JPH11297348A - Elastic band or sheet for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the performance deterioration due to dissolution, the occurrence of stresses due to the volume expansion of a battery element at the electric charging and an increase of inter-electrode distance due to volume shrinkage at the electric discharging by providing an elastic band or sheet which is not dissolved or decomposed, when it is kept in contact with an electrolyte and has rubber elasticity expandable to follow the volume change of the battery element. SOLUTION: This band or sheet for a battery is made of olefin, fluorine or silicone rubber, the strength at the time of elongation of 5% after being kept in contact with a specific battery electrolyte is preferably set to 1 kgf/mm<2> or below, and the restoration factor is set to 90% or above. Sufficient winding slackness of a battery element is obtained, the stress due to the volume expansion of a negative electrode active material at the time of an electric charging is mitigated, and the volume shrinkage at the time of an electric discharge can be followed. The weight reduction factor after the contact with the electrolyte is preferably set to below 20%. The winding end section of the battery element spirally wound after sheet-like electrodes and a separator are laminated is bound regularly and fixed by this band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band or sheet used for fixing a battery element comprising a laminate of an electrode and a separator, in particular, a spiral formed by laminating a sheet-like electrode and a separator and then spirally winding the same. The present invention relates to a battery elastic band or sheet (hereinafter, referred to as an elastic band) for binding and fixing a winding end portion of a battery cell element.

[0002]

2. Description of the Related Art Conventionally, secondary batteries of various structures have been known, but with the spread of small electronic devices in recent years, secondary batteries as power source batteries have been increased in capacity and density. Is required. For this reason, a conventional aqueous electrolyte battery, such as a Ni-Cd battery, is being replaced with a lithium battery, which is an organic electrolyte battery. In this lithium battery, the structure of the battery element of the lithium ion battery, which is a rechargeable lithium secondary battery, is a spiral structure in which sheet-like electrodes are stacked via a separator, which is a porous film, and then spirally wound. Is common. This battery element is usually housed in a battery case in a state where the winding end of the laminate is fixed with an adhesive or an adhesive tape so as to prevent the winding from being loosened.

[0003]

However, in this lithium ion battery, lithium ions are dedoped from the positive electrode during charging, pass through the separator, and are doped into the negative electrode. As a result of incorporating lithium into the active material, expansion of the negative electrode active material is caused. Many carbon materials are used as the negative electrode active material, and among them, it is said that graphite-based materials have a large degree of expansion due to lithium ion doping. Here, in the battery element structure, the winding end portion is fixed with an adhesive or an adhesive tape so as not to be loosened. As a result, it is possible to suppress expansion of the battery element during battery charging. Has become. When the expansion of the element at the time of filling the battery is suppressed in this manner, stress is caused inside the battery, and this stress causes the destruction of the positive / negative active material and the separator, a decrease in the adhesion between the current collector and the active material, and the like. However, the battery characteristics (cycle characteristics) deteriorated. In particular, when a graphite-based material is used for the negative electrode active material, the tendency is large for the reasons described above. Further, when the adhesive is significantly dissolved and decomposed in the electrolytic solution, there is a concern that the adhesive component is diffused into the electrolytic solution, thereby lowering the battery characteristics due to the decrease in the electrolytic solution characteristics.

[0004]

The elastic band according to the present invention comprises:
It has been made to solve such a problem and has a function of fixing the battery element, and has an appropriate rubber elasticity without substantially dissolving or decomposing the elastic band even after contact with the battery electrolyte. As a result, at the time of charging, the band expands following the volume expansion of the battery element, so that the volume expansion is not suppressed and the stress is relaxed, so that the stress applied to the constituent materials of the element can be reduced. Can be avoided. Also, at the time of discharge, following the volume contraction of the element,
The contraction of the band can prevent the battery element from being unnecessarily loosened due to volume shrinkage, and can prevent deterioration of battery characteristics due to an increase in the distance between the positive electrode and the negative electrode due to excessive loosening. In addition, since the elastic band does not substantially dissolve or decompose in the electrolytic solution, it is possible to avoid a decrease in battery characteristics due to these.

That is, the present invention relates to a band or sheet used for fixing a battery element comprising a laminate of an electrode and a separator, wherein the band or sheet substantially dissolves or dissolves in an environment where the band or sheet comes into contact with a battery electrolyte. The present invention relates to an elastic band or sheet for a battery, wherein the elastic band or the sheet does not decompose, is rubber elastic, and can expand and contract according to a change in volume of the battery element.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is important that the elastic band for a battery of the present invention has rubber elasticity in an environment where the elastic band is in contact with the battery electrolyte. Here, having rubber elasticity in an environment in contact with the battery electrolyte preferably means that the elastic band has a strength at 5% elongation of 1 kgf / mm 2 or less, particularly after contact with a specific battery electrolyte described below, particularly 0.5-0.05kgf / m
m2 and a restoration rate of 90% or more, particularly 95 to 100%. This 5% elongation strength is 1kgf / mm
If it exceeds 2, the winding of the battery element may be insufficiently loosened, the expansion of the battery element due to the volume expansion of the negative electrode active material at the time of charging the battery is suppressed, and the stress is not alleviated. Is increased, and the deterioration of the battery characteristics due to these cannot be avoided. Further, when the restoration rate is less than 90%, the elastic band may not sufficiently contract following the volume contraction of the battery element at the time of discharging, so that excessive loosening due to the volume contraction of the element cannot be suppressed. However, it is not preferable because deterioration in battery characteristics due to an increase in the distance between the positive electrode and the negative electrode due to the loosening of the winding cannot be avoided. These strengths and restoration rates can be obtained by measurement in Examples described later. The elastic band preferably has a weight reduction rate of less than 20%, particularly 15 to 0% after dissolving or decomposing after contacting the battery electrolyte.
When the weight reduction rate is 20% or more, the rate of deterioration of the electrolyte properties due to the diffusion of the band component into the electrolyte increases, and the deterioration of the battery properties due to these increases is not preferable. This weight loss rate can be obtained by measuring the change in weight in the examples described later. Further, the thickness of the elastic band can be generally set to about 10 to 150 μm.

The specific constituent material of such an elastic band is as follows:
Although not particularly limited as long as it has the above functions, preferably the above properties, for example, polyisobutylene, ethylene-
Examples include olefin rubbers such as propylene rubber, fluorine rubbers such as vinylidene fluoride and propylene hexafluoride copolymer, silicone rubbers such as polydimethylsiloxane, and crosslinked rubbers as necessary. Can be

[0008]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it should not be construed that the invention is limited thereto. The elastic bands shown in Table 1 were obtained, and the band strength, restoration rate, and weight loss rate after immersion in the electrolytic solution were evaluated by the following methods, and the results are shown in the table.

[0009]

[Table 1]

(Strength at 5% elongation) Using the obtained elastic band as an electrolyte solvent, ethylene carbonate (E
C): immersed in a solvent adjusted with dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1: 1: 1 (volume ratio) and then taken out after storage at 60 ° C. for 1 day,
Tensile strength-elongation is measured at a speed of 3 mm / min with a tensile tester, and the strength at 5% elongation is read and calculated by the following equation. Strength at 5% elongation (kgf / mm2) = Strength at 5% elongation (kgf) / cross-sectional area (mm2)

(Restoration rate) The obtained elastic band was used as an electrolyte solvent for ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DE).
C) = 1: 1: 1 (volume ratio), immersed in a solvent adjusted, then stored at 60 ° C. for 1 day, taken out, and measured with a tensile tester at a rate of 3 mm / min until elongation reached 5%. Stretch, leave for 10 minutes, release the stretch, leave for 10 minutes, measure the length, and calculate by the following formula. Restoration rate (%) = (1− (length after stretching−initial length))
/ Initial length) x 100

(Weight loss rate) The weight of each sufficiently dried base material is measured with a weighing instrument, and is defined as an initial weight. On the other hand, as an electrolyte solvent, ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DE
C) = 1: 1: 1 (volume ratio) is adjusted, and each elastic band is immersed in this. Next, after storage at 60 ° C. for 1 day, the product was taken out and dried sufficiently, and the weight was measured with a weighing scale to obtain the weight after immersion. The weight loss rate was calculated by the following equation for the initial weight and the weight after immersion. Weight reduction rate (%) = 100− (weight after immersion / initial weight) × 100

[0013]

As described above, according to the elastic band or sheet for a battery of the present invention, the expansion of the battery element at the time of charging the battery is not suppressed, the stress is relaxed, and the stress applied to the constituent material of the element can be reduced. There is an effect that deterioration of battery characteristics due to these can be avoided. In addition, since the elastic band does not substantially dissolve or decompose in the electrolytic solution, it is possible to avoid a decrease in battery characteristics due to these.

Claims (4)

[Claims] 1. A band or sheet used for fixing a battery element comprising a laminate of an electrode and a separator,
The elasticity for a battery, wherein the band or sheet does not substantially dissolve or decompose in an environment in contact with a battery electrolyte, is rubber elastic, and can expand and contract following a change in volume of the battery element. Band or sheet. 2. The elastic band or sheet has a rubber elasticity such that after contact with the battery electrolyte, the band or sheet has a strength of 5 kg or less of 1 kgf / mm 2 or less and a recovery rate of 90% or more. The elastic band or sheet for a battery according to claim 1, wherein: 3. The elastic band or sheet for a battery according to claim 1, wherein the elastic band or the sheet has a weight reduction rate of less than 20% due to dissolution or decomposition after contact with the battery electrolyte. . 4. The elastic band for a battery according to claim 1, wherein the battery element is a spiral-type battery element formed by laminating a sheet-like electrode and a separator and then spirally winding the laminate. Or a sheet.