JP3336998B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement in cycle characteristics of a so-called lithium secondary battery such as a metal lithium secondary battery and a lithium ion secondary battery. It is.

[0002]

2. Description of the Related Art Metallic lithium, lithium alloy,
In addition, many studies have been conducted on a so-called lithium secondary battery using a carbon material capable of doping / dedoping lithium with the expectation that a high voltage and a high energy density will be obtained. And, as a non-aqueous solvent for the electrolyte of the lithium secondary battery, ethylene carbonate, propylene carbonate,
Carbonates such as diethyl carbonate are widely used.

For example, when these carbonates and the like are used as a solvent for an electrolytic solution, the carbonates and the like are decomposed by repeated charge and discharge, and lithium carbonate (L
It is known to form i ₂ CO ₃ ) coatings. Aurb
ach et al. Electrochem. Soc. , 143 volumes, 3809 pages,
According to (1996), this Li ₂ CO ₃ coating has good lithium ion conductivity, protects the electrode surface, and has a function of preventing further decomposition reaction of carbonate ester and the like. It plays an important role in batteries.

On the other hand, as a supporting salt to be dissolved in a non-aqueous solvent, a lithium salt containing a halogen element such as LiBF ₄ , LiPF ₆ and LiClO ₄ is generally used. However, in an electrolyte using such a lithium salt as a supporting salt, hydrogen halide (HX: X is F, C) such as hydrogen fluoride (HF) or hydrogen chloride (HCl) is used as a free acid.
halogen element such as 1). Further, these hydrogen halides are also generated by a reaction between water in the electrolytic solution and these supporting salts.

[0005] These hydrogen halides react with Li on the electrode surface.
It reacts with ₂ CO ₃ or lithium precipitated by reduction on the surface of the negative electrode to form lithium fluoride (Li) having low ionic conductivity.
F) and lithium halides (LiX: X is a halogen element such as F, Cl, etc.) such as lithium chloride (LiCl). Therefore, a lithium secondary battery using a non-aqueous electrolyte containing hydrogen halide as a free acid inhibits normal exchange of lithium ions between the electrode and the electrolyte and increases the internal resistance of the battery. This is not preferred. Further, it is said that lithium halide is formed in a film form on the electrode surface, and the film becomes thicker as charge and discharge cycles are repeated, which is a factor that causes the cycle deterioration of the secondary battery to progress.

[0006] Regarding such a problem, for example, a method of removing HF or moisture of a free acid which causes a LiF coating has been reported. For example, a material in which a lithium compound is added to a carbon material to be a negative electrode to neutralize an acid component (JP-A-7-23529)
No. 7, Japanese Patent Application Laid-Open No. 7-192760), a method in which an alkali metal fluoride is added to an electrolytic solution (Japanese Patent Application Laid-Open No. 7-220758), a method in which a calcium salt is added to an electrolytic solution (Japanese Patent Application Laid-Open No. 7-192760), One that removes free acid and moisture by treating with Al ₂ O ₃ or the like (JP-A-5-315006).

However, in the method of adding a metal salt to these electrolytes and negative electrodes, a reaction between the additive and the free acid generates a protic by-product. For example, Japanese Patent Application Laid-Open No. Hei 7-23
In the method of adding lithium carbonate disclosed in Japanese Patent No. 5297, carbonic acid (H ₂ CO ₃ ) is produced as a double product. When such a protic compound is present in the battery system,
It has a problem that it reacts with lithium of the negative electrode and is not preferable.

Further, in the method in which the electrolytic solution is preliminarily treated with an adsorbent such as Al ₂ O ₃ , it is not possible to treat the water mixed in at the time of producing the battery or after producing the battery. Furthermore, even if any of the above methods is adopted, it was impossible to remove lithium halide once formed in a film form on the surface of the negative electrode. On the other hand, using a carbon material for the negative electrode,
Lithium-ion rechargeable batteries using lithium composite oxide for the positive electrode have the advantages of low risk of dendrite deposition on the negative electrode surface and high energy density. As a result, they have already been put into practical use and widely used in the fields of information-related equipment and communication equipment. Also, in the field of automobiles, the development of electric vehicles has been rushed due to resource and environmental issues, and lithium-ion secondary batteries are expected as a power source for driving the vehicles.

At present, lithium ion secondary batteries mainly use LiCoO ₂ having a layered rock salt structure as a positive electrode. However, cobalt, which is a constituent element, is scarce as a resource and is very expensive. Therefore, in the case of a large-capacity lithium ion secondary battery used for an electric vehicle power source, L
The use of iCoO ₂ has a problem that the battery itself becomes very expensive. As a positive electrode material that can constitute a 4V-class lithium ion secondary battery, a layered rock salt structure LiNiO ₂ , a spinel structure LiMn ₂ O _{4, and the} like are known in addition to the layered rock salt structure LiCoO ₂ . Among them, LiMn ₂ O ₄ is expected to be used as a positive electrode material of a lithium ion secondary battery used for an electric vehicle power supply because it is inexpensive and has little risk of ignition.

When considering the use as a power source for an electric vehicle, a battery is required to have characteristics specific to the use. Cars must be considered for being left outdoors. If left in the hot summer sun, the battery will be placed in a high-temperature environment of about 60 ° C, so its capacity will not deteriorate even at high temperatures. It is. That is, this is a characteristic that the high-temperature cycle characteristic is excellent.

The above-mentioned formation of a lithium halide film on the surface of the negative electrode is no exception in a lithium ion secondary battery using this LiMn ₂ O ₄ as a positive electrode, and the amount of film formation increases as the temperature increases. Therefore, in the case of applications that are placed in a high-temperature environment, such as power supplies for electric vehicles,
The deterioration of the battery due to the formation of the lithium halide coating becomes a more serious problem.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and removes a lithium halide film such as LiF on the surface of a negative electrode to remove an ion between the electrolyte and the surface of the negative electrode active material. It is an object of the present invention to improve conductivity, to suppress an increase in battery impedance (internal resistance) of a so-called lithium secondary battery, and to improve charge / discharge cycle characteristics. Further, the present invention provides a non-aqueous electrolyte secondary battery using a spinel-structured lithium manganese composite oxide as a positive electrode material, with less deterioration even when placed in a high temperature environment, that is, high temperature charge / discharge cycle characteristics. It is an object of the present invention to provide a good secondary battery.

The inventor of the present invention has been studying a method for removing a film of lithium halide such as LiF formed on the surface of the negative electrode, and has further studied a method of using a lithium manganese oxide having a spinel structure as a positive electrode material. Experiments were repeated on the relationship between the composition of the lithium manganese composite oxide and the formation of the lithium halide coating, and the following invention was reached.

[0014]

A nonaqueous electrolyte secondary battery according to the present invention comprises a negative electrode using lithium metal, a lithium alloy or a carbon material capable of doping / undoping lithium, a positive electrode, and a lithium salt. A non-aqueous electrolyte secondary battery having a non-aqueous electrolyte dissolved in an aqueous solvent, wherein the positive electrode has a composition formula
Li _{1 + x} Mn _2-xy Al _y O ₄ (0 ≦ x ≦ 0.5, 0.01
≦ y ≦ 0.5) spinel structure lithium manganese
The non-aqueous electrolyte contains boron trifluoride and / or a Werner complex of boron trifluoride.

That is, according to the present invention, in a lithium secondary battery, by adding boron trifluoride (BF ₃ ) to a nonaqueous electrolyte, lithium halide such as LiF generated on the surface of the negative electrode is eluted into the electrolyte. It is to let. Therefore, in the lithium secondary battery in which BF ₃ is added to the electrolyte, it is possible to suppress an increase in battery impedance due to the formation of a lithium halide film such as LiF on the negative electrode surface.

Furthermore, the non-aqueous electrolyte secondary battery of the present invention, it is preferable to adopt the embodiment of the lithium negative electrode Ru using <br/> doping / dedoping available carbon material. Using a carbon material as the negative electrode active material, a so-called lithium ion secondary battery capable of suppressing dendrite deposition on the negative electrode surface,
By using an inexpensive and highly safe spinel-structured lithium manganese composite oxide as the positive electrode active material, the nonaqueous electrolyte secondary battery of this embodiment can be used as a large capacity battery. Next battery.

Further, in the non-aqueous electrolyte secondary battery of the present invention , the composition formula Li _{1 + x} Mn _2-xy Al _y O ₄ (0 ≦ x
≦ 0.5, 0.01 ≦ y ≦ 0.5)
A structure lithium manganese composite oxide is used. By substituting a part of the Mn site in the crystal structure of the lithium manganese composite oxide with Al, the structure of the composite oxide itself is stabilized, and the formation of a lithium halide film on the negative electrode surface is suppressed. Thus, the non-aqueous electrolyte secondary battery of the present invention becomes a non-aqueous electrolyte secondary battery having good cycle characteristics even in a high-temperature use environment.

[0018]

Next, the effect of adding boron trifluoride (BF ₃ ) to the non-aqueous electrolyte, which is a main feature of the non-aqueous electrolyte secondary battery of the present invention, will be described. For example, when the film formed on the negative electrode surface is LiF, by dissolving BF ₃ in the electrolytic solution, LiF generated on the negative electrode surface is complexed with BF ₃ to form LiBF ₄ according to the following chemical formula 1. .

BF ₃ + LiF → LiBF ₄ (Formula 1) When BF ₃ is added as an electrolyte solution as a Werner type complex, for example, when a BF ₃ diethyl ether complex is added, the surface of the negative electrode is formed according to the following formula (2). The generated LiF reacts with the BF ₃ diethyl ether complex to form LiBF ₄ and diethyl ether.

(C ₂ H ₅ ) ₂ OBF ₃ + LiF → LiBF ₄ + (C ₂ H ₅ ) ₂ O (Formula 2) LiBF ₄ and the non-aqueous solvent thus generated are eluted into the electrolytic solution. Therefore, the lithium secondary battery using the electrolyte solution to which BF ₃ is added can prevent an increase in battery impedance due to deposition of LiF without forming a LiF coating on the negative electrode surface.

When the film formed on the surface of the negative electrode is LiCl, the reaction proceeds as in the following formula (3) or (4). BF ₃ + LiCl → LiBF ₃ Cl (Chemical Formula ₃ ) (C ₂ H ₅ ) ₂ OBF ₃ + LiCl → LiBF ₃ Cl + (C ₂ H ₅ ) ₂ O (Chemical Formula 4) In this case, similarly, formation of a LiCl coating on the negative electrode surface Is suppressed.

Thus, the presence of the free acid on the negative electrode surface
In cases where a film of lithium halide forms.
BF_ThreeBy adding halogen
Increases battery impedance by suppressing lithium halide precipitation
Can be prevented. On the other hand, BF_Threeof
Lithium carbonate (Li_TwoCO_Three)
Fruit, BF_ThreeIs Li_TwoCO_ThreeDoes not react with
Was. Therefore, in a lithium secondary battery,
Li required for protection_TwoCO_ThreeFilm is BF _ThreeFor the addition of
Therefore, it became clear that it was not affected at all.

Summarizing the above, a secondary battery using a non-aqueous electrolyte to which BF ₃ is added can prevent the formation of a lithium halide film without disintegrating the Li ₂ CO ₃ film. It exerts a control effect on the negative electrode surface coating and can be expected to improve cycle characteristics.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
As the negative electrode active material, metal lithium, a lithium alloy, or a carbon material capable of doping / dedoping lithium is used. Li-Al alloy, Li-Mg alloy, Li-Hg alloy, Li-Pt alloy, Li-Sn-N
i alloy, Li-Ga-In alloy, Li-Zn alloy, Li
-Al-Ni alloy, Li-Al-Ag alloy, Li-Al
-Mn alloy and the like. Also, as a carbon material,
Graphites (natural graphite, artificial graphite, etc.), cokes (petroleum coke, pitch coke, coal coke, etc.), carbon black (acetylene black, furnace black, etc.), glassy carbon, calcined organic polymer material, carbon fiber, etc. Is mentioned.

In particular, a carbon material was used as a negative electrode active material.
The so-called lithium-ion secondary battery has a
Less problem of drite deposition and good cycle characteristics
It is a good secondary battery. Considering this point, the negative electrode active material
As a mixture of one or more of the above various carbon materials
It is desirable to use it.

The positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention
Is represented by the composition formula Li _{1 + x} Mn _2-xy Al _y O ₄ (0 ≦ x ≦
0.5, 0.01 ≦ y ≦ 0.5)
A lithium-manganese composite oxide is used. Spinel structure
Lithium manganese composite oxide constitutes 4V class battery
In addition to what can be done, it is relatively inexpensive and has the danger of ignition
Low cost and safety of secondary batteries
It is suitable from the viewpoint of this.

Among the lithium manganese composite oxides,
Compositional formula Li _{1 + x} Mn in which Mn site is replaced by Li or Al
Is represented by the _2-xy M _y O _4, the crystal structure is stabilized
ing. Al, which is a substitution element for the Mn site, absorbs Li.
Acts to suppress the collapse of the spinel structure during storage and release.
You. Al is about 60 ° C. for lithium ion secondary batteries.
Even when used at relatively high temperatures.
Of lithium halide coating on negative electrode surface
The effect to control is great. About the effect of suppressing film formation
Although the mechanism is not clear, the inventors
Is found. Probably M with other elements such as Al
Substitution of the n-site results in the formation of a spinel structure.
Crystals are stabilized, and manganese ion elution into the electrolyte is suppressed.
The decomposition of the electrolyte with Mn ²⁺ as the active center is not reduced
It is thought to be because.

[0028] In the spinel structure lithium manganese composite oxide represented by the composition formula _{Li 1 + x Mn 2-xy} Al y O 4,
The value of x in the composition formula is taken into consideration, such as securing the discharge capacity.
Then, 0 ≦ x ≦ 0.5. Further, BF ₃ added as described above
Considering that the effect of is fully obtained, the value of y is y ≧
0.01, taking into account securing the discharge capacity of the battery
And y ≦ 0.5.

The spinel structure lithium manganese composite oxide represented by the composition formula _{Li 1 + x Mn 2-xy} Al y O 4 is not particularly limited in its production method, for example, solid-phase reaction shown below It can be manufactured by a method. A powdery raw material to be a lithium source, a raw material to be a manganese source, and a raw material to be an aluminum source are respectively described as Li, Mn, and Al.
Are molar ratios of Li: Mn: Al = (1 + x) :( 2-x
-Y): The mixture is mixed so as to be y, and the mixture is baked in an oxygen atmosphere at a temperature of about 500 to 1000 ° C. for about 6 to 48 hours to synthesize. LiOH.H ₂ O, Li ₂ CO _{3 and the} like are used as a raw material serving as a lithium source, and Mn (OH) ₂ and MnCO ₃ are used as a raw material serving as a manganese source.
And the like as a raw material serving as an aluminum source is Al (OH)
₃ etc. can be used respectively.

As described above, the nonaqueous electrolyte secondary battery of the present invention can take various forms of secondary batteries. In order to describe the configuration of the positive electrode and the negative electrode in more detail, among these secondary batteries, a lithium ion secondary battery is particularly taken as an example, and the configuration of the positive electrode and the negative electrode of this lithium ion secondary battery is described below. explain.

The positive electrode of a lithium ion secondary battery is prepared by mixing a conductive material and a binder with a positive electrode active material, adding an appropriate solvent as needed, and forming a paste-like positive electrode mixture from a metal foil. Is formed by applying and drying the surface of the current collector, and if necessary, increasing the active material density by pressing or the like.
The positive electrode active material includes the above-described composition formula Li _{1 + x} Mn _2-xy Al
Of the powder of the spinel structure lithium transition metal composite oxide represented by _y O _4, it can be used by mixing one thing or two or more ones.

The conductive material used for the positive electrode is for ensuring the electrical conductivity of the positive electrode active material layer, and may be one of powdered carbon materials such as carbon black, acetylene black, graphite or the like. A mixture of more than one species can be used. The binder plays a role of binding the active material particles, and a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used. An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent in which the active material, the conductive material, and the binder are dispersed. An aluminum foil or the like can be used for the positive electrode current collector.

The negative electrode of the lithium ion secondary battery uses the above-described carbon material capable of doping / dedoping lithium as a negative electrode active material, a binder is mixed with the carbon material, and an appropriate solvent is added as necessary. The paste-like negative electrode mixture was applied to the surface of a metal foil current collector in the same manner as the positive electrode, and dried,
It is formed by increasing the active material density by pressing or the like as necessary. Like the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride or the like can be used as a binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode and the negative electrode face each other to constitute the battery. However, in order to separate the positive electrode and the negative electrode and hold the non-aqueous electrolyte, A separator is interposed between the anode and the negative electrode. As this separator, a thin microporous film such as polyethylene or polypropylene can be used. The non-aqueous electrolyte which is a feature of the non-aqueous electrolyte secondary battery of the present invention is obtained by dissolving a supporting salt in a non-aqueous solvent. Non-aqueous electrolytes are required to have properties such as good electrical conductivity, high chemical and electrochemical stability to electrodes, and excellent thermal stability.

Under such requirements, Li is used as a supporting salt.
BF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , L
Fluorine-containing lithium salt such as iN (CF ₃ SO ₂ ) ₃ , LiC
lO ₄ chlorine-containing lithium salt such like can be used.
One of these lithium salts may be used alone, or two or more thereof may be used in combination.
In the case of a lithium ion secondary battery, it is preferable to use a fluorinated lithium salt because the electric conductivity of the electrolytic solution is good. Among the above fluorinated lithium salts, considering that LiF is regenerated as LiBF ₄ by the action of BF ₃ , it is desirable to use LiBF ₄ as the main supporting salt.

From the characteristics required for the above non-aqueous electrolyte, the non-aqueous solvent may include one or more of aprotic organic solvents such as cyclic carbonate, chain carbonate, cyclic ester, cyclic ether or chain ether. A mixed solvent composed of two or more types can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate.Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.Examples of the cyclic ester include gamma butyl lactone and gamma. Examples of barrel lactone include cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, and examples of chain ether include dimethoxyethane and ethylene glycol dimethyl ether.

In the non-aqueous electrolyte secondary battery of the present invention,
Add BF ₃ to the non-aqueous solvent. This addition of BF ₃ may be those added directly by a method such as bubbling BF ₃ gas, ethers, esters, alcohols, Werner the nonaqueous solvent and BF ₃ such as ketones The type complex may be added to the electrolytic solution. Further, both direct addition and addition as a complex may be performed.

As an example of the Werner type complex, (CH
_ThreeOH) BF_Three, (C_TwoH_FiveOH) BF _Three, (C₆H₆OH)
BF_ThreeAlcohol complexes such as (CH_Three)_TwoOBF_Three, (C_Two
H_Five)_TwoOBF_Three, [(CH_Three)_ThreeCOCH_Three] BF_Three, C_FourH
₈OBF_ThreeEther complexes such as (CH_ThreeNH_Two) BF_Three,
(C_TwoH_FiveNH_Two) BF_Three, [(C_TwoH_Five)_TwoNH] BF_Three,
[(C_TwoH_Five)_ThreeN] BF_ThreeAmine complexes such as [S (C
H_Three)_Two] BF_Three, [S (C_TwoH_Five)_Two] BF_ThreeEtc. Sulfi
Do complex, [(CH_ThreeO)_TwoCO] BF_Three, [(C_TwoH_FiveO)_Two
CO] BF_ThreeAnd the like.

The desirable amount of BF ₃ to be added depends on the positive electrode, the surface area of the negative electrode, and the amount of the electrolytic solution. However, as a result of the study on the present invention, 0.5 wt.
5 wt% or less than% (if added as Werner complexes, for BF ₃ weight in the complex) be becomes more large effect with respect to improvement of the cycle characteristics.
The non-aqueous electrolyte secondary battery of the present invention configured as described above can have various shapes such as a cylindrical type and a laminated type. Whichever shape you take,
A separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and a connection is made between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal communicating to the outside using a current collecting lead or the like, and the electrode body is connected to the electrode body. It is impregnated with a non-aqueous electrolyte, and is sealed in a battery case.

[0040]

EXAMPLES [Confirmation of Effect of Addition of BF ₃ to Nonaqueous Electrolyte] A lithium ion secondary battery was fabricated as an example based on the above embodiment, and BF was added to the nonaqueous electrolyte for comparison. _A secondary battery to which ₃ was not added was prepared as a comparative example, and a charge / discharge cycle test was performed on both of the secondary batteries. confirmed. Hereinafter, the results of the charge and discharge cycle tests of the secondary batteries of Examples and Comparative Examples will be described. The non-aqueous electrolyte secondary battery of the present invention is not limited to the following examples.

<Examples 1 and 2> As a positive electrode active material, LiMn ₂ O ₄ powder having a spinel structure (manufactured by Honjo Chemical) was used. To 90 parts by weight of LiMn ₂ O ₄ , 7 parts by weight of carbon powder as a conductive material and 7 parts by weight of polyvinylidene fluoride as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added as a solvent to prepare a positive electrode mixture. . This positive electrode mixture was applied to one side of an aluminum foil current collector at a thickness of 100 μm, dried, and then punched into a disk having a diameter of 15 mm to obtain a positive electrode.

As the negative electrode active material, artificial graphite powder (MCMB manufactured by Osaka Gas Chemicals) was used. 95 parts by weight of the artificial graphite were mixed with 5 parts by weight of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone was added as a solvent to prepare a negative electrode mixture. This negative electrode mixture was applied to one side of a copper foil current collector at a thickness of 100 μm, dried, and then dried to a diameter of 1 μm.
A negative electrode was punched out into a 7 mmφ disk shape.

The positive electrode and the negative electrode are opposed to each other with a separator interposed therebetween, and impregnated and impregnated with a non-aqueous electrolyte solution A or a non-aqueous electrolyte solution B described below and sealed in a battery case to form a coin-type lithium ion battery. Produced. The separator was a polyethylene film (manufactured by Tonen Chemical) having a diameter of 19 m.
Those punched to mφ were used. Non-aqueous electrolytes are ethylene carbonate (EC) and diethyl carbonate (D
EC) was mixed at a volume ratio of 1: 1 with a solution prepared by dissolving LiBF ₄ at a concentration of 1 M as a supporting salt in a mixed solvent. The non-aqueous electrolytic solution A is prepared by adding (C ₂ H ₅ )
It was prepared by adding 0.5 wt% of ₂ OBF ₃ (wt% of BF _{3 in} the complex when the whole electrolytic solution was 100 wt%, the same applies hereinafter). The non-aqueous electrolyte B is prepared by adding (C ₂ H ₅ ) ₂
The OBF ₃ was prepared by adding 1.0 wt%. A lithium ion secondary battery using the non-aqueous electrolyte A was a secondary battery of Example 1, and a battery using the non-aqueous electrolyte B was a secondary battery of Example 2.

Comparative Example 1 Examples 1 and 2 above
And a lithium ion secondary battery different from the secondary battery only in the non-aqueous electrolyte was prepared, and the secondary battery of Comparative Example 1 was obtained. The non-aqueous electrolyte of the secondary battery of this comparative example was prepared by adding a mixture of EC and DEC at a volume ratio of 1: 1 without adding (C ₂ H ₅ ) ₂ OBF _3, and adding LiBF ₄ as a supporting salt to the mixed solvent. Is a non-aqueous electrolyte obtained by dissolving only 1M in a concentration of 1M.

<Charge / Discharge Cycle Test 1>
A charge / discharge cycle test was performed on the secondary batteries of Example 2 and Comparative Example 1. The charge / discharge cycle test was performed at room temperature (2
Under a constant current of 1 mA / cm ^{2 under} a constant current of 1 mA / cm ^{2 to} a final voltage of 4.2 V.
1 that discharges to a final voltage of 3.0 V with a constant current of ²
The discharge capacity is measured in each cycle. As a result of this test, it was found that each secondary battery had a weight of 2 per unit weight of the positive electrode material (total of active material, conductive material and binder).
The discharge capacity after 0 cycle and 50 cycles is shown in FIG.
Shown in

As shown in FIG. 1, with respect to the discharge capacity after 20 cycles, a relatively large discharge capacity can be obtained even in the secondary battery of Comparative Example 1 to which BF ₃ was not added. However, the cycle proceeds thereafter, and after 50 cycles, it is clear that the secondary battery of Comparative Example 1 has a smaller discharge capacity than the secondary batteries of Example 1 and Example 2 to which BF ₃ was added. Was. From this, it was confirmed that when BF ₃ was added, the cycle characteristics were improved.

<Embodiment 3> This embodiment relates to a cylindrical battery. The same positive electrode mixture and negative electrode mixture as in the above example were applied and dried at a thickness of 100 μm per side on both sides of a strip-shaped aluminum foil current collector and a copper foil current collector, respectively, to form a sheet-shaped positive electrode and a negative electrode. Produced. The sheet-shaped positive electrode and the sheet-shaped negative electrode were wound with a separator made of the same material as that used in Examples 1 and 2 to form a roll-shaped electrode body.

Then, the non-aqueous electrolyte was mixed with EC and DEC at a volume ratio of 1: 1 in a mixed solvent of LiB as a supporting salt.
The F ₄ was dissolved in a concentration of 1M, further (C ₂ H _{5) 2} OBF
₃ was added at 2.0 wt%. The above-mentioned roll-shaped electrode body was housed in a 18650 type battery case, and after injecting and impregnating this non-aqueous electrolyte, the battery case was closed to produce a cylindrical lithium ion secondary battery, and the secondary battery of Example 3 was produced. And

<Comparative Example 2> The secondary battery of Example 3 was
Producing a lithium ion secondary battery that differs only in the non-aqueous electrolyte
Then, the secondary battery of Comparative Example 2 was obtained. Of the secondary battery of this comparative example.
The non-aqueous electrolyte is (C _TwoH_Five)_TwoOBF_ThreeWithout adding EC
A supporting solvent is added to a mixed solvent obtained by mixing DEC with DEC in a volume ratio of 1: 1.
As LiBF_FourNon-aqueous solution only dissolved in 1M
Electrolyte.

<Charge / Discharge Cycle Test 2> A charge / discharge cycle test was performed on the secondary batteries of Example 3 and Comparative Example 2. This charge / discharge cycle test was performed at room temperature (25 ° C.) at a current density of 1 mA /
The battery was charged to a final voltage of 4.2 V with a constant current of ² cm ² , and then a final voltage of 3.0 with a constant current of 1 mA / cm ^2.
One cycle of discharging to V is defined as one cycle, and the discharge capacity of each cycle is measured. FIG. 2 shows the relationship between the number of cycles up to 100 cycles and the discharge capacity retention ratio (discharge capacity / initial discharge capacity × 100 (%) in each cycle) of each secondary battery as a result of this test.

As is clear from FIG. 2, the secondary battery of Comparative Example 2 using the non-aqueous electrolyte containing no BF ₃ was compared with the secondary battery using the non-aqueous electrolyte containing BF _3. It was confirmed that the secondary battery was a secondary battery with little capacity deterioration. If the results of the charge / discharge cycle test 1 are also considered comprehensively, cycle deterioration is suppressed by adding BF ₃ to the non-aqueous electrolyte for any type of battery, and the cycle is repeated. As a result, it was also confirmed that the effect of adding BF ₃ became significant.

<Embodiment 4> The non-aqueous electrolyte secondary battery of this embodiment is an embodiment of a coin-type battery constructed in the same manner as in Embodiments 1 and 2. The difference from the first and second embodiments is that LiClO ₄ is used as a supporting salt of the non-aqueous electrolyte. 15 mm each used in Examples 1 and 2
φ, 17mmφ disk-shaped positive and negative electrodes, 19mmφ
And a non-aqueous electrolyte solution described below was injected and impregnated, and then sealed in a battery case to produce a coin-type lithium ion secondary battery. The non-aqueous electrolyte used in the secondary battery of the present example was prepared by mixing Li as a supporting salt in a mixed solvent of EC and DEC mixed at a volume ratio of 1: 1.
Dissolve ClO ₄ to a concentration of 1M and add (C ₂ H ₅ ) ₂ O
It was prepared by adding BF ₃ to 1.0 wt%.

<Comparative Example 3>
Producing a lithium ion secondary battery that differs only in the non-aqueous electrolyte
Then, the secondary battery of Comparative Example 3 was obtained. Of the secondary battery of this comparative example.
The non-aqueous electrolyte is (C _TwoH_Five)_TwoOBF_ThreeWithout adding EC
A supporting solvent is added to a mixed solvent obtained by mixing DEC with DEC in a volume ratio of 1: 1.
As LiClO_FourWas only dissolved at a concentration of 1M.
It is a water electrolyte.

<Charge / Discharge Cycle Test 3> A charge / discharge cycle test was performed on the secondary batteries of Example 4 and Comparative Example 3. In the present charge / discharge cycle test, as in the above charge / discharge cycle tests 1 and 2, at a normal temperature (25 ° C.), a constant current of a current density of 1 mA / cm ² was charged to a final voltage of 4.2 V, and then a current density of 1 mA / cm ² The discharge at a constant current of cm ^{2 to} a final voltage of 3.0 V is defined as one cycle, and the discharge capacity in each cycle is measured. As a result of this test, the relationship between the number of cycles up to 50 cycles and the discharge capacity per unit weight of the positive electrode material and the relationship between the number of cycles and the discharge capacity retention ratio of each secondary battery are shown in FIGS. Shown in

As is apparent from FIGS. 3 and 4, BF
Compared to the secondary battery of Comparative Example 2 using the non-aqueous electrolyte without adding ₃ , the secondary battery of the embodiment using the non-aqueous electrolyte with BF ₃ added has less capacity deterioration. It was confirmed that there was. Therefore, it can be seen that the effect of adding BF ₃ can be obtained even when the supporting salt is LiClO ₄ , and that the non-aqueous electrolyte secondary battery using any lithium salt containing a halogen element as the supporting salt can be obtained. Even if it did, it could be estimated that it was effective for improvement of cycle characteristics.

[Al in Li _{1 + x} Mn _2-xy Al _y O ₄
Based on the relationship] above embodiments of the replacement ratio and the high-temperature cycle characteristics, the composition formula in the positive electrode active material _{Li 1 + x Mn 2-xy} Al y
Various lithium ion secondary batteries in which the substitution ratio of Mn sites with Al was changed using a spinel-structured lithium manganese composite oxide represented by O ₄ were produced as examples. Then, with respect to the lithium ion secondary batteries of these examples, the upper limit of the actual use temperature range of the batteries is considered to be 60%.
A charge-discharge cycle test was performed at
The effect of improving high cycle characteristics by l-substitution was investigated. Also,
For comparison, a secondary battery in which BF ₃ was not added to the non-aqueous electrolyte was also prepared as a comparative example, and the high-temperature cycle characteristics were examined. Hereinafter, the results of the charge and discharge cycle tests of the secondary batteries of Examples and Comparative Examples will be described. The non-aqueous electrolyte secondary battery of the present invention is not limited to the following examples.

Example 5 Four kinds of lithium manganese composite oxides having a spinel structure were used as a positive electrode active material. Each composition formula is Li _1.05 Mn _1.90 Al _0.05 O ₄ , L
i _1.05 Mn _1.85 Al _0.10 O ₄ , Li _1.05 Mn _1.80 Al
_0.20 O ₄ and Li _1.05 Mn _1.95 O ₄ . The synthesis of these lithium manganese composite oxides is performed by the production method exemplified in the above embodiment, and LiOH.H ₂ O as the lithium source, and manganese aluminum coprecipitated hydroxide (Mn (OH) ₂ , Al as the manganese source and the aluminum source). Using (OH) ₃ ), they are mixed at a predetermined mixing ratio, the respective mixtures are weighed so as to be 3.0 kg, and the weighed mixtures are respectively mixed under an atmosphere of an oxygen flow rate of 3.0 L / min. Heating was carried out to 750 ° C. and held for 18 hours.

Using each of the above lithium manganese composite oxides as a positive electrode active material, 84 parts by weight of this positive electrode active material were mixed with 10 parts by weight of carbon powder as a conductive material and 6 parts by weight of polyvinylidene fluoride as a binder. , N as a solvent
50 parts by weight of -methyl-2-pyrrolidone were added and kneaded to obtain a positive electrode mixture. This positive electrode mixture was applied on both sides of a 20 μm-thick aluminum foil current collector to form a positive electrode sheet.

As the negative electrode active material, artificial graphite powder (MCMB, manufactured by Osaka Gas Chemicals) was used. 96 parts by weight of the artificial graphite were mixed with 4 parts by weight of polyvinylidene fluoride as a binder, and 50 parts by weight of N-methyl-2-pyrrolidone as a solvent were added and kneaded to obtain a negative electrode mixture. This negative electrode mixture has a thickness of 1
The negative electrode sheet was coated on both sides of a 0 μm copper foil current collector.

The non-aqueous electrolyte is ethylene carbonate (E
C) and diethyl carbonate (DEC) in a volume ratio of 1:
LiBF ₄ was added as a supporting salt to the mixed solvent mixed in 1.
First, a solution dissolved in a concentration of M is prepared, and B is added to this solution.
2.0% by weight of DEC saturated solution of F ₃ (1
(At 100 wt%). Incidentally, BF ₃ in this non-aqueous electrolyte is 0.74 wt%.

The DEC saturated solution of BF ₃ was prepared as follows. First, 26.1 g of LiB
Mixing the F ₄ and 3.48g of B ₂ O _3, was added dropwise concentrated sulfuric acid 20mL with pressure equalizing dropping funnel to the mixture. The dropping time was about 10 minutes. By this operation, BF ₃ is generated according to the following reaction formula. 6LiBF ₄ + B ₂ O ₃ + 6H ₂ SO ₄ → 8BF ₃ + 6L
iHSO ₄ + 3H ₂ O Generated BF ₃ was combined with argon gas in 10 mL of DE.
C was bubbled to obtain a saturated solution of BF ₃ in DEC. The time required for bubbling was 24 hours.

Using the above positive electrode sheet, negative electrode sheet and non-aqueous electrolyte, a cylindrical battery was produced as follows. First, the positive electrode sheet and the negative electrode sheet were opposed to each other via a polyethylene film (manufactured by Tonen Chemical Co., Ltd.) having a thickness of 25 μm serving as a separator, and wound to form a roll-shaped electrode body. Next, the electrode body was housed in a 18650 type battery can (diameter 18 mm, height 65 mm) by welding a lead wire to the body of the battery can body and welding a lead wire to the cap of the battery can cap, and impregnated with a non-aqueous electrolyte. After that, the battery can was sealed by caulking the cap to the main body to complete the battery. Although the capacity of the completed battery depends on the type of the positive electrode active material, it was about 500 mAh, and the theoretical capacity ratio of the positive electrode to the negative electrode was 1: 1.5.

These batteries use Li _1.05 M as a positive electrode active material.
The battery using n _1.90 Al _0.05 O ₄ was referred to as a secondary battery of Example 5-1. Hereinafter, Li _1.05 Mn _1.85 Al _0.10 O ₄ was used, respectively.
Using the secondary battery of Example 5-2 and Li _1.05 M
The battery using n _1.80 Al _0.20 O ₄ was used in Example 5-3, and the battery using Li _1.05 Mn _1.95 O ₄ was used in Example 5.
-4 secondary battery.

Comparative Example 4 A lithium ion secondary battery different from the secondary battery of Example 5 only in the non-aqueous electrolyte was produced. The nonaqueous electrolyte of the secondary battery of this comparative example was prepared by adding LiF as a supporting salt to a mixed solvent in which EC and DEC were mixed at a volume ratio of 1: 1 without adding BF _3.
This is a non-aqueous electrolyte in which F ₄ is only dissolved at a concentration of 1M. As in the case of Example 5, the cathode active material was Li _1.05 Mn.
_1.90 Al _0.05 O ₄ as the secondary battery of Comparative Example 4-1 that using a secondary battery of Comparative Example 4-2 that using a respectively Li _1.05 Mn _1.85 Al _0.10 O ₄ or less, Li _1.05 Mn
_The battery using _1.80 Al _0.20 O ₄ was compared with the secondary battery of Comparative Example 4-3, and the battery using Li _1.05 Mn _1.95 O ₄ was used in Comparative Example 4-
The secondary battery was No. 4.

<Charge / Discharge Cycle Test 4>
And the secondary batteries of Comparative Example 4
An electric cycle test was performed. The charge / discharge cycle test
Considering the upper limit temperature of the actual operating temperature range of the lithium ion secondary battery
Current density of 1.1 mA / cm under 60 ° C.
^TwoIs charged to a final voltage of 4.2 V with a constant current of
After that, the current density is 1.1 mA / cm^TwoEnd voltage at constant current of
One cycle that discharges to 3.0 V is defined as one cycle.
This is to measure the discharge capacity of the vehicle. Results of this test
Maintain the discharge capacity of each secondary battery after 500 cycles
Rate (discharge capacity at 500th cycle / initial discharge capacity × 10
0%) is shown in Table 1 below.

[0066]

[Table 1] As is clear from Table 1, each of the secondary batteries of Example 5 in which BF ₃ was added to the nonaqueous electrolyte used the spinel-structured lithium manganese composite oxide represented by the same composition formula as the positive electrode active material. It can be seen that all the secondary batteries are superior in the capacity retention ratio after the high-temperature cycle charge / discharge as compared with the respective secondary batteries of Comparative Example 4. From this,
The nonaqueous electrolyte secondary battery of the present invention is effective in improving the high-temperature cycle characteristics of a lithium ion secondary battery using a lithium manganese composite oxide as a positive electrode, regardless of whether the Mn site is replaced with Al. It can be confirmed that there is.

Next, the respective secondary batteries of Example 5 to which BF ₃ was added will be compared. The secondary batteries of Examples 5-1 to 5-3 using the lithium manganese composite oxide in which the Mn site was substituted with Al were compared with the secondary batteries of Example 5-4 using the non-substituted lithium manganese composite oxide. It can be seen that a large capacity is maintained after the high-temperature charge / discharge cycle. From a different perspective, the following can be understood. The secondary battery of Example 5-4 uses the same positive electrode active material and has a 3.8% improvement in the capacity retention ratio as compared with Comparative Example 4-4 using a non-aqueous electrolyte solution to which BF ₃ is not added. It is. On the other hand, in Example 5 using a lithium manganese composite oxide in which 0.05 equivalents of Mn sites were substituted by Al.
The secondary battery of No. 1 was 4.8 compared to the secondary battery of Comparative Example 4-1.
%, And the secondary battery of Example 5-2 using the equivalent of 0.10 has a 5.3% improvement over the secondary battery of Comparative Example 4-2. The secondary battery of Example 5-3 using the replacement of 20 equivalents showed an improvement of 7.5% compared to the secondary battery of Comparative Example 4-3. Summarizing these facts, in the nonaqueous electrolyte secondary battery of the present invention, by using a spinel-structured lithium manganese composite oxide in which a part of Mn sites is substituted with Al for the positive electrode active material, It is confirmed that the formation of the lithium halide coating is further suppressed, and the nonaqueous electrolyte secondary battery has a small capacity deterioration even when used at a high temperature.

[0068]

According to the present invention, a non-aqueous electrolyte secondary battery is configured so that BF ₃ is added to the non-aqueous electrolyte.
With such a configuration, formation of a lithium halide coating on the surface of the negative electrode can be suppressed. From this, the non-aqueous electrolyte secondary battery of the present invention is a secondary battery in which the ionic conduction between the negative electrode and the electrolyte is good, the battery impedance is small, and the discharge capacity is small even by repeated charging and discharging. Becomes Further, when a lithium salt containing fluorine is used as a supporting salt, the generated lithium halide can be regenerated as a supporting salt.

[0069] Further, in the composition formula _{Li 1 + x Mn 2-xy} Al y O 4
The spinel structure lithium manganese composite oxide
By using the carbon material for the negative electrode and the carbon material for the negative electrode, a non-aqueous electrolyte secondary battery having good cycle characteristics even at a high temperature can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the discharge capacity after 20 cycles and 50 cycles per unit weight of a positive electrode material of the secondary batteries of Example 1, Example 2, and Comparative Example 1.

FIG. 2 shows 10 of the secondary batteries of Example 3 and Comparative Example 2;
Diagram showing the relationship between the number of cycles up to 0 cycles and the discharge capacity retention ratio

FIG. 3 shows 50 of the secondary batteries of Example 4 and Comparative Example 3.
Diagram showing the relationship between the number of cycles and the discharge capacity per unit weight of the positive electrode material up to the cycle

FIG. 4 shows 50 of the secondary batteries of Example 4 and Comparative Example 3.
Diagram showing the relationship between the number of cycles and the discharge capacity retention rate up to the cycle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-38031 (JP, A) JP-A-9-270259 (JP, A) JP-A-4-289662 (JP, A) JP-A-11- 149943 (JP, A) European Patent Application Publication 903798 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4/36- 4/62

Claims (2)

(57) [Claims] (1) lithium metal, lithium alloy or lithium
Negative electrode using carbon material that can be doped / dedoped with aluminum
, A positive electrode, and a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent.
A non-aqueous electrolyte secondary battery having a dissolution solution, wherein the positive electrode has a composition formula of Li _{1 + x} Mn _2-xy Al _y O ₄ (0 ≦ x ≦
0.5, 0.01 ≦ y ≦ 0.5)
The lithium manganese composite oxide is used, and the non-aqueous electrolyte is boron trifluoride and / or trifluoride.
That the Werner-type complex of boron nitride is contained.
Characteristic non-aqueous electrolyte secondary battery. 2. Doping / dedoping lithium into the negative electrode.
2. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte is a carbon material.
Next battery.