Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1997-09-30
2001-03-13
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S251000, C429S247000
Reexamination Certificate
active
06200706
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nonwoven fabric for separators of non-aqueous electrolyte batteries and a non-aqueous electrolyte battery using the same in which adhesion of separators to electrodes is superior; battery processability such as rollability with electrodes is excellent; no internal short-circuit is caused due to contact between electrodes brought about by shrinking or burning of the nonwoven fabric even when the electrodes generate heat by external short-circuit; thus, ignition of batteries can be prevented; and storage characteristics are excellent.
BACKGROUND
Hitherto, as separators for non-aqueous electrolyte batteries, for example, JP-A-6-325747 discloses microporous films comprising a high molecular weight polyethylene having an intrinsic viscosity [&eegr;] of 5 dl/g or higher. As separators for lithium cells, JP-A-3-105851 discloses microporous films comprising a composition composed of an ultra-high-molecular-weight polyethylene having a weight-average molecular weight of 7×10
5
or higher and a polyethylene having a weight-average molecular weight
umber-average molecular weight of 10-300.
These separators have a shut-down function for preventing ignition of batteries. The shut-down function is a function to prevent ignition due to melting of Li when electrodes cause external short-circuit and a great current passes therethrough to generate heat and the battery temperature reaches 180° C. Specifically, separators melt before ignition of Li and result in clogging of open pore portions, whereby the battery reaction is stopped and generation of heat is inhibited. For example, the shut-down occurs at about 120° C. when a porous body of polyethylene is used as a separator and at about 140° C. when a porous body of polypropylene is used as a separator, and, as a result, generation of heat of battery stops to inhibit increase of temperature. However, in case much heat is generated which cannot be overcome by the shut-down function, melting of separator proceeds to cause complete melting of separators or cracking of separators, and as a result electrodes contact with each other, and thus a short-circuit current again flows, resulting in heat generation state, which leads to ignition.
Furthermore, these separators are relatively more uniform than the conventional nonwoven fabrics, but require complicated production steps and need high cost, and furthermore can hardly provide stable performance.
Recently, separators comprising nonwoven fabrics in place of microporous films are being developed from the points of easiness in production and stability of quality. For example, nonwoven fabrics for separators of batteries comprising specific fibers are disclosed in JP-A-5-74442 and JP-A-5-335005. However, when these nonwoven fabrics are used as separators, variation in thickness is greater than microporous films and adherence to electrodes constituting the batteries extremely decreases. Therefore, there is a problem that electrodes of sufficient volume cannot be incorporated into batteries in construction of batteries, and thus a satisfactory current capacity cannot be obtained when fabricated as a battery. Furthermore, in many cases, there occurs a slippage or a gap between electrode and separator in fabrication of batteries and processability is deteriorated.
The object of the present invention is to provide a nonwoven fabric for separators of non-aqueous electrolyte batteries and a non-aqueous electrolyte battery using the same in which adhesion of separators to electrodes is superior; there occurs no slippage or gap between electrode and separator; processability such as rollability with electrodes is excellent; no internal short-circuit occurs due to contact between electrodes or shrinking or burning of the nonwoven fabric even when the electrodes generate heat due to external short-circuit; ignition of batteries can be prevented; and a high current capacity and excellent battery characteristics and storage characteristics can be obtained.
DISCLOSURE OF INVENTION
The present first invention relates to a nonwoven fabric for separators of non-aqueous electrolyte batteries which is produced by a wet paper making process, characterized in that the nonwoven fabric has a thickness non-uniformity index (Rpy) of 1000 mV or less in machine direction, the Rpy being determined in the following manner.
Thickness non-uniformity index (Rpy): A sample is allowed to run between two spherical tracers. Variation of thickness of the sample in machine direction is measured using a film thickness measuring equipment which measures the variation of sample thickness as an electric signal through an electric micrometer by scanning the sample at a constant rate of 1.5 m/min in machine direction after zero point adjustment under the condition of ±15 &mgr;m/±3 V in sensitivity range of the electric micrometer. The resulting signal value is subjected to fast Fourier transform by a FFT analyzer using hanning window as a time window, and a power spectrum (unit: mV
2
) is obtained by additive averaging of addition of 128 times. The power values in the frequency band of 2-25 Hz are totalled and the total is multiplied by ⅔. The resulting value is raised to one-second power to obtain the thickness non-uniformity index (Rpy) (unit: mV).
The present second invention relates to a nonwoven fabric for separators of non-aqueous electrolyte batteries which is produced by a wet paper making process, characterized in that the nonwoven fabric has a center surface average roughness SRa of 6 &mgr;m or less in whole wavelength region measured using a tracer method three-dimensional surface roughness meter.
BEST MODE FOR CARRYING OUT THE INVENTION
As elements constituting the nonwoven fabric for separator of non-aqueous electrolyte battery according to the present invention, there are used materials such as inorganic fibers, whiskers, organic fibers, etc.
The inorganic fibers are preferably at least one kind of inorganic fibers selected from micro-glass fibers, alumina fibers, alumina-silica fibers and rock wools.
In the nonwoven fabric for separator of non-aqueous electrolyte battery characterized by containing a whisker comprising an inorganic compound, the composition of the whisker is preferably at least one member selected from Al
2
O
3
, 9Al
2
O
3
.2B
2
O
3
, SiC, Si
3
N
4
, K
2
O.6TiO
2
, K
2
Ti
6
O
13
, TiO
2
, BaTiO
3
, Mg
2
B
2
O
5
and ZnO.
Average fiber diameter of the inorganic fibers is preferably 3 &mgr;m or less, and amount of the inorganic fibers in the nonwoven fabric is preferably 20-80% by weight.
The micro-glass fibers preferably comprise at least one of E glass containing 1% by weight or less of sodium oxide (in terms of Na
2
O) and silica glass containing 99% by weight or more of silicon dioxide (in terms of SiO
2
).
In the nonwoven fabric for separator of non-aqueous electrolyte batteries characterized by containing organic fibers, it is preferred that at least a part of the organic fibers are fibrillated to 1 &mgr;m or less in fiber diameter.
Furthermore, it is preferred that the nonwoven fabric contains organic fibers at least a part of which are fibrillated to 1 &mgr;m or less in fiber diameter and has a void content of 35-80%.
Furthermore, it is preferred that the nonwoven fabric for separator of non-aqueous electrolyte battery contains organic fibers at least a part of which are fibrillated to a fiber diameter of 1 &mgr;m or less and has a gas permeability of 100 mmHg or higher.
The organic fibers preferably contain one kind or more organic fibers selected from the group consisting of polypropylene fibers, polyethylene fibers, polymethylpentene fibers and acrylic fibers.
It is preferred to contain heat resistant organic fibers having a melting point or heat decomposition point of 25° C. or higher. The heat resistant organic fibers more preferably comprise one kind or more fibers selected from the group consisting of aramid fibers, polyphenylene sulfide fibers, polyarylate fibers, polyether ketone fibers, polyimide fibers, polye
Ashida Tetsuya
Tsukuda Takahiro
Kalafut Stephen
Martin Angela J.
Mitsubishi Paper Mills Limited
Pillsbury & Winthrop LLP
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