JPH11297354A - Nonaqueos electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery, in which a raw material which is inexpensive and rich in natural resources is used as a positive electrode active material, deterioration can be suppressed as much as possible under an environment where temperature is equal to room temperature or more, cycle characteristics and conservative characteristics are improved under high temperatures, and preferable output characteristics are obtained. SOLUTION: This nonaqueous electrolyte secondary battery comprises a positive electrode 2 containing manganate oxide or composite oxide of lithium and manganese, a negative electrode 1 containing a material whereby doping/un- doping of lithium metal, lithium alloy, or lithium can be made, and non-aqueous electrolyte, at least, LiBF4 having density of 2.0 mol/l to 5.0 mol/l is dissolved in non-aqueous solvent containing ethylene carbonate of 20 to 30% by volume.

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 electric devices, and more particularly to an improvement of a positive electrode.

[0002]

2. Description of the Related Art Along with the remarkable progress of various electronic devices in recent years, research on a secondary battery which can be used continuously for a long time and which can be recharged as an economical power source has been advanced. As typical nonaqueous electrolyte secondary batteries, lead storage batteries, nickel cadmium storage batteries, lithium secondary batteries, and the like are known.

[0003] Above all, a lithium secondary battery has a higher energy density than a lead storage battery or a nickel cadmium storage battery, so that it is possible to realize a further lighter weight and higher capacity, and it is possible to realize a mobile phone or a notebook. It has been put to practical use as a power source for portable electronic devices such as portable personal computers.

[0004] In recent years, interest in global environmental pollution and global warming has been increasing around the world, and high-performance electric vehicles and hybrid vehicles that exhibit great effects have been proposed as countermeasures. The light-weight and high-capacity lithium secondary battery as described above is expected to be put to practical use as an effective power source for high-performance battery vehicles, hybrid vehicles, and the like.

In a conventional lithium secondary battery, for example, a composite oxide of lithium and cobalt (hereinafter, referred to as lithium-cobalt composite oxide) such as LiCoO ₂ is used as a positive electrode, and lithium is doped and dedoped as a negative electrode. Is used in a carbonate-based non-aqueous solvent such as propylene carbonate or dimethyl carbonate as a non-aqueous electrolyte.
Obtained by dissolving an electrolyte such as F ₆ are used.

[0006]

However, since the lithium-cobalt composite oxide used for the positive electrode contains Co, the raw material cost is high and the amount of resources is not abundant, so that large consumption is expected. It is not suitable for use in power sources such as electric vehicles.

Therefore, instead of the lithium cobalt composite oxide, a relatively rich and inexpensive manganese oxide or a composite oxide of lithium and manganese (hereinafter referred to as lithium manganese composite oxide) is used. ) Is expected as a positive electrode for secondary batteries for electric vehicles and hybrid vehicles.

[0008] Secondary batteries for electric vehicles and hybrid vehicles are required to be lightweight and have a large capacity, good output characteristics, long life and good durability. Furthermore, it is conceivable that these electric vehicles and hybrid vehicles are exposed to a large temperature change from a low temperature to a high temperature depending on environmental conditions such as the climate of a region where the electric vehicle or hybrid vehicle is used. Therefore, it is essential that these secondary batteries for electric vehicles and hybrid vehicles have excellent capacity, output characteristics, and life performance under all temperature conditions from low to high temperatures.

However, for example, LiMn ₂ O ₄ which is a lithium manganese composite oxide is used as a positive electrode, and LiPF is contained in a non-aqueous solvent such as carbonate ester as a non-aqueous electrolyte.
Lithium secondary battery using an electrolyte consisting of ₆ dissolved at a concentration of 1 mol / l and using a graphite carbon material that can be doped and dedoped with lithium ions as the negative electrode is the 38th Battery Symposium. 2A17, 2A18
As shown in the Journal of the Society of Japan, there is a problem that storage characteristics and cycle characteristics are significantly deteriorated at high temperatures.

One of the causes of deterioration of storage characteristics and cycle characteristics at such a high temperature is that the electrolyte LiPF
₆ is very unstable to moisture, so when a small amount of water is present in the battery, the water reacts with LiPF ₆ , which adversely affects battery characteristics, especially at high temperatures. it is conceivable that.

Therefore, LiBF having a relatively high thermal decomposition temperature is used.
A lithium secondary battery using ₄ as an electrolyte in a non-aqueous electrolyte has also been proposed. In this lithium secondary battery, since LiBF ₄ used as an electrolyte is more stable against moisture, storage characteristics and cycle characteristics at high temperatures are slightly improved compared to a lithium secondary battery using LiPF ₆ as an electrolyte. Be looked at. However, the lithium secondary battery using LiBF ₄ as the electrolyte, compared with the lithium secondary batteries using LiPF ₆ as an electrolyte, since the electric conductivity of LiBF ₄ is lower than the electrical conductivity of LiPF _6,
There is a problem that output characteristics are deteriorated.

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. It is another object of the present invention to provide a non-aqueous electrolyte secondary battery in which cycle characteristics and storage characteristics at high temperatures are improved and good output characteristics are obtained.

[0013]

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 a battery, by using a non-aqueous electrolyte containing LiBF ₄ dissolved in a predetermined concentration in a non-aqueous solvent containing a predetermined amount of ethylene carbonate as a non-aqueous electrolyte, battery characteristics in an environment at room temperature or higher are improved. And completed the present invention.

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 doped or dedoped. And a non-aqueous electrolyte.

In particular, in the non-aqueous electrolyte secondary battery according to the present invention, the non-aqueous electrolyte comprises ethylene carbonate
It is characterized in that at least LiBF ₄ is dissolved at a concentration of 2.0 mol / l to 5.0 mol / l in a nonaqueous solvent containing 0% to 30% by volume.

As described above, the non-aqueous electrolyte secondary battery according to the present invention uses LiB having a high thermal decomposition temperature in the non-aqueous electrolyte.
F ₄ is used as an electrolyte, a solvent containing ethylene carbonate having a high dielectric constant is used as a non-aqueous solvent, and
The concentration of iBF _{4 and} the content of ethylene carbonate are specified respectively. Thereby, in the nonaqueous electrolyte secondary battery according to the present invention, the properties such as thermal stability, electric conductivity, and viscosity of the nonaqueous electrolyte are optimized. The battery has improved characteristics and excellent output characteristics.

Here, the concentration of the electrolyte is 2.0 mol.
If it is too small, the cycle characteristics, initial capacity, and output characteristics at high temperatures deteriorate. On the other hand, if the concentration of the electrolyte is more than 5.0 mol / l, the viscosity of the non-aqueous electrolyte becomes too high, so that it becomes difficult for the non-aqueous electrolyte to sufficiently penetrate the electrode. As a result, the initial capacity and output characteristics are reduced.

On the other hand, if the content of ethylene carbonate in the non-aqueous solvent is less than 20% by volume, the electric conductivity of the non-aqueous electrolyte becomes low, so that the initial capacity, output characteristics, and cycle characteristics at high temperatures are deteriorated. descend. On the other hand, if the content of ethylene carbonate in the non-aqueous solvent is more than 30% by volume, the non-aqueous electrolyte becomes viscous at a low temperature, and the capacity at a low temperature decreases.

[0019]

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.

In particular, in the non-aqueous electrolyte secondary battery to which the present invention is applied, the non-aqueous electrolyte comprises ethylene carbonate
In a non-aqueous solvent containing 0% to 30% by volume, at least LiBF ₄ contains 2.0 mol / l to 5.0 mol / l.
Characterized by being dissolved at a concentration of

[0022] Thus, in the non-aqueous electrolyte used in the present invention, using LiBF ₄ as an electrolyte, the LiBF ₄
Is 2.0 mol / l to 5.0 mol / l. More preferably, the concentration of LiBF ₄ is 2.0 mol
/ L to 3.0 mol / l.

LiBF ₄ has a hygroscopic property and is stable against moisture, and has a higher thermal decomposition temperature, for example, 200 ° C. than other known electrolytes such as LiPF ₆ . As described above, according to the nonaqueous electrolyte secondary battery to which the present invention is applied, since the LiBF ₄ having a high thermal decomposition temperature is used as the electrolyte at a predetermined concentration, the cycle characteristics and storage characteristics particularly at high temperatures are improved.

Here, the concentration of the electrolyte is 2.0 mol / l
If it is too small, the initial capacity, the output characteristics, and the cycle characteristics at high temperatures will deteriorate. On the other hand, if the concentration of the electrolyte is more than 5.0 mol / l, the viscosity of the non-aqueous electrolyte becomes too high, so that it becomes difficult for the non-aqueous electrolyte to sufficiently penetrate the electrode. As a result, the initial capacity and output characteristics are reduced.

Further, as described above, in the non-aqueous electrolyte used in the present invention, a solvent containing ethylene carbonate having a high dielectric constant is used as the non-aqueous solvent, and this ethylene carbonate is used in the entire amount of the non-aqueous electrolyte. 20% by volume
-30% by volume.

As described above, in the nonaqueous electrolyte secondary battery to which the present invention is applied, the nonaqueous electrolyte contains 20 to 30% by volume of ethylene carbonate having a high dielectric constant, so that the electric conductivity is reduced. Even if a relatively low LiBF ₄ is used as the electrolyte, properties such as electric conductivity and viscosity of the non-aqueous electrolyte can be made favorable, and output characteristics can be effectively improved.

If the content of ethylene carbonate is less than 20% by volume, the electric conductivity of the non-aqueous electrolyte decreases, so that the initial capacity, output characteristics, and cycle characteristics at high temperatures deteriorate. On the other hand, when the content of ethylene carbonate is too large, the non-aqueous electrolyte becomes viscous at a low temperature, so that the capacity at a low temperature decreases.

As described above, the non-aqueous electrolyte secondary battery to which the present invention is applied uses LiBF ₄ having a high thermal decomposition temperature as an electrolyte and contains ethylene carbonate having a high dielectric constant in the non-aqueous electrolyte. The solvent is used as a non-aqueous solvent, and the concentration of LiBF _{4 and} the content of ethylene carbonate are specified respectively. Thereby, in the nonaqueous electrolyte secondary battery according to the present invention, the properties such as thermal stability, electric conductivity, and viscosity of the nonaqueous electrolyte are optimized. The battery has improved characteristics and excellent output characteristics.

As the non-aqueous solvent used in the present invention, the following solvents are used in addition to the above-mentioned ethylene carbonate. In particular, as the non-aqueous solvent used in the present invention, to increase the electrical conductivity of the non-aqueous electrolyte, and to obtain an optimum viscosity, a cyclic carbonate having a relatively high dielectric constant such as ethylene carbonate, It is preferable to use a combination with a chain carbonate having a low viscosity.

Specifically, examples of the non-aqueous solvent other than the above-mentioned ethylene carbonate include cyclic carbonates such as propylene carbonate and butylene carbonate, and chain carbonates such as dimethyl carbonate and diethyl carbonate. Further, as the non-aqueous solvent, for example, lactones such as γ-butyrolactone and γ-valerolactone, and other esters such as ethyl acetate and methyl propionate may be used in combination.

A non-aqueous electrolyte secondary battery according to the present invention comprising the non-aqueous electrolyte having the above-described structure has a positive electrode and a negative electrode having the following structures.

The positive electrode used in the present invention contains either manganese oxide or lithium manganese composite oxide as a positive electrode active material. Here, the manganese oxide or the lithium manganese composite oxide preferably has a spinel-type crystal structure represented by the 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). The LiMn ₂ O ₄ spinel is subjected to an acid treatment to desorb Li, thereby obtaining a λ-Mn having a spinel structure.
O ₂ can be obtained.

Examples of the lithium manganese composite oxide include 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,
As the lithium manganese composite oxide, for example, Li _x
A transition metal such as Co, Ni, or Cr may be added to Mn ₂ O ₄ (0 <x ≦ 1). Also, Li _y Mn ₂ O ₄ .xV ₂ O ₅ having a quaternary spinel structure (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. In addition, these lithium manganese composite oxides, for example, using manganese oxide and lithium nitrate, oxide, hydroxide and the like as starting materials,
These are mixed in an amount according to the composition, and
It can be obtained by firing in a temperature range of ° C.
When a positive electrode is formed using such a positive electrode active material, a known conductive agent, a binder, and the like are added to form the positive electrode.

The manganese oxide and the lithium manganese composite oxide used as the positive electrode active material in the present invention are manganese, which is a raw material, much cheaper than cobalt and nickel, and are rich in resources. It can be said that it is a substance suitable for practical use. Therefore, it can be said that the nonaqueous electrolyte secondary battery to which the present invention is applied using manganese oxide or lithium manganese oxide as the positive electrode active material is advantageous in terms of manufacturing cost.

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.

Examples of the lithium alloy include 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 non-graphitizable carbon material, furfuryl alcohol or furfural made 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 obtained by introducing a functional group containing oxygen (so-called oxygen cross-linking) into petroleum pitch having a specific H / C atomic ratio 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 is 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.

The specific means for introducing a functional group containing oxygen into the petroleum pitch 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 ), 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, 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 the starting material for graphitizable carbon, coal and pitch are representative.

The pitch is obtained by distillation (vacuum distillation, normal pressure distillation, steam distillation) from tar, 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 materials for the high molecular compound include polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin.

These starting materials can be used in 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 (eg, carboxylic acids, carboxylic anhydrides, 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 by 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-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 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 the material which can be doped with and dedoped with lithium include polymers such as polyacetylene and polypyrrole and oxides such as SnO ₂ .

In order to produce a positive electrode and a negative electrode using the above-mentioned positive electrode active material and negative electrode active material, the positive electrode and the negative electrode can be produced 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.

As described above, 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, the separator, the battery can, or the battery shape and the like, like the conventional non-aqueous electrolyte secondary battery,
Various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape can be used, and any shape can be applied to a wound type, a laminated type, and a large type.

[0066]

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

Here, in order to evaluate the effect of the composition of the non-aqueous electrolyte on the characteristics of the battery, a cylindrical non-aqueous electrolyte secondary battery as shown in FIG. 1 was produced as follows.

Example 1 First, a strip-shaped negative electrode 1 was produced as follows.

First, 90% of graphite powder was used as the negative electrode active material.
Parts by weight and 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, and disperse it in N-methyl-2-pyrrolidone as a solvent to obtain a paste-like negative electrode mixture slurry. I got

The negative electrode current collector 10 has a thickness of 15 μm.
m-shaped copper foil is prepared, and the above-mentioned negative electrode mixture slurry is uniformly applied to both surfaces of the negative electrode current collector 10, dried, and then compression-molded at a constant pressure by a roller press to produce a band-shaped negative electrode 1. did.

On the other hand, a belt-shaped positive electrode 2 was produced as follows.

First, 9 parts of LiMn ₂ O ₄ were used as the positive electrode active material.
0 parts by weight, 6 parts by weight of graphite powder as a conductive additive, and 4 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture, and N-methyl-2-pyrrolidone as a solvent was prepared. To obtain a paste-like positive electrode mixture slurry.

The positive electrode peripheral body 11 has a thickness of 20 μm.
m of aluminum foil was prepared, the positive electrode mixture slurry was uniformly applied to both surfaces of the positive electrode peripheral body 11, dried, and then compression-molded with a roller press to produce a belt-shaped positive electrode 2.

As shown in FIG. 1, the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 manufactured as described above were interposed via a separator 3 made of a microporous polypropylene film having a thickness of 25 μm. Positive electrode 2, separator 3
And wound a number of times to produce a spiral electrode body of a predetermined size.

The spiral electrode body thus manufactured is
The insulated plates 4 were placed on the upper and lower surfaces and stored in a nickel-plated iron battery can 5.

The negative electrode lead 12 made of nickel was led out of the negative electrode peripheral body 10 and pressed against the battery can 5 in order to obtain the negative electrode peripheral current. In addition, in order to obtain an electric charge of the positive electrode, one end of an aluminum positive electrode lead 13 is attached to the positive electrode 2, and the other end is electrically connected to the battery lid 7 via a current interrupting thin plate 8 which interrupts current according to the internal pressure of the battery. Connected.

Next, the electrolytic solution shown in the following Table 1 was injected into the battery can 5.

[0078]

[Table 1]

Then, the battery can 5 and the battery cover 7 are caulked through the sealing gasket 6 coated with Alfalt, thereby fixing the current blocking thin plate 8, the PTC element 9 and the battery cover 7, and 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 6 and Comparative Examples 1 to Comparative Examples
5 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 electrolyte was changed to the value shown in Table 1.

With respect to the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 manufactured as described above, the initial capacity, output characteristics,
The low-temperature characteristics, cycle characteristics under high temperature, and storage characteristics under high temperature were evaluated.

<Evaluation Method of Initial Capacity> The charging voltage was set to 4.2 V and the charging current was set to 1000
After charging was performed under the conditions of 2.5 mA and a charging time of 2.5 hours, the discharge current was set to 500 mA, and the final voltage was set to 2.7.
Discharge was performed under the condition of 5 V, and the capacity at the time of discharge was determined.
Here, this discharge capacity was used as the initial capacity.

<Evaluation Method of Output Density> Each of the batteries after the initial capacity measurement was charged again under the same conditions as those at the time of the initial capacity measurement, and thereafter, until the depth of discharge (DOD) became 70%.
After discharging at a discharge current of 700 mA and adjusting the depth of discharge, discharging was performed for 10 seconds at a discharge current of 500 mA, 1000 mA, and 3000 mA, and a discharge current-voltage characteristic (discharge IV characteristic) was obtained from the cell voltage at that time. The output was determined under the condition of a cutoff voltage of 2.75V. This output value was divided by the cell weight to obtain an output density.

<Evaluation Method of Low-Temperature Characteristics> Each of the batteries after the initial capacity measurement was charged again under the same conditions as in the initial capacity measurement, and then the discharge current was set to 500 in a -20 ° C. thermostat.
The discharge was performed under the conditions of mA and a final voltage of 2.75 V, and the capacity at the time of discharge was determined. Then, the ratio of the discharge capacity to the initial capacity at this time was determined with the initial capacity being 100%.

<Evaluation Method of High-Temperature Cycle Characteristics> Each of the prepared batteries was charged under the conditions of a charging voltage of 4.2 V, a charging current of 1000 mA, and a charging time of 2.5 hours. Discharge was performed under the conditions of a current of 700 mA and a final voltage of 2.75 V, which was defined as one cycle. And after repeating this charge / discharge cycle and performing charge / discharge of 300 cycles,
The discharge capacity was determined, and the ratio of the discharge capacity to the initial capacity was determined with the initial capacity being 100%. At this time, all of the above steps were performed under a temperature condition of 60 ° C.

<Evaluation Method of High-Temperature Storage Characteristics> Each battery after the initial capacity measurement was stored in a thermostat at 60 ° C. for 15 days, and then charged and discharged again under the same conditions as in the initial capacity measurement to obtain a discharge capacity. Then, the ratio of the discharge capacity to the initial capacity was determined with the initial capacity being 100%.

Table 1 shows the above measurement results.

Examples 1 to 6 were conducted in a non-aqueous solvent containing 20 to 30% by volume of ethylene carbonate.
It has a non-aqueous electrolyte obtained by dissolving LiBF ₄ at a concentration of 2.0 mol / l to 5.0 mol / l. Thus, Examples 1 to 6 containing a predetermined amount of ethylene carbonate and LiBF ₄ were, as apparent from the results in Table 1,
The initial capacity, power density, low temperature characteristics, high temperature cycle characteristics and high temperature storage characteristics are good values.

On the other hand, in Comparative Example 1 in which the concentration of LiBF ₄ is lower than the predetermined concentration, the initial capacity, the output density and the high-temperature cycle characteristics are particularly lower than those in Examples 1 to 6. In Comparative Example 2 in which the concentration of LiBF ₄ is higher than the predetermined concentration, the initial capacity and the output density are particularly lower than those in Examples 1 to 6.

Therefore, it has been found that the concentration of LiBF ₄ in the non-aqueous electrolyte is preferably 2.0 mol / l to 5.0 mol / l.

In Comparative Example 3 in which the amount of ethylene carbonate is smaller than the predetermined amount, the initial capacity, power density, and high-temperature cycle characteristics are particularly lower than those in Examples 1 to 6. Further, Comparative Example 4, in which the amount of ethylene carbonate is larger than the predetermined amount, is particularly low in low-temperature characteristics as compared with Examples 1 to 6.

Therefore, it was found that the content of ethylene carbonate in the non-aqueous solvent is preferably 20% by volume to 30% by volume.

In Comparative Example 5 using LiPF ₆ instead of LiBF ₄ as the electrolyte, the high-temperature storage characteristics and high-temperature cycle characteristics were particularly deteriorated. From this, it was found that LiBF ₄ is preferable as the electrolyte from the viewpoint of storage characteristics at high temperatures and cycle characteristics.

From the above results, a positive electrode containing manganese oxide or lithium manganese oxide, a negative electrode made of a material capable of doping and undoping lithium, and a predetermined amount of LiBF _{4 in} a solvent containing a predetermined amount of ethylene carbonate were used. By combining with the dissolved non-aqueous electrolyte,
It has been found that a non-aqueous electrolyte secondary battery having improved cycle characteristics and storage characteristics at high temperatures and excellent levels of initial capacity, output characteristics, and low-temperature characteristics can be obtained.

[0095]

As described above in detail, in the nonaqueous electrolyte secondary battery according to the present invention, in the nonaqueous electrolyte, LiBF ₄ having a high thermal decomposition temperature is used as an electrolyte, and ethylene carbonate having a high dielectric constant is used. Is used as a non-aqueous solvent, and the concentration of LiBF ₄ and the content of ethylene carbonate in the non-aqueous solvent are specified, respectively. Thereby, in the non-aqueous electrolyte secondary battery according to the present invention, the properties of the non-aqueous electrolyte, such as thermal stability, electric conductivity, and viscosity, are optimized, so that the battery characteristics deteriorate under an environment of room temperature or higher. Can be suppressed as much as possible, and high reliability having excellent cycle characteristics, storage characteristics and output characteristics can be obtained.

[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]

Reference Signs List 1 negative electrode, 2 positive electrode, 3 separator, 4 insulating plate, 5 battery can, 6 insulating sealing gasket, 7 battery lid

Claims (2)

[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; and an ethylene carbonate. At least 2.0 mol of LiBF ₄ is contained in the non-aqueous solvent containing 20% to 30% by volume.
A non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte is dissolved at a concentration of 0.1 mol / l to 5.0 mol / l. 2. 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.