JPH06231745A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a good battery properly and high safety by forming a separator of the predetermined size polyethylene microporous membrane. CONSTITUTION:A positive electrode 1 and a negative electrode 2 are stored inside a negative electrode can 7 via a separator 3, to which a non-aqueous electrolyte is injected. The separator 3 consists of a polyethylene microporous membrane which is 20-40mum in the thickness and 0.20-0.40mum in the greatest pore diameter. A carbon material, which can store a lithium ion, or a metal oxide is used for the negative electrode 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a separator in a non-aqueous electrolyte secondary battery using a carbon material or a metal oxide capable of inserting and extracting lithium ions in the negative electrode. Regarding the improvement of.

[0002]

2. Description of the Related Art In the case of a non-aqueous electrolyte secondary battery using lithium metal or a lithium alloy as a negative electrode material, repeated charging and discharging results in dendrite (dendritic charge) on the negative electrode. Lithium deposited) is generated. When this dendrite penetrates the separator, both positive and negative electrodes are short-circuited.
Called. ), The cycle life becomes shorter. There is also a risk of fever.

In order to prevent this dendrite short circuit, it is necessary to use a separator which is thick and has a small maximum pore size and is tough. Therefore, in the conventional non-aqueous electrolyte secondary battery, the thickness of the separator is 50
A polypropylene microporous membrane having a pore size of not less than μm and a maximum pore size of not more than 0.10 μm is used.

On the other hand, in the case of the non-aqueous electrolyte secondary battery of the present invention, which uses a carbon material or a metal oxide as a negative electrode material, the negative electrode material is merely a host which absorbs and releases lithium ions in the electrode reaction. , Do not generate dendrites.

However, conventionally, also in the battery of this system, the same separator as that described above was used without distinction.

The inventors of the present invention have made extensive studies and found that it is meaningless to use a polypropylene microporous membrane having a thickness of 50 μm or more and a maximum pore diameter of 0.10 μm or less in the battery of this system. However, it was found that there is a problem in terms of battery characteristics such as high rate discharge characteristics and reliability (safety).

The present invention was made on the basis of such findings, and an object thereof is to provide a non-aqueous electrolyte secondary battery having excellent battery characteristics and high reliability (safety). is there.

[0008]

A non-aqueous electrolyte secondary battery according to the present invention (hereinafter, sometimes referred to as "the present battery") for achieving the above object comprises a positive electrode and lithium ion. In a non-aqueous electrolyte secondary battery comprising a negative electrode made of a carbon material or a metal oxide capable of storing and releasing, and a separator that separates the positive and negative electrodes from each other, the separator has a thickness of 20 to 40 μm and a maximum pore diameter of 0. 20-0.
It consists of a 40 μm polyethylene microporous membrane.

In the battery of the present invention, a polyethylene microporous membrane having the above-mentioned specific thickness and maximum pore size is used as the separator.

The reason why the thickness and the maximum pore size of the separator are restricted to the ranges of 20 to 40 μm and 0.20 to 0.40 μm, respectively, is that when the thickness is less than 20 μm or when the maximum pore size exceeds 0.40 μm, the powder. This is because a short circuit is likely to occur, and when the thickness exceeds 40 μm or the maximum pore size is less than 0.20 μm, the internal resistance due to the separator increases and the discharge capacity, especially the high rate discharge capacity, is drastically reduced. Here, the powder short circuit means that a protrusion (a powder made of carbon powder or active material powder and having a diameter of about 10 μm) existing on the surface of the electrode penetrates the separator to cause a short circuit. By the way, when making electrodes,
Although care is taken to prevent such protrusions from forming, the protrusions are still generated on the surface of the electrode quite frequently in the method of producing an electrode by coating on the current collector.

The reason why the material of the separator is specified as polyethylene is that in order to prevent the battery temperature from rising abnormally and ensure safety, it melts before reaching an abnormally high temperature and becomes porous. This is because clogging is preferable, and in this respect, polyethylene having a low melting point is considered to be preferable to polypropylene having a high melting point. Polyethylene is generally weaker in strength than polypropylene, but since no dendrite is produced in the battery of the present invention, there is no practical problem.

A carbon material or a metal oxide capable of inserting and extracting lithium ions is used for the negative electrode in the battery of the present invention.

Preferred examples of the carbon material include graphite and coke, and examples of the metal oxide include iron oxide, tungsten oxide and niobium oxide. These negative electrode materials are usually kneaded with a binder and, if necessary, a conductive agent and used as a negative electrode mixture.

In order to improve the battery characteristics and safety of a non-aqueous electrolyte secondary battery using a carbon material or a metal oxide capable of occluding and releasing lithium ions as a negative electrode, the present invention is a separator having a thickness, a maximum pore diameter and a material. The present invention has the greatest feature in that it is improved. Therefore, other members in the battery of the present invention, such as the positive electrode and the non-aqueous electrolyte, are not particularly limited.

For example, as the positive electrode active material, modified Mn
O ₂ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , L
Various materials that have been conventionally proposed or put into practical use for non-aqueous electrolyte secondary batteries, such as iMn ₂ O ₄ , can be used.

[0016]

In the battery of the present invention, since a polyethylene microporous membrane having a thickness and a maximum pore size within a specific range is used as a separator, it is excellent in battery characteristics such as high rate discharge characteristics and powder short circuit occurs. Hateful. In addition, polyethylene melts before the battery temperature rises abnormally, causing clogging, so that abnormal heat generation is less likely to occur as compared with a battery using a polypropylene separator.

[0017]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

(Production Examples 1 to 12) AA type non-aqueous electrolyte secondary batteries (cells of the present invention) were produced.

[Positive electrode] LiCoO ₂ as a positive electrode active material
A acetylene black as a conductive agent and a fluororesin dispersion as a binder in a weight ratio of 90:
The mixture was mixed at 6: 4 to obtain a positive electrode mixture. Then, this positive electrode mixture is applied to an aluminum foil as a current collector, and then 25
A vacuum heat treatment was performed at 0 ° C. for 2 hours to produce a positive electrode.

[Negative Electrode] Fluororesin dispersion as a binder was mixed with graphite powder of 400 mesh pass at a weight ratio of 95: 5 to obtain a negative electrode mixture. Next, this negative electrode mixture was applied to a copper foil as a current collector, and then 250
A negative electrode was prepared by vacuum heat treatment at ° C for 2 hours.

[Non-Aqueous Electrolyte] LiPF 6 was added to an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.
₆ was dissolved at a ratio of 1 mol / liter to prepare a non-aqueous electrolyte solution.

[Separator] Maximum pore size is 0.05 μm
And only the thickness is 20, 30, 40, 50, 60, 70μ
A microporous membrane made of polyethylene or polypropylene different from m was used.

[Production of Battery] A non-aqueous electrolyte secondary battery PE using the positive and negative electrodes, non-aqueous electrolyte and separator described above.
1 to PE6 (batteries using a polyethylene microporous membrane for the separator. The larger the battery number, the thicker the separator thickness) and PP1 to PP6 (batteries using the polypropylene microporous membrane for the separator. Larger number The thickness of the separator is thicker).

FIG. 1 shows the produced non-aqueous electrolyte secondary battery PE.
1 is a cross-sectional view schematically showing the battery 1 shown in FIG.
It comprises a positive electrode 1, a negative electrode 2, a separator 3 separating these two electrodes, a positive electrode lead 4, a negative electrode lead 5, a positive electrode external terminal 6, a negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a state of being spirally wound via the separator 3 in which the non-aqueous electrolyte solution is injected, and the positive electrode 1 is externally connected to the positive electrode via the positive electrode lead 4. The terminal 6 and the negative electrode 2 are connected to the negative electrode can 7 via the negative electrode lead 5 so that chemical energy generated inside the battery can be taken out as electric energy to the outside.

(Production Examples 13 to 24) Non-aqueous electrolyte secondary batteries PE7 to PE12 and PP7 were produced in the same manner as in Production Examples 1 to 12 except that lithium metal foil was used for the negative electrode.
-PP12 was produced.

[Cycle Life of Each Battery] A cycle test is conducted in which one cycle includes a step of charging to a final charge voltage of 4.1 V at 200 mA and then discharging to a final discharge voltage of 2.75 V at 200 mA. The cycle life of each battery manufactured in 1. was examined. The cycle life (times) was evaluated by the total number of cycles until the discharge capacity decreased to 50% of the initial discharge capacity. The results are shown in Figure 2.

FIG. 2 is a graph showing the relationship between the thickness of the separator and the cycle life, and is a graph showing the cycle life (times) on the vertical axis and the thickness (μm) of the separator on the horizontal axis.

From the figure, when graphite is used for the negative electrode,
Although there is no significant difference in cycle life even if the thickness and material of the separator is different, when lithium metal is used for the negative electrode, the cycle life becomes longer as the thickness of the separator becomes thicker, and the separator made of polypropylene and When compared with a polyethylene separator, it can be seen that the polypropylene separator generally has a longer cycle life. The latter reason is that in a battery of a system that produces dendrites, a dendrite short circuit is less likely to occur when a polypropylene separator having high strength is used.

(Production Examples 25 to 31) As a separator,
Maximum pore size is 0.05μm, thickness is only 10, 15, 2
Non-aqueous electrolyte secondary batteries PE13 to PE19 were produced in the same manner as in Production Examples 1 to 12 except that a polyethylene microporous membrane different from 0, 30, 40, 45, and 50 μm was used.

[Discharge Capacity of Each Battery and Probability of Short Circuit Immediately after Battery Preparation] For each battery, 200 mA and 1000
The discharge capacity when discharged at mA and the short-circuit probability immediately after the battery was manufactured were examined. The short-circuit probability is a value calculated from the data for 1000 batteries. The results are shown in Fig. 3.

FIG. 3 is a diagram showing the relationship between the thickness of the separator and the discharge capacity and the short circuit probability. The left vertical axis and the right vertical axis respectively show the discharge capacity (mAh) and the short circuit probability (%).
Further, it is a graph in which the thickness (μm) of the separator is plotted on the horizontal axis.

From FIG. 3, in the case of 200 mA discharge, the discharge capacity hardly decreases due to the increase in the thickness of the separator, whereas in the case of 1000 mA discharge (high rate discharge),
It can be seen that when the thickness of the separator exceeds 40 μm, the discharge capacity decreases to 400 mAh or less.

From the figure, the thickness of the separator is 20
It can be seen that when the thickness is not less than μm, the short-circuit probability is zero or almost zero, whereas when the thickness of the separator is less than 20 μm, powder short-circuit occurs, and the short-circuit probability increases.

(Production Examples 32 to 39) As a separator,
The thickness is 30 μm and only the maximum pore size is 0.05, 0.1,
0.15, 0.2, 0.3, 0.4, 0.45, 0.5
Non-aqueous electrolyte secondary batteries PE20 to PE27 were produced in the same manner as in Production Examples 1 to 12 except that a polyethylene microporous membrane different from μm was used.

[Discharge Capacity of Each Battery and Probability of Short Circuit Immediately after Battery Preparation] For each battery, 200
The discharge capacity when discharged at mA and 1000 mA and the short-circuit probability immediately after the battery was manufactured were examined. The results are shown in Fig. 4.

FIG. 4 is a graph showing the relationship between the maximum pore size of the separator and the discharge capacity and the short circuit probability. The left vertical axis and the right vertical axis respectively show the discharge capacity (mAh) and the short circuit probability (%).
And the maximum pore diameter (μm) of the separator is plotted on the horizontal axis.

From FIG. 4, in the case of 200 mA discharge, the discharge capacity hardly decreases due to the decrease in the maximum pore size of the separator, whereas in the case of 1000 mA discharge (high rate discharge), the maximum pore size of the separator is 0.2 μm. It can be seen that the discharge capacity is remarkably reduced when it is less than 1.

From the figure, when the maximum pore size of the separator is 0.40 μm or less, the short-circuit probability is zero or almost zero, whereas the maximum pore size of the separator is 0.40.
It can be seen that when the thickness exceeds μm, a powder short circuit occurs, so that the short circuit probability increases.

In summary, in a battery that does not generate dendrites by repeated charging and discharging, the thickness is 20
It is understood that when a polyethylene microporous film having a pore size of ˜40 μm and a maximum pore size of 0.20 to 0.40 μm is used as the separator, an excellent high rate discharge property and a property balance of prevention of powder short circuit are realized.

In the above examples, the non-aqueous electrolyte secondary battery using graphite for the negative electrode has been described as an example, but metal oxides such as iron oxide, tungsten oxide, niobium oxide capable of occluding and releasing lithium can be used. Even when a product or coke is used for the negative electrode, the same excellent effect can be obtained.

[0041]

In the battery of the present invention, since the separator having the specific thickness and the maximum pore size is used, the high rate discharge characteristic is excellent and the powder short circuit hardly occurs. In addition, since the material of the separator is polyethylene, when the battery temperature rises to some extent, the separator melts and causes clogging, and as a result, the battery reaction stops, so the battery temperature does not rise abnormally and reliability is improved. (Safety) is high. As described above, the present invention has excellent unique effects.

[Brief description of drawings]

FIG. 1 is a sectional view of an AA battery of the present invention.

FIG. 2 is a relationship diagram between a separator thickness and a cycle life.

FIG. 3 is a relationship diagram of a thickness of a separator, a discharge capacity, and a short circuit probability.

FIG. 4 is a relationship diagram of the maximum pore size of the separator, the discharge capacity, and the short circuit probability.

[Explanation of symbols]

 PE1 battery of the present invention 1 positive electrode 2 negative electrode 3 separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nishio 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Denki Within the corporation

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode using a carbon material or a metal oxide capable of inserting and extracting lithium ions, and a separator separating the positive and negative electrodes from each other. Separator thickness is 20-4
A non-aqueous electrolyte secondary battery comprising a polyethylene microporous membrane having a pore size of 0 μm and a maximum pore size of 0.20 to 0.40 μm. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon material is graphite or coke. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal oxide is iron oxide, tungsten oxide or niobium oxide.