Carbon Materials for Advanced Technologies Episode 11 ppsx

380 2000 lorn 0 0 4 8 12 16 SCATTERING ANGLE (deg.) C k2 (k2 ) Fig. 28. (a) Small angle scattering intensity versus scattering angle for Br1000. The solid line IS a fit using equation (6) with RE = 5.5 A. (b) Natural log of the scattered intensity versus k2. The straight-line fit allows R, to be extracted from eq. (6). The large intensity at very small k is caused by the scattering from macropores or mesopores in the sample 381 R=B, /A, 10 20 30 40 SCATTERING ANGLE (deg.) Fig. 29. Schematic graph showing the definition ofthe parameter, R, used to empirically estimate the fraction of single graphene layers in hard carbon samples. Figure 30 shows a series of calculated patterns for carbon samples with a fraction, f, of carbon atoms in randomly oriented single layers, a fraction 2/3( 1- f) in bilayers and a fraction 1/3(1-f) in trilayers [12]. These curves can be used to estimate the dependence of the ratio, €2, defined by Fig. 29, on the single layer fraction. Figure 31 shows the dependence of R on single layer fraction for the calculated patterns in Fig. 30, and for another set of calculated patterns (not shown) where the fraction of carbon atoms in bilayers and trilayers was taken to be %(l-f) [12]. Both curves in Fig. 31 clearly show that R decreases as the single layer content of the sample increases and is fairly insensitive to how the carbon is distributed in bilayers and trilayers. 3 82 Fig. 30. Calculated (002) Bragg peaks for various single layer fractions of the sample from reference 12. The calculations assumed that a fraction, f, of the carbon was in single layers and that fractions 2/3(1-f) and 1/3(1-f) were included in bilayers and trilayers respectively. 3.5 2 Layer, 0.67(1-f); 3 Layer, 0.33(1-f) 3.0 PL 0 F 2.5 - a w 0 > 4 2.0 - 4 x e e 0 1.5 - I 0.2 0.3 0.4 0.5 0.6 0.7 SINGLE LAYER FRACTION Fig. 31. The dependence of R on single-layer fraction for the calculated patterns of Fig. 30 , and for a second set of calculations where the fraction of carbon atoms rn bilayers and trilayers is equal [12]. 3 83 5.3 Mechanism of lithium insertion The materials made near 1000°C from the three resins have little hydrogen content. These materials show bgh capacity (up to 550 mAh/g), little charge- discharge hysteresis, and appear well-suited for application in lithium-ion batteries. The mechanism for lithium insertion on the low voltage plateau is believed to be the adsorption of lithium onto internal surfaces of nanopores formed by single, bi, and bilayer graphene sheets which are arranged like a "house of cards" as shown in Fig. 24. Additional samples were prepared from the three resins and were heated at temperatures between 940" and IIOO", under different inert gas flow rate and with different heatmg rates. The samples have different microporosities and show different capacities for lithium insertion. The results for all the carbons prepared from resins are shown in Fig. 32, which shows the reversible capacity plotted as a function of R. The reversible capacity for Li insertion increases as R decreases. This result is consistent with the result reported in reference 12, 0 0 0 I- 0. O 4 p1 500 e. 0 0 0 0 0. 1.3 1.4 1.5 1.6 1.7 1.8 R Fig. 32. Reversible capacity of microporous carbon prepared from phenollc resins heated between 940 to 1100°C plotted as a function of the X-ray ratio R. R is a parameter which is empirically correlated to the fraction of single-layer graphene sheets in the samples. 3 84 which suggusts that Li atoms can be adsorbed onto the internal surface of micropores in the hard carbon samples as shown in Fig. 24. If there are more micropores (or small R for the sample), then the capacity is larger. A lithium cluster in the micropores of the carbon sample has a very similar environment as lithium atoms in metallic lithium. Hence, we observe long low- voltage plateaus on both discharge and charge for lithium insertion in the microporous carbon. Since these materials have significant microporosity, we expect their bulk densities to be low. For example, the tap density (100 taps) of BrlOOO was measured to be 0.81 glcc, compared to 1.34 glcc for the synthetic graphitic carbon powder, MCMl32700, measured by the same method. 6 Carbons Used in Commercial Applications Most commercial lithium-ion cells maufactured today use graphitic carbons from region 1 of Fig. 2. These are of several forms, with mesocarbon microspheres and natural graphites being the most commonly used. The specific capacity of these carbons is near 350 mAWg. Sony Energytec uses a disordered hard carbon of the type described in region 3 of Fig. 2. These carbons have been produced by a number of Japanese manufacturers including Kureha [4 11 and Mitsubishi Gas [40]. Our recent work [44], and other work in the patent literature shows how such carbons can be produced from natural precursors like sugar and wood. This suggests that it should ultimately be possible to prepare such carbons very cheaply. The specific capacity of region-3 carbons which are in commercial production are around 500 mAWg. There are numerous alternatives to pure carbons for use in Li-ion batteries, Wilson et al. 1451 have shown how disordered carbons containmg silicon nanoclusters can use the large alloying capacity of silicon for Li, in addition to the insertion capacity of the carbon itself. These materials can have reversible capacities up to 500mAWg. They are prepared by chemical vapor deposioon methods and hence are a lab curiosity at the moment. In an effort to make these materials more practical, Wilson et al. [46] examined the products of the pyrolysis of siloxane polymers and found they could have reversible capacihes near 600 &g. A recent patent filing by Selko [47] showed that Si0 (a mixture of nanometer sized amorphous Si and amorphous SiO, regions within particles) has a voltage of about 0.3V versus Li metal and a capacity for lithium near 11 OOmAWg. Our preliminary experiments have confiied this result, but 385 do not show good cycle life. In another recent patent filing, researchers at Fuji [48] have shown that SnO, SnO, and amorphous SiSnO, all have large reversible capacities (> 500 mAh/g) for lithium below about 0.8V. Fuji has even announced plans to commercialize a cell with one of the anodes described in ref. 48. It is clear that there is enormous activity in the the search for better and cheaper anode materials for Li-ion batteries. In fact, it is not certain at this time whether carbon will remain the material of choice for this application. Nevertheless, large strides toward the opfimization and understanding of carbons for Li-ion batteries have been made in the last 5 to 10 years. If continued progress is made, we can expect to see carbon materials in Li-ion batteries for a long time to come. 7 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16 17. 18. 19 References T. Nagaura and K. Tozawa, Prog. Batt. Solar Cells 9,209 (1990). J.R. Dahn, A.K. Sleigh, Hang Shi, B.W. Way, W.J. Weydanz, J.N. Reimers, Q. Zhong, and U. von Sacken, “Carbons and Graphites as Substitutes for the Lithium Anode”, in Lithium Batteries, G. Pistoia, Elsevier, North Holland S. Hossain, “Rechargeable Lithium Batteries (Ambient temperature)”, in Handbook of Batteries, 2nd edition, D. Linden, McGraw-Hill Inc. (1 995). J.R. Dahn, U. von Sacken, M.W. Juzkow, and H. Al-Janaby, J. Electrochem. Soc. 138, 2207 (I 991). J.R Dahn, Tao Zheng, Yinghu Liu, J.S. Xue, Science 270, 590 (1995). Tao Zheng, J.N. Reimers, and J.R. Dahn, Phys. Rev. B 51, 734-741 (1995). Tao Zheng and J.R. Dahn, Phys. Rev. B53,3061-3071 (1996) Tao Zheng, Yinghu Liu, E.W. Fuller, Sheilla Tseng, U. von Sacken, and J.R. Dah, J. Electrochem. SOC. 142,258 1 (1995). Tao Zheng, J.S. Xue, and J.R. Dahn, Chemistry of Materials, 8, 389 (1996) Tao Zheng, W.R. McKinnon, and J.R. Dahn, J. Electrochem SOC., 143 (71, Tao Zheng, Q. Zhong, and J.R. Dahn, J Electrochem. SOC. 142, L21l (1995). Yinghu Liu, J.S Xue, Tao Zheng, and J.R. Dahn, Carbon 34, 193 (1 996). Tao Zheng, W. Xing and J.R. Dahn, Carbons Prepared from Coals for Anodes oflithiurn-Ion Cells, Carbon, 34(12), pp. 1501-1507 (1996). Hang Shi, Ph.D. Thesis, Simon Fraser University (1993). Hang Shi, J.N. Reimers, and J.R. Dahn, J. Appl. Cryst. 26, 827 (1993). P. Scherrer, Nachr Gottinger Gesell., 98 (191 8). B.E. Warren, Phys. Rev. 9,693 (1941). B.E. Warren,X-RayDiSfraction, p. 254, Dover, N.Y. (1990). A. Guinier, G. Fournet, Smalldngle Scatterzng of X-Rays Sons, N. Y., 1955). (1993). pp. 2137-2145 (1996). (John Wiley & 20. 21. 22 23. 24. 25. 26. 27. 28 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. M. Kalliat, C.Y. Kwak and P.W. Schmidt, in “New Approaches in Coal Chemisty”, edited by B.D. B laustein, B.C. Bockrath and S. Friedman, American Chemical Society, Washington, D.C., p. 3, (1981). R.E. Franklin, J. Chem. Phys. 47,573 (1950). For examples, see paper in volumes 1 and 2 in Chemisty and Physics of Carbon, edited by P.L. Walker, Jr., Marcel Dekker Inc., N.Y. (1965, 1966). B.E. Warren,Phys. Rev. 9,693 (1941). E. Peled, J. Electrochem. SOC. 126, 2047 (1979). R. Fong, U. von Sacken, and J.R. Dahn, J. Electrochem. SOC. 137, 2009 (1 990). R.C. Boehm, and A. Banerjee, J. Chem. Phys. 96, 1150 (1992). Tao Zheng, and J.R. Dahn, Synth. Met. 73, 1 (1995). S. Yata, H. Kinoshita, M. Komori, N. Ando, T. Kashiwamura, T. Harada, K. Tanaka, and T. Yamabe, Synth. Met. 62, 153 (1994). A. Mabuchi, K. Tokumitsu, H. Fujimoto, and T. Kasuh, In Proc. 7th Int. Meeting on Lithium Batteries, May 15-20 (1994), Boston, USA, paper I-A-10, p. 207 of ext. abs.; also see H. Fujimoto, A. Mabuchi, K. Tokumtsu, and T Kasuh, ibid, paper 11-B-12, p. 540. K. Sato, M. Noguchi, A. Demachi, N. Oki, and M. Endo, Science 264, 556 (1994). J.S. Xue, A.M. Wilson, and J.R. Dahn, Canadian patent application, filed May 20 (1995). B.R. Puri, “Surface Complexes on Carbons”, in Chemisty and Physics of Carbons, edited by P.L. Walker, Jr., Vol. 6, Marcel Dekker Inc., N.Y. (1970) For example, see Tao Zheng’s Ph.D. Thesis, Simon Fraser University, Canada (1 996). R.E. Franklin, Acta Cryst. 4,253 (1951). R. Diamond, in Proc. Third Con$ on Carbon, p. 367, Buffalo, New York (1957), published by Pregammon Press, New York (1959). T. Enoki, S. Miyajima, M. Sano, and H. Inokuchi, J. Mater. Res. 5,435 (1990). P. Papanek, M. Radosavljievic, and J.E. Fischer, Chem. Mater., 8(7), pp. 1519- 1526 (1996). L.S. Selwyn, W.R. McKinnon, U. von Sacken, and C.A. Jones, Solid State Ionics 22, 337 (1987). A Omaru, H. Azuma, M. Aoki, A. Kita, and Y. Nishi, paper #25, 182”d meeting of the Electrochemical Society, Toronto, Canada. Extended Abstracts of Battery Division, p. 34 (1992). Y. Takahashi, J. Oishi, Y Miki, M. Yoshimura, K. Shibahara, and H. Sakamoto, 35“ Battery Symposium in Japan, Nov. 14-16, Nagoya, Japan, paper 2B05, extended abstracts, page 39 (1994). N. Sonobe, M. Ishikawa, and T. Iwasaki, 35” Battery Symposium in Japan, Nov. 14-16, Nagoya, Japan, paper 2B09, extended abstracts, page 47 (1994). E. Fitzer, W. Schaefer, and S. Yamada, Carbon 7, 643 (1969). U. von Sacken, Q. Zhong, Tao Zheng, and J.R. Dahn, PhenoZic Resin Precursor Pregraphitic Carbonaceous Insertion Compounds and Use as Anodes in Rechargeable Batteries, Canadian Patent Application #2,146,426 (1995). 387 44. Weibing Xing, J.S. Xue and J.R. Dah, Optimizing Pyrolysis of Sugar Carbons for Use as Anode Materials in Lithium-Ion Batteries, J. Electrochem SOC., 143, 3046 (1996); Weibing Xing, J.S. Xue, Tao Zheng, A. Gibaud and J.R. Dahn, Correlation between Lithium Intercalation Capacity and Microstructure in Hard Carbons, J. Electrochem. SOC., 143,3482 (1996). A.M. Wilson and J.R. Dahn, J. Electrochem. SOC. 142,326 (1995). A.M. Wilson, J.N. Reimers, E.W. Fuller and J.R. Dahn, Solid State Ionics, 74, 249 (1 994). K. Tahara, H. Ishikawa, F. Iwasaki, S. Yahagi, A. Sakata, and T. Sakai, European Patent Application #93 11 1938.2, (1993). Y. Idota, M. Mishima, Y. Miyaki, T. Kubota and T. Miyasaka, Canadian Patent Application 2,134,052 (1994). 45. 46. 47. 48. 389 CHAPTER 12 Fusion Energy Applications LANCE L. SNEAD Oak Ridge National Laboratory P.Q. Box 2008 Oak Ridge, Tennessee 37831-6087, U.S.A. 1 Introduction 1. I Background When two light elements collide with sufficient energy they may "fuse" and form a krd, heavier, element. A simple mass balance would show that there is a small mass loss in this process, correspondmg to a significant energy release. Many light elements can undergo exothermic fusion reactions, but fusion of the isotopes of hydrogen and helium are the easiest reactions to induce. The most probable fusion reactions and their released energies are: 1H' + 1H' + 1D2 f positron = 1.4 MeV 1H' + ID2 + 2~e3 = 5.5MeV IH' + 1~3 + 2~4 = 19.9MeV 1D2 + 1D2 + 2He3 + neutron = 3.3 MeV ID2 + ID2 + 1~3 + IH' = 4.0MeV 1D2 + 1T' + 2He4 + neutron = 17.6MeV ID^ + 2~~3 + 2~~4 + H = 18.2MeV Fusion requires high temperature (energies) to cause the atoms to bind together. The likelihood of atoms fusing together is hghly dependent on the individual isotopes and their temperature. It can be shown that the D+T reaction is the easiest reaction to drive. However, the inherent rahoactivity and expense of tritium has restricted its use, while the lighter hydrogen isotopes have been extensively used. The gaseous temperatures required for D+T reaction are related to the kinetic energy of the ions, and are in excess of 50 million degrees Kelvin. While significant power has been produced from fusion systems, the total amount of power produced in any reactor is much less than the power added to the system to drive the fusion process. The cvent goal of fusion programs worldwide is to achieve "ignition," where the plasma begins a self-sustaining burn from which more power is generated than consumed in the fusion process. [...]... displacement energy of the higher-Z target atoms For example, approximately 20 eV is required to hsplace an atom of carbon from the surface, while 220 eV is required for an atom of tungsten In the sub-keV energy range of plasma fuels, the high yield materials are therefore carbon and beryllium As the impacting ion energy increases, the sputtering yield for all materials decreases as the depth of interaction... called the catastrophic 'lcarbon bloom," i.e., self accelerating sputtering of carbon As can be seen in Fig 12b, this problem is worst for carbon self-impacts at grazing angles to the surface 4.2 Chemical erosion For intermediate temperatures from 400-1000°C (Fig 1l), the volatilization of carbon atoms by energetic plasma ions becomes important As seen in the upper curve of Fig 11, helium does not have... irradiation on some graphite or CFC materials studied for fusion applications [I21 0 m Mitsubishi Kasei MKC-1PH CFC to yo-Tanso IG -110 Graphite Showa-Denko CC-3 12 Felt CFC (11 ti fibers) X-direction Y-direction Z-direction Toyo Tanso CX2002U CFC (1 to fibers) 8.83 11. 5 34.0 31.3 74.0 98.0 - 87.6 87.2 14.9 18.5 Unirradiated Irradiated 35.2+/-1.8 38.4+/-2.2 90.5+/-5.9 110 .8+/-8.4 103.9+/-6.8 98.4+/-2.7... pile grade A graphite demonshates this point For the extremely damaging irradiation temperature of -2OO0C, it is seen in Fig 7 that the absolute reduction (l!&,,m-KJis substantially greater for the high thermal conductivity materials compared to the lower grade CFCs and graphite, although the normalized fraction is approximately the same for all of the carbon materials in Fig 7 Moreover, a saturation... Wrought 200 300 400 500 Ee 600 700 800 900 Application Temperature (C) Fig 3 Thermal shock figure of merit for selected plasma facing materials 1000 399 Finally, it should be noted that there are many issues regarding the selection of carbon materials as PFCs other than their thermal shock behavior For example, the issues of radiation damage, erosion, and hydrogen retention are three leading drawbacks... fiber development, very high thermal conductivity materials have been recently demonstrated and become attractive for high heat flux applications The highest thermal conductivities have been demonstrated for CFCs made from highly crystalline graphite fibers which have intrinsic conductivities approaching that of pyrolitic graphite For example, vapor grown carbon fibers [28] have a thermal conductivity... be attributed to the use of graphite and carbon- fiber composites (CFCs), as well as other low atomic number plasma-facing materials such as beryllium With the use of advanced materials, it is possible that the next planned experiment, the International Thermonuclear Experimental Reactor (ITER), will demonstrate an ignited fusion plasma and provide a test bed for a demonstration fusion power reactor... lines which travel helically through a toroidal vacuum vessel For a non-collisional plasma, the ions can therefore be heated by various external means to the extreme temperature necessary for the fusion reaction to take place The tokamak concept is the basis for the four largest present day fusion machines (Table I), and is the premise for the proposed ITER machine currently under design by the European... occurs, at a neutron dose of 1 dpa Data for higher irradiation temperatures 1271 shows that the higher thermal conductivity materials have a slightly larger fractional change in thermal conductivity (K,,.,lK,,,,in) compared to lower conductivity materials, although the absolute value of the irradiated thermal conductivity is still greater for the higher conductivity materials - An algorithm has been developed... thennomechanical requirements for the f i s t wall are not as severe A convenient comparison for the heat loadings given in Table 1 is the maximum output from a conventionalpropane torch, which is approximately 10 MW/mz, or about the maximum heat flux seen in current fusion devices Table 1 Materials and heat loads for the major fusion machines world wide (see Section 1.3 for definitions of divertor . in the the search for better and cheaper anode materials for Li-ion batteries. In fact, it is not certain at this time whether carbon will remain the material of choice for this application understanding of carbons for Li-ion batteries have been made in the last 5 to 10 years. If continued progress is made, we can expect to see carbon materials in Li-ion batteries for a long time. graphitic carbons from region 1 of Fig. 2. These are of several forms, with mesocarbon microspheres and natural graphites being the most commonly used. The specific capacity of these carbons