JP2000357535A - Rectangular lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rectangular lithium secondary battery with enhanced contact between electrodes, high charge/discharge cycle characteristics, and good load characteristics. SOLUTION: Element pressing plates 4, 4 having a circular arc cross section bent at a specified curvature are interposed between the inner surfaces of the long sidewall surface parts 2a, 2a of a rectangular battery case 2 and both plane parts 1a, 1a of a wound electrode element 1 facing the inner surfaces of the surface parts 2a, 2a. Each apex of projecting surfaces of the element pressing plates 4, 4 is arranged so as to come in contact with around the central part of the both plane parts 1a, 1a of the electrode element 1, the element pressing plates 4, 4 are brought into close contact with the both plane parts 1a, 1a of the electrode element 1 to interpose it between them, and thereby contact between the electrodes of the electrode element 1 is uniformly kept.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prismatic lithium secondary battery, and more particularly to a prismatic lithium secondary battery having good electrode-to-electrode adhesion and improved charge / discharge cycle characteristics and load characteristics.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and thinner,
There is an increasing demand for a prismatic lithium secondary battery (hereinafter, referred to as a prismatic battery) having a high energy density and having better space efficiency than a cylindrical battery. FIG. 3 is a schematic exploded perspective view of a conventional prismatic battery. The prismatic battery shown in FIG. 3 has a positive electrode plate and a negative electrode plate which are insulated via a separator, wound in a spiral shape, and crushed in a diametrical direction to be flattened to form a flat electrode. 1 and
A metal rectangular battery case 2 in which the electrode element 1 is housed and whose cross section is substantially rectangular;
And a cover element 3 for closing the open end of the cover.

FIG. 4 shows the state of pressure between electrodes of the electrode element 1 before being inserted into the battery case 2.
Description will be made with reference to a schematic sectional view of FIG. FIG.
The length and the direction of the arrow in (a) represent the magnitude and direction of the inter-electrode pressure at the point indicated by a dot, respectively, and the same applies to the subsequent drawings. As shown in the figure, the pressure applied between the electrodes in the vicinity of the flat portion 1a of the electrode element 1 is smaller than that in the vicinity of the corner portion 1b due to the curvature when the electrode plate is bent. Therefore, when the electrode element 1 is inserted into the battery case 2 without taking any measures, the adhesion between the electrodes is not uniform, so that the reaction efficiency between the electrodes becomes uneven, and the charge / discharge cycle characteristics and load characteristics are reduced. Would.

In order to solve the above-mentioned problem, conventionally, FIG.
(B) As shown in FIG.
By disposing the two in close contact with each other such that the inner surface of a presses the flat portion 1a of the electrode element 1, uniformity of the pressure applied to the entire flat portion 1a of the electrode element 1 is maintained. Although not shown, a flat plate element pressing plate may be disposed between the two to increase the pressing force on the flat portion 1a of the electrode element 1.

[0005]

However, since the battery case 2 is weaker than a cylindrical one, the battery case 2 is deformed by expansion and contraction of the electrode element 1 during charging and discharging. In a state where the electrode element 1 and the battery case 2 are expanded, as shown in FIG.
The pressing force on the flat portion 1a of the electrode element 1 by the long side wall surface portion 2a of the battery case 2 is weakened. In particular, since the vicinity of the center of the long side wall surface portion 2a of the battery case 2 swells most, the adhesion between the electrodes near the center of the flat portion 1a of the electrode element 1 facing the electrode case is significantly reduced. As a result, the reaction efficiency between the electrodes becomes uneven, and the charge / discharge cycle characteristics and load characteristics are reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a prismatic lithium secondary battery having excellent charge-discharge cycle characteristics and load characteristics by improving the adhesion between electrodes. Is to do.

[0007]

In order to achieve the above-mentioned object, the present invention provides a positive electrode plate and a negative electrode plate which are insulated via a separator, wound spirally and crushed in the diameter direction. A wound electrode element formed in a flat shape, a metal square battery case in which the electrode element is housed and a cross section of which is substantially rectangular, and a lid element for closing an open end of the battery case are provided. In the prismatic lithium secondary battery, an element having a curved cross section formed in a circular arc shape with a predetermined curvature between a long side wall surface portion of the battery case and a flat portion of the electrode element facing the battery case. A prismatic lithium secondary battery, wherein the pressing plate is arranged such that the apex of the convex surface thereof is in contact with the vicinity of the center of the plane portion of the electrode element and the element pressing plate and the electrode element are brought into close contact with each other. did.

[0008]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic exploded perspective view of a prismatic lithium secondary battery to which the present invention is applied, and its main configuration is basically the same as that of the prior art. Therefore, in the following, portions characteristic of the present invention will be extracted and described, and description of other portions will be omitted.

A feature of the present invention is that the rectangular battery case 2 is provided between the inner surfaces of the long side walls 2a, 2a on the long side and the flat surfaces 1a, 1a of the spirally wound electrode element 1 facing the inner surfaces. The element pressing plates 5, 5 which are curved at a predetermined curvature and whose cross section is formed in an arc shape are interposed. More specifically, the pressing plates 4, 4 are arranged so that the vertices of the convex surfaces thereof are in contact with the vicinity of the center of both flat portions 1 a, 1 a of the electrode element 1. The electrode elements 1 are sandwiched between the two flat portions 1a, 1a so as to maintain uniform adhesion between the two electrode plates in the electrode elements 1. Here, on the bottom of the two pressing plates 4, 4, there is provided a connecting band 5 for integrating them. The width of the element pressing plate 4 is set to about 程度 of the width of the electrode element 1 in the long side direction.

In the embodiment described below, the pressure plate 5
Is manufactured by processing a square stainless steel plate, its material, dimensions, shape, etc. are appropriately set according to the size and use of the entire prismatic battery,
For example, the shape of the stainless steel plate may be substantially elliptical.

FIG. 2 is a schematic sectional view showing a pressurized state inside the electrode element 1 having the above configuration. The vicinity of the center of both flat portions 1a, 1a of the electrode element 1 is pressed most, and both corner portions 1b,
As the pressure approaches 1b, the pressing force decreases, and no pressure is applied at both corners 1b, 1b. As a result, the electrode element 1 can be charged and discharged.
Since the adhesion between the inner electrodes is uniformly maintained, the reaction between the electrodes proceeds smoothly, and the charge / discharge cycle characteristics and the load characteristics are improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A prismatic lithium secondary battery according to an embodiment of the present invention was manufactured as follows. The positive electrode is the active material L
91 parts by weight of iCoO ₂ , 6 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride as a binder are dispersed and mixed in N-methyl-2-pyrrolidone as a solvent to form a slurry to form a positive electrode slurry. And The positive electrode slurry thus prepared was a current collector having a thickness of 20 μm.
Was uniformly coated on the aluminum foil of Example 1 and dried, and then rolled with a roll press to obtain a positive electrode plate.

Next, the negative electrode is prepared by dispersing and mixing 90 parts by weight of a carbon material (natural graphite) as an active material and 10 parts by weight of polyvinylidene fluoride as a binder in N-methyl-2-pyrrolidone as a solvent. Into a negative electrode slurry. The negative electrode slurry thus prepared was uniformly coated on a 20 μm-thick copper foil as a current collector, dried, and then dried.
It was rolled with a roll press to obtain a negative electrode plate.

Subsequently, the above-mentioned positive electrode plate and negative electrode plate are wound many times around a core having a diamond-shaped cross section via a separator made of a microporous polyethylene film having a thickness of 25 μm.
The flat wound electrode element 1 was produced by pulling out the core from the wound electrode laminate and crushing it in the diameter direction. The electrode element 1 thus manufactured is inserted into a nickel-plated iron prismatic battery case 2 together with the element pressing plate 4. The pressure plate 4 is made of stainless steel and has an arc-shaped cross section in the long side direction of the electrode element 1, which is arranged between the electrode element 1 and the battery case 2. Here, the dimensions of the battery case are 50 mm in height, 34 mm in width, and 10 mm in thickness. The pressing plate 4 has a length of 20 mm square and a width of 0.2 mm.
A 2 mm stainless steel plate was fabricated by processing the convex surface into a circular arc having a height of 2 mm. Next, a positive electrode lead made of aluminum is connected to the lid element 3 by welding.
And the battery case 2 were fixed by laser welding.
Next, 1 mol of LiPF ₆ per liter was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 to prepare an electrolytic solution. The battery was sealed to seal the prismatic battery.

Further, as a conventional prismatic battery, a prismatic lithium secondary battery in which the element pressing plate 4 was not inserted was prepared in the same manner as in the above procedure, and a comparative test was conducted between the conventional battery and the embodiment battery according to the present invention. Was done. The test results are shown below.

Table 1 shows the results of a comparative test of the discharge capacity retention ratio. 0.75 A, 4.2 V for each battery
Was charged at a constant current and a constant voltage of 0.65 A, and was discharged at a constant current of 0.65 A until the voltage became 3 V, and this was repeated 100 cycles.
Here, the discharge capacity retention ratio is 100% of the initial discharge capacity.
This is the discharge capacity at the cycle.

[0017]

[Table 1]

Table 2 shows the battery capacity at each discharge current.

[Table 2]

From the above results, it can be understood that the prismatic lithium secondary battery of the present invention in which the pressure plate is inserted is superior in both the charge / discharge cycle characteristics and the load characteristics to the conventional prismatic battery.

[0020]

As is apparent from the above description, according to the present invention, a predetermined curvature is formed between the long side wall surface of the rectangular battery case and the flat surface of the flat wound electrode element facing the long side wall surface. An element pressing plate having a curved cross section formed in an arc shape is disposed such that the apex of the convex surface thereof is in contact with the vicinity of the center of the plane portion of the electrode element, and the element pressing plate is brought into close contact with the electrode element. Therefore, even during charging and discharging, the adhesion between the electrodes in the electrode element is uniformly maintained, the reaction between the electrodes proceeds smoothly, and the charge and discharge cycle characteristics and load characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a schematic exploded perspective view of a prismatic lithium secondary battery to which the present invention is applied.

FIGS. 2A and 2B are schematic cross-sectional views for explaining a pressurized state inside a spirally wound electrode element inserted into a rectangular battery case relating to the rectangular battery of the present invention, wherein FIG. )
Indicates an inflated state.

FIG. 3 is a schematic exploded perspective view of a conventional prismatic lithium secondary battery.

FIG. 4 is a schematic cross-sectional view for explaining a pressurized state inside a spirally wound electrode element for a conventional prismatic battery,
(A) is before insertion into a prismatic battery case, (b) is normal time in a state of being inserted into a prismatic battery case,
(C) shows an expanded state of (b).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wound electrode element 1a Flat part 1b Corner part Two prismatic battery case 2a Long side wall surface part 3 Lid element 4 Element pressing plate 5 Connecting band

Claims (1)

[Claims] A wound electrode element in which a positive electrode plate and a negative electrode plate are insulated via a separator, wound spirally and crushed in a diametrical direction to be flattened, and this electrode In a prismatic lithium secondary battery including a metal prismatic battery case in which an element is housed and a cross section of which is substantially rectangular and a lid element that closes an open end of the battery case, a long side wall of the battery case An element pressing plate, which is curved at a predetermined curvature and whose cross section is formed in an arc shape, is provided between a surface portion and a flat portion of the electrode element facing the electrode portion. A prismatic lithium secondary battery characterized by being disposed so as to be in contact with a vicinity thereof and having the element pressure plate and the electrode element adhered to each other.