JPH11233140A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the degradation of a battery and to enhance preservation characteristic by providing a positive electrode containing a manganese oxide or complex oxides of lithium and manganese, a negative electrode composed chiefly of a material capable of being doped and undoped with lithium metal, a lithium alloy, or lithium, and a nonaqueous electrolyte obtained by the dissolving of an electrolyte in a nonaqueous solvent containing a phosphoric ester compound. SOLUTION: The phosphoric ester represented by the formula is used and preferably contained in a nonaqueous solvent by not less than 3 vol.% to not more than 20 vol.%. In the formula, R1 , R2 , and R3 are each an alkyl group or aryl group. For example, triethyl phosphate, triphenyl phosphate, ethyldimethyl phosphate, and the like are used, with trimethyl phosphate being particularly desirable. An electrolytic solution contains LiBF4 as an electrolyte, and a manganese oxide or complex oxides of lithium and manganese for use in the positive electrode should preferably have a spinel type crystalline structure. A phosphoric ester compound inhibits the elution of Mn in the positive electrode material into the nonaqueous electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to an improvement in a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, many portable electronic devices such as a camera-integrated video tape recorder, a portable telephone, and a portable computer have appeared, and their size and weight have been reduced.
Researches on batteries serving as portable power sources for these electronic devices, particularly secondary batteries, have been actively conducted.

A secondary battery using a non-aqueous electrolyte, in particular, a lithium ion battery can obtain a higher energy density than a conventional aqueous electrolyte secondary battery, such as a lead battery or a nickel cadmium battery. Therefore, expectations are increasing and the market is growing remarkably.

[0004] As a non-aqueous electrolyte used for such a lithium or lithium ion secondary battery, for example, LiPF ₆ is dissolved as an electrolyte in a carbonate-based non-aqueous solvent such as propylene carbonate (PC) or diethyl carbonate. These are widely used because they have relatively high conductivity and are stable in potential.

[0005] As the positive electrode active material used in the lithium or lithium-ion secondary battery, for example, Li _x Mn ₂ O ₄ having a high discharge potential, Li _x M _y O
₂ (M is either Ni or Co, and the value of x changes with charge and discharge, but x 合成 1 and y ≒ 1 at the time of synthesis).

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

[0007] However, cobalt, which is a raw material of this composite oxide, is scarce in resources and is ubiquitous in countries with few ore deposits that can be used commercially. In the future, supply will be uncertain.

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

As such a positive electrode active material, for example,
Nickel and manganese are possible. 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.

In recent years, positive electrode active materials using manganese as a raw material have been actively studied. Specifically, manganese oxides composed of various manganese raw materials, various manganese raw materials and lithium raw materials have been used as the positive electrode active material. Various types of composite oxides of lithium and manganese (hereinafter, referred to as lithium-manganese composite oxides), which are synthesized, have been reported.

[0011] Li _x Mn _y O As the lithium manganese complex oxide having, for example, a spinel structure
₄ (x ≒ 1, Y ≒ 2). This Li _x Mn _y O ₄
The lithium-manganese composite oxide represented by (x ≒ 1, 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. is there.

[0012]

However, a non-aqueous electrolyte secondary battery using these manganese oxides or lithium manganese composite oxides as a positive electrode active material deteriorates when used in an environment at room temperature or higher. There is a disadvantage that it 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, large-sized non-aqueous electrolyte secondary batteries have been developed in various fields for use in electric vehicles or road leveling. 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, it is strongly demanded to minimize deterioration of the battery in an environment at a temperature higher than room temperature.

Therefore, the present invention has been proposed in view of the conventional circumstances, and the use of inexpensive and resource-rich raw materials as a positive electrode active material minimizes deterioration and improves storage characteristics. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that non-aqueous electrolysis using manganese oxide or a composite oxide of lithium and manganese as a cathode material. In a liquid secondary battery, it has been found that by including a phosphate ester compound in one component of the non-aqueous electrolyte, deterioration of the battery is reduced, and the present invention has been completed.

That is, a 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. And a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, and the non-aqueous electrolyte contains a phosphate compound represented by the following formula (2). It is characterized by doing.

[0017]

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The nonaqueous electrolyte secondary battery according to the present invention contains a phosphate compound in the nonaqueous electrolyte, and since the phosphate compound is stable to oxidation, the positive electrode material is contained in the nonaqueous electrolyte. It is considered that Mn in the solution is suppressed from being eluted. As a result, the non-aqueous electrolyte secondary battery according to the present invention,
Deterioration is suppressed as much as possible, resulting in excellent storage characteristics, especially continuous charging characteristics.

The phosphate compound used in the present invention is preferably contained in a nonaqueous solvent in an amount of 3% by volume or more and 20% by volume or less. Here, the lower limit of the content is preferably 3% by volume from the viewpoint of exerting the effect of suppressing the deterioration of the battery,
The upper limit of the content is preferably 20% by volume from the viewpoint of not deteriorating other battery characteristics such as capacity.

[0020]

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 manganese oxide or lithium manganese composite oxide, and a material capable of doping and undoping lithium metal, a lithium alloy or lithium. And a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent.

In particular, in the non-aqueous electrolyte secondary battery to which the present invention is applied, the non-aqueous electrolyte contains a phosphate compound represented by the following chemical formula (3).

[0023]

Embedded image

Specific examples of the phosphate compound include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, triphenyl phosphate, ethyl dimethyl phosphate, and methyl ethyl butyl phosphate. No. Among them, trimethyl phosphate is preferred.

As described above, the non-aqueous electrolyte secondary battery to which the present invention is applied contains the above-mentioned phosphate compound in the non-aqueous electrolyte, and the phosphate compound is stable to oxidation. It is considered that the elution of Mn in the positive electrode material into the electrolytic solution is largely suppressed. As a result, the non-aqueous electrolyte secondary battery according to the present invention is minimized in deterioration and excellent in storage characteristics, particularly continuous charging characteristics.

Here, the continuous charging characteristic is a characteristic in which a small amount of current is passed through the battery so as to compensate for the capacity loss due to self-discharge of the battery, and the battery is always kept in a charged state.

It is preferable that the phosphate compound is contained in the non-aqueous solvent in an amount of 3% by volume or more and 20% by volume or less. Here, the lower limit of the content is preferably 3% by volume from the viewpoint of suppressing the deterioration of the battery, and the upper limit of the content is 20% by volume from the viewpoint of not deteriorating other battery characteristics such as capacity.
Is good.

The non-aqueous electrolyte used in the present invention is obtained by dissolving an electrolyte in a non-aqueous solvent containing the above-mentioned phosphate compound.

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 usual 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 .

Among them, LiBF ₄ is particularly preferred as the electrolyte used in the present invention. At this time, this LiBF ₄
Is 0.5 mol / liter to 5
Preferably it is mol / l. If the concentration of LiBF ₄ dissolved in the non-aqueous solvent is too high or too low, sufficient conductivity cannot be obtained.

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.

Materials 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 graphitized when heat-treated at about 2800 to 3000 ° C.

As a starting material for producing the above non-graphitizable carbon material, furfuryl alcohol or a furfural resin composed of a homopolymer or copolymer of furfural is preferable. That is, if 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 the H / C atomic ratio needs to be 0.6 to 0.8 in order to obtain non-graphitizable carbon.

Specific means for introducing a functional group containing oxygen 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 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 oxygen-containing functional group 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 performing a pre-heat treatment such as pitching of the following starting materials. 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, pentaphene, 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, asphalt, etc. obtained by high-temperature pyrolysis of coal tar, ethylene bottom oil, crude oil, etc., thermal polycondensation, extraction, chemical polycondensation. And the pitch generated during wood carbonization.

The raw material of the polymer compound includes 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 for the coal, pitch, and polymer compound naturally undergo 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 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-described 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 compared as follows.

Crystallinity is more difficult to graphitize carbon than activated carbon,
It becomes higher in the order of graphitizable carbon and graphite. The density of the crystals increases in the order of non-graphitizable carbon, graphitizable carbon, and graphite in the order of activated carbon. Further, the porosity of the crystal becomes larger in the order of graphitizable carbon, non-graphitizable carbon, and activated carbon than graphite. The firing temperature is higher in the order of non-graphitizable carbon, easily graphitizable carbon, and graphite than in activated carbon. In addition, conductivity becomes higher in the order of non-graphitizable carbon, easily graphitizable carbon, and graphite than in activated carbon.

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

The lithium alloy used as the material of the negative electrode includes, for example, a lithium-aluminum alloy.

On the other hand, as the positive electrode used in the present invention,
It is preferable to contain either manganese oxide or lithium manganese composite oxide as the positive electrode active material. Here, the manganese oxide or the lithium manganese composite oxide has a spinel-type crystal structure represented by a general formula AB ₂ X ₄ .

As the manganese oxide, for example, λ-M
nO 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). This λ-MnO ₂ has a spinel structure, and Li
It is produced by subjecting Mn ₂ O ₄ spinel to acid treatment to desorb Li.

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, Ti, N
a metal selected from the group consisting of i, Zn and Fe, 0 <y
<1) and the like. Among them, LiCo _0.2 Mn _1.8 O
_In No. ₄ , excellent cycle characteristics were obtained under a large discharge capacity. In addition, as lithium manganese composite oxide,
For example, Li ⁺¹ , Mg is added to Li _x Mn ₂ O ₄ (0 <x ≦ 1).
²⁺ , Zn ^2+, etc. further,
Li _y Mn ₂ O ₄ .xV ₂ O ₅ (0
<X ≦ 0.3, 0 <y ≦ 1.5).

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.

Incidentally, 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, manganese oxide and lithium manganese composite oxide used as the positive electrode active material in the present invention are practically used because manganese, which is a raw material thereof, is much cheaper than cobalt and nickel and is rich in resources. It can be said that it is a preferable substance.

In order to produce a positive electrode and a negative electrode using the above-mentioned positive electrode active material and negative electrode active material, they can be produced by a conventional method using a conventionally known binder resin, conductive material, 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.

The mixing ratio between 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 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 nonaqueous electrolyte secondary battery, such as a separator, a battery can, or a battery shape, are similar to the conventional nonaqueous electrolyte secondary battery, and are cylindrical, square, coin-shaped, and button-shaped. Various shapes of molds can be used, and any shape can be applied to a thin type or a large type.

[0067]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results. Here, in order to evaluate the influence of the content of the phosphate compound contained in the nonaqueous electrolyte on the characteristics of the battery, a lithium ion secondary battery as shown below was produced.

Example 1 First, a negative electrode active material was synthesized as follows.

A petroleum pitch was prepared as a starting material, and the petroleum pitch was calcined in an inert gas stream at 1000 ° C. to obtain a non-graphitizable carbon material having properties similar to glassy carbon. Then, when the obtained non-graphitizable carbon material was subjected to X-ray diffraction measurement, the (002) plane spacing was 0.3
It was 76 nm, and the true specific gravity was 1.58 g / cm ³ .

Then, the non-graphitizable carbon material is pulverized,
A carbon material powder having an average particle size of 10 μm was obtained.

Next, the negative electrode 1 shown in FIG. 1 was prepared using the hard graphite sample powder obtained as described above as a negative electrode active material.

90 parts by weight of this carbon material powder and polyvinyldene fluoride (PVDF) 10
Parts by weight to prepare a negative electrode mixture.
By dispersing in methyl-2-pyrrolidone, a negative electrode agent slurry (paste-like) was obtained.

Then, as the negative electrode peripheral body 10, a 10 μm thick
The negative electrode current collector 10 was prepared by uniformly applying and drying the negative electrode mixture slurry on both surfaces of the negative electrode current collector 10, and then compression-molded at a constant pressure to prepare the negative electrode band 1.

On the other hand, the positive electrode active material was produced as follows.

Lithium carbonate and manganese carbonate are mixed at a ratio of 1/2, and this mixture is heated to an air temperature of 80%.
Calcination at 0 ° C. yielded LiMn ₂ O ₄ .

Here, when this LiMn ₂ O ₄ was analyzed by X-ray diffraction, it was found that it had a spinel structure.

Then, 91 parts by weight of the LiMn ₂ O ₄ powder, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. A positive electrode mixture slurry (paste) was obtained by dispersing in N-methylpyrrolidone as a solvent.

The positive electrode current collector 11 has a thickness of 20 μm.
m, and a positive electrode current collector 1 was prepared.
The positive electrode mixture slurry was uniformly applied to both surfaces of No. 1 and dried, followed by compression molding to produce a belt-shaped positive electrode 2.

The strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 produced as described above are interposed between a negative electrode 1, a separator 3 and a positive electrode 2 via a separator made of a microporous polypropylene film having a thickness of 25 μm as shown in FIG. And a separator 3 in this order, and then wound many times to produce a spiral electrode body having an outer diameter of 18 mm.

Next, the spirally wound electrode body manufactured as described above was housed in a nickel-plated iron battery can 5 with the insulating plates 4 placed on both upper and lower surfaces.

Then, the aluminum positive electrode lead 13 was led out from the positive electrode current collector 11 and welded to the current interrupting thin plate 8, and the nickel negative electrode lead 12 was drawn out from the negative electrode current collector 10 and welded to the battery can 5.

Next, a non-aqueous electrolyte was injected into the battery can 5. This non-aqueous electrolyte contains ethylene carbonate (EC)
LiPF ₆ at a concentration of 1.5 mol / l in a non-aqueous electrolyte obtained by mixing 8.5% by volume, 48.5% by volume of dimethyl carbonate (DMC) and 3.0% by volume of trimethyl phosphate. Was used.

Next, the battery can 5 is caulked through an insulating sealing gasket 6 coated on the surface with asphalt to thereby provide a safety valve device 8 having a current cutoff mechanism and a PTC element 9.
In addition, the battery cover 7 is fixed, and the airtightness in the battery is maintained,
Finally, a cylindrical non-aqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

Examples 2 to 16, Comparative Example 1 and Comparative Example
Example 2 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the composition of the non-aqueous solvent and the electrolyte in the non-aqueous electrolyte were as shown in Tables 1 and 2.

The abbreviations in Tables 1 and 2 indicate the following solvents. Propylene carbonate to P
C, ethylene carbonate as EC, dimethyl carbonate as DMC, methyl ethyl carbonate as MEC, trimethyl phosphate as TMP, triethyl phosphate as TEP, and triphenyl phosphate as TPhP.
And In Table 1, those using LiPF ₆ as the electrolyte in the non-aqueous electrolyte are listed.
One using LiBF ₄ as the electrolyte in the non-aqueous electrolyte is cited.

[0086]

[Table 1]

[0087]

[Table 2]

The continuous charging characteristics and capacity of the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 16 and Comparative Examples 1 and 2 manufactured as described above were evaluated as follows. did.

<Evaluation of Continuous Charging Characteristics> First, each battery was continuously charged at 60 ° C. and 4.2 V. When each battery is continuously charged for a long time, Mn in the positive electrode active material dissolves in the non-aqueous electrolyte and precipitates on the negative electrode surface, causing a fine internal short circuit and increasing the charging current.

Therefore, the time required for the charging current to rise to 10 mA was measured.

<Evaluation of Capacity> First, 2
The battery was charged under the conditions of 3 ° C., constant current of 1 A, maximum voltage of 4.2 V, and constant current and constant voltage of 3 hours. Next, each of the charged batteries was discharged at a constant current of 1000 mA and a cut-off voltage of 2.5 V to obtain a final capacity.

The results are shown in Tables 3 and 4. Table 3 shows that LiPF ₆ was used as the electrolyte in the non-aqueous electrolyte.
And Table 4 lists those using LiBF ₄ as the electrolyte in the non-aqueous electrolyte.

[0093]

[Table 3]

[0094]

[Table 4]

As is evident from the results in Table 3, Examples 1 to 7 in which the phosphate compound was contained in the non-aqueous electrolytic solution did not contain the phosphate compound in the non-aqueous electrolytic solution. The time required for the charging current to reach 10 mA was longer than in Example 1, and it was found that the continuous charging characteristics were improved.

Similarly, as is apparent from the results in Table 4, Examples 8 to 16 in which the phosphate compound was contained in the nonaqueous electrolytic solution were the phosphate ester compounds in the nonaqueous electrolytic solution. The charging current is 1 compared to Comparative Example 2 containing no compound.
The time to reach 0 mA was longer, indicating that the continuous charging characteristics were improved.

From this, it was found that the storage characteristics were improved by including the phosphate compound in the non-aqueous electrolyte, regardless of the type of the phosphate compound.

Further, as is apparent from the results in Table 3, the phosphate ester compound was contained in the non-aqueous electrolyte at 3% by volume or more.
In Examples 1 to 5 containing 0% by volume or less, the continuous charge characteristics are improved and the decrease in capacity is small and there is no practical problem as compared with Comparative Example 1 containing no phosphate compound. Level.

On the other hand, as is clear from the results in Table 3, the non-aqueous electrolyte solution containing the phosphoric acid ester compound in an amount of 20% by volume or more contained the non-aqueous electrolyte in Comparative Example 7 containing no phosphoric acid ester compound. Although the continuous charging characteristics are significantly improved as compared with 1, the capacity is reduced by 10% or more, which is not practically preferable. Further, in Example 6, in which the content of the phosphate compound in the non-aqueous electrolyte was only a small amount of 3% by volume or less, excellent continuous charging characteristics as in Examples 1 to 5 were obtained. Not been.

Similarly, as is apparent from the results in Table 4, the phosphate ester compound was contained in the non-aqueous electrolyte at 3% by volume.
Examples 8 to 14 containing 20% by volume or less as described above.
In Comparative Example 2, the continuous charge characteristics were improved and the decrease in capacity was small and the level was not problematic in practical use as compared with Comparative Example 2 containing no phosphate compound.

On the other hand, as is apparent from the results in Table 4, the non-aqueous electrolytic solution containing the phosphate compound in an amount of 20% by volume or more contained a non-aqueous electrolyte in Comparative Example 16 containing no phosphate compound. Although the continuous charge characteristics are significantly improved as compared with 2, the capacity is reduced by 10% or more, which is not preferable in practical use. Further, in Example 15 in which the content of the phosphate compound in the non-aqueous electrolyte was only a small amount of 3% by volume or less, excellent continuous charging characteristics as in Examples 8 to 16 were obtained. Not been.

From the above results, it was found that it is practically preferable that the amount of the phosphate compound contained in the non-aqueous electrolyte be 3% by volume or more and 20% by volume or less based on the non-aqueous solvent. .

Examples 8 to 1 in which LiBF ₄ is contained as an electrolyte contained in the nonaqueous electrolyte
No. ₆ shows that the continuous charge characteristics are more improved when the same amount of the phosphate compound is added to the non-aqueous solvent than in Examples 1 to 7 in which LiPF ₆ is contained as the electrolyte. I understood.

From these results, it was found that LiBF ₄ is preferable as the electrolyte in the non-aqueous electrolyte used in the present invention.

[0105]

As described in detail above, the non-aqueous electrolyte secondary battery according to the present invention contains a phosphate compound in the non-aqueous electrolyte, and the phosphate compound is stable against oxidation. Therefore, elution of Mn in the positive electrode material into the non-aqueous electrolyte can be significantly suppressed. as a result,
In the nonaqueous electrolyte secondary battery according to the present invention, deterioration is suppressed as much as possible, and storage characteristics, particularly continuous charge characteristics, can be improved, and the performance of the battery can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a cylindrical nonaqueous electrolyte secondary battery to which the present invention is applied.

[Explanation of symbols]

1 negative electrode, 2 positive electrode, 3 separator, 4 insulating plate, 5
Battery can, 6 Insulation sealing gasket, 7 Battery lid

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 solution in which an electrolyte is dissolved, wherein the non-aqueous electrolyte solution contains a phosphate compound represented by Chemical Formula 1. Embedded image 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the phosphate compound is contained in the non-aqueous solvent in an amount of 3% by volume or more and 20% by volume or less. 3. The method according to claim 1, wherein the non-aqueous electrolyte is L
The non-aqueous electrolyte secondary battery according to claim 1, further comprising iBF ₄ . 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.