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A Streamlined Route to Synthesize LiFePO4/C in an Unrestricted Environment


In this dissertation, a practical and streamlined route for the synthesis of carbonized lithium iron phosphate (LiFePO4, LFP) is developed via a solid state-based lithiation process performed under an unrestricted environment. Extensive characterization and analysis are performed to study the reaction mechanism, crystallinity of synthesized product, oxidation protection during synthesis reaction, carbonization of LFP, and synthesis scale-up.

The main motivation of this work is to achieve good quality carbonized LFP product, by minimizing the oxidation of LFP during synthesis, while combining the synthesis and carbonization of LFP into a single step process. Chapter 1 introduces the background of Li-ion battery, commercialized cathode materials, and the approaches developed for LFP synthesis. In Chapter 2, well-crystallized LFP is synthesized via a solid state-based lithiation process using lithium acetate (C2H3LiO2) and iron phosphate (FePO4) as starting materials. Two key findings are identified for achieving good crystalline LFP in an unrestricted environment synthesis: 1) using quartz FePO4 (rather than amorphous FePO4) thermodynamically activates and accelerates the LFP synthesis reaction; and, 2) C2H3LiO2 in liquid state accelerates the lithiation process by increasing the uniformity of mixing and contact surface area between particles during lithiation. Compared to conventional solid state synthesis, the required synthesis time is significantly reduced from several hours down to 30 minutes. In Chapter 3, a carbon source (i.e. gelatin) is added as a sacrificial material to help inhibit the oxidation of LFP by 1) reacting and consuming part of the oxygen in the environment; and, 2) acting as a reducing agent for oxidized LFP. The thermal decomposition process of the carbon source, starting at the low temperature range, is investigated to understand its critical role in inhibiting LFP oxidation during reaction. Highly crystalline LFP is successfully synthesized by oxidation protection. In Chapter 4, an auto pressure release method for scaling-up and streamlined synthesis process is developed to auto-release the increased inner pressure caused by the gaseous byproducts during LFP synthesis. To further improve the quality of LFP, water is used as a sacrificial material to deoxygenate the reaction system and protect LFP from oxidation. The step-by-step development of a streamlined synthesis process for carbonized LFP with good quality is successfully achieved. In Chapter 5, the developmental evolution of this approach and the resolved issues through this dissertation are summarized and discussed.

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