JP2011258348A - Negative electrode for lithium secondary battery, lithium secondary battery and method of manufacturing negative electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve battery characteristics of an electrode formed by a film-shaped carbon material.SOLUTION: A negative electrode for a lithium secondary battery includes a collector 22 and an active material film 24. The active material film 24 is comprised of an amorphous carbon film in which an atom ratio Csp/Cspsatisfies 0<Csp/Csp≤0.25, where Cspis defined as a ratio of the number of atoms of carbon having an sphybrid orbit to the number of atoms of total carbon formed as a deposition film on the collector 22, and Cspis defined as a ratio of the number of atoms of carbon having an sphybrid orbit to the number of atoms of total carbon. Furthermore, it is more preferable that the active material film 24 contains nitrogen at 20 atom% or less and hydrogen at 15 atom% or less. Moreover, it is preferable for the active material film to have an inter-layer distance d of a carbon layer within a range of 0.35 nm<d<0.45 nm, which is calculated from a broad diffraction peak that appears within a range where 2θ in an X-ray diffraction measurement is 20° or more and 25° or less.

Description

  The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing a negative electrode for a lithium secondary battery.

  Conventionally, as a negative electrode for a lithium secondary battery, a flat thin film portion formed so as to cover the surface of a substrate, and a hexagonal mesh surface structure that is vertically arranged with respect to the flat thin film portion and regularly arranged There has been proposed a method in which a graphite thin film including an upstanding thin film portion is formed on a molybdenum or single crystal silicon substrate surface by a plasma jet method (see, for example, Patent Document 1).

JP 9-315808 A

  However, the electrode of Patent Document 1 described above uses graphite as a thin film, and for example, load characteristics such as rapid charging are not yet sufficient, and it has been demanded to further improve battery characteristics.

  The present invention has been made in view of such problems, and in an electrode in which a carbon material is formed in a film shape, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a lithium secondary battery that can further improve battery characteristics. The main object is to provide a method for producing a negative electrode for a secondary battery.

As a result of diligent research to achieve the above-described object, the present inventors have determined that the ratio of the number of carbon atoms having sp ² hybrid orbits to the total number of carbon atoms is Csp ^2, and the sp ³ hybridization to the total number of carbon atoms. If the atomic ratio Csp ³ / Csp ² is within a suitable range when the ratio of the number of carbon atoms having orbits is Csp ³ , the charge / discharge efficiency, load characteristics, and charge / discharge durability of an electrode formed of a carbon material in a film shape The inventors have found that the battery characteristics such as the property can be further improved, and have completed the present invention.

That is, the negative electrode for a lithium secondary battery of the present invention, current collector and, Csp the ratio of the number of atoms of carbon having sp ² hybrid orbital for the number of atoms of the total carbon formed as a deposited film on the current collector ² And an atomic ratio Csp ³ / Csp ² where the ratio of the number of carbon atoms having sp ³ hybrid orbits to the total number of carbon atoms is Csp ³ is 0 <Csp ³ / Csp ² ≦ 0.25 And an active material film made of a carbonaceous film.

  The lithium secondary battery of the present invention includes the above-described negative electrode for a lithium secondary battery, a positive electrode having a positive electrode active material, an ion conductive medium that is interposed between the positive electrode and the negative electrode, and conducts lithium ions. , With.

The method for producing a negative electrode for a lithium secondary battery according to the present invention includes at least one of a carbocyclic compound gas containing carbon having sp ² hybrid orbitals and a carbocyclic compound gas containing carbon having sp ³ hybrid orbitals. Is introduced into a reaction vessel in which a current collector is arranged and discharged, so that the ratio of the number of carbon atoms having sp ² hybrid orbits to the total number of carbon atoms is Csp ² and the total carbon atoms The current ratio so that the atomic ratio Csp ³ / Csp ² is in the range of 0 <Csp ³ / Csp ² ≦ 0.25, where Csp ³ is the ratio of the number of carbon atoms having sp ³ hybrid orbitals to the number. Forming an active material film made of an amorphous carbon film on the body.

The present invention can further improve battery characteristics. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, in general, amorphous carbon, which is a negative electrode active material, has a gradient in potential shape during charge / discharge compared to a graphite negative electrode, and its operating potential is far from the lithium metal deposition potential. For this reason, it is considered to be a negative electrode active material that is safer than graphite negative electrodes in large applications and that can easily charge and discharge a large current. On the other hand, it could not be said that the charge / discharge efficiency and durability performance of the graphite negative electrode were sufficient. In the present invention, the atomic ratio Csp ³ / Csp ² between the atomic ratio Csp ^{2 of} carbon having sp ² hybrid orbital and the atomic ratio Csp ^{3 of} carbon having sp ³ hybrid orbital in the amorphous carbon film is preferably in the preferred range. (0 <Csp ³ / Csp ² ≦ 0.25). In this regard, for example, it is considered that delocalization of π electrons is promoted and high conductivity is exhibited when the atomic ratio Csp ^{2 of} carbon having sp ² hybrid orbits in the amorphous carbon film is increased. In addition, when the atomic ratio Csp ^{3 of} carbon having sp ³ hybrid orbits in the amorphous carbon film increases, it is considered that the distance between carbon layers formed by carbon having sp ² hybrid orbitals is further increased. In this way, when the atomic ratio Csp ³ / Csp ² is in the range of 0 <Csp ³ / Csp ² ≦ 0.25, the lithium ion conduction path is ensured in the film without deficiency, so that excellent chargeability is achieved. It is presumed that the discharge efficiency is exhibited and the charge / discharge durability characteristics are excellent. In addition, since it is amorphous carbon, the potential shape at the time of charging and discharging is inclined compared to graphite, and its operating potential is far from the lithium metal deposition potential, and it is assumed that the load characteristics are better. The

1 is a configuration diagram showing an example of a schematic configuration of a coin-type battery 10. The block diagram which shows an example of the outline of a structure of the chemical vapor deposition apparatus. An example of the 13C-NMR spectrum of an amorphous carbon film. The X-ray-diffraction measurement result of an amorphous carbon film (Experimental example 1). The charge / discharge curve of Experimental Example 1. The charge / discharge curve of Experimental Example 7. The discharge curve of the load characteristic test of Experimental example 1. The discharge curve of the load characteristic test of Experimental example 6.

  Next, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an example of a schematic configuration of a coin-type battery 10 according to an embodiment of the present invention. FIG. 2 is a configuration diagram illustrating an example of a schematic configuration of the chemical vapor deposition apparatus 30. A lithium secondary battery of the present invention includes the negative electrode for a lithium secondary battery of the present invention, a positive electrode having a positive electrode active material, and an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions. Yes. A coin-type battery 10 as a lithium secondary battery of the present invention shown in FIG. 1 includes a cup-shaped battery case 11, a positive electrode 12 provided inside the battery case 11, and a separator 14 with respect to the positive electrode 12. A non-aqueous electrolyte 17 as an ion conducting medium containing a supporting salt, a gasket 15 formed of an insulating material, and a gasket disposed in an opening of the battery case 11. And a sealing plate 16 for sealing the battery case 11 via 15. Here, the negative electrode 20 is a negative electrode for a lithium secondary battery according to the present invention, and is an active current comprising a conductive current collector 22 and an amorphous carbon film formed by vapor deposition on the current collector 22. And a material film 24.

The negative electrode for a lithium secondary battery of the present invention is to a current collector, and Csp ² the ratio of the number of atoms of carbon having sp ² hybrid orbital for the number of atoms of the total carbon formed as a deposited film on the current collector on the body all Amorphous carbon in which the atomic ratio Csp ³ / Csp ² satisfies 0 <Csp ³ / Csp ² ≦ 0.25 when the ratio of the number of carbon atoms having sp ³ hybrid orbits to the number of carbon atoms is Csp ³ And an active material film made of a film. In this negative electrode for a lithium secondary battery, an active material film is formed as a deposited film on a current collector. That is, the active material film is formed on the current collector without containing the binder component. For example, without adding other components such as a binder as compared with a coated electrode in which a negative electrode active material is coated on a current collector or a crimped electrode in which a negative electrode active material is pressure-bonded on a current collector. Since the electrode can be formed, the purity of the active material film can be further increased, and the battery characteristics can be further improved. In addition, since the active material film is made of an amorphous carbon film, for example, the potential shape at the time of charging / discharging is inclined as compared with graphite, and the operating potential is away from the lithium metal deposition potential. In comparison, the safety is high and the load characteristics are better. Note that this active material film is preferably made of only an amorphous carbon film in consideration of purity, but may contain materials other than the amorphous carbon film. The amorphous carbon film may have a layered structure.

  In the negative electrode for a lithium secondary battery of the present invention, the current collector is, for example, copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al—Cd alloy, or the like. For example, the surface of copper or the like treated with carbon, nickel, titanium, silver, or the like can be used for the purpose of improving the conductivity, conductivity, and reduction resistance. For these, the surface can be oxidized. Examples of the shape of the current collector include a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded shape, a lath body, a porous body, a foamed body, and a formed body of fiber groups. The thickness of the current collector is, for example, 1 to 500 μm.

In the negative electrode for a lithium secondary battery of the present invention, the atomic ratio Csp ³ / Csp ² of the active material film (amorphous carbon film) satisfies 0 <Csp ³ / Csp ² ≦ 0.25. When the atomic ratio Csp ³ / Csp ² exceeds the value 0, the distance between the carbon layers formed by the carbon having sp ² hybrid orbitals is further increased, and the lithium ion conduction path is ensured without deficiency in the film. It is inferred to show charge / discharge efficiency and charge / discharge durability characteristics. When the atomic ratio Csp ³ / Csp ² is 0.25 or less, the atomic ratio Csp ^{2 of} carbon having sp ² hybrid orbitals in the amorphous carbon film increases, and the delocalization of π electrons is promoted and is high. It is presumed to show conductivity. The atomic ratio Csp ³ / Csp ² is more preferably in the range of 0.04 ≦ Csp ³ / Csp ² ≦ 0.235, and further preferably in the range of 0.04 ≦ Csp ³ / Csp ² ≦ 0.05. Similarly, the atomic ratio Csp ² is preferably in the range of 80 at% or more and less than 100 at%, preferably in the range of 82 at% or more and 96 at% or less, and more preferably in the range of 95 at% or more and 96 at% or less. preferable. The atomic ratio Csp ³ is preferably in the range of 4 at% to less than 20 at%, preferably in the range of 4 at% to 18 at%, and more preferably in the range of 4 at% to 5 at%. Note that “the atomic ratio Csp ^{2 of} carbon having sp ² hybrid orbits with respect to the total number of carbon atoms” and “atomic ratio Csp ^{3 of} carbon having sp ³ hybridizing orbits with respect to the total number of carbon atoms” are sp ² hybrids. The ratio of the total number of carbon atoms with orbital and the total number of carbon atoms with sp ³ hybridized orbital is the total number of carbon atoms. In addition, the number of carbon atoms having each hybrid orbital is a value measured using a high-power decoupling method (HD-MAS-NMR) in which solid angle NMR performs quantitative magic angle spinning.

  In the negative electrode for a lithium secondary battery of the present invention, the active material film preferably contains 20 at% or less of nitrogen. Nitrogen atoms act as n-type donors in the amorphous carbon film and effectively excite the electrons bound to the donor level to the conduction band. The conductivity is further increased, which is preferable. On the other hand, when the nitrogen content exceeds 20 at%, the termination of molecules is promoted by the formation of C≡N bonds (triple bonds), and therefore the nitrogen content is preferably 20 at% or less. Further, the nitrogen content is more preferably 10 at% or less, and further preferably 5 at% or less. Here, the nitrogen content ratio at% refers to the ratio of carbon (C), nitrogen (N), and hydrogen (H) to the total number of atoms. The number of atoms of carbon (C) and nitrogen (N) can be quantified by Rutherford backscattering method (RBS). The number of atoms of carbon (C) and nitrogen (N) can be measured by, for example, electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES). . The number of atoms of hydrogen (H) can be quantified by elastic recoil detection method (ERDA).

In the negative electrode for a lithium secondary battery of the present invention, the active material film preferably contains 15 at% or less of hydrogen. By reducing the hydrogen content in the amorphous carbon film, molecular termination due to C—H bonds (σ bonds) is suppressed, and it is assumed that π electrons increase and show high conductivity. Is done. When charging / discharging as a negative electrode active material in a non-aqueous electrolyte, particularly when the hydrogen content exceeds 15 at%, the hydrogen content may cause an irreversible reaction, and the load characteristics and charge / discharge durability characteristics deteriorate. It is thought that. Further, it is known that when a carbon material is used in a non-aqueous electrolyte, a surface film is formed in a low potential region below 1 V of lithium reference, and this greatly affects battery characteristics. It is considered that the amount of hydrogen and nitrogen contained in the amorphous carbon film affect the properties of the surface coating, and in particular, durability performance and load by making the amount of hydrogen 15 at% or less and the amount of nitrogen 20 at% or less. It seems that the film is suitable for the characteristics. For the above reason, the hydrogen amount is more preferably 15 at% or less, and further preferably 10 at% or less. Further, the amount of hydrogen is preferably 1 at% or more, and more preferably 5 at% or more. A hydrogen amount of 1 at% or more is preferable because the atomic ratio Csp ^{3 of} carbon having sp ³ hybrid orbitals is relatively increased and the distance between carbon layers formed by carbon having sp ² hybrid orbitals is further increased.

  In the negative electrode for a lithium secondary battery of the present invention, the active material film has a carbon layer interlayer distance d calculated from a broad diffraction peak appearing in the range of 2θ of 20 ° to 25 ° in X-ray diffraction measurement. It is preferably in the range of 0.35 nm <d ≦ 0.51 nm, more preferably in the range of 0.35 nm <d <0.45 nm, and in the range of 0.37 nm <d <0.41 nm. Further preferred. When X-ray diffraction measurement is performed with a Cu tube, the broad diffraction peak that appears in the range where the angle 2θ is 20 ° or more and 25 ° or less corresponds to the (002) plane of the graphite skeleton defined by the hexagonal system, The average surface distance can be calculated by the Bragg equation. This average interplanar spacing corresponds to the interlayer distance d of graphite having a layer structure, and is known to be 0.34 nm in the case of graphite. When the interlayer distance d of the amorphous carbon film is 0.51 nm or less, the interaction between π electrons between the surfaces increases and the conductivity is further improved due to the decrease in the surface spacing. On the other hand, if the interlayer distance d equivalent to graphite is 0.34 nm, the characteristics of graphite as the negative electrode active material will appear, and the operating potential will be lowered to near lithium reference 0.1 V, which is not preferable. For this reason, when the interlayer distance d exceeds 0.35 nm and is 0.51 nm or less, and further below 0.45 nm, it is optimized from the viewpoint of both conductivity and lithium ion conductivity. It is assumed that excellent load characteristics and charge / discharge durability characteristics can be obtained.

Next, the manufacturing method of the negative electrode for lithium secondary batteries is demonstrated. The method for producing a negative electrode for a lithium secondary battery of the present invention includes at least one of a carbocyclic compound gas containing carbon having sp ² hybrid orbital and a carbocyclic compound gas containing carbon having sp ³ hybrid orbital. By introducing the source gas into a reaction vessel in which a current collector is arranged and discharging, the ratio of the number of carbon atoms having sp ² hybrid orbits to the total number of carbon atoms is Csp ² and the total number of carbon atoms is sp ³ atomic ratio Csp ³ / Csp ² when the ratio of the number of atoms of carbon bearing the hybrid orbital was Csp ³ is, 0 <Csp ³ / Csp in on the current collector such that the range of ² ≦ 0.25 Forming an active material film made of an amorphous carbon film. In this step, it is preferable that a raw material gas further containing at least one of carbocyclic compound gas containing nitrogen and carbon and nitrogen gas is introduced into the reaction vessel to form an active material film containing 20 at% or less of nitrogen. By so doing, higher charge / discharge efficiency and charge / discharge durability characteristics can be obtained. In addition, in the manufacturing method of the negative electrode for lithium secondary batteries, you may add suitably the process used as the aspect of the negative electrode for lithium secondary batteries mentioned above.

  In the negative electrode for a lithium secondary battery, the amorphous carbon film can be formed by a known CVD method or PVD method such as a plasma CVD method, an ion plating method, or a sputtering method. As represented by the sputtering method, since the PVD method has directivity in film formation, it is necessary to arrange a plurality of targets in the apparatus, or to rotate the substrate to be formed, etc. The structure of the film forming apparatus becomes complicated and expensive. On the other hand, since the plasma CVD method uses a reactive gas to form a film, it can form a film uniformly regardless of the shape of the substrate, and the structure of the film forming apparatus is simple and inexpensive, which is preferable. Examples of the plasma CVD method include a high frequency plasma CVD method using high frequency discharge, a microwave plasma CVD method using microwave discharge, and a direct current plasma CVD method using direct current discharge. Of these, the DC plasma CVD method is suitable. According to the direct current plasma CVD method, the film forming apparatus may be composed of a vacuum furnace and a direct current power source, and film formation can be easily performed on substrates having various shapes. Further, even when the reaction gas concentration is increased and the film forming pressure is set to 100 Pa or more, stable discharge can be obtained. Hereinafter, the amorphous carbon film forming method of the present invention will be described as a preferred embodiment using the plasma CVD method.

  As shown in FIG. 2, the chemical vapor deposition apparatus 30 is configured as a DC plasma CVD film forming apparatus that applies a DC voltage to form an amorphous carbon film on the surface of a processing target 31 (current collector). . The chemical vapor deposition apparatus 30 includes a chamber 32 capable of sealing a processing space 32 a containing a processing target 31, a base 34 on which the processing target 31 has conductivity and a processing space 32 a inside the chamber 32. A gas introduction pipe 36 for introducing a raw material gas used for film treatment, a gas exhaust pipe 38 for depressurizing the processing space 32a, and an application device 40 for applying a DC voltage to the process target 31 via the base 34. Yes. A gas cylinder 44 is connected to the gas introduction pipe 36 via a valve 42. The source gas can be introduced from the gas cylinder 44 into the processing space 32a through the gas introduction pipe 36. The gas exhaust pipe 38 is connected to a decompression device 50 such as a rotary pump 48 and a diffusion pump 49 via a valve 46. The decompression device 50 can decompress the processing space 32 a through the gas exhaust pipe 38. Since this chemical vapor deposition apparatus 30 forms a film by applying a DC voltage, it is possible to produce an active material film having a relatively large area.

  Using this chemical vapor deposition apparatus 30, an amorphous carbon film is formed on the surface of the current collector as the processing object 31. First, the processing target 31 is placed on the base 34, the chamber 32 is sealed, and the decompression device 50 is operated to exhaust the gas in the processing space 32a. When forming an amorphous carbon film on the processing object 31, first, nitrogen gas or the like may be introduced into the chamber 32 from the gas introduction pipe 36. Next, when a DC voltage is applied between the base plate 34 and the conductive anode plate provided inside the chamber 32 by the applying device 40, discharge starts. At this time, a DC voltage may be applied, and the temperature of the process target 31 may be raised to a predetermined film formation temperature by ion bombardment. The film forming temperature is preferably in the range of 300 ° C. to 700 ° C., more preferably in the range of 450 ° C. to 650 ° C., and further in the range of 500 ° C. to 600 ° C. preferable. When the film forming temperature is in the range of 300 ° C. or higher and 700 ° C. or lower, it is preferable because it is easy to suppress peeling of the film or to prevent occurrence of granulation.

Subsequently, in the chemical vapor deposition apparatus 30, the source gas is introduced from the gas introduction pipe 36 into the processing space 32 a. The source gas contains at least one of a carbocyclic compound gas containing carbon having sp ² hybrid orbitals and a carbocyclic compound gas containing carbon having sp ³ hybrid orbitals. Examples of the carbocyclic compound gas containing carbon having an sp ² hybrid orbital include toluene, xylene and the like in addition to aromatic compounds such as benzene and naphthalene. Examples of the carbocyclic compound gas containing carbon having sp ³ hybrid orbitals include toluene, xylene, ethylbenzene, cyclohexene, and the like. The source gas preferably further contains at least one of a carbocyclic compound gas containing nitrogen and carbon and a nitrogen gas. In this way, nitrogen can be introduced into the amorphous carbon film. The carbocyclic compound gas containing nitrogen and carbon includes nitrogen-containing heterocyclic compounds such as pyridine, pyrazine, pyrrole, imidazole and pyrazole, as well as nitrogen-containing functional groups connected to aromatic compounds such as aniline and azobenzene. Etc. For example, a raw material gas further containing at least one of a carbocyclic compound gas containing nitrogen and carbon and a nitrogen gas may be introduced into the chamber 32 to form an active material film containing 20 at% or less of nitrogen. If it carries out like this, a battery characteristic can be improved further. This source gas may contain an inert gas. As the inert gas, for example, a rare gas such as Ar or He can be used. Thereafter, when a DC voltage is applied between the anode plate provided inside the chamber 32 and the base 34, discharge starts and an amorphous carbon film is formed on the surface of the processing object 31.

  In this method for manufacturing a negative electrode for a lithium secondary battery, the flow rate of the entire raw material gas can be, for example, 5 sccm or more and less than 80 sccm, and more preferably 20 sccm or more and 60 sccm or less. Here, the flow rate (sccm) refers to a cc / min value when the standard temperature is 25 ° C. Among these, the flow rates of the carbocyclic compound gas and the carbocyclic compound gas are preferably 5 sccm or more and 50 sccm or less, and more preferably 10 sccm or more and 20 sccm or less. The flow rate of nitrogen gas supplied when nitrogen is introduced into the amorphous carbon film is preferably 5 sccm or more and 50 sccm or less, and more preferably 10 sccm or more and 20 sccm or less. The flow rate of the inert gas is preferably 5 sccm or more and 50 sccm or less, and more preferably 10 sccm or more and 20 sccm or less. The flow rate of the inert gas is preferably about twice the flow rates of the carbocyclic compound gas and the carbocyclic compound gas. When film formation is performed at such a flow rate, a more preferable amorphous carbon film can be formed. An amorphous carbon film can be formed by such a manufacturing method.

The positive electrode of the lithium secondary battery of the present invention is, for example, a mixture of a positive electrode active material, a conductive material, and a binder, and an appropriate solvent is added to form a paste-like positive electrode material, which is applied to the surface of the current collector. It may be dried and compressed to increase the electrode density as necessary. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _(1-x) MnO ₂ (0 <x <1, etc., the same shall apply hereinafter), Li _(1-x) Mn Lithium manganese composite oxide such as ₂ O ₄ , lithium cobalt composite oxide such as Li _(1-x) CoO ₂ , lithium nickel composite oxide such as Li _(1-x) NiO ₂ , lithium such as LiV ₂ O ₃ Vanadium composite oxides, transition metal oxides such as V ₂ O _{5, and the} like can be used. Of these, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiV ₂ O ₃ are preferable. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. About the shape of an electrical power collector, the structure similar to a negative electrode can be utilized.

As the ion conduction medium of the lithium secondary battery of the present invention, a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, or the like can be used. Examples of the solvent for the nonaqueous electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t -Chain carbonates such as butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane and diethoxyethane, nitriles such as acetonitrile and benzonitrile,
Examples include furans such as tetrahydrofuran and methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. The cyclic carbonates are considered to have a relatively high relative dielectric constant and increase the dielectric constant of the electrolytic solution, and the chain carbonates are considered to suppress the viscosity of the electrolytic solution.

The supporting salt contained in the lithium secondary battery of the present invention is, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Examples include LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. This electrolyte salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration of the electrolyte salt is 0.1 mol / L or more, a sufficient current density can be obtained, and when the concentration is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

  Further, instead of the liquid ion conducting medium, a solid ion conducting polymer may be used as the ion conducting medium. As the ion conductive polymer, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and a supporting salt can be used. Further, an ion conductive polymer and a non-aqueous electrolyte can be used in combination. In addition to the ion conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, an inorganic solid powder bound by an organic binder, or the like can be used as the ion conductive medium.

  The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin fine olefin resin such as polyethylene or polypropylene is used. A porous membrane is mentioned. These may be used alone or in combination.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

According to the lithium secondary battery of the present embodiment described in detail above, in the negative electrode for a lithium secondary battery, the atomic ratio Csp ³ / Csp ² of the amorphous carbon film is 0 <Csp ³ / Csp ² ≦ 0.25. Since the lithium ion conduction path is ensured in the film without deficiency, it has excellent charge / discharge efficiency and charge / discharge durability characteristics. In addition, since the amorphous carbon film contains nitrogen atoms that act as n-type donors in an amount of 20 at% or less, the electrons bound to the donor level are effectively excited to the conduction band. The electrical conductivity of can be further increased. Furthermore, since the amorphous carbon film contains 15 at% or less of hydrogen, the termination of molecules due to C—H bonds (σ bonds) is suppressed by reducing the hydrogen content, so that π electrons increase. And high conductivity. At this time, when charging / discharging in the non-aqueous electrolyte as the negative electrode active material, particularly when the hydrogen content is 15 at% or less, the irreversible reaction caused by the contained hydrogen can be further suppressed. Furthermore, since the interlayer distance d of the amorphous carbon film is in the range of 0.35 nm <d ≦ 0.45 nm, the interlayer distance d is suitable and optimized from the viewpoints of both conductivity and lithium ion conductivity. And exhibits excellent load characteristics and charge / discharge durability characteristics. And since the negative electrode active material is an active material film made of an amorphous carbon film, the potential shape at the time of charging and discharging is inclined as compared with the graphite negative electrode, and its operating potential is away from the lithium metal deposition potential, High safety and easy to charge / discharge large current. Therefore, battery characteristics such as charge / discharge efficiency, load characteristics, and charge / discharge durability can be further improved.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  Below, the example which produced the lithium secondary battery of this invention concretely is demonstrated as an experiment example.

[Experimental Example 1]
(Preparation of negative electrode for lithium secondary battery)
An amorphous carbon film was formed by a plasma CVD method using a disc-shaped current collector (diameter: 16 mm) made of stainless steel and toluene as a carbocyclic compound gas containing carbon having sp ² hybrid orbitals. In the formation of the amorphous carbon film, a chemical vapor deposition apparatus 30 capable of applying a DC voltage is used, and 10 sccm of toluene as a carbocyclic compound gas containing carbon having sp ² hybrid orbitals and sp ³ hybrid orbitals (standard temperature 25 ° C.). , The same applies hereinafter), 20 sccm using nitrogen gas as the nitrogen source, 20 sccm argon gas as the inert gas, and the film formation temperature of 600 ° C. were obtained. A negative electrode for a secondary battery was obtained. Table 1 shows the manufacturing conditions. Table 1 also shows the contents of Experimental Examples 2 to 7 described later. The film thickness of the produced amorphous carbon film was 3 μm.

[Experimental Examples 2 to 4]
A negative electrode for a lithium secondary battery of Experimental Example 2 was obtained through the same steps as in Experimental Example 1 except that the above-described nitrogen gas was not supplied. Further, the above-described nitrogen gas was not supplied, and a film obtained at the temperature of 550 ° C. was subjected to the same steps as in Experimental Example 1, and the obtained product was used as the negative electrode for the lithium secondary battery of Experimental Example 3. In addition, the above-described toluene was replaced with benzene as a carbocyclic compound gas containing carbon having sp ² hybrid orbitals, and obtained through the same steps as in Experimental Example 1 except that the film formation temperature was 400 ° C. Was used as the negative electrode for a lithium secondary battery of Experimental Example 4.

[Experimental Examples 5 to 7]
Further, it is obtained through the same steps as in Experimental Example 1 except that 50 sccm of methane is supplied as a gas containing carbon instead of toluene and nitrogen gas is supplied at 100 sccm and the film forming temperature is set to 450 ° C. This was used as the negative electrode for a lithium secondary battery of Experimental Example 5. Further, in place of the above-described toluene, 10 sccm of benzene, nitrogen gas was not supplied, and the film formation temperature was changed to 500 ° C. A negative electrode for a secondary battery was obtained. In addition, 50 sccm of methane was supplied as a gas containing carbon instead of toluene as described above, nitrogen gas was not supplied, argon gas was supplied at 30 sccm, and the film formation temperature was set to 400 ° C. The product obtained through the steps was used as the negative electrode for a lithium secondary battery of Experimental Example 7.

[Experimental Example 8]
Graphite (manufactured by Aldrich) was used as Experimental Example 8. This Experimental Example 8 is a reference value obtained by measuring graphite particles, not a carbon film.

(Composition analysis of amorphous carbon film)
Composition analysis (C, N, H) of the amorphous carbon film was performed by ERDA-RBS measurement using Pelletron 3SDH manufactured by National Electrostatistics. The content element ratio (C / N / H ratio) was calculated from the obtained spectrum result so as to fit the theoretical calculation value. Measurement conditions were such that the incident ions were 4 He ⁺⁺ , the incident energy was 2.3 MeV, the incident angle was 75 deg, the incident beam diameter was 2 mm, and the irradiation amount was 0.1 to 20 μC. The C and N contents in the amorphous carbon film were quantified by Rutherford backscattering method (RBS method). In the RBS measurement, an RBS detector (for C and N) was used, and the energy and yield of the scattered He ions were detected under the conditions that the detected ions were He ions, the scattering angle was 160 deg, and the aperture size was 8 mm in diameter. Moreover, H content was quantified by the elastic recoil particle detection method (ERDA method). In the ERDA measurement, a hydrogen forward scattering (HFS) detector (for H) is used, the detected ions are H ions, the scattering angle is 30 deg, the aperture size is 8 mm × 2 mm, and the H energy struck by He Was detected. Regarding the contents of C and N in the amorphous carbon film, electron probe microanalysis (EPMA; EPMA-V6 manufactured by Shimadzu Corporation), X-ray photoelectron spectroscopy (XPS; ESCA5500 manufactured by ULVAC-PHI), Auger Measurements such as electron spectroscopy (AES; ULVAC-PHI PHI700) were also performed to confirm that the measurement results were valid.

(Quantification of atomic ratios Csp ² and Csp ³ of amorphous carbon film)
The ratio of the number of carbon atoms having sp ² hybrid orbits to the total number of carbon atoms is defined as atomic ratio Csp ^2, and the ratio of the number of carbon atoms having sp ³ hybridized orbits to the total number of carbon atoms is defined as atomic ratio Csp ³ . The atomic ratio Csp ² and the atomic ratio Csp ³ were quantified. As a method for determining the atomic ratio Csp ² and the atomic ratio Csp ^3, a nuclear magnetic resonance method (NMR) having the highest quantitativeness was adopted in the structure definition of many organic materials and inorganic materials. For the measurement of the atomic ratio Csp ² and the atomic ratio Csp ³ , a high-power decoupling method (HD-MAS) that performs magic angle spinning with quantitativeness in solid-state NMR was used. FIG. 3 is an example of a 13C-NMR spectrum of an amorphous carbon film. As shown in FIG. 3, peaks due to atomic ratios Csp ² and Csp ³ are observed near 130 ppm and 30 ppm, respectively. The atomic ratio Csp ³ / Csp ² of the atomic ratio Csp ² and the atomic ratio Csp ³ was calculated from the area ratio of the portion surrounded by each peak and the baseline.

(X-ray diffraction measurement)
X-ray diffraction measurement of the amorphous carbon films of Experimental Examples 1 to 8 was performed. A powder sample prepared by collecting an amorphous carbon film formed on a current collector in a powder state was measured with an XRD apparatus (RINT2200 manufactured by Rigaku). The measurement was performed using Cu-Kα rays (wavelength 1.54051Å) as radiation, using a single crystal monochromator of graphite for monochromatic X-rays, setting the applied voltage to 40 kV and the current 30 mA. Further, the measurement was performed at a scanning speed of 3 ° / min and an angle range of 2θ from 2 ° to 80 °.

(Preparation of bipolar evaluation cell)
A non-aqueous electrolyte was prepared by adding lithium hexafluorophosphate to a non-aqueous solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 30:70 so as to be 1 mol / L. Using the electrode formed with an amorphous carbon film of Experimental Examples 1 to 7 formed on a disk-shaped stainless steel substrate, using the electrode as a working electrode and a lithium metal foil (thickness 300 μm) as a counter electrode, A bipolar evaluation cell was fabricated with a separator impregnated with a non-aqueous electrolyte (Tonen Tapils) sandwiched between them.

(Charge / discharge test)
Using the above bipolar evaluation cell, a charge / discharge test was conducted under a temperature environment of 20 ° C. with a lower limit voltage of 0 V and an upper limit voltage of 3.0 V. The rated capacity of the amorphous carbon film was arbitrarily set to 250 mAh / g, and the current value capable of energizing 250 mAh / g for 1 hour with respect to the film weight was defined as 1C. An irreversible capacity ratio at the time of initial charge / discharge when the charge / discharge operation at a current value of 0.1 C is defined as a reduction capacity Qred for the first reduction (charge) capacity and an oxidation capacity Qoxy for the oxidation (discharge) capacity. Ri (%) was defined as irreversible capacity ratio Ri (%) = [(Qred−Qoxi) / Qred × 100]. In addition, this charge / discharge operation is repeated three times to obtain a discharge state, and an initial state is obtained. Under a temperature environment of 20 ° C., the cell in the initial state is charged at 0.1 C and discharged at 0.1 C. The ratio Rr (%) of the discharge capacity Q (4C) of 4C to the capacity Q (0.1C) was defined as load characteristics Rr (%) = [Q (4C) / Q (0.1C) × 100]. Further, a charge / discharge test of the cell in the initial state is performed, and the discharge with respect to the discharge capacity Q (1st) oxi is performed using the discharge capacity Q (1st) oxi of the first charge / discharge operation and the discharge capacity Q (10th) oxy of the tenth time. The ratio of the capacity Q (10th) oxy was defined as charge / discharge durability Rc (%) = [Q (10th) oxy / Q (1st) oxy × 100], and the charge / discharge durability characteristics were evaluated.

(Experimental result)
Table 2 shows the evaluation results of the negative electrodes for lithium secondary batteries and the bipolar evaluation cells of Experimental Examples 1 to 7. Table 2 shows the composition ratio (at%) of the number of atoms of carbon (C), nitrogen (N), and hydrogen (H), the ratio of atomic ratios Csp ² and Csp ^{3 to} the total number of carbon atoms (at%), The atomic ratio Csp ³ / Csp ² , interlayer distance d (nm), irreversible capacity ratio Ri (%), load characteristic Rr (%), and charge / discharge durability Rc (%) are shown together. 4 is an X-ray diffraction measurement result of the amorphous carbon film (Experiment 1), FIG. 5 is a charge / discharge curve of Experiment 1, and FIG. 6 is a charge / discharge curve of Experiment 7. 7 is a discharge curve of the load characteristic test of Experimental Example 1, and FIG. 8 is a discharge curve of the load characteristic test of Experimental Example 6. As shown in FIG. 4, diffraction peaks corresponding to the (002) plane and the (101) plane of the graphite skeleton defined by the hexagonal system are present in the range where the diffraction angle 2θ is 20 ° or more and 25 ° or less and in the vicinity of 42 °. Appeared. Since these peaks were broad halo patterns, it was confirmed that this amorphous carbon film was an amorphous carbon film having no long-range order and no crystal structure. Also in Experimental Examples 2 to 4 and 7, a halo pattern appeared, and it was confirmed that the film was an amorphous carbon film having no crystal structure. Based on these XRD patterns, the interlayer distance d of the carbon layer was calculated from the peak corresponding to the diffraction on the (002) plane of the graphite skeleton. As shown in Table 2, when the interlayer distance d is in the range of 0.35 nm <d <0.55 nm, the irreversible capacity ratio, load characteristics, and charge / discharge durability are good. It was revealed that better battery characteristics were exhibited when the distance d was in the range of 0.35 nm <d <0.45 nm.

In addition, as shown in FIG. 6, Experimental Example 7 includes an amount of hydrogen in the film that greatly exceeds 15 at%, and a carbon Csp ² amount of 65 at% that is significantly less than 80 at%, and Csp ³ corresponds to 35 at%. The amorphous carbon film had the properties of a diamond-like carbon (hard carbon) film, and such an amorphous carbon film did not exhibit charge / discharge behavior as shown in FIG. 6 and Table 2. On the other hand, as shown in FIG. 5 and Table 2, the amorphous carbon film shown in Experimental Example 1 was chargeable / dischargeable, and the irreversible capacity ratio was also good. Further, as shown in FIG. 8, in Experimental Example 6 in which the atomic ratio Csp ³ / Csp ² exceeds 0.35, the load characteristics are low, and as shown in Table 2, the irreversible capacity ratio and the charge / discharge durability are also low. Became clear. On the other hand, as shown in FIG. 7 and Table 2, the amorphous carbon film shown in Experimental Example 1 had better irreversible capacity ratio, load characteristics, and charge / discharge durability. Further, as shown in Table 2, the amount of hydrogen in the film is 15 at% or less, the amount of nitrogen is 20 at% or less, the atomic ratio Csp ^{2 of} carbon is 80 at% or more, and the atomic ratio Csp ³ / Csp ² is 0 <Csp ³ / Experimental Examples 1 to 4 satisfying Csp ² ≦ 0.25 were favorable results in irreversible capacity ratio, load characteristics, and charge / discharge durability. Furthermore, it has been revealed that better battery characteristics are exhibited when the interlayer distance d is in the range of 0.35 nm <d <0.45 nm.

As shown in Table 2, in Experimental Example 2, the hydrogen amount is 7 at%, which is even smaller than the film of Experimental Example 3, and the atomic ratio Csp ^{2 of} carbon is 95 at%, which is higher than that of Experimental Example 3, and the interlayer distance d However, it was 0.38 nm which was smaller than Experimental Example 3. The amorphous carbon film of Experimental Example 2 exhibited charge / discharge characteristics that were even better than Experimental Example 3. Further, the amount of hydrogen and the atomic ratio Csp ² of carbon are almost equal to those of the membrane of Experimental Example 2. In Experimental Example 1 in which nitrogen is further contained in this membrane, the smallest irreversible capacity ratio, the most excellent load characteristics and charge are obtained. Discharge durability was shown. In the case of Experimental Example 4 in which the amount of hydrogen in the amorphous carbon film, the amount of nitrogen, and the atomic ratio Csp ² satisfy the conditions and only the interlayer distance d is large, the charge / discharge behavior is relatively good. Less than 3 characteristics. In addition, although the hydrogen amount in the amorphous carbon film satisfies the condition of 15 at% or less, the experimental example 5 including 27 at% of the nitrogen amount exceeding 20 at% has lower charge / discharge characteristics than the experimental example 4. . In the case of Experimental Example 6 in which the atomic ratio Csp ^{2 of} carbon is 74 at% lower than 80 at%, although the hydrogen amount in the amorphous carbon film satisfies the condition of 15 at% or less, the charge / discharge characteristics equivalent to those in Experimental Example 5 are obtained. Some characteristics were lower than those of Experimental Examples 1 to 4.

DESCRIPTION OF SYMBOLS 10 Coin type battery, 11 Battery case, 12 Positive electrode, 14 Separator, 15 Gasket, 16 Sealing plate, 17 Non-aqueous electrolyte, 20 Negative electrode, 22 Current collector, 24 Active material film, 30 Chemical vapor deposition apparatus, 31 Process object, 32 chamber, 32a processing space, 34 base, 36 gas introduction pipe, 38 gas exhaust pipe, 40 application device, 42 valve, 44 gas cylinder, 46 valve, 48 rotary pump, 49 diffusion pump, 50 decompression device.

Claims (7)

A current collector,
The ratio of the number of carbon atoms formed as a vapor deposition film on the current collector and having sp ² hybrid orbitals to the total number of carbon atoms is Csp ^2, and the number of carbon atoms having sp ³ hybrid orbitals to the total number of carbon atoms is proportions atomic ratio Csp ³ / Csp ² when the Csp ^3, the active material layer made of amorphous carbon film satisfying ^{0 <Csp 3 / Csp 2 ≦} 0.25,
A negative electrode for a lithium secondary battery comprising:   The negative electrode for a lithium secondary battery according to claim 1, wherein the active material film contains 20 at% or less of nitrogen.   The negative electrode for a lithium secondary battery according to claim 1, wherein the active material film contains 15 at% or less of hydrogen.   The active material film has an interlayer distance d of 0.35 nm <d <0.45 nm calculated from a broad diffraction peak in which 2θ in an X-ray diffraction measurement is 20 ° or more and 25 ° or less. The negative electrode for a lithium secondary battery according to any one of claims 1 to 3, which is in a range. The negative electrode for a lithium secondary battery according to any one of claims 1 to 4,
A positive electrode having a positive electrode active material;
An ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions;
Rechargeable lithium battery. A source gas containing at least one of a carbocyclic compound gas containing carbon having sp ² hybrid orbital and a carbocyclic compound gas containing carbon having sp ³ hybrid orbital is placed in a reaction vessel in which a current collector is arranged. By introducing and discharging, the ratio of the number of carbon atoms having sp ² hybrid orbitals to the total number of carbon atoms is Csp ² and the ratio of the number of carbon atoms having sp ³ hybrid orbits to the total number of carbon atoms is Csp. ^An active material film made of an amorphous carbon film is formed on the current collector so that the atomic ratio Csp ³ / Csp ² is ^{3 in} the range of 0 <Csp ³ / Csp ² ≦ 0.25. The manufacturing method of the negative electrode for lithium secondary batteries including a process.   In the step, a raw material gas further containing at least one of carbocyclic compound gas containing nitrogen and carbon and nitrogen gas is introduced into the reaction vessel to form the active material film containing nitrogen at 20 at% or less. Item 7. A method for producing a negative electrode for a lithium secondary battery according to Item 6.

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