JPH0831411A - Manufacture of negative electrode for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain the negative electrode, which has a high energy density and in which generation of a short circuit due to the dendrite is eliminated, by forming a layer, which includes the organic material, on the surface of a collector of a negative electrode, and heating it for carbonation, and laminating a carbon material included layer thereon. CONSTITUTION:A layer, which includes the organic material such as pitch, polyacrylonitrile to be carbonated by heating, is formed on the surface of a collector of a negative electrode of a non-aqueous electrolyte secondary battery. This layer is heated at the carbonating temperature of the organic material or more for carbonating. (graphitization is included.) A layer including carbon material is laminated on the carbon layer obtained by the first process. Or, hydrocarbon such as benzene and methane is heated in the gas phase so as to form a thermal decomposition carbon layer on the surface of the collector of the negative electrode, and a layer including carbon material is laminated thereon. The carbon layer formed by the first process is made of the carbon material at less than 200mAh/g of discharging capacity, and the carbon of the carbon included layer formed by the second process is made of the carbon material at 200mAh/g or more of discharging capacity.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to a method for manufacturing the negative electrode.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium as a negative electrode have high electromotive force and are expected to have higher energy density than conventional nickel-cadmium storage batteries and lead storage batteries, and many studies have been conducted. However, when metallic lithium is used for the negative electrode, dendrites are generated during charging and short circuits easily occur inside the battery, resulting in a battery with low reliability. In order to solve this problem, the use of an alloy negative electrode of lithium and aluminum (Al) or lead (Pb) was studied. When these alloy negative electrodes are used, Li is occluded in the negative electrode alloy by charging, and dendrite is not generated, so that the battery has high reliability. However, since the discharge potential of the alloy negative electrode is about 0.5 V more noble than that of metallic Li, the voltage of the battery is also 0.5 V lower, which lowers the energy density of the battery.

[0003] On the other hand, researches using an intercalation compound of a carbon material such as graphite and Li as a negative electrode active material have been actively conducted. Also in this compound negative electrode, Li enters the carbon layer by charging and dendrite is not generated. Discharge potential is metal L
Since it is only about 0.1 V more than i, the decrease in battery voltage is small. This can be said to be a more preferable negative electrode. Usually, a carbonaceous material is obtained by decomposing an organic substance by heating at about 400 to 3000 ° C. in an inert atmosphere to carbonize and further graphitize. The starting material of the carbonaceous material is almost always an organic substance, and by heating up to around 1500 ° C., which is a carbonization step, almost only carbon atoms remain, and a graphite structure is developed by heating up to a high temperature near 3000 ° C. As the organic raw material, pitch in the liquid phase, coal or a mixture of coke and pitch is used, and in the solid phase, wood raw material, furan resin, phenol resin, epoxy resin, cellulose, Polyacrylonitrile, rayon, etc. are used. Also,
In the gas phase, hydrocarbon gases such as methane and propane are used. The shape of the carbon material is usually powder.

In order to manufacture a battery using such a powdery electrode material, in the case of a cylindrical battery or a prismatic battery, it is processed into a sheet-shaped negative electrode plate, and in the case of a coin battery, it is processed into a negative electrode molded body. Used. Therefore, at least a so-called binder which functions to bind the negative electrode carbon powders to each other is usually added to the negative electrode. As this binder,
Various materials such as rubber, polyolefin resin, fluorine resin, and acrylic resin are used according to the negative electrode material and required battery characteristics. All of them are used for maintaining the shapes of the negative electrode plate and the negative electrode molded body in the manufacturing process and for obtaining excellent battery characteristics.

[0005]

Although it is possible to obtain an excellent secondary battery by using the above-mentioned binder for the negative electrode plate or the negative electrode molded body, there are the following problems. (1) Since the conventional binder does not participate in the charge / discharge of the battery itself, it causes a decrease in the negative electrode capacity and reduces the battery capacity. (2) The conventional binder has an excellent function of binding the negative electrode carbon powders to each other, but the binding state between the metal current collector and the negative electrode carbon powder is not so excellent, and is associated with charge / discharge. Due to the expansion and contraction of the electrodes, the current collector and the electrode molded body do not come into sufficient contact with each other, and in the worst case, peeling or dropping occurs. SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, an object of the present invention is to provide a negative electrode that provides a highly reliable non-aqueous electrolyte secondary battery with higher energy density and no short circuit due to dendrite.

[0006]

The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention comprises forming a layer containing an organic material which is carbonized by heating on the surface of a negative electrode current collector and then applying the organic material to the layer. The method has a first step of carbonizing (including graphitizing) by heating at a temperature higher than the carbonization temperature, and a second step of laminating a layer containing a carbon material on the carbon layer obtained above. Also,
The method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention comprises a first step of heating hydrocarbons in a vapor phase to form a pyrolytic carbon layer on the surface of a negative electrode current collector, and the pyrolytic carbon layer. It has a 2nd process of laminating | stacking the layer containing a carbon material on it.

Here, the carbon layer formed in the first step is made of a carbon material having a discharge capacity of less than 200 mAh / g, and the carbon of the layer containing carbon formed in the second step has a discharge capacity of 200 mAh / g. It is preferably made of a carbon material of g or more. The carbon layer obtained in the first step is the second
Corresponding to 0.5 to 20 wt% of the carbon material of the layer obtained in the step is desirable. Further, when forming the wound electrode group, it is preferable to have a step of heating in a hydrogen atmosphere between the first step and the second step. The heating temperature in this hydrogen atmosphere is 600 to 1000 ° C.
Is preferred. The organic material to be carbonized is at least selected from the group consisting of petroleum pitch, coal pitch, resin pitch, polyacrylonitrile, coke, cellulose, furan resin, phenol resin, epoxy resin and rayon. It is preferably one. The heating temperature in this case is preferably in the range of 600 to 1000 ° C.

The hydrocarbons used as the raw material gas in the present invention may be any of aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, etc. , A hydroxyl group, a sulfone group, a nitro group, a nitroso group, an amino group and a carboxyl group). Specific examples thereof include methane, ethane, propane, butane, pentane, hexane, cyclohexane, naphthalene, anthracene, pyrene, benzene, toluene, pyridine, allylbenzene, hexamethylbenzene, aniline, phenol, 1,2- Examples include dibromoethylene, 2-butyne, acetylene, biphenyl, diphenylacetylene, styrene, acrylonitrile, pyrrole, thiophene and their derivatives. Among them, at least one selected from the group consisting of benzene, acetylene, ethylene, methane, ethane and propane is preferable. The heating temperature in this case is 600 to 1000.
The range of ° C is desirable. Further, as the negative electrode current collector, copper,
Nickel or an alloy containing it can be used. The shape of the current collector may be any of flat plate, foam, and net.

[0009]

According to the above-mentioned constitution of the present invention, after the layer containing the organic material is formed on the surface of the negative electrode current collector, the organic material is carbonized by heating it to the carbonization temperature of the organic material or higher, It is considered that it will change to a graphitized state. In this carbonization or graphitization reaction process, not only does the organic material undergo such a state change, but the reaction proceeds while firmly adhering and adhering to the surface of the negative electrode current collector. As a result, after heating, it adhered to the negative electrode current collector sufficiently firmly.
A closely adhered carbon body or graphite body is formed. Then, by laminating a layer containing a carbon material on it, a layer containing carbon is laminated on the carbon layer, so that both layers are in the same material because they are of the same kind of material, and are in a state of being sufficiently adhered.
In this way, a carbon electrode body or a graphite electrode body that is sufficiently firmly adhered and adhered to the negative electrode current collector is formed. As a result, the negative electrode has a high capacity and particularly excellent cycle characteristics. Similarly, by similarly pyrolyzing hydrocarbons in the gas phase to form the pyrolytic carbon layer on the surface of the negative electrode current collector, and then laminating a layer containing a carbon material thereon The effect of is obtained.

As described above, according to the present invention, even when carbon or graphite formed in contact with the current collector is a material having a large discharge capacity, a sufficient contact state with the current collector can be secured. It is very meaningful. However, when it is attempted to form carbon or graphite formed in contact with the current collector with a material having a large discharge capacity, it involves an industrially rather complicated process. The carbon material formed on the surface of the negative electrode current collector has a small discharge capacity, preferably 200 mAh /
A carbon material of g or less is preferable. With such a configuration, the carbon material in direct contact with the current collector has a relatively small expansion / contraction during charging / discharging, so that the contact with the current collector is sufficient even after a long-term charge / discharge cycle. It is a thing. As a result, a negative electrode having excellent cycle characteristics can be obtained. Moreover, the manufacturing process is simple and has great industrial significance.
Further, in the wound type battery, the current collector becomes hard due to the heating process described above, which makes winding difficult. Therefore, a layer containing an organic material is formed on the surface of the negative electrode current collector, heated to the carbonization temperature of the organic material or higher, and then heated in a hydrogen atmosphere and annealed to harden the current collector before heating. It is possible to obtain a negative electrode plate that can be wound by returning to the closed state.

[0011]

The present invention will be described in more detail with reference to its examples. Example 1 First, a layer containing an organic material was formed on the surface of a negative electrode current collector, heated to a temperature equal to or higher than the carbonization temperature of this organic material, and then a layer containing a carbon material was laminated thereon. The negative electrode will be described. In this example, petroleum pitch was used as the organic material and graphite was used as the carbon material. The procedure for producing the test cell shown in FIG. 1 is as follows. A paste-like solution obtained by dissolving 100 g of pitch in 1 liter of toluene in advance was applied to a copper core material, dried at 100 ° C., and then heated at 900 ° C. for 20 hours in an argon stream. Then, graphite 10
To 0 g, 200 g of a 2 wt% aqueous solution of sodium salt of carboxymethyl cellulose as a pasting agent was added, and 5 g of a styrene-butadiene rubber binder was further added, and the mixture was dried to form a graphite layer. As a comparative example, the paste solution was applied to a copper core material,
After drying at 0 ° C., a negative electrode in which the same graphite layers as above were laminated was prepared. Further, as a conventional example, a graphite layer similar to the above was directly formed on a current collector to prepare a negative electrode.

These negative electrode plates were punched into a disk shape having a diameter of 17.5 mm and pressure-molded to obtain test electrodes. FIG.
Indicates a test cell. The test electrode 1 is arranged in the center of the case 2, and a separator 3 made of a microporous polypropylene film is arranged thereon. On this separator,
After injecting a non-aqueous electrolyte consisting of a mixed solution of ethylene carbonate and dimethoxyethane in a volume ratio of 1: 1 in which 1 mol / l lithium perchlorate (LiClO ₄ ) was dissolved, a disc-shaped disc having a diameter of 17.5 mm Stick metal Li4,
A sealing plate 6 having a polypropylene gasket 5 attached to the outer peripheral portion is combined with the case 2 for sealing. With respect to these cells, cathodic polarization (corresponding to charging when the electrode 1 is regarded as a negative electrode) was performed at a constant current of 0.8 mA until the electrode became 0 V with respect to the Li counter electrode, and then the electrode 1 was 1.
Anodic polarization (corresponding to discharge) was performed until it reached 0V. This cathode polarization and anode polarization were repeated to evaluate the electrode characteristics. Table 1 shows the discharge capacity per 1 g of the electrode mixture in the first cycle and the discharge capacity in the 100th cycle and the cycle capacity retention rate of the cells using the electrodes of the examples, the comparative examples and the conventional example. The discharge capacity of the cell of the example is extremely large. The discharge capacity retention ratio at the 100th cycle was also highest in the cells of the examples.

[0013]

[Table 1]

[Embodiment 2] In this embodiment, a pyrolytic carbon layer obtained by pyrolyzing a hydrocarbon in a gas phase is formed on the surface of a negative electrode current collector, and then a layer containing a carbon material is laminated thereon. The obtained negative electrode will be described. Benzene is used as a hydrocarbon, and this is used at 900 ° C. in an argon stream for 2 hours.
It was heated for 0 hour for carbonization, and a pyrolytic carbon layer was formed on the surface of the copper core material as the negative electrode current collector. Then, as in Example 1, a paste containing graphite and a styrene-butadiene rubber binder was applied and a graphite layer was laminated. As a conventional example, a negative electrode in which the same graphite layer was directly formed on the current collector was also prepared. The structure of the test cell and its evaluation method are described in Example 1.
Is the same as Table 2 shows the initial capacity and the capacity retention rate after 100 cycles. The discharge capacity of the cell of this example is extremely large. Further, the discharge capacity retention ratio at the 100th cycle also showed a high value in the cell of this example. As described above, the negative electrode of the present invention has high capacity and excellent cycle characteristics.

[0015]

[Table 2]

Example 3 In this example, the discharge capacity of the carbon material formed on the surface of the current collector was investigated in detail. First, layers containing 6 kinds of carbon materials each having a discharge capacity of 100 to 300 mAh / g were formed by the following method. Toluene 1 to carbon material 100g beforehand
The paste solution prepared by adding liter was applied to a copper core material and dried at 100 ° C. Then, as in Example 1, a paste containing graphite and a styrene-butadiene rubber binder was applied to deposit a graphite layer. As a conventional example, a negative electrode in which the same graphite layer was directly formed on the current collector was similarly prepared. The structure of the test cell and its evaluation method are the same as in Example 1. The initial capacity and the capacity retention rate after 100 cycles were examined for cells using seven different types of negative electrode plates as described above. Table 3 shows the results. The discharge capacity does not differ so much depending on the type of carbon material formed on the current collector, but the discharge capacity retention ratio at the 100th cycle is 200 mAh / second as the discharge capacity of the carbon material formed on the current collector.
It can be seen that those of g or less are excellent.

[0017]

[Table 3]

[Embodiment 4] In this embodiment, a layer containing an organic material is formed on the surface of a negative electrode current collector, heated to the carbonization temperature of the organic material or higher, and then heated in a hydrogen atmosphere, and then, A negative electrode obtained by laminating a layer containing a carbon material thereon was examined. In this example, coal pitch was used as the organic material and graphite was used as the carbon material. In this example, the cylindrical battery shown in FIG. 2 was constructed and the characteristics were examined. A battery was manufactured by the following procedure. LiMn _1.8 Co _0.2 O ₄ , which is the positive electrode active material, is
i ₂ CO ₃ , Mn ₃ O _4, and CoCO ₃ were mixed at a predetermined molar ratio, and heated at 900 ° C. to synthesize. Further, this was classified into 100 mesh or less to obtain a positive electrode active material. To 100 g of the above positive electrode active material, 10 g of carbon powder as a conductive agent, 8 g of an aqueous dispersion of polytetrafluoroethylene as a binder and pure water were added to form a paste, which was applied to a titanium core material, It was dried and rolled to obtain a positive electrode. The weight of the positive electrode active material was 5 g.

The negative electrode was manufactured as follows. First, 100 g of coal-based pitch was dissolved in 1 liter of toluene, the paste solution was applied to a copper core material, dried at 100 ° C., and then heated at 900 ° C. for 20 hours in an argon stream. This was heated in a hydrogen atmosphere at 700 ° C. for 20 hours. Then, as in Example 1, a paste containing graphite and a styrene-butadiene rubber binder was applied to deposit a graphite layer. As a comparative example, the paste solution was applied to a copper core material, dried at 100 ° C., and then heated at 900 ° C. for 20 hours in an argon stream, and then a graphite layer similar to the above was laminated. That is, heating in a hydrogen atmosphere is not performed. As a conventional example, a negative electrode in which the same graphite layer was directly formed on the current collector was also prepared. In each battery, the weight of each graphite used in one battery was 2 g.

A microporous polypropylene film was used as the material for the separator. The electrode body is a positive electrode plate 1 having a positive electrode lead 14 made of the same material as the core material attached by spot welding.
1, a negative electrode plate 12 having a negative electrode lead 15, and a strip-shaped separator 13 interposed between both electrode plates and wider than the both electrode plates.
And were spirally wound. Further, polypropylene insulating plates 16 and 17 are arranged above and below the electrode body, respectively, and inserted into a battery case 18 to form a step on the upper part of the battery case 18. A mixed solution of ethylene carbonate and dimethoxyethane in an equal volume ratio in which 1 / l of lithium perchlorate was dissolved was injected and sealed with a sealing plate 19 to obtain a battery. 20 is a positive electrode terminal.

The initial capacity and the capacity retention rate after 100 cycles of the battery using the three different kinds of negative electrode plates were examined. Battery has a charge / discharge current of 0.5 mA / c
A charge / discharge cycle test was performed at m ² and a charge / discharge voltage range of 4.3V to 3.0V. Table 4 shows the initial capacity and the capacity retention rate after 100 cycles. The discharge capacity of the battery according to this example is extremely large. The discharge capacity retention rate at the 100th cycle was also highest in the battery of this example. The battery of Comparative Example could not be spirally wound because the negative electrode plate was hard and poor in flexibility.

[0022]

[Table 4]

[Embodiment 5] In this embodiment, the type of organic material was examined. A cylindrical battery using a negative electrode obtained by forming a layer containing each organic material on the surface of a negative electrode current collector, heating the organic material to a carbonization temperature or higher, and then laminating a layer containing a carbon material thereon. Will be described. In this example, graphite was used as the carbon material. The organic materials examined are petroleum pitch, coal pitch, resin pitch, polyacrylonitrile, coke, cellulose, furan resin, phenol resin, epoxy resin and rayon. In this example, the cylindrical battery shown in FIG. 2 was constructed and the characteristics were examined. The manufacturing method and evaluation method of the electrode and the battery are the same as in Example 4. As a comparative example,
A negative electrode in which a graphite layer similar to the above was directly formed on the current collector was also prepared. In each battery, the weight of each graphite used in one battery was 2 g. Table 5 shows the initial capacity and the capacity retention rate after 100 cycles. It can be seen that the batteries of this example all have a higher capacity than the comparative batteries and have excellent cycle characteristics.

[0024]

[Table 5]

Example 6 In this example, the heating temperature of the organic material was examined. Petroleum pitch was used as the organic material, and graphite was used as the carbon material. The negative electrode plate was produced as follows. First, 100 g of petroleum pitch was dissolved in 1 liter of toluene, the paste solution was applied to a copper core material and dried at 100 ° C., and then 400 ° C., 600 ° C., 900 ° C., 1000 in an argon stream.
C., 1050.degree. C. and 1200.degree. C. were respectively heated for 20 hours. Then, a graphite layer was laminated. As a conventional example, a negative electrode in which a graphite layer was directly formed on a current collector was similarly prepared. A battery was constructed in exactly the same manner as in Example 4 except that the above heating temperature was different. Since the melting point of copper as the core material was 1083 ° C., the copper plate was melted at 1200 ° C., so that the electrode could not be produced.

As described above, the initial discharge capacities of the batteries using the six types of negative electrode plates obtained by the different manufacturing methods, and 10
The capacity retention rate after 0 cycle was examined. The battery has a charge / discharge current of 0.5 mA / cm ² , and a charge / discharge voltage range of 4.3 V to 3.0.
A charge / discharge cycle test was performed at V. Table 6 shows the initial capacity and the capacity retention rate after 100 cycles. A large discharge capacity was obtained when the heating temperature was in the range of 600 ° C to 1000 ° C. It is considered that when the heating temperature is lower than 600 ° C., the petroleum pitch does not carbonize sufficiently, so that it does not act as an active material that absorbs and releases lithium, and as a result, the discharge capacity of the negative electrode becomes small. This can be seen from the fact that it showed the same initial discharge capacity and cycle maintenance rate as those of the comparative battery which was not heated at all. On the other hand, when the heating temperature exceeds 1000 ° C., excessive carbonization causes rapid carbonization and partial vaporization, which causes deterioration of the structure of the negative electrode plate, which lowers the strength of the negative electrode plate and collects the negative electrode current. It is considered that the initial discharge capacity and the capacity retention rate due to the charge / discharge cycle became low due to the decrease in the property.

[0027]

[Table 6]

In the above-mentioned embodiments, graphite is used as the carbon material, but it is reversible with respect to charging and discharging such as natural graphite, artificial graphite, carbon fiber, graphite whiskers, and non-graphitizable carbon. Needless to say, the same effect can be obtained by using the negative electrode carbon material. Incidentally, as the positive electrode in the embodiment has been described LiMn _1.8 Co _0.2 O _4, the negative electrode described in the present invention, In addition, LiC
_{oO 2, LiNiO 2, LiFeO 2} , γ -type LiV it goes without saying that the same effect even when combined with a positive electrode having a reversible against ₂ O _5, etc. beginning with charging discharging. Further, in the embodiment, the case of using the cylindrical battery is described, but the technical ideas such as the capacity increase described in the present invention are the same, and therefore the present invention is not limited to this structure, and a coin type battery is used. The same invention effect can be obtained in a secondary battery having a rectangular shape, a flat shape, or the like.

[0029]

As described above, according to the present invention, it is possible to obtain a negative electrode that has a high energy density and that provides a highly reliable non-aqueous electrolyte secondary battery that does not cause a short circuit due to dendrites.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a test cell used in an example of the present invention.

FIG. 2 is a vertical cross-sectional view of a cylindrical battery used in an example of the present invention.

[Explanation of symbols]

 1 Negative electrode 2 Case 3 Separator 4 Metal Li 5 Gasket 6 Sealing plate 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead plate 15 Negative electrode lead plate 16 Upper insulating plate 17 Lower insulating plate 18 Battery case 19 Sealing plate 20 Positive electrode terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Ito 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In the company

Claims (8)

[Claims] 1. A first step of forming a layer containing an organic material that is carbonized by heating on the surface of a negative electrode current collector, and then heating the organic material to a temperature equal to or higher than the carbonization temperature to carbonize the organic material. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising a second step of laminating a layer containing a carbon material on the obtained carbon layer. 2. A first step of heating hydrocarbons in a gas phase to form a pyrolytic carbon layer on the surface of a negative electrode current collector; and a step of laminating a layer containing a carbon material on the pyrolytic carbon layer. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which has the step of 2. 3. The carbon layer formed in the first step is made of a carbon material having a discharge capacity of less than 200 mAh / g, and the carbon of the layer containing carbon formed in the second step has a discharge capacity of 20.
The carbon material of 0 mAh / g or more, claim 1 or 2
A method for producing a negative electrode for a non-aqueous electrolyte secondary battery as described above. 4. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, further comprising a step of heating in a hydrogen atmosphere between the first step and the second step. 5. The organic material is petroleum pitch, coal pitch,
The non-aqueous electrolyte secondary according to claim 1, which is at least one selected from the group consisting of resin pitch, polyacrylonitrile, coke, cellulose, furan resin, phenol resin, epoxy resin and rayon. Manufacturing method of negative electrode for battery. 6. The hydrocarbons are benzene, acetylene,
The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, which is at least one selected from the group consisting of ethylene, methane, ethane and propane. 7. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the heating temperature is in the range of 600 to 1000 ° C. 8. The heating temperature in a hydrogen atmosphere is 600.
The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein the temperature is in the range of 1000 ° C to 1000 ° C.