JP2556840B2 - Negative electrode for non-aqueous lithium secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a negative electrode for a non-aqueous lithium secondary battery, and particularly to an alkali metal such as lithium (Li) or potassium (K), an alkaline earth metal, a rare earth metal or a transition metal. The present invention relates to an electrode active material for a battery that uses a do-band substance or an electrode active material for a battery that uses a halogen, a halogen compound or oxyacid as a do-band substance.

<Prior Art> In recent years, research has been actively conducted to apply a carbon material to a battery electrode. For example, there is a material that uses activated carbon or activated carbon as an electrode material, but since these layers have no regularity in the stacking of hexagonal mesh planes created by carbon atoms, it is not possible to dope each ion and form an interface with the electrolyte. It only forms an electric double layer. Therefore, when this is used for the negative electrode material, cation doping is unlikely to occur, and only an amount of electric capacity corresponding to the ions stored in the electric double layer can be obtained. Further, a hexagonal mesh plane formed by carbon atoms arranged regularly is called a graphite structure. It has a layered structure in which hexagonal mesh plane carbon layers are laminated in parallel. The dopant substance can enter and leave between the layers, but the layer spacing is as narrow as 3.354Å, and the hexagonal mesh planes are laminated very regularly, so the amount of the dopant substance doped at around room temperature is small. There are also carbon materials that have an intermediate structure between a layered structure called amorphous carbon called activated carbon, which is completely irregular, and a structure in which carbon atoms are regularly arranged, such as graphite. To do. These are generally referred to as turbostratic structures, but carbon materials that fall into this category are widespread.

<Object of the Invention> An object of the present invention is to provide a negative electrode for a non-aqueous lithium secondary battery, which has a significantly large electric capacity as compared with a conventional carbon material and is made of carbon having good charge-discharge repeating characteristics. .

<Summary of Invention> As a result of evaluating various carbon materials as electrode materials using an alkali metal such as lithium or sodium as a dopant substance, the following has been found. That is, it has a structure having a slightly disordered structure and selective orientation as compared with carbon having a highly oriented graphite structure, and exhibits the best characteristics as an electrode material. The results of analyzing the detailed data of the carbon material exhibiting this good characteristic by each means will be described below.

The layer spacing on the carbon plane was determined by the X-ray diffraction method. As a result, the spacing between good electrode materials is 3.37Å ~ 3.55.
It took the value of Å. Further, it does not show a sharp peak like graphite, but shows a rather wide diffraction peak. When the crystallite size is determined using the method of determining the crystallite size from the half width of the diffraction peak, the crystallite size in the C-axis direction from the diffraction peak of the (002) plane is 20Å to 1000Å (110 The diffraction peaks on the) plane hardly appear, and even if they do appear, they are very broad, so the crystallite size in the ab axis direction is considered to be very small. Further, the backscattered electron diffraction pattern of this carbon material also has a broad ring shape, which reflects that the crystallite is very fine. These rings correspond to (002), (004), (006) reflections of the graphite structure. On the other hand, as a result of examining these diffractive rings in more detail, it was found that each ring was not uniform but had an arcuate or broad spot, and thus the orientation of each crystallite was not random, and the (00l) plane of each crystallite was Were found to be aligned in a particular direction. When this is further quantified, the relative inclination in the c-axis direction between the crystallites is within a range of ± 75 degrees, and the carbon material of the present invention has an orientational arrangement mainly composed of the crystallites having the above orientation. It is characterized as having a carbon material. Further, the Raman spectrum of 1360 cm ^-1 derived from the imperfections of the graphite structure was observed in addition to the Raman spectrum of 1580 cm ^-1 derived when graphite structure viewed progress to graphitization by laser Raman spectroscopy, the carbon material It can be seen that has an incomplete crystal structure compared to graphite. With the progress of graphitization, the peak at 1360 cm ^-1 decreases and the peak at 1580 cm ^-1 due to the lattice vibration peculiar to graphite increases. Order to attain the object of the present invention when 0.4 or more viewed peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the Raman spectrum 1.0
It is the following. As described above, a carbon body having a larger interplanar spacing and a smaller crystallite size than graphite and having a certain degree of orientation with each other exhibits good characteristics as an electrode material. A carbon body that satisfies the above conditions is difficult to obtain by firing a powder body or a fibrous body. That is, the carbon spacing and the crystallite size have the same physical properties as those of the present invention, but the orientation between the crystallites is irregular, and therefore the discharge capacity is small and long-term repetition of charge and discharge is not possible. It becomes unbearable.

A carbon body that can achieve the object of the present invention is achieved by the following production method. That is, the material of the present invention made of carbon is formed by vapor-depositing a hydrocarbon or a hydrocarbon compound as a starting material by supplying this to a reaction system and then thermally decomposing it on a substrate. As the hydrocarbon compound, one obtained by adding or substituting a characteristic group containing at least one element selected from oxygen, nitrogen, sulfur or halogen to a part of hydrocarbon is used. When such a carbon material is used for a battery electrode containing an alkali metal or the like as a dopant substance, the following effects are obtained.

(1) Compared to graphite materials manufactured by conventional manufacturing methods, such as those manufactured by carbonizing organic fibers, highly oriented pyrolytic graphite, and natural graphite, doping with a dopant substance is more likely to occur, and the electrical capacity is large. .

(2) Since a thin film or the like can be directly formed on the substrate, the internal resistance is small and the utilization rate of the active material is high.

(3) The electrode can be made thin and can be manufactured in any shape.

In addition to the above-mentioned alkali metals, alkaline earth metals, rare earth metals or transition metals can be used as the dopant substance. Furthermore, the dopant is not limited to these, and halogen, a halogen compound, oxyacid, or the like can be used. These dopants are doped during the manufacturing process.

<Example 1> FIG. 1 is a block diagram of a carbon material generator used in Example 1 of the present invention. Hydrocarbons used as starting materials and hydrocarbon compounds partially containing various characteristic groups include, for example, aliphatic hydrocarbons, preferably unsaturated hydrocarbons, aromatic compounds and alicyclic compounds. These are 10
It is pyrolyzed at 00 ℃. Specifically, acetylene, diphenyl, acetylene, acrylonitrile, 1.2-dibromoethylene, 2-butyne, benzene, toluene, pyridine, aniline, phenol, diphenyl, anthracene, pyrene, hexamethylbenzene, styrene, allylbenzene, cyclohexane, normal hexane. , Pyrrole, thiophene, etc.

Depending on the kind of the hydrocarbon compound used, the supply method to the reaction tube, which will be described later, is controlled to be a few millimoles / hour or less by using a bubbler method, an evaporation method or a sublimation method. If the supply amount is large, soot-like carbon deposits are produced, and the object of the present invention is not achieved. The substrate on which the carbon material is deposited and produced is
It must be one that does not deteriorate at the reaction temperature of about 1000 ° C.

 Hereinafter, the manufacturing process will be described.

Argon gas is supplied from an argon gas control system 2 into a bubble container 1 containing benzene which has been subjected to a purification operation by vacuum distillation to bubble benzene, and benzene molecules are transferred to a quartz reaction tube 4 through a Pyrex glass tube 3. To send. At this time, the temperature of the liquid benzene in the bubble container 1 is kept constant and the flow rate of the argon gas is adjusted by the valve 5 to control the supply amount of benzene molecules into the reaction tube 4 to several millimoles per hour. On the other hand, let argon gas flow from the dilution line 6,
The number density and the flow rate of benzene molecules in the argon gas in the glass tube 3 immediately before being fed to the reaction tube 4 are optimized. A sample stage 7 on which a substrate is placed is disposed in the reaction tube 4, and a heating furnace 8 is provided around the outer periphery of the reaction tube 4. By this heating furnace 8, the deposition generation substrate in the reaction tube 4 is maintained at a temperature of about 1000 ° C. When the benzene molecule is fed into the reaction tube 4, the benzene molecule is thermally decomposed in the reaction tube 4, and a carbon deposit is formed on the substrate. The gas into the reaction tube 4 is introduced into the exhaust system 10 via the exhaust pipe 9,
It is removed from the reaction tube 4. The benzene molecules introduced into the reaction tube 4 are heated at a temperature of about 1000 ° C. to be thermally decomposed and sequentially grown and formed on the substrate. In this case, the grown carbon becomes a thin film having a metallic luster, and the reaction proceeds at a lower temperature as compared with the conventional method of forming a graphite material by a manufacturing method, and thus physical properties suitable for achieving the object of the present invention are obtained. A carbon material having a value can be realized. Further, by selecting the starting material to be used, the supply amount of the starting material, the supply rate, and the reaction temperature, it is possible to arbitrarily control the anisotropy and the like. An X-ray diffraction diagram of this carbon body using CuKd as a light source is shown in FIG.

Bragg equation from this diffraction peak The average interplanar spacing of the (002) plane obtained from was 3.45Å,
From the peak half-value width β The crystallite size in the c-axis direction obtained from the above was 27.2Å.

FIG. 3 is a Raman spectrum of this carbon body using an argon laser. When viewed peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the figure, it was 0.8. In addition, when a diffraction photograph of an electron beam is obtained by the reflection high-energy electron diffraction (RHEED) method, the (002), (004), (006) reflections show broad spots, and the orientation of each crystallite is considerably large. It was often found that the distribution in the c-axis direction was within ± 18 degrees.

The carbon thin film thus produced was held by a current collecting net to prepare an electrode. This is designated as test pole A. Test pole A
Was placed in an electrolytic bath as shown in FIG. 4, and a charge / discharge test was performed by doping / dedoping lithium element using lithium metal as a counter electrode and lithium as a dopant material. Fourth
In the figure, 12 is a test electrode A made of a carbon body according to the present embodiment,
Reference numeral 13 is a current collector, 14 is a counter electrode, 15 is lithium used as a reference electrode, 16 is an electrolytic solution made of propylene carbonate in which 1 mol of lithium perhydrochloride is dissolved, and 17 is an electrolytic cell. FIG. 5 is a potential change diagram with respect to a lithium reference electrode at 25 ° C. when various carbon materials are doped and dedoped with lithium. Curve A in FIG. 5 is a potential change curve of the carbon material according to this example. In the curve A, the direction in which the potential approaches 0 V is dope (charge), and the direction in which the potential is high is dedope (discharge). FIG. 6 shows changes in discharge capacity in a test in which various carbon materials are charged and discharged with a constant current between 0 V and 2.5 V with respect to a lithium reference electrode. Curve A in FIG.
Shows the characteristic curve of this embodiment. As is clear from this result, there is almost no capacity deterioration due to repeated charging and discharging, and the repeating characteristics are very good.

By using such an electrode material as described above, a negative electrode of a non-aqueous lithium secondary battery that can be charged and discharged can be formed.

<Example 2> A carbon body was deposited on a nickel substrate by the same manufacturing method as in Example 1. Various characteristics of this carbon body were determined by the same methods as in Example 1 above. As a result, the average interplanar spacing of the (002) plane was 3.37Å as shown in Fig. 7.
Peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 was 0.50 as shown in Figure 8. The distribution of each crystallite in the c-axis direction by reflection high-energy electron diffraction was within ± 60 degrees.

A lead wire was taken out from the carbon body manufactured as described above and used as a test electrode B as an electrode. Using this as a dopant material in the same manner as in Example 1, a charging / discharging test by doping / dedoping was performed. Curve B in FIG. 5 is a potential change curve of the carbon material according to this example. Curve B in FIG. 6 shows the change in discharge capacity in the repeated test of the carbon material according to this example. As is clear from this result, the discharge capacity and the repeating characteristics are very good. The carbon body obtained by using the production method shown in this example has an average layer spacing of 3.37Å to 3.55Å, and the peak intensity at 1580 cm ^-1 in the Raman spectrum of the laser is 1360 cm.
The peak intensity ratio of ^-1 was 0.4 or more and 1.0 or less. The relative inclination in the c-axis direction between the crystallites obtained by reflection high-energy electron diffraction is ± 75 ° or less, preferably ± 60 ° or less.

Those satisfying these physical property values can be achieved only by the manufacturing method described in this example, and use soot-like carbon deposits obtained at lower temperatures and highly oriented graphitized carbon bodies obtained at higher temperatures. Does not exhibit the electrode characteristics as described above. However, the object of the present invention can be achieved by optimizing by a photo CVD method or a plasma CVD method other than thermal energy.

Further, in this embodiment, 1 mol of lithium perchlorate was used as the electrolyte and propylene carbonate was used as the electrolytic solution, but the present invention is not limited to this, and lithium hexafluoroarsenate is used as the other electrolyte. , Lithium borofluoride, lithium trifluorosulfonate, etc.,
In addition, as the electrolyte, dimethyl sulfoxide, gamma-butyl lactone, sulfolane tetrahydrofuran, 2-
Methyltetrahydrofuran, 1.2-dimethoxyethane, 1.3
Examples include organic solvents such as dioxolane and water, and these may be used alone or in combination.

Comparative Example 1 A carbon body was deposited on a quartz substrate at 1200 ° C. in the same manner as in Example 1. This was stripped from the substrate and heat-treated at 2800 ° C. to obtain a highly oriented graphitized carbon body. FIG. 9 shows the X-ray diffraction data of this carbon body. The spacing between (002) planes of this carbon body was 3.36Å. Further, the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the Raman spectrum of 0.1, was an electrode test electrode C in the carbon material the same manner as in Example 1. The test electrode C was placed in an electrolytic cell as shown in FIG. 4, and a charge / discharge test was conducted in the same manner as in Example 1. Curve c in FIG. 5 is a potential change curve of the carbon material according to this comparative example. As a result, the discharge capacity was smaller than that of the electrodes of Examples 1 and 2, and it was unsuitable as an electrode material.

<Comparative Example 2> 50 unrefined petroleum coke obtained by removing volatile components from crude oil
Heat treated at 0 ° C. The X-ray diffraction pattern of this carbon powder is shown in Fig. 11.
Shown in the figure. From this diffraction peak, the average interplanar spacing of the (002) plane was 3.45Å. Also, in the Raman spectrum, 15
Peak intensity ratio of 1360 cm ^-1 to the peak intensity of 80 cm ^-1 is
It was 0.8. The results are shown in FIG. Further, according to the diffraction pattern of the electrode obtained by pressing this carbon body by reflection high-energy electron diffraction, it was found that each ring of the diffraction pattern was uniform and had no orientation. A foamed nickel substrate was filled with this carbon body and pressed to obtain an electrode, which was used as a test electrode D. The test electrode D was placed in an electrolytic cell as shown in FIG. 4, and a charge / discharge test was conducted in the same manner as in Example 1. Curve D in FIG. 5 is a potential curve of the carbon material according to this comparative example. From this result, the discharge capacity is smaller than that in Examples 1 and 2. However, the initial charge / discharge characteristics are shown in Comparative Example 1
Was better than. The test electrode D was subjected to a repeated charge / discharge test in the same manner as in Example 1. Curve D in FIG. 6 shows the result of this comparative example. From this result, it is confirmed that the electrode having no crystallite orientation at all causes deterioration in capacity due to repeated charge and discharge, and it is difficult to withstand long-term use.A small amount of carbon material having selective orientation was included. It can be seen that the carbon material is suitable as the electrode.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a carbon material production apparatus used for explaining one embodiment of the present invention. 2 and 7 are X-ray diffraction patterns of the carbon material according to the present invention. 3 and 8 are characteristic diagrams showing Raman spectra of the carbon material according to the present invention. FIG. 4 is a schematic view of an apparatus for measuring electrode characteristics of a carbon material according to the present invention. FIG. 5 is a charge / discharge characteristic diagram of the carbon material according to the present invention and the existing carbon material. FIG. 6 is a cycle characteristic diagram of the discharge capacity of the carbon material according to the present invention and the existing carbon material. 9 and 11 are X-ray diffraction patterns of existing carbon materials. 10 and 12 are characteristic diagrams showing Raman spectra of existing carbon materials. 1 ... Bubble container, 2 ... Argon gas control system, 3 ...
Pyrex glass tube, 4 ... reaction tube, 5 ... valve,
6 ... Dilution line, 7 ... Sample stand, 8 ... Heating furnace, 9 ...
… Exhaust pipe.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomonari Suzuki, 22-22 Nagaike-cho, Abeno-ku, Osaka (72) Yoshikazu Yoshimoto, 22-22 Nagaikecho, Nagano-cho, Abeno-ku, Osaka-shi, SHARP Co., Ltd. Sharp Co., Ltd., 22-22 Nagaike-cho, Abeno-ku, Osaka (56) Reference JP 62-90863 (JP, A) JP 60-182670 (JP, A) JP 60-20466 (JP, A)

Claims (2)

(57) [Claims] 1. A negative electrode for a non-aqueous lithium secondary battery, which is prepared by doping and undoping a dopant material between layers formed by a hexagonal network of carbon, which is a carbon material having a selective orientation, which is superior to graphite. Te of dopant material doped so as undoped occurs easily and the electric capacity is increased, the average spacing of the hexagonal mesh is 3.55Å from 3.37 Å, and to the peak intensity of 1580 cm ^-1 in the argon laser Raman spectra of 1360 cm ^-1 identified by the peak intensity ratio of 0.4 to 1.0 (average spacing of the hexagonal mesh is not less than 3.43A, and the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon laser Raman spectrum excluding 0.6 or higher) is A negative electrode for a non-aqueous lithium secondary battery, comprising a carbon material having a layered structure of graphite having a slight disordered structure as a main component. 2. The selective orientation of the carbon material is such that the relative inclination in the C-axis direction between crystallites in the diffraction pattern of the (002) plane in reflection high-energy electron diffraction is ± 75 ° or less. A negative electrode for a non-aqueous lithium secondary battery according to claim 1.