Carbons disordered

It has been reasonably well established that the intercalation capacity of lithium and operating voltage of the lithium-ion battery depend on the properties of the SEI. The formation of the SEI, in turn, is strongly affected by the crystal structure of graphite. Successful development of negative electrodes for lithium- 

Many materials given the name graphite actually have a considerable amount of stacking disorder. For carbons in general, the situation is more complex. Most cokes, petroleum cokes, carbon blacks, carbon fibers, pyrolyzed polymers and mesocarbon microspheres have disordered structures. In such structures the size of the crystallites is small and there is a high probability of random stacking (shifts or rotations) of adjacent carbon layers. This type of disorder is called turbostratic disorder. Hundreds of carbons are commercially available however, selecting the best carbon for use in lithium-ion cells is a subject for much current research. 

Electrochemical and spectroscopic methods have been used to investigate irreversible-loss mechanisms of lithium intercalation in disordered polymethacrylo-nitrile carbons. Voltammetric measurements show that the solvent readily decomposes at potentials 1.2 V positive of the reversible lithium potential. Evidence for hydrocarbon, carbonate and alkylcarbonate formation in the surface film is found with the help of combined XPS and SIMS analysis. 

XPS measurements of the pristine soft carbon sample (not presented here) revealed a sharp C-ls peak located at 284.4 eV. Broadening of the peak during sputtering was observed. This probably follows the partial destruction of the initial carbon crystallites caused by argon-ion bombardment. A similar phenomenon was described by Lascovich et aV The surface was found to contain 93 atomic percent C, about 3% O, and various impurities originating from the glove-box atmosphere. 

Formation of PF compounds (-12%), found in the SEI formed in LiPF electrolyte might proeeed in accordance with reaction (4.1). 

---

The structure refinement program for disordered carbons, which was recently developed by Shi et al [14,15] is ideally suited to studies of the powder diffraction patterns of graphitic carbons. By performing a least squares fit between the measured diffraction pattern and a theoretical calculation, parameters of the model structure are optimized. For graphitic carbon, the structure is well described by the two-layer model which was carefully described in section 2.1.3. 

Key Words—Vibrations, infrared, Raman, disordered carbons, carbon nanotubes, normal modes. 

Similar results were found by Bacsa el al. [26] for cathode core material. Raman scattering spectra were reported by these authors for material shown in these figures, and these results are discussed below. Their HRTEM images showed that heating core material in air induces a clear reduction in the relative abundance of the carbon nanoparticles. The Raman spectrum of these nanoparticles would be expected to resemble an intermediate between a strongly disordered carbon black synthesized at 850°C (Fig. 2d) and that of carbon black graphitized in an inert atmosphere at 2820°C (Fig. 2c). As discussed above in section 2, the small particle size, as well as structural disorder in the small particles (dia. —200 A), activates the D-band Raman scattering near 1350 cm . ... 

Figure 4. Schematic drawing of a non-graphitic (disordered) carbon [21.

The use of non-graphitic (disordered) carbons as anode materials in lithium ion cell is highly attractive for two reasons ... 

Xing and Dahn recently reported [70] that <2 R for disordered carbon and MCMB 2800 can be markedly reduced from about 180 and 30mAhg l to less than 50 and lOmAhg-1 respectively, when the carbon anode and cell assembly are made in an inert atmosphere and never come in contact with air. This indicates that these carbons contain nanopores that... 

This work is based on the doctoral thesis of Prasad Rao [8] it stemmed from the early work of Santiago, Mulay et al. (Cf. ref. 2a). Amorphous (disordered) carbons (Cabot Co. s Monarch 700, CSX-203, etc.) were used after appropriate desulfurization. Some of these carbons were graphitlzed at high temperatures (2773 K). The above CMC samples were doped with boron in the range from 170 to 260 ppm. 

Non-cardiac Anemia, anxiety disorders, carbon monoxide poisoning, cocaine use, esophageal reflux, peptic ulcer, pleuritis, pneumonia, pneumothorax, pulmonary embolus, pulmonary hypertension, thyrotoxicosis... 

In the following part of this paper, in-situ 7Li-NMR is used to better know the state(s) of lithium reversibly stored in disordered carbons. 

In this paper, we presented new information, which should help in optimising disordered carbon materials for anodes of lithium-ion batteries. We clearly proved that the irreversible capacity is essentially due to the presence of active sites at the surface of carbon, which cause the electrolyte decomposition. A perfect linear relationship was shown between the irreversible capacity and the active surface area, i.e. the area corresponding to the sites located at the edge planes. It definitely proves that the BET specific surface area, which represents the surface area of the basal planes, is not a relevant parameter to explain the irreversible capacity, even if some papers showed some correlation with this parameter for rather low BET surface area carbons. The electrolyte may be decomposed by surface functional groups or by dangling bonds. Coating by a thin layer of pyrolytic carbon allows these sites to be efficiently blocked, without reducing the value of reversible capacity. 

HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY IMAGE ANALYSIS OF DISORDERED CARBONS USED FOR ELECTROCHEMICAL STORAGE OF ENERGY... 

Disordered carbons usually exhibit a multiscale organization (structure, microtexture, texture)4. Structurally, they are made of more or less distorted polyaromatic layers, nanometric in size. The spatial association or the layers, from the nanometric to the micrometric scales, gives rise to different microtextures (lamellar, porous, concentric, fibrous, etc.) forming the carbons skeleton4. The multiscale organization is the fingerprint of the kind of precursor and of the formation conditions (temperature, pressure, strains, time, etc.) met either in laboratory experiments or in Nature, and is directly related with numerous properties. 

As far as the diffraction data (as well electron and X-ray diffraction) of disordered carbons are concerned, only averaged data can be obtained from the broad and faint bands due to the reflections on the nanometer-size... 

---