JP2001283849A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqoues electrolyte battery with little deterioration of capacity in a charge and discharge cycle and with superb safety. SOLUTION: With the nonaqous electrolyte secondary battery, a positive active material includes a lithium metal oxide as expressed in a composition formula of LixMO2 (where, M is at least a kind selected from the group of Co, Ni, Fe, Al, Mg, Ti, Cr, Ga, Cu, and B, and (x) is in the range of: 0.4<=x<=1.0) and lithium hydroxide, the content of the latter to be 0.001 to 1 wt.% of the above lithium metal oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 satisfies such a requirement is an active material such as lithium metal or a lithium alloy, or a host material containing lithium ions (here, the host material refers to a material capable of inserting and extracting lithium ions). Lithium intercalation compound occluded in carbon is used as a negative electrode material, and LiCl
This is a non-aqueous electrolyte secondary battery using an aprotic organic solvent in which a lithium salt such as O ₄ and LiPF ₆ is dissolved as an electrolyte.

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.

[0004] Each of the positive electrode plate and the negative electrode plate is formed into a thin sheet or foil shape, 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.

[0005] 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 diverse. For example, portable AV equipment and the like often use batteries assembled in series or in parallel. When used as an assembled battery, variation in performance between batteries becomes a problem. If 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 is overcharged. In the worst case, the battery may run out of heat and may burst 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 lithium cobaltate is not used. May generate heat and, in the worst case, lead to thermal escape, which may cause rupture or ignition.

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.

[0009]

However, when a part of Co of lithium cobalt oxide is replaced with an element such as Al, the amount of cobalt used for the battery reaction contained in the active material is reduced. In such a case, a problem such as lowering of the energy density occurs inevitably.

The positive electrode active material has a composition formula LixMO
_When a lithium metal composite oxide represented by ₂ (where M is at least one of transition metals) is used, the positive electrode active material becomes thermally unstable in an overcharged state, which may cause a battery explosion or the like. Had become.

Therefore, 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 without lowering the energy density of the battery, and to achieve excellent safety. It aims to supply a non-aqueous electrolyte battery. Still another object is to provide a non-aqueous electrolyte battery having excellent discharge characteristics.

[0012]

SUMMARY OF THE INVENTION The non-aqueous electrolyte secondary battery according to the present invention has been made in view of the above-mentioned problems, and the present inventor has proposed that lithium hydroxide (LiOH) contained in a lithium metal oxide. ). Lithium hydroxide is widely used as a starting material for lithium metal oxides.
However, little consideration has been given to the effect of lithium hydroxide remaining on the lithium metal oxide after the synthesis on battery safety. The present inventor has found the following inventions as a result of earnest research.

That is, according to the present invention, in a non-aqueous electrolyte secondary battery, the positive electrode active material has a composition formula LixMO ₂ (where M
Are Co, Ni, Fe, Al, Mg, Ti, Cr, Ga,
At least one member selected from the group consisting of Cu and B, and x is 0.
4 ≦ x ≦ 1.0) and the content of lithium hydroxide relative to the weight of the lithium metal oxide is 0.001-1 w.
By setting it to t%, the above-mentioned problem is to be solved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a nonaqueous electrolyte secondary battery, wherein the positive electrode active material has a composition formula LixMO ₂ (where M
Are Co, Ni, Fe, Al, Mg, Ti, Cr, Ga,
At least one member selected from the group consisting of Cu and B, and x is 0.
4 ≦ x ≦ 1.0) and the content of lithium hydroxide relative to the weight of the lithium metal oxide is 0.001-1 w.
t%.

In the present invention, a composition formula LixMO ₂ (where M is Co, Ni, Fe, A
1, at least one selected from the group consisting of Mg, Ti, Cr, Ga, Cu, and B, and x is in the range of 0.4 ≦ x ≦ 1.0)
By using a lithium metal oxide represented by
This is because a nonaqueous electrolyte secondary battery having a high discharge voltage and, as a result, a high energy density can be obtained.

In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode active material contains a lithium metal oxide and lithium hydroxide, and the content of lithium hydroxide is 0.001 to 1 wt% based on the weight of the lithium metal oxide. Range. In a conventional non-aqueous electrolyte secondary battery, when it is in an overcharged state, the positive electrode active material becomes thermally unstable, causing thermal runaway. In this case, the battery is in a dangerous state such as explosion.

As in the present invention, when a certain amount of lithium hydroxide is present in the positive electrode active material, when the battery is overcharged, the positive electrode active material before the battery becomes thermally unstable becomes unstable. At the potential, the electrolytic solution reacts with lithium hydroxide to generate heat, and the safety valve is operated to prevent the battery from exploding.

When the amount of lithium hydroxide is smaller than 0.001 wt%, the heat generated by the reaction between the electrolyte and lithium hydroxide does not reach the time when the safety valve is operated, and the effect of the addition of lithium hydroxide is not observed. I can't.

When the amount of lithium hydroxide is more than 1 wt%, since lithium hydroxide itself is an insulator, electric contact inside the positive electrode mixture becomes poor, and the capacity decrease due to charge / discharge cycles becomes large. Battery characteristics such as

As a result, when a non-aqueous electrolyte secondary battery is formed using the positive electrode active material according to the present invention, when the battery is in an abnormal state such as an overcharged state without lowering the energy density of the battery. In addition, a battery with excellent safety can be obtained.

As the negative electrode material of the non-aqueous electrolyte secondary battery of the present invention, alloys of lithium with Al, Si, Pb, Sn, Zn, Cd and the like, LiFe ₂ O ₃ , WO ₂ , MoO _{2 and the} like can be used. A transition metal oxide, graphite, carbonaceous material such as carbon, lithium nitride such as Li ₅ (Li ₃ N), or metal lithium foil, or a mixture thereof may be used. As the solvent for the electrolytic solution, 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, dimethylformamide, Dimethylacetamide,
A polar solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof can be used. Also,
Examples of lithium salts dissolved in an organic solvent include LiPF ₆ ,
LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , LiCF ₃
SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ C
F ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COCF
A salt such as ₂ CF ₃ ) ₂ or a mixture thereof may be used.
Further, as the separator, 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.

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.

[0024]

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 prepared as follows. That is, lithium hydroxide and cobalt oxide are mixed by a ball mill so that the molar ratio of Li / Co becomes 1.01 / 1.00,
After calcining for an hour, it was further calcined at 900 ° C. for 10 hours to synthesize a positive electrode active material.

The obtained positive electrode active material was analyzed by X-ray diffraction.
It was confirmed to be LiCoO ₂ . Further, by grinding and classifying the positive electrode active material, the D50% particle size is 4.5 μm.
Of the positive electrode active material was obtained. 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 5 kg of purified water
Was mixed and left standing at an ambient temperature of 25 ° C. for 1 hour, followed by suction filtration. This operation was repeated until the concentration of lithium hydroxide (LiOH) in the filtrate became 1 ppm or less. The concentration of LiOH in the filtrate was measured using an ICP emission spectrometer (LRLS-AP manufactured by Jarrell Ash).
It was determined by quantifying the i element. In addition, LiOH
Is also determined from the neutralization titration. Further, the positive electrode active material after the water washing was subjected to a vacuum drying treatment at 130 ° C. for 48 hours.

The positive electrode plate has the above-mentioned active material held on a current collector. As the current collector, an aluminum foil having a thickness of 20 μm was used. For the positive electrode plate, 6 parts of polyvinylidene fluoride as a binder and 3 parts of acetylene black as a conductive agent were mixed together with 91 parts of an active material, and N-methylpyrrolidone was appropriately added to prepare a mixture prepared in a paste form. After that, the mixture was applied to both surfaces of a current collector material and dried to produce a current collector material.

When the positive electrode active material contains lithium hydroxide, a certain amount of lithium hydroxide was added to the paste and mixed to obtain a positive electrode mixture.

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. Was prepared by coating and drying. A 14 μm thick copper foil was used as the current collector of the negative electrode plate.

In the non-aqueous electrolyte secondary battery according to the present invention, the oval wound 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 non-aqueous electrolyte. FIG. 1 shows the external appearance of the metal-laminated resin film case.

In FIG. 1, reference numeral 1 denotes a bag-shaped unit 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 of the battery and the polyethylene microporous membrane, also, the electrolyte, the LiPF ₆ 1 mol / l comprising ethylene carbonate: diethyl carbonate = 4: 6
(Volume ratio).

The dimensions of the electrode plate are as follows.
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 portion of the electrode is covered with a tape for winding made of polyethylene (here, an adhesive is applied to one side) and the width of the electrode (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, sealing and welding were performed to produce a prototype laminated single cell having a nominal capacity of 520 mAh.

As described above, the positive electrode active material is LiCoO
Consisting of _two batteries 1-1, consisting of lithium hydroxide positive electrode active material and LiCoO ₂ (LiOH), 1-2 to the battery including the lithium hydroxide 0.0005wt% ~2.00wt%
1-12 were created.

Next, a cycle life test was performed on the 520 mAh laminated cells 1-1 to 1-12 of Example 1. Then, the initial capacity and the capacity retention at 45 ° C. were measured.

First, at an ambient temperature of 25 ° C. and a current of 520 mA
After performing a constant current / constant voltage charge for 3 hours under a condition of / voltage 4.2V, after a pause of 10 minutes, a discharge current of 520 mA,
The discharge capacity when two charge / discharge cycles such as discharging under the condition of a final voltage of 2.75 V were repeated was defined as the initial capacity. Next, the battery for which the initial capacity confirmation test was completed was further repeated 300 cycles at an ambient temperature of 45 ° C., and the ratio obtained by dividing the discharge capacity at the 300th cycle by the initial capacity was defined as the capacity retention rate. Table 1 shows the results of the cycle life test.

[0040]

[Table 1]

As is clear from Table 1, the capacity retention ratio of the batteries 1-11 and 1-12 in which the content of lithium hydroxide exceeded 1.00 wt% was inferior,
In any of the batteries 1-1 to 1-10, the capacity retention rate was 80%.
% Abnormal and showed good cycle life characteristics.

Next, a safety test was performed on the 520 mAh laminated cells 1-1 to 1-12 of Example 1.
An overcharged battery was subjected to a safety test by charging the battery to a voltage of 10 V at an ambient temperature of 25 ° C. and a current of 730 mA.

Further, after performing constant-current / constant-voltage charging for 3 hours under the conditions of a current of 520 mA and a voltage of 4.3 V, a 1-mm-diameter needle is inserted into the battery to simulate an internal short circuit. The test was performed.

Table 2 shows the results of these safety tests.
The numbers in Table 2 indicate the number of batteries that burst and fired, respectively, for the number of test batteries of 20.

[0045]

[Table 2]

As is evident from Table 2, the battery 1-1 containing no lithium hydroxide and the battery 1-2 having a lithium hydroxide content of less than 0.001% by weight are both ruptured and ignited. While in danger,
In the batteries 1-3 to 1-12, very safe results were obtained with almost no rupture or ignition.

The battery surface temperature during the overcharge test was 500 ° C. maximum for Battery 1-1 and Battery 1-2.
On the other hand, in the batteries 1-3 to 1-12, the battery surface temperature was able to be suppressed to 120 ° C. or less at the maximum.

As described above, by setting the content of lithium hydroxide in the positive electrode active material to 0.001 to 1% by weight, a non-aqueous electrolyte which has a small capacity reduction even in a charge / discharge cycle and is excellent in safety. A secondary battery is obtained.

Example 2 Example 1 was used as a positive electrode active material.
Instead of LiCoO ₂ used in the above, LiCo _0.8 Ni
Except that _0.2 O ₂ was used, batteries 2-1 to 2-1 were the same as those in Example 1.
2-12 were fabricated, and the same test as in Example 1 was performed.
As a result, the capacities of the batteries 2-3 to 2-10 containing 0.001 to 1 wt% of lithium hydroxide were all 80%.
As described above, in the overcharge test and the nail penetration test, a non-aqueous electrolyte secondary battery was obtained which did not cause rupture or ignition, had a small capacity reduction even in a charge / discharge cycle, and was excellent in safety.

[0050]

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, since a non-aqueous electrolyte battery having excellent discharge characteristics can be provided, 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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bag-shaped cell case 2 Power generation element 3 Center axis of winding of winding element 4 Positive electrode lead terminal 5 Negative electrode lead terminal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Tagawa No. 1, Nishinosho Inonoba-machi, Kichijo-in, Minami-ku, Kyoto, Kyoto Inside Nippon Battery Co., Ltd. (72) Inventor Yuichi Ito, Kichijo-in, Nitta-ku, Minami-ku, Kyoto No. 5 Nodancho F-term in S-Melcotech Co., Ltd. (Reference) 5H029 AJ02 AJ12 AK03 AL06 AM03 AM04 AM05 AM07 BJ02 BJ14 HJ01 5H050 AA03 AA15 BA17 CA08 CB07 DA09 EA12 EA24 HA01 HA02

Claims (1)

[Claims] The positive electrode active material has a composition formula of LixMO ₂ (where M is Co, Ni, Fe, Al, Mg, Ti, Cr,
At least one selected from the group consisting of Ga, Cu, and B, x
Contains a lithium metal oxide represented by the following formula: 0.4 ≦ x ≦ 1.0), and the content of lithium hydroxide relative to the weight of the lithium metal oxide is 0.001.
Non-aqueous electrolyte secondary battery characterized in that the content is -1 wt%.