JP2001297763A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light and safe nonaqueous electrolyte secondary cell. SOLUTION: A double oxide of lithium and cobalt with the resistance coefficient of more than 1 mΩ.cm and less than 40 Ω.cm, where ; the bulk density of powder is 3.8 g/cm3, is used as a cathode activator of the nonaqueous electrolyte secondary cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery.

A typical battery that meets such requirements is:
In particular, an active material such as lithium metal or a lithium alloy, or a lithium intercalation compound in which lithium ions are occluded in carbon, which is a host material (here, a host material refers to a material that can occlude and release lithium ions). This is a non-aqueous electrolyte secondary battery in which an aprotic organic solvent in which a lithium salt such as LiClO 4 or LiPF 6 is dissolved is used as an anode material and an electrolyte is used.

This non-aqueous electrolyte secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on a negative electrode current collector as a support, and a reversible electrochemical reaction with lithium ions such as a lithium-cobalt composite oxide. The positive electrode plate, which holds the positive electrode active material that reacts on the positive electrode current collector that is the support, from the separator that holds the electrolytic solution and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes Has become.

[0005] Each of the positive electrode plate and the negative electrode plate is formed into a thin sheet or foil, and is a power generating element formed by sequentially laminating or spirally winding through a separator. Then, the power generating element is housed in a battery container made of a metal such as stainless steel, nickel-plated iron, or aluminum, and after injecting the electrolytic solution, hermetically sealed with a lid plate to assemble the battery.

[0006] With the recent diversification of equipment using lithium ion secondary batteries, the operating environment and battery connection methods required for lithium ion secondary batteries have also become diversified. For example, portable AV equipment and the like often use batteries assembled in series or in parallel.

[0007] When used as an assembled battery, variations in performance between batteries become a problem, and when charging and discharging are repeated in a state where there is variation between batteries, the battery is likely to be in an unsafe state. . In particular, when a battery with poor charge / discharge performance is forcibly charged, the battery becomes overcharged,
In the worst case, it may lead to thermal runaway and rupture or ignite. Therefore, a safe battery is required even when the battery is abnormal such as overcharging.

However, lithium cobalt oxide, which is widely used as a positive electrode active material of a lithium ion battery, has poor thermal stability. Therefore, when the battery is in an abnormal state such as an overcharged state or an internal short circuit, the battery cannot be used. May generate heat and, in the worst case, lead to thermal escape, which may cause rupture or ignition.

[0009]

As a means for solving the above problem, a method for improving the thermal stability of lithium cobalt oxide can be considered. In JP-A-11-7958, the thermal stability of lithium cobalt oxide is improved by substituting a part of Co with an element such as Al.

However, the lithium cobalt oxide, Co
When a part of is replaced with an element such as Al, a problem that the energy density is inevitably occurs.

Accordingly, an object of the present invention is to suppress the heat generation of a battery even in an abnormal state such as an overcharged state or an internal short circuit without lowering the energy density of the battery,
An object of the present invention is to provide a non-aqueous electrolyte battery having excellent safety and excellent discharge characteristics.

[0012]

The nonaqueous electrolyte secondary battery according to the present invention has a powder packing density of 3.8 as a positive electrode active material.
The resistance coefficient at g / cm ³ is 1 mΩ · cm or more and 40 m
An object of the present invention is to solve the above-mentioned problem by using a lithium-cobalt composite oxide of Ω · cm or less.

When a non-aqueous electrolyte secondary battery is constructed using this positive electrode active material, it is possible to reduce the energy density of the battery and reduce the energy density of the battery even when the battery is in an abnormal state such as an overcharged state or an internal short circuit. The heat generated by the battery is suppressed, and the safety is excellent.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a lithium active material having a resistance coefficient of 1 mΩ · cm to 40 mΩ · cm at a powder filling density of 3.8 g / cm ³ as a positive electrode active material for a nonaqueous electrolyte secondary battery. A cobalt composite oxide is used.

When a non-aqueous electrolyte secondary battery is constructed using this positive electrode active material, the battery can be used in an abnormal state such as an overcharged state or an internal short circuit without lowering the energy density of the battery. The heat generated by the battery is suppressed, and the safety is excellent.

That is, by setting the specific resistance of the lithium-cobalt composite oxide powder as the positive electrode active material to an optimum value, even if the battery is overcharged, the positive electrode active material does not decompose and the battery explodes. And so on.

When the powder packing density of the lithium cobalt composite oxide is 3.8 g / cm ³ , the resistance coefficient is 1 mΩ · cm.
In the following cases, the specific resistance of the positive electrode active material powder is too small to be effective in preventing explosion of the battery, and when the resistance coefficient is 40 mΩ · cm or more, a decrease in capacity in a charge / discharge cycle is caused. It is large and has a poor high-rate discharge characteristic, which is a drawback when the battery is actually used.

For measuring the powder resistance of the lithium-cobalt composite oxide, a powder resistance measuring instrument shown in FIG. 2 was used. FIG.
, 11 is a compression rod, 12 is a sleeve, 13 is a compression tray, 14 is a projection of the compression rod, 15 is a projection of the compression tray, and 16 is a sample powder.

The compression rod 1 has an outer diameter of 8 mm and a length of 115 c.
m, made of copper, the sleeve 2 has an outer diameter of 40 mm, a length of 90 mm,
The compression tray 3 is made of beryllium copper having an outer diameter of 60 mm, a height of 10 mm and a central part having an outer diameter of 8 mm and a height of 10 mm. A projection 14 is attached to the compression rod 1, and a projection 15 is attached to the compression tray 3.

This powder resistance measuring instrument can measure the resistance by changing the packing density of the powder, and shows that the resistance decreases as the packing density increases.
When the packing density becomes 3.8 g / cm ³ or more, the resistance becomes a substantially constant value.

In the present invention, the resistance when the powder density was 2 g and the packing density was 3.8 g / cm ³ was measured using this powder resistance measuring instrument. From the obtained powder resistance R, the cross-sectional area S of the compression rod, and the pellet height L,
The resistance coefficient ρ was determined from the equation ρ = R × S / L.

As the negative electrode material of the non-aqueous electrolyte secondary battery of the present invention, as a material capable of occluding and releasing lithium or lithium ion, Al, Si, Pb, Sn, Zn,
Alloys of Cd and the like with lithium, LiFe ₂ O ₃ , WO ₂ , M
A transition metal oxide such as oO _{2, a} lithium nitride such as Li ₅ (Li ₃ N), a carbonaceous material such as graphite or carbon, a metal lithium foil, or a mixture thereof may be used.

In the present invention, the solvent for the electrolytic solution includes cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, sulfolane, and the like. Dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran,
A polar solvent such as 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof can be used.

Further, a lithium salt dissolved in an organic solvent may be used.
And LiPF₆, LiBF_Four, LiAsF₆, LiC
F_ThreeCO_Two, LiCF_ThreeSO_Three, LiN (SO_TwoCF_Three)_Two,
LiN (SO_TwoCF_TwoCF_Three)_Two, LiN (COCF_Three)_TwoYou
And LiN (COCF_TwoCF_Three) _TwoSuch as salt or this
These mixtures may be used.

Further, as the isolator, an insulating polyolefin microporous membrane such as polyethylene or polypropylene,
A solid polymer electrolyte, a gel electrolyte in which an electrolyte solution is contained in a solid polymer electrolyte, and the like can also 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.

The power generating element according to the present invention may be either a positive electrode plate or a negative electrode plate formed in the form of a thin sheet or foil, laminated in order, or spirally wound. .

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.

[0028]

Next, the present invention will be described based on preferred embodiments. It should be noted that the present invention is not limited at all by the present embodiment, and can be appropriately changed without changing the gist of the present invention.

[Example 1] First, a positive electrode A was produced as follows. That is, lithium carbonate and cobalt hydroxide are mixed in a ball mill so that the molar ratio of Li / Co becomes 1.01 / 1.00, and the mixture is calcined in air at 600 ° C. for 1 hour, and then 900 ° C. For 10 hours to synthesize a positive electrode active material.

The positive electrode active material was pulverized and classified to obtain a positive electrode active material having a D50% particle size of 4.5 μm. The average particle diameter was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, SALD-2000J). Further, 5 kg of this active material and 2 kg of purified water were mixed with a planetary mixer for 10 minutes, allowed to stand at an ambient temperature of 25 ° C. for 1 hour, and then subjected to suction filtration.

Further, a vacuum drying treatment was performed at 130 ° C. for 48 hours to obtain a positive electrode having a resistance coefficient of 1.2 mΩ · cm and a D50% particle size of 4.5 μm at a powder packing density of 3.8 g / cm ^3. Material was obtained. The resistance coefficient was determined using the powder resistance meter shown in FIG.

The positive electrode plate is one in which the above-mentioned active material is held on a current collector. As the current collector, an aluminum foil having a thickness of 20 μm was used. The positive electrode plate was prepared by mixing 6 parts of polyvinylidene fluoride as a binder and 3 parts of acetylene black as a conductive agent with 91 parts of an active material, adding N-methylpyrrolidone as appropriate, preparing a paste, and then collecting the paste. It was manufactured by applying and drying both sides of an electric conductor material.

The negative electrode plate was prepared by mixing 92 parts of graphite (graphite) as a host substance and 8 parts of polyvinylidene fluoride as a binder on both sides of a current collector, and adding N-methylpyrrolidone as appropriate to form a paste. Was prepared by coating and drying. A 14 μm thick copper foil was used as the current collector of the negative electrode plate.

[0034] In the nonaqueous electrolyte secondary battery according to the present invention, the elliptical wound type power generating element comprising the positive electrode plate, the separator and the negative electrode plate is formed by heat-welding a metal laminated resin film together with a nonaqueous electrolytic solution. FIG. 1 shows the external appearance of the metal-laminated resin film case.

In FIG. 1, reference numeral 1 denotes a bag-shaped cell case,
Is a power generation element, 3 is a winding center axis of the winding element, 4 is a positive lead terminal, and 5 is a negative lead terminal.

The separator was a microporous polyethylene membrane, and the electrolyte was a mixed solution of ethylene carbonate: diethyl carbonate = 4: 6 (volume ratio) containing 1 mol / l of LiPF6.

The dimensions of the electrode plate are as follows: the positive electrode plate has a thickness of 180 μm;
Width 49mm, separator thickness 25μm, width 53mm,
The negative electrode plate has a thickness of 170 μm and a width of 51 mm, and the lead terminals are welded to the positive electrode plate and the negative electrode plate, respectively, and superimposed in order, with a rectangular core of polyethylene as a center, and a long side having a winding center axis of a power generating element. Was wound in an elliptical spiral shape so as to be parallel to the above, thereby forming a power generating element having a size of 50 × 35 × 4 mm.

Then, the insulating part of the electrode is covered with a tape for winding made of polyethylene (here, an adhesive is applied on one side) to the electrode width (the length of the power generation element parallel to the winding central axis of the power generation element). Was attached to the side wall of the power generation element parallel to the winding center axis, and the power generation element was stopped and fixed.

This is housed in a metal-laminated resin film case, and the elliptical wound-type power generating element is housed so that the winding center axis is perpendicular to the opening surface of the bag-shaped metal-laminated resin film case, and the lead terminals are fixed. And seal the electrolyte.
Each electrode and the separator were sufficiently wetted, and vacuum injection was performed in such an amount that no free electrolyte solution was present outside the power generating element. Finally, a sealed unit cell having a nominal capacity of 500 mAh was prototyped by performing sealing welding.

Example 2 Lithium carbonate and cobalt hydroxide were mixed in a ball mill so that the molar ratio of Li / Co was 1.01 / 1.00, and calcined at 600 ° C. for 1 hour in air. After that, the resultant was further baked at 900 ° C. for 10 hours to synthesize a positive electrode active material. This positive electrode active material was pulverized and classified to obtain a D50% particle size of 4.5 μm.
Of the positive electrode active material was obtained.

Further, 5 kg of this active material and 10 k of purified water
g was mixed with a planetary mixer for 10 minutes, and allowed to stand at an ambient temperature of 25 ° C. for 1 hour, followed by suction filtration. Further, a vacuum drying treatment is performed at 130 ° C. for 48 hours, and the resistance coefficient at a powder packing density of 3.8 g / cm 3 is 5 mΩ.
・ Cm, D50% A positive electrode active material having a particle size of 4.5 μm was obtained. Hereinafter, a laminated battery was produced in the same manner as in Example 1 using this positive electrode active material.

Example 3 Lithium carbonate and cobalt hydroxide were mixed in a ball mill so that the molar ratio of Li / Co was 1.01 / 1.00, and calcined at 600 ° C. for 1 hour in air. After that, the resultant was further baked at 900 ° C. for 10 hours to synthesize a positive electrode active material. This positive electrode active material was pulverized and classified to obtain a D50% particle size of 4.5 μm.
Of the positive electrode active material was obtained.

Further, 5 kg of this active material and 10 k of purified water
g, and allowed to stand at an ambient temperature of 25 ° C. for 1 hour.
Suction filtration was performed. Further, the above operation was performed five times.
The sample thus obtained was subjected to a vacuum drying treatment at 130 ° C. for 48 hours to give a resistance coefficient of 38 mΩ · cm at a powder packing density of 3.8 g / cm ³ and a D50% particle size of 4.5 μm.
m of the positive electrode active material was obtained. Hereinafter, a laminated battery was produced in the same manner as in Example 1 using this positive electrode active material.

Comparative Example 1 Lithium carbonate and cobalt hydroxide were mixed in a ball mill so that the molar ratio of Li / Co was 1.01 / 1.00, and the mixture was calcined at 600 ° C. for 1 hour in air. After that, the resultant was further baked at 900 ° C. for 10 hours to synthesize a positive electrode active material. By pulverizing and classifying this positive electrode active material, the powder packing density is 3.8 g.
/ Cm ³ , the resistance coefficient is 0.8 mΩ · cm, D50
% Active material was obtained. Hereinafter, a laminated battery was produced in the same manner as in Example 1 using this positive electrode active material.

Comparative Example 2 Lithium carbonate and cobalt hydroxide were mixed in a ball mill so that the molar ratio of Li / Co was 1.01 / 1.00, and calcined in air at 600 ° C. for 1 hour. After that, the resultant was further baked at 900 ° C. for 10 hours to synthesize a positive electrode active material. This positive electrode active material is pulverized and classified to have a D50% particle size of 4.5 μm.
Of the positive electrode active material was obtained.

Further, 5 kg of this active material was added to 10 k of purified water.
g, and allowed to stand at an ambient temperature of 90 ° C. for 1 hour, followed by suction filtration. Further, a vacuum drying treatment is performed at 130 ° C. for 48 hours, and when the powder packing density is 3.8 g / cm ³ , the resistance coefficient is 45.0 mΩ · cm, and the D50% particle size is 4.
A positive electrode active material of 5 μm was obtained. Hereinafter, a laminated battery was produced in the same manner as in Example 1 using this positive electrode active material.

First, Examples 1, 2, and 3 and Comparative Example 1,
A cycle life test was performed on the two 500 mAh laminated cells. The initial capacity and the capacity retention at 45 ° C. were measured for each battery.

First, at an ambient temperature of 25 ° C. and a current of 500 m
A / constant current / constant voltage charging under the condition of A / voltage 4.1 V for 3 hours, and after a pause of 10 minutes, discharging current of 500 m
A, two charge / discharge cycles were performed under the condition that discharge was performed under the condition of a final voltage of 2.75 V, and the discharge capacity at that time was defined as the initial capacity. Next, the battery for which the confirmation test of the initial capacity was completed was further repeated 300 cycles at an ambient temperature of 45 ° C., and the discharge capacity at the 300th cycle was determined. Here, the ratio when the discharge capacity at the 300th cycle was divided by the initial capacity was defined as the capacity retention rate. Table 1 shows the results of Examples and Comparative Examples.

[0049]

[Table 1]

As is clear from Table 1, the capacity retention of the battery of Comparative Example 2 was poor, while Examples 1, 2, and 3 and Comparative Example 1 exhibited good cycle life characteristics. 1, 2, and 3 exhibited particularly excellent cycle life characteristics. Thus, it was found that by limiting the powder specific resistance of the positive electrode active material, the batteries of the examples had better cycle life characteristics than the batteries of the comparative examples.

Next, the 500 mAh laminated single cells of Examples 1, 2, and 3 and Comparative Examples 1 and 2
A safety test was performed. Each battery was charged to a voltage of 10 V at a current of 730 mA at an ambient temperature of 25 ° C. to test the safety of the battery in an overcharged state. The results are shown in Table 2.

After performing constant-current / constant-voltage charging for 3 hours under the conditions of a current of 500 mA and a voltage of 4.3 V, a test was conducted to determine the safety when a needle of φ1 mm was inserted into the battery to simulate an internal short circuit. Table 2 also shows the results obtained. In addition,
The numbers in the table indicate the number of batteries that burst and fired, respectively, for the number of test batteries of 20.

[0053]

[Table 2]

As is clear from Table 2, all of the batteries of Comparative Example 1 fell into a dangerous state involving rupture and ignition, whereas the batteries of Example and Comparative Example 2 ruptured and fired.
Very safe results were obtained without causing ignition.

The surface temperature of the battery when the overcharge test was performed was higher than that of the battery of Comparative Example 1 at 500 ° C. or higher. Battery No. 2 was able to reduce the battery surface temperature to a maximum of 120 ° C. or less. This indicates that the safety of the battery was improved by increasing the powder specific resistance of the positive electrode active material.

[0056]

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery which is highly safe even under abnormal conditions involving heat generation, without deteriorating battery characteristics, especially cycle life characteristics. it can. Furthermore, a nonaqueous electrolyte battery having excellent discharge characteristics can be provided. Therefore, the industrial value of the present invention is extremely large.

[Brief description of the drawings]

FIG. 1 is an external view of a nonaqueous electrolyte secondary battery.

FIG. 2 is a schematic diagram of an apparatus for measuring a powder specific resistance.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 bag-shaped unit cell case 2 power generation element 3 winding center axis of winding element 4 positive electrode lead terminal 5 negative electrode lead terminal 11 compression rod 12 sleeve 13 compression tray 14 projection of compression rod 15 projection of compression tray 16 sample powder

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ05 AJ12 AK03 AL07 AM03 AM05 AM07 BJ02 BJ14 DJ16 HJ08 HJ20 5H050 AA03 AA07 AA15 BA17 CA08 CB08 DA02 FA05 FA17 HA08 HA17

Claims (1)

[Claims] 1. The method of claim 1, wherein the positive electrode active material has a powder packing density of 3.8 g /
The resistance coefficient at cm ³ is 1 mΩ · cm or more and 40 mΩ · c
A non-aqueous electrolyte secondary battery comprising a lithium-cobalt composite oxide having a particle size of not more than m.