JP2002343354A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery of high energy density, excellent in safety, and excellent in charge/discharge cycle characteristics. SOLUTION: With the nonaqueous electrolyte secondary battery, a mixture of lithium manganese aluminum complex oxide as expressed in Lix Mn3-x-y Aly O4 (where, 1.2>=x>=1.0, 0.1>=y>=0.01) and lithium nickel cobalt aluminum complex oxide as expressed in LiNiz Co1-z-w Alw O2 (where, 1.0>z>=0.5, 0.1>=w>=0.01) is used for a positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic electrolyte secondary battery.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery has a feature of high energy density and is suitable for a power supply for electronic equipment such as a cellular phone, a power supply for an electric vehicle, and the like. As a positive electrode active material of an organic electrolyte secondary battery, lithium manganese oxide (Li
Mn ₂ O ₄ ) or lithium cobalt oxide (LiCo
O ₂ ) and lithium metal oxides such as lithium nickel oxide (LiNiO ₂ ) are used. These active materials are used as a positive electrode by being held by a foil material such as aluminum, titanium, and stainless steel.

As the negative electrode, a carbon material capable of occluding and releasing lithium ions, oxides, sulfides and the like are used. These carbon materials are held on a stainless steel foil material, brass, phosphor bronze, aluminum bronze foil material, copper foil, or the like, and used as a negative electrode.

The solvent used for the electrolyte is not limited as long as it can dissolve the lithium salt, but an aprotic organic solvent having a large dielectric constant is particularly preferable. For example, propylene carbonate, ethylene carbonate, tetrahydrofuran, dimethyl carbonate, dimethyl carbonate, acetonitrile, etc. These solvents can be used alone or in a suitable mixture.

[0005] Examples of the electrolyte dissolved in the organic solvent include lithium perchlorate, lithium borofluoride, and the like.
Lithium salts that generate stable anions, such as lithium hexafluoroantimonate and lithium hexafluorophosphate, are used.

Further, a polyolefin-based microporous membrane is generally used as a separator. As the battery case and the lid plate for sealing the battery, stainless steel, aluminum, an aluminum alloy, or iron plated with nickel is used.

Each of the positive electrode plate and the negative electrode plate is formed into a thin sheet or foil shape and sequentially laminated or spirally wound through a separator to form an electrode plate group. The battery is stored in a cylindrical or square battery container made of metal such as nickel-plated iron or aluminum, injected with an electrolytic solution, and hermetically sealed with a lid plate to assemble the battery.

[0008]

The positive electrode material of a nonaqueous electrolyte secondary battery for a consumer has been lithium-ion.
Cobalt composite oxides have been used. Lithium-cobalt composite oxides have a high energy density and can provide high-capacity batteries, but have poor thermal stability during overcharging. It was extremely difficult to ensure the safety of

For these reasons, a lithium-manganese composite oxide having excellent thermal stability has been applied as a positive electrode active material for a large capacity battery. However, for example, lithium, represented by _{Li x} Mn _2-x O ₄
Since the manganese composite oxide has a small discharge capacity per unit weight, a large capacity cannot be obtained when applied to a battery, and further, there is a problem in cycle life characteristics. Particularly at high temperatures, manganese elutes from the positive electrode active material, causing a passive film of manganese to form on the negative electrode surface,
There is a problem that the charge / discharge characteristics of the negative electrode are significantly reduced.

Therefore, a new positive electrode active material for use in a non-aqueous electrolyte secondary battery having high energy density, excellent safety, and excellent cycle life characteristics at high temperatures has been demanded.

[0011]

SUMMARY OF THE INVENTION claims 1 invention, the non-aqueous electrolyte secondary battery, the positive electrode Li x _{Mn 3-x- y}
Al _y O ₄ (However, 1.2 ≧ x ≧ 1.0, 0.1 ≧ y ≧
Lithium-manganese-aluminum composite oxide represented by 0.01) and _{LiNi z Co 1-Z-w} Al w O 2
(However, 1.0> z ≧ 0.5, 0.1 ≧ w ≧ 0.01)
Or a mixture of a lithium-nickel-cobalt-aluminum composite oxide represented by the formula:

According to the first aspect of the present invention, the security is high,
Moreover, a high capacity non-aqueous electrolyte secondary battery can be obtained.

According to a second aspect of the present invention, in the non-aqueous electrolyte secondary battery, the lithium-manganese-aluminum composite oxide is added to the total of the lithium-manganese-aluminum composite oxide and the lithium-nickel-cobalt-aluminum composite oxide. It is characterized in that the content is 10 to 80% by weight.

According to the second aspect of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery which reduces the elution of manganese from the positive electrode and has excellent charge-discharge cycle life characteristics at high temperatures.

[0015]

The non-aqueous electrolyte secondary battery comprising a [form embodiment of the present invention includes a positive electrode is _{Li x Mn 3-x-y} Al y O 4 ( where,
1.2 ≧ x ≧ 1.0, 0.1 ≧ y ≧ 0.01) and a lithium-manganese-aluminum composite oxide and L
_{iNi z Co 1-Z-w} Al w O 2 ( where, 1.0> z
.Gtoreq.0.5, 0.1.gtoreq.w.gtoreq.0.01).

The above-mentioned lithium-manganese-aluminum composite oxide stabilizes the crystal structure of the lithium-manganese composite oxide due to the presence of aluminum and suppresses the elution of manganese. In addition, this lithium
The manganese-aluminum composite oxide has a lower energy density than the lithium-cobalt composite oxide, but the calorific value during abnormalities such as overcharging of the battery is small,
Excellent heat stability.

On the other hand, the above-mentioned lithium-nickel-cobalt-aluminum composite oxide has a high energy density and can provide a high-capacity battery, but is inferior in thermal stability.

According to the present invention, as a positive electrode active material, a lithium-manganese-aluminum composite oxide having a slightly lower energy density but excellent in thermal stability and a lithium-nickel-cobalt-aluminum composite oxide having a higher energy density are used. By using a mixture with, the calorific value associated with battery abnormalities is small, high safety, high capacity can be achieved, and the proportion of lithium-manganese-aluminum composite oxide in the positive electrode active material By reducing the amount of manganese, the amount of manganese eluted from the positive electrode is reduced, and a battery having excellent charge-discharge cycle life characteristics at high temperatures can be obtained.

Used for the positive electrode of the non-aqueous electrolyte secondary battery of the present invention
Li_xMn_3-xyAl_yO ₄Lichi represented by
In the manganese-aluminum composite oxide, x
The reason for setting ≧ 1.0 and 0.1 ≧ y ≧ 0.01 is as follows.
It is.

It is thought that manganese ions are eluted from lithium manganate of the positive electrode as a cause of cycle deterioration at a high temperature of a battery to which lithium manganate is applied, and this manganese ion lowers the charge / discharge performance of the negative electrode. .
The amount of manganese eluted depends on the Li / Mn ratio in the active material,
It has been found that suppression can be achieved by the substitution amount of a different element. Table 1 shows the relationship.

As the x value is increased, the discharge capacity is reduced, but the manganese elution amount is also reduced, and the effect is saturated at about x = 1.2. Also, as the y value is increased, the manganese elution amount decreases, and the effect is almost saturated at y = 0.1. Therefore, the indicated composition can be recommended as the value of x and y.

[0022]

[Table 1]

[0023] In the non-aqueous _{LiNi z Co 1-Z- w Al} w O 2 lithium-nickel-cobalt-aluminum composite oxide represented by the use in the positive electrode electrolyte secondary battery of the present invention, 1.0> z ≧ 0.5 and 0.1 ≧
The reason for setting w ≧ 0.01 is as follows.

LiNiO called lithium nickelate
_{Although the} active material represented by the chemical formula ₂ has a large discharge capacity, it generates an extremely large amount of heat when the active material is heated in a charged state, which causes a problem in terms of safety when applied to a battery. Therefore, it has been found that when a part of nickel is replaced with cobalt, the calorific value is reduced. However,
Since the discharge capacity also decreases, it is necessary to determine an optimum mixing ratio. Table 2 shows the relationship. From Table 2,
A composition having a large discharge capacity and a small calorific value is the title composition.

[0025]

[Table 2]

Furthermore, in the positive electrode of the non-aqueous electrolyte secondary battery of the present invention, lithium manganese is used. The reason why the mixing ratio of the lithium-manganese-aluminum composite oxide to the total of the aluminum composite oxide and the lithium-nickel-cobalt-aluminum composite oxide is 10 to 80% by weight is as follows.

That is, the merits of high capacity obtained by mixing a lithium-nickel-cobalt-aluminum composite oxide and the high safety obtained by mixing a lithium-manganese-aluminum composite oxide are as follows. Since it can be obtained by mixing the two active materials to a certain degree or more, it is preferable to determine the mixing ratio depending on the use of the battery depending on whether to secure more safety or to increase the energy density.

According to the experimental data described in the section of Examples, when the mixing ratio of the lithium-manganese-aluminum composite oxide is larger than the range of the present invention, the capacity retention of the battery decreases and the lithium-nickel-cobalt. When the mixing ratio of the aluminum composite oxide is larger than the range of the present invention, it is difficult to ensure the safety of the battery. As the solvent of the electrolytic solution of the present invention, cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, Examples of polar solvents such as dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, or lithium salts such as LiPF ₆ and LiBF _4. Li
AsF ₆ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , Li
N (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ )
₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂
A salt such as CF ₃ ) ₂ or a mixture thereof may be used.
Further, as the isolator, an insulating polyolefin microporous membrane such as polyethylene or polypropylene, a polymer solid electrolyte, a gel electrolyte in which an electrolyte is contained in a polymer solid electrolyte, or the like can be used. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination. further,
When a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the electrolyte contained in the polymer and the electrolyte contained in the pores may be different.

Further, as a material capable of inserting and extracting lithium or lithium ion as a negative electrode material, Al, S
alloy of lithium with i, Pb, Sn, Zn, Cd, etc., L
transition metal oxides such as iFe ₂ O ₃ , WO ₂ and MoO ₂ ;
Carbonaceous materials such as graphite and carbon, Li ₅ (Li
_{3 N)} lithium nitride such or metal lithium foil, or it may be a mixture thereof.

The power generating element according to the present invention may be any of a positive electrode plate and a negative electrode plate each formed into a thin sheet or foil, laminated one after another, or spirally wound. .

Further, as the shape of the battery, various shapes such as a square type, a cylindrical type, and a long cylindrical type can be used. In addition, the material of the battery case may be any of a sheet in which a metal foil and a resin film are bonded, iron, or aluminum.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on preferred embodiments.

Example 1 As a positive electrode active material, Li was used.
_1.1 Lithium-manganese-aluminum composite oxide represented by Mn _1.84 Al _0.06 O ₄ and LiNi
Using a mixture of a lithium-nickel-cobalt-aluminum composite oxide represented by _0.8 Co _0.15 Al _0.05 O ₂ , seven types of non-aqueous electrolyte batteries having different mixing ratios were produced.

The positive electrode plate was prepared by mixing 82 parts by weight of an active material obtained by mixing a lithium-manganese-aluminum composite oxide and a lithium-nickel-cobalt-aluminum composite oxide on both surfaces of an aluminum foil having a thickness of 0.02 mm; 10 parts by weight of graphite and 8 parts by weight of polytetrafluoroethylene (PTFE) as a binder were applied, dried, and rolled.

The negative electrode plate was prepared by mixing 92 parts by weight of a carbon material capable of being doped with and dedoped with lithium and 8 parts by weight of polyvinylidene fluoride as a binder on both sides of a 0.01 mm thick copper foil to form a paste. After coating, drying and rolling, a negative electrode lead made of nickel was attached to the end of the negative electrode by ultrasonic welding.

Next, the positive electrode plate and the negative electrode plate are
After drying at 0 ° C. for 10 hours, the resultant was spirally wound through a separator to obtain an electrode plate group.

FIG. 1 shows a structural example of a cylindrical non-aqueous electrolyte secondary battery according to the first embodiment of the present invention. In FIG. 1, 1 is a battery case also serving as a negative electrode terminal, 2 is a positive electrode plate, 3 is a negative electrode plate,
4 is a separator, 5 is a positive electrode lead, 6 is a negative electrode lead,
Reference numeral 7 denotes a positive electrode terminal, 8 denotes a safety valve, 9 denotes a PTC element, 10 denotes a gasket, 11 denotes an insulating plate, and the positive electrode plate 2, the separator 4, and the negative electrode plate 3 are wound to form an electrode plate group. It is housed inside.

As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate at a ratio of 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Although FIG. 1 shows a cylindrical organic electrolyte secondary battery, a rectangular organic electrolyte secondary battery has essentially the same configuration.

Table 3 summarizes the compositions of the positive electrode active materials of the seven types of nonaqueous electrolyte batteries produced here.

[0040]

[Table 3]

The seven types of batteries manufactured here were subjected to a terminal voltage of 4.1 at 5 A corresponding to an hour rate at room temperature.
After charging at a constant current up to V, the battery was further charged for 3 hours based on a constant voltage charging method. Subsequently, constant current discharge was performed at a current of 5 A corresponding to an hourly rate until the terminal voltage reached 2.75 V. At this time, the initial discharge capacity obtained in the one-hour rate discharge and the volume energy density of the battery calculated based on the discharge capacity were obtained.

Next, seven types of batteries were placed at room temperature.
After charging at a constant current of 5 A corresponding to an hour rate until the terminal voltage reached 4.1 V, charging was further performed for 3 hours based on the constant voltage charging method. After that, the diameter of 1
mm of stainless steel nail was penetrated, and the battery surface temperature and battery behavior at that time were measured.

Further, the seven types of batteries were charged at 45 ° C. at a constant current of 5 A corresponding to an hour rate until the terminal voltage reached 4.1 V, and then at a constant current of 5 A, the terminal voltage was further increased. Until the voltage reached 2.75 V. This charge / discharge was repeated 500 cycles, and the discharge capacity of the battery was determined. Then, the discharge capacity at the 500th cycle with respect to the initial discharge capacity of each battery was calculated as a capacity retention rate.

Table 4 summarizes the data obtained by the above measurements.

[0045]

[Table 4]

From Table 4, comparing the volume energy densities of the seven types of batteries, the greater the content of the lithium-nickel-cobalt-aluminum composite oxide in the positive electrode active material, the higher the energy density and the higher the lithium-manganese content. -It was shown that the higher the content ratio of the aluminum composite oxide, the lower the energy density.

Regarding the safety, in the battery 7 in which the positive electrode active material is only lithium / nickel / cobalt / aluminum composite oxide, the battery ruptured and fired in the nail penetration test. In the batteries 1 to 6 containing 10 wt% or more of the lithium-manganese-aluminum composite oxide, although the battery surface temperature was considerably increased, the battery did not ignite, indicating high safety.

This is because the lithium-manganese-aluminum composite oxide having excellent thermal stability is mainly used in the positive electrode active material, and the heat generation start temperature of the positive electrode active material is lithium-manganese-aluminum composite oxide. And lithium
It is considered that this is because instantaneous heat generation was suppressed unlike the nickel-cobalt-aluminum composite oxide.

Further, the batteries 2 to 7 to which the lithium / nickel / cobalt / aluminum composite oxide was added were better than the battery 1 in which the lithium / manganese / aluminum composite oxide was used alone as the positive electrode active material. The capacity retention after 500 cycles was shown to be high.

This is due to the fact that as the mixing ratio of the lithium-manganese-aluminum composite oxide decreases, the amount of manganese eluted from the positive electrode decreases, and the charge / discharge characteristics of the negative electrode are maintained even after a lapse of cycles. it is conceivable that.

Example 2 Lithium was used as the positive electrode active material.
_1.1 Lithium-manganese-aluminum composite oxide represented by Mn _1.88 Al _0.02 O ₄ and LiNi
Seven types of non-aqueous solutions using a mixture of lithium-nickel-cobalt-aluminum composite oxide represented by _0.8 Co _0.15 Al _0.05 O ₂ and changing the mixing ratio in the same manner as in Example 1. An electrolyte battery was manufactured.

As a result, a result similar to that of Example 1 was obtained. The battery using the positive electrode active material according to the present invention had high energy density, excellent safety, and excellent charge-discharge cycle characteristics. It has been shown.

Example 3 Lithium was used as the positive electrode active material.
_1.1 Lithium-manganese-aluminum composite oxide represented by Mn _1.84 Al _0.06 O ₄ and LiNi
Seven kinds of non-aqueous liquids using a mixture of lithium-nickel-cobalt-aluminum composite oxide represented by _0.5 Co _0.45 Al _0.05 O ₂ and changing the mixing ratio in the same manner as in Example 1. An electrolyte battery was manufactured.

As a result, a result similar to that of Example 1 was obtained. The battery using the positive electrode active material according to the present invention had high energy density, excellent safety, and excellent charge-discharge cycle characteristics. It has been shown.

[0055]

According to the present invention, as a positive electrode active material, a lithium-manganese-aluminum composite oxide having a slightly lower energy density but excellent thermal stability and a lithium-nickel-cobalt-aluminum composite having a high energy density are used. By using a mixture with an oxide, the calorific value associated with battery abnormalities is small, safety is high, high capacity can be achieved, and the lithium-manganese-aluminum composite oxide cathode active material contains By reducing the proportion of manganese, the amount of manganese eluted from the positive electrode is reduced, and a battery having excellent charge / discharge cycle life characteristics at high temperatures can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a cylindrical non-aqueous electrolyte secondary battery of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5 Positive electrode lead 6 Negative electrode lead 7 Positive electrode terminal 8 Safety valve 9 PTC element 10 Gasket 11 Insulating plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiro Shizuki 1 No. 1 Nishinosho Inono Babacho, Kichijoin, Minami-ku, Kyoto-shi, Japan F-term (reference) 5H029 AJ03 AJ05 AJ12 AK03 AL01 AL02 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 BJ02 BJ14 HJ01 HJ02 5H050 AA07 AA08 AA15 BA17 CA07 CA29 CB02 CB08 CB09 CB12 CB25 DA07 DA08 DA10 DA11 EA09 EA24 HA01 HA02

Claims (2)

[Claims] 1. A positive electrode _{Li x Mn 3-x-y} Al y O 4
(However, 1.2 ≧ x ≧ 1.0, 0.1 ≧ y ≧ 0.01)
In lithium-manganese-aluminum composite oxide represented as _{LiNi z Co 1-Z-w} Al w O 2 ( where,
1.0> z ≧ 0.5, 0.1 ≧ w ≧ 0.01). A non-aqueous electrolyte secondary battery comprising a mixture of lithium-nickel-cobalt-aluminum composite oxides represented by the following formula: 2. The lithium-manganese-aluminum composite oxide has a content of 10 to 80% by weight based on the total of the lithium-manganese-aluminum composite oxide and the lithium-nickel-cobalt-aluminum composite oxide. The non-aqueous electrolyte secondary battery according to claim 1.