JPH07153495A - Secondary battery - Google Patents

Abstract

PURPOSE:To prevent the capacity deterioration caused by charge/discharge cycles by adding and mixing one or more oxides selected among Al2O3, In2O3, SnO2, ZnO to a lithium containing composite oxide, and generating the positive electrode of a lithium ion secondary battery. CONSTITUTION:MnO2 and Li2 CO3 are mixed at the atomic ratio of 1:2 between Li and Mn, and the mixture is baked in the air at 800 deg.C for 20hrs to obtain LiMn2O4, for example. Al2O3 is selected among Al2O3, In2O3, SnO2, and ZnO, and Al2O3 of 2 pts.wt. and graphite of 8 pts.wt. are added to LiMn2O3, of 87 pts.wt. to obtain slurry by wet blending. The slurry is uniformly applied on both faces of an aluminum foil having the thickness of 0.02mm, for example, and serving as a positive electrode current collector, and it is pressed and molded by a roller press machine after drying to form a band-like positive electrode 2. A porous polypropylene separator 3 is sandwiched between a negative electrode 1 and the positive electrode 2, and they are wound into a roll shape into a wound body to obtain a battery element. The capacity deterioration caused by charge/discharge cycles can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art As electronic devices are becoming smaller and lighter, there is a growing demand for high energy density secondary batteries as their power sources. In order to meet the demand, attention has been paid to non-aqueous electrolyte secondary batteries, and attempts have been made to put them into practical use. In particular, the so-called lithium secondary battery, which uses lithium metal for the negative electrode, seemed to have the greatest potential, but the metallic lithium negative electrode became powdered due to repeated charging and discharging, and its performance was significantly deteriorated. Because it deposits on dendrites and causes an internal short circuit,
There is a problem with the practical cycle life, and it is still difficult to put it into practical use. Therefore, recently, a non-aqueous electrolyte secondary battery having a carbon electrode as a negative electrode, which utilizes the movement of lithium ions into and out of carbon, is under development. This battery is
It was introduced to the world for the first time in 1990 under the name of lithium-ion secondary battery (Progress I magazine).
n Batteries & SolarCells,
Vol. 9, 1990, p209), and nowadays it is recognized in the battery industry and academic societies as to be called the next-generation secondary battery "lithium ion secondary battery", and its practical application is being spurred. Typically, a lithium-containing composite oxide (for example, LiMn ₂ O ₄ , LiCoO ₂ , L) is used as a positive electrode material.
iNiO ₂ etc.) and a carbonaceous material such as coke or graphite is used for the negative electrode. In fact, the positive electrode is LiCo
O ₂ is used, and a special carbon material (pseudo-graphite material having a certain degree of disordered layer structure) is used for the negative electrode, and 200 Wh /
A small amount of lithium ion secondary batteries having an energy density of about 1 have already been put into practical use. The energy density of existing nickel-cadmium batteries is 100-150 Wh / l,
The energy density of lithium-ion secondary batteries is much higher than that of existing batteries. However, the major drawback is that the cost of raw materials is quite high. When considering an inexpensive lithium-ion secondary battery, the price reduction of cobalt cannot be expected in the future due to resource reasons. However, lithium manganese composite oxides (LiMn ₂ O ₄ , LiMnO _2, etc.) are extremely attractive in terms of inexpensive materials. Another drawback is that the capacity of lithium ion secondary batteries deteriorates significantly with charge and discharge cycles. In addition, when the lithium manganese composite oxide is used as the positive electrode material, the deterioration is extremely large. The carbon negative electrode is extremely charged because lithium ions are doped into carbon in the electrode during charging, and lithium ions are undoped from the carbon during discharging, and the carbon itself does not undergo a large change in crystal structure during charge / discharge, which is extremely high. Stable charge / discharge characteristics are exhibited, the characteristic deterioration due to charge / discharge is small, and specifically, the charge / discharge can be repeated 1000 times or more. However, the deterioration of the capacity associated with the actual cycle of the lithium-ion secondary battery is dominated by the deterioration of the characteristics of the positive electrode, and cannot be said to be a sufficiently satisfactory level.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to improvement of cycle characteristics of a non-aqueous electrolyte secondary battery containing a lithium-containing composite oxide as a main positive electrode active material.

[0004]

[Means for Solving the Problem] The means for solving the problem is selected from Al ₂ O ₃ , In ₂ O ₃ , SnO ₂ , and ZnO mixed with a lithium-containing composite oxide that is a positive electrode active material in a positive electrode. One or more kinds of oxides are added.

[0005]

[Function] A lithium-containing composite oxide (LiMn ₂ O
₍₄ , LiMnO ₂ , LiCoO ₂ , LiNiO ₂ etc.) is used, any of the composite oxides becomes dedoped with lithium ions and becomes unstable in the charged state.
Therefore, as charging and discharging are repeated many times, the positive electrode active material gradually changes and loses the charging and discharging function, and the capacity deteriorates with the cycle. Therefore, the present inventor has conducted intensive studies for the purpose of stabilizing the positive electrode active material in a charged state,
By mixing one or more oxides selected from Al ₂ O ₃ , In ₂ O ₃ , SnO ₂ , and ZnO with the active material and adding it to the positive electrode, the stability of the positive electrode active material in a charged state is increased and the It was discovered that the capacity of the non-aqueous electrolyte secondary battery is extremely small with the discharge cycle.

[0006]

The present invention will be described in more detail with reference to the following examples.

Example 1 The present invention will be described with reference to FIG. 1 for a specific cylindrical battery. FIG. 1 shows the overall structure of the battery of this embodiment. A battery element which is a power generation element for carrying out the present invention was prepared as follows. Mesocarbon micro beads heat-treated at 2800 ° C. (d002 = 3.3
10 parts by weight of polyvinylidene fluoride (PVDF) as a binder was added to 90 parts by weight of 7Å), and wet mixed with N-methyl-2-pyrrolidone as a solvent to form a slurry (paste form). Then, this slurry was uniformly applied to both surfaces of a 0.01 mm-thick copper foil serving as a current collector, dried, and then pressure-molded with a roller press to form a strip-shaped negative electrode (1). Then, the positive electrode was prepared as follows. Commercially available manganese dioxide (MnO ₂ ) and lithium carbonate (Li ₂ C
O ₃ ) was mixed so that the atomic ratio of Li and Mn was 1: 2, and this was baked in air at 800 ° C. for 20 hours to prepare LiMn ₂ O ₄ . 87 of this LiMn ₂ O _4
2 parts by weight of Al ₂ O _{3 and} 8 parts by weight of graphite were added to the parts by weight and mixed well, and further 3 parts by weight of polyvinylidene fluoride as a binder and N-methyl-2-pyrrolidone as a solvent were added and wet mixed. Make a slurry (paste). The thickness of this slurry to be a positive electrode current collector is 0.02 mm
The aluminum foil was evenly applied on both sides, dried, and then pressure-molded with a roller press to form a strip-shaped positive electrode (2). The negative electrode (1) and the positive electrode (2) thus prepared were wound into a roll with a porous polypropylene separator (3) sandwiched between them to prepare a battery element as a wound body having an average outer diameter of 15.7 mm. Next, the insulating plate (5) is placed on the bottom of the nickel-plated iron battery can (4) to house the battery element. Weld the negative electrode lead (6) taken out from the battery element to the bottom of the battery can and insert 1 into the battery can.
A mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which mol / liter of LiPF ₆ is dissolved is injected as an electrolytic solution. Then, the insulating plate (5) is also installed on the upper part of the battery element, the gasket (7) is fitted, and the explosion-proof valve (8) is installed inside the battery as shown in FIG. The positive electrode lead (9) taken out from the battery element is welded before injecting the electrolytic solution into this explosion-proof valve. On the explosion-proof valve, a closing lid body (10) serving as a positive electrode external terminal is overlapped with a doughnut-type PTC switch (11) sandwiched therebetween, and the edge of the battery can is crimped, and the battery structure shown in FIG. A battery (A) having a height of 65 mm was completed.

Comparative Example The positive electrode to be used was prepared by a conventional method, and the other examples were all prepared in Example 1.
A battery (X) according to the conventional method was prepared in the same manner as in. The positive electrode according to the conventional method is prepared as follows. 8 parts by weight of graphite was mixed with 89 parts by weight of the powdery LiMn ₂ O ₄ prepared in Example 1, and 3 parts by weight of polyvinylidene fluoride as a binder and N-methyl-2-pyrrolidone as a solvent were added. Wet mix and slurry (paste)
To This slurry is used as a positive electrode current collector with a thickness of 0.02.
mm aluminum foil was evenly applied on both sides, dried, and pressure-molded with a roller press to form a strip-shaped positive electrode (2c). After that, the positive electrode (2c) and the same negative electrode (1) as that prepared in Example 1 were wound into a roll with a porous polypropylene separator (3) interposed therebetween, and a battery having an average outer diameter of 15.7 mm. A device was prepared, and thereafter, a battery (X) was prepared in the same manner as in Example 1.

Example 2 87 parts by weight of LiMn ₂ O ₄ prepared in Example 1 was added with S.
₂ parts by weight of nO _{2 and} 8 parts by weight of graphite are mixed, and further 3 parts by weight of polyvinylidene fluoride as a binder and N-methyl-2-pyrrolidone as a solvent are added and wet mixed to form a slurry (paste form). Subsequently, the slurry was uniformly applied on both sides of a 0.02 mm-thick aluminum foil serving as a positive electrode current collector, dried and then pressure-molded with a roller press to form a strip-shaped positive electrode (2b). After that, this positive electrode (2b) and the same negative electrode (1) as that prepared in Example 1 were wound into a roll with a porous polypropylene separator (3) interposed therebetween, and a battery having an average outer diameter of 15.7 mm. A device was prepared and a battery (B) was prepared in the same manner as in Example 1 after that.

Test Results In the batteries thus prepared in Examples 1 and 2 and Comparative Example, after the aging period of 12 hours was passed at room temperature for the purpose of stabilizing the inside of the battery, the charging upper limit voltage was 4.2 V. The battery was charged at room temperature for 8 hours, and all batteries were discharged at a constant current of 800 mA to a final voltage of 3.0 V at the same temperature to obtain the initial discharge capacity of each battery. Thereafter, each battery was subjected to a charge / discharge cycle test in a high temperature bath at 40 ° C. The charging current is 400 mA, the charging upper limit voltage is set to 4.2 V, and charging is performed for 4 hours. The discharging is performed at a constant current discharge of 800 mA up to the final voltage of 3.0 V, charging and discharging are repeated, and 40 cycles and 100 The discharge capacity at 800 mA discharge of each battery at the time of the cycle was determined. The results are summarized in Table 1. As shown in Table 1, the batteries (A) and (B) according to the present invention show a small decrease in capacity even after repeated charging and discharging, and the capacity of the batteries (X) according to the prior art at each of 40 and 100 cycles. The difference can be quite large. When a lithium-manganese composite oxide (LiMn ₂ O ₄ ) is used as the positive electrode active material like the lithium-ion battery prepared in this example, a particularly high temperature condition is observed as in the battery (X) in the prior art. In the charge / discharge cycle at, the capacity decreases sharply. At the time of 100 cycles, the capacity is already about half of the initial capacity. However, as shown in Table 1, Al ₂ O ₃ and Sn were added to the positive electrode.
In the batteries (A) and (B) according to the present invention in which O ₂ is added and mixed, the degree of deterioration is extremely small even in a battery using a lithium manganese composite oxide (LiMn ₂ O ₄ ) as the positive electrode active material, and the cycle is 100 cycles. A discharge capacity of 870-880 mAh is obtained at that time. This is about 230 Wh / l in terms of energy density, which is higher than the initial energy density of currently commercialized lithium ion secondary batteries using cobalt. Also, regarding the change in internal resistance, at the end of 100 cycles,
It was confirmed that in the battery (X) manufactured by the conventional method, a change of several tens of milliohms was observed, whereas in the batteries of the present invention, both (A) and (B) showed a very small change of several milliohms. As described above, the present invention can greatly improve the deterioration of capacity due to cycling, which is the biggest drawback of lithium ion secondary batteries. Note as an example of the effect appears most pronounced in the present invention in the above embodiment described the case of using the LiMn ₂ O ₄ as a cathode active material, the positive electrode of LiCoO ₂ and LiNiO ₂ and the like other lithium-containing composite oxide The present invention also exhibits an improvement effect in a non-aqueous electrolyte secondary battery used as an active material.
Further, in the above-mentioned embodiment, Al ₂ O ₃ is mixed with the positive electrode active material.
Although the case where SnO ₂ and SnO ₂ are added to form a positive electrode has been described, In ₂ O ₃ and ZnO have similar addition effects.

[0011]

As described above, in the present invention, a lithium-containing composite oxide (for example, LiMn ₂ O ₄ , LiC) is used.
(OO ₂ , LiNiO ₂ etc.) to Al ₂ O ₃ , In ₂ O ₃ ,
By adding and mixing one or more kinds of oxides selected from SnO ₂ and ZnO to form a positive electrode of a lithium ion secondary battery, the capacity of the lithium ion secondary battery with charge / discharge cycles, which has been a major drawback so far. Deterioration can be greatly improved. In particular, in a lithium ion secondary battery using a lithium manganese composite oxide as a positive electrode active material, a remarkably improved effect, a high capacity, long life and inexpensive lithium ion secondary battery that can sufficiently replace an existing secondary battery. Now that we can provide batteries, their industrial value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structures of batteries in Examples and Comparative Examples.

[Explanation of symbols]

1 is a negative electrode, 2 is a positive electrode, 3 is a separator, 4 is a battery can, 5
Is an insulating plate, 6 is a negative electrode lead, 7 is a gasket, 8 is an explosion-proof valve, 9 is a negative electrode lead, and 10 is a closing lid.

Claims (2)

[Claims] 1. A battery having a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution, wherein a lithium-containing composite oxide is used as an active material in the positive electrode, wherein Al ₂ O ₃ , In mixed with the active material
A non-aqueous electrolyte secondary battery characterized in that one or more kinds of oxides selected from ₂ O ₃ , SnO ₂ and ZnO are added. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a lithium manganese composite oxide (eg, LiMn ₂ O ₄ ) is used as an active material in the positive electrode.