JP2002190299A - Method for manufacturing nonaquoeus electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a capacity drop which accompanies the process in charge/ discharge cycle by removing moisture adsorbed into a micropore of a carbonaceous material in a heating process. SOLUTION: A powder-like carbonaceous material is prepared as a negative electrode active material carrier. Then, the powder-like carbonaceous material is heated at 300-1500 deg.C, and the heated carbonaceous material is coated on a band-like collector 9, thus a negative electrode 11 is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery having a negative electrode mainly composed of a lithium-doped and undoped carbon material, and more particularly to a method for manufacturing a negative electrode. It is.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has enabled electronic devices to become smaller and lighter one after another. Along with that, more and more batteries are used as mobile power sources,
Compact, lightweight and high energy density ones are required.

Conventionally, aqueous batteries such as lead batteries and nickel-cadmium batteries have been the mainstream as secondary batteries for general use. These batteries have excellent cycle characteristics, but are not sufficiently satisfactory in terms of battery weight and energy density.

Recently, as a secondary battery, a non-aqueous electrolyte secondary battery using lithium or a lithium alloy for a negative electrode has been replaced by a lead battery or a nickel cadmium battery, which are insufficient in battery weight and energy density. Research and development are actively conducted.

[0005] This battery has excellent features of high energy density, low self-discharge, and light weight. However, this battery has a drawback in that, as the charge / discharge cycle progresses, lithium grows in a dendrite shape at the time of charging at the negative electrode, and the dendrite-like crystal is likely to reach the positive electrode and cause an internal short circuit. , A major obstacle to its practical application.

On the other hand, according to a nonaqueous electrolyte secondary battery using a carbon material as a negative electrode active material carrier for a negative electrode,
Lithium previously supported on the carbon material of the negative electrode by chemical and physical methods, lithium contained in the crystal structure of the positive electrode active material, and lithium dissolved in the electrolytic solution are respectively transferred to the carbon layer at the negative electrode during charge and discharge. Doped and undoped from the carbon layer. For this reason, even if the charge / discharge cycle progresses, precipitation of dendrite-like crystals is not seen at the time of charging in the negative electrode, and internal short circuit hardly occurs,
It shows good charge / discharge cycle characteristics. In addition, since the energy density is high and the weight is low, development is proceeding toward practical use.

The above-mentioned negative electrode is usually manufactured using a negative electrode mixture obtained by mixing a powdery carbon material and a binder.

[0008] Applications of the non-aqueous electrolyte secondary battery as described above include a video camera and a laptop personal computer. Since many of such electronic devices consume relatively large current, the batteries need to be able to withstand heavy loads.

Therefore, as a battery structure, a spiral wound electrode structure formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode in the longitudinal direction thereof through a strip-shaped separator is effective. According to the battery having the spirally wound electrode structure, the electrode area can be increased, so that the battery can withstand heavy load.

[0010]

In order to provide a secondary battery having excellent performance over a long period of time as a power supply for an electronic device as described above, it is necessary to minimize a decrease in capacity accompanying the progress of a charge / discharge cycle. is necessary.

In terms of this capacity, the performance of the conventional non-aqueous electrolyte secondary battery was not always sufficient.

The present inventors have conducted intensive studies on the cause of the capacity reduction in the non-aqueous electrolyte secondary battery. As a result, during the storage period until the carbon material obtained by firing the organic material and the like was used for the production of the negative electrode, Moisture is adsorbed in the fine pores of the carbon material, and this water reacts with lithium ions on the surface of the pores of the carbon material during the charging reaction, so that the lithium ions are changed into non-dischargeable lithium compounds. It has been found that it decreases as the charge / discharge cycle progresses.

The present invention has been made on the basis of the above-described findings, and an object of the present invention is to improve charge / discharge cycle characteristics in a nonaqueous electrolyte secondary battery having a negative electrode mainly composed of a carbon material. It is an object of the present invention to provide a manufacturing method which can be performed.

[0014]

In order to achieve the above object, the present invention provides a belt-like current collector by molding a negative electrode mixture mainly composed of a carbon material which can be doped with lithium and de-doped. In a method for manufacturing a nonaqueous electrolyte secondary battery including the configured negative electrode and a positive electrode configured by molding a positive electrode mixture containing lithium on a belt-shaped current collector, a powdery carbon material is obtained. Then, the carbon material is subjected to heat treatment at a temperature of 300 to 1,500 ° C., and thereafter, the negative electrode is manufactured by applying the heat-treated carbon material to a belt-shaped current collector. is there. In this case, the heat treatment is preferably performed in a vacuum or an inert gas atmosphere. Further, it is preferable to use a composite metal oxide containing lithium or an interlayer compound containing lithium as the active material of the positive electrode.

The carbon material has a (002) plane spacing (lattice spacing) of 3.70 ° or more and a true density of 1.70 g.
/ Cm ³ and a carbonaceous material that does not have an exothermic peak at 700 ° C. or more in differential thermal analysis in an air stream. Since such a carbonaceous material has very good characteristics as a negative electrode material, a battery with a higher capacity can be obtained.

The carbonaceous material can be produced by, for example, carbonizing an organic material by a method such as firing at a temperature of, for example, about 700 to 1,500 ° C. The carbon material can be generally classified into a carbonaceous material and a graphite material, but the carbonaceous material is preferable as the negative electrode material as described above.

As a starting material for the carbonaceous material, furan resin composed of a homopolymer or copolymer of furfuryl alcohol or furfural is preferable. Specific furan resins include furfural + phenol,
Polymers composed of furfuryl alcohol + dimethylol urea, furfuryl alcohol, furfuryl alcohol + formaldehyde, furfuryl alcohol + furfural, furfural + ketones and the like can be mentioned. By firing such a furan resin, a carbonaceous material having the above-described properties can be obtained.

Further, a petroleum pitch having a hydrogen / carbon atom ratio of 0.6 to 0.8 is used as a starting material, and an oxygen crosslink for introducing a functional group containing oxygen is applied to the starting material to thereby obtain an oxygen content of 10 to 20. The carbonaceous material obtained by calcining the precursor after obtaining the precursor by weight is also preferable because it has the properties described above.

In addition, when the furan resin or the petroleum pitch is carbonized, if a phosphorus compound or a boron compound is added, a carbonaceous material having a large doping amount with respect to lithium can be obtained. Is preferred.

After the carbon material obtained as described above is pulverized into a powder so as to have an average particle diameter of preferably several to several tens of μm, using the powdered carbon material, for example,
A negative electrode can be manufactured by applying a negative electrode mixture slurry in which a negative electrode mixture obtained by mixing this carbon material and a binder is dispersed in a solvent to a metal current collector or the like.

Prior to the production of the negative electrode, the powdery carbon material is heat-treated. The temperature of this heat treatment is 300 to 1.5.
The temperature is about 00 ° C., preferably 300 to 1,100 ° C., and more preferably 500 to 1,000 ° C. This heat treatment is preferably performed in a vacuum or in an inert gas atmosphere.

When the negative electrode is manufactured from a negative electrode mixture composed of a powdery carbonaceous material and a binder as described above, for example, the binder contained in the negative electrode mixture is subjected to heat treatment at the above-described high temperature. Then, the properties of the binder may change,
In the process after obtaining the negative electrode mixture, the heat treatment temperature is restricted. However, according to the production method of the present invention,
There is no such restriction at all, and the negative electrode can be manufactured by, for example, obtaining the above-described negative electrode mixture after sufficiently removing water from the carbon material.

It is preferable that the carbon material subjected to the heat treatment as described above is used immediately after the treatment (because moisture may be adsorbed again in the fine pores) in the production of the negative electrode.
Alternatively, it is preferable to store in a dryer so that the relative humidity in the dryer is 2% or less.

The positive electrode active material of the non-aqueous electrolyte secondary battery according to the present invention includes 25 g / g of the carbon material of the negative electrode.
A material containing lithium corresponding to a charge / discharge capacity of 0 mAh or more, for example, a general formula LiMO ₂ (where M is Co, Ni
It is preferable to use a composite metal oxide represented by the following formula (1) or an intercalation compound containing lithium. In particular, since high voltage and high energy density are obtained and cycle characteristics are excellent, LiCoO ₂ , LiC
o _0.8 Ni _0.2 O ₂ is preferred.

As the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery according to the present invention, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent (organic solvent) can be used.

Here, the organic solvent is not particularly limited. For example, propylene carbonate,
Ethylene carbonate, 1,2-dimethoxyethane,
1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-
1,3-Dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, and the like can be used alone or as a mixture of two or more.

As the electrolyte to be dissolved in the organic solvent, any of conventionally known electrolytes can be used, such as LiClO ₄ ,
LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C _{6
H 5) 4, LiCl, LiBr} , CH 3 SO 3 Li, C
F ₃ SO ₃ Li and the like.

The non-aqueous electrolyte may be a solid, for example, a polymer complex solid electrolyte.

[0029]

As described above, the powdery carbon material is 300 to 1,
By performing the heat treatment at a temperature of 500 ° C., the moisture adsorbed in the fine pores of the carbon material is removed. As a result, during the charging reaction, the lithium ions do not react with moisture on the surface of the micropores of the carbon material to change into a non-dischargeable lithium compound, and the capacity is prevented from decreasing with the progress of the charge / discharge cycle. Can be.

Further, since the above-described heat treatment for the carbon material is performed before the negative electrode is manufactured using the carbon material, other materials and other steps are adversely affected by the heat treatment during the manufacture of the negative electrode. Will not be given.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to FIGS.

Embodiment 1

FIG. 1 is a schematic vertical sectional view of a non-aqueous electrolyte secondary battery of this embodiment. FIG. 2 is a perspective view of a strip-shaped negative electrode which can be used in this battery. Was produced as follows.

First, the negative electrode 1 was manufactured as follows. After oxygen crosslinking for introducing 10 to 20% by weight of a functional group containing oxygen into petroleum pitch as a starting material, the oxygen-crosslinked precursor is placed in an inert gas stream in a stream of 1,2.
By calcining at 000 ° C., a carbonaceous material having properties close to glassy carbon was obtained.

As a result of X-ray diffraction measurement of this carbonaceous material, the (002) plane spacing was 3.76 °, and the true specific gravity was measured by a pycnometer method to be 1.58 g / cm ^3. Met. Further, when a differential thermal analysis was performed in an air stream, no exothermic peak was found at 700 ° C. or higher.

The carbonaceous material is pulverized to an average particle size of 10
μm carbonaceous material powder.

The above-mentioned carbonaceous material powder was subjected to a heat treatment at 1,000 ° C. for 4 hours in a stream of argon gas. With respect to the carbonaceous material powder after the heat treatment, the sample is reheated at 1,000 ° C., the generated water is introduced into the electrolytic cell with a dry argon carrier gas, and the water content is measured by the Karl Fischer method. As a result, it was 221 ppm.

The carbonaceous material obtained as described above was used as a negative electrode active material carrier, and 90 parts by weight of the carbonaceous material powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed. The negative electrode mixture was prepared. This adjustment is
Immediately after the above-mentioned heat treatment of the carbonaceous material, the heat treatment was performed. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry (paste).

Next, this negative electrode mixture slurry was coated with a thickness of 10
A uniform coating is applied to both sides of the negative electrode current collector 9, which is a strip of copper foil having a thickness of μm, and dried. After the drying, compression molding is performed by a roller press, and as shown in FIG. A negative electrode 1 having a negative electrode mixture layer 1a was obtained.

The thickness of the negative electrode mixture layer 1a after molding was 80 μm on both sides and was the same, and the width of the strip-shaped negative electrode 1 was 3 μm.
The length was 3.5 mm and the length was 700 mm.

Next, the positive electrode 2 was produced as follows. LiCoO ₂ was obtained by mixing 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate and calcining the mixture in air at 900 ° C. for 5 hours.

Using this LiCoO ₂ as a positive electrode active material, 91 parts by weight of LiCoO ₂ were mixed with 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder to form a positive electrode mixture. . This positive electrode mixture was dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry (paste).

Next, this positive electrode mixture slurry was coated with a thickness of 2
The positive electrode current collector 10, which was a 0-μm band-shaped aluminum foil, was uniformly coated on both surfaces and dried. After the drying, compression molding was performed with a roller press to obtain a band-shaped positive electrode 2.

The thickness of the positive electrode mixture after molding was the same at 80 μm on both sides, and the width of the band-shaped positive electrode 2 was 31.5 m.
m and length were 650 mm.

The strip-shaped negative electrode 1 produced as described above
And a band-shaped positive electrode 2 and a pair of band-shaped separators 3a and 3b made of a microporous polypropylene film having a thickness of 25 μm and a width of 36 mm, and in the order of the negative electrode 1, the separator 3a, the positive electrode 2 and the separator 3b. The laminated electrode body having the four-layer structure was spirally wound many times along the length direction with the negative electrode 1 inside, thereby producing a wound electrode body 15. At this time, the wound final end of the wound electrode body 15 was fixed with an adhesive tape.

The inner diameter of the hollow portion at the center of the spirally wound electrode body 15 was 3.5 mm, and the outer diameter was 19.7 mm. The core 33 is located in this hollow portion.

The spirally wound spirally wound electrode body 15 produced as described above was accommodated in a nickel-plated iron battery can 5 as shown in FIG.

In order to collect the current of the negative electrode 1 and the positive electrode 2 respectively, a negative electrode lead 11 made of nickel is attached to the negative electrode current collector 9 in advance, and this is led out from the negative electrode 1 to remove the battery can 5.
And a positive electrode lead 12 made of aluminum was attached to the positive electrode current collector 10 in advance, which was led out from the positive electrode 2 and welded to the projection 34a of the metal safety valve 34.

Thereafter, a non-aqueous electrolyte obtained by dissolving LiPF ₆ as a lithium salt in a mixed solvent of equal volume of propylene carbonate and 1,2-dimethoxyethane at a ratio of 1 mol / l is injected into the battery can 5. Then, the wound electrode body 15 was impregnated.

Before and after this, disk-shaped insulating plates 4a and 4b were disposed in the battery can 5 so as to face the upper end surface and the lower end surface of the wound electrode body 15, respectively.

Thereafter, the battery can 5, the safety valve 34 whose outer periphery is in close contact with each other, and the metal battery cover 7 are each caulked through an insulating sealing gasket 6 whose surface is coated with asphalt to thereby form the battery can. 5 was sealed. As a result, the battery lid 7 and the safety valve 34 were fixed, and the airtightness in the battery can 5 was maintained. At this time, the lower end of the gasket 6 in FIG. 1 was in contact with the outer peripheral surface of the insulating plate 4a, so that the insulating plate 4a was in close contact with the upper surface of the wound electrode body 15.

As described above, the diameter 20 mm and the height 4
A 2 mm cylindrical non-aqueous electrolyte secondary battery was manufactured. The battery of Example 1 is referred to as Battery A for convenience as shown in Table 1 below.

The above cylindrical non-aqueous electrolyte secondary battery is
In order to form a double safety device, a safety valve 34, a stripper 36, and an intermediate fitting body 35 made of an insulating material for integrating the safety valve 34 and the stripper 36 are provided. Although not shown, the safety valve 34 is provided with a cleavage portion that is cleaved when the safety valve 34 is deformed, and the battery cover 7 is provided with a hole.

If the internal pressure of the battery rises for some reason, the safety valve 34 is deformed upward in FIG. 1 around the projection 34a, so that the connection between the positive electrode lead 12 and the projection 34a is established. It is configured to cut off the battery current when cut off, or to exhaust gas generated in the battery due to the cleavage of the safety valve 34 being opened.

Embodiment 2

In the present embodiment, the same carbonaceous material as that of the first embodiment is used, and the steps until the powder of the carbonaceous material is obtained are the same as those of the first embodiment, but the subsequent heat treatment is performed as follows. went.

The above-mentioned powdery carbonaceous material was heat-treated at 300 ° C. for 10 hours in a vacuum. A cylindrical non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that the heat-treated carbonaceous material was used as the negative electrode active material carrier. This battery was used as shown in Table 1 below.
And

The water content of the carbonaceous material after the heat treatment was measured by the same method as in Example 1 and found to be 393 ppm.

Comparative Example

As a comparative example for confirming the effect of the present invention, the following battery was manufactured. That is, the first embodiment
The steps up to obtaining the carbonaceous material powder using the same carbonaceous material as in Example 1 are the same as in Example 1, but thereafter, in the same manner as in Example 1 except that a carbonaceous material not subjected to heat treatment was used. Thus, a cylindrical nonaqueous electrolyte secondary battery was manufactured. This battery is referred to as Battery C as shown in Table 1 below.

The water content of the above carbonaceous material powder was measured by the same method as in Example 1.
It was 1405 ppm.

With respect to the three types of batteries A, B, and C described above, the charging upper limit voltage was set to 4.1 V, the battery was charged at a constant current of 1 A for 2 hours, and the final voltage was changed at a constant load of 7.5 Ω. The charge / discharge cycle for discharging to 2.75 V was repeated. The capacity at 10 cycles in this charge / discharge cycle was measured as the initial capacity, and the discharge capacity at 100 cycles was measured. The ratio between the discharge capacity at 100 cycles and the initial capacity (capacity at 100 cycles / initial capacity) was defined as the capacity retention ratio. The results are shown in Table 1 below.

[0063]

[Table 1]

From the results shown in Table 1 above, the non-aqueous electrolyte secondary batteries A and B according to the production method in which the present invention is applied and the carbon material powder is subjected to heat treatment and then the negative electrode 1 is produced,
It can be seen that the capacity retention ratio is greatly improved as compared with the nonaqueous electrolyte secondary battery C according to the conventional manufacturing method.

This is because the carbonaceous material powder as the negative electrode material is reheated at a high temperature (300 to 1,500 ° C.) separately from the sintering of the starting material for obtaining the carbonaceous material. It is considered that the effect of removing the moisture adsorbed in the fine pores was exhibited. It is considered that the moisture adsorbed in the fine pores of the carbonaceous material reacts with lithium ions on the surface of the fine pores during the charging reaction to generate a lithium compound that cannot be discharged, thereby causing a reduction in capacity. This is clear from the residual moisture values of the batteries A, B, and C. The carbonaceous material used for the negative electrode is a so-called glassy or nearly glassy material, and has pores with a very small diameter as compared with activated carbon and other carbon materials. For this reason, the water once adsorbed in the micropores is difficult to remove. Conventionally, the negative electrode mixture slurry was applied to the negative electrode current collector 9 and then dried at a temperature of, for example, about 80 to 200 ° C. If the drying temperature is higher than this temperature, the properties of PVDF as a binder may change, which is not preferable. Therefore, the moisture trapped in the micropores of the carbonaceous material is
It could hardly be removed at the conventional drying temperature. On the other hand, according to the production method of the present invention, moisture can be sufficiently removed from the fine pores of the carbonaceous material without adversely affecting the binder and other production steps.

In Examples 1 and 2, the heat treatment after obtaining the powdery carbonaceous material was performed in an atmosphere heating furnace and a vacuum heating furnace. Various devices such as an induction heating furnace and a forced hot air circulation furnace can be used. Even in this case, the temperature at which the carbonaceous material powder is heated is, as described above, 300 to 1,500.
° C, preferably from 300 to 1,100 ° C, more preferably from 500 to 1,000 ° C.

In the method of heating a carbonaceous material as described above, moisture generated by heating a sample at 1,000 ° C. is introduced into an electrolytic cell with a dry argon carrier gas, and the Karl Fischer In the method of measuring the moisture value by the method, the carbonaceous material is heat-treated so that the moisture value becomes 2,000 ppm or less, preferably 1,200 ppm or less. As a result, a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics can be efficiently manufactured with small variations.

In Examples 1 and 2 according to the present invention, the carbonaceous material powder was heated and immediately mixed with a binder to prepare a negative electrode mixture. After storing in a drier such as a desiccator in an atmosphere having a humidity of 2% or less, a negative electrode mixture can be prepared by mixing with a binder at an appropriate time.

In this embodiment, the manufacturing method of the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery using a wound electrode body. However, the present invention is not limited to this. The present invention may be applied to a non-aqueous electrolyte secondary battery such as a cylindrical type, or may be applied to the manufacture of a button-type or coin-type non-aqueous electrolyte secondary battery. Further, a graphite material can be used as the carbon material.

[0070]

According to the present invention, a negative electrode formed by molding a negative electrode mixture mainly composed of a carbon material capable of doping and undoping lithium into a belt-like current collector, and a belt-like current collector In a method for producing a non-aqueous electrolyte secondary battery having a positive electrode formed by molding a positive electrode mixture containing lithium, a powdery carbon material is obtained, and then the carbon material is 300 to 1, A heat treatment is performed at a temperature of 500 ° C., and thereafter, a negative electrode is manufactured by applying the heat-treated carbon material to a belt-shaped current collector, thereby forming a belt-like shape using a powdery carbon material. The above-mentioned non-aqueous electrolyte in which a decrease in capacity due to the progress of a charge / discharge cycle is reduced without adversely affecting other materials of the negative electrode manufactured by applying to the current collector and other manufacturing processes of the negative electrode. It is possible to manufacture the following cell.
Therefore, in addition to the conventionally known high energy density and high capacity, the above-mentioned non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics can be manufactured. Furthermore, since the negative electrode was manufactured by applying to the belt-shaped current collector using the powdered carbon material after the heat treatment, a high-strength negative electrode could be manufactured by a simple process,
In particular, the strength of a spirally wound electrode body that can be manufactured by spirally winding a large number of times is large, and its manufacture is easy. In addition, since a band-shaped current collector having a very small water content can be used, the water content of the negative electrode as a whole can be extremely reduced in combination with the low residual water content of the powdery carbon material after the heat treatment. For this reason, the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a cylindrical non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 2 is a perspective view showing a strip-shaped negative electrode of the battery shown in FIG. 1 before a wound electrode body is manufactured.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode 1a Negative electrode mixture layer 2 Positive electrode 9 Negative electrode current collector

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tomoaki Sato 1-1, Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture F-term in Sony Energy Tech Koriyama Factory 5H050 AA07 BA17 CA08 CB07 DA04 FA17 GA02 GA22 GA27 HA14

Claims (3)

[Claims] 1. A negative electrode formed by molding a negative electrode mixture mainly composed of a carbon material capable of doping and undoping lithium into a belt-like current collector, and a positive electrode comprising lithium in a belt-like current collector In a method for producing a nonaqueous electrolyte secondary battery including a positive electrode constituted by molding a mixture, a powdery carbon material is obtained,
A heat treatment at a temperature of 1,500 ° C., and thereafter, applying the heat-treated carbon material to a belt-shaped current collector to produce the negative electrode; Battery manufacturing method. 2. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the heat treatment is performed in a vacuum or in an inert gas atmosphere. 3. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein a composite metal oxide containing lithium or an intercalation compound containing lithium is used as an active material of the positive electrode. .