Electrode assembly for secondary battery and method for fabricating the same

Abstract

A roll electrode assembly of a secondary battery includes a positive electrode rolled having a plurality of turns, a negative electrode rolled having a plurality of turns, and first and second separators each rolled to have a plurality of turns. Each turn of the first separator is disposed between each outer surface of the turns of the negative electrode and each inner surface of the turns of the positive electrode. Each turn of the second separator is disposed between each outer surface of the turns of the positive electrode and each inner surface of the turns of the negative electrode. The thickness of the second separator is thinner than that of the first separator.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a secondary battery and, more particularly, to an electrode assembly of a secondary battery, which is designed to enhance battery safety, and a method for making the same.

2. Description of Prior Art

A secondary battery comprises an electrode assembly disposed within a can containing an electrolyte. The electrode assembly comprises positive and negative electrodes on which positive and negative active materials are deposited respectively. Therefore, the charging and discharging of the second battery is realized by the physical and chemical reactions occurring between active materials and the electrolyte.

In such a secondary battery, a capacity ratio of the negative active material to the positive active material (N/P ratio) is usually maintained within a range of 1.2-1.4 to obtain a reserve for sufficient absorption of ions released from the positive electrode into the negative electrode.

If the N/P ratio is less than 1, a metal oxide material is precipitated within the secondary battery or the electrolyte may leak since ions discharged from the positive electrode cannot be completely absorbed into the negative electrode. This
where,

• • A is the difference between the amount of the positive active material and the amount of the negative active material;
  • ΔL is the length difference between the positive and negative electrodes; and
  • T is a thickness of the active material of the electrode.

The difference between the amount of the negative and positive active material causes variations in the capacity ratio difference between the taken from FIG. 1 of Applicant's U.S. Pat. No. 6,258,478 issued on 10 Jul. 2001, , which have a different thickness, are alternately disposed between the positive and negative electrodes 2a and 2b. Particularly, it is shown that the thickness of the first separator 2cc is greater than that of the second separator 2c. The thickness of the first separator is 2-3 times that of the second separator. More preferably, the thickness of the first separator is about 30-45 μm, while the thickness of the second separator is about 15-23 μm.

In the straight portion St of the roll electrode assembly which has no portion having the a N/P ratio less than 1, the thickness of the first separator 2cc may be equal to that of the second separator 2c.

Accordingly, the cross-sectional distance cut between adjacent positive and negative electrode electrodes where the N/P ratio is less than 1 becomes longer due to the thicker separator 2cc. As the result, even when the metal oxide material is precipitated and is grown due to the length difference in local length between the positive and negative electrodes at the curved portion of the roll electrode assembly, the precipitated metal oxide material can not penetrate the separator 2cc and make contact with the positive electrode, thereby preventing the a short circuit and an explosion of the battery.

It is to be understood that the form of the invention shown and described is to be taken as exemplary, presently preferred embodiments. Various modifications and changes may be made without departing from the sprit and scope of the invention as set forth in the claims. It is intended that the following claims be interpreted to embrace all such modifications and changes.

For example, the concept of the present invention may be applied to cylindrical type batteries that also have the N/P ratio less than 1 between the positive and negative electrodes.

Claims

1. A roll electrode assembly of a secondary battery, comprising:

a positive electrode deposited with a positive active material;

a negative electrode deposited with a negative active material and adjacent to the positive electrode; and

successive turns of a separator disposed between the positive and negative electrodes, the successive turns having alternately different thicknesses,

wherein, the adjacent positive and negative electrodes have variable negative-to-positive active material ratio capacity ratios, and a thickness of the separator disposed between a portion of the adjacent positive and negative electrodes where the negative-to-positive active material capacity ratio is less than 1 is greater than that a thickness of the other another portion where the capacity ratio is higher than 1.

2. A roll electrode assembly of a secondary battery, comprising:

a positive electrode rolled having a plurality of turns;

a negative electrode rolled having a plurality of turns, each turn of the negative electrode being adjacent to each turn of the positive electrode; and

first and second separators each rolled to have a plurality of turns, each turn of the first separator being disposed between each outer surface of the turns of the negative electrode and each inner surface of the turns of the positive electrode, and each turn of the second separator being disposed between each outer surface of the turns of the positive electrode and each inner surface of the turns of the negative electrode,

wherein the thickness of the first separator is greater than that of the second separator, and

wherein when the roll electrode assembly is for a battery having, in a cross section, a straight portion and a curved portion, with the thickness of the first and the second separators equal in the straight portion.

3. The roll electrode assembly of claim 2 wherein the thickness of the first separator is 2-3 times that of the second separator.

4. The roll electrode assembly of claim 2 wherein the thickness of the first separator is about 30-45 μm.

5. The roll electrode assembly of claim 2 wherein the thickness of the second separator about 15-23 μm.

6. A roll electrode assembly of a secondary battery, comprising:

a positive electrode deposited with a positive active material;

a negative electrode deposited with a negative active material and adjacent to the positive electrode;

a first separator disposed between the positive and negative electrodes; and

a second separator disposed between the positive and negative electrodes, wherein,;

the adjacent positive and negative electrodes have having variable negative-to-positive active material ratio capacity ratios, and the first and second separators having different thicknesses, with a thickness of the first separator disposed between a portion of the adjacent positive and negative electrodes where the negative-to-positive active material capacity ratio is less than 1 is being greater than that of a thickness of the second separator disposed between a portion of the adjacent positive and negative electrodes where the negative-to-positive active material capacity ratio is higher than 1.

7. The roll electrode assembly of claim 6 wherein the thickness of the first separator is 2-3 times that of the second separator.

8. The roll electrode assembly of claim 6 wherein the thickness of the first separator is about 30-45 μm.

9. The roll electrode assembly of claim 6 wherein the thickness of the second separator is about 15-23 μm.

10. A roll electrode assembly of a secondary battery, comprising:

a positive electrode rolled into a plurality of turns;

a negative electrode rolled into a plurality of turns, each turn of the negative electrode being adjacent to each turn of the positive electrode; and

first and second separators each rolled to have a plurality of turns, each turn of the first separator being disposed between a corresponding neighboring outer surface of the turns of the negative electrode and a corresponding neighboring inner surface of the turns of the positive electrode, and each turn of the second separator being disposed between a corresponding neighboring outer surface of the turns of the positive electrode and a corresponding neighboring inner surface of the turns of the negative electrode;

a thickness of the first separator being greater than a thickness of the second separator in a curved portion of a cross-section of the secondary battery, and the thicknesses of the first and the second separators being equal in a straight portion of the cross-section of the secondary battery.

11. A roll electrode assembly of a secondary battery, comprising:

a positive electrode deposited with a positive active material;

a negative electrode deposited with a negative active material neighboring the positive electrode;

a first separator disposed between the positive and negative electrodes; and

a second separator disposed between the positive and negative electrodes;

adjacent positive and negative electrodes having variable negative-to-positive active material capacity ratios, and the first and the second separators having different thicknesses alternately positioned between the positive and negative electrodes, with a thickness of the first separator disposed between a portion of the adjacent positive and negative electrodes where the negative-to-positive active material capacity ratio is less than 1 being greater than a thickness of the second separator disposed between a portion of the adjacent positive and negative electrodes where the negative-to-positive active material capacity ratio is higher than 1; and

the thicknesses of the first and the second separators being equal in a straight portion of a cross-section of the secondary battery.