JP2000123878A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cross-sectional noncircular shape causing no energy density loss without deteriorating safety by providing an electrode body wound so that the lengthwise directions of a positive electrode plate and a negative electrode plate become the inverse direction at winding start time and fixing a negative electrode positioned on the electrode body inmost periphery to a separator. SOLUTION: A separator opposed to a negative electrode positioned on the electrode body inmost periphery is desirably fixed to a positive electrode opposed to the separator. An electrode body 12 forms a structure of mutually hooking an almost hook-shaped positive electrode plate 2 and a negative electrode plate 3 through the separator 4 in the vertical direction to the winding axis, that is, in the winding start part in a central longitudinal sectional view. A covering film 7 of PVdF is formed in, for example, about 35 mm of the winding start part of the negative electrode plate 3 to be used as a paste agent for fixing the opposed separator 4. The electrode body 12 is fastened in winding to be housed in an Al alloy battery vessel 6. A lead terminal is connected to a negative electrode terminal 11, the battery vessel 6 is sealed by a lid plate, and an electrolyte is reserved in the battery vessel 6 in a vacuum from a reserve port.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices such as a portable radio telephone, a portable personal computer, and a portable video camera have been developed, and various electronic devices have been reduced in size to be portable. Along with this, a battery having a high energy density and a light weight is also adopted as a built-in battery. A typical battery that satisfies such a requirement is an active material such as lithium metal or lithium alloy, or a host material containing lithium ions (here, a host material refers to a material that can occlude and release lithium ions). Lithium intercalation compound occluded in a certain carbon is used as a negative electrode material, and LiC
This is a non-aqueous electrolyte secondary battery using an aprotic organic solvent in which a lithium salt such as l04 and LiPF6 is dissolved as an electrolyte.

This non-aqueous electrolyte secondary battery has a negative electrode plate in which the above-mentioned negative electrode material is held on both sides of a negative electrode current collector as a support, and a reversible lithium ion such as a lithium cobalt composite oxide. A positive electrode plate holding a positive electrode active material that performs an electrochemical reaction on both sides of a positive electrode current collector that is a support thereof,
It consists of a separator that holds the electrolyte and intervenes between the negative electrode plate and the positive electrode plate to prevent a short circuit between the two electrodes.
In the case of a non-cylindrical battery, the positive electrode plate and the negative electrode plate are each formed into a thin sheet or foil, and are wound in a spiral and non-circular cross-section through a separator, for example, in an elliptical cross-section. The outermost periphery is stopped with a tape to form an electrode body. At this time, as shown in FIG. 1, at the beginning of winding, the negative electrode plate and the positive electrode plate are bent in the same direction with the separator interposed therebetween, and the separator is folded in two at the core, and the positive electrode plate and the negative electrode plate Are configured to be isolated when wound. The completed electrode body is stored in a battery container made of metal such as stainless steel, nickel-plated iron, or aluminum, and the terminal lead connected to the cover plate and the lead of the electrode body are connected to form a cover. The board is fixed. Then, the electrolyte is injected and sealed, and the battery is assembled. However, in the above-described structure of the electrode body, since the positive electrode mixture located on the innermost side of the positive electrode plate at the beginning of winding does not contribute to the reaction because there is no opposite negative electrode mixture, the energy density is reduced. Have been forced. Therefore, it cannot be said that this is an unfavorable structure in a battery that is required to be miniaturized and have high energy density. In order to solve this problem, as shown in FIG. 2, the positive electrode plate and the negative electrode plate are partially overlapped with each other via a separator, and the longitudinal directions of the positive electrode plate and the negative electrode plate are opposite to each other. And a structure in which a hook-shaped positive electrode plate and a hook-shaped negative electrode plate are sandwiched between separators at the beginning of winding. According to this structure, there is no loss in energy density because the positive electrode mixture layer and the negative electrode mixture layer are always arranged to face each other.

[0004]

However, although the above-mentioned electrode body has no loss of energy density, when it is wound flat, a gap is formed in the center portion at the beginning of winding.
As a result, the distance between the positive electrode and the negative electrode becomes non-uniform, the electrolyte infiltrates into the gap, the charge level at the time of charging increases, and lithium is deposited. This precipitation of lithium (hereinafter, referred to as electrodeposition) has caused a new problem of causing a problem such as a decrease in capacity and eventually an internal short circuit.
Therefore, the present invention has been made to solve the above-described problem, and has been made to provide a non-equipped electrode body having a flat shape without causing a decrease in battery safety and without loss of energy density. An object of the present invention is to provide a water electrolyte secondary battery.

[0005]

Accordingly, a non-aqueous electrolyte secondary battery according to the first invention is an electrode body in which a positive electrode, a negative electrode, and a separator are wound in a flat shape. An electrode body wound so that the longitudinal directions of the positive electrode plate and the negative electrode plate are opposite to each other, wherein the negative electrode located at the innermost periphery of the electrode body and the separator facing the negative electrode are fixed. Features. A second invention according to the first invention is characterized in that a separator facing the negative electrode located at the innermost periphery of the electrode body and a positive electrode facing the separator are fixed.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 3 is an explanatory view of the non-aqueous electrolyte secondary battery according to the present invention.

In a non-aqueous electrolyte secondary battery 1 according to the present embodiment, an electrode body 12 including a positive electrode plate 2, a negative electrode plate 3, and a separator 4 is made of an aluminum alloy battery container together with a non-aqueous electrolyte (not shown). 6 is stored.

[0008] The positive electrode plate 2 is a current collector in which a lithium-cobalt composite oxide is held as an active material. The current collector is an aluminum foil having a thickness of 20 μm. The positive electrode plate is
8 parts of polyvinylidene fluoride as a binder and 5 parts of acetylene black as a conductive agent are mixed together with 87 parts of an active material, and N-methylpyrrolidone is appropriately added to prepare a paste. And dried.

The current collector of the negative electrode plate 3 is a copper foil having a thickness of 14 μm. The negative electrode plate is prepared by mixing 86 parts of graphite (graphite) as a host substance and 14 parts of polyvinylidene fluoride as a binder, and applying a paste prepared on both surfaces of the current collector, followed by drying. Made. In addition, the lead connection part (not shown) of each electrode plate was not applied.

[0010] The separator 4 is a polyethylene microporous membrane. The electrolyte was ethylene carbonate: diethyl carbonate = 1: 1 containing LiPF6 at 1 mol / l.
(Volume ratio). The respective dimensions are as follows: the positive electrode plate 2 has a thickness of 180 μm and a width of 29 mm; the separator has a thickness of 25 μm and a width of 33 mm;
It is 0 μm and 31 mm wide. Then, lead terminals (20, 30) are welded to the positive electrode plate 2 and the negative electrode plate 3, respectively, and the front ends of the positive electrode plate 2 and the negative electrode plate 3 are overlapped with the separator 4 interposed therebetween. The flat electrode body 12 was manufactured by winding the positive electrode plate 2, the negative electrode plate 3, and the separator 4 around the overlapped portion as a winding axis. That is, the electrode body 12 is in a direction perpendicular to the winding axis,
In other words, the structure is such that the substantially hook-shaped positive electrode plate 2 and the substantially hook-shaped negative electrode plate 3 are hooked to each other via the separator 4 at the beginning of winding, as viewed from the central longitudinal cross section. At this time, about 35 m from the leading end of the negative electrode plate 3 where the winding starts.
m is immersed in a PVdF solution (N-methyl-2-pyrrolidone) to form a PVdF coating film 7 in advance on the winding start portion of the negative electrode plate 3. The coating film 7 acts as a glue for fixing the negative electrode (the portion where the negative electrode plate 3 starts to be wound) where the coating film is formed by charging and discharging the battery, and the separator facing the negative electrode. Next, the electrode body 1
2 was wound and stored in an aluminum alloy battery container 6. Next, the lead terminal is connected to the negative electrode terminal 11 of the lid plate,
The battery container was sealed with a lid plate. Next, each electrode and the separator were sufficiently wetted with the electrolytic solution, and the amount of free electrolytic solution outside the electrode group was vacuum-injected from an injection hole (not shown) formed in the container. As described above, 100 batteries A according to the present embodiment having a design capacity of 600 mAh were manufactured. Next, 100 batteries B according to the present invention were manufactured in the same manner as described above. However, it is added that the PVdF solution is also applied to the positive electrode surface facing the separator facing the negative electrode at the beginning of winding to form a coating film. Next, 100 conventional comparative batteries C were manufactured in the same manner as above. However, the difference is that a coating film is not formed on the tip portion (starting portion of winding) of the negative electrode plate. [Tests and Results] Battery A and Battery B According to the Present Invention
And the conventional battery C were left for several hours, charged at a current of 0.5 C for 3 hours, charged at a constant current and a constant voltage up to 4.1 V to a fully charged state, and discharged under a condition of a current of 1 C to 2.75 V. A characteristic test was performed. Table 1 shows the results.

[0011]

[Table 1]

Table 1 shows that batteries A and B according to the present invention did not show any internal short circuit due to electrodeposition. And it was shown that the capacity retention after 300 cycles was also superior to the conventional battery. In addition, in the battery according to the present invention, battery B
Turned out to be better. In the above, P
Although the VdF solution was used, PVdF powder may be adhered to an electrode plate or a separator and fixed by charging. Note that the paste is not limited to PVdF, and any paste may be used as long as it does not adversely affect battery characteristics. In particular,
Examples thereof include polyacrylonitrile, polyethylene oxide, polyaniline, polyimide and the like, and their foams and porous bodies. Further, here, it is fixed by charging, but means for fixing physically may be used. Specifically, it may be directly glued or may be simply crimped.

[0013]

According to the present invention, a non-aqueous electrolyte secondary battery provided with an electrode body wound in a non-circular cross section without lowering battery safety and without loss of energy density. Can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a structure of a wound electrode.

FIG. 2 is an explanatory view showing a structure of a wound electrode.

FIG. 3 is an explanatory diagram of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Positive electrode plate 3 Negative electrode plate 4 Separator 12 Electrode body 6 Battery container 7 Coating film 20 Positive electrode lead terminal 30 Negative electrode lead terminal

Continued on the front page F term (reference) 5H028 AA01 BB07 CC08 CC13 5H029 AJ12 AK03 AL07 AM02 AM03 AM07 BJ03 BJ14 CJ05 CJ07 HJ12

Claims (2)

[Claims] An electrode body in which a positive electrode, a negative electrode, and a separator are wound in a flat shape, and the electrode body wound so that the longitudinal directions of the positive electrode plate and the negative electrode plate are opposite at the beginning of winding. A non-aqueous electrolyte secondary battery, comprising: a negative electrode located at the innermost periphery of the electrode body; and a separator facing the negative electrode. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a separator facing the negative electrode located at the innermost periphery of the electrode body and a positive electrode facing the separator are fixed.