SPECIFIC SEPARATOR COMPRISING AN ELECTROLYTE FOR AN ELECTROCHEMICAL ACCUMULATOR AND ELECTROCHEMICAL CELL FOR AN ACCUMULATOR COMPRISING SUCH A SEPARATOR

Abstract

The invention relates to a separator for an electrochemical accumulator comprising a substrate provided with cavities, said substrate consisting of one or more polymers, at least one of which is a polymer from the family of polyaryletherketones, all or part of said cavities being filled in whole or in part by a gelled polymer electrolyte.

Claims

1. A separator for an electrochemical accumulator comprising a substrate provided with cavities, said substrate consisting of one or more polymers, at least one of which is a polymer from the family of polyaryletherketones, all or part of said cavities being filled in whole or in part by a gelled polymer electrolyte, wherein the gelled polymer electrolyte comprises: (A) a matrix comprising: (A-1) an organic portion comprising at least one fluorinated polymer (F) comprising at least one repeating unit derived from the polymerisation of a fluorinated monomer and at least one repeating unit derived from the polymerisation of a monomer comprising at least one hydroxyl group, optionally in the form of a salt; and (A-2) an inorganic portion formed, in whole or in part, of one or more oxides of at least one element M selected from Si, Ti and Zr and combinations thereof; and (B) a liquid electrolyte confined or trapped within the matrix.

2. The separator according to claim 1, wherein the substrate consists only of one or more polymers from the family of polyaryletherketones.

3. The separator according to claim 1 or 2, wherein the polyaryletherketones are polymers comprising repeating units, of which more than 50 mol % of said repeating units are repeating units comprising an —Ar—C(O)—Ar′-group, wherein Ar and Ar′, identical or different from each other, are aromatic groups, these units being called units (R.sub.pAEK).

4. The separator according to claim 3, wherein the units (R.sub.PAEK) are selected from the group consisting of the units of formulas (J-A) to (J-O) as defined below: ##STR00012## ##STR00013## wherein: each R′, identical or different, is selected from the group consisting of halogen atoms, alkyl, alkylvinyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, sulphonate, phosphonate, alkali or alkaline earth metal alkylphosphonate, amine and quaternary ammonium groups; j′ is zero or an integer ranging from 1 to 4.

5. The separator according to claim 4, wherein j′ is equal to zero.

6. The separator according to any one of claims 3 to 5, wherein the repeating units (R.sub.PAEK) are selected from those of formulas (J′-A) to (J′-O) as defined below: ##STR00014##

7. The separator according to any one of the preceding claims, wherein the substrate is a polyetheretherketone substrate.

8. The separator according to any one of the preceding claims, wherein the substrate is in the form of a grid resulting from an interlacing of polymer strands.

9. The separator according to any one of the preceding claims, wherein the substrate is in the form of a grid having a lozenge-shaped mesh.

10. The separator according to any one of the preceding claims, wherein the gelled polymer electrolyte further occupies all or part of the surface of the substrate in the form of a layer.

11. The separator according to any one of the preceding claims, wherein the fluorinated polymer (F) comprises, as repeating units derived from the polymerisation of a fluorinated monomer, a repeating unit derived from the polymerisation of a monomer from the class of C.sub.2-C.sub.8 perfluoroolefins, such as hexafluoropropene and a repeating unit derived from the polymerisation of a monomer from the class of C.sub.2-C.sub.8 hydrogenated fluoroolefins.

12. The separator according to any one of the preceding claims, wherein the repeating unit(s) derived from the polymerisation of a monomer comprising at least one hydroxyl group, optionally in the form of a salt, are one or more repeating units derived from the polymerisation of a monomer of formula (I) below: ##STR00015## wherein R.sup.9 to R.sup.11 represent, independently of each other, a hydrogen atom or a C.sub.1-C.sub.3 alkyl group and R.sup.12 is a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group.

13. The separator according to any one of the preceding claims, wherein the liquid electrolyte trapped within the matrix is an ion-conducting electrolyte comprising at least one organic solvent, at least one metal salt and optionally a compound from the family of vinyl compounds.

14. A method for preparing a separator as defined according to claim 1, comprising the following steps: a step of depositing, in all or part of the cavities of the substrate, a gelled polymer electrolyte composition; a step of drying the composition thus deposited.

15. The preparation method according to claim 14, wherein, when the substrate is a grid, the deposition step is carried out on both faces of the grid.

16. The preparation method according to claim 14 or 15, wherein the deposition step is carried out by the die coating technique.

17. An electrochemical cell for electrochemical accumulator comprising a positive electrode, a negative electrode and a separator as defined according to any one of claims 1 to 13 which is interposed between the positive electrode and the negative electrode.

18. The electrochemical cell for an electrochemical accumulator according to claim 17, wherein the negative electrode and the positive electrode comprise a liquid electrolyte trapped within a polymer matrix.

19. The electrochemical cell according to claim 18, wherein the polymer matrix is made of at least one gelling polymer (FF), the gelling polymer(s) (FF) being selected from fluorinated polymers comprising at least one repeating unit derived from the polymerisation of a fluorinated monomer and at least one repeating unit derived from the polymerisation of a monomer comprising at least one carboxylic acid group, optionally in the form of a salt.

20. An electrochemical accumulator comprising at least one electrochemical cell as defined according to any one of claims 17 to 19.

Description

BRIEF DESCRIPTION OF FIGURES

[0229] FIG. 1, already described above, is a photograph of a lozenge-shaped mesh grid which can be used for the separators of the invention.

[0230] FIG. 2, already described above, illustrates the die coating technique implemented for the preparation of a separator in accordance with the invention.

[0231] FIG. 3 illustrates, for formation cycles at C/20, the evolution of the voltage U (in V) as a function of the imposed current I (in A) over time t (in h) (respectively the curves a and b for the current and the curves c and d for the voltage) in the context of example 1.

[0232] FIG. 4 illustrates the evolution of the voltage U (in V) as a function of the discharge capacity C (in mAh) (curve a for the accumulator compliant with the invention and curve b for the non-compliant accumulator) in the context of Example 1.

[0233] FIG. 5 illustrates a tensile test (evolution of the force F (in N) as a function of the deformation D (in mm)) (curve a for the separator which is in accordance with the invention and curve b for the separator which is not in accordance with the invention) in the context of Example 1.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

Example 1

[0234] This example relates to the preparation of an accumulator comprising a separator in accordance with the invention.)

1° Preparation of the Separator in Accordance with the Invention

[0235] First, a gelled polymer electrolyte composition is prepared.

[0236] To do this, 10 g of a copolymer comprising repeating units derived from the polymerisation of vinylidene fluoride (VDF), 2-hydroxyethyl acrylate (HEA) and hexafluoropropene (HFP), this polymer being called PVdF-HEA-HFP(VDF 96.8 mol %-HEA 0.8 mol % and HFP 2.4 mol %) and having an intrinsic viscosity of 0.08 g/L are introduced into a double-walled synthesis reactor of 300 mL previously inerted with argon, then 67 mL of anhydrous acetone at 99.9% purity are added. The mixture is mechanically stirred for 30 min at 60° C. under an argon stream. Then 0.10 g of dibutyltin dilaurate (DBTL) are added and the resulting mixture is stirred for 90 minutes at 60° C. under an argon stream. 0.40 g of 3-(triethoxysilyl)propyl isocyanate (TSPI) are then added and the mixture is stirred for 90 minutes at 60° C. under an argon stream. 37.50 g of electrolyte (composed of a mixture (EC:PC) in mass proportion (1:1) (EC designating ethylene carbonate and PC designating propylene carbonate), vinylene carbonate (up to of 2% by mass) and a lithium salt LiPF.sub.6 (1 M)) are added and the mixture is stirred for 30 min at 60° C. under an argon stream. 2.50 g of formic acid are then added and the mixture is stirred for 30 minutes at 60° C. under an argon stream. Finally 3.47 g of tetraethoxysilane are added and the mixture is stirred for 30 minutes at 60° C. under an argon stream.

[0237] The substrate used in this example is a substrate in the form of a polyetheretherketone grid with a thickness of 50 μm with a lozenge-shaped mesh. The long diagonal of the mesh measures 1.96 mm and the polymer strand has a width of 0.114 mm. The used PEEK grid is marketed under the reference 2PEEK4.5-077F from the supplier Dexmet Corporation.

[0238] The gelled electrolyte composition is deposited on one of the faces of the aforementioned substrate by a comma bar coating method in a dry atmosphere (Dew point: −20° C.) at a speed of 1 m/min. The composition thus deposited is subjected to drying in line in a 1.5 m long oven which is regulated between 40 to 60° C. depending on the drying zones.

[0239] The mechanical properties of the separator in accordance with the invention are evaluated on a Shimadzu AG-X brand traction bench equipped with a 50 N force sensor. The sample of the separator is pre-cut in the form of a width 4 mm and gauge length of 25 mm. The pulling speed is 50 mm/min. FIG. 5 shows that the tensile force of the separator according to the invention (a) is 2.53 N on average, while the tensile force of the separator in the absence of the polyetheretherketone substrate (b) is 0.18N. The tensile strength is therefore much higher for the separator according to the invention.

B) Preparation of the Electrodes

[0240] For the preparation of the inks intended for the preparation of the electrodes, the same gelling polymer is used, whether for the positive electrode or the negative electrode. This is the polymer comprising repeating units derived from the polymerisation of vinylidene fluoride (96.7 mol %), acrylic acid (0.9 mol %) and hexafluoropropene (2.4 mol %) and having an intrinsic viscosity of 0.30 L/g in dimethylformamide at 25° C. This polymer is designated below by the terminology “Polymer 1”. This is incorporated into the ink intended for the manufacture of the electrodes in the form of an acetone solution in which 10% of polymer 1 has been dissolved at 60° C.

*Preparation of the Negative Electrode

[0241] To do this, a mixture of 75% by mass of graphite (D.sub.50=20 μm) and 25% by mass of graphite (D.sub.50=3.5 μm) was added to the solution of Polymer 1 mentioned in the preceding paragraph, so that the mass ratio of (graphite/Polymer 1) is 90/10. To the resulting mixture, there was also added a liquid electrolyte composed of a mixture (EC:PC) in mass proportion (1:1) (EC designating ethylene carbonate and PC designating propylene carbonate), vinylene carbonate (up to 2% by mass) and a lithium salt LiPF.sub.6 (1 M). The liquid electrolyte was added so as to obtain a mass ratio (M.sub.electrolyte/(M.sub.electrolyte+M.sub.polymer 1))×100 equal to 75%.

[0242] The whole placed in the closed tank of 500 mL of a mixer of the disperser type, in order to avoid the evaporation of acetone, was mixed for 20 minutes at 4000 revolutions per minute in a dry atmosphere (Dew point: −20° C.).

[0243] This ink is then deposited on a copper current collector by a comma bar coating method in a dry atmosphere (dew point −20° C.) at a speed of 1 m/min. The composition thus deposited is subjected to drying in line in a 1.5 m long oven regulated between 40 to 60° C. according to the drying zones. The resulting layer constituting a negative electrode was die-cut to obtain a square electrode area of 17.22 cm.sup.2 (41.5 mm*41.5 mm).

*Preparation of the Positive Electrode

[0244] To do this, a mixture of 50% by mass of carbon black C-NERGY® C65 and 50% by mass of carbon fibres obtained in the vapor phase called “VGCF fibres” and LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2 (called NMC) was added to the solution of Polymer 1 mentioned in the paragraph above so that the mass ratio of ((VGCF+C65+NMC)/polymer 1) was 92.8/7.2 with a mass ratio of (VGCF+C65)/NMC equal to 7.7/92.3. To the resulting mixture, there was also added a liquid electrolyte composed of a mixture (EC:PC) in mass proportion (1:1) (EC designating ethylene carbonate and PC designating propylene carbonate), vinylene carbonate (up to 2% by mass) and a lithium salt LiPF.sub.6 (1 M). The liquid electrolyte was added so as to obtain a mass ratio (M.sub.electrolyte/(M.sub.electrolyte+M.sub.polymer 1))×100 equal to 85.7%.

[0245] The whole placed in the closed tank of 500 mL of a mixer of the disperser type in order to avoid the evaporation of the acetone was mixed for 30 minutes at 4000 revolutions per minute in a dry atmosphere (Dew point −20° C.).

[0246] This ink is then deposited on an aluminum current collector by a comma bar coating method in a dry atmosphere (Dew point −20° C.) at a speed of 1 m/min. The composition thus deposited is subjected to drying in line in a 1.5 m long oven regulated between 40 to 60° C. according to the drying zones. The resulting layer constituting a positive electrode was die-cut to obtain a square electrode area of 16 cm.sup.2 (40 mm*40 mm).

3-Preparation of the Accumulator and Results

[0247] The separator is brought into contact with the negative electrode mentioned above, then the positive electrode is stacked on this assembly.

[0248] The stack is packed in a flexible sachet of the “coffee bag” type then hermetically sealed by heat sealing.

[0249] The characteristics of the accumulator in terms in particular of nominal voltage, cycling terminals, surface capacity and estimated practical capacity are set out in the table below in comparison with a similar accumulator, prepared using the same inks for the formation of the electrodes on a gelled polymer electrolyte film as described above, but said film not being impregnated on a polyetheretherketone substrate.

[0250] The table below presents comparative results in terms of nominal voltage, cycling terminals, surface capacity and estimated practical capacity.

TABLE-US-00001 Characteristics of the In accordance with Not in accordance accumulator the invention with the invention Nominal voltage (V) 3.65 3.65 Cycling terminals (V) 2.8-4.15 2.8-4.15 Mass of active material (mg) 238.95 244.36 Basis weight of AM (mg/cm.sup.2) 14.93 15.27 Surface capacity (mAh/cm.sup.2) 29 2.13 Estimated practical capacity 33 34 (mAh)

[0251] It emerges from this table that the accumulator which is in accordance and the accumulator which is not in accordance with the invention have similar characteristics, which allow better comparing their electrochemical performances.

[0252] FIG. 3 illustrates, for formation cycles at C/20, the evolution of the voltage U (in V) as a function of the imposed current I (in A) over time t (in h) (respectively the curves a and b for the imposed current of the accumulator which is in accordance with the invention and the accumulator which is not in accordance with the invention and the curves c and d for the evolution of the voltage for the accumulator which is in accordance with the invention and the accumulator which is not in accordance with the invention). It shows that the charge and discharge profiles during the formation cycles at C/20 are similar between the cell including a separator which is in accordance with the invention compared to that which is not in accordance with the invention. Only the charging and discharging times are slightly different.

[0253] FIG. 4 illustrates the evolution of the voltage U (in V) as a function of the discharge capacity C (in mAh) (curve a for the accumulator which is in accordance with the invention and curve b for the non-compliant accumulator). It shows that the measured capacities are close to the estimated capacities listed in the table above and that the presence of a separator in accordance with the invention does not alter these properties.

[0254] FIG. 5 illustrates a tensile test (evolution of the force F (in N) as a function of the deformation D (in mm)) (curve a for the separator which is in accordance with the invention and curve b for the separator which is not in accordance with the 'invention). It demonstrates that the mechanical properties of the separator which is in accordance with invention are reinforced compared to the separator which is not in accordance with the invention. Indeed, the tensile strength is much higher when the substrate of the gelled polymer electrolyte is used.