Chunbao Xu B.E. Chemical Engineering 1996 Beijing University of Chemical Technology, Beijing, China M.S. Chemical Engineering 2001 Tsinghua University, Beijing, China chunbao.xu@chbe.gatech.edu

Projects:

1. Continuous Hydrothermal Synthesis of Nanostructured LiFePO4 and its Electrochemical Performance

Currently, LiCoO₂ is the most widely used cathode material in Li-ion rechargeable batteries. However, it is relatively expensive and toxic. Many efforts have therefore been devoted to finding a cheap, effective replacement for LiCoO₂. Among the materials under development, LiFePO₄ appears to be particularly promising because it can be synthesized from low cost starting materials, it is relatively non-toxic, and it has an intermediate voltage value of 3.45 V, and a high theoretical capacity of 170 mAh/g. The main obstacle to reaching its theoretical performance at ambient temperatures is the poor ionic conductance of both LiFePO₄ and its delithiated phase FePO₄. In addition, lithium ions are also slow to diffuse across the two phase boundary. To address these issues, synthesis techniques are being investigated to minimize particle size without compromising purity, and to incorporate additives.

LiFePO₄ is generally prepared via a solid-state synthesis. However, this process is costly and very time consuming. Furthermore, solid-state synthesis leads to LiFePO₄ particles of large average size, typically more than 30 μm, which is deleterious to its electrochemical performance. Therefore, investigations of alternative synthetic processes have received much attention. Low temperature solution methods are especially interesting, since they provide intimate mixing of the components in the solution allowing finer particles and high-purity materials to be produced by rapid homogeneous nucleation. Methods that employ near- and super- critical fluids as solvents afford a convenient means for control of solvent properties via adjustments in temperature or pressure. In this project, a novel continuous hydrothermal technique, which offers the advantages of short residence time, control over product size and morphology, and ease of scale-up, is being used to produce nanostructured LiFePO₄ with enhanced electrochemical performance. Literature results have clearly indicated that a proper morphology and a suitable particle size & size distribution of LiFePO₄ are critically important to assure its performance as an effective cathode in lithium cells. By carefully controlling the synthesis parameters, particle size and morphology are being optimized. The synthesized materials are being formulated into electrodes and tested in lithium-ion battery systems.

2. Continuous Hydrothermal Synthesis of Polymer-Coated Magnetic Metal Oxide Nanoparticles

Magnetic nanoparticles are of current interest because of the novel physical properties of nanoscale magnetic systems, and because of their potential applications in high density information storage, magnetic refrigeration, targeted drug delivery, and sensor technology. In this project, a continuous hydrothermal process is being used for the synthesis of metal oxide nanoparticles with a polymer coating. In particular, cobalt ferrite, CoFe₂O₄, which is a well-known hard magnetic material with very high cubic magnetocrystalline anisotropy, high coercivity, and moderate saturation magnetization, has been chosen as a model oxide in this study.

Publications: