JPH09106818A - Manufacture of negative electrode for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a non-aqueous electrolyte secondary battery which high entering dencity and excellent cycle property and is free of dendrites by eliminating capacity decrease due to the difference between a charging capacity and a discharging capacity in the first time charging and dischaging. SOLUTION: The negative electrode manufacturing method of the present invention involves a process to heat a carbon material in reduced pressure or a process to heat a carbon material together with a lithium compound in an inert atmosphere. The method also involves a process to carbonize the carbonizable material by adding a lithium compound to a solid-phase carbonizable material or a liquid-phase carbonizable material and carrying out heating treatment in an inert atmosphere.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an improvement in a negative electrode of a non-aqueous electrolyte secondary battery. More specifically, a non-aqueous electrolyte comprising a positive electrode having reversibility for charging and discharging, a non-aqueous electrolyte containing a lithium salt, and a negative electrode having a carbon material having reversibility for charging and discharging as an active material. The present invention relates to a method for manufacturing a negative electrode used in a secondary battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium as a negative electrode have a high electromotive force, and are expected to have a higher energy density than conventional nickel-cadmium storage batteries and lead storage batteries, and are being actively researched. However, when metallic lithium is used for the negative electrode, dendrites are likely to occur during charging, which may cause a short circuit inside the battery, making it difficult to secure high reliability as a battery. In order to solve this problem, the use of an alloy negative electrode of lithium, aluminum and lead has been studied. When these alloy negative electrodes are used, lithium is occluded in the negative electrode alloy by charging, and dendrites are not generated, resulting in a highly reliable battery. However, since the discharge potential of the alloy negative electrode is about 0.5 V noble as compared with metallic lithium, the battery voltage is also 0.5 V lower,
This also reduces the energy density of the battery.

On the other hand, researches using an intercalation compound of a carbon material such as graphite and lithium as a negative electrode active material have been actively conducted. In this compound negative electrode, lithium enters between layers of the carbon material by charging, and dendrite is not generated. Since the discharge potential is no more than about 0.1 V as compared with metallic lithium, the decrease in battery voltage is small. Therefore, it can be said that it is 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 it, and further performing graphitization. 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 3000
The graphite structure develops by heating to a high temperature close to ℃. As the organic raw material, in the liquid phase, pitch, cortall,
Alternatively, a mixture of coke and pitch or the like is used, and in the solid phase, wood raw material, furan resin, phenol resin, epoxy resin, cellulose, polyacrylonitrile, rayon or the like is used. In the gas phase, hydrocarbon gas such as methane and propane is used.

[0004]

It is known that the carbon material usually has a larger charge capacity than the discharge capacity in the first charge / discharge. In other words, in the first charge / discharge, the amount of electricity that does not contribute to the discharge is consumed. This charge / discharge capacity difference is called “capacity loss” or “retention”. A material containing lithium in the positive electrode, such as Li
This difference in charge and discharge capacity is a serious problem in a lithium ion secondary battery that uses CoO ₂ and uses a carbon material for the negative electrode. Since the capacity of this battery is governed by the positive electrode, part of the lithium given from the positive electrode to the negative electrode during the first charging is consumed without being used for discharging. As a result, the battery capacity is reduced by the amount of lithium consumed. In order to solve this problem, it is an object of the present invention to provide a negative electrode that provides a highly reliable non-aqueous electrolyte secondary battery with higher energy density and without short circuit due to dendrite.

[0005]

The method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention comprises a step of subjecting a carbon material having reversibility to charge and discharge to heat treatment under reduced pressure. Further, in particular, the step of heating under reduced pressure is disadvantageous from an industrial viewpoint of equipment and productivity as a practical problem, so that as a further development of the present invention,
A lithium compound is added to the carbon material and heat treatment is performed in an inert atmosphere. The heat treatment may be performed after the carbon material is not in the powder state but formed on the electrode. That is, it is a method in which a layer of a carbon material is formed on the surface of a current collector by coating or the like, and this is heated under reduced pressure or heat-treated in an inert atmosphere together with a lithium compound. The carbon material used here has a (002) plane spacing of 3.37 to 3.90 in the X-ray wide-angle diffraction method using a Cu-Kα radiation source.
Angstrom, the size of the crystallite in the c-axis direction is 5 to
It is preferably 150 Å.

Further, according to the present invention, when a carbon material obtained by heating a solid phase carbonized material or a liquid phase carbonized material in an inert atmosphere to be carbonized is used, the following method is adopted. That is, a lithium compound is added to a solid-phase carbonized material or a liquid-phase carbonized material and heated in an inert atmosphere to carbonize the solid-phase carbonized material or the liquid-phase carbonized material. It is a method for manufacturing a negative electrode for a secondary battery.
Further, a step of forming a solid-phase carbonized material or a liquid-phase carbonized material on the surface of the negative electrode current collector, a step of adding a lithium compound thereto, and heating the same in an inert atmosphere, It is a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which has a step of carbonizing a liquid phase carbonized material.

The lithium compound is preferably at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium oxide, lithium chloride, and lithium nitrate. The liquid-phase carbonization material is preferably at least one selected from petroleum pitch, coal pitch and resin pitch. Further, as the solid-phase carbonization material, polyacrylonitrile, coke,
At least one selected from cellulose, furan resin, phenol resin, epoxy resin and rayon is suitable. Here, when the weights of the carbon material, the solid-phase carbonized material or the liquid-phase carbonized material and the lithium compound added thereto are W ₁ and W ₂ , respectively, the ratio W ₂ / W ₁ is 1/100 to 100.
The range of / 100 is appropriate.

The heating temperature is preferably in the range of 200 ° C. to 1400 ° C. when heating the carbon material under reduced pressure. Also,
Also when heating the carbon material together with the lithium compound in an inert atmosphere, the range of 200 ° C to 1400 ° C is preferable. When using a solid-phase carbonized material, the temperature range is 400 to 2000 ° C., and when using a liquid-phase carbonized material, 400 to 300 ° C.
A range of 0 ° C is suitable for each.

According to the present invention, by heating the carbon material under reduced pressure, the effects of improving the surface condition of the carbon material, reducing impurities, and removing substances that do not contribute to charge and discharge can be obtained. Further, in place of the complicated and low productivity process of heating under reduced pressure, when a lithium compound is added to a carbon material, a solid-phase carbonized material or a liquid-phase carbonized material, and the mixture is heated in an inert atmosphere, Effects such as improvement of the surface condition, reduction of impurities, and removal of substances that do not contribute to charge / discharge can be obtained. Furthermore, it is conceivable that this treatment causes the carbon material to react with lithium in advance to reduce the consumption of lithium on carbon during the first charging. As a result, the lithium consumed in the negative electrode during the first charge is reduced, and it is possible to obtain a highly reliable secondary battery having a higher energy density and not causing a short circuit due to dendrites.

In the case where the technique of heating the carbon material according to the present invention under reduced pressure is combined with the technique of adding the lithium compound to the carbon material, the solid-phase carbonized material or the liquid-phase carbonized material and heating it in an inert atmosphere Needless to say, is more effective. Further, according to the production method of the present invention, the step of heating a negative electrode plate containing a carbon material under reduced pressure, or by adding a lithium compound to the negative electrode plate and heating in an inert atmosphere, carbon material,
Compared with the case where the solid-phase carbonized material or the liquid-phase carbonized material is used, higher reproducibility can be realized, and there is an effect that the manufacturing variation of the negative electrode plate can be reduced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail by way of its examples. [Example 1] An example of heat-treating a carbon material under reduced pressure will be described. In this example, the carbon material used was obtained by heating petroleum pitch at 1000 ° C. in a nitrogen atmosphere. This carbon material has an average particle size of 20 μm, and C
(002) in the X-ray wide-angle diffraction method using the u-Kα radiation source
The interplanar spacing (d ₀₀₂ ) is 3.4 Å, and the crystallite size (Lc) in the c-axis direction is 10 Å. The negative electrode was prepared by heating the above carbon material, which is a negative electrode active material, to 700 ° C. under reduced pressure. A negative electrode, in which the above carbon material was not heated under reduced pressure and used as an active material as it is, is used as a comparative example. 1 g of polyethylene powder as a binder was mixed with 10 g of these carbon materials, and 0.1 g of this mixture was added to a diameter of 1
It was pressure-molded into a 7.5 mm disk.

A test cell as shown in FIG. 1 was assembled using the carbon electrode thus obtained. Reference numeral 1 denotes this carbon electrode, which is arranged in the center of the metal case 2. On this electrode 1,
After placing the separator 3 made of microporous polypropylene and injecting the non-aqueous electrolyte, a disc-shaped metallic lithium 4 having a diameter of 17.5 mm is attached to the inside, and the sealing plate 6 having the polypropylene gasket 5 attached to the outer peripheral portion is attached. Combined and sealed. The electrolytic solution was prepared by dissolving lithium perchlorate (LiClO ₄ ) in a mixed solvent of ethylene carbonate and dimethoxyethane at a volume ratio of 1: 1 at a ratio of 1 mol / l. Regarding the test battery having the above configuration, first, 0.5 m
At constant current of A, cathode polarization is performed until the carbon electrode becomes 0 V with respect to the lithium counter electrode (corresponding to charging when the carbon electrode is regarded as a negative electrode), and then anode polarization (discharging is performed until the electrode becomes 1.0 V). Equivalent to). This cathodic polarization and anodic polarization were repeated 10 times, and the capacity at the 10th cycle was taken as the initial capacity. The capacity was evaluated based on the weight of carbon. Further, a charge / discharge cycle test was conducted in which the above constant current test was repeated 100 cycles. The results are shown in Table 1.

[0013]

[Table 1]

The battery according to the present invention has an extremely large discharge capacity as compared with the comparative example. Moreover, there is no difference between the charge capacity and the discharge capacity in the first cycle. On the other hand, in the battery of the comparative example, the difference between the charge capacity and the discharge capacity in the first cycle was 120 mAh / g. As described above, this charge / discharge capacity difference is referred to as “capacity loss” or “retention”, and for example, LiCoO ₂ containing lithium is used for the positive electrode and a negative electrode is used in the lithium ion secondary battery using the carbon material for the negative electrode. The difference in charge and discharge capacity is a serious problem. Since the capacity of this battery is governed by the positive electrode, part of the lithium given from the positive electrode to the negative electrode during the first charging is consumed without being used for discharging. As a result, the battery capacity is reduced by the amount of lithium consumed. Also, 10
The discharge capacity retention rate at the 0th cycle was also high in the battery of the present invention. As is apparent from the above, the battery using the negative electrode according to the present invention has a high capacity and excellent cycle characteristics.

Example 2 The crystal structure of the carbon material was examined. The interplanar spacing (d) of the (002) plane in the X-ray wide-angle diffraction method using the Cu-Kα radiation source of the carbon material used for the test
₀₀₂ ) and the crystallite size (Lc) in the c-axis direction are shown in Table 2. These carbon materials were heated to 700 ° C. under reduced pressure in the same manner as in Example 1, and then molded into electrodes to assemble a test battery as shown in FIG. The discharge capacity and the discharge capacity retention rate at the 100th cycle were examined. Table 2 shows the results.
The capacity was evaluated based on the weight of carbon.

[0016]

[Table 2]

The spacing (d ₀₀₂ ) of the (002) plane is 3.3.
A carbon material having a crystallite size (Lc) in the c-axis direction of 7 to 3.90 angstroms in the range of 5 to 150 angstroms has a large discharge capacity. Moreover,
The carbon material in this range has a difference of 0 between the charge capacity and the discharge capacity in the first cycle. A carbon material having d ₀₀₂ smaller than 3.37 angstrom has a high degree of crystallinity, and is often carbonized (graphitized) at a high temperature close to 3000 ° C. Therefore, in such a carbon material, it is considered that there is no effect of removing ungrown carbon components or reducing surface impurities by further heating under reduced pressure (in vacuum). On the other hand, a carbon material having a d ₀₀₂ of greater than 3.90 Å has a considerably complicated surface structure and functional group state, and it is considered that the carbon material cannot be sufficiently modified by heating under reduced pressure.

[Example 3] In the same manner as in Example 1, the carbon material obtained by heating petroleum pitch at 1000 ° C in a nitrogen atmosphere was evaluated by constructing a cylindrical battery. First, 5 g of a styrene-butadiene rubber binder was mixed with 100 g of the above-mentioned carbon material, which is a negative electrode active material, heated to 700 ° C. under reduced pressure, and the mixture was made into a paste using a petroleum solvent. This paste was applied to a copper core material and dried at 100 ° C. to prepare a negative electrode plate. For comparison, the above carbon powder was not heated under reduced pressure, and a negative electrode was produced as it was as an active material. The weight of carbon in each electrode was 2 g. The positive electrode active material includes Li ₂ CO ₃ , Mn ₃ O ₄ and CoCO.
LiMn _1.8 Co _0.2 O ₄ synthesized by mixing ₃ and ₃ at a predetermined molar ratio and heating at 900 ° C. was used. This positive electrode active material is classified to 100 mesh or less 10
To 0 g, 10 g of carbon powder as a conductive agent and 8 g of an aqueous dispersion of polytetrafluoroethylene as a binder in a solid content were added to form a paste, which was applied to a titanium core material.
After drying, it was rolled to obtain a positive electrode. Weight of positive electrode active material is 5g
And Microporous polypropylene was used as the material of the separator.

Insulating plates 16 and 1 made of polypropylene are formed on the upper and lower sides of the electrode plate group in which the positive electrode plate 11, the negative electrode plate 12 and the separator 13 interposed between both electrode plates are spirally wound.
7 is placed and inserted in the battery case 18, a step is formed on the upper part of the battery case 18, a non-aqueous electrolyte is injected, and the battery is sealed with a sealing plate 19 to produce a sealed battery as shown in FIG. did. The electrolytic solution is prepared by dissolving lithium perchlorate in a mixed solvent of ethylene carbonate and dimethoxyethane in a volume ratio of 1: 1 at a ratio of 1 mol / l. Reference numerals 15 and 16 respectively denote leads connected to the positive electrode 11 and the negative electrode 12 by spot welding. 2
0 is a positive electrode terminal. A battery using two different types of negative electrode plates as described above 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 4.3 V to 3.0 V to examine the initial capacity and the capacity retention rate at the 100th cycle. Table 3 shows the results. The battery according to the present invention had an extremely large discharge capacity and a high discharge capacity retention ratio at the 100th cycle.

[0020]

[Table 3]

[Embodiment 4] In this embodiment, a material obtained by adding a lithium compound to a carbon material and heating it will be described. As the negative electrode active material, a carbon material 100 obtained by heating petroleum pitch at 1000 ° C. in a nitrogen atmosphere in the same manner as in Example 1.
Lithium hydroxide (50 g) was added to g, and the mixture was heated to 700 ° C. in an argon atmosphere and used. In the present example, similar tests were conducted using lithium carbonate, lithium carbonate, lithium oxide, lithium chloride, and lithium nitrate as the lithium compound. In the comparative example, a carbon material was used in which a lithium compound was not added and heating was not performed. First, 5 g of a styrene-butadiene rubber binder was mixed with 100 g of each of the above carbon material powders, and the mixture was made into a paste using a petroleum solvent and applied to a copper core material at 100 ° C. Dried. Thus, a negative electrode containing 2 g of the carbon material was obtained. The positive electrode has an active material of LiMn _1.8 Co _0.2 O
_It has the same configuration as in Example 3 using ₄ . Example 3 in which the positive electrode plate is combined with the different types of negative electrode plates as described above
A cylindrical battery similar to the above is configured, and the charge / discharge current is 0.5 mA /
A charging / discharging cycle test was performed in a cm ² range of charging / discharging voltage of 4.3V to 3.0V. Table 4 shows the initial capacity and the capacity retention rate at the 100th cycle.

[0022]

[Table 4]

The battery according to the present invention had an extremely large discharge capacity and a high discharge capacity retention ratio at the 100th cycle. Further, it was found that lithium carbonate, lithium carbonate, lithium oxide, lithium chloride, and lithium nitrate had the same effect as lithium hydroxide.

[Embodiment 5] In this embodiment, polyacrylonitrile, coke, cellulose, furan resin, phenol resin, epoxy resin, solid phase carbonized material,
Rayon and cellulose were used respectively. First, 50 g of lithium hydroxide was added to 100 g of polyacrylonitrile, which is a solid carbonized material, and sufficiently mixed, and then heated to 700 ° C. in an argon stream. The obtained powder was used as a negative electrode active material, and 100 g thereof was mixed with 5 g of a styrene-butadiene rubber binder. A petroleum-based solvent is added to this mixture to form a paste, which is applied to a copper core material at 100 ° C.
And dried to prepare a negative electrode plate. For comparison, 700% without adding lithium hydroxide to polyacrylonitrile
A powder obtained by heating to ° C was used as a negative electrode active material, and a negative electrode plate was prepared in the same manner as above. In addition to polyacrylonitrile as a solid-phase carbonization material, coke, cellulose, furan resin, phenol resin, epoxy resin, and rayon were treated in exactly the same manner to prepare a negative electrode plate. did.
In each case, the weight of the negative electrode active material was 2 g.

Using these negative electrode plates, a cylindrical battery having the structure shown in FIG. 2 was prepared in the same manner as in Example 3. A charge / discharge cycle test was performed on these batteries at a charge / discharge current of 0.5 mA / cm ² and a charge / discharge voltage range of 4.3V to 3.0V. Table 5 shows the initial capacity and the capacity retention rate at the 100th cycle.

[0026]

[Table 5]

The battery according to the present invention has an extremely large discharge capacity, and the difference between the charge capacity and the discharge capacity in the first cycle is zero. On the other hand, in the battery of the comparative example, the difference between the charge capacity and the discharge capacity in the first cycle was 150 mAh or more.
The discharge capacity retention rate at the 100th cycle was also high in the battery according to the present invention. As described above, it was found that the battery using the negative electrode according to the present invention has a high capacity and excellent cycle characteristics. In addition, although the example using LiMn _1.8 Co _0.2 O ₄ as the positive electrode active material has been described in the examples, the negative electrode according to the present invention is not limited to this.
_{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 and charging discharging.

[Embodiment 6] In this embodiment, a resin pitch is used as the liquid carbonization material. First, 50 g of lithium hydroxide was added to 100 g of polyvinyl chloride pitch as a resin pitch and mixed sufficiently, and then heated to 700 ° C. in an argon stream. The obtained powder was used as a negative electrode active material, and styrene-butadiene rubber was mixed as a binder into this powder, which was used as a negative electrode active material, and 100 g thereof was mixed with 5 g of a styrene-butadiene rubber binder. A petroleum solvent was added to this mixture to form a paste, which was applied to a copper core material and dried at 100 ° C. to prepare a negative electrode plate. For comparison, a powder obtained by directly heating to 700 ° C. without adding quinoline to polyvinyl chloride pitch was used as a negative electrode active material, and a negative electrode plate was prepared in the same manner as above. In addition to the resin pitch as the liquid-phase carbonization material, petroleum pitch and coal pitch were treated in exactly the same manner, and then a negative electrode plate was produced. As a comparative example, for resin-based pitch, petroleum pitch, and coal pitch as liquid-phase carbonization materials, powder obtained by directly heating to 700 ° C. without adding lithium hydroxide was used as a negative electrode active material. A plate was made. In each case, the weight of the negative electrode active material was 2 g.

Using these negative electrode plates, a cylindrical battery having the structure shown in FIG. 2 was prepared in the same manner as in Example 3. A charge / discharge cycle test was performed on these batteries at a charge / discharge current of 0.5 mA / cm ² and a charge / discharge voltage range of 4.3V to 3.0V. Table 6 shows the initial capacity and the capacity retention rate at the 100th cycle. The battery according to the present invention had an extremely large discharge capacity and a high discharge capacity retention ratio at the 100th cycle.

[0030]

[Table 6]

[Embodiment 7] In this embodiment, the mixing ratio of the lithium compound to the carbon material was examined. As the carbon material, the one obtained by heating petroleum pitch at 1000 ° C. in a nitrogen atmosphere as in Example 1 was used. This carbon material has an average particle size of 20 μm and a d ₂₀₀ of 3.
At 4 angstroms, Lc is 10 angstroms. Lithium hydroxide was added to 100 g of the above carbon material at various ratios, and then heated to 700 ° C. in an argon atmosphere. Here, when the weight of the carbon material is W ₁ and the weight of lithium hydroxide is W ₂ , the value of W ₂ / W ₁ is 0/100.
From 120 to 100/100. The powder of the carbon material treated as described above was used as the negative electrode active material. For comparison, an active material was prepared by adding no lithium compound to the above carbon material and not heating it. A negative electrode plate was produced using these active materials in exactly the same manner as in Example 3, and was combined with the same positive electrode plate as in Example 3 to form a cylindrical battery. Charge / discharge current of 0.5 mA / c for batteries using various negative plates
A charge / discharge cycle test was performed at m ² and a charge / discharge voltage range of 4.3V to 3.0V. Table 7 shows the initial capacity and the capacity retention rate at the 100th cycle.

[0032]

[Table 7]

The discharge capacity showed an extremely large value in the range of W ₂ / W ₁ from 1/100 to 100/100. Further, the discharge capacity retention ratio at the 100th cycle also showed a high value in the same weight range. When the value of W ₂ / W ₁ is less than 1/100, it is considered that the effects of improving the surface condition of the carbon material, reducing impurities, and removing substances that do not contribute to charge and discharge are not sufficient. On the other hand, the value of W ₂ / W ₁ is 100/10
If it exceeds 0, excess lithium compound is present in the negative electrode, which is considered to adversely affect the discharge capacity and cycle characteristics. In addition, the same study was carried out on the carbon material obtained by carbonizing the solid phase carbonized material and the liquid phase carbonized material. As a result, when the weight of any one of the carbon material, the solid-phase carbonized material or the liquid-phase carbonized material is W ₁ and the weight of lithium hydroxide is W ₂ , the value of W ₂ / W ₁ is 1
It was found that the discharge capacity was large in the range of / 100 to 100/100 and that excellent cycle characteristics were obtained. Further, as the lithium compound, it was confirmed that lithium carbonate, lithium oxide, lithium chloride, and lithium nitrate had the same effect as lithium hydroxide.

[Embodiment 8] In this embodiment, an example of producing a negative electrode plate containing a carbon material and then performing heat treatment under reduced pressure will be described. A carbon material obtained by heating petroleum pitch at 1000 ° C. in a nitrogen atmosphere was used. This carbon material has an average particle size of 20 μm, d ₂₀₀ of 3.4 angstroms, and Lc of 10 angstroms. Styrene-butadiene rubber as a binder was added to the above carbon material at a weight ratio of 100: 10, and then made into a paste using a petroleum solvent, and this paste was applied to a copper core material,
It was dried at 200 ° C. to prepare a negative electrode plate. The weight of the negative electrode active material was 2 g. Then, the negative electrode plate was placed under reduced pressure to 700
Heated to ° C. On the other hand, a comparative example uses the above negative electrode plate as it is without being subjected to the heat treatment. Using these negative electrode plates, a cylindrical battery was constructed in the same manner as in Example 3. A charge / discharge cycle test was performed on these batteries under the same conditions as described above. Table 8 shows the initial capacity and the capacity retention rate at the 100th cycle. The battery according to the present invention had an extremely large discharge capacity and a high discharge capacity retention ratio at the 100th cycle.

[0035]

[Table 8]

[Embodiment 9] In this embodiment, a method of forming a solid-phase carbonized material on the surface of a negative electrode current collector and a method of manufacturing a negative electrode having a step of adding a lithium compound thereto and then heating the material will be examined. did. Polyacrylonitrile was used as the solid-phase carbonization material. Styrene-butadiene rubber was added to polyacrylonitrile at a weight ratio of 100: 10, and then made into a paste using a petroleum solvent, which was applied to a copper core material and dried at 200 ° C. to prepare a negative electrode plate. Was produced. The weight of the solid-phase carbonized material applied is 2 g.
After adding 1 g of lithium hydroxide to this electrode plate, it was heated at 700 ° C. in an argon stream to obtain a negative electrode plate. On the other hand, as a comparative example, the negative electrode plate was heated at 700 ° C. in an argon stream without adding lithium hydroxide. A cylindrical battery was constructed using these negative electrode plates in the same manner as in Example 3, and a charge / discharge cycle test was performed under the same conditions as described above. Table 9 shows the initial capacity and the capacity retention rate at the 100th cycle. The battery according to the present invention has an extremely large discharge capacity,
The discharge capacity retention rate at the 100th cycle also showed a high value.

[0037]

[Table 9]

[Embodiment 10] In this embodiment, a negative electrode having a step of forming a liquid-phase carbonized material on the surface of a negative electrode current collector, a step of adding a lithium compound to it, and a step of heating the same. The manufacturing method was examined. As a liquid-phase carbonization material, styrene-butadiene rubber was added to polyvinyl chloride pitch, which is a resin pitch, at a weight ratio of 100: 10, and then made into a paste using a petroleum solvent,
This was applied to a copper core material and dried at 200 ° C. to prepare a negative electrode plate. The weight of the liquid-phase carbonized material applied is 2 g. After adding 1 g of lithium hydroxide to this electrode plate, it was heated at 700 ° C. in an argon stream to obtain a negative electrode plate. on the other hand,
As a comparative example, the negative electrode plate was heated at 700 ° C. in an argon stream without adding lithium hydroxide. A cylindrical battery was constructed using these negative electrode plates in the same manner as in Example 3, and a charge / discharge cycle test was performed under the same conditions as described above.
Table 10 shows the initial capacity and the capacity retention rate at the 100th cycle.

[0039]

[Table 10]

The battery according to the present invention had an extremely large discharge capacity and a high discharge capacity retention ratio at the 100th cycle. Furthermore, in the examples, the above carbon material was used as the carbon material, but reversibility with respect to charging and discharging including natural graphite, artificial graphite, carbon fiber, graphite whiskers, non-graphitizable carbon, etc. It is needless to say that the same effect can be obtained when the negative electrode carbon material is used.

Example 11 In this example, the heating temperature under reduced pressure in Example 3 was examined.
The heating temperature was changed in the range of 100 to 1600 ° C. A battery was constructed in the same manner as in Example 3 except for the above, and the characteristics were examined. The results are shown in Table 11.

[0042]

[Table 11]

A large discharge capacity and excellent cycle characteristics were obtained in the heating temperature range of 200 ° C to 1400 ° C. When the heating temperature is lower than 200 ° C., the ungrown carbon is not sufficiently removed, which adversely affects the charge / discharge reaction of the carbon material, and as a result, the discharge capacity of the battery is considered to be small.
On the other hand, when the heating temperature exceeds 1400 ° C., the discharge capacity is similarly large, but the cycle characteristics are poor. Although the detailed cause is not clear, it is considered that the carbon material is adversely affected on its surface by excessive heating.

[Embodiment 12] In this embodiment, the heating temperature when the carbon material to which the lithium compound is added in Embodiment 4 is heated in an argon atmosphere was examined. The heating temperature was changed in the range of 100 to 1600 ° C. Except for this, a battery was constructed in exactly the same manner as in Example 4, and the characteristics were examined. Table 12 shows the results.

[0045]

[Table 12]

A large discharge capacity and excellent cycle characteristics were obtained in the heating temperature range of 200 ° C to 1400 ° C. As in the case of Example 11, when the heating temperature is lower than 200 ° C., the ungrown carbon is not sufficiently removed, which adversely affects the charge / discharge reaction of the carbon material and, as a result, when the discharge capacity of the battery is small. Conceivable. On the other hand, the heating temperature is 1400 ° C
If it exceeds, the discharge capacity is also large, but the cycle characteristics are inferior. It is considered that the carbon material had an adverse effect on the surface of the carbon material due to excessive heating.

[Embodiment 13] In this embodiment, the heating temperature for heating the solid-phase carbonized material to which the lithium compound was added in Embodiment 5 in an argon atmosphere was examined. The heating temperature was changed in the range of 300 to 2500 ° C.
Except for this, a battery was constructed in exactly the same manner as in Example 5, and the characteristics were examined. The results are shown in Table 13.

[0048]

[Table 13]

A large discharge capacity and excellent cycle characteristics were obtained in the heating temperature range of 400 ° C to 2000 ° C. When the heating temperature is lower than 400 ° C., it is considered that the polyacrylonitrile 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 is small. On the other hand, when the heating temperature exceeds 2000 ° 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 causes the negative electrode plate to collect. It is considered that the initial discharge capacity and the capacity retention rate due to the charge / discharge cycle were low because the electrical property also decreased.

[Embodiment 14] In this embodiment, the heating temperature for heating the liquid phase carbonized material to which the lithium compound is added in Embodiment 6 in an argon atmosphere was examined. The heating temperature was changed in the range of 300 to 3200 ° C.
A battery was constructed in the same manner as in Example 6 except for the above, and the characteristics were examined. Table 14 shows the results.

[0051]

[Table 14]

A large discharge capacity and excellent cycle characteristics were obtained when the heating temperature was in the range of 400 ° C to 3000 ° C. When the heating temperature is lower than 400 ° C., it is considered that the coal 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 is small. On the other hand, when the heating temperature exceeds 3000 ° C., excessive carbonization causes rapid carbonization and partial vaporization to cause deterioration of the negative electrode structure, which is considered to result in a low capacity retention rate due to charge / discharge cycles. Also,
Heating above 3000 ° C. is not easy to carry out industrially from the economical viewpoint.

Example 15 In this example, the heating temperature for heating the negative electrode plate containing the lithium compound in Example 9 in an argon atmosphere was examined. The heating temperature was changed in the range of 100 to 1200 ° C. A battery was constructed in the same manner as in Example 9 except for the above, and the characteristics were examined.
Table 15 shows the results.

[0054]

[Table 15]

A large discharge capacity and excellent cycle characteristics were obtained in the heating temperature range of 200 ° C to 1000 ° C. When the heating temperature is lower than 200 ° C., the petroleum solvent does not vaporize sufficiently, which adversely affects the charge / discharge reaction of the carbon material.
As a result, the discharge capacity of the battery is considered to be small. Since the melting point of copper, which is the core material, is 1083 ° C.,
When heated at 00 ° C., the copper plate was melted and a battery could not be produced.

[Embodiment 16] In this embodiment, Embodiment 10 will be described.
In, the heating temperature when heating the negative electrode plate containing the lithium compound in an argon atmosphere was examined. The heating temperature was changed in the range of 300 to 1200 ° C. Except for this, a battery was constructed and characteristics were examined in exactly the same manner as in Example 10. Table 16 shows the results.

[0057]

[Table 16]

A large discharge capacity and excellent cycle characteristics were obtained in the heating temperature range of 400 ° C to 1000 ° C. When the heating temperature is lower than 400 ° C., it is considered that the 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 is small. Further, at 1200 ° C., the copper plate was melted, so that the battery could not be manufactured.

[0059]

As described above, according to the present invention, it is possible to obtain a negative electrode which provides a highly reliable non-aqueous electrolyte secondary battery having a high energy density and not causing a short circuit due to dendrite.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a test cell for evaluating a negative electrode in an example of the present invention.

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

[Explanation of symbols]

 1 Carbon Electrode 2 Case 3 Separator 4 Metal Lithium 5 Gasket 6 Sealing Plate 11 Positive Electrode 12 Negative Electrode 13 Separator 14 Positive Electrode Lead 15 Negative Electrode Lead 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 (12)

[Claims] 1. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising a step of heating a carbon material under reduced pressure. 2. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which comprises a step of heating a carbon material together with a lithium compound in an inert atmosphere. 3. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the heating step is performed after forming the electrode containing the carbon material. 4. The carbon material has an interplanar spacing of (002) planes of 3.37 to 3 by an X-ray wide-angle diffraction method using a Cu—Kα radiation source.
4. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the size of the crystallite in the c-axis direction is 3.90 angstroms and 5 to 150 angstroms. 5. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising a step of adding a lithium compound to a solid-phase carbonized material and heating the solid-state carbonized material in an inert atmosphere to carbonize the solid-phase carbonized material. 6. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which comprises the step of adding a lithium compound to a liquid-phase carbonized material and heating it in an inert atmosphere to carbonize the liquid-phase carbonized material. 7. A step of forming a solid-phase carbonized material on the surface of a negative electrode current collector, a step of adding a lithium compound thereto, and heating this in an inert atmosphere to carbonize the solid-phase carbonized material. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which has a step. 8. A step of forming a liquid-phase carbonized material on the surface of a negative electrode current collector, a step of adding a lithium compound thereto, and heating this in an inert atmosphere to carbonize the liquid-phase carbonized material. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which has a step. 9. The lithium compound is lithium hydroxide,
The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 2, 5, 6, 7, and 8, which is at least one selected from the group consisting of lithium carbonate, lithium oxide, lithium chloride, and lithium nitrate. . 10. 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 200 to 1400 ° C. 11. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 5, wherein the heating temperature is in the range of 400 to 2000 ° C. 12. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 6, wherein the heating temperature is in the range of 400 to 3000 ° C.