T. Muraliganth

Nanostructured electrode materials for electrochemical energy storage and conversion

Nanostructured materials play an important role in advancing the electrochemical energy storage and conversion technologies such as lithium ion batteries and fuel cells, offering great promise to address the rapidly growing environmental concerns and the increasing global demand for energy. In this review, we summarize some of the recent progress and advances in our laboratory on nanostructured electrode materials for lithium ion batteries and platinum-based and platinum-free nanoalloy electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). Materials design, novel chemical synthesis and processing, advanced materials characterization, and electrochemical evaluation data are presented.

Dimensionally Modulated, Single-Crystalline LiMPO4 (M= Mn, Fe, Co, and Ni) with Nano-Thumblike Shapes for High-Power Energy Storage

We demonstrate an efficient and rapid microwave irradiated solvothermal method to prepare nanostructured lithium metal phosphates LiMPO(4) (M = Mn, Fe, Co, and Ni) within a short reaction time (5-15 min) at temperatures as low as 300 degrees C without requiring any post annealing at elevated temperatures. The highly viscous, high-boiling tetraethyleneglycol used as the solvent not only provides a reducing atmosphere to prevent the oxidation of M(2+) to M(3+) but also inhibits the agglomeration of the nanoparticles formed. The enhanced reaction rates facilitated by the dielectric volumetric heating of the microwave absorbing reactants led to the formation of highly crystalline, phase-pure LiMPO(4) powders. The samples are characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and electrochemical measurements in lithium cells. High-resolution TEM studies reveal the formation of single-crystalline LiMPO(4) with nano-thumblike shapes. The dimensionally modulated nano-thumblike shapes with the lithium diffusion direction (b axis) along the shorter dimension are particularly beneficial to achieve high-power capability in lithium ion cells. Subsequent networking of the single-crystalline LiMPO(4) nano-thumps with multiwalled carbon nanotubes by a simple solution-based mixing at ambient temperatures to overcome the electronic conductivity limitations offers excellent electrochemical performance in lithium ion cells.

Nanoscale networking of LiFePO4nanorods synthesized by a microwave-solvothermal route with carbon nanotubes for lithium ion batteries

LiFePO4nanorods with a controlled size have been synthesized by a rapid microwave-solvothermal method within 5 minutes at temperatures as low as 300 °C without requiring any post annealing in reducing gas atmospheres. Subsequently, the LiFePO4nanorods have been networked with electronically conducting multi-walled carbon nanotubes (MWCNT) at ambient -temperature to overcome the poor electronic conductivity limitation of LiFePO4. The samples have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman scattering, scanning electron microscopy, transmission electron microcopy, and electrochemical measurements in lithium cells. The aspect ratio of the LiFePO4nanorods has been varied by changing the reactant concentrations and reaction conditions. The LiFePO4-MWCNT nanocomposite offers enhanced discharge capacity (161 mAh/g) with excellent capacity retention and power capability compared to the pristine LiFePO4nanorods (146 mAh/g) due to the electronically conductive nanoscale networking provided by the carbon nanotubes. The synthesis and processing approach presented here offer a simple, cost effective method to obtain high performance LiFePO4.

Nanostructured Electrode Materials for Lithium-Ion Batteries

Electrochemical energy storage systems are becoming increasingly important with respect to their use in portable electronic devices, medical implant devices, hybrid electric and electric vehicles, and storage of solar and wind energies. Lithium-ion batteries are appealing for these needs because of their high energy density, wide range of operating temperatures, and long shelf and cycle life. However, further breakthroughs in electrode materials or improvements in existing electrode materials are critical to realize the full potential of the lithium-ion technology. Nanostructured materials present an attractive opportunity in this regard as they could offer several advantages such as fast reaction kinetics, high power density, good cycling stability with facile strain relaxation compared to their bulk counterparts. In this chapter, we present an overview of the latest progress on the nanostructured anode and cathode materials for lithium-ion batteries.