METHOD FOR MANUFACTURING BASE MATERIAL POWDER HAVING CARBON NANO-COATING LAYER, METHOD FOR MANUFACTURING MgB2 SUPERCONDUCTOR USING THE METHOD, MgB2 SUPERCONDUCTOR, METHOD FOR MANUFACTURING POSITIVE ELECTRODE MATERIAL FOR LITHIUM ION BATTERY, LITHIUM ION BATTERY, AND METHOD FOR MANUFACTURING PHOTOCATALYST

Abstract

Provided is a method for manufacturing a base material powder having a carbon nanocoating layer, the method including adding a polycyclic aromatic hydrocarbon to a base material powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the base material powder with a layer of carbon having a thickness of 0.1 nm to 10 nm. According to the method, when a source of carbon that covers a base material powder is appropriately selected, the base material powder having the carbon nanocoating layer can be provided, which does not have a possibility of causing inconveniences in the applications of a final manufactured product of the base material powder and exhibits satisfactory productivity of the base material powder, and from which a modified final manufactured product is obtained.

Claims

1-18. (canceled)

19. A method for manufacturing a base material powder having a carbon nanocoating layer, the method comprising adding a polycyclic aromatic hydrocarbon to a base material powder; heating the mixture at a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon; and thereby coating the surface of the base material powder with from 1 layer to 300 layers of carbon atoms.

20. A method for manufacturing a base material powder having a carbon nanocoating layer, the method comprising adding a polycyclic aromatic hydrocarbon to a base material powder; heating the mixture at a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon; and thereby coating the surface of the base material powder with a layer of carbon having a thickness of from 0.1 nm to 10 nm.

21. The method for manufacturing a base material powder having a carbon nanocoating layer according to claim 19, wherein the base material powder is a base material powder for a lithium ion battery positive electrode material selected from the group consisting of SnO.sub.2 powder, LiVPO.sub.4 powder, LiFePO.sub.4 powder, LiNi.sub.0.5Mn.sub.15O.sub.4 powder, LiMnPO.sub.4 powder, Li.sub.2FeSiO.sub.4 powder, V.sub.2O.sub.5 powder, MnO.sub.2 powder, LiCoO.sub.2 powder, LiNiO.sub.2 powder, LiNi.sub.0.5Mn.sub.0.5O.sub.2 powder, LiMn.sub.2O.sub.4 powder, Li.sub.2S powder, and SiO.sub.2 powder; or a base material powder selected from the group consisting of a laminate of Ag powder and TiO.sub.2 powder, and B powder.

22. The method for manufacturing a base material powder having a carbon nanocoating layer according to claim 19, wherein the polycyclic aromatic hydrocarbon is selected from the group consisting of coronene, anthanthrene, benzo(ghi)perylene, circulene, corannulene, dicoronylene, diindenoperylene, helicene, heptacene, hexacene, kekulene, ovalene, zethrene, benzo[a]pyrene, benzo[e]pyrene, benzo[a]fluoranthene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene, dibenz[a,j]anthracene, olympicene, pentacene, perylene, picene, tetraphenylene, benz[a]anthracene, benzo[a]fluorene, benzo[c]phenanthrene, chrysene, fluoranthene, pyrene, tetracene, triphenylene, anthracene, fluorene, phenalene, and phenanthrene.

23. The method for manufacturing a base material powder having a carbon nanocoating layer according to claim 19, wherein the polycyclic aromatic hydrocarbon is solid at ambient temperature and atmospheric pressure and has a boiling point temperature that is lower than the thermal decomposition temperature, and the ratio C:H between the number of carbon atoms and the number of hydrogen atoms in the polycyclic aromatic hydrocarbon is 1:0.5 to 1:0.8.

24. A composite of a base material powder and carbon produced by the method according to claim 19.

25. An electrode obtainable by mixing the composite according to claim 24 with a binder and then molding the mixture.

26. A method for manufacturing MgB.sub.2 superconductor by pressure molding a mixture of Mg powder or MgH.sub.2 powder and B powder and then heat-treating the molded product, the method comprising: adding a polycyclic aromatic hydrocarbon to the B powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the B powder with from 1 layer to 300 layers of carbon atoms or with a layer of carbon having a thickness of from 0.1 nm to 10 nm; and mixing the B powder having a surface covered with carbon atoms or carbon, with the Mg powder or MgH.sub.2 powder.

27. The method for manufacturing MgB.sub.2 superconductor according to claim 26, wherein the amount of addition of the polycyclic aromatic hydrocarbon is 0.1 mol % to 40 mol % relative to the theoretical or experimental production amount of MgB.sub.2.

28. The method for manufacturing MgB.sub.2 superconductor according to claim 26, wherein a metal tube is packed with the mixture, and the metal tube is pressure-molded and then heat-treated.

29. A method for manufacturing MgB.sub.2 superconductor using a base material powder having a carbon nanocoating layer produced by the method according to claim 19, the base material powder being B powder, the method comprising packing a metal tube with the B powder having a carbon nanocoating layer and a Mg rod, pressure molding the metal tube, and then heat-treating the metal tube.

30. A MgB.sub.2 superconductor obtained by the method for manufacturing MgB.sub.2 superconductor according to claim 26, the MgB.sub.2 superconductor being a MgB.sub.2 wire having one MgB.sub.2 core.

31. A MgB.sub.2 superconductor obtained by the method for manufacturing MgB2 superconductor according to claim 26, wherein the MgB.sub.2 superconductor is a multicore MgB.sub.2 wire having plural MgB.sub.2 cores.

32. A method for manufacturing a positive electrode material for a lithium ion battery, the positive electrode material having a metal oxide or a metal sulfide constituting a positive electrode material for a secondary battery using a non-aqueous electrolyte, and a carbon film coating the surface of the metal oxide or the metal sulfide, and the metal oxide or the metal sulfide being formed from a base material powder for lithium ion battery positive electrode material selected from the group consisting of SnO.sub.2, LiVPO.sub.4, LiFePO.sub.4, LiNi.sub.0.5Mn.sub.1.5O.sub.4, LiMnPO.sub.4, Li.sub.2FeSiO.sub.4, V.sub.2O.sub.5, MnO.sub.2, LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.0.5Mn.sub.0.5O.sub.2, LiMn.sub.2O.sub.4, Li.sub.2S and SiO.sub.2, the method comprising adding a polycyclic aromatic hydrocarbon to the base material powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the base material powder with from 1 layer to 300 layers of carbon atoms.

33. A method for manufacturing a positive electrode material for a lithium ion battery, the positive electrode material having a metal oxide or a metal sulfide constituting a positive electrode material for a secondary battery using a non-aqueous electrolyte, and a carbon film covering the surface of the metal oxide or the metal sulfide, and the metal oxide or the metal sulfide being formed from a base material powder for a lithium ion battery positive electrode material selected from the group consisting of SnO.sub.2, LiVPO.sub.4, LiFePO.sub.4, LiNi.sub.0.5Mn.sub.1.5O.sub.4, LiMnPO.sub.4, Li.sub.2FeSiO.sub.4, V.sub.2O.sub.5, MnO.sub.2, LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.0.5Mn.sub.0.5O.sub.2, LiMn.sub.2O.sub.4, Li.sub.2S and SiO.sub.2, the method comprising adding a polycyclic aromatic hydrocarbon to the base material powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the base material powder with a layer of carbon having a thickness of from 0.1 nm to 20 nm.

34. A lithium ion battery comprising: a positive electrode having a positive electrode active material provided on a positive electrode current collector; and a negative electrode facing the positive electrode, with a liquid electrolyte being disposed therebetween, wherein the positive electrode active material has a base material powder formed from a lithium metal oxide, and a carbon coating layer coating the periphery of the base material powder, and the carbon coating layer is manufactured by the method according to claim 32.

35. A method for manufacturing a photocatalyst, the photocatalyst using silver particles and TiO.sub.2 particles and employing the TiO.sub.2 particles as a base material powder, with the surface of the base material powder being coated with a carbon film, the method comprising adding a polycyclic aromatic hydrocarbon to the base material powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the base material powder with from 1 layer to 300 layers of carbon atoms.

36. A method for manufacturing a photocatalyst, the photocatalyst using silver particles and TiO.sub.2 particles and employing the TiO.sub.2 particles as a base material powder, with the surface of the base material powder being coated with a carbon film, the method comprising adding a polycyclic aromatic hydrocarbon to the base material powder, heating the mixture to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and is lower than or equal to the relevant boiling point temperature +300° C., and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon, and thereby coating the surface of the base material layer of carbon having a thickness of from 0.1 nm to 10 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0073] FIG. 1A is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0074] FIG. 1B is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0075] FIG. 1C is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0076] FIG. 1D is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0077] FIG. 1 E is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0078] FIG. 1F is a diagram illustrating the chemical formulae of the chemical substances used as the polycyclic aromatic hydrocarbon according to an embodiment of the present invention.

[0079] FIG. 2 is a configuration diagram explaining an apparatus for producing the positive electrode material for a lithium ion battery of the present invention.

[0080] FIG. 3 is a configuration diagram of a carbon coating apparatus used in Example 1 of the present invention.

[0081] FIG. 4 is a transmission electron microscopic image of a boron nanopowder that was heat-treated in a vacuum for 3 hours at 630° C. together with coronene in one of the examples of the present invention.

[0082] FIG. 5 is a boron mapping diagram for a boron nanopowder that was heat-treated together with coronene in a vacuum for 3 hours at 630° C.

[0083] FIG. 6 is a carbon mapping diagram for a boron nanopowder that was heat-treated together with coronene in a vacuum for 3 hours at 630° C.

[0084] FIG. 7 is a diagram illustrating the results of an infrared spectroscopic analysis of B powder after a vacuum heat treatment, a mixed powder of coronene and B (non-heat-treated), B powder, and coronene powder.

[0085] FIG. 8 is a diagram illustrating the X-ray diffraction patterns of B powder after a vacuum heat treatment, a mixed powder of coronene and B (non-heat-treated), B powder, and coronene powder.

[0086] FIG. 9 is a transmission electron microscopic image of a LiFePO.sub.4 powder that was heat-treated together with coronene in a vacuum for one hour at 700° C. in another embodiment of the present invention.

[0087] FIG. 10 is a carbon mapping diagram corresponding to the transmission electron microscopic image of the LiFePO.sub.4 powder of FIG. 9.

[0088] FIG. 11 is a lithium mapping diagram corresponding to the transmission electron microscopic image of the LiFePO.sub.4 powder of FIG. 9.

[0089] FIG. 12 is an iron mapping diagram corresponding to the transmission electron microscopic image of the LiFePO.sub.4 powder of FIG. 9.

[0090] FIG. 13 is a phosphorus mapping diagram corresponding to the transmission electron microscopic image of the LiFePO.sub.4 powder of FIG. 9.

[0091] FIG. 14 is an oxygen mapping diagram corresponding to the transmission electron microscopic image of the LiFePO.sub.4 powder of FIG. 9.

[0092] FIG. 15 is a high-resolution transmission electron microscopic image of a LiFePO.sub.4 powder that was heat-treated together with coronene in a vacuum for one hour at 700° C.

[0093] FIG. 16 is a set of Raman scattering shift diagrams of a LiFePO.sub.4 powder that was heat-treated together with coronene in a vacuum for one hour at 700° C. and of a LiFePO.sub.4 powder that was not heat-treated in a vacuum.

[0094] FIG. 17 is a set of diagrams explaining the particle size distribution of LiFePO.sub.4 base material particles used for a positive electrode material, in which FIG. 17(A) shows the case of LiFePO.sub.4 base material particles having no carbon support layer as a Comparative Example, and FIG. 17(B) shows the case of LiFePO.sub.4 base material particles having a carbon support layer.

[0095] FIG. 18 is a cross-sectional diagram schematically illustrating a test lithium secondary battery (coin cell) related to a Test Example of the present invention.

[0096] FIG. 19 is a diagram explaining the details of the trial manufacture specifications related to the coin cell illustrated in FIG. 18, and showing the mechanical design values of the positive electrode and the negative electrode.

[0097] FIG. 20 is a diagram explaining the details of a test product produced according to the trial manufacture specifications related to the coin cell illustrated in FIG. 18.

[0098] FIG. 21 is a diagram explaining the discharge capacity characteristics of the test product related to a Test Example of the present invention.

[0099] FIG. 22 is a graph showing a charge-discharge curve explaining the discharge capacity characteristics of the test product related to a Test Example of the present invention.

DESCRIPTION OF EMBODIMENTS

[0100] Hereinafter, embodiments of the present invention will be explained in detail using the drawings and the tables.

[0101] First, an embodiment in which the method for manufacturing a base material powder having a carbon nanocoating layer of the present invention is applied to a method for manufacturing MgB.sub.2 superconductor, will be described. Meanwhile, with regard to the terms used in the present specification, the definitions are described below.

[0102] The “internal Mg diffusion method” is a method for producing wire by disposing an Mg rod inside a metal tube, packing the gaps between the metal tube and the Mg rod with B powder, processing this composite into wire, and then heat-treating the wire.

[0103] The “powder-in-tube method” is a method for producing wire by packing a metal tube with a raw material powder of a superconductor, processing the composite into wire, and then heat-treating the wire.

[0104] The “critical current density Jc” refers to the maximum superconducting current density that can be passed per unit cross-sectional area of a superconducting wire. Usually, the critical current density refers to a value per unit cross-sectional area of the superconductor core in the wire.

[0105] According to the present embodiment, MgB.sub.2 superconductor is produced by pressure molding a mixture of Mg powder or MgH.sub.2 powder and B powder, and heat-treating the molded product.

[0106] In regard to the Mg powder, MgH.sub.2 powder and B powder used as raw materials, powders having a purity or a particle size similar to those of the conventional powders such as described in Patent Literatures 1 to 3 related to the proposal of the present applicant, can be used by appropriately regulating the mixing ratio of the powders. For example, in regard to the particle size, the average particle size of the Mg powder or the MgH.sub.2 powder is preferably in the range of 200 nm to 50 μm, and the average particle size of the B powder is preferably in the range of 50 nm to 1 μm. In regard to the mixing ratio, it is preferable that the powders are mixed at a molar ratio in the range of Mg or MgH.sub.2/B=0.5/2 to 1.5/2, and it is more preferable that the powders are mixed at a molar ratio in the range of 0.8/2 to 1.2/2. Then, appropriate amounts of a polycyclic aromatic hydrocarbon and SiC can be added to the mixture of Mg or MgH.sub.2 powder and B powder, or to B powder, and the mixture can be sufficiently mixed in a ball mill or the like.

[0107] In regard to the polycyclic aromatic hydrocarbon (nanographene), various compounds among those compounds having a carbocyclic ring or a heterocyclic ring with three or more rings may be considered, and the number of carbon atoms of the polycyclic aromatic hydrocarbon is not particularly limited; however, the number of carbon atoms is preferably in the range of 18 to 50. The polycyclic aromatic hydrocarbon may have various functional groups as long as the operating effects of the present invention are not inhibited, and the polycyclic aromatic hydrocarbon can be appropriately selected in consideration of the easy availability, handleability, price, and the like. For example, a typical example of the substituent may be an alkyl group having 1 to 8 carbon atoms, and particularly 1 to 4 carbon atoms, or the like. More specific examples thereof include coronene, anthracene, perylene, and biphenyl listed in Table 1 and Table 2 (FIGS. 1A to 1F); alkyl-substituted carbocyclic aromatic hydrocarbons; and heterocyclic aromatic hydrocarbons such as thiophene. Furthermore, in regard to the amount of addition of the polycyclic aromatic hydrocarbon, it is preferable to add the polycyclic aromatic hydrocarbon at a proportion of 0.1 mol % to 40 mol % relative to the theoretical or experimental production amount of MgB.sub.2.

TABLE-US-00001 TABLE 1 Chemical Melting point Boiling point Name formula [° C.] [° C.] Coronene (or superbenzene) C.sub.24H.sub.12 438 525 Anthanthrene C.sub.22H.sub.12 261 497 Benzo(ghi)perylene C.sub.22H.sub.12 278 500 Circulene C.sub.28H.sub.14 295 604 Corannulene C.sub.20H.sub.10 268 438 Dicoronylene C.sub.20H.sub.10 Not published Not published Diindenoperylene C.sub.32H.sub.16 Not published >330 Helicene C.sub.26H.sub.16 Not published Not published Heptacene C.sub.30H.sub.18 Not published 677 Hexacene C.sub.26H.sub.16 Not published 604 kekulene C.sub.48H.sub.24 Not published Not published Ovalene C.sub.32H.sub.14 475 Not published Zethrene C.sub.24H.sub.14 262 583 Benzopyrene C.sub.20H.sub.12 179 495 Benzo(a)pyrene C.sub.20H.sub.12 179 495 Benzo(e)pyrene C.sub.20H.sub.12 178 493 Benzo(a)fluoranthene C.sub.20H.sub.12 150 468 Benzo(b)fluoranthene C.sub.20H.sub.12 168 481 Benzo(j)fluoranthene C.sub.20H.sub.12 165 480 Benzo(k)fluoranthene C.sub.20H.sub.12 217 480 Dibenz(a,h)anthracene C.sub.22H.sub.14 262 524 ± 17 Dibenz(a,j)anthracene C.sub.22H.sub.14 196 524 ± 17

TABLE-US-00002 TABLE 2 Chemical Melting point Boiling point Name formula [° C.] [° C.] Olympicene C.sub.19H.sub.12 Not published 511 Prentacene C.sub.22H.sub.14 268 524 ± 17 Perylene C.sub.20H.sub.12 276 497 Picene C.sub.22H.sub.14 366 519 Tetraphenylene C.sub.24H.sub.16 232 578 ± 17 Benz(a)anthracene C.sub.18H.sub.12 158 438 Benzo(a)fluorene C.sub.17H.sub.12 189.5 405 Benzo(c)phenanthrene C.sub.18H.sub.12 159 436 ± 12 Chrysene C.sub.18H.sub.12 254 448 Fluoranthene C.sub.16H.sub.10 110.8 375 Pyrene C.sub.16H.sub.10 145 404 Tetracene C.sub.18H.sub.12 357 437 ± 12 Triphenylene C.sub.18H.sub.12 198 438 Anthracene C.sub.14H.sub.10 218 340 Fluorene C.sub.13H.sub.10 116 295 Phenalene C.sub.13H.sub.10 70-75 290 Phenanthrene C.sub.14H.sub.10 101 332

[0108] Meanwhile, the boiling points and melting points of the polycyclic aromatic hydrocarbons (nanographenes) of Table 1 and Table 2 described above, are based on the database of SciFinder (American Chemical Society; https://scifinder.cas.org/scifinder/), and in a case in which measured values are not available, the boiling points and the melting points are based on calculated values (Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02).

[0109] A mixture such as described above is processed into a bulk material or a wire, and methods and conditions similar to the conventional methods and conditions for superconducting wire may be employed. A bulk material can be produced by performing pressure molding and a heat treatment, and for example, pressing using a conventional mold may be used. The pressure is preferably 100 kg/cm.sup.2 to 300 kg/cm.sup.2. A wire can be produced by, for example, packing a metal tube made of iron or the like with a mixture, processing the composite into a tape or a wire using a rolling roll or the like, and then heat-treating the tape or wire. In regard to the conditions, conditions similar to the conventional conditions may be employed. That is, according to the common usage, production can be carried out by performing a heat treatment under the conditions of temperature and time that are sufficient to obtain an MgB.sub.2 superconducting phase, in an inert atmosphere of argon, vacuum or the like.

[0110] Furthermore, the metal tube used, the heat treatment temperature, and the heat treatment time are not intrinsic to the substitution of B sites with C, and therefore, various metal tubes, heat treatment temperatures, and heat treatment times can be selected.

[0111] The MgB.sub.2 superconductor of the present invention obtained as described above is useful for the capacity enhancement of superconducting linear motor cars, MRI medical diagnostic apparatuses, semiconductor single crystal pulling apparatuses, superconducting energy storages, superconducting rotating machines, superconductor transformers, superconducting cables, and the like.

[0112] Next, an embodiment in which the method for manufacturing a base material powder having a carbon nanocoating layer of the present invention is applied to a method for manufacturing a positive electrode material for a lithium ion battery, will be described. Here, the case of using LiFePO.sub.4 will be described as an example.

[0113] In regard to the LiFePO.sub.4 powder used as a raw material, a powder having purity or a particle size such as those of conventional powders can be used by appropriately regulating the mixing ratio. For example, in regard to the particle size, the average particle size of the LiFePO.sub.4 powder is preferably in the range of 200 nm to 50 μm. Regarding the mixing ratio, it is preferable to mix the powders at a molar ratio in the range of LiFePO.sub.4/C=1.0/0.001 to 1.0/5.0, and it is more preferable that the powders are mixed at a molar ratio in the range of 1.0/0.01 to 1.0/1.0. In a case in which the amount of addition of carbon is less than 0.1 mol %, there is a disadvantage that a satisfactory carbon coating film is not formed, which is not preferable. In a case in which the amount of addition of carbon is more than 500 mol %, there is a disadvantage that a non-uniform thick carbon coating layer is formed, which is not preferable. Then, an appropriate amount of a polycyclic aromatic hydrocarbon is added to the LiFePO.sub.4 powder, and the mixture can be sufficiently mixed in a ball mill or the like.

[0114] Meanwhile, the lithium-containing powder for a positive electrode is not limited to the LiFePO.sub.4 powder, and examples of the lithium-containing powder that are conventionally used include LiCoO.sub.2 powder, LiNiO.sub.2 powder, LiNi.sub.0.5Mn.sub.0.5O.sub.2 powder, LiMn.sub.2O.sub.4 powder, LiMnPO.sub.4 powder, and LiFeSiO.sub.4 powder, as well as LiVPO.sub.4 powder, LiNi.sub.0.5Mn.sub.1.5O.sub.4 powder, V.sub.2O.sub.5 powder, SiO.sub.2 powder, MnO.sub.2 powder, and Li.sub.2S powder.

[0115] In regard to the polycyclic aromatic hydrocarbon (nanographene), various substances among those compounds having a carbocyclic ring or a heterocyclic ring with three or more rings may be considered, and the number of carbon atoms of the polycyclic aromatic hydrocarbon is not particularly limited; however, the number of carbon atoms is preferably in the range of 18 to 50. The polycyclic aromatic hydrocarbon may have various functional groups as long as the operating effects of the present invention are not inhibited, and the polycyclic aromatic hydrocarbon may be appropriately selected in consideration of easy availability, handleability, price, and the like. For example, a typical example of the substituent may be an alkyl group having 1 to 8 carbon atoms, and particularly 1 to 4 carbon atoms, or the like. More specific examples include coronene, anthracene, perylene, and biphenyl listed in Table 1 and Table 2 described above; alkyl-substituted carbocyclic aromatic hydrocarbons; and heterocyclic aromatic hydrocarbons such as thiophene.

[0116] Furthermore, in regard to the amount of addition of the polycyclic aromatic hydrocarbon, it is essential to express the amount of addition in the unit of mol % of carbon described above; however, in regard to the production operation, it is convenient to replace the mol % of carbon with mol % or mass% of the polycyclic aromatic hydrocarbon.

[0117] FIG. 2 is a configuration diagram explaining an apparatus for producing the positive electrode material for a lithium ion battery of the present invention. In the diagram, the production apparatus is configured to include a container 10, a vacuum state retaining means 20, a heating apparatus 30, a heat treatment controlling apparatus 40, and a conveyance apparatus 50.

[0118] The container 10 is a container for accommodating a mixture obtained by adding a polycyclic aromatic hydrocarbon to a base material powder used for a positive electrode material for a lithium ion battery, and the container is formed from a material which is not reactive with the base material powder or the polycyclic aromatic hydrocarbon. Examples of the relevant material include ceramics, metals, and glass.

[0119] The vacuum state retaining means 20 is a means for maintaining the container 10 in a state of accommodating the mixture, to be in a vacuum state. For example, in a case in which the container 10 is made of glass, a vacuum pump, a burner that seals glass, and the like are used. In a case in which the container 10 is made of ceramics, a vacuum container that covers the entirety of the ceramic container 10, and a vacuum pump are used. In a case in which the container 10 is made of a metal, a vacuum container that covers the entirety of the metal container 10, and a vacuum pump may be used, and a vacuum state may be drawn inside the metal container 10 by connecting a vacuum pump to the metal container 10.

[0120] The heating apparatus 30 is an apparatus that heats the container 10 in a state of accommodating the mixture, to a temperature that is higher than or equal to the boiling point of the polycyclic aromatic hydrocarbon and lower than or equal to the (boiling point temperature +300° C.), and that is higher than or equal to the thermal decomposition temperature of the polycyclic aromatic hydrocarbon. For example, the heating apparatus 30 is a combination of refractory bricks and an electric heater.

[0121] The heat treatment controlling apparatus 40 controls the heating time in the heating apparatus 30 to be secured for a predetermined time in which the surface of the base material powder is covered with from 1 layer to 300 layers of carbon atoms. The heat treatment controlling apparatus 40 includes a temperature sensor that measures the internal temperature of the container 10, or a regulator that controls the amount of heat generation of the heating apparatus 30. For the regulator, a temperature regulating system memorizing the heat treatment pattern of the heating apparatus 30 may be used.

[0122] The conveyance apparatus 50 is a mechanism that conveys the container 10 in a vacuum state with the mixture accommodated therein into the heating apparatus 30, and also includes a mechanism that conveys the container 10 after being heat-treated in the heating apparatus 30 to the outside of the heating apparatus 30. For the conveyance apparatus 50, for example, a manipulator or a conveyance robot can be employed.

[0123] Hereinafter, the present invention will be explained in more detail by way of Examples. The present invention is definitely not intended to be limited by the following Examples.

EXAMPLES

Example 1

[0124] FIG. 3 is a configuration diagram of a carbon coating apparatus used in the Examples of the present invention. In the diagram, reference numeral 70 represents a mixed powder of B+coronene, reference numeral 80 represents a glass tube, and reference numeral 90 represents a heat treatment furnace. An amorphous B nanopowder (manufactured by Pavezyum Company, Turkey) having a particle size of about 250 nm and a coronene (C.sub.24H.sub.12) solid powder having a particle size of several millimeters (mm) were weighed such that the amount of carbon with respect to B was 5 atom%. The powders were mixed in a mortar, and the mixture was vacuum sealed in a quartz tube. This was transferred into a heat treatment furnace and was subjected to a heat treatment for 3 hours at 630° C. Furthermore, for a comparison, the same mixture was subjected to a heat treatment for 1 hour at 520° C., which is lower than the boiling point (525° C.) of coronene. An observation of the structure of the B powder obtained after the heat treatment was made by transmission electron microscopy. For a sample that had been heat-treated at 630° C., FIG. 4 presents a transmission electron microscopic image; FIG. 5 presents the analysis results for B (boron mapping diagram); and FIG. 6 presents the analysis results for carbon (carbon mapping diagram).

[0125] It can be seen from FIG. 5 that an amorphous layer having a thickness of 3 nm to 4 nm exists on the surface of the B particles, and it can be seen from FIG. 6 that this layer is a layer containing carbon. FIG. 7 shows the results of an infrared spectroscopic analysis of a vacuum sealed and heat-treated B powder, a mixed powder of B and coronene (non-heat-treated), only B powder, and coronene powder. FIG. 8 shows the results of X-ray diffraction.

[0126] In regard to the infrared spectroscopic analysis, peaks characteristic to the C—H bond of coronene are seen in the sample that was heat-treated at 520° C.; however, these peaks have almost disappeared in the B powder sample that was heat-treated at 630° C. Furthermore, in regard to the X-ray diffraction, peaks of coronene are seen to a slight extent in the sample that was heat-treated at 520° C.; however, the peaks of coronene or the peaks of the oligomers resulting from condensation of coronene are not seen in the sample that was heat-treated at 630° C. The melting point of coronene is 438° C., while the boiling point is 525° C., and it is assumed that at the heat treatment temperature 630° C., coronene is evaporated to become a gas. According to Non-Patent Literature 3, it is reported that in a case in which coronene is vaporized by heating, condensation between coronene occurs in sequence, oligomers are formed while hydrogen is extracted, and thereby carbon is left at or above 600° C. Furthermore, it is also speculated from Non-Patent Literature 4 that a portion of coronene exists on the surface of the B powder particles even at a temperature higher than or equal to the boiling point, is converted to carbon by thermal decomposition, and exists in that state on the surface of B particles. Therefore, it is considered that the deposit layer having a thickness in the order of nanometers on the surface of B particles that were heat-treated at 630° C. in this experiment is a carbon layer.

Example 2

[0127] Next, an MgB.sub.2 superconducting wire was produced by the internal Mg diffusion method using the carbon-coated B powder produced in Example 1. An Mg rod having a diameter of 2 mm was disposed at the center of an iron tube having an outer diameter of 6 mm and an inner diameter of 4 mm, the gaps between the iron tube and the Mg rod were packed with B powder. This was processed into a wire having a diameter of 0.6 mm by means of a grooved roll and die wire drawing. This wire was heat-treated in an argon atmosphere at 657° C. for 8 hours. For a comparison, an MgB.sub.2 wire was produced in the same manner using a carbon-coated B powder produced by the RF plasma method. Table 3 shows the critical current densities at 4.2 K and 10 teslas of the two wires in comparison. Since the B powder according to the present invention does not contain impurities such as CI, the B powder exhibits a higher critical current density than the B powder in the case of the RF plasma method.

TABLE-US-00003 TABLE 3 Substrate (base material) Coating Positive electrode LiVOP.sub.4 C material for Li ion LiFePO.sub.4 C secondary battery Li.sub.2S C LiNi.sub.0.5Mn.sub.1.5PO.sub.4 C

Comparative Example 1

[0128] In regard to the carbon-coated B powder, it has been reported that when a B nanopowder is produced by the RF plasma method using BCl.sub.3 as a raw material, if methane gas is introduced, a carbon-coated B nanopowder is obtained. However, since the carbon-coated B powder produced by this method has Cl incorporated therein as an impurity, in a case in which MgB.sub.2 superconductor is produced using this B powder, there is a problem that the critical current density, which is important for practical use, is low due to the Cl impurity. Furthermore, since the RF plasma method is applied, there is a problem that it is not only difficult to control the amount of carbon coating, but also, mass production is difficult due to high cost. Since the carbon-coated B powder according to the present invention does not contain impurities such as Cl, a higher critical current density is obtained compared to the carbon-coated B powder containing Cl as described above. Furthermore, the present invention has a feature that not only the amount of carbon coating can be controlled simply by varying the ratio between the B and coronene to be incorporated, but also mass production is easy.

Example 3

Novel Production of Base Material Particles Having Carbon Support Layer

[0129] A commercially available LiFePO.sub.4 nanopowder having an average particle size of about 5 μm and a solid coronene (C.sub.24H.sub.12) powder were weighed such that the amount of carbon (C) with respect to LiFePO.sub.4 was 5 mol %, the powders were mixed in a mortar, and the mixture was vacuum sealed in a quartz tube. This was subjected to a heat treatment for one hour at 700° C. An observation of the structure of the LiFePO.sub.4 powder obtained after the heat treatment was made by transmission electron microscopy.

[0130] FIG. 9 is a transmission electron microscopic image of a LiFePO.sub.4 powder that was vacuum heat-treated together with coronene for one hour at 700° C. as an embodiment of the present invention. FIG. 10 to FIG. 14 are diagrams showing the elemental analysis mapping of C, Li, Fe, P, and O, respectively, for the LiFePO.sub.4 powder that was vacuum heat-treated together with coronene for one hour at 700° C.

[0131] It is confirmed from FIG. 9 that a layer having a thickness of 3 nm to 4 nm exists on the surface of LiFePO.sub.4 particles. Also, it is understood from FIG. 10 to FIG. 14 that this layer is a layer containing C. Since the melting point of coronene is 438° C., and the boiling point is 525° C., it may be assumed that at the heat treatment temperature 700° C., coronene does not exist on the surface of the LiFePO.sub.4 particles. According to Non-Patent Literature 1 described above, it is reported that in a case in which coronene is heated, condensation between coronene molecules occurs in sequence, oligomers are formed while hydrogen is extracted, and most of hydrogen is extracted at or above 600° C., so that the layer is converted to carbon.

[0132] FIG. 15 presents a high-resolution transmission electron microscopic image, and it is understood from this that this carbon layer is amorphous. Therefore, it is assumed that the deposit layer having a thickness in the order of nanometers, which covers the surface of LiFePO.sub.4 particles that were heat-treated at 700° C. in this experiment is an amorphous carbon layer. This heat treatment process is considered to involve the following. When the heat treatment temperature rises, first, coronene melts and infiltrates into LiFePO.sub.4 powder, and coronene covers the surface of individual LiFePO.sub.4 powder particles. It is speculated that when this temperature reaches 600° C. or higher, the coronene on the surface of the LiFePO.sub.4 particles is decomposed, and carbon remains in an amorphous form. Since this coronene on the surface of the LiFePO.sub.4 particles becomes a barrier, and aggregation and coarsening of the LiFePO.sub.4 particles is suppressed, as illustrated in FIG. 9, the LiFePO.sub.4 particles can maintain a size at the nanometer level even after a heat treatment. This is a major advantage for an electrode material.

[0133] In amorphous carbon, conductive sp.sup.2 bonds and insulating sp.sup.a bonds are co-present; however, regarding a coating film of an electrode material, it is necessary that conductive sp.sup.2 bonds exist in a large quantity. FIG. 16 shows the Raman scattering shift of a carbon-coated LiFePO.sub.4 powder obtained through a heat treatment at 700° C., and a LiFePO.sub.4 powder that was not carbon-coated. The carbon-coated LiFePO.sub.4 exhibits two peaks (D and G peaks), and it can be seen that these peaks are attributable to the carbon coating layer. From Non-Patent Literature 2, the ratio of sp.sup.2 bonds can be evaluated from the ratio of peak intensities of the D peak and the G peak, I(D)/I(G), and the magnitude of the shift of the G peak based on graphite, can be evaluated, and from the data of FIG. 16, the proportion of sp2 bonds is evaluated to be 80% or more. From the above results, it is considered that the carbon nanofilm produced herein has sufficient electrical conductivity, and is suitable as a carbon film coating for an electrode material.

Comparative Example 1

Novel Production of Base Material Particles Having Carbon Support Layer

[0134] Several methods of coating the surface of LiFePO.sub.4 particles with C have been reported, and one of them is the method of using methanol as described above (Non Patent Literature 6). LiFePO.sub.4 is introduced into a kiln having a rotating function (rotary kiln), and then the temperature is increased to 600° C. Subsequently, methanol vapor is supplied into this furnace by using nitrogen as a carrier gas, and thereby a carbon-supported LiFePO.sub.4/C composite positive electrode material is obtained.

[0135] However, this method requires a rotary kiln, the process is not simple, and the method is not necessarily an inexpensive method. According to one Example of the present invention, a convenient method of vacuum sealing LiFePO.sub.4 and coronene in a glass tube and heating the tube is used, and this method is characterized in that mass production is easily achieved. Furthermore, the present invention also has an advantage that the amount of C coating can be controlled simply by varying the ratio between LiFePO.sub.4 and coronene.

Test Example 1

Production of Electrode Sheet

[0136] Next, the production of an electrode sheet for a lithium ion battery related to an embodiment of the present invention using the base material particles having a carbon support layer produced in Example 3 as a positive electrode material, will be explained. The electrode sheet has a positive electrode sheet and a negative electrode sheet as a pair.

[0137] FIG. 17 is a diagram explaining the particle size distribution of the LiFePO.sub.4 base material particles used for the positive electrode material, and FIG. 17(A) shows the case of the LiFePO.sub.4 base material particles having no carbon support layer (hereinafter, may be described as “LFP”) as Comparative Example 2, while FIG. 17(B) shows the case of the LiFePO.sub.4 base material particles having a carbon support layer (hereinafter, may be described as “c-LFP”) as Example 3. The particle size distribution of the LFP is similar to the bell-shaped distribution illustrated in FIG. 17(A), and the average particle size is 5.0 μm, while the maximum particle size is 60 μm. Coarse particles having a size that is about twelve times the average particle size are co-present. The particle size distribution of the c-LFP is similar to the bell-shaped distribution illustrated in FIG. 17(B), and the average particle size is 5.8 μm, while the maximum particle size is 17 μm. Aggregates or lumps are co-present.

[0138] Next, positive electrode sheets were produced using the LFP base material particles of Comparative Example 2 and the c-LFP base material particles of Example 3.

[0139] With regard to the LFP composition, LFP powder as a positive electrode material, acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in water, as a mixture composition, such that the mass ratio of those components would be 86:7:7, and thus a paste for forming a positive electrode active material layer was prepared. Upon the preparation of this paste, normal methylpyrrolidone (NMP) was used as a solvent, and the paste contained 50.7% of non-volatile components (NV).

[0140] With regard to the c-LFP composition, the c-LFP powder as a positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in water, as a mixture composition, such that the mass ratio of those components would be 86:7:7, and thus a paste for forming a positive electrode active material layer was prepared.

[0141] Each of the pastes of these compositions was applied on one surface of a positive electrode current collector (aluminum foil) and dried, and thereby a positive electrode active material layer was formed on one surface of the positive electrode current collector. For the application process, a thin film was produced using a doctor blade, and the gap was 350 μm. The amount of coating of the paste for forming a positive electrode active material layer was regulated such that the amount of coating after drying would be about 18 mg/cm.sup.2 (on the basis of the solid content).

[0142] Regarding the negative electrode substrate, a graphite composition was selected. As a mixture composition for a negative electrode sheet, graphite powder as a negative electrode active material, carboxymethyl cellulose (CMC) as a thickening material, and a styrene-butadiene rubber (SBR) as a binder were mixed in water such that the mass ratio of those components would be 97.5:1.5:1, and thus a paste for forming a negative electrode active material layer was prepared. Upon the preparation of this paste, water (H.sub.2O) was used as a solvent, and the paste contained 50.7% of non-volatile components (NV).

[0143] The paste of this composition was applied on one surface of a negative electrode current collector (copper foil) and dried, and thereby, a negative electrode active material layer was formed on one surface of the negative electrode current collector. For the application process, a thin film was produced using a doctor blade, and the gap was 180 μm. The amount of coating of the paste for forming a positive electrode active material layer was regulated such that the amount of coating after drying would be about 7 mg/cm.sup.2 (on the basis of the solid content).

Test Example 2

Production of Lithium Ion Battery

[0144] Lithium secondary batteries (coin cells) were constructed using the positive electrode sheets of the LFP composition and the c-LFP composition obtained in Test Example 1. The production of the lithium secondary batteries was carried out as follows.

[0145] FIG. 18 is a cross-sectional diagram schematically illustrating a test lithium secondary battery (coin cell) related to one Test Example of the present invention. In the diagram, a coin cell 60 is a coin cell intended for an evaluation of the charge-discharge performance, and is, for example, a container made of stainless steel, having a diameter of 20 mm and a thickness of 3.2 mm (2032 type). A positive electrode (working electrode) 61 is an electrode produced by punching the positive electrode sheet described above into a circular shape having a diameter of 16 mm. A negative electrode (opposite electrode) 62 is an electrode produced by punching the negative electrode sheet described above into a circular shape having a diameter of 16 mm. A separator 63 is a porous polypropylene sheet having a diameter of 22 mm and a thickness of 0.02 mm, and is impregnated with a liquid electrolyte. A gasket 64 maintains a container (negative electrode terminal) 65 and a lid (positive electrode terminal) 66 in an insulated state at predetermined positions. Meanwhile, in the coin cell 60, a non-aqueous liquid electrolyte is incorporated together with the positive electrode 61, the negative electrode 62, and the separator 63.

[0146] Here, regarding the non-aqueous liquid electrolyte, a product obtained by incorporating LiPF.sub.6 as a supporting salt at a concentration of about 1 mol/liter into a mixed solvent including ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7, was used. Thereafter, the coin cell was subjected to an initial charge-discharge treatment (conditioning) by a conventional method, and thus a test lithium secondary battery was obtained.

[0147] FIG. 19 is a diagram explaining the details of the trial manufacture specifications related to the coin cell illustrated in FIG. 18, and showing the mechanical design values of the positive electrode and the negative electrode. In regard to the positive electrode of the LFP composition, the thickness of the Al foil is 20 μm, the thickness of the electrode plate is 123 μm, the coating width is 16φ, the coating area is 2.0 cm.sup.2, the mixture density is 1.8 g/cm.sup.3, the mixture surface density is 18.3 mg/cm.sup.2, the specific capacity at the initial charge is 160 (mAh/g), and the discharge specific capacity is 150 (mAh/g). In regard to the positive electrode of the c-LFP composition, the specifications are the same as those of the positive electrode of the LFP composition, except that the thickness of the electrode plate is 116 μm, the mixture density is 1.8 g/cm.sup.3, the mixture surface density is 18.1 mg/cm.sup.2.

[0148] In regard to the negative electrode of the LFP composition, the thickness of the Cu foil is 18 μm, the thickness of the electrode plate is 70 μm, the coating width is 16φ, the coating area is 2.0 cm.sup.2, the mixture density is 1.5 g/cm.sup.3, the mixture surface density is 7.6 mg/cm.sup.2, the use capacity at the initial charge is 389 (mAh/g), and the discharge use capacity is 350 (mAh/g). In regard to the negative electrode of the c-LFP composition, the specifications are the same as those of the negative electrode of the LFP composition, except that the mixture surface density is 7.7 mg/cm.sup.2.

[0149] FIG. 20 is a diagram explaining the details of a test product produced under the trial manufacture specifications related to the coin cell illustrated in FIG. 19. Two test products of LFP-01 and LFP-02 were produced as coin cells of the LFP composition. The positive electrode weight of LFP-01 was 47.85 mg, the negative electrode weight was 47.69 mg, the positive electrode basis weight was 18.401 mg/cm.sup.2, the negative electrode basis weight is 7.627 mg/cm.sup.2, the A/C ratio was 1.14, and the design capacity was 4.77 mAh. The specifications of LFP-02 are also the same as those of LFP-01. Furthermore, also for CLFP-01 and CLFP-02, the values illustrated in FIG. 20 are obtained. The third values described in bold letters are respectively an average value of LFP-01 and LFP-02 and an average value of CLFP-01 and CLFP-02.

Test Example 3

Test for Charge-Discharge Characteristics of Lithium Ion Battery

[0150] Each of the test lithium secondary batteries obtained as described above was subjected to a charge-discharge test. In a discharge capacity test, the battery was charged at a constant current (2.25 mA) under the temperature conditions of room temperature, 21° C., until the voltage between terminals reached 4.0 V, and then was charged for 1.5 hours at a constant voltage of 4.0 V. The battery obtained after such CC-CV charging was discharged at a constant current (0.90 mA) under the temperature conditions of room temperature, 21° C., until the voltage between terminals reached 2.0 V, and the battery capacity at that time was measured.

[0151] The results are presented in FIG. 21 and FIG. 22. FIG. 21 is a diagram explaining the discharge capacity characteristics of the test product related to one Test Example of the present invention. In the coin cell of the LFP composition, the specific capacity is about 48 mAh/g, and the ratio with respect to the design value is only about 32%. On the contrary, in the coin cell of the c-LFP composition, the specific capacity is about 96 mAh/g, and the ratio with respect to the design value is increased to about 64%.

[0152] FIG. 22 is a graph showing a charge-discharge curve explaining the discharge capacity characteristics of a test product related to one Test Example of the present invention. In the coin cell of the c-LFP composition, since LiFePO.sub.4 base material particles having a carbon support layer are used, the discharge capacity is increased to about twice compared to the coin cell of the LFP composition.

[0153] From these results, it was confirmed that when a LiFePO.sub.4 positive electrode sheet having a carbon support layer on the surface of the positive electrode active material layer is used, a lithium secondary battery having excellent charge-discharge characteristics can be constructed.

[0154] Particular embodiments of the present invention have been illustrated and explained; however, it is clearly to those skilled in the art that various other variations and modifications can be made without deviating from the spirit and the scope of the present invention. Therefore, all those variations and modifications within the scope of the present invention are intended to be handled in the appended claims.

[0155] For example, in regard to the method for manufacturing a superconductor, the aromatic hydrocarbon to be used may be, in addition to coronene, any aromatic hydrocarbon that is vaporized by heating and undergoes polymerization/condensation. Furthermore, in regard to the amount of addition of the aromatic hydrocarbon, since the amount of carbon adhering to the surface of boron powder varies with the amount of addition, the amount of addition can be changed as necessary. Furthermore, in regard to the heat treatment temperature, coronene undergoes polymerization and condensation at or above 600° C., and in order to obtain almost only carbon, it is necessary to perform a heat treatment at or above 600° C. In regard to other aromatic hydrocarbons, since each of the aromatic hydrocarbons has an intrinsic temperature at which polymerization or condensation proceeds, it is necessary to perform a heat treatment at or above the temperature.

[0156] Furthermore, regarding the aromatic hydrocarbon used according to the embodiments of the method for manufacturing a positive electrode material for a lithium ion battery of the present invention, coronene is taken as an example; however, the present invention is not intended to be limited to this, and any aromatic hydrocarbon which is vaporized by heating and undergoes polymerization/condensation may be used, in addition to coronene. Furthermore, in regard to the amount of addition of the aromatic hydrocarbon, since the amount of carbon adhering to the surface of LiFePO.sub.4 powder varies with the amount of addition, the amount of addition can be changed as necessary. Furthermore, in regard to the heat treatment temperature, coronene undergoes polymerization and condensation at or above 600° C., and in order to obtain almost only carbon, it is necessary to perform a heat treatment at or above 600° C. However, in regard to other aromatic hydrocarbons, since each of the aromatic hydrocarbons has an intrinsic temperature at which polymerization or condensation proceeds, it is necessary to perform a heat treatment at or above the temperature.

[0157] Furthermore, in regard to the lithium ion battery of the present invention, a coin cell type Example has been described; however, the lithium ion battery may have a shape other than a coin cell type that is generally used by those skilled in the art, or may be of a wound electrode body type or a laminated electrode body type.

INDUSTRIAL APPLICABILITY

[0158] According to the method for manufacturing a base material powder having a carbon nanocoating layer of the present invention, it is possible to conveniently provide a carbon coating layer having a thickness at a nanometer level on various substrates (base materials) only by heat-treating a base material and a polycyclic aromatic hydrocarbon together in a vacuum, and the production method can be applied to MgB.sub.2 superconductor, lithium ion batteries, photocatalysts, tribology, and the like.

[0159] According to the method for manufacturing MgB.sub.2 superconductor of the present invention, addition of a polycyclic aromatic hydrocarbon (nanographene) to a MgB.sub.2 superconducting wire with excellent uniformity can be realized, and a MgB.sub.2 superconducting wire having high critical current density (Jc) characteristics and a critical current density (Jc) with less fluctuation can be provided. The MgB.sub.2 superconductor thus produced is suitable for the use in superconducting linear motor cars, MRI medical diagnostic apparatuses, semiconductor single crystal pulling apparatuses, superconducting energy storages, superconducting rotating machines, superconducting transformers, superconducting cables, and the like.

[0160] According to the method for manufacturing a positive electrode material for a lithium ion battery of the present invention, it is possible to conveniently provide a carbon coating layer having a thickness at a nanometer level on various substrates (base materials), only by heat-treating a base material and a polycyclic aromatic hydrocarbon together in a vacuum, and this method can be applied to lithium ion batteries, and the like.

[0161] Furthermore, according to the lithium ion battery of the present invention, by using a lithium-containing positive electrode sheet such as a LiFePO.sub.4 positive electrode sheet having a carbon support layer on the surface of a powder of a positive electrode active material, a lithium secondary battery having excellent charge-discharge characteristics can be constructed.

REFERENCE SIGNS LIST

[0162] FIGS. 2, 3, and 18

[0163] 10 CONTAINER

[0164] 20 VACUUM STATE RETAINING MEANS

[0165] 30 HEATING APPARATUS

[0166] 40 HEAT TREATMENT CONTROLLING APPARATUS

[0167] 50 CONVEYANCE APPARATUS

[0168] 60 COIN CELL

[0169] 61 POSITIVE ELECTRODE (WORKING ELECTRODE)

[0170] 62 NEGATIVE ELECTRODE (OPPOSITE ELECTRODE)

[0171] 63 SEPARATOR

[0172] 64 GASKET

[0173] 65 CONTAINER (NEGATIVE ELECTRODE TERMINAL)

[0174] 66 LID (POSITIVE ELECTRODE TERMINAL)

[0175] 70 B+CORONENE MIXED POWDER

[0176] 80 GLASS TUBE

[0177] 90 HEAT-TREATMENT FURNACE