Aerosol Synthesis Of Cathode Materials For Li-Ion Batteries (2011)

Rapid advancement of technologies for production of next-generation Li-ion batteries will be critical to address the Nation's need for clean, efficient and secure transportation system and renewable energy storage system. Advancements in materials are believed to be essential to meet the growing demand of high-performance materials for Li-ion batteries, as well as to bring down the battery cost: material cost) to a reasonable level. In the past decade, the primary focus in the Li-ion battery research has been to develop new materials, which are essential to improve the performance of the electrodes in terms of energy density, power density and cycle life. However, no single material has satisfied all the necessary criteria because there is a trade-off between energy and power in Li-ion batteries. Fortunately, by tailoring the nano-scale architectures, some of the "less robust" high-energy materials have yielded superior power density over their bulk materials, and these nanostructured materials have come to the forefront of the battery material research. A typical example is the Li-excess composite materials adopting nanostructured morphology. These materials can attain nearly twice the capacity of commercial LiCoO2. This high capacity has traditionally been a challenge to bulk composite materials, especially at elevated charge/discharge current density and at low temperature. Despite rapid advances in material development, to date, less attention has been placed on developing approaches to commercial scale production of materials with nano to micron features. Conventional processes such as solid-state reaction and wet-chemistry processes have notable challenges for large-scale material synthesis of nanostructured materials, including difficulty in controlling particle size, morphology and sometimes stoichiometry. They can also be energy-intensive, and have challenges associated with consistent production of uniform powders at scale-up. Motivated by the above, this work aims to develop new processes that are commercially viable for large-scale production of state-of-the-art battery materials. Aerosol synthesis is a standard industrial method for producing powders with controlled particle size. The materials producing in aerosol processes can have a variety of morphologies, from one-dimensional to three-dimensional structures. Spherical particles are desirable in the Li-ion battery industry because high packing density is required. In this research, spray pyrolysis and flame spray pyrolysis are successfully developed to produce high-quality, spherical cathode materials. These processes have many advantages over conventional processes including:: 1) the ability to consistently produce uniform porous spherical particles,: 2) low-cost,: 3) simplicity, and: 4) precise control over particle composition and crystal structure. This research will not only provide a basic understanding of the aerosol process for synthesizing nanostructured cathode materials, but also strategies for industry practice in aerosol processing of state-of-the-art battery materials. The dissertation includes the following achievements in developing an aerosol approach to synthesis of cathode materials. This work, for the first time, demonstrates the synthesis of spherical-shape spinel cathode powders using a hydrogen diffusion flame. A basic understanding of the relationship between flame temperature and structure, physical and chemical properties of the produced powder, and electrochemical system are provided. In particular, flame-made nanostructured 4 V LiMn2O4 and 5 V LiNi0.5Mn1.5O4 cathode materials have shown comparable performance to those from conventional processes. A spray pyrolysis was also developed to address the synthetic conditions for synthesizing the integrated layered-layered xLi2MnO3·(1-x)LiNi0.5Mn0.5O2 and layered-spinel Li(1.2-δ)Ni0.2Mn0.6O(2-δ/2) composite materials for high-energy Li-ion batteries. The composite materials obtained from spray pyrolysis shared some common morphological characteristics: spherical in shape, meso- to macro porous, polycrystalline, highly uniform inter- and intra-particles. In particular, the layered Li1.2Ni0.2Mn0.6O2: equivalent to 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2) material displayed the highest capacity: c.a. 250 mAhg-1) among all cathode materials ever made with spray pyrolysis. Furthermore, the nanostructured composite materials showed electrochemical performance comparable to, and in some aspect better than those materials produced via coprecipitation, the standard method of synthesis.