FR3073672A1 - PROCESS FOR PREPARING AN ELECTROCHEMICAL CELL FOR LITHIUM BATTERY COMPRISING A SPECIFIC GELIFIED ELECTROLYTE - Google Patents

Abstract

The invention relates to a method for preparing an electrochemical cell for a lithium battery comprising a positive electrode and a negative electrode disposed on either side of a gelled electrolyte, comprising the following steps: a) a production step a cell comprising the positive electrode, the negative electrode disposed on either side of a membrane comprising at least one polymer capable of gelling in contact with a dinitrile solvent; b) a step of bringing said assembly into contact with a composition comprising at least one dinitrile solvent and at least one lithium salt, whereby the membrane gels, thus forming the gelled electrolyte.

Description

PROCESS FOR THE PREPARATION OF AN ELECTROCHEMICAL CELL FOR A LITHIUM BATTERY COMPRISING A SPECIFIC GELLED ELECTROLYTE

DESCRIPTION

TECHNICAL AREA

The present invention relates to a process for the preparation of an electrochemical cell for a lithium battery comprising a specific gelled electrolyte, this process of the invention being easier to implement than the conventional manufacturing processes for this type of cell and which can be transposed to all types of architecture (such as wired architecture) while not sacrificing the final properties of the gelled electrolyte in terms of mechanical properties and conduction properties and allowing flexible cells to be obtained and deformable.

The general field of the invention can thus be defined as that of lithium batteries and, more specifically, batteries of the lithium-ion type.

Batteries of the lithium-ion type are increasingly used as a stand-alone energy source, in particular in portable electronic equipment (such as mobile phones, laptops, tools), where they are gradually replacing accumulators nickel-cadmium (NiCd) and nickel-metal hydride (NiMH). They are also widely used to provide the power supply necessary for new micro applications, such as smart cards, sensors or other electromechanical systems.

Batteries of the lithium-ion type operate on the principle of insertion-disinsertion (or lithiation-delithiation) of lithium according to the following principle.

During the discharge of the battery, the lithium disinserted from the negative electrode in ionic form Li ⁺ migrates through the ionic conductive electrolyte and is interposed in the crystal lattice of the active material of the positive electrode. The passage of each Li ⁺ ion in the internal circuit of the battery is exactly compensated by the passage of an electron in the external circuit, thus generating an electric current. The density of mass energy released by these reactions is both proportional to the potential difference between the two electrodes and to the quantity of lithium which will be inserted in the active material of the positive electrode.

When charging the battery, the reactions occurring within the battery are the reverse reactions of the discharge, namely that:

the negative electrode will insert lithium into the network of the material constituting it; and

- the positive electrode will release lithium.

By this operating principle, batteries of the lithium-ion type therefore require the presence at the electrodes of a material capable of inserting or removing lithium.

To ensure this functioning, the batteries include, for each cell as illustrated in FIG. 1 attached in the appendix, the following essential constituent elements:

a current collector 3 associated with the positive electrode which may be in the form of a metal strip, for example, an aluminum strip;

a positive electrode 5 comprising, as active material, a lithium insertion material, such as a material of formula LiM ¹ PO4, in which M ¹ is a transition element (in particular, LiFePO4), a material of oxide type of at least one transition metal of formula LiMeO ₂ with Me being an element chosen from Ni, Co, Mn and mixtures thereof (in particular, LiCoO ₂ , LiNio, 33Mn ₀ , 33Co ₀ , 330 ₂ );

the electrolyte 7 conventionally consisting of a liquid electrolyte which soaks a porous separator, this electrolyte having to allow the displacement of the lithium ions from the positive electrode to the negative electrode in the process of charging and from the negative electrode to the electrode positive in the discharge process, this liquid electrolyte consisting of a solvent or mixture of organic solvents (for example, carbonate solvents) and at least one lithium salt (such as LiPF ₆ ), the resulting mixture having to be, as far as possible may be, free of water and oxygen;

a negative electrode 9 comprising, as active material, a carbonaceous material (such as graphite), silicon or, in the case of power electrodes, a material of the lithium titanate type (such as Li ₄ Ti50i ₂ );

a current collector 11 associated with the negative electrode which may be in the form of a metal strip, for example, a copper strip, when the active material of the negative electrode is a carbonaceous material or an aluminum strip, when the active material of the negative electrode is a material of the lithium titanate type, the positive electrode, the electrolyte and the negative electrode constituting the “electrochemical core” of the cell.

It is understood that a battery may comprise only a single electrochemical cell as shown, for example, in FIG. 1 or may comprise several electrochemical cells generally connected in series and forming a stack of electrochemical cells, for example, in opposite such as the flat stack or the wound stack.

The cell or cells making up a lithium-ion battery are contained in a package which can take different forms depending on the desired applications:

-a rigid packaging, for example, a box containing the lithium battery;

-a flexible package, for example, in the form of a pouch containing the lithium battery.

This latter type of packaging is particularly appreciated when it comes to designing thin and flexible batteries and is more specifically in the form of a flexible composite material comprising a stack of aluminum layers covered by a polymer layer ( for example, polyethylene, polypropylene, polyamide) via an adhesive layer of polyester-polyurethane.

The production of these batteries with this type of packaging conventionally comprises the following operations:

an operation of placing a basic cell (namely a positive electrode and a negative electrode each associated with a current collector disposed on either side of a porous separator) in the envelope constituting the 'packaging, tabs for the recovery of current out of the envelope;

an operation for introducing the liquid electrolyte into the envelope, the base cell thus bathing in the electrolyte and the latter permeating the porosity of the porous separator;

-a sealing operation, by heat-sealing, of the envelope to seal the battery and thus avoid the leakage of liquid electrolyte outside thereof.

To overcome the drawbacks associated with a liquid electrolyte and with a view in particular to simplifying the design of the batteries by dispensing with the use of a porous separator, the use of solid electrolytes and, in particular electrolytes, can be envisaged gelled.

The gelled electrolytes, as their name suggests, are in the form of a gel, that is to say a solid three-dimensional network diluted in a liquid medium and composed, by mass and volume, mainly of liquid, which medium liquid is, in the context of electrolytes, the organic solvent (s) of the electrolyte, which also comprises at least one lithium salt, the solid appearance being imparted by one or more polymers. It is understood that this or these polymers are capable of gelling and swelling in contact with the organic solvent or solvents constituting the electrolyte to form the electrolyte thus gelled (hence the name sometimes used of gelled polymer electrolyte). The gelled electrolytes do not flow and do not give rise to any risk of leakage, as is the case with liquid electrolytes simply trapped in the porosity of a porous separator. In addition, the gelled electrolytes are self-supporting and therefore do not require the addition of a porous separator.

As specified above, the gelled electrolytes assume the presence of at least one gelling polymer and at least one organic solvent capable of gelling the said polymer (s).

In this regard, specific solvents from the dinitrile family having particularly advantageous properties (in terms of melting point, usable temperature range) are described for their capacity to gel polymers and thus to form gel electrolytes for batteries in lithium in FR 3 040 550. More specifically, the preparation of an electrolyte ink is described by mixing a dinitrile solvent with suitable polymers followed by gelling on the substrate and then cutting the gel obtained for integrate it into a battery assembly.

In view of that which exists, while retaining the use of solvents of the dinitrile family for their advantageous properties, the authors of the present invention have set themselves the objective of proposing a process for the preparation of an electrochemical cell for lithium battery. with gelled electrolyte having, among others, the following advantages:

-a simpler implementation than conventional manufacturing processes for this type of cells;

-a process transposable to all types of architecture, whether planar architectures or more complex architectures, such as wireframe architecture.

STATEMENT OF THE INVENTION

Thus, the invention relates to a process for preparing an electrochemical cell for a lithium battery comprising a positive electrode and a negative electrode arranged on either side of a gelled electrolyte comprising the following steps:

a) a step of producing a cell comprising the positive electrode, the negative electrode arranged on either side of a membrane comprising at least one polymer capable of gelling in contact with a dinitrile solvent;

b) a step of bringing said assembly into contact with a composition comprising at least one dinitrile solvent and at least one lithium salt, whereby the membrane gels thus forming the gelled electrolyte.

Also, in the process of the invention, the formation of the gelled electrolyte occurs once the assembly of the cell has been carried out, at the very least, with the precursor of the electrochemical cell, since between the positive electrode and the negative electrode is initially placed, not an electrolyte, but a membrane comprising at least one polymer capable of gelling on contact with a dinitrile solvent, which membrane becomes the gelled electrolyte after being brought into contact with a dinitrile solvent. This membrane can thus be described as a “post-gellable” membrane.

Because the formation of the gelled electrolyte occurs after assembly of a cell directly precursor of the electrochemical cell, the method allows, in addition to the fact of a simple and rapid implementation:

to prevent the risks of leakage, because the membrane absorbs by gelling the liquid composition, which is not the case with electrochemical cells with liquid electrolyte, in particular that with flexible envelope, where the various electrochemical elements bathe in the 'liquid electrode after filling the envelope;

-to be very flexible in terms of cell geometry, because the gelled electrode directly adopts the geometry of the membrane by simple gelling thereof, this variety of accessible geometry making it possible to envisage the use of the cells obtained by the method in fields of application, such as the medical field, the field of intelligent textiles.

Finally, the fact of using a dinitrile solvent in the composition makes it possible to avoid the use of CMR solvents (CMR meaning carcinogenic, mutagenic and reprotoxic), such as N-methylpyrrolidone (NMP).

The method of the invention comprises, firstly, a step of producing a cell comprising the positive electrode and the negative electrode arranged on either side of a membrane comprising at least one polymer capable of gelling at contact with a dinitrile solvent.

The positive electrode and the negative electrode are also conventionally associated with a current collector, for example, a metal strip. Whether for the positive electrode and the negative electrode, they can be in the form of a composite material comprising a polymer matrix (or a polymeric binder) in which are dispersed at least one active lithium insertion material and optionally at least one electronic conductive material, in particular when the cell is a cell intended for a lithium-ion battery.

For the positive electrode, the active material can be a lithium insertion material, the discharge voltage of which is greater than 4.5V expressed with respect to the Li ⁺ / Li couple. A material meeting this specificity may be a material of the lithiated material type with a spinel structure, this material being known by the name of "5V spinel". Thus, the positive electrode can comprise, as active material, at least one lithiated oxide comprising manganese with a spinel structure of formula (I) below:

LiNii-xIVIni + xCU (l) in which 0 <x <l.

In particular, a lithiated oxide conforming to this definition and particularly advantageous is the oxide of formula LiNioyMni ^ O ^ which has the particularity of having a potential for insertion / disinsertion of lithium of the order of 4.7V (this potential being expressed in relation to the reference couple Li + / Li).

As a variant of the abovementioned lithiated oxides of the abovementioned formula (I), the positive electrode may comprise, as active material, a lithiated oxide of one of the following formulas (II) or (III):

LiNi _x IVInyCo _z O2 Lii _{+ x} (Nii / 3Mni / 3Coi / 3) i_ _x O2 (II) (III) in which 0 <x, y, z <l and x + y + z = l.

Like other active materials, the positive electrode can also include:

a material of formula LiM ¹ PO4, in which M ¹ is a transition element, materials of this type possibly being LiFePO4, LiCoPO ₄ or LiNiPO ₄ ;

a material of formula LiMeO ₂ with Me being an element chosen from Ni, Co, Mn;

a material of formula LiM ₂ O ₄ with M 'being an element chosen from

Mn, Co and Ni;

-a material of formula LiNii. _x Co _x O ₂ with 0 <x <l.

For the negative electrode, the active material can be carbon, for example, in one of its allotropic forms, such as graphite, lithium or a lithium alloy, a mixed lithium oxide, such as Li ₄ Ti50i ₂ or LiTiO ₂ .

Finally, whether for the negative electrode or the positive electrode, the electronic conductive material, when it is present, may preferably be a carbonaceous material, namely a material comprising carbon in the elementary state. .

As carbon material, mention may be made of carbon black.

The polymeric binder can be chosen from:

* fluorinated (co) polymers possibly conducting protons, such as:

-fluoropolymers, such as a polytetrafluoroethylene (known under the abbreviation PTFE), a polyvinylidene fluoride (known under the abbreviation PVDF);

-fluorinated copolymers, such as poly (vinylidene fluoride-cohexafluoropropene) (known by the abbreviation PVDF-HFP);

- fluorinated polymers which conduct protons, such as Nafion®;

* elastomeric polymers, such as a styrene-butadiene copolymer (known under the abbreviation SBR), an ethylene-propylene-diene monomer copolymer (known under the abbreviation EPDM);

* polymers from the family of polyvinyl alcohols; and * mixtures thereof.

The two electrodes can be prepared beforehand by depositing on an current collector an ink comprising the ingredients of the composite material (namely, active material, polymeric binder (s) and possibly electronic conductive material) in dispersion in a solvent organic followed by removal by drying of the organic solvent.

The membrane can also be prepared beforehand, for example, by dissolving at least one polymer capable of gelling in contact with a dinitrile solvent followed by deposition of said resulting solution on a substrate followed finally by drying and cutting the membrane in the desired format before placing it between the negative electrode and the positive electrode to form the cell.

The step of producing a cell can also be carried out by extrusion, and more specifically, for example, by the following sequence of operations:

an operation for producing an electrode (positive or negative) by extrusion;

an operation for producing the membrane by extrusion, this membrane thus extruded being collaminated on the electrode previously produced;

an operation for producing the electrode of opposite polarity by extrusion, this electrode then being colaminated on the membrane previously produced, whereby the lithium battery cell results.

As a variant, if the desired cell does not have a planar architecture but an architecture in the form of wire or cable, the production of the cell by extrusion can be carried out by concentric extrusion of the various elements of the cell (i.e., the two electrodes arranged on either side of the membrane). To do this, it may be necessary to adapt the extrusion head to the level of the extruder. This embodiment can also be qualified as “co-extrusion”.

Once the cell has been made and before implementation of step b), the cell can be placed in an envelope, for example, a flexible envelope in the form of a flexible composite material comprising a stack of layers, example, in aluminum covered by a polymer layer (for example, polyethylene, polypropylene, a polyamide) via an adhesive layer of polyester-polyurethane, step b) being thus implemented by injecting the composition directly into the envelope containing the cell.

It should be noted that if the cell is intended for a lithium metal battery, the negative electrode will not consist of a composite material as defined above but rather of a sheet of metallic lithium or of lithium alloy.

As mentioned above, the membrane disposed between the negative electrode and the positive electrode comprises at least one polymer capable of gelling in contact with a dinitrile solvent, which polymer can in particular be chosen from:

poly (meth) acrylate (co) polymers, such as polymethyl methacrylates (also called PMMA), n-butyl polymethacrylates (also called PBMA), isobutyl polymethacrylates, poly (n-butyl methacrylate -isobutyl co-methacrylate) (also known as P (BMA-co-isoBMA)), poly (n-butyl methacrylate-methyl co-methacrylate) (also known as P (BMA-co-MMA));

-perfluorinated (co) polymers, such as polyvinylidene fluorides (also known as PVDF) and poly (vinylidene fluoride-co-hexafluoropropylene) (also known as PVDF-HFP);

polyacrylonitriles (also known as PAN) and copolymers based on acrylonitrile, such as poly (styrene-co-acrylonitrile) (also known as PSa);

polyethylene oxides (also known as POE);

-polyvinylpyrrolidones (also known as PVP);

- acrylic polymers, such as poly (acrylic acid) (also called PAAc); and

-the mixtures of these.

In addition to the presence of one or more gelling polymers, the membrane can also comprise one or more other polymers, which can contribute to the mechanical strength of the gelled electrolyte, as may be the case for an elastomeric polymer.

More specifically, the membrane may comprise a mixture of several polymers capable of gelling on contact with a dinitrile solvent and, even more specifically, a mixture of two polymers capable of gelling on contact with a dinitrile solvent, an example of a particularly advantageous mixture. being a mixture of a poly (ethylene oxide) and a perfluorinated polymer, such as a poly (vinylidene fluoride). Even more specifically, a mixture of polymers which is particularly suitable for constituting the membrane is a mixture of a poly (ethylene oxide) and a poly (vinylidene fluoride) in identical proportions (ie 50: 50). Poly (ethylene oxide) is capable of forming a gel by its capacity to swell on the order of 200% in the presence of the electrolytic composition, poly (vinylidene fluoride) also participating in the formation of a gel while by providing mechanical strength to the gelled electrolyte.

Other mixtures of polymers can be envisaged to constitute the membrane, such as a mixture of a poly (ethylene oxide) and a poly (acrylic acid), a mixture of a poly (vinylpyrrolidone) and d 'an elastomeric polymer.

Such a membrane can be obtained by the following operations:

an operation for dissolving the two aforementioned polymers in a polar aprotic solvent, such as dimethylformamide (DMF);

an operation for depositing the solution obtained on a substrate, for example, made of polytetrafluoroethylene, the surface of which can be treated by corona treatment in order to increase its surface energy and allow complete wettability by the solution;

a drying operation of the deposit thus carried out to remove the solvent, this drying operation being able to be implemented in an oven, for example, at 60 ° C. for 24 hours;

an operation for detaching the substrate from the material thus dried;

an operation for cutting the material into a membrane in the desired format before assembling the latter in the cell.

The method of the invention comprises, after the step of producing the cell, a step of bringing said assembly into contact with a composition comprising at least one dinitrile solvent and at least one lithium salt, whereby the membrane gels forming thus the gelled electrolyte.

The dinitrile solvent advantageously corresponds to the following formula (IV):

ΝΞο - R ¹ -ΟΞν (IV) in which R ¹ is an alkylene group and, more specifically, an alkylene group comprising 1 or 2 carbon atoms, either a methylene group -CH ₂ or an ethylene group -CH ₂ -CH ₂ -,

By way of example, a particularly advantageous dinitrile solvent is succinodinitrile of formula (V) below:

(V)

The special feature of this solvent is that it is a non-flammable, non-toxic and non-volatile hyperplastic crystalline organic compound at cell operating temperatures, given that its boiling point is around 266 ° C and its melting point is about 57 ° C, which improves the safety of the cell. Because of its strong polarity, it also makes it possible to dissolve lithium salts and to obtain a gel, as soon as it is brought into contact with a gelable polymer, for example, a gelable polymer such as those explicitly mentioned above. above. What is more, it exhibits electrochemical stability over a large window of potentials. It is thus possible to work in coexistence with electrodes comprising active electrode materials capable of delivering a high nominal voltage, such as a voltage of the order of 5 V. What is more, it makes it possible to obtain gelled electrolyte, which has a lower sensitivity to humidity compared to conventional liquid electrolytes.

The lithium salt or salts suitable for use with a dinitrile solvent, such as succinodinitrile, can be chosen from lithium b / s-trifluoromethanesulfonylimide (also called LiTFSI), lithium b / s (oxalato) borate (called also LiBOB), LiPF ₆ , LiCIO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , LiN (C ₂ F ₅ SO ₂ ) and mixtures thereof.

Advantageously, the lithium salt used consists of LiTFSI, LiTFSI having the peculiarities of not degrading in the presence of water and of exhibiting great thermal and chemical stability. This lithium salt can advantageously be used in admixture with LiBOB, in particular in cells for lithium metal batteries, since LiBOB is capable of creating a passivation layer at the lithium metal / membrane interface and thus avoiding degradation reactions of the negative electrode.

Thus, an advantageous composition which can be used for the implementation of step b) is a composition comprising, as the dinitrile solvent, succinodinitrile and as the lithium salt, a mixture of LiTSI and LiBOB.

When step a) of making the cell is carried out by extrusion, step b) can be implemented by injection into the extruder via an injector located on one of the heating zones downstream of zone d introduction of the constituent materials of the cell elements.

Other characteristics and advantages of the invention will appear from the additional description which follows and which relates to particular embodiments.

Of course, this additional description is given only by way of illustration of the invention and in no way constitutes a limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1, already described, shows an exploded view of a lithium battery cell with planar architecture.

FIG. 2 is a graph illustrating the evolution of the stress C (in N) as a function of the deformation D (in mm) of the gelled electrolyte obtained in accordance with the method of the example below.

DETAILED PRESENTATION OF A PARTICULAR EMBODIMENT

EXAMPLE

The present example illustrates the preparation of an electrochemical cell in accordance with the method of the invention in the form of a button cell comprising:

as a negative electrode, a negative electrode made up of metallic lithium; and

as a positive electrode, an electrode comprising, as active material, LiFePO ₄ ;

a gelled electrolyte disposed between said positive electrode and the negative electrode, the composition of which will be explained below.

The negative electrode is obtained by cutting, from a metallic lithium strip, a disc with a diameter of 16 mm.

The positive electrode is obtained by coating, on a current collector consisting of an aluminum strip, of an ink consisting of a dispersion comprising dimethylformamide, LiFePO ₄ (80% by mass), carbon nanotubes (2% by mass ), Super P® carbon black (3% by mass) and a POE / PVDF mixture (50/50) (15% by mass), the dry extract of this dispersion being 20%. The electrode has the same gelation matrix (POE / PVDF) as the membrane and will be post-gelled simultaneously when brought into contact with the electrolyte. Once deposited, the layer is dried and the electrode is cut in the form of a disc with a diameter of 14 mm.

The button cell is made from these electrodes by stacking:

-a negative electrode disc;

-a positive electrode disc; and

-a membrane composed of a mixture of POE / PVDF polymers (50/50).

This membrane is obtained beforehand by the following operations:

an operation for dissolving the two aforementioned polymers, namely POE and PVDF in dimethylformamide;

an operation for depositing the solution obtained on a polytetrafluoroethylene substrate, the surface of which has been treated by corona treatment in order to increase its surface energy and allow complete wettability by the solution;

a drying operation of the deposit thus carried out to remove the solvent, this drying operation being carried out in an oven at 60 ° C for 24 hours;

an operation for detaching the substrate from the material thus dried;

-an operation of cutting the material into the membrane in the form of a 16.5 mm disc.

Once the cell has been assembled, it is then brought into contact for 30 seconds with an electrolytic solution consisting of succinodinitrile (20 pL) in which are dissolved LiTFSI (1 mole per liter of electrolytic solution) and LiBOB ( 2% by mass relative to the total mass of the electrolytic solution).

At the end of this contacting step, the membrane gels to thus form a gelled electrolyte having a thickness of 25 to 30 μm.

This gelled electrolyte thus obtained has the following properties:

-an ionic conductivity determined by impedance spectroscopy of 5 * 10 ' ² S / cm at 25 ° C;

-a ductile material as illustrated by the stress curve C (in N) as a function of the deformation D (in mm) (Figure 2 attached), this curve having the typical appearance of a ductile material with two distinct zones : an elastic zone a) and a plastic region b);

a Young's modulus of the order of 226 MPa, which attests to a flexible material.

Claims (18)

1. Process for the preparation of an electrochemical cell for a lithium battery comprising a positive electrode and a negative electrode arranged on either side of a gelled electrolyte comprising the following steps: a) a step of producing a cell comprising the positive electrode, the negative electrode arranged on either side of a membrane comprising at least one polymer capable of gelling in contact with a dinitrile solvent; b) a step of bringing said assembly into contact with a composition comprising at least one dinitrile solvent and at least one lithium salt, whereby the membrane gels thus forming the gelled electrolyte. 2. Preparation process according to claim 1, in which the positive electrode and the negative electrode are associated with a current collector. 3. Preparation process according to claim 1 or 2, in which the positive electrode and the negative electrode are in the form of a composite material comprising a polymer matrix, in which is dispersed at least one active material for inserting the lithium. 4. Preparation process according to claim 3, in which the positive electrode comprises, as active material: a lithiated oxide comprising manganese with a spinel structure of formula (I) below: LiNi _Vx Mn _{1 + x} O ₄ (l) in which 0 <x <l; a lithiated oxide of one of the following formulas (II) or (III): LiNi _x M n _y Co ₂ O ₂ U i _{+ x} (N i 1/3 Μ n 1 / 3CO1 / 3) i_ _x O2 (U) (m) in which 0 <x, y, z <l and x + y + z = 1; a material of formula LIMVCU, in which M ¹ is a transition element; a material of formula LiMeO ₂ with Me being an element chosen from Ni, Co, Mn; a material of formula LiM ₂ O ₄ with M 'being an element chosen from Mn, Co and Ni; or -a material of formula LiNii_ _x Co _x O ₂ with 0 <x <l. 5. The preparation method according to claim 3 or 4, wherein the active material of the negative electrode is carbon or a lithium oxide. 6. The preparation method according to claim 1, wherein the negative electrode is made of lithium or of a lithium alloy. 7. Preparation process according to any one of the preceding claims, further comprising, before the implementation of step a), a step of prior preparation of the membrane. 8. Preparation process according to claim 7, in which the membrane is prepared by dissolving at least one polymer capable of gelling in contact with a dinitrile solvent followed by deposition of said resulting solution on a substrate followed finally drying and cutting the membrane in the desired format before placing it between the negative electrode and the positive electrode to form the cell. 9. Preparation process according to any one of the preceding claims, in which the step of producing a cell is carried out by extrusion. 10. Preparation process according to any one of the preceding claims, in which the polymer or polymers capable of gelling in contact with a dinitrile solvent are chosen from: poly (meth) acrylate (co) polymers, such as polymethyl methacrylates, n-butyl polymethacrylates, isobutyl polymethacrylates, poly (n-butyl methacrylate-isobutyl co-methacrylate), poly (nbutyl methacrylate-methyl co-methacrylate); -perfluorinated (co) polymers, such as polyvinylidene fluorides and polyvinylidene fluoride-co-hexafluoropropylene); polyacrylonitriles and copolymers based on acrylonitrile, such as poly (styrene-co-acrylonitrile); polyethylene oxides; -polyvinylpyrrolidones; - acrylic polymers, such as poly (acrylic acid); and -the mixtures of these. 11. Preparation process according to any one of the preceding claims, in which the membrane comprises a mixture of polymers capable of gelling in contact with a dinitrile solvent. 12. Preparation process according to any one of the preceding claims, in which the membrane comprises a mixture of two polymers capable of gelling on contact with a dinitrile solvent. 13. Preparation process according to any one of the preceding claims, in which the membrane comprises a mixture of a poly (ethylene oxide) and a perfluorinated polymer, such as a poly (vinylidene fluoride). 14. Preparation process according to any one of the preceding claims, in which the membrane consists of a mixture of a polyethylene oxide) and a polyvinylidene fluoride) in identical proportions. 15. Preparation process according to any one of the preceding claims, in which the dinitrile solvent corresponds to the following formula (IV): (IV) in which R ¹ is an alkylene group and, more specifically, an alkylene group comprising 1 or 2 carbon atoms. 16. A method of preparation according to any one of the preceding claims, in which the dinitrile solvent is succinodinitrile of formula (V) below: 17. Preparation process according to any one of the preceding claims, in which the lithium salt (s) are chosen from lithium bistrifluoromethanesulfonylirnide (also known as LiTFSI), lithium Ws (oxalato) borate (also known as LiBOB), LiPFs , LICICU, LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , UN ^ FsSC ^) and mixtures thereof. 18. Preparation process according to any one of the preceding claims, in which the lithium salt consists of LiTFSI in admixture with LiBOB.