JPH07118308B2 - Electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrode and a battery using the same, 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 as a dopant. Battery electrode or halogen, halogen compound,
The present invention relates to a battery electrode using oxygen acid as a dovant substance.

<Prior art and its problems> In recent years, secondary batteries using alkali metals such as lithium have been attracting attention due to miniaturization and power saving of electronic devices, etc. There is. However, in a battery in which a metal is used alone as an electrode, there is a problem that the negative electrode metal grows in a dendrite shape due to repeated charging / discharging and causes an internal short circuit, which makes it extremely difficult to put it into practical use as a secondary battery. As an improvement measure, the development of materials that can absorb and release metal atoms such as lithium in the negative electrode is progressing, and materials that can efficiently absorb and release metal atoms such as metals such as low melting point alloys and organic materials. Was found. Above all, a secondary battery utilizing electrochemically inserting various substances between layers of a layered compound such as graphite has been actively developed. In particular, graphite is considered to be a promising material as an electrode material for secondary batteries because it can insert both an electron donating substance and an electron accepting substance. However, any graphite is powder, film,
It is made of foil, fiber, etc., and when using these to form an electrode, it is difficult to add a molding form, and a complicated process of fixing these materials to the electrode substrate that serves as the current collector is required. Become. For that reason, auxiliary materials such as a binder and a conductive material are required in addition to the charge carriers, and the capacity per unit weight or unit volume is reduced.

A structure in which a carbon body is deposited on a conductive substrate such as aluminum by a CVD method or the like and is used as an electrode is also conceivable. However, since this carbon body is usually a carbon body having a low degree of graphitization, the above-mentioned problem You cannot solve the point. In order to obtain highly crystalline graphite capable of forming an intercalation compound, it is necessary to treat these carbon bodies at a high temperature of at least 2000 ° C. or higher, and there is no battery electrode substrate capable of withstanding such a high temperature.

<Purpose of the invention> The present invention has been made in view of the above conventional circumstances, and an electrode base material having a catalytic action for promoting high crystallization of nickel or the like as a substrate during the process of manufacturing an electrode such as a thermal decomposition CVD method. By using it, thermal decomposition around 1000 ℃, which is below the melting point of metal
By making it possible to deposit graphite by the CVD method and achieving a marked improvement in the crystallinity of the resulting graphite (graphitization), by coating the above metal substrate with graphite with good adhesion, it is possible to achieve a significantly higher electrical conductivity than conventional graphite electrodes. It is an object to provide an electrode showing capacity and a battery using the same.

<Outline of the Invention> The present invention uses a hydrocarbon or a hydrocarbon compound as a raw material.
Highly crystalline heat is applied to the above substrate by using a catalytic substrate such as iron, cobalt, nickel or their alloys in a relatively low temperature atmosphere that does not deteriorate the metal substrate around 00 ° C or lower. A high capacity electrode obtained by depositing decomposed graphite and coating the electrode substrate is characterized.

The graphite electrode that can achieve the object of the present invention is achieved by the following manufacturing method. That is, the highly crystalline pyrolytic graphite is formed by vapor-phase deposition method by pyrolysis by using hydrocarbon or hydrocarbon compound as a starting material and supplying it to the reaction system to form a nickel base material having a catalytic action for high crystallization. It is what is done. As the hydrocarbon compound, a compound 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. The following effects can be obtained when the structure covered and connected by the highly crystalline pyrolytic graphite is used for the electrode of the battery containing the alkali metal or the like as the dopant substance.

(1) Compared to graphite materials manufactured by conventional manufacturing methods such as carbonization of organic fibers, highly oriented pyrolytic graphite (HOPG), and natural graphite, dope dedoping of the dopant substance is more likely to occur, and the electric capacity is increased. Is also big.

(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 electrodes can be thinned and can be manufactured on a substrate having an arbitrary shape.

<Example> FIG. 1 is a block diagram of a graphite electrode manufacturing apparatus used in an example of the present invention. Examples of hydrocarbons used as starting materials and hydrocarbon compounds partially containing various characteristic groups include aliphatic hydrocarbons, preferably unsaturated hydrocarbons, aromatic compounds, and alicyclic compounds. These are 1000
It is pyrolyzed at temperatures around ℃ or below. 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 described later is controlled by a bubbler method, an evaporation method or a sublimation method to a supply amount of several millimoles or less per hour. As a base electrode substrate on which pyrolytic graphite is formed, a nickel base material is used as an example.

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, an argon gas is caused to flow from the dilution line 6 to optimize the benzene molecule number density and the flow rate in the argon gas in the glass tube 3 immediately before being fed to the reaction tube 4.
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.
With this heating furnace 8, the deposition electrode substrate in the reaction tube 4 is
The temperature is maintained at around 00 ℃ or below. 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 exhausted through the exhaust pipe 9
It is introduced into 10 and removed from the reaction tube 4. The benzene molecules introduced into the reaction tube 4 are heated at a temperature of about 1000 ° C. or lower and thermally decomposed, and graphite is successively grown and formed on the electrode substrate. At this time, the pyrolytic graphite that is grown and formed becomes a graphite with excellent crystallinity by introducing the catalytic effect of nickel, and at the same time graphitization is achieved at a low temperature that does not deteriorate or melt the electrode substrate, The decomposed graphite film firmly covers the nickel base material. According to the above-mentioned manufacturing method, graphitization proceeds at a lower temperature as compared with the conventional graphite material forming method, so that a graphite electrode suitable for achieving the object of the present invention can be realized.
Further, by selecting a starting material to be used, a supply amount of the starting material, a supply rate, and a reaction temperature, there is an advantage that the crystallinity and the like can be arbitrarily controlled. CuKα of this pyrolytic graphite
Fig. 2 shows the X-ray diffraction pattern with the X-ray as the radiation source.

Bragg's equation from this diffraction peak The average interplanar spacing of the (002) plane was calculated by (3.36 ± 0.01)
Å, and from the half-value width β of the peak, The size of the crystallite in the C-axis direction determined from the above was 350Å.

A lead wire is taken out from the nickel of the graphite electrode thus manufactured, and this is used as a test electrode A. A test electrode A was arranged in an electrolytic cell as shown in FIG. 3, and a lithium metal was used as a counter electrode and lithium was used as a dopant substance to conduct a charge / discharge test by doping / dedoping lithium element. In FIG. 3, 12 is a test electrode A made of the graphite electrode according to this example, 13 is a counter electrode, 14 is lithium used as a reference electrode, 15 is an electrolytic solution made of propylene carbonate in which 1 mol of lithium perhydrochloride is dissolved, 16 is an electrolytic cell. FIG. 4 is a potential change diagram with respect to a lithium reference electrode at 25 ° C. when various graphite electrodes are doped or dedoped with lithium. Curve A in FIG. 4 is a potential change curve of the graphite electrode 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. 5 shows the graphite electrode according to the present embodiment with respect to the lithium reference electrode.
The change in discharge capacity in the test of charging and discharging with a constant current between 0 V and 2.5 V is shown. The curve in FIG. 5 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.

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

In this example, 1 mol of lithium perchlorate was used as the electrolyte,
I explained using propylene carbonate as the electrolyte,
The present invention is not limited to this, and other electrolytes include lithium hexafluoroarsenate, lithium borofluoride, lithium trifluorosulfonate, and the like, and electrolytes such as dimethyl sulfoxide, gamma-butyl lactone, Examples thereof include organic solvents such as sulfolane tetrahydrofuran, 2-methyltetrahydrofuran, 1.2-dimethoxyethane, and 1.3-dioxirane, and water, and these may be used alone or in combination.

Further, the interplanar spacing of the pyrolytic graphite of the graphite electrode obtained by using the production method shown in this example is obtained from 3.35Å to 3.55Å depending on the raw material supply rate and the reaction temperature. Even if an electrode is used, it exhibits high electric capacity and good charge / discharge repeating characteristics.

In addition, what shows the above-mentioned electrode characteristics is not limited only to the manufacturing method described in the present embodiment. The object of the present invention can be achieved by optimizing by a CVD method such as resistance heating or high frequency induction heating.

<Comparative example> A graphite fiber was sandwiched between commercially available nets to collect electrodes. The test electrode B was placed in an electrolytic cell as shown in FIG. 3, and a charge / discharge test was conducted in the same manner as in the above-mentioned examples. Curve B in FIG. 4 is a potential change curve of the carbon electrode obtained by sandwiching the current collecting net according to this comparative example. From these results, the discharge capacity was small compared with the electrodes of the above-mentioned examples, and it was unsuitable as an electrode.

<Effects of the Invention> The electrode obtained by forming highly crystalline graphite on a conductive substrate having a catalytic action such as nickel by a vapor phase deposition method by low temperature pyrolysis is strong against charge-discharge cycle and over-discharge. Moreover, since it is not necessary to add a new conductive material, the packing density of the electrode is increased, and as a result, high density characteristics are exhibited. Moreover, since the process is simplified, it is very effective as an electrode for a secondary battery. The battery obtained by using the electrode of the present invention has good charge / discharge cycle characteristics, and can be widely used in various fields as a small-sized and low-cost battery.

[Brief description of drawings]

FIG. 1 is a block diagram of a graphite electrode manufacturing apparatus used to explain one embodiment of the present invention. FIG. 2 is an explanatory diagram showing an example of the X-ray diffraction result of the pyrolytic graphite of the graphite electrode according to the present invention. FIG. 3 is a schematic view showing an example of an apparatus for measuring the electrode characteristics of the graphite electrode according to the present invention. FIG. 4 is a charge / discharge characteristic diagram of a graphite electrode and graphite according to an embodiment of the present invention. FIG. 5 is a cycle characteristic diagram of a discharge capacity of a graphite electrode according to an example of the present invention. 1 ... Valve container, 2 ... Argon gas control system, 3 ...
Baylex glass tube, 4 ... reaction tube, 5 ... valve,
6 ... Dilution line, 7 ... Sample stand, 8 ... Heating furnace, 9 ...
… Exhaust vibrator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor ▲ Yoshi ▼ Takatsu 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Shigeo Nakajima 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka No. 22, 22 Inventor, Yoshimitsu Tajima, Osaka Prefecture, Osaka City, 22-22 Nagaike-cho, Abeno-ku, Osaka Prefecture (72) No. 22, 22 Inventor, Hideaki Tanaka, 22-22, Nagaike-cho, Abeno-ku, Osaka, Osaka In-house (72) Inventor Nobuhiro Yanagisawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) In-house Motoo Mouri 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation ( 72) Inventor Mitsuyo Kasahara, 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (56) References JP-A-60-36315 (JP, A) JP 59-18578 (JP, A) JP 60-182670 (JP, A) The Institute of Electrical Engineers of Japan A, 105 [6] (SHO 60-6) P.A. 34

Claims (4)

[Claims] 1. An electrode comprising graphite as an electrode active material, wherein the graphite is composed of a highly crystalline pyrolytic graphite of a hydrocarbon or a hydrocarbon compound, and is on an electrode substrate made of a metal exhibiting a catalytic action for promoting graphitization. An electrode formed by direct vapor deposition to cover the metal electrode substrate. 2. The electrode according to claim 1, wherein the metal electrode substrate is iron, cobalt, nickel or an alloy of these metals. 3. The electrode according to claim 1, wherein the pyrolytic graphite is doped with an alkali metal, an alkaline earth metal, a rare earth metal or a transition metal. 4. The electrode according to claim 1, wherein the pyrolytic graphite is doped with halogen, a halogen compound or oxyacid.