JP2801934B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a nonaqueous electrolyte secondary battery using lithium as a negative electrode active material, in particular, suppressing the generation of dendrites of lithium detached from a lithium negative electrode, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery that prevents internal short circuit and improves charge / discharge cycle characteristics.

<< Conventional Technology >> Non-aqueous electrolyte batteries using lithium as the negative electrode active material are known as batteries with excellent self-discharge and low storage stability, and are used for long-life electronic watches and various electronic devices. It is used as a power supply for memory backup.

By the way, this type of nonaqueous electrolyte battery is usually used as a primary battery, but development of a secondary battery that can be used as a power source that can be used economically for a long time is desired. In particular, a non-aqueous electrolyte battery using lithium as a negative electrode is expected to be a secondary battery having a high battery voltage and a high energy density.

However, in this non-aqueous electrolyte secondary battery, lithium is deposited on the negative electrode surface in the form of resin due to the dendrite phenomenon during charging, and this resinous crystal penetrates through the separator, causing an internal short circuit, resulting in a decrease in discharge performance or a decrease in battery performance. There was a risk of causing accidents such as rupture and fire. This phenomenon was particularly noticeable at the edge of the lithium negative electrode due to the edge effect.

That is, in a portion where the positive electrode of the lithium negative electrode faces the positive electrode, transfer of lithium ions at the time of charge / discharge is ideally performed, but a general lamination state is as shown in FIG. 2 and the width of the lithium negative electrode 3 are the same, and the edges of the positive electrode 2 and the negative electrode 3 are aligned with the separator 1 interposed therebetween, or the width of the positive electrode 2 is larger than that of the negative electrode 3 as shown in FIG. Is also wide, the current concentrates on a portion having less resistance during charging, and dendrite is likely to be generated at the edge.

For this reason, as shown in, for example, JP-A-1-128371, a structure has been developed in which the width of lithium is made larger than that of the positive electrode to suppress the generation of dendrite due to the edge effect.

<< Problems to be Solved by the Invention >> However, although dendrite is suppressed in this structure, the following inconvenience has occurred particularly when applied to a spiral type secondary battery.

In other words, since metallic lithium is formed thinly and is a soft metal, a positive electrode-separator-lithium negative electrode is laminated, spirally wound, and in a state where it is housed in a battery case, its lower edge is inside the case. When it hits the bottom, the negative electrode part wider than the positive electrode part is crushed by the load, and this part comes into contact with the positive electrode, causing the internal short circuit to occur easily, and increasing the amount of lithium used.
There is a disadvantage that materials are easily wasted.

An object of the present invention is to solve the above-mentioned drawbacks, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the distance between edges is increased to increase resistance and thereby suppress the generation of dendrite. Is what you do.

<< Means for Solving the Problems >> In order to achieve the object, the present invention arranges the edges of the positive electrode and the lithium negative electrode to have substantially the same size, and reduces the thickness of the end of the positive electrode facing the lithium negative electrode. It is characterized in that it is formed thinner than other parts.

<< Operation >> According to the above configuration, the distance between the positive electrode and the negative electrode at the edge portion is widened, and the reaction at the time of charging is limited in this portion, thereby suppressing the generation of dendrite.

Since the widths of the positive electrode and the lithium negative electrode are uniform, even if the end portion is pressed for some reason, the relatively hard positive electrode will support this load, and the deformation of the lithium negative electrode can be prevented in advance.

<< Embodiment >> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIGS. 1 and 2 show a first embodiment in which the present invention is applied to a spiral type non-aqueous electrolyte secondary battery.

In the battery shown in the figure, a positive electrode 10 and a lithium negative electrode 12 are stacked with a polypropylene separator 14 interposed therebetween, spirally wound, and housed in a cylindrical case 18 with insulating plates 16 arranged above and below. After the non-aqueous electrolyte is injected, the upper opening of the case 18 is closed with a terminal plate 22 through a sealing gasket 20.
It was sealed with.

The lithium negative electrode 12 is electrically connected to a case 18, and the positive electrode 10 is electrically connected to a terminal plate 22 via a lead plate 26 derived from a current collector 24 formed of a porous plate provided therein. A non-aqueous electrolyte battery having this portion as a positive electrode and the bottom of the case 18 as a negative electrode is formed.

In the above configuration, as shown in FIG. 2, the width W1 of the separator 14 is the widest,
Is narrower than this, and the positive and negative electrode widths are set to equal widths.

Thin portions 10a are formed at both edges in the width direction of the positive electrode 10, and the thickness T2 thereof is set smaller than the thickness T1 of the general portion.

The positive electrode 10 is formed by applying a positive electrode active material obtained by adding a binder and a solvent such as manganese dioxide containing lithium and Teflon to both surfaces of the current collector 24, and rolling by a roller after a drying step. At this time, a roller R whose end is machined as shown in FIG. 3 so that thin portions 10a are formed at both ends of the positive electrode is used.

Therefore, the distance between the poles at both edges is increased by an amount corresponding to the decrease in the thickness, and the resistance of this portion at the time of charging is increased, thereby reducing the involvement in the reaction. As a result, the generation of dendrites at both edges is suppressed. It is.

Also, in this case, the load of the seating portion in the state of being housed in the case 18 is supported by the edge of the relatively hard positive electrode 10, and even if the lithium negative electrode 12 is thin and soft, the lithium negative electrode 12 may be deformed. And an internal short circuit due to deformation is prevented.

Note that, even in the present invention, the cycle life differs depending on the thickness T2 and the width w of the thin portion 10a.

That is, when the thickness T2 of the thin portion 10a is close to the thickness T1 of the general portion, the resistance of the thin portion 10a is naturally close to that of the general portion, and the desired effect cannot be obtained. In addition, if it is thin, the positive and negative electrode active materials cannot be used effectively.

If the width w is too wide, the positive and negative electrode active materials cannot be effectively utilized, and if the width w is narrow, the desired effect cannot be obtained.

Therefore, as a result of examining the relationship between the dimensional relationship and the cycle life of the CR6 · H type battery, the results shown in the following table were obtained.

The width of the positive electrode was 40 mm and the thickness of the general part was 0.3 mm, and the width of the lithium negative electrode was 40 mm and the thickness was 0.1 mm.

Also, the thickness T2 of the edge of the positive electrode is 0.27, 0.24, 0.21 mm,
The width w was changed to 0.5, 1.0, and 2.0 mm on one side, respectively.

Each of the above dimensions is spirally wound through a separator by a conventional method to create a CR6 / H type battery.
It was subjected to a cycle characteristic test.

 The charge-discharge cycle characteristics test conditions are as follows.

After discharging at a constant voltage of 200 mA to a starting voltage of 2.0 V, charging was performed at 100 mA at a starting voltage of 3.8 V, and a cycle test was performed using this as one cycle. In addition, the cycle life was set at the time when the capacity decreased to 50% of the initial capacity.

From the results shown in the following table, it was found that the thickness of the thin portion 10a was in the range of 0.25 to 0.27 mm and the width was preferably 38 to 39 mm for the CR6 · H type battery.

However, it goes without saying that the above numerical values are not always constant according to the specifications and dimensions of the battery.

FIG. 3 shows a second embodiment in which the present invention is applied to a button-type non-aqueous electrolyte secondary battery. This battery has a positive electrode formed in a disk shape inside a flat positive electrode can 30. 32 and
As a result, the large-diameter separator 34 and the disc-shaped lithium negative electrode 36 having the same diameter as the positive electrode 32 are laminated, and the negative electrode terminal plate 40 is sealed via the gasket 38.

Also in this embodiment, a thin portion 32a thinner than the general portion is formed at the peripheral portion of the positive electrode 32, and the distance between the electrodes at the end portion during charging is increased to suppress the occurrence of dendrite. .

<< Effects of the Invention >> As described in detail in each of the above embodiments, in the nonaqueous electrolyte secondary battery according to the present invention, the distance between the positive and negative electrodes at the edges increases, and this portion is The reaction is restricted, so that the generation of dendrite can be suppressed.

In addition, the effective use of the active material can be achieved without excessive use of lithium as in conventional devices.

Also, in the present invention, since the width of the positive electrode and the lithium negative electrode are uniform, even if the edge is pressed, the hard positive electrode will support this load, preventing internal short circuit due to deformation of the lithium negative electrode beforehand. it can.

[Brief description of the drawings]

FIG. 1 is a half sectional explanatory view of a spiral type nonaqueous electrolyte secondary battery according to a first embodiment of the present invention, FIG. 2 is a sectional view showing a dimensional relationship between a lithium negative electrode, a separator and a positive electrode in the battery, and FIG. FIG. 4 is a schematic view of a rolling roller, FIG. 4 is a half-sectional view showing a second embodiment in which the present invention is applied to a button-type nonaqueous electrolyte secondary battery, and FIGS. FIG. 4 is an explanatory cross-sectional view illustrating a dimensional relationship between a lithium negative electrode, a separator, and an end of a positive electrode in a battery. 10,32… Positive electrode 10a, 32a …… Thin section 12,36 …… Lithium negative electrode 14,34 …… Separator

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuzo Tanaka 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 4 / 00-4/04 H01M 4/36-4/62 H01M 10/36-10/40

Claims (1)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery in which a positive electrode and a lithium negative electrode are laminated with a separator interposed therebetween: The edges of the positive electrode and the lithium negative electrode are made to have substantially constant dimensions, and face the lithium negative electrode. A non-aqueous electrolyte secondary battery characterized in that the thickness of the end portion of the positive electrode is formed thinner than other portions.