JPH11250914A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with stable storage characteristics by using inexpensive, abundant resources for a positive active material. SOLUTION: A nonaqueous electrolyte secondary battery has a positive electrode pellet 2 containing manganese oxide or a composite oxide of lithium and manganese, a negative electrode pellet 3 containing lithium metal, a lithium alloy, or a material capable of doping/undoping lithium, and a nonaqueous electrolyte prepared by dissolving an electrolyte in a nonaqueous solvent, and especially, the nonaqueous electrolyte contains an alkali metal fluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeable / dischargeable non-aqueous electrolyte secondary battery used as a power source for various electronic devices, and more particularly to an improvement of a positive electrode.

[0002]

2. Description of the Related Art In recent years, with the remarkable progress of various electronic devices, researches on secondary batteries which can be used continuously for a long time and which can be recharged as an economical power source have been advanced. As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium secondary batteries, and the like are known. In particular, lithium secondary batteries have advantages such as high output and high energy density.

[0003] Such a lithium secondary battery contains a positive electrode containing an active material which reversibly electrochemically reacts with lithium ions, and a material capable of doping and undoping lithium metal, a lithium alloy or lithium. A negative electrode,
And a non-aqueous electrolyte.

In general, as a negative electrode active material used for a negative electrode, for example, lithium metal, a lithium alloy such as LiAl, a conductive polymer which can be doped with lithium such as polyacetylene or polypyrrole, and lithium ions are incorporated into a crystal. Intercalation compounds and the like.

On the other hand, as a positive electrode active material used for the positive electrode, a metal oxide, a metal sulfide, a polymer, or the like is used, and examples thereof include TiS ₂ , MoS ₂ , NbSe ₂ , and V ₂ O ₅ . In particular, as the positive electrode active material having a high discharge _{potential, Li X Mn 2 O 4,} Li x M y O 2 (M is Ni or Co, the value of X varies with charging and discharging, in the combined x ≒ 1, y ≒ 1). Further, a mixture or a solid solution obtained by adding one kind or several kinds of other elements to a complex oxide represented by these compounds has also been proposed.

[0006] In the discharge reaction of a lithium secondary battery using these materials, lithium ions dissolve into the nonaqueous electrolyte at the negative electrode, and lithium ions are incorporated into the positive electrode active material at the positive electrode. Conversely, in the charging reaction, the reverse reaction of the discharging reaction proceeds, and lithium ions are eliminated from the positive electrode.

That is, in a lithium secondary battery, charge and discharge can be repeated by repeating a reaction in which lithium ions from a negative electrode enter and leave a positive electrode active material.

[0008]

As a positive electrode active material having a high discharge potential and a high energy density, Li _x
A lithium ion secondary battery using a composite oxide made of Co _y O ₂ has been put to practical use.

[0009] However, cobalt, which is a raw material of this composite oxide, is scarce in terms of resources and is ubiquitous in countries with few ore deposits that are commercially available. In the future, supply will be uncertain.

Therefore, in order to spread such a non-aqueous electrolyte secondary battery more widely, it is desired to use a cathode active material which is cheaper, has abundant resources, and is excellent in performance. I was

In order to solve such a problem, Li _x
Examples of the positive electrode active material having the same discharge potential and energy density as Co _y O ₂ include Li _x NiO ₂ and Li _x M
n ₂ O _{4 and the} like have been proposed. Nickel is an inexpensive material as compared with cobalt, but it goes without saying that it is more desirable to produce a positive electrode active material using a raw material that is less expensive and has less supply concerns. On the other hand, manganese is cheaper than cobalt and nickel, and is very rich in resources. In particular, manganese is a material in which manganese dioxide is distributed in large quantities as a material for manganese dry batteries, alkaline manganese dry batteries, and lithium primary batteries, and there is very little concern in terms of material supply.

Therefore, research on a positive electrode active material using manganese as a raw material has been actively conducted in recent years. Various composite oxides of lithium and manganese (hereinafter, referred to as lithium manganese composite oxide) synthesized from various manganese raw materials and lithium raw materials have been reported.
Li _x Mn _y O ₄ having a spinel crystal structure (x ≒ 1,
y ≒ 2). The _{Li x Mn y O 4 (x} ≒ 1,
The lithium manganese composite oxide represented by y ≒ 2) is a material having a potential of 3 V or more with respect to lithium by electrochemical oxidation and having a theoretical charge / discharge capacity of 148 mAh / g.

However, a non-aqueous electrolyte secondary battery using these manganese oxides or lithium manganese composite oxides as a positive electrode active material has a drawback that deterioration when used in an environment above room temperature is extremely large. . This is because manganese oxide and lithium manganese composite oxide are destabilized at high temperatures, and Mn is eluted into the non-aqueous electrolyte.

In particular, in recent years, development of large non-aqueous electrolyte secondary batteries for electric vehicles or road leveling has been carried out in various fields. In this large non-aqueous electrolyte secondary battery,
As the size of the battery increases, the internal heat generated during use cannot be ignored, and the temperature inside the battery may be relatively high even when the ambient temperature is around room temperature. In addition, even a relatively small battery used for a small portable device or the like may be used in a high temperature environment such as the interior of a car in the middle of summer, and the inside of the battery may be relatively hot. . As described above, it is considered that the battery is often used in an environment at a temperature higher than room temperature. Therefore, there is a strong demand for minimizing the deterioration of the battery in an environment at a temperature higher than room temperature.

Accordingly, the present invention has been proposed in view of the conventional circumstances, and uses a low-cost and resource-rich raw material as a positive electrode active material to minimize deterioration under an environment of room temperature or higher. An object of the present invention is to provide a non-aqueous electrolyte secondary battery with improved storage characteristics.

[0016]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a non-aqueous electrolyte secondary battery using manganese oxide or lithium manganese composite oxide as a cathode material. In the battery, it has been found that the deterioration of the battery under an environment of room temperature or more is suppressed as much as possible by including an alkali metal fluoride in the positive electrode, and the present invention has been completed.

That is, the non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode containing manganese oxide or a composite oxide of lithium and manganese, and a lithium metal, a lithium alloy or lithium doped or dedoped. And a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent. The positive electrode contains an alkali metal fluoride.

Here, the fluoride of the alkali metal is
0.5% by weight or more and 10% by weight per dry weight in the positive electrode
It is preferably contained below. As the alkali metal fluoride, at least one of LiF, NaF, and KF can be suitably used.

As described above, in the non-aqueous electrolyte secondary battery according to the present invention, since the alkali metal fluoride is contained in the positive electrode, a small amount of impurities present in the non-aqueous electrolyte and the charge and discharge accompanying The impurities generated in the non-aqueous electrolyte selectively react with the alkali metal fluoride contained in the positive electrode. Therefore, the non-aqueous electrolyte secondary battery according to the present invention, the reaction between the positive electrode active material comprising a manganese oxide or a lithium manganese composite oxide in the positive electrode and the impurity is effectively suppressed,
Deterioration of the positive electrode active material is suppressed as much as possible, resulting in excellent storage characteristics.

Further, in the nonaqueous electrolyte secondary battery according to the present invention, the content of the alkali metal fluoride in the positive electrode is specified to be 0.5% by weight or more and 10% by weight or less per dry weight. Thereby, the charge and discharge capacity of the battery is sufficiently ensured, and the deterioration of the positive electrode active material is suppressed, so that the storage characteristics are improved.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode containing a manganese oxide or a lithium manganese composite oxide, and a lithium metal, a lithium alloy or a material capable of doping and undoping lithium. And a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent.

In particular, in the nonaqueous electrolyte secondary battery to which the present invention is applied, the positive electrode contains an alkali metal fluoride. Examples of the alkali metal fluoride include NaF, LiF, and KF.

As described above, in the nonaqueous electrolyte secondary battery to which the present invention is applied, since the positive electrode contains the alkali metal fluoride, it is possible to reduce the amount of impurities and charge / discharge present in the nonaqueous electrolyte. Accordingly, impurities generated in the non-aqueous electrolyte selectively react with the alkali metal fluoride contained in the positive electrode. Therefore, in the nonaqueous electrolyte secondary battery to which the present invention is applied, the reaction between the positive electrode active material composed of manganese oxide or lithium manganese composite oxide in the positive electrode and the impurities is effectively suppressed, and the positive electrode active material Is suppressed as much as possible, resulting in excellent storage characteristics.

The amount of the alkali metal fluoride contained in the positive electrode is preferably 0.5% by weight or more and 10% by weight or less based on the dry weight. This is for the following reason. The alkali metal fluoride does not contribute to the charge / discharge reaction of the battery, and the active material filling amount of the positive electrode and the negative electrode inside the battery container must be reduced by the occupied volume. Therefore, when an excessively large amount of an alkali metal fluoride is added to the positive electrode, the charge / discharge capacity of the battery is reduced. Further, if only a very small amount of an alkali metal fluoride is added to the positive electrode, the effect of suppressing the deterioration of the positive electrode active material in the present invention is not exhibited.

As described above, in the nonaqueous electrolyte secondary battery to which the present invention is applied, since the content of the alkali metal fluoride contained in the positive electrode is regulated, the charge / discharge capacity of the battery can be sufficiently increased. As a result, deterioration of the positive electrode active material is suppressed, and storage characteristics are improved, and high reliability is obtained.

Further, the positive electrode used in the nonaqueous electrolyte secondary battery to which the present invention is applied contains the above-mentioned alkali metal fluoride, and contains either manganese oxide or lithium manganese composite oxide as a positive electrode active material. Contained as
Here, the manganese oxide or the lithium manganese composite oxide preferably has a spinel-type crystal structure represented by a general formula AB ₂ X ₄ .

As the manganese oxide, for example, λ
—MnO ₂ , a composite of MnO ₂ and V ₂ O _5, and a ternary composite oxide MnO ₂ .xV ₂ O ₅ (0 <x ≦ 0.3). The LiMn ₂ O ₄ spinel is subjected to an acid treatment to desorb Li, thereby obtaining a λ-M having a spinel structure.
nO ₂ can be generated.

As the lithium manganese composite oxide, for example, Li _x Mn _2-z O ₄ (0 <X ≦ 1.33,0
_{≦ Z ≦ 0.33), LiMn 2} -y M y O 4 (M is Ge, T
a metal selected from the group consisting of i, Ni, Zn and Fe;
0 <y <1). Among them, LiCo _0.2 M
With n _1.8 O ₄ , excellent cycle characteristics are obtained under a large discharge capacity. As the lithium manganese composite oxide, for example, L _x Mn ₂ O ₄ (0 <x ≦ 1)
Also, one doped with i ⁺¹ , Mg ²⁺ , Zn ²⁺ or the like can be given. Further, Li _y Mn ₂ O _4.
xV ₂ O ₅ (0 <x ≦ 0.3, 0 <y ≦ 1.5) is also included.

These lithium manganese composite oxides
A positive electrode active material that can generate a high battery voltage and has excellent energy density. When a positive electrode is formed using such a positive electrode active material, a known conductive agent, a binder, and the like are added.

By the way, Li _x Co _y O ₂ is widely known as a positive electrode active material having a high discharge potential and energy density, and a lithium ion secondary battery using this Li _x Co _y O ₂ has been put to practical use. ing. However, as described above, cobalt, which is a raw material of the composite oxide,
It is scarce in resources, has large price fluctuations, and is accompanied by supply insecurity. Therefore, Li _x Co _y using Co
O ₂ is an unsuitable material for further widespread use of nonaqueous electrolyte secondary batteries. On the other hand, the manganese oxide and lithium manganese composite oxide used as the positive electrode active material in the present invention, manganese as a raw material thereof is much cheaper than cobalt or nickel, and is rich in resources. Therefore, it can be said that the material is practically suitable.

On the other hand, the negative electrode used in the present invention is mainly composed of a lithium metal, a lithium alloy, or a material which can be doped or undoped with lithium.

The lithium alloy includes, for example, a lithium-aluminum alloy.

Examples of the material which can be doped with and dedoped with lithium include carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon black, and activated carbon. Can be used alone or as a mixture. The particle size of the carbon particles is preferably several μm to several tens μm, and if the particle size is too small or too large, it becomes difficult to uniformly disperse these carbon particles in the binder. As a result, the electric resistance of the film may be too high.

Here, non-graphitizable carbon (hard carbon)
Is a carbon material that does not graphitize even when heat-treated at about 3000 ° C., and graphitizable carbon (soft carbon)
It is a carbon material that becomes graphitic when heat treated at about 2800 ° C. to 3000 ° C.

As a starting material for producing the above-mentioned non-graphitizable carbon material, furfuryl alcohol or furan resin composed of a homopolymer or copolymer of furfural is preferable. This is because the carbon material obtained by carbonizing this furan resin has a (002) plane spacing of 0.37 nm or more,
This is because, at a true density of 1.70 g / cc or less, there is no oxidation exothermic peak at 700 ° C. or more in differential thermal analysis (DTA).

As another starting material, an organic material in which a functional group containing oxygen is introduced into a petroleum pitch having a specific H / C atomic ratio (so-called oxygen cross-linking) is also carbonized similarly to the above-mentioned furan resin. It can be used because it sometimes becomes a carbon material having excellent characteristics.

The petroleum pitch includes tars obtained by high-temperature pyrolysis of coal tar, ethylene bottom oil, crude oil, etc.,
It is obtained by distillation (vacuum distillation, normal pressure distillation, steam distillation) from asphalt or the like, thermal polycondensation, extraction, chemical polycondensation, or the like.

At this time, the H / C atomic ratio of the petroleum pitch is important, and it is necessary to set the H / C atomic ratio to 0.6 to 0.8 in order to obtain non-graphitizable carbon.

The specific means for introducing an oxygen-containing functional group into these petroleum pitches is not limited. For example, a wet method using an aqueous solution of nitric acid, mixed acid, sulfuric acid, hypochlorous acid or the like, or an oxidizing gas (air, oxygen, etc.) ), And a reaction with a solid reagent such as sulfuric acid, ammonium nitrate, ammonium persulfate, and ferric chloride.

For example, when a functional group containing oxygen is introduced into petroleum pitch by the above method, the carbonization process (about 400
C) without melting in the solid state to obtain the final carbon material, which is similar to the process of producing non-graphitizable carbon.

The petroleum pitch into which the functional group containing oxygen has been introduced by the above-described method is carbonized into an electrode material, but the conditions for carbonization are not particularly limited. The (002) plane spacing is 0.
The carbonization condition may be set so as to obtain a carbon material satisfying the characteristics of 37 nm or more, true density of 1.70 g / cc or less, and having no exothermic oxidation peak at 700 ° C. or more by differential thermal analysis (DTA). For example, by setting conditions such that the oxygen content of a precursor obtained by oxygen-crosslinking petroleum pitch is 10% by weight or more, (0000)
2) The plane spacing can be 0.37 nm or more. Therefore, the oxygen content of the precursor is preferably set to 10% by weight or more, and is practically in the range of 10 to 20% by weight.

The organic material to be crosslinked with oxygen may have an H / C atomic ratio of 0.6 to 0.8, and can be obtained by subjecting the following starting materials to preheat treatment such as pitching. Can be used.

Examples of such starting materials include phenolic resins, acrylic resins, vinyl halide resins, polyimide resins, polyamideimide resins, polyamide resins, conjugated resins, organic polymer compounds such as cellulose and derivatives thereof, and naphthalene. And condensed polycyclic hydrocarbon compounds such as phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, and other derivatives (eg, carboxylic acids, carboxylic anhydrides, and carboxylic imides thereof), and mixtures of the above compounds. Various pitches, acenaphthylene, indole,
Condensed heterocyclic compounds such as isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine, and derivatives thereof.

As the organic material used as a starting material for graphitizable carbon, coal and pitch are representative.

The pitch is obtained by distillation (vacuum distillation, normal pressure distillation, steam distillation) from tars and asphalt obtained by pyrolysis of coal tar, ethylene bottom oil, crude oil, etc., hot polycondensation, extraction, chemical polycondensation. And the pitch generated during wood carbonization.

The raw materials for the high molecular compound include polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, 3,5-dimethylphenol resin and the like.

These starting materials have a maximum of 4
It exists in a liquid state at about 00 ° C., and when held at that temperature, the aromatic rings are condensed and polycyclized to be in a stacked orientation state. When the temperature becomes about 500 ° C. or more, a solid carbon precursor, that is, semi-coke To form Such a process is called a liquid phase carbonization process and is a typical production process of graphitizable carbon.

The raw materials of the coal, pitch, and polymer compound are naturally subjected to the above-mentioned liquid carbon process when carbonized.

Other starting materials include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, and other derivatives (for example, carboxylic acids, carboxylic anhydrides, and carboxylic imides thereof). Etc.), a mixture of the above compounds, acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline,
Phthalazine, carbazole, acridine, phenazine,
Condensed heterocyclic compounds such as phenanthridine and derivatives thereof can also be used.

When a carbon material is obtained using the above-mentioned raw material organic material, for example, after carbonizing at 300 to 700 ° C. in a nitrogen stream, the temperature is increased in a nitrogen stream at a rate of 1 to 20 ° C./min. What is necessary is just to bake on conditions of 1300 degreeC and holding time at the ultimate temperature 0-5 hours. Of course, in some cases, the carbonization operation may be omitted.

The above-described carbonization and firing may be performed after the phosphorus compound is added to the starting material or precursor of the non-graphitizable carbon and the graphitizable carbon described above.

When graphite (graphite) is used for the negative electrode of the present invention, natural graphite or artificial graphite obtained by heat-treating the above-mentioned graphitizable carbon as a precursor at a high temperature of 2000 ° C. or more is used. Can be.

The properties of graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon) and activated carbon described above are as follows.

The crystallinity increases in the order of activated carbon, non-graphitizable carbon, graphitizable carbon, and graphite. The density of the crystal increases in the order of activated carbon, non-graphitizable carbon, graphitizable carbon, and graphite. Further, the porosity of the crystal increases in the order of graphite, graphitizable carbon, non-graphitizable carbon, and activated carbon. The firing temperature is higher in the order of activated carbon, non-graphitizable carbon, graphitizable carbon, and graphite. The conductivity is activated carbon, non-graphitizable carbon, graphitizable carbon,
It becomes higher in the order of graphite.

In addition to the above, examples of materials which can be doped and dedoped with lithium include polymers such as polyacetylene and polypyrrole and oxides such as SnO ₂ .

In order to prepare a positive electrode and a negative electrode using the above-described positive electrode active material and negative electrode active material, the positive electrode and the negative electrode can be manufactured by a conventionally known method using a binder resin, a conductive material, a solvent and the like.

As the binder resin, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and the like can be preferably used.
As the conductive material, graphite or the like can be preferably used.

As the solvent for dissolving the binder resin, various polar solvents capable of dissolving the above-mentioned fluorine-based binder resin can be used. For example, dimethylformamide, dimethylacetamide, methylformamide, N-methyl Pyrrolidone can be preferably used. In particular, when polyvinylidene fluoride (PVDF) is used as the fluorine-based binder resin,
N-methylpyrrolidone can be preferably used. Note that the mixing ratio of the active material and the binder resin described above can be appropriately determined according to the shape of the electrode and the like.

The non-aqueous electrolyte used in the present invention comprises:
It is obtained by dissolving an electrolyte in the non-aqueous solvent.

As the non-aqueous solvent, non-aqueous solvents used in conventional non-aqueous electrolytes can be used. For example, cyclic carbonates such as propylene carbonate and ethylene carbonate, diethyl carbonate, dimethyl carbonate and the like can be used. And carboxylic acid esters such as methyl propionate and methyl butyrate, and ethers such as γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran and dimethoxyethane. These may be used alone or in combination of two or more. In particular, from the viewpoint of oxidation stability, it is preferable to include a carbonate ester.

As the electrolyte dissolved in the non-aqueous solvent, an electrolyte used in a normal battery electrolyte can be used. For example, LiPF ₆ , LiBF ₄ , LiA
sF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (SO ₂
CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , L
lithium salts such as iSiF ₆ .

The non-aqueous electrolyte secondary battery according to the present invention is constituted by appropriately combining the above-described positive electrode, negative electrode and non-aqueous electrolyte. In addition, other configurations of the non-aqueous electrolyte secondary battery, for example,
Separator, battery can, or battery shape, etc., like conventional non-aqueous electrolyte secondary batteries, can be cylindrical, square, coin, button-shaped various shapes, any shape It can also be applied to thin and large types.

[0064]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results.

Here, in order to evaluate the characteristics of the battery by adding an alkali metal fluoride to the positive electrode, a coin-type battery as shown in FIG. 1 was manufactured as follows.

Example 1 First, a positive electrode pellet 2 was prepared as follows.

First, manganese carbonate powder and lithium carbonate powder were mixed using an agate mortar so that the ratio Li / Mn of Li to Mn was 1/2.

Then, the mixed powder was heated at 800 ° C. in air at normal pressure using an electric furnace to obtain a lithium manganese composite oxide. When this sample was analyzed by powder X-ray diffraction, it was consistent with LiMn ₂ O ₄ described in ISDD card 35-782. Further, the obtained lithium manganese composite oxide had a spinel type crystal structure.

Then, LiF powder, graphite as a conductive additive, and polyvinylidene fluoride as a binder were mixed with the obtained lithium manganese composite oxide powder, and dimethylformamide was added dropwise and kneaded as appropriate. Thereafter, the dried mixture was pulverized to obtain a positive electrode mixture. At this time, the mixing amount of LiF was 0.5% by weight based on the dry weight of the positive electrode mixture.

Then, this positive electrode mixture was pressure-formed together with an aluminum mesh, and punched into a circular shape having a diameter of 15.5 mm, whereby a positive electrode pellet 2 was obtained.

Next, a lithium metal foil was applied with a diameter of 15.5 mm.
The negative electrode pellet 3 was produced by punching out into a circular shape, and the negative electrode pellet 3 was pressure-bonded to a previously prepared battery lid 4 by a pressure press device.

Then, the positive electrode pellet 2 was placed in a battery can 5, and a polypropylene separator 6 was placed on the positive electrode pellet 2. A non-aqueous electrolyte obtained by dissolving 1 mol / l of LiPF _{6 in} propylene carbonate was poured into the mixture, and the battery cover 4 to which the negative electrode pellet 3 was pressed was attached.
Was placed thereon, swaged with a gasket 7 and sealed to produce a coin-type battery.

Example 2 A coin-type battery was manufactured in the same manner as in Example 1 except that the amount of LiF mixed in the positive electrode mixture was 5% by weight based on the dry weight of the positive electrode mixture.

Example 3 A coin-type battery was manufactured in the same manner as in Example 1, except that the amount of LiF mixed in the positive electrode mixture was 10% by weight based on the dry weight of the positive electrode mixture.

Example 4 The procedure of Example 4 was repeated except that NaF was mixed in the positive electrode mixture instead of LiF, and the amount of NaF mixed in the positive electrode mixture was 0.5% by weight based on the dry weight of the positive electrode mixture. In the same manner as in Example 1, a coin-type battery was produced.

Example 5 The procedure of Example 5 was repeated except that NaF was mixed in the positive electrode mixture instead of LiF, and the amount of NaF mixed in the positive electrode mixture was 5.0% by weight based on the dry weight of the positive electrode mixture. In the same manner as in Example 1, a coin-type battery was produced.

Example 6 Example 10 was repeated except that NaF was mixed in the positive electrode mixture instead of LiF, and the amount of NaF mixed in the positive electrode mixture was 10.0% by weight based on the dry weight of the positive electrode mixture. In the same manner as in Example 1, a coin-type battery was produced.

Example 7 KF was mixed in the positive electrode mixture instead of LiF.
A coin-type battery was produced in the same manner as in Example 1, except that the amount of F mixed into the positive electrode mixture was 0.5% by weight based on the dry weight of the positive electrode mixture.

Example 8 Instead of LiF, KF was mixed in the positive electrode mixture.
A coin-type battery was produced in the same manner as in Example 1, except that the amount of F mixed in the positive electrode mixture was 5.0% by weight based on the dry weight of the positive electrode mixture.

Example 9 KF was mixed in the positive electrode mixture instead of LiF.
The amount of F mixed in the positive electrode mixture was 1 to the dry weight of the positive electrode mixture.
A coin-type battery was produced in the same manner as in Example 1 except that the content was changed to 0.0% by weight.

[0081] without mixing NaF in Comparative Examples cathode mixture, otherwise Example 1
In the same manner as in the above, a coin-type battery was produced.

<Evaluation of Charge / Discharge Cycle> For the batteries prepared in Examples 1 to 9 and Comparative Example, the battery temperature was set at 6
At 0 ° C., the following charge / discharge test was performed.

First, the current density was set to 0.2 for each battery.
At 7 mA / cm ² , constant current charging was performed until the circuit voltage reached 4.2 V, and then constant voltage charging was performed with the voltage kept constant at 4.2 V from the time the circuit voltage reached 4.2 V until full charge. Was.

Next, each of the charged batteries was discharged until the final voltage reached 3.7V. This charge / discharge was defined as one cycle.

Then, the above-mentioned charge / discharge cycle was repeated for each battery, and the discharge capacity was obtained from the amount of electricity after each charge / discharge cycle for each battery, and finally the capacity retention was obtained from the value. The results are shown in FIGS. 2, 3 and 4. Here, the capacity retention rate is obtained by assuming that the discharge capacity after the first cycle is 100% and the ratio of the discharge capacity in each cycle.

As is clear from the results shown in FIGS. 2, 3 and 4, Examples 1 to 9 in which the alkali metal fluoride was mixed in the positive electrode mixture, contained the alkali metal in the positive electrode mixture. It was found that the deterioration of the discharge capacity due to the charge / discharge cycle was suppressed, irrespective of the type of the alkali metal, as compared with the comparative example in which no fluoride was mixed.

Therefore, in the non-aqueous electrolyte secondary battery to which the present invention is applied, deterioration of battery characteristics due to charge / discharge cycles is effectively suppressed by mixing alkali metal fluoride into the positive electrode mixture. It turns out that it can.

As is apparent from the results shown in FIGS. 2, 3 and 4, the third and fourth embodiments, the fifth and sixth embodiments, and the like.
When comparing Example 8 and Example 9, respectively, Example 3 and Example 4, Example 5 and Example 6, and Example 8 and Example 9 differ from each other in the amount of addition of the alkali metal fluoride. Nevertheless, there is not much difference in the effect of deterioration of the discharge capacity due to the charge / discharge cycle. From this,
In the positive electrode mixture, which is the amount of the alkali metal fluoride added in each of Examples 4, 6, and 9, the ratio of 10% by weight in the positive electrode mixture is not enough to sufficiently exhibit the cycle deterioration suppressing effect. However, even if the amount of addition of the alkali metal fluoride is increased beyond this range, it is not considered that the remarkable effects of the fourth, sixth, and ninth embodiments or more are exhibited.

Further, the fluoride of the alkali metal does not contribute to the charge / discharge reaction of the battery, and the amount of the active material filled in the positive electrode and the negative electrode in the battery container must be reduced by the occupied volume. Therefore, if an excessively large amount of the alkali metal fluoride is mixed, the charge / discharge capacity of the battery is reduced. Therefore, it can be said that it is not desirable to increase the addition amount of the alkali metal fluoride beyond the range where the effect of suppressing the battery performance deterioration is sufficiently ensured.

From these facts, in the non-aqueous electrolyte secondary battery to which the present invention is applied, in order to have a sufficient effect on suppressing the battery performance deterioration and not to greatly reduce the initial discharge capacity of the battery, it is necessary to use an alkali metal fluoride. Is preferably 0.5% by weight or more and 10% by weight or less based on the dry weight of the positive electrode mixture, more preferably 0.5% by weight or more,
It can be said that it is better to be 5.0% by weight or less.

[0091]

As described above, according to the present invention, since the positive electrode contains an alkali metal fluoride, the deterioration of the positive electrode active material can be suppressed as much as possible, and the positive electrode can be used even in a severe environment such as a high temperature environment. It is possible to provide a non-aqueous electrolyte secondary battery having excellent storage characteristics that can be endured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a coin-type non-aqueous electrolyte secondary battery to which the present invention is applied.

FIG. 2 is a diagram showing a relationship between a charge / discharge cycle and a capacity retention in Examples 1 to 3 and Comparative Example.

FIG. 3 is a diagram showing a relationship between a charge / discharge cycle and a capacity retention in Examples 4 to 6 and Comparative Example.

FIG. 4 is a diagram showing a relationship between a charge / discharge cycle and a capacity retention in Examples 7 to 9 and Comparative Example.

[Explanation of symbols]

1 coin-type battery, 2 positive electrode pellet, 3 negative electrode pellet, 4 battery cover, 5 battery can, 6 separator,
7 Gasket

Claims (4)

[Claims] A positive electrode containing a manganese oxide or a composite oxide of lithium and manganese; a negative electrode containing a lithium metal, a lithium alloy, or a material capable of doping and undoping lithium; a non-aqueous solvent And a non-aqueous electrolyte in which an electrolyte is dissolved, wherein the positive electrode contains an alkali metal fluoride. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the alkali metal fluoride is contained in the positive electrode in an amount of 0.5% by weight or more and 10% by weight or less based on dry weight. battery. 3. The fluoride of an alkali metal is Li
The non-aqueous electrolyte secondary battery according to claim 2, wherein the secondary battery is at least one of F, NaF, and KF. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the manganese oxide or the composite oxide of lithium and manganese used for the positive electrode has a spinel-type crystal structure.