JPH04349369A - Cylindrical nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a lithium secondary battery having an extended charge- discharge cycle life by suppressing concentrated generation of dendrite on the peripheral part in a negative pole-like shape. CONSTITUTION:In a nonaqueous electrolyte secondary battery consisting of a group of pole plates and a nonaqueous electrolyte sealed in a container wherein the group of the pole plates consist of a negative pole 3 using metal lithium as its active substance and a positive pole. 1 and they are rolled spirally while having a separator 2 interposed between them, the width of the positive pole 1 is made wider than that of the negative pole 3 and an electrically insulating material 4 insoluble in the electrolyte is applied to the peripheral part of the positive pole electrode surface where the positive pole 1 can not face to the negative pole 3, so that concentrated generation of dendrite in the peripheral part of the negative pole is suppressed. Thus dendrite generation along the anode periphery is suppressed, and a lithium secondary battery having a long charge-discharge cycle life can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical nonaqueous electrolyte secondary battery, and more particularly to a cylindrical nonaqueous electrolyte secondary battery using metallic lithium as a negative electrode active material.

0002

[Prior Art] In a battery that uses metallic lithium as the negative electrode active material and a non-aqueous electrolyte as the electrolyte, in order to increase the electrode area and improve battery characteristics during large current discharge, the positive electrode plate and the negative electrode plate are layered through a separator and rolled into a spiral,
A battery is configured. Furthermore, extremely thin separators (thickness 20 to 50 μm) are used to increase the battery capacity and shorten the distance between the electrodes to improve the discharge reaction.

0003

[Problems to be Solved by the Invention] However, many problems still remain in the non-aqueous electrolyte secondary battery using metallic lithium as the negative electrode active material. One of them is the short charge/discharge cycle life due to deterioration of the negative electrode plate. this is,
Lithium, which is the negative electrode active material, precipitates in the form of dendrites on the negative electrode during charging, penetrates the separator, or climbs over the edge of the separator and comes into contact with the positive electrode, causing an internal short circuit. In particular, current concentration tends to occur around the electrode plate, and the resulting increase in current density tends to generate dendrites.

[0004] In order to prevent the dendrites generated around the electrode plate from climbing over the separator, it is disclosed in Japanese Patent Application Laid-Open No. 1-1283.
No. 71 discloses making the width of the negative electrode plate larger than the width of the positive electrode plate. In particular, it is said that it is preferable to increase the size by 0.5 to 2.0 mm on one side.

However, when the width of the negative electrode plate is made wider than that of the positive electrode plate, the following new risk of internal short circuit occurs. This danger is that if even a small amount of force is applied to the electrode plate during winding, the edge of the positive electrode plate will dig into the separator, making it easy to tear it. This is a particularly serious problem when thin separators are used to increase battery capacity.

[0006]

[Means for Solving the Problems] The present invention has been made to solve these problems. A cylindrical non-aqueous electrolyte in which a negative electrode containing metallic lithium as an active material and a positive electrode are placed in a container with a separator interposed between them, a group of spirally wound electrode plates, and a non-aqueous electrolyte sealed in a container. In a secondary battery, the width of the positive electrode is made larger than the width of the negative electrode, and an electrically insulating substance that is insoluble in the electrolyte is applied to the periphery of the positive electrode surface where the positive electrode no longer faces the negative electrode. This can prevent dendrites generated around the negative electrode plate from climbing over the edge of the separator and coming into contact with the positive electrode, and can also prevent the edge of the positive electrode plate from breaking the separator.

FIG. 1 is a cross-sectional view showing the structure of a cylindrical non-aqueous electrolyte secondary battery. It has a structure in which it is provided facing the negative electrode 3, and
This is wound into a spiral shape to form a cylindrical structure. The structure is such that the electrode plate group and the non-aqueous electrolyte are sealed in a container C column.

In the present invention, the width of the positive electrode 1 is larger than the width of the negative electrode 3, as shown in the main part in FIG. It has a structure in which a chemical substance 4 (for example, EDPM) is provided.

By making the width of the positive electrode larger than the width of the negative electrode, the edge of the positive electrode plate will not dig into the negative electrode. At this time, it is conceivable that the edge of the negative electrode plate may bite into the positive electrode plate. However, negative electrode plates that use lithium as the negative electrode active material are usually metal lithium plates or aluminum and lithium alloy plates, so they are extremely soft and unlikely to damage the separator. It is certain that the negative electrode plate is less likely to damage the separator than the stainless steel plate that is often used as the positive electrode plate substrate material.

[0010] Furthermore, by applying an electrically insulating substance that is insoluble in the electrolytic solution to the peripheral part of the positive electrode surface where the positive electrode cannot face the positive electrode, current concentration in the peripheral part of the electrode can be prevented. It can be expected to suppress the occurrence of dendrites in the area.

Furthermore, by coating an electrically insulating substance that is insoluble in the electrolytic solution, when the negative electrode plate is sandwiched between the positive electrode plates from above and below in the thickness direction via a separator, the area near the edge of the negative electrode plate is electrolyzed. It is wrapped in a material that is insoluble in the liquid and electrically insulating, so even if dendrites were to occur, it would be almost impossible for the dendrites to break through this material and touch the positive electrode.

In order to make the width of the positive electrode wider than the width of the negative electrode, it is sufficient to make at least one side of the electrode as wide as the thickness of the negative electrode. When the difference in width between the positive electrode and the negative electrode is small, an electrically insulating substance that is insoluble in the electrolytic solution may be applied in a heaping manner to areas around the positive electrode that cannot face the negative electrode. From the viewpoint of workability, it is desirable to ensure that the difference in width between the positive electrode and the negative electrode on one side of the electrode is equal to or larger than the thickness of the negative electrode. However, making the width of the positive electrode plate unnecessarily wider than that of the negative electrode plate is not desirable because it narrows the portion of the positive electrode plate that faces the negative electrode plate, that is, the area that effectively acts as the electrode of the battery.

[0013] The thickness of the above substance is preferably 1/2 or more of the thickness of the negative electrode. This is because if it is less than 1/2, current concentration in the peripheral area of the electrode is prevented, and there is a possibility that the effect of suppressing the generation of dendrites in this area may not be exhibited.

[0014] Here, many substances can be used as the substance that is insoluble in the electrolytic solution and has electrical insulation properties. For example, it may be an organic polymer such as ethylene propylene terpolymer (EPDM). All you need to do is dissolve it in a volatile organic solvent, apply it to areas around the positive electrode that cannot face the negative electrode, and then dry it. If the thickness after drying is less than half of the thickness of the negative electrode, the EPDM may be raised by repeating coating and drying. Or, if you want to reduce the number of repetitions of coating and drying,
What is necessary is to increase the amount of EPDM dissolved in the organic solvent. Also,
An adhesive resin tape such as cellophane tape having a thickness of about one-half or more than the thickness of the negative electrode may be attached to the area around the positive electrode that cannot face the negative electrode. There are no particular limitations on materials or methods.

[0015]

[Function] Negative electrode 3 with metallic lithium as active material and positive electrode 1
This is a non-aqueous electrolyte secondary battery in which a group of electrode plates wound in a spiral with a separator 2 interposed therebetween and a non-aqueous electrolyte are sealed in a container C, and the width of the positive electrode 1 is By making the width of the negative electrode larger than the width of the negative electrode 3 and applying an electrically insulating substance 4 that is insoluble in the electrolytic solution to the periphery of the positive electrode surface where the positive electrode 1 cannot face the negative electrode 3, the periphery of the negative electrode shape is Intensive generation of dendrites in the area is suppressed. By suppressing the generation of dendrites, a lithium secondary battery with an extended charge/discharge cycle life can be obtained.

[0016]

EXAMPLES Next, the present invention will be explained in detail using preferred examples.

In the following test, a cylindrical lithium secondary battery having the configuration shown below was prepared and used for the test.

Positive electrode: amorphous vanadium pentoxide powder + ethylene propylene terpolymer (EPDM)
A mixture of 2.5 wt% cyclohexane solution + acetylene black (weight ratio 90:3:7) was applied onto a metal current collector (made of stainless steel) with a width of 38 mm and dried.

Negative electrode: Metal lithium (width 36 mm, thickness 0
．． 15mm)

Electrolyte: 1.5M concentration of lithium hexafluoroarsenate (LiAsF6) in ethylene carbonate (EC)
/2 methyltetrahydrofuran (2MeTHF) (volume ratio 1/1) solution

Separator: 25 μm thick polypropylene porous membrane

[0022] Atmosphere: Argon

The completed battery has a discharge current of 3 mA/c
m2, constant current of charging current 0.5 mA/cm2, 1.
Charge and discharge cycles were repeated within the voltage range of 8-3.3V.

[0024]

Example 1 Before assembling a battery, a cyclohexane solution containing 15 wt % ethylene propylene terpolymer (EPDM) was coated on both sides of the positive electrode plate in a width of 1 mm to frame the positive electrode plate and dried. The thickness of the EPDM after drying was approximately 80 μm on one side. Thereafter, the negative electrodes were stacked with a separator in between and wound in a spiral shape, and then inserted into a container and an electrolytic solution was injected to complete Battery A.

[0025]

[Comparative Example 1] A battery B similar to Example 1 was completed except that the cyclohexane solution of EPDM was not applied around the positive electrode plate.

FIG. 3 shows the relationship between the number of charge/discharge cycles and the utilization rate of the positive electrode when the initial capacity is 100% for the batteries A and B.

As is clear from FIG. 3, the charge/discharge cycle life of the battery is extended by implementing the present invention.

When the discharge capacity of each battery was reduced to half, the battery was disassembled and the surface of the negative electrode was observed using an electron microscope. Almost no dendrites were generated around the negative electrode of battery A, whereas many dendrites were generated around the negative electrode of battery B.

[0029]

[Effects of the Invention] As is clear from the above results, a negative electrode containing metallic lithium as an active material and a positive electrode are arranged in a spirally wound electrode group with a separator interposed therebetween, and a non-aqueous electrolyte. is a non-aqueous electrolyte secondary battery sealed in a container, the width of the positive electrode is larger than the width of the negative electrode, and the electrolyte is placed around the positive electrode surface where the positive electrode no longer faces the negative electrode. By applying an electrically insulating substance that is insoluble in the negative electrode, the generation of dendrites around the negative electrode can be suppressed, making it possible to obtain a lithium secondary battery with a long charge-discharge cycle life. Therefore, its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of an example of a non-aqueous electrolyte lithium secondary battery according to the present invention.

FIG. 2 is a detailed longitudinal cross-sectional view of a portion of the spiral electrode group inside the battery shown in FIG. 1;

FIG. 3 is a diagram showing the relationship between the number of charge/discharge cycles and the positive electrode utilization rate when the initial capacity is 100% in non-aqueous electrolyte lithium secondary batteries according to examples and comparative examples of the present invention.

[Explanation of symbols]

1 Positive electrode 2 Separator 3 Negative electrode 4. Material (EPDM) C Container

Claims (2)

[Claims] Claim 1: A cylinder in which a negative electrode containing metallic lithium as an active material and a positive electrode are arranged in a spiral shape with a separator interposed therebetween, and a non-aqueous electrolyte is sealed in a container. type non-aqueous electrolyte secondary battery, the width of the positive electrode is made larger than the width of the negative electrode, and a periphery of the positive electrode surface where the positive electrode cannot face the negative electrode is insoluble in the electrolyte and electrically insulating. A cylindrical non-aqueous electrolyte secondary battery coated with a chemical substance. 2. The cylindrical non-aqueous electrolyte secondary battery according to claim 1, wherein the electrolyte-insoluble and electrically insulating substance is ethylene propylene terpolymer (EPDM).