JP2000040499A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a battery which suppresses a decrease in charge / discharge cycle life due to depletion of an electrolytic solution due to charge / discharge. SOLUTION: In a non-aqueous electrolyte secondary battery using a rechargeable positive electrode and negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte, a metal carbonate particle or a metal oxide particle has a positive electrode plate. A microporous polyolefin membrane fixed to a surface in contact with at least one of the first and negative electrode plates 3 is used as the separator 5.

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 thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices such as personal computers and mobile phones have been rapidly becoming smaller and lighter and cordless.
A secondary battery having a high energy density is required as a power source for these drives. Among them, a non-aqueous electrolyte secondary battery using lithium as an active material is particularly expected as a battery having a high voltage and a high energy density. Conventionally, this battery uses metallic lithium for the negative electrode, molybdenum disulfide, manganese dioxide, vanadium pentoxide, etc. for the positive electrode,
A three-volt battery was realized.

However, when lithium metal is used for the negative electrode, dendritic lithium called dendrite is deposited during charging, and the dendritic lithium deposited on the electrode plate is separated from the electrode plate during repetition of charge and discharge. It floats in the liquid and contacts the positive electrode, causing a micro short circuit, and the charge and discharge efficiency is 1
Therefore, the cycle life is shortened. In addition, dendritic lithium has a large surface area and high reactivity, and thus has a problem in terms of safety.

Therefore, recently, instead of metallic lithium,
Lithium ion secondary batteries using carbon materials for the negative electrode and lithium-containing oxides for the positive electrode have been the focus of research, and some have been commercialized. In this battery, since lithium exists in the negative electrode as occluded ions in carbon,
It is considered to be very safe without any problems as in the conventional lithium metal system.

[0005]

On the other hand, the lithium-containing oxide used for the positive electrode of this battery system has a high potential of 4 volts relative to lithium. For this reason, the organic solvent in the electrolyte is more likely to be oxidized and decomposed than the conventional 3 volt-class lithium secondary battery, and the electrolyte is depleted with charge and discharge, which may cause a reduction in the charge and discharge cycle life. In addition, carbon used for the negative electrode, particularly graphite, has high reactivity with the electrolytic solution, and also in this case, the electrolytic solution may be depleted, and the charge-discharge cycle life characteristics may be significantly reduced.

An object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a non-aqueous electrolyte secondary battery having particularly excellent charge-discharge cycle life characteristics.

[0007]

In order to solve the above-mentioned problems, a non-aqueous electrolyte secondary battery according to the present invention comprises a metal carbonate particle or a metal oxide particle having a surface in contact with at least one of a positive electrode and a negative electrode. Is used as a separator. According to the above configuration, since the separator has irregularities, a large amount of the electrolyte can be retained in a gap formed between the positive electrode or the negative electrode plate and the separator, and gas generation or film formation in the electrolyte and the positive electrode or the negative electrode can be performed. It is possible to provide a battery in which the depletion of the electrolytic solution due to the irreversible reaction is suppressed and the battery has excellent charge / discharge cycle life characteristics.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention uses a microporous polyolefin membrane in which metal carbonate particles or metal oxide particles are fixed on a surface in contact with at least one of a positive electrode and a negative electrode as a separator. Preferably, any one of calcium carbonate, magnesium carbonate, barium carbonate, and strontium carbonate particles is used for metal carbonate particles, and any one of calcium oxide, magnesium oxide, aluminum oxide, and cobalt oxide particles is used for metal oxide particles. Things. The particle diameter of the metal carbonate particles or metal oxide particles is preferably 2 μm or more and 30 μm or less. With such a configuration, since the separator has irregularities, a large amount of the electrolytic solution can be retained in a gap formed between the positive electrode or the negative electrode and the separator, and gas generation between the electrolytic solution and the positive electrode or the negative electrode can be achieved. Alternatively, it is possible to provide a battery having excellent charge / discharge cycle life characteristics in which the depletion of the electrolytic solution due to the irreversible reaction due to the formation of a film is suppressed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Embodiment 1 FIG. 1 shows a longitudinal section of a cylindrical lithium ion secondary battery of the present invention. This lithium ion secondary battery was manufactured as follows.

In FIG. 1, a positive electrode plate 1 is made of lithium cobalt oxide (LiCoO ₂ ) as an active material, mixed with 3% by weight of acetylene black as a conductive material, and then used as an aqueous solution of polytetrafluoroethylene resin as a binder. A mixture obtained by kneading the dispersion by 7% by weight into a paste is applied to both surfaces of a current collector made of aluminum foil, dried and rolled. The positive electrode lead plate 2 is spot-welded to its end.

The negative electrode plate 3 is made of graphite as an active material, and a mixture obtained by kneading a 3% by weight aqueous dispersion of styrene / butadiene rubber as a binder into a paste is applied to both sides of a copper foil current collector. Coated, dried and rolled. A negative electrode lead plate 4 is spot-welded to an end of the negative electrode plate 3.

As the separator 5, a separator made of a polyethylene separator having a thickness of 30 μm and calcium carbonate particles having a particle diameter of 0.5 μm fixed on one side was used. Then, the negative electrode plate 3, so that the rough surface of the separator faces the positive electrode,
The separator 5 and the positive electrode plate 1 were spirally wound to form an electrode body (electrode plate group).

Next, the upper and lower portions of the electrode plate group were heated with warm air to thermally shrink the separator 5. Then, the bottom insulating plate 6 was attached to the lower side of the electrode plate group, housed in the battery case 7, and the negative electrode lead plate 4 was spot-welded to the battery case 7. An upper insulating plate 8 is mounted on the upper side of the electrode plate group, and a battery case 7 is provided.
After grooving at the top of the sample, a non-aqueous electrolyte was injected. As the non-aqueous electrolyte, a solution prepared by dissolving lithium hexafluorophosphate in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed was used. After the assembly sealing plate 9 in which the gasket was previously incorporated and the positive electrode lead plate 2 were laser-welded, the assembly sealing plate 9 was attached to the battery case 7 and the battery was assembled by caulking and sealing. The dimensions of this battery are 16 m outside diameter
m, total height 50 mm.

(Examples 2 to 10) The same procedure as in Example 1 was carried out except that the particle size of calcium carbonate fixed on one surface of a polyethylene separator having a thickness of 30 μm was changed to a value shown in Table 1. The batteries of Examples 2 to 10 were produced.

Comparative Example A comparative example battery was produced in the same manner as in Example 1 except that a separator having a thickness of 30 μm made of polyethylene and not fixing calcium carbonate particles was used.

[0017]

[Table 1]

Each of the batteries of Examples 1 to 10 and the battery of the comparative example were prepared in a quantity of 5 cells each, and were charged and discharged at 20 ° C. for 2 hours with a maximum current of 500 mA and a final voltage of 4.2 volts. Current 700 mA, discharge end voltage 3.0
After repeating charge and discharge of these batteries for 4 cycles under the condition of constant current discharge of volts, charge and discharge were performed at a discharge current of 140 mA in the fifth cycle, a discharge current of 1400 mA in the sixth cycle, and again in the seventh and subsequent cycles. The charge and discharge were repeated with a discharge current value of 700 mA. The capacity ratio of these batteries at a discharge current of 1400 mA (discharge capacity / discharge current value of 140 at a discharge current value of 1400 mA)
Table 2 shows the average value of the discharge capacity at the time of mA × 100) and the average value of the number of cycles at the time when the discharge capacity at the fourth cycle was reduced to half of the initial capacity.

[0019]

[Table 2]

From the results shown in Table 2, the batteries of Examples 1 to 10 all had an increased cycle life as compared with the batteries of Comparative Example. Also, the cycle life increased as the particle size of the calcium carbonate particles increased. This is because unevenness is formed on the separator, so that a large amount of electrolyte can be retained in the gap formed between the positive electrode plate and the separator, and irreversible due to gas generation or film formation between the electrolyte and the positive electrode This is because the depletion of the electrolyte due to the reaction can be suppressed.

However, in Examples 1 and 2, the cycle life was not significantly increased as compared with Examples 3 to 10. this is,
Since the separator does not have sufficient unevenness with the particle size of the calcium carbonate particles, a large amount of the electrolyte cannot be retained in a gap formed between the positive electrode plate and the separator, and the depletion of the electrolyte is suppressed. Because they cannot do it. Therefore, in order to improve the charge / discharge cycle life characteristics, it is necessary to use a separator on which calcium carbonate particles having a particle diameter of 2 μm or more are fixed.

Further, the batteries of Examples 9 and 10 show sufficient characteristics regarding the cycle life,
The capacity ratio at a discharge current of 1400 mA is significantly lower than the others. This is because the distance between the positive electrode plate and the negative electrode plate increases as the particle size of the calcium carbonate particles increases. That is, the ionic conductivity of the organic solvent is small, and in the case of large current discharge, the movement of lithium ions in the electrolyte is rate-determining. If the distance between the positive electrode plate and the negative electrode is too large, large current discharge becomes difficult to perform. Furthermore, if the particle size is too large, the ratio of the positive electrode and the negative electrode in the battery decreases because the thickness of the separator becomes too thick,
This leads to a decrease in battery capacity. For this reason, when the particle diameter is 40 μm or more, the charge / discharge cycle life characteristics are satisfied. However, in consideration of large current discharge and other characteristics, the particle diameter of the calcium carbonate particles is preferably 30 μm or less.

In this embodiment, the case where the calcium carbonate particles are fixed to the severator on the surface facing the positive electrode has been described. The same effect was obtained within the scope of the present invention even when fixed to. Similar effects were obtained within the scope of the present invention when the particles to be fixed were magnesium carbonate, barium carbonate, strontium carbonate, calcium oxide, magnesium oxide, aluminum oxide, and cobalt oxide. Further, in the examples, the case where polyethylene was used as the separator was shown, but the same effect was obtained within the scope of the present invention by using other polyolefin microporous membranes.

[0024]

As described above, the present invention is characterized in that a microporous polyolefin membrane in which metal carbonate particles or metal oxide particles are fixed to a surface in contact with at least one of a positive electrode and a negative electrode is used as a separator. By configuring the battery using such a separator, a large amount of electrolyte can be retained in a gap formed between the positive electrode plate or the negative electrode plate and the separator because unevenness is formed on the separator, and the electrolyte and It is possible to provide a battery having excellent charge-discharge cycle life characteristics in which the depletion of the electrolytic solution due to irreversible reaction caused by gas generation or film formation of the positive electrode or the negative electrode is suppressed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Positive electrode lead plate 3 Negative electrode plate 4 Negative electrode lead plate 5 Separator 6 Bottom insulating plate 7 Battery case 8 Upper insulating plate 9 Assembly sealing plate

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masanori Kitagawa 1006 Kadoma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. F term (reference) 5H021 CC00 CC03 EE04 EE22 HH03 5H029 AJ05 AK03 AL07 AM03 AM05 AM06 BJ02 BJ14 DJ04 DJ13 DJ16 EJ05 EJ12 HJ05

Claims (4)

[Claims] In a non-aqueous electrolyte secondary battery using lithium as an active material, a rechargeable positive electrode and a negative electrode via a separator, and using a non-aqueous solvent as an electrolyte, metal carbonate particles or A non-aqueous electrolyte secondary battery using a microporous polyolefin membrane, in which metal oxide particles are fixed to a surface in contact with at least one of a positive electrode and a negative electrode, as a separator. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal carbonate is any one of calcium carbonate, magnesium carbonate, barium carbonate, and strontium carbonate. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal oxide is any one of calcium oxide, magnesium oxide, aluminum oxide, and cobalt oxide. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the particle size of the metal carbonate or metal oxide is 2 μm or more and 30 μm or less.