EP0931364A1

EP0931364A1 - Electrochemical accumulator with electrolyte reserve

Info

Publication number: EP0931364A1
Application number: EP98937601A
Authority: EP
Inventors: Stéphane Senyarich; Christian Pineau
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel CIT SA; Alcatel Lucent SAS
Priority date: 1997-07-10
Filing date: 1998-07-09
Publication date: 1999-07-28
Also published as: JP2001500314A; FR2766015A1; WO1999003164A1; WO1999003164A8; FR2766015B1

Abstract

The invention concerns an electrochemical accumulator comprising a generally cylindrical or prismatic chamber (5) containing liquid electrolyte (4) and electrochemical set (6) comprising at least an alternation of a positive electrode, a separator and a negative electrode, said accumulator comprising, at least partially between the chamber closed end constituting the accumulator base and the electrochemical set, at least one electrolyte reserve means, comprising a porous material, in contact with said set. Said accumulator is characterised in that said porous material is resistant to the electrolyte, not less hydrophilic than the separator and practically incompressible, preferably said porous material is a polyolefin made hydrophilic if necessary.

Description

Electrochemical cell with electrolyte reserve

The present invention relates to an electrochemical accumulator comprising an enclosure, generally cylindrical or prismatic, comprising liquid electrolyte and an electrochemical bundle comprising at least one alternation of positive electrode, separator and negative electrode. In particular, the invention relates to alkaline accumulators operating for example from nickel - cadmium or nickel - metal hydride electrochemical couples.

In recent alkaline cylindrical accumulators, operating for example from electrochemical couples nickel - cadmium or nickel - metal hydride, the energy density is so high that the active material is extremely confined, which involves a strong reduction in the porosity of the electrodes. On the other hand, the electrolyte, which allows the functioning of the electrode and which is housed in the porosity of the assembly made up of the electrodes and the separator during the filling of the accumulator, must occupy a larger volume within from the accumulator if the amount of active ingredient increases. The problem that arises is therefore to introduce the quantity of electrolyte necessary for the correct functioning of the accumulator, even though the pore volume of the assembly consisting of the electrodes and the separator is insufficient.

Indeed, when one seeks to introduce the quantity of electrolyte necessary for the proper functioning of the accumulator, it can no longer be absorbed by the porous, saturated system. Then part of the volume of the electrolyte remains and floats above the coil, the coil being the assembly consisting of the electrodes and the separator which are spiral together. Under these conditions it is then impossible to close the cover which seals the accumulator without causing an electrolyte overflow, unless removing the excess electrolyte which floats. Such a reduction in the amount of electrolyte introduced into the accumulator is to the detriment of the electrochemical performance of said accumulator. It is therefore interesting to find a method for introducing the entire volume of electrolyte necessary for the correct functioning of the accumulator.

This is why it has been envisaged to use electrolyte reserves by means of a porous material constituting a means of reserve of the electrolyte, generally placed at the bottom of the accumulator as described for example in the application for European patent EP-A2-0 391 720 or US Pat. No. 4,460,666 However, such systems pose the problem of crushing the reserve means consisting mainly of untreated porous materials, which involves a loss of porosity of the reserve means and so in the long term the problem posed is not solved. In addition, such systems do not guarantee the presence of electrolyte within said practically permanent material during use. So, at the end of the life of the accumulator, if said means is drained the separator of the accumulator cannot draw from this reserve of electrolyte, which decreases the service life of such a system And if said material is less hydrophilic than the separator, it is emptied as soon as the filling is completed by the separator and the electrolyte floats

The object of the present invention is an electrochemical accumulator comprising an enclosure, generally cylindrical or prismatic, comprising liquid electrolyte and an electrochemical bundle comprising at least one alternation of positive electrode, separator and negative electrode, said accumulator comprising, at least in part between the closed end of the enclosure constituting the bottom of the accumulator and the electrochemical bundle, at least one electrolyte reserve means, comprising a porous material, in contact with said bundle, said accumulator being characterized in that said porous material is resistant to the electrolyte, of hydrophilicity greater than or equal to that of the separator and practically incompressible

An embodiment of the accumulator according to the invention is such that it further comprises at least one means of incompressibility of said reserve means, preferably located at least in part between the reserve means and the electrochemical bundle

Preferably said reserve means is full, that is to say that it comprises practically only porous material. For example said reserve means is a washer fitted to the bottom of the accumulator.

Said accumulator also has the advantage of allowing the introduction into it of the volume of electrolyte necessary for its proper functioning. Such a volume of electrolyte is calculated from the amount of active material present in said accumulator, then it is generally empirically adjusted, as known to those skilled in the art

By the treatment which it has undergone, the porous material of the reserve means retains its hydrophilicity practically permanently, which is measured at the level of conditions of use of the accumulator, for example by test at 10 ° C. for approximately 10 days Furthermore, said material resists the electrolyte, which is measured in terms of the conditions of use of the accumulator, for example by test at 40 ° C for one year

The hydrophilicity of the porous material of the reserve means is at least equal to that of the separator Thus said material retains its volume of electrolyte just after filling, before closing the accumulator

The porous material of the reserve means is almost incompressible, which is measured for example by the following test under compression corresponding to a pressure of 5 MPa, the thickness must decrease by at most 25%

The porous material is generally the same as that constituting the separator, preferably chosen from the group formed by non-woven polyolefin felts if necessary, made hydrophilic, said polyolefin being generally chosen from the group formed by the following elements: polypropylenes, polyethylenes and propylene-ethylene copolymers

Said polyolefin has been made hydrophilic, if necessary, generally by at least one treatment chosen from the following treatments: grafting of acrylic acid, sulfonation, corona treatment and plasma treatment, all these treatments being well known to those skilled in the art

The reserve means according to the invention is preferably a part whose periphery is of shape substantially identical to the shape of the walls of the enclosure, and generally of size identical to or less than that of the walls of the enclosure, and thickness for example between 0.1 and 5 mm for a cylindrical enclosure of AA format (R6)

The porous material generally has a grammage of between 20 and 300 g / m ²

The incompressibility means is generally made of any material which gives it adequate mechanical and chemical resistance. In particular, said means can be made of plastic such as PVC (Polyvinyl Chloride).

Preferably, said incompressibility means is such that it allows between 5 and 95% of contact ace between said beam and said reserve means, compared to the contact which would be established in the absence of said incompressibility means. example if the enclosure is cylindrical and if the reserve means is a porous washer with a diameter substantially equal to the internal diameter of the enclosure, and with the closest surface area possible from that of the bottom of the enclosure, the incompressibility means can be a studded washer also of diameter substantially equal to the internal diameter of the enclosure, and comprising perforations whose surface is between 5 and 95% of the surface of the studded washer

A preferred incompressibility means according to the invention comprises a contact means located between said beam and said reserve means, as well as at least one means for maintaining said contact means situated for example between said contact means and the end closed of the enclosure Thus, in the case of the example described above, the studs of the studded washer are the means for holding said washer, the contact means being said perforated washer itself

The invention relates more particularly to alkaline accumulators, and in particular those in which the active material of the positive electrode is metal oxide, and in particular nickel oxide, and in which the active material of the negative electrode contains cadmium or else a hydrurable metal, for example an alloy powder of type A'B ' _y , where y is between 1 and 2.5, where A' is at least one element chosen from the group formed by Ti, Zr, Hf and where B 'is at least one element chosen from the group formed by V, Mn, Cr, Ni, Co, Fe, Mo and Al, or else an alloy powder of type AB _X , where x is included between 4.8 and 5.4, where A is at least one element chosen from the group formed by La, Ce, Nd, Pr Y and the misch-metals, generally rich in La or Ce, and where B is at least an element chosen from the group formed by Ni, Mn, Al, Co, Fe, Cu and Mo, or any other hydridable alloy known to those skilled in the art

The invention will be better understood and other advantages and features will appear on reading the following description, given without limitation, with reference to Figures 1 to 3

Figure 1 shows a cylindrical accumulator in section l-l just before filling with electrolyte, comprising a porous washer and a studded washer

Figure 2 is a partial view it shows a studded washer as shown in Figure 1, seen from below

FIG. 3 represents a cylindrical accumulator in axial section just before it is filled with electrolyte, comprising a porous washer In FIG. 1, the cylindrical electrochemical accumulator according to the present invention comprises, inside a cylindrical casing 5, electrodes 6 provided with a connection 7 and wound in a spiral around an axial chimney 8 used for the electrolyte filling

The external periphery of all of the spiral electrodes is generally not strictly cylindrical so that there remains a conduit 9 for the evacuation of the air displaced by the electrolyte In fact, during the spiraling of the electrodes, it is observed outside the coil obtained an excess thickness constituted by the end of the wound electrodes Introduced into a perfectly cylindrical envelope, all of the electrodes leave at the location of this excess thickness over the entire height of the cylindrical envelope a conduit allowing the rising air In addition, because of the rigidity of the electrodes, the winding thereof has multiple facets leaving voids between the turns of the coil where the electrolyte or air can circulate For example the figure 1 shows a substantially cylindrical conduit 9 whose section perpendicular to the axis of the enclosure is substantially a crown

The electrolyte which is introduced into the axial chimney 8 flows downwards where it reaches the bottom of the casing above a washer 3 pierced with holes 2 II spreads through the electrodes as well as below the washer 3 in a porous washer 4, while expelling the air, which is evacuated outside by the conduit 9

The washer 3 may comprise, as shown in FIG. 2, holes 2 and bosses 1, the latter are represented diagrammatically by a circle surrounding a cross. The washer 3 may be of diameter less than the internal diameter of the envelope around its entire periphery. , as shown in FIGS. 1 and 2 The washer 3 can also have tongues which come to bear against the internal wall of the envelope and keep it against a displacement which would offset it (not shown) The number of holes drilled in the washer can be significant with respect to the number of bosses (fig 2) or significantly lower In FIG. 1, the surface of the holes 2 is for example approximately equal to 10% of the surface of the washer 3 Similarly , the washer 4 can be of diameter smaller than the internal diameter of the envelope, as shown in FIG. 1 It can be circumscribed below the studded washer 3, as shown in the figures 1 and 2, or a diameter slightly different from that of said studded washer 3 (not shown) In FIG. 3, the electrochemical accumulator comprises, inside a cylindrical casing 5, electrodes 6 provided with a connection 7 and wound in a spiral around an axial chimney 8 used for filling with electrolyte A l reverse of the accumulator of Figure 1, there is not specifically provided a conduit for the evacuation of the air displaced by the electrolyte Nevertheless it can be estimated that there is sufficient space for the passage of said air , for the reasons explained above

The electrolyte which is introduced into the axial chimney 8 flows downwards where it reaches the bottom of the envelope on the porous washer 4 II spreads in the electrodes as well as in the washer 4, while driving out the air The washer 4 may have a diameter substantially equal to the internal diameter of the envelope, as shown in FIG. 3

Examples

The examples which follow illustrate the invention, without however limiting its scope. They relate to a cylindrical accumulator operating from the electrochemical couple nickel - metal hydride, the size of the container being in AA format The active material of the positive electrode is nickel hydroxide, the active material of the negative electrode is an alloy powder of type AB ₅ , where A is a misch-metal rich in Ce, and where B is

Nι _{3 55} Cθo ₇₅ Alo ₃ Mn ₀₄ The numerical data are summarized in a final table

Example 1 (comparative)

An accumulator 1 consists of a positive electrode, a separator, a volume V, substantially equal to 2.15 cm ³ , of alkaline electrolyte necessary for the proper functioning of the amount of active material present in the accumulator , and a negative electrode The accumulator 1 is filled by pouring the electrolyte onto the bobbin, it is found that part of the volume V does not manage to penetrate the bobbin and floats on the surface of the latter The volume supernatant is withdrawn using a syringe, it is equal to 0.1 cm ³ After collection, the accumulator 1 can be closed

After having undergone specific electrical training, typically consisting of two successive charge and discharge cycles, the accumulator 1 is charged for two hours at a C regime (full charge of the element carried out in one hour). At the end of these two hours, the internal pressure of the accumulator 1 is 7 bars (1 bar = 10 ⁵ Pa).

The accumulator 1 is then successively discharged and charged at a rate of C (discharge and full charge of the accumulator in one hour). Its lifespan is 500 cycles.

Example 2 (comparative)

An accumulator 2 is identical to the accumulator 1. The accumulator 2 is filled by centrifugation and just after this step, no supernatant liquid is observed. However, a few minutes after filling, there is a supernatant liquid which is raised along the reel. The supernatant volume is withdrawn using a syringe: it is equal to 0.1 cm ³ . After removal, the accumulator 2 can be closed.

After having undergone a specific electrical formation identical to that of Example 1, the accumulator 2 is charged for two hours at a rate of C (full charge of the element carried out in one hour). At the end of these two hours the internal pressure of the accumulator 2 is 7 bars.

The accumulator 2 is then successively discharged and charged at a rate of C (discharge and full charge of the accumulator in one hour). Its lifespan is 500 cycles.

Example 3 (comparative)

An accumulator 3 is identical to accumulator 1. A plastic PVC washer supporting crampons oriented downwards, identical to that of FIG. 2, is introduced into the bottom of the bucket before the introduction of the spool. The accumulator 3 is then filled by centrifugation and just after this step, no supernatant liquid is observed. However, a few minutes after filling, there is a supernatant liquid which is raised along the reel. The supernatant volume is removed at using a syringe it is equal to 0.1 cm ³ After removal, the accumulator 3 can be closed

After having undergone specific electrical training identical to that of Example 1, the accumulator 3 is charged for two hours at a rate of C (full charge of the element carried out in one hour). At the end of these two hours, the internal pressure of the accumulator 3 is 7 bars

The accumulator 3 is then successively discharged and charged at a rate of C (discharge and full charge of the accumulator in one hour) Its lifespan is 500 cycles

Example 4 (according to the invention)

An accumulator 4 is identical to accumulator 1 A washer, as shown in FIG. 3, of non-woven poiypropylene felt, made hydrophilic by grafting treatment of acrylic acid, is introduced into the bottom of the cup before the introduction of the reel Such a material meets the mechanical incompressibility test, therefore is practically incompressible, resists the electrolyte and has a hydrophilicity greater than or equal to that of the separator The accumulator 4 is then filled by centrifugation and just after this step, we does not observe supernatant liquid One thus waits 1 hour without detecting the presence of supernatant liquid The accumulator 4 can thus be closed with the quantity V of electrolyte

After having undergone a specific electrical formation identical to that of Example 1, the accumulator 4 is charged for two hours at a rate of C (full charge of the element carried out in one hour). At the end of these two hours, the internal pressure of the accumulator 4 is 7 bars

The accumulator 4 is then successively discharged and charged at a rate of C (discharge and full charge of the accumulator in one hour) Its lifespan is 700 cycles Example 5 (according to the invention)

An accumulator 5 is identical to accumulator 1 The washer of nonwoven felt rendered hydrophilic described in Example 4, as well as the rigid studded washer described in Example 3 and placed above (in contact with the spool) the felt washer, are introduced at the bottom of the bucket before the introduction of the reel. The plastic washer is perforated in order to allow the electrolyte present in the nonwoven washer to join the separator as the electrolyte is consumed during cycling. The accumulator 5 is then filled by centrifugation and just after this step, no supernatant is observed. One thus waits 1 hour without detecting the presence of supernatant. The accumulator 5 can thus be closed with the quantity V of electrolyte.

After having undergone a specific electrical formation identical to that of Example 1, the accumulator 5 is charged for two hours at a rate of C (full charge of the element carried out in one hour). At the end of these two hours, the internal pressure of the accumulator 5 is 7 bars

The accumulator 5 is then successively discharged and charged at a rate of C (discharge and full charge of the accumulator in one hour) Its lifespan is 700 cycles

Tablea

Claims

1 / Electrochemical accumulator comprising an enclosure comprising liquid electrolyte and an electrochemical bundle comprising at least one alternation of positive electrode, of separator and of negative electrode, said accumulator comprising, at least partly between the closed end of the enclosure constituting the bottom of the accumulator and the electrochemical bundle, at least one electrolyte reserve means, comprising a porous material, in contact with said bundle, said accumulator being characterized in that said porous material is resistant to electrolyte, of hydrophilicity greater than or equal to that of the separator and practically incompressible.

2 / accumulator according to claim 1 such that said porous material is chosen from the group formed by non-woven polyolefin felts.

3 / accumulator according to claim 2 such that said polyolefin is chosen from the group formed by the following elements: polypropylenes, polyethylenes and propyiene-ethylene copolymers.

4 / accumulator according to claim 3 such that said polyolefin has been made hydrophilic by at least one treatment chosen from the following treatments: acrylic acid grafting, sulfonation, corona treatment and plasma treatment.

5 / accumulator according to one of claims 1 to 4 as it further comprises at least one means of incompressibility of said reserve means.

6 / accumulator according to claim 5 such that said incompressibility means is located at least partly between the reserve means and the eiectrochemical bundle.

It accumulator according to one of claims 5 or 6 as it allows between 5 and 95% of contact between said beam and said reserve means, compared to the contact which would be established in the absence of said incompressibility means.

8 / accumulator according to one of claims 5 to 7 such that said incompressibility means comprises a contact means located between said beam and said reserve means, as well as at least one means for holding said contact means.

9 / accumulator according to claim 8 such that said holding means is located between said contact means and the closed end of the enclosure.