Tri D. Tran

Commercial Carbonaceous Materials as Lithium Intercalation Anodes

Commercial carbonaceous materials were examined as lithium intercalation anodes in propylene carbonate (carbons) and ethylene carbonate/dimethyl carbonate (graphites) electrolytes. The reversible capacity (180--355 mAh/g) and the irreversible capacity loss (15--200% based on reversible capacity) depends on the type of binder, carbon type, morphology, and phosphorus doping concentration. A carbon-based binder was chosen for electrode fabrication, producing mechanically and chemically stable electrodes and reproducible results. Several types of graphites had capacity approaching LiC{sub 6}. Petroleum fuel green cokes doped with phosphorus gave more than a 20% increase in capacity compared to undoped samples. Electrochemical characteristics are related to scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer, Emmett, and Teller method measurements.

Rate effect on lithium-ion graphite electrode performance

The electrochemical performance of lithium-ion graphite electrodes with particle diameter in the range of 6–44 µm was evaluated at different discharge (intercalation)/charge (deintercalation) rates (C to C/60). The electrode capacity depends on both the average particle size and rate. With a simple rate programme, the electrode performance is dependent on the cycling rate. The capacity of small graphite particles (6 µm) at C/2 rate was 80% of that achieved at C/24 rate (∼372 mAh g−1). The capacity of large graphite particles (44 µm) obtained at fast rates (C/2) was only 25% of that obtained under near-equilibrium conditions (C/24). The electrode capacity, however, is nearly independent of the charge rate when the electrode is fully intercalated using a modified rate programme containing a constant-voltage hold at 0.005 V (vs Li+/Li) for several hours. The electrochemical behaviour is related to the physicochemical properties of the graphite particles.

Microstructural Characterization of Lithiated Graphite

The microstructures of lithiated graphite were studied using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). HRTEM shows lattice images of the (001) layers of LiC{sub 6} with layer spacing of 3.70 {angstrom}, consistent with XRD. The morphology and distribution of the LiC{sub 6} and LiC{sub 12} phases were investigated by dark field image and selected-area electron diffraction in TEM. The results indicate that LiC{sub 6} and LiC{sub 12} phases can coexist in the lithiated graphite particle. The application is to lithium rechargeable batteries.

Sensitivity of 2,6-Diamino-3,5-Dinitropyrazine-1-Oxide

ABSTRACT The thermal and shock sensitivities of plastic bonded explosive formations based on 2,6-diamino-3,5-dinitropyrazine-1-oxide (commonly called LLM-105 for Lawrence Livermore Molecule #105) are reported. The One-Dimensional Time to Explosion (ODTX) apparatus was used to generate times to thermal explosion at various initial temperatures. A four-reaction chemical decomposition model was developed to calculate the time to thermal explosion versus inverse temperature curve. Three embedded manganin pressure gauge experiments were fired at different initial pressures to measure the pressure buildup and the distance required for transition to detonation. An Ignition and Growth reactive model was calibrated to this shock initiation data. LLM-105 exhibited thermal and shock sensitivities intermediate between those of triaminotrinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX).

Thermal and electrochemical studies of carbons for Li-ion batteries: 2. Correlation of active sites and irreversible capacity loss

Abstract Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) involving air oxidation of fluid coke, coal-tar pitch delayed coke and needle coke suggested that active sites are present which can be correlated to the crystallographic parameters, L a and L c , and the d (002) spacing. This finding was extended to determine the relationship between active sites on carbon and their role in catalyzing electrolyte decomposition leading to irreversible capacity loss (ICL) in Li-ion batteries. Electrochemical data from this study with graphitizable carbons and from published literature were analyzed to determine the relationship between the physical properties of carbon and the ICL during the first charge/discharge cycle. Based on this analysis, we conclude that the active surface area, and not the total BET surface area, has an influence on the ICL of carbons for Li-ion batteries. This conclusion suggests that the carbon surface structure plays a significant role in catalyzing electrolyte decomposition.

Thermal and electrochemical studies of carbons for Li-ion batteries: 1. Thermal analysis of petroleum and pitch cokes

Abstract Thermal analyses involving simultaneous thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the air oxidation of petroleum (fluid and needle cokes) and coal-tar pitch cokes. The intent of this study is to understand the relationship between the structure of carbonaceous materials and their thermal oxidation behavior in air (Part 1). A correlation between the thermal oxidative properties of cokes and their electrochemical Li-intercalation performance is discussed in the following paper (Part 2). The carbon samples were heat-treated at temperatures up to 2800°C, and three thermal parameters were determined — ignition temperature ( T i ), temperature maximum ( T m ) in the DTA curves, and the temperature at which 15% carbon weight loss was attained ( T 15 ). The measurements showed trends that are consistent with prior reports that the active sites on the surface and not the total surface area (TSA) are responsible for the thermal behavior of the carbons. Because of the difference in the graphitizability of petroleum and pitch cokes that was obtained by heat treatment, variations in the thermal parameters were observed. Needle cokes are the most easily graphitized and this is reflected in the higher values of the thermal parameters compared to the fluid and pitch cokes.

Lithium intercalation in heat-treated petroleum cokes

Abstract Petroleum needle cokes were processed by air-milling and heat treatment at three temperatures 1800, 2100 and 2350 °C, to produce a final average particle size of 10 p.m. The effects of air-milling (before and after heat treatment) on the physical and microstructural properties of the petroleum coke particles were examined. The results obtained for electrochemical lithium intercalation/de-intercalation in 0.5 M LiN(CF3SO2)2/EC:DMC electrolyte using these petroleum cokes after the different processing conditions are reported.

Lithium intercalation studies of petroleum cokes of different morphologies

Abstract Petroleum cokes with different morphologies are studied in lithium intercalation experiments. Several types of calcined petroleum cokes with varying microstructures and surface morphologies are heat treated at temperatures approaching 2800°C. The physical and structural properties are studied by multi-point N 2 gas adsorption analysis, particle size measurements, electron microscopies and X-ray diffraction (XRD) analysis. Changes in the properties of materials during heat treatment are significant. The effects of the coke structures and heat treatment conditions on their electrochemical lithium intercalation behavior will be discussed.

Transmission electron microscopy of carbons for lithium intercalation

Transmission electron microscopy (TEM) is a powerful tool which we are applying to study the microstructure of carbonaceous materials that are used as lithium-intercalation electrodes in lithium-ion cells. The results of our study on the relationship between the physicochemical properties of carbon, with strong emphasis on the microstructure observed by TEM, and their capability for electrochemical intercalation of lithium will be summarized. In addition, progress on the fabrication of a microcell for in situ TEM of lithium-intercalation in carbon will be discussed.

Mechanical Mocks for Insensitive High Explosives

Three mechanical mocks were formulated and tested as replacements for the current mock for insensitive explosives LX-17-1 and PBX 9502 because its binder was no longer available. The three polymers evaluated were a butyl/isobutyl acrylate copolymer, ethyl cellulose and a new fluoropolymer, PFR 91. The glass transitions of these polymers were 35, 130, and −10°C, respectively. Two inert fillers, talc and cyanuric acid, were used in the new formulations. Pressing densities and mechanical and thermal properties were used to characterize these mocks. The mock based on the acrylic copolymer most closely emulated these insensitive high explosives.