FR2545276A1 - VEIL SEPARATOR FOR ALKALINE ELECTROLYTE BATTERIES - Google Patents

Abstract

A SAILING SEPARATOR IS DESCRIBED FOR ALKALINE ELECTROLYTE BATTERIES OF WHICH FIBERS ARE, AT LEAST 20 BY WEIGHT, HOLLOW POLYPROPYLENE FIBERS, PREFERABLY WITH PERIPHERAL LAYER WITH OPEN DOORS. THIS ALKALI RESISTANT SEPARATOR ALLOWS TO OBTAIN A CAPACITY NEVER REACHED UNTIL HERE TO BIND AND RETAIN ELECTROLYTE SOLUTIONS, BECAUSE OF HOLLOW VOLUMES OF FIBERS, EVEN AT HIGH TEMPERATURE AND UNDER QUICK DISCHARGE CONDITIONS. IN OTHER PROPOSALS ACCORDING TO THE INVENTION, THE ADVANTAGEOUS TYPES OF REINFORCEMENT FOR SAIL OF THIS TYPE ARE PRESENTED.

Description

Veil separator for batteries with alkaline electrolytes The invention is

  relates to a sail separator for batteries

with alkaline electrolytes.

  In a known manner, separators of this type consist of a veil of polyamide or polypropylene fibers. The former are characterized by a high absorption capacity and possibility of retention for the liquid electrolyte, which

  which provides a high discharge intensity of the batteries.

  Their serious disadvantages however reside, at higher temperature (around 800 C) in their defective resistance with regard to alkaline solutions and with regard to oxidation The separators send with, or in, polypropylene fibers do not present these disadvantages and are even particularly advantageous for a low consumption of electric current; their capacity of absorption and

  retention of electrolyte solutions is unpleasant, however

  wholly weak Treatment of the polypropylene fibers with active substances on the surface can only be done under conditions; a separator impregnated in this way will quickly become unusable, if the battery is asked for a short discharge with a high intensity, because it cannot permanently retain under these conditions

  the required amount of electrolyte -

  The object of the invention is to synthesize the known advantageous properties of a polypropylene fiber separator and the possibility of absorption and retention, so as to be available at any time, even under difficult temperature conditions and of

  discharge, sufficient amount of electrolyte.

  The perfect way to reach this object is, according to the-

  vention, to use a separating veil made up of at least 20% in

  weight of polypropylene hollow fibers with a titration of 5 from

  niers, a length _ 100 mm and an inside diameter

C 15 microns.

  It is certainly known, from document US-PS 4,226,921, to use

  read in the separators for high temperature alkali-sulfur cells, hollow fibers, preferably arranged in parallel, in materials

  temperature stable, such as glass or ceramic

  that the object of these separators is, however, unlike the invention, to separate two electrolyte baths, such as for example Nax Syet Na as well as to selectively allow permeability for Na ions. Such batteries work at temperatures at surroundings

  of 400 C and, in essence, require entirely different conditions

  separator rents as alkaline electrolyte batteries.

  We also know from document DE-OS 26 30 374 a pro-

  production of hollow polypropylene fibers and their use

  as an ultrafilter, membrane support, for reverse osmosis or as a gas separation membrane The objects targeted here (passage through a material) and the fields of application are not

  comparable with those mentioned for the present invention.

  The separator according to the invention is resistant to alkalis and

  on oxidation, it has a high capacity for absorbing electricity.

  trolyte and it guarantees even for high discharge rates, the existence

  tence of a continuous layer of electrolyte.

  Hollow fibers do not necessarily have to have a circular section. Any form of section is authorized, provided

  that there exists in the longitudinal axis of the fibers a hollow volume conti-

naked and emerging.

  Do not exceed the values indicated for the title, the

  length of strand and the inside diameter of the fibers, otherwise the separation

  erator would have a too coarse structure which would be detrimental to the absorption capacity of the electrolyte solution For the same reason it is necessary to prescribe a proportion of hollow fibers of at least

20% by weight.

  From this knowledge, we propose a partial separator

  particularly advantageous from the point of view of the indicated data of the pro-

  pale and made up of a veil comprising 40% by weight of hollow polypropylene fibers of 3 denier title, fiber length 51 mm and

inner diameter 10 microns.

  One can undertake the manufacture of fiber veils, according to the embodiments, described above and below, of the invention, according to the known process consisting of carding and detaching In a

  advantageous version of the separator according to the invention; the hollow fibers

  its polypropylene ses have a peripheral structure with open pores The manufacture of these fibers is for example described in the document mentioned DE-OS 26 30 374 The pores of the channels participate in another increase in the amount of electrolyte which can be

fixed in the separator.

  First of all, when the veil consists only of hollow polypropylene fibers, it is necessary to undertake the fixing of the veil using a thermoplastic resin, for example sprayed on the fibers in the form of an emulsion A necessary condition is here on the one hand the resistance of the liaison resin with respect to alkaline electrolyte solutions, on the other hand care must be taken

  whereas, in particular in the case of the use of porous hollow fibers,

  its polypropylene, the resin covers the veil only by areas,

  as is necessary for satisfactory fixation.

  This embodiment of the separator represents a variant of -

  the invention of a particularly attractive price.

  The separator veil can also be mixed

  other synthetic fibers, as long as these fibers are also

  slightly resistant to alkalis This is how another advantageous embodiment of the invention consists in thermally fixing the web, in a manner known per se, using thermoplastic olefinic binding fibers. secure fixing by

  simple spot bonding The porosity and capacity of the volu-

  the hollow of the separator not being compromised.

  Bicomponent fibers, with a polypropylene core

  lene and a peripheral polyethylene layer are particularly suitable

  for this purpose; these two-component fibers already provide

  low number a significant reinforcement of the veil, which makes it possible to choose

  if the quantity of polypropylene hollow fibers is high, this in

  the advantage of a high liquid absorption capacity.

  A variant to be expected as particularly advantageous

  siste that all of the material of the separator is made

  bicomponent fibers, the core of which is a hollow fiber of

  lypropylene and whose peripheral layer is in polyolefin Here also the veil is thermally bonded only to the crossing points of the fibers The advantage resides in that here each fiber takes part in the mission to maintain the solution of the electrolyte in its own hollow volume The intermediate volumes between fibers act on the

same way.

  No reported binder degrades the absorption capacity of

  separator for electrolyte The advantages mentioned far outweigh

  the fact that in this form of execution there is no

  porosity of the peripheral layer of the polypropylene fiber.

  Another improvement in the electrolyte absorption capacity of the battery separator according to the invention is possible if the entire fiber complex is treated with a known surfactant, resistant to alkaline solutions and HLB value

  (hydrophilic-lipophilic balance) between 12 and 15.

  Other characteristics and advantages of the invention will be

  better understood on reading the following description from several

examples of realization.

Example 1.

  A veil of 75 g / m 2 was made with a mixture of 50% by weight of polypropylene hollow fibers with a length of 51 mm, a 3 denier titer and 50% by weight of two-component fibers 51 mm long, 1.5 denier, made of a polypropylene core and a peripheral layer of polyetilene This veil was then heat treated without pressure for one minute at

    C A calendar to be followed under a pressure of 100 kg / m 2.

  Comparative example 1 a A veil of 75 g / m 2 made of fibers with two components of

  51 mm long, 1.5 denier title and a polypropylene core

  lene as well as a peripheral layer of polyethylene was subjected to a heat treatment and a calendering process in the same

provided that in Example 1.

  Then the fiber complex was treated with polyoxyethyl ether.

  nonylphenil, a nonionic surfactant with an HLB value

  (hydrophilic-lipophilic balance) of 13.1.

  Comparative example 1 b A 75 g / m 2 veil was made from 100% two-component fibers, 51 mm long, 3 denier in title and having a polyamide core with a melting point high and a peripheral layer of polyamide with a low melting point. The fiber complex was heat treated for one minute without pressure and

  then subjected to the calendering process.

Example 2

  The veil of Example 1 was then treated with polyoxyethyl ether.

  nonylphenyl with an HLB value of 13.1.

  The retention capacity was measured using the following method

  of the electrolyte of the different separators and the measurements are compared.

  The start weight of each sample was a O (g) The sample was immersed at room temperature in a potash solution of

  density of 1.3 g / cm 3 then wrung for 5 minutes in a centrifuge

  geuse at the speed of 2500 rpm After this treatment the sample was weighed again The value obtained was a 1 (g) The retention capacity of the electrolyte A (%) is calculated according to the following formula aa A ÂO xl O (%) ao The retention capacity of electrolyte B (%) was calculated using the same formula. This corresponds to the case where the sample was immersed in a potassium hydroxide solution with a density of 1.3 g / cm. for one month at 80 ° C. The behavior of the separators with regard to their electrolyte retention capacity under intensity of

  high discharge: if there is no loss of electrolyte under de-

  repeated charge at 600 C, the separator is classified as very good It is

  classified as bad if there is a loss of electrolyte.

  The following table summarizes the results of the above measurements.

  Example Example xample xample Comparative comparative temperature measurement 1 1 a 1 b 2

ability to re

election

  trolyte A% 8.1 5.5 8.2 12.5 Ambient temperature Behavior Very good bad Very 600 C under discharge good good high

Claims (6)

  1 Veil separator for batteries with alkaline electrolytes, characterized in that the veil consists of at least 20% by weight of polypropylene hollow fibers having a 5 denier titrec, a length __ 100 mm and an internal diameter; 15 microns. 2 separator according to claim 1, characterized in that   the veil is made up for 40% by weight of hollow poly-   propylene with a title of 3 deniers, a length of 51 mm and a inner diameter of 10 microns.   3 Separator according to claim 1 or claim 2, characterized in that the hollow polypropylene fibers have   a peripheral structure with open pores.   4 separator according to any one of claims 1, 2   or 3, characterized in that the web is bonded in zones by a resin thermoplastic.   Separator according to any one of claims 1, 2 or   3, characterized in that the web is thermally fixed by points   through olefinic binding fibers.   6 Separator according to claim 5, characterized in that the thermoplastic bonding fibers consist of a core   of polypropylene and a peripheral layer of polyethylene.   7 Separator according to claim 6, characterized in that the web is made of 100% two-component fibers, the core of which is a hollow polypropylene fiber according to claim 1 and the peripheral layer of which is made of polyethylene, and in   what it is thermally linked to the crossing points of the fibers.   8 Separator according to any one of the preceding claims.   teeth, characterized in that all the fibers of the web are treated with a non-ionic surfactant, resistant to alkalis and of a   HLB value (hydrophilic-lipophilic balance) between 12 and 15.