Mkhitar Hobosyan

Low-cost carbon-silicon nanocomposite anodes for lithium ion batteries

The specific energy of the existing lithium ion battery cells is limited because intercalation electrodes made of activated carbon (AC) materials have limited lithium ion storage capacities. Carbon nanotubes, graphene, and carbon nanofibers are the most sought alternatives to replace AC materials but their synthesis cost makes them highly prohibitive. Silicon has recently emerged as a strong candidate to replace existing graphite anodes due to its inherently large specific capacity and low working potential. However, pure silicon electrodes have shown poor mechanical integrity due to the dramatic expansion of the material during battery operation. This results in high irreversible capacity and short cycle life. We report on the synthesis and use of carbon and hybrid carbon-silicon nanostructures made by a simplified thermo-mechanical milling process to produce low-cost high-energy lithium ion battery anodes. Our work is based on an abundant, cost-effective, and easy-to-launch source of carbon soot having amorphous nature in combination with scrap silicon with crystalline nature. The carbon soot is transformed in situ into graphene and graphitic carbon during mechanical milling leading to superior elastic properties. Micro-Raman mapping shows a well-dispersed microstructure for both carbon and silicon. The fabricated composites are used for battery anodes, and the results are compared with commercial anodes from MTI Corporation. The anodes are integrated in batteries and tested; the results are compared to those seen in commercial batteries. For quick laboratory assessment, all electrochemical cells were fabricated under available environment conditions and they were tested at room temperature. Initial electrochemical analysis results on specific capacity, efficiency, and cyclability in comparison to currently available AC counterpart are promising to advance cost-effective commercial lithium ion battery technology. The electrochemical performance observed for carbon soot material is very interesting given the fact that its production cost is away cheaper than activated carbon. The cost of activated carbon is about

Enabling nanoenergetic materials with integrated microelectronics and MEMS platforms

15/kg whereas the cost to manufacture carbon soot as a by-product from large-scale milling of abundant graphite is about

MEMS microthrusters with nanoenergetic solid propellants

1/kg. Additionally, here, we propose a method that is environmentally friendly with strong potential for industrialization.

Solution-combustion synthesis and magnetodielectric properties of nanostructured rare earth ferrites

This paper reports our findings in novel enabling high-energy-density nanostructured materials for micro-propulsion and other applications. In order to ensure the overall functionality, the system-level solution is achieved by integrating of synthesized nanoenergetic materials using microelectromechanical systems (MEMS). The MEMS solution provides high performance and enabling systems capabilities, while nanoenergetic materials guarantee safety, high stored energy capacity, high specific energy, stability, high energy and gas release rates, complete burning, etc. The system-level design and integration of self-assembled nanoenergetic materials by using MEMS imply development of NanoEnergetic MEMS Platforms. These systems have a wide range of applications, such as various explosives, propulsion systems, etc. The proposed nanoenergetic materials improve the overall power and energetic capabilities due to: 1. High stored energy, which reaches up to 25.7 kJ/cm3; 2. Ability to vary and refine properties of devised materials by adjusting molecular structure, enthalpy, stoichiometry, porosity and density; 3. Stability, compatibility, robust packaging and safety. Our studies indicate that the synthesized Al/Bi2O3 and Al/I2O5 nanocomposites ensure energy release and generate transient pressure impulses which are three times higher than traditional nano-thermite reactive mixtures. We address and provide systems-level design solutions solving integration, packaging, diagnostics, control and other problems

Electrochemical features of combustion-synthesized lithium cobaltate as cathode material for lithium ion battery

Solid propellants are used in various flight and underwater systems as well as in propulsion platforms. Micromachining, microelectromechanical systems (MEMS) and automatic dispensing of high-energy-density nanoenergetic materials are examined for current and next generation of application-specific flight and underwater platforms. The integrated MEMS-technology microthrusters with the optimized-by-design nanostructured propellants ensure the expected thrust-to-weight and thrust-to-power ratios, specific impulse, effective exhaust velocity, thrust, energy density, controlled combustion, etc. The flight-proven propulsion and micromachining technologies are suitable in a wide range of applications, such as payload delivery, stabilization, guidance, navigation, etc. Compared with mono- and bi-propellant, ion, laser, plasma, Hall-effect and other thrusters, our solution ensures fabrication simplicity, affordability, robustness, integration, compatibility, safety, etc. The experimental substantiation, evaluation and characterization of fabricated proof-of-concept devices with nanoenergetic propellants are reported.

Carbon combustion synthesis of lithium cobaltate

Rare earth ferrites exhibit remarkable magnetodielectric properties that are sensitive to the crystallite size. There is a major challenge to produce these materials in nanoscale due to particles conglomeration during the ferrite nucleation and synthesis. In this paper we report the fabrication of nanostructured particles of rare earth ferrites in the Me-Fe-O system (Me = Y, La, Ce, and Sm) by Solution-Combustion Synthesis (SCS). The yttrium, lanthanum, cerium, samarium and iron nitrates were used as metal precursors and glycine as a fuel. Thermodynamic calculations of Y(NO3)3-2Fe(NO3)3−nC2H5NO2 systems producing Y3Fe5O12 predicted an adiabatic temperature of 2250 K with generating carbon dioxide, nitrogen and water vapor. The considerable gas evolution helps to produce the synthesized powders friable and loosely agglomerated. Adjusting the glycine/metal nitrates ratio can selectively control the crystallite size and magnetodielectric properties of the ferrites. Increasing the glycine content increased the reaction temperature during the SCS and consequently the particle size. Magnetization of zero-field-cooled (ZFC) and field-cooled (FC) ferrites in the temperature range of 1.9–300 K showed different patterns when the fraction of glycine was increased. Analysis of ZFC and FC magnetization curves of annealed samples confirmed that nanoparticles exhibit superparamagnetic behavior. The increasing concentration of glycine leads to escalation of blocking temperature. Reduction of dielectric permittivity (ɛr) toward frequency indicates the relaxation processes in the composites, and the values of ɛr are shifted upward along the operating temperature.

Charge and Discharge Behaviour of Li-Ion Batteries at Various Temperatures Containing LiCoO2 Nanostructured Cathode Produced by CCSO

Lithium cobaltate (LiCoO2) was produced by carbon combustion synthesis of oxide (CCSO) using carbon nanoparticles as a fuel. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm (specific surface 80 m2/g) gives rise to a self-propagating thermal wave with maximum temperatures of up to 900°C. The thermal front rapidly propagates through the mixture of solid reactants converting it to lithium cobaltate. XRD data suggest that the as-synthesized products were single phase. Carbon is not incorporated in the product and is evolved from the reaction zone as gaseous CO2. Thermogravimetric analysis was used to identify the features of interaction in the LiNO3-Co3O4-C system. The key features affecting the process-carbon pre-concentration in the reacting mixture and oxygen infiltration to the reaction zone-led to the formation of layered structure of LiCoO2 and affected the particle sizes. The synthesized crystalline nanoparticles were nearly spherical, and their average particle diameters ranged between 60 and 200 nm.