JP2003323916A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of preventing battery degradation caused by entry of water into a battery case. <P>SOLUTION: In the battery case, a porous member having pores with a pore diameter allowing entry of a water molecule and prohibiting entry of a molecule grater than the water molecule. This structure avoids disturbing water absorption by entry of nonaqueous solvent and the like into the pores, thus realizing efficient water removal. This effectively prevents battery degradation. By using synthetic zeolite as the porous member, even if entered water and lithium salt are reacted to produce hydrogen fluororide acid, the hydrogen fluoride acid can be removed by chemisorption. Moreover, providing the porous member within a positive electrode active material prevents degradation of charge collectors caused by the hydrogen fluoride acid, thus effectively preventing battery degradation. <P>COPYRIGHT: (C)2004,JPO

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 a lithium ion secondary battery, since a lithium compound is used as an active material, it is impossible to use an aqueous solvent having high reactivity with lithium. Therefore, a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent that does not chemically react with lithium is used.

[0003]

However, it is usual that a small amount of water is mixed in the non-aqueous solvent, and it is difficult to completely remove this water at the manufacturing stage of the battery. Further, even after the battery is assembled, water in the external environment may enter the battery through the gap of the sealing port in the battery case.

Particularly, as the lithium salt, LiBF ₄ , Li
When a fluorine compound such as PF ₆ is used, the fluorine compound may react with water to generate hydrofluoric acid. This hydrofluoric acid corrodes metals such as aluminum used for the current collector and the battery case, which causes deterioration of the battery.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery capable of preventing deterioration of the battery due to mixing of water in the battery case. is there.

[0006]

Means for Solving the Problems The present inventor has been earnestly studied to provide a non-aqueous electrolyte secondary battery capable of preventing deterioration of the battery due to mixing of water in the battery case. It has been found that it is effective to dispose a porous body having pores inside the battery case. In particular, by making the pore size of the pores large enough to allow water molecules to enter but not larger than water molecules, molecules such as non-aqueous solvents enter the pores and interfere with water adsorption. It was found that water can be removed efficiently by avoiding the above-mentioned problems, and the present invention has been completed.

That is, the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolytic solution prepared by dissolving an electrolyte in a non-aqueous solvent, and a battery case containing the positive electrode, the negative electrode and the non-aqueous electrolytic solution. A non-aqueous electrolyte secondary battery, wherein the battery case is provided with a porous body in which pores having a pore diameter capable of allowing water molecules to enter while restricting entry of molecules larger than the water molecules are formed. It is characterized by being.

The porous material of the present invention is not particularly limited as long as it has pores capable of adsorbing water and does not react with lithium or a non-aqueous electrolyte. Specific examples include a calcined alumina body having a pore size of about 3 angstroms, synthetic zeolite, and synthetic zeolite.

Further, the shape and arrangement of the porous body are not particularly limited as long as the porous body can be brought into contact with water mixed in the battery case and take the water into the pores.
For example, it may be formed in a plate shape and laid in the battery case, may be formed in a thin layer and arranged along the inner wall surface of the battery case, and may be formed in a granular shape in the active material layer. It may be mixed or dispersed in the non-aqueous electrolyte.

The present invention provides a lithium salt, LiBF ₄ ,
It is particularly effective when a fluorine-based compound such as LiPF ₆ is used. These fluorine compounds react with water to generate hydrofluoric acid, which causes deterioration of the battery. However, when the porous body of the present invention is used to adsorb and remove water, the generation of fluorine compounds occurs. This is because it is possible to suppress In such a case, it is preferable to use a porous body that also has a function of removing the generated hydrofluoric acid by chemisorption. Examples of such a porous material include calcined alumina, synthetic zeolite, and synthetic zeolite.

In particular, the current collector on the positive electrode side is usually made of aluminum, and this aluminum is easily corroded by hydrofluoric acid. Therefore, it is preferable to mix the porous body of the present invention into the positive electrode active material. By doing so, it is possible to suppress generation of hydrofluoric acid near the positive electrode, prevent corrosion of the current collector, and effectively prevent deterioration of the battery.

The amount of the porous body provided in the battery can be determined by the amount of the electrolytic solution used in the battery, the concentration of water contained in the electrolytic solution and the water absorption capacity of the porous body. Obtaining the weight of water existing in the electrolyte from the weight of the electrolyte and the concentration of water contained in the electrolyte, and obtaining the weight (Wg) of the porous body required to completely absorb the water. You can The larger the weight of the porous body in the battery, the more effective it is to remove water. However, when the weight of the porous body in the battery increases, the weight of the active material in the battery decreases correspondingly, and the energy density of the battery decreases. In an actual battery, not all of the electrolytic solution is in contact with the porous body, and water is also brought into the battery from the electrodes and separators other than the electrolytic solution. It is preferable to have the body inside the battery.

[0013]

EFFECTS OF THE INVENTION AND EFFECTS OF THE INVENTION According to the present invention, pores are formed in the battery case, the pores having a pore size that allows the entry of water molecules while restricting the entry of molecules larger than the water molecules. A porous body is provided. According to this structure, water molecules can enter the pores, but non-aqueous solvent molecules that are bulkier than the water molecules cannot enter the pores. Therefore, it is possible to prevent non-aqueous solvent molecules from being adsorbed in the pores and hindering the adsorption of water, and to adsorb water efficiently to the porous body. Thereby, the deterioration of the battery can be effectively prevented.

An alumina fired body is used as the porous body. As a result, even when the mixed water reacts with the lithium salt to generate hydrofluoric acid, the hydrofluoric acid can be removed by chemisorption. Furthermore, by mixing the porous body in the positive electrode active material layer, deterioration of the current collector due to hydrofluoric acid can be prevented, and deterioration of the battery can be effectively prevented.

[0015]

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

<Example 1> 1. A molecular sieve 3A (manufactured by Manax Co., Ltd.) having a pore size of 3 Å was used as the raw material porous body.

2. Preparation of Battery 1) Preparation of Positive Electrode LiCoO ₂ was used as the positive electrode active material. 91.0 g of this positive electrode active material, 6.0 g of polyvinylidene fluoride as a binder, 3.0 g of acetylene black as a conductive agent, and 0.2 g of the molecular sieve 3A described in 1 above.
Were mixed and N-methylpyrrolidone was added to prepare a positive electrode mixture paste. This paste was uniformly applied on both sides of a current collector made of an aluminum foil having a thickness of 20 μm, dried and then pressed. In this way, a strip-shaped positive electrode sheet having the positive electrode active material layer was produced. The total thickness of the positive electrode active material layer was 170 μm on both sides. A positive electrode lead made of a 100 μm thick aluminum piece was welded to one end of this positive electrode sheet.

2) Preparation of Negative Electrode Graphite was used as the negative electrode active material. 92.0 g of this graphite was mixed with 8.0 g of polyvinylidene fluoride as a binder, and N-methylpyrrolidone was added to prepare a negative electrode mixture paste. This paste
A strip-shaped negative electrode sheet was produced by uniformly applying both surfaces of a current collector made of a copper foil having a thickness of 15 μm, and by the same method as the above positive electrode sheet. The total thickness of the negative electrode active material layer is 1 on both sides.
It was 80 μm.

3) Preparation of non-aqueous electrolyte solution Ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 to prepare a non-aqueous solvent. L, which is a lithium salt as an electrolyte, is added to this non-aqueous solvent.
iPF ₆ was added to a concentration of 1.2 mol / l to prepare a non-aqueous electrolytic solution.

4) Preparation of battery A positive electrode sheet, a separator, a negative electrode sheet and a separator are
The positive electrode lead and the negative electrode lead were laminated in this order with the end portions on the welded side on the same side, to obtain a laminated body. This laminated body was wound in an elliptical spiral shape around a polyethylene rectangular core as a center to manufacture a power generation element. A polyethylene microporous membrane was used as the separator.

The power generating element was housed in an iron prismatic battery case, and the positive electrode lead and the negative electrode lead were connected to respective terminals provided on the battery lid. Then, after the battery case and the lid are joined by laser welding, the non-aqueous electrolyte solution 5.4 prepared in 3) above is injected from the injection port provided in the battery lid.
ml was poured. Then, the liquid injection port was sealed. In this way, the outer dimensions are 34 mm wide, 67 mm high, and 6.
A rectangular non-aqueous electrolyte secondary battery (hereinafter referred to as battery A) having a nominal capacity of 1000 mAh with a size of 2 mm was produced.

3. Charge / Discharge Cycle Test A 10-cell battery A was subjected to a charge / discharge test at 25 ° C. under the following conditions. Charging was performed at a constant current of 1000 mA to 4.1 V, and at a constant voltage of 4.1 V for a total of 5 hours, and discharging was performed at a constant current of 1000 mA to 2.75 V. This charging / discharging was made into 1 cycle, and charging / discharging of 300 cycles was performed.

Example ₂ 91.0 g of LiCoO ₂ ,
6.0 g of polyvinylidene fluoride and 3.0 g of acetylene black were mixed and N-methylpyrrolidone was added to prepare a positive electrode mixture paste. A positive electrode sheet was produced in the same manner as in Example 1 using this paste. Graphite 9
2.0 g, polyvinylidene fluoride 8.0 g, and molecular sieve 3A 0.2 g were mixed, and N-methylpyrrolidone was added to prepare a negative electrode mixture paste. Using this paste, a strip-shaped negative electrode sheet was produced in the same manner as in Example 1. A battery (hereinafter, referred to as battery B) was manufactured and tested in the same manner as in Example 1 except for the above.

Comparative Example 1 The positive electrode sheet was the same as that in Example 2 and the negative electrode sheet was the same as in Example 1. A battery (hereinafter, referred to as battery C) was manufactured and tested in the same manner as in Example 1 except for the above.

<Results and Discussion> Table 1 shows the discharge capacity at the first cycle, the discharge capacity at the 300th cycle, and the discharge capacity retention rate of the batteries of Examples and Comparative Examples. Here, the "discharge capacity retention rate" is represented by the ratio (%) of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle. The data in Table 1 shows the average value of the measured values of 10 cells for each battery.

[0026]

[Table 1]

FIG. 1 shows a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity of each battery. In FIG. 1, symbol ● is battery A, symbol ■ is battery B,
The symbol ▲ indicates the battery C.

From Table 1 and FIG. 1, the discharge capacity retention rate of the battery A having the molecular sieve 3A in the positive electrode active material layer and the battery B having the molecular sieve 3A in the negative electrode active material layer was 90% or more. On the other hand, the discharge capacity retention rate of the battery C having no molecular sieve 3A in the battery case was 80% or less. Further, in comparison between Battery A and Battery B, it was found that the discharge capacity retention rate was higher in Battery A, and it is most preferable that the molecular sieve 3A is arranged in the positive electrode active material layer.

As is clear from the above results, the battery case is provided with a porous body in which pores having a pore size capable of allowing the entry of water molecules and restricting the entry of molecules larger than water molecules are formed. As a result, this porous body absorbs water,
Generation of a fluorine compound can be suppressed, and a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity for batteries of Examples and Comparative Examples.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5H029 AJ07 AK03 AL07 AM03 AM05                       AM07 CJ08 DJ08 DJ13 DJ16                       HJ06                 5H050 AA13 BA17 CA08 CB08 DA02                       DA15 EA14 FA13 FA17 GA10                       HA06

Claims (3)

[Claims] 1. A non-aqueous electrolyte comprising a positive electrode, a negative electrode, a non-aqueous electrolytic solution prepared by dissolving an electrolyte in a non-aqueous solvent, and a battery case accommodating the positive electrode, the negative electrode and the non-aqueous electrolytic solution. A secondary battery, wherein the battery case is provided with a porous body in which pores having a pore size capable of allowing the entry of water molecules while restricting the entry of molecules larger than the water molecules are formed. A non-aqueous electrolyte secondary battery characterized by: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the porous body is a synthetic zeolite. 3. The positive electrode includes a current collector formed of aluminum and a positive electrode active material layer formed on the surface of the current collector, and the porous body is arranged in the positive electrode active material layer. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is provided.