The electrochemical behavior, dispersibility, tap density and suspension viscosity of the synthesized powders were investigated. Using hierarchical LFP particles leads to significantly low suspension viscosities and remarkable increase in the tap density compared to its nanosized counterparts reported in literature.

Subject Keywords

Lithium iron phosphate, Scalable synthesis of electroactive particles, Polyol method, Hierarchical particles, Suspension rheology

URI

https://hdl.handle.net/11511/99603

Collections

Graduate School of Natural and Applied Sciences, Thesis