JPH11307128A - Lithium ion secondary battery - Google Patents

Abstract

(57) [Problem] To provide a lithium ion secondary battery capable of suppressing generation of dendrite due to deposition of lithium on a negative electrode side lead wire connecting portion of a negative electrode current collector. SOLUTION: A positive electrode plate 1 and a negative electrode plate 2 are spirally wound via a separator 3 to form an electrode plate group. A nonporous blocking portion 3c for preventing lithium ions from moving between the negative electrode side lead wire connecting portion 2c of the inner winding layer 3b of the separator 3 and the other end 1d of the positive electrode plate 1 is provided between the two. Form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery having an electrode group in which a positive electrode plate and a negative electrode plate are spirally wound via a separator. It is about.

[0002]

2. Description of the Related Art Lithium batteries using metallic lithium as a negative electrode active material have high energy, but so-called dendrites in which lithium deposits in a needle shape on the negative electrode plate due to repeated charge and discharge. When the dendrite grows greatly and breaks through the separator to reach the positive electrode plate, a short circuit occurs in the battery, which significantly deteriorates the battery performance and, in the worst case, may cause the battery to burst or explode. Therefore, a lithium ion secondary battery using a carbon material capable of doping and undoping lithium as a negative electrode material of a negative electrode plate and using a transition metal oxide as a positive electrode material of a positive electrode plate has been proposed. As this type of battery, a negative electrode plate having a negative electrode material layer formed on a negative electrode current collector made of a metal foil and a positive electrode plate having a positive electrode material layer made of a transition metal oxide are spirally wound via a separator. A spiral-type lithium-ion secondary battery in which the above-described electrode group is disposed in a battery can is known.

[0003]

Normally, in a spiral-wound lithium ion secondary battery, a part of the negative electrode current collector is exposed from one end in the longitudinal direction of the negative electrode plate and connected to the negative electrode terminal of the battery. A negative-electrode-side lead wire connection portion to which the lead wire is connected is formed. The negative-electrode-side lead wire connection portion faces the end portion of the positive electrode plate via the separator winding layer located inside. Such a negative electrode side lead wire connection portion
Since the metal surface directly faces the positive electrode via the separator, lithium may be deposited on the surface to generate dendrites depending on the charging conditions of the battery. When the battery is charged under normal charging conditions, the potential of the negative electrode plate does not decrease to the deposition potential of lithium, so that lithium does not precipitate at the negative-wire-side lead wire connection portion. The potential of the negative electrode plate may be lower than the deposition potential of lithium depending on conditions such as the constant voltage value and the like. In that case, there was a problem that lithium was deposited at the negative electrode side lead wire connection portion of the current collector.

An object of the present invention is to provide a lithium ion secondary battery capable of suppressing generation of dendrite due to deposition of lithium on a negative electrode side lead wire connecting portion of a negative electrode current collector.

[0005]

According to the present invention, there is provided a lithium ion secondary battery, comprising: a strip-shaped positive electrode plate in which a positive electrode current collector supports a positive electrode material layer mainly composed of a transition metal oxide; A negative electrode current collector and a strip-shaped negative electrode plate carrying a negative electrode material layer mainly composed of a carbon material capable of doping and undoping lithium are spirally wound through a strip-shaped separator. It has a plate group. Then, a part of the positive electrode current collector is exposed from one longitudinal end of the positive electrode plate located on the inner peripheral side of the electrode plate group to form a positive electrode side lead wire connection portion,
A part of the negative electrode current collector is exposed from one longitudinal end of the negative electrode plate located on the outer peripheral side of the electrode plate group to form a negative electrode side lead wire connection part. Further, the positive lead wire connection portion and the negative lead wire connection portion are disposed between two adjacent separator winding layers formed by the wound separator,
The other end in the longitudinal direction of the wound positive electrode plate is disposed so as to face the negative electrode side lead wire connection portion with a separator winding layer positioned inside therebetween.

In the present invention, a portion of the separator (hereinafter simply referred to as a blocking portion) located between the negative electrode side lead wire connection portion and the other end of the positive electrode plate is configured so that lithium ions do not pass therethrough.

According to the present invention, the movement of lithium ions between the negative electrode side lead wire connection portion and the other end of the positive electrode plate is prevented, so that the potential of the negative electrode plate is reduced during the rapid charging or the like. Even when the potential becomes lower than the deposition potential, it is possible to prevent lithium from being deposited on the negative electrode side lead wire connecting portion of the negative electrode current collector.

As a specific method for preventing lithium ions from passing therethrough, the blocking portion of the separator may be made non-porous. Further, if the entire surface is opposed to the negative electrode side lead wire connection portion, the movement of lithium ions can be largely prevented.

In order to almost completely prevent the movement of lithium ions between the positive electrode plate and the negative electrode side lead wire connection portion of the negative electrode current collector, it is necessary to provide an opposing portion entirely opposed to the negative electrode side lead wire connection portion. The blocking portion may be formed so as to have a pair of extending portions extending from the facing portion to both sides in the circumferential direction of the electrode plate group.

The blocking portion can be easily formed by thermally shrinking a part of the separator made of a synthetic resin sheet. The separator may be a sheet made of polyethylene, polypropylene, or a laminate of polyethylene and polypropylene and formed with a large number of through holes that allow the passage of ions. Such materials are
Since heat shrinkage is easy, the blocking portion can be easily formed.

[0011]

(Embodiment 1) FIG. 1 is a sectional view of an electrode group of a lithium ion secondary battery (nominal capacity: 1000 mAh) of this embodiment. As shown in FIG.
A strip-shaped positive plate 1 and a strip-shaped negative plate 2 are spirally wound with a strip-shaped separator 3 interposed therebetween. The positive electrode plate 1 is configured by forming a positive electrode material layer 1b mainly composed of a metal oxide made of lithium cobalt oxide on both surfaces of a positive electrode current collector 1a made of aluminum foil, and has a thickness of 150 μm. . Specifically, the positive electrode plate 1 is made by mixing a positive electrode material made of lithium cobalt oxide (LiCoO2), a conductive auxiliary material made of carbon, and polyvinylidene fluoride (PVDF) at a weight ratio of 85: 5: 10 by using a kneaded material. -Disperse in methyl-2-pyrrolidone to make a slurry. The slurry was applied to a positive electrode current collector 1a (aluminum foil) and dried to produce a product.
At one end of the positive electrode current collector 1a on the inner peripheral side of the electrode plate group of the positive electrode plate 1, a positive electrode side lead wire connection portion 1c is formed in which a positive electrode material layer is not formed and a part of the current collector is exposed. Have been. This positive electrode side lead wire connecting portion 1c is connected to the other end 2 in the longitudinal direction of the negative electrode plate 2 with the outer winding layer 3a of the separator 3 interposed therebetween.
and a lead wire (not shown) connected to the positive electrode terminal. As the positive electrode material, other than lithium cobaltate, lithium nickelate, lithium nickelate in which nickel sites are partially replaced with lithium cobaltate, lithium manganate, or the like can be used.

The negative electrode plate 2 includes a negative electrode current collector 2a made of copper foil.
A negative electrode material layer 2b containing an amorphous carbon material as a main component is formed on both surfaces thereof, and has a thickness of 200 μm. Specifically, the negative electrode plate 2 forms a slurry by dispersing a kneaded material obtained by kneading a negative electrode material made of amorphous carbon and PVDF at a weight ratio of 90:10 in N-methyl-2-pyrrolidone, and forming a slurry. The slurry was applied to the negative electrode current collector 2a (copper foil) and dried to produce the slurry. At one end of the negative electrode current collector 2a on the outer peripheral side of the electrode plate group of the negative electrode plate 2, a negative electrode side lead wire connection portion 2c is formed in which a negative electrode material layer is not formed and a part of the current collector is exposed. ing. The negative-electrode-side lead wire connecting portion 2c faces the other end 1d in the longitudinal direction of the positive electrode plate 1 via the inner winding layer 3b of the separator 3, and is connected to a lead wire (not shown) connected to the negative electrode terminal. Have been. In addition, graphite etc. can be used for a negative electrode material other than amorphous carbon.

The separator 3 includes an outer winding layer 3a wound around the outside of the negative electrode plate 2 and an inner winding layer 3b wound around the inside of the negative electrode plate 2. Each of the outer winding layer 3a and the inner winding layer 3b has a structure in which a large number of holes are formed in a polyethylene film so that ions can move, and has a thickness of 25 μm. Such a large number of holes are artificially formed, and as the separator 3, for example, those sold by Tonen Chemical Co., Ltd. under the trade name of E25MMS can be used.

At a portion between the negative-electrode-side lead wire connecting portion 2c of the inner winding layer 3b of the separator 3 and the other end 1d of the positive electrode plate 1, a blocking portion 3c for blocking the movement of lithium ions in both of them is provided. Is formed. As shown in the schematic diagram of FIG. 2, the blocking portion 3c thermally shrinks a part of the inner winding layer 3b of the separator 3 at a temperature of 200 ° C. using a pair of heat sealers H in the winding process of the electrode plate. It is formed by doing. The pair of heat sealers H move in the direction of the arrow to thermally contract a part of the inner winding layer 3b of the separator 3. That is, the inner winding layer 3b of the separator 3 has the blocking portion 3c and the porous portion 3d. The blocking portion 3c has an opposing portion 3c1 entirely opposed to the negative electrode lead wire connecting portion 2c, and a pair of extending portions 3c2, 3c2 extending from the opposing portion 3c1 to both sides in the circumferential direction of the electrode plate group. . The length of the pair of extension portions 3c2, 3c2 extending on both sides in the circumferential direction is set to a size that can sufficiently prevent the movement of lithium ions.

The lithium ion secondary battery of the present embodiment is manufactured as follows using the electrode group having such a structure. First, the electrode plate group is inserted into the battery can, and the battery can and the negative electrode-side lead wire are spot-welded. Next, a predetermined amount of an electrolytic solution containing 1 mol / l lithium hexafluorophosphate in a mixed solvent of propylene carbonate and dimethyl carbonate having a volume ratio of 3: 5 is poured into the battery can. Next, after the lid and the positive electrode side lead wire are spot-welded, the lid is caulked to a battery can via an insulator to complete the battery. (Embodiment 2) The lithium ion secondary battery of this embodiment has the same structure as that of Embodiment 1 except that a separator is formed by using polypropylene instead of polyethylene.

(Comparative Example 1) The lithium ion secondary battery of the present comparative example does not have the blocking portion 3c, uses a separator in which the entire inner winding layer of the separator is a porous portion, and otherwise uses the same as the embodiment. It has the following structure.

Next, a life characteristic test was performed using each of the above lithium ion secondary batteries. Specifically, the charging under the conditions 1 to 3 shown in Table 1 below and the discharging performed at a current value of 1000 mA up to a final voltage of 25 V are performed at a temperature of 25 ± 2 ° C., respectively, and the discharge capacity in the first cycle is reduced. 7 of discharge capacity
Number of cycles when the value falls below 0% (number of life cycles)
Was measured. That is, in each condition, the discharge condition and the temperature condition are the same, and only the charge condition is different as shown in Table 1. Table 2 shows the measurement results.

[0018]

[Table 1]

[Table 2] From Table 2, the lithium ion secondary batteries of Examples 1 and 2 are:
It can be seen that the cycle life is longer than that of the lithium ion secondary battery of Comparative Example 1. In particular, under the conditions 2 and 3 in which the potential of the negative electrode plate tends to be lower than the deposition potential of lithium, it is apparent that the difference in cycle life is remarkable. In addition, when the batteries of Examples 1 and 2 were disassembled after one cycle under each condition, no lithium deposition was observed at any negative electrode side lead wire connection portion. On the other hand, in the battery of Comparative Example 1, 1
After dismantling after the cycle, in conditions 2 and 3,
Precipitation of lithium was observed at the negative electrode side lead wire connection.

In this embodiment, an amorphous carbon material is used as the negative electrode material. However, it goes without saying that graphite may be used as the negative electrode material.

[0020]

According to the present invention, since the movement of lithium ions between the negative electrode side lead wire connection portion and the other end of the positive electrode plate is prevented, the potential of the negative electrode plate during rapid charging or the like is reduced. Even when the potential becomes equal to or lower than the deposition potential of lithium, it is possible to prevent lithium from being deposited on the negative electrode side lead wire connecting portion of the negative electrode current collector. Therefore, even when the potential of the negative electrode plate becomes equal to or lower than the deposition potential of lithium during rapid charging or the like, it is possible to prevent lithium from being precipitated at the negative electrode side lead wire connection portion of the negative electrode current collector. As a result, an internal short circuit of the battery can be prevented, and the life of the battery can be extended.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electrode group of a lithium ion secondary battery (nominal capacity: 1000 mAh) according to an embodiment of the present invention.

FIG. 2 is a view used to explain a mode of forming a blocking portion of a separator in the lithium ion secondary battery according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 1a Positive electrode current collector 1b Positive electrode material layer 1c Positive electrode side lead wire connection part 2 Negative electrode plate 2a Negative electrode current collector 2b Negative electrode material layer 2c Negative electrode lead wire connection part 3 Separator 3a Outer winding layer 3b Inner winding layer 3c blocking part 3c1 facing part 3c2, 3c2 a pair of extension parts

Claims (5)

[Claims] 1. A belt-like positive plate in which a positive electrode current collector carries a positive electrode material layer mainly containing a transition metal oxide containing lithium, and a negative electrode current collector capable of doping and undoping lithium. A strip-shaped negative electrode plate on which a negative electrode material layer containing a carbon material as a main component is supported; and an electrode plate group spirally wound via a band-shaped separator, and an inner peripheral side of the electrode plate group. A part of the positive electrode current collector is exposed from one end in the longitudinal direction of the positive electrode plate located at a positive electrode side lead wire connection part is formed, and the negative electrode located on the outer peripheral side of the electrode plate group A part of the negative electrode current collector is exposed from one end in the longitudinal direction of the plate to form a negative electrode side lead wire connection portion, and the positive electrode side lead wire connection portion and the negative electrode side lead wire connection portion are wound. Two adjacent separator turns formed by the turned separator The other end in the longitudinal direction of the wound positive electrode plate is disposed between the layers, and is disposed so as to face the negative electrode side lead wire connection portion with the separator wound layer positioned inside therebetween. A lithium ion secondary battery, wherein a portion of the separator located between the negative electrode side lead wire connection portion and the other end of the positive electrode plate is configured to prevent lithium ions from passing therethrough. A lithium ion secondary battery characterized in that: 2. The lithium ion secondary battery according to claim 1, wherein the portion of the separator is non-porous and entirely faces the negative electrode side lead wire connection portion. 3. The device according to claim 1, wherein the portion has an opposing portion entirely opposing the negative electrode lead wire connecting portion, and a pair of extending portions extending from the opposing portion to both sides in the circumferential direction of the electrode plate group. The lithium ion secondary battery according to claim 2, wherein: 4. The separator according to claim 1, wherein the separator is formed of a porous synthetic resin sheet having ion permeability, and the portion is formed by heat-shrinking a part of the synthetic resin sheet. 3. The lithium ion secondary battery according to 2. 5. The separator includes a sheet made of polyethylene, polypropylene, or a laminate of polyethylene and polypropylene, formed with a large number of through holes that allow the passage of ions, and the portion is formed with the through holes. The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is not used.