FR3007206A1 - METHOD FOR MANUFACTURING SECONDARY BATTERY - Google Patents

Abstract

This method of manufacturing a secondary battery comprises the following steps: depositing on a substrate at least one battery core comprising two electrodes of opposite signs, an electrode separator; the electrode separator being positioned between the two electrodes; depositing a resin layer so as to cover the entire core of the cell and a portion of the substrate at the periphery of the cell core; polymerization of the resin.

Description

FIELD OF THE INVENTION The invention relates to a method of manufacturing a secondary battery comprising in particular a step of encapsulation by deposition of a resin. The fields of use of the present invention relate in particular to applications requiring a flexible battery, such as, for example, textiles.

STATE OF THE PRIOR ART A secondary battery is a rechargeable battery which comprises a battery core consisting of two electrodes between which an electrolyte is inserted. This electrolyte is generally supported by an electrode separator. These elements can be protected and electrically isolated from the outside of the battery by a flexible or rigid housing.

By way of example, FIG. 1 illustrates a lithium-ion secondary battery (1) whose stack core comprises: a positive electrode (3) consisting of at least one lithium cation insertion material; an electrode separator (4); a negative electrode (5). The two positive (3) and negative (5) electrodes are respectively associated with the current collectors (2) and (6).

The battery core is completely covered by the package or housing (7). On the other hand, part of the current collectors (2) and (6) remains visible, outside the packaging (7), so that the battery can be electrically connected.

The packaging of the battery may notably consist of a metal structure electrically isolated from the battery. However, this kind of packaging may lack flexibility in relation to the needs of certain applications.

As regards so-called flexible packaging, it may in particular be a multilayer composite material comprising a stack of layers. This type of stack may consist of an aluminum sheet covered with polyethylene, polypropylene, or polyamide. An adhesive layer, in particular polyester-polyurethane, can ensure the cohesion of the stack. The electrochemical core of the cell and the current collectors connecting the electrodes are placed inside this composite package. The tabs for current recovery, extending the current collectors, out of the packaging to ensure electrical connections. A liquid electrolyte is then introduced into the pouch before heat sealing the packaging to ensure the tightness of the electrochemical system. Although relatively satisfactory, this type of solution involves a multi-step process at the end of which the package can in particular delaminate, or break. In addition, this type of encapsulation of the electrochemical core is generally carried out by heat sealing the package, a step during which the current collectors can be damaged. The present invention makes it possible to remedy these pitfalls by means of a method making it possible to seal and electrically insulate the battery core by encapsulation. This method makes it possible to prepare a secondary battery that does not require a heat-sealing step. SUMMARY OF THE INVENTION The Applicant has developed a method for preparing a secondary battery, the battery core is covered with a protective layer. It may especially be a lithium-ion type battery or an alkaline battery (zinc-nickel for example). The invention consists in encapsulating a battery core deposited on a substrate by means of a polymerizable resin. More specifically, the subject of the invention relates to a method of manufacturing a secondary battery, comprising the following steps: depositing on a substrate at least one battery core comprising two electrodes of opposite signs, a separator electrodes; the electrode separator being positioned between the two electrodes; depositing a layer of polymerizable resin, so as to cover all of the cell core and a portion of the substrate at the periphery of the cell core; - polymerization of the resin.

When the battery is lithium-ion type, the positive-sign electrode is a lithiated electrode. On the other hand, in a zinc-nickel alkaline secondary battery, the positive electrode is based on zinc, whereas the negative electrode is on the basis of nickel. According to a particular embodiment, the constituents of the cell core, but also the substrate and the polymerized resin exhibit mechanical flexibility properties. This method thus makes it possible, if necessary, to maintain the flexibility of the battery / substrate assembly.

By flexible means a material having the property to resume, partially or preferably completely, its shape after being compressed, twisted or stretched. The packaging of the cell is constituted by the assembly between the polymerized resin and the part of the substrate on which the resin covers the substrate. It advantageously has flexibility and sealing properties. This resin / substrate package is advantageously electronically insulating. The substrate may be of polymeric type. It has a thickness advantageously less than 150 micrometers, and more advantageously between 20 and 100 micrometers. It may in particular be made of at least one material chosen from the group comprising the following compounds: polyacrylates (AA); acrylonitrile-butadiene-styrene (ABS); ethylene vinyl alcohol (E / VAL); fluoroplastics (PTFE), (FEP, PFA, CTFE); impact polystyrene (HIPS: high impact polystyrene); melamine formaldehyde (MF); liquid crystal polymers (LCP); polyacetal (POM); acrylo nitrile (PAN); phenol-formaldehyde plastic (PF); polyamide (PA); polyamide-imide (PAI); polyaryl ether ketone (PAEK) polyether ether ketone (PEEK); cis 1,4-polybutadiene (PBD); trans 1,4-polybutadiene (PBD); poly 1-butene (PB); polybutylene terephthalate (PBT); polycaprolactam; polycarbonate (PC); polycarbonate / acrylonitrile butadiene styrene (PC / ABS); poly 2,6-dimethyl-1,4-phenylene ether (PPE); polydicyclopentadiene (PDCP); polyester (PL); polyether ether ketone (PEEK); polyetherimide (PEI); polyethylene (PE, LDPE, MDPE, HDPE, UHDPE); polyethylenechlorinates (PEC); poly (ethylene glycol) (PEG); polyethylene hexamethylene dicarbamate (HDPE); polyethylene oxide (PEO); polyethersulfone (PES); polyethylene sulphide (PES); polyethylene terephthalate (PET); phenolics (PF); poly hexamethylene adipamide (PHMA); poly hexamethylene sebacamide (PHMS); polyhydroxyethyl methacrylate (HEMA); polyimide (PI such as KAPTON); polyisobutylene (PM); polyketone (PK); polylactic acid (PLA); poly methyl methacrylate (PMMA); poly methyl pentene (PMP); poly m-methyl styrene (PMMS); poly p-methyl styrene (PPMS); polyoxymethylene (POM); poly pentamethylene hexamethylene dicarbamate (PPHD); poly-methylenylene; isophthalamide (PMIA); polyphenylene oxide (PPO); poly p-phenylene sulphide (PPS); poly p-phenylene terephthalamide (PPTA); polyphthalamide (PTA); polypropylene (PP); poly propylene oxide (PPDX); poly styrene (PS); polysulfone (PSU); poly tetrafluoroethylene (PTFE); poly (trimethylene terephthalate) (PTT); polyurethane (PU); polyvinyl butyral (PVB); polyvinyl chloride (PVC); polyvinylidene chloride (PVDC); polyvinylidene fluoride (PVDF); poly vinyl methyl ether (PVME); poly (vinyl pyrrolidone) (PVP) silicone (SI); styrene-acrylonitrile resin (SAN); thermoplastic elastomers (TPE); thermoplastic polymers (TP); and urea-formaldehyde (UF). It may also be paper, and more particularly paper having barrier properties so that it is not impregnated with resin core. The first step of the method - object of the invention consists in depositing at least one stack core on the substrate. The stack core is advantageously a stack of a first electrode, an electrode separator, and a second electrode of opposite sign to the first. According to a particular embodiment, a plurality of stack cores may be deposited so as to form a stack. Each cell core comprises at least one positive electrode / electrode separator / negative electrode assembly. Advantageously, each of the electrodes of the cell or cores is associated with a current collector. The current collector is in contact with the face of the electrode opposite to the electrode separator. It can thus make it possible to ensure the electrical contact with the outside of the battery. The current collector or collectors can in particular be deposited by printing on the substrate. They are made of an electrically conductive material. Typically, it is a metal strip of a metal which can be chosen especially in the group comprising aluminum, copper, nickel or stainless steel ...

It can also be carbon nanotubes or metal particles. In general, the current collector of the negative electrode may be copper when the electrode is graphite carbon, or aluminum when the electrode is titanate. In addition, the current collector of the positive electrode is advantageously aluminum, particularly in the case of a lithium-ion secondary battery whose positive electrode is lithiated.

The deposition of the electrochemical core is carried out by successive deposition of the different layers according to methods forming part of the knowledge of those skilled in the art. According to a particular embodiment, in the method according to the invention, the cell core can be produced according to the following steps: depositing a first current collector; depositing a first electrode, advantageously a negative electrode; depositing an electrode separator; depositing a second electrode of opposite sign to the first electrode; depositing a second current collector.

According to another particular embodiment, in the method according to the invention, the cell core can be produced according to the following steps: depositing a first negative electrode on a current collector, advantageously by printing; depositing this current collector on a substrate; depositing an electrode separator on the first electrode, advantageously by printing; depositing, on the electrode separator, a second electrode of sign opposite to the first electrode, advantageously by printing; depositing a second current collector on the second electrode, advantageously by spraying. Advantageously, the electrode separator covers the entirety of the first electrode and partially the first current collector.

The negative electrode may in particular be made from graphite or titanate material Li4Ti5012 in the case of power electrodes of a lithium-ion battery. The negative electrode may be printed with an ink of negative electrode material on a substrate or on a current collector. It is advantageously printed by screen printing through a screen (stencil) in a specific pattern. The thickness of the layer thus printed depends on the rheology of the ink, the thickness of the stencil and the pressure applied to the screen-printing doctor.

Advantageously, the negative electrode ink is based on a solvent that does not make it possible to solubilize the electrode separator, and does not require further densification.

The deposit is then dried, preferably between 60 and 120 ° C, for a time depending on the dry extract of the ink, as well as the thickness of the layer. The dried ink can then be densified by calendering to reduce the contact resistances of the electronic conduction network and adjust the final porosity. With regard to the electrode separator, it can be composed of a microporous polymer or composite separator. impregnated with organic electrolyte, allowing, in the case of a lithium-ion battery, the displacement of the lithium ion of the positive electrode towards the negative electrode and vice versa (case of the charge or the discharge) thus generating the current. For example, a separator based on PVdF-HFP (polyvinylidene fluoride - cohexafluoropropene) can be printed from an ink according to the technique described above, directly on the first electrode.

After deposition, the separator ink is advantageously dried at 60 to 120 ° C. The separator thus obtained may be porous or dense depending on the formulation used. It can then be soaked with electrolyte.

The electrolyte is generally a mixture of organic solvents, such as carbonates, in which an alkali metal salt is added. This salt may especially be a lithium salt, for example LiPF6 or LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) in lithium-ion batteries. As far as possible, this mixture is free of traces of water or oxygen. The insertion material constituting the positive electrode can be deposited on the electrode separator, or on a current collector, by various techniques of electrode ink deposition such as coating, screen printing, jet of ink or spray. For example, a lithiated iron phosphate ink (lithium ion battery) can be printed directly on the electrode separator. Advantageously, the positive electrode ink is based on a solvent which does not make it possible to solubilize the electrode separator, and does not require further densification. The positive electrode inks are preferably aqueous inks comprising a polyacrylic acid type polymeric binder.

The lithiated positive electrode of a lithium-ion battery consists of at least one lithium cation insertion material, for example LiFePO4 (lithium iron phosphate), or transition metal oxides (lamellar materials: oxide lithiated cobalt, LiCoO2; LiNi0.33Mno.33Coo.3302 ...).

The second current collector may result from sputtering, on the second electrode, a suspension of carbon nanotubes or metal particles. As already indicated, the polymerizable resin is deposited after formation of the cell core on the substrate. The resin layer may be printed, in particular by screen printing. Thus, the encapsulation of the secondary battery can be carried out by screen printing through a stencil screen to dimensions greater than that of the electrochemical core so as to completely encapsulate the cell core which is advantageously a stack consisting of the electrodes, the separator, and if necessary current collectors.

In general, when the electrodes of the secondary battery are associated with current collectors, they are not covered by the resin to allow electrical connections. In general, the resin has the following properties: potential electrochemical compatibility in the electrolytic medium; sealing vis-à-vis the liquid electrolyte; final flexibility once cured; low permeability to water vapor; high viscosity to avoid pollution of electrode materials before polymerization. Thus, in order to ensure the tightness of the package, the resin, and more particularly the bonding of the resin, is advantageously compatible with the substrate.

In addition, the resin is advantageously chemically compatible (particularly electrolyte) and electro chemically with the materials to resist the operating potentials of the battery in question.

On the other hand, the encapsulation adheres to the substrate on which the electrochemical core is deposited and seals against the electrolyte. The adhesion of the resin to the substrate is carried out during the polymerization step.

Typically, the resin covers the battery core but it can still leave some of the current collectors protrude to allow the electrical connection of the battery once it is packaged. The resin may especially be chosen from the group comprising photosensitive resins such as acrylate resins, epoxies, and polymethyl methacrylate (PMMA). These may be DELO-PHOTOBONDe 4496 and PB493 resins marketed by SYNEO.

The resin may also include pigments, coupling agents, or adhesion aids with the substrate and / or stack components. According to a particular embodiment, the resin may comprise at least one monomer, advantageously of the same nature as the polymer essentially constituting the resin. The presence of this monomer can thus make it possible to dilute the resin and thus to adjust its viscosity before polymerization. The resin is advantageously polymerized by exposure to ultraviolet radiation. Advantageously, the resins used are photosensitive and have the following properties: Viscosity (mPa / s) before polymerization 17000-50000 Photopolymerization wavelength range (nm) 320-450 Minimum exposure time (s) at 60 mW / cm 2 for photopolymerization 20-50 Elongation at break (%) after polymerisation 280-300 Water absorption (%) after polymerization 0.7-2.5 Withdrawal (%) 6-7 Glass transition temperature (° C) after polymerization 21-61 By shrinkage is meant the difference between the surface covered by the resin before and after polymerization. The withdrawal is expressed as a percentage. The UV irradiation phase at the appropriate wavelength makes it possible to polymerize the resin which passes from a viscous consistency to an elastic solid state. The polymerization is carried out in a few seconds and does not generate gaseous releases since the resin is formulated without solvent to 100% solids in liquid monomers and oligomers.

By polymerization of the resin is also meant its crosslinking. The polymerization of the resin is advantageously carried out in the presence of a photoinitiator, and / or a thermo-initiator.

The polymerized resin layer has a thickness which is advantageously between 20 and 100 micrometers. Depending on the desired applications, the package may be a flexible package leading to thin and flexible batteries, or a rigid package that is to say a housing enclosing the secondary battery. Those skilled in the art will know how to choose the appropriate resin for this purpose. The process may also comprise a step of incorporating an electrolyte, advantageously after polymerization of the resin. The electrolyte can be injected through the polymerized resin. The electrolyte may also be in the form of a gel which is already present in the electrodes and in the separator before polymerization. According to a particular embodiment, the sealing of the stack can be improved by depositing an additional polymeric layer on the resin layer. This additional layer has impermeability properties, and a very small thickness to maintain the flexibility of the battery.

This additional layer can thus make it possible to extend the life of the battery since the first resin layer deposited can possibly be degraded by the electrochemical operating conditions of the battery (gas, moisture, water vapor, etc.). . This additional layer may in particular be made of a material chosen from the group comprising silicon oxides and aluminum oxides. Its thickness is advantageously between 10 and 100 nanometers. This additional layer is advantageously deposited after introduction of the electrolyte. It is advantageously of the same nature as the first resin layer. According to another particular embodiment, the substrate may also be covered with a similar additional layer. It is deposited on the substrate before depositing the battery core. The present invention also relates to the secondary battery, advantageously of lithium-ion type, obtained according to the method described above, but also its use in particular in the fields of electronics and textiles. It can in particular be implemented in flexible screens, sensors, intelligent packaging ... This secondary battery advantageously has flexibility properties. The method - object of the invention, can also be implemented so as to manufacture several secondary batteries in parallel on the same substrate. These batteries can then be disconnected by cutting the substrate or connected together. Advantageously, the secondary battery can have the following advantages: interconnection of systems to be fed via a common substrate; versatility of the materials used (substrate, coating) in terms of properties; - flexibility and fineness of the finished product; - low cost process. The invention and the advantages thereof will become more apparent from the following figures and examples, given to illustrate the invention and not in a limiting manner. DESCRIPTION OF THE FIGURES FIG. 1 schematically illustrates an encapsulated secondary battery. Figure 2 shows the cyclic voltammetric curves showing the electrochemical stability of a polymerized acrylate resin sample and a polypropylene sample.

FIG. 3 represents the graph corresponding to the capacity of a lithium-ion battery according to the invention as a function of the charging and discharging cycles. EXAMPLES OF THE EMBODIMENT OF THE INVENTION Electrochemical stability (FIG. 2): Firstly, the electrochemical stability of the PB493 acrylic resin (from SYNEO) was studied by cyclic voltammetry (three electrode method).

This study was carried out in a system comprising a stainless steel working electrode, a stainless steel counter electrode and a polyacrylate reference electrode (PB493 polymerized) in a reference electrolyte (LP10, the composition of which is specified below). ).

The cyclic voltammetric curves of FIG. 2 were obtained between 1 and 5.5V with a scanning speed of 1mV / s. The electrochemical stability of the PB493 acrylic resin was compared to that of a polypropylene membrane (Celgard 2400).

The curves in FIG. 2 show that there is no degradation phenomenon of the acrylate polymer between the 2V and 5V potentials in comparison with the polypropylene (Celgard 2400) which is commonly used as a separator in the batteries with respect to its In addition, the current densities obtained are very low (less than 15 × 10 -6 A) over this interval. The acrylate polymer thus has a stability compatible with its use in a lithium-ion secondary battery. As an example, the carbon graphite / LiFePO4 system operates between 2.6V and 3.7V potentials.

Preparation of a lithium-ion battery according to the invention: A battery comprising the following elements was produced: a positive electrode consisting, by weight, of 90.5% LiFePO4; 2.5% SP carbon; 2.5% VGCF carbon fiber (vapor phase growth carbon fiber); 4.5% polyvinylidene fluoride (Solef® 5130, 46% solids); - a polypropylene electrode separator (Celgard® C2400); a negative electrode consisting of, by weight, 73.5% of Hitachi SMG-20 graphite; 24.5% SFG6 graphite; 1% carboxymethylcellulose CMC; 1% NRB 2890 to 42% solids (NRB 2890 = acrylonitrile / butadiene copolymer latex). Before assembly of the battery core, the electrodes were printed on metal current collectors. The electrochemical core thus formed was then transferred to a PET substrate and then dried for 48 hours under vacuum at 60.degree.

The encapsulation was then carried out in a glove box (bonding of PB493 resin and exposure to UV for 20 seconds). The electrode separator was impregnated with an LP10 electrolyte consisting of a solution of lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol.L-1 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC). The proportions EC / PC / DMC are 1: 1: 3 by volume and 2% by weight of vynilene carbonate (VC) were also added to the mixture. The electrolyte was introduced by a syringe by piercing the resin. The orifice was then clogged with another resin addition and then re-irradiated with UV for 20 seconds.

The lithium-ion battery thus obtained was tested according to the following protocol: charging and discharging cycles at C / 20-D / 20 (formation stage); succession of charges and discharges under regime C / 10-D / 10.

The calculated capacity of 16.5mAh was correctly restored during the formation step and operation in the C / 10-D / 10 regime shows no significant loss due to encapsulation during the first cycles (FIG. 3). In addition, the acrylate resin used to encapsulate the battery is compatible with a use requiring a flexible battery. The flexibility of the battery as well as the adhesion of the acrylate resin to the PET substrate is satisfactory. No phenomenon of leakage or detachment was observed. On the other hand, the tests carried out show the adhesion of the cell to the substrate and to the coating, even after subjecting the cell to mechanical strain stresses. No delamination was observed.

Claims (10)

REVENDICATIONS1. A method of manufacturing a secondary battery, comprising the following steps: depositing on a substrate at least one battery core comprising two electrodes of opposite signs, an electrode separator; the electrode separator being positioned between the two electrodes; depositing a resin layer so as to cover the entire battery core and a part of the substrate at the periphery of the battery core; - polymerization of the resin. 2. A method of manufacturing a secondary battery according to claim 1, characterized in that at least one electrode comprises a current collector in contact with the face of the electrode opposite to the electrode separator. 3. A method of manufacturing a secondary battery according to claim 1 or 2, characterized in that the polymerization of the resin is carried out by exposure to ultraviolet radiation. 4. A method of manufacturing a secondary battery according to one of claims 1 to 3, characterized in that the resin is a material selected from the group consisting of acrylate resins, epoxies, and polymethyl methacrylate. 5. A method of manufacturing a secondary battery according to one of claims 1 to 4, characterized in that the substrate is in the form of a sheet of at least one material selected from the group consisting of the following compounds: polyacrylates (AA); acrylonitrile-butadiene-styrene (ABS); ethylene vinyl alcohol (E / VAL); fluoroplastics (PTFE), (FEP, PFA, CTFE); impact polystyrene (HIPS: high impact polystyrene); melamine formaldehyde (MF); liquid crystal polymers (LCP); polyacetal (POM); acrylo nitrile (PAN); phenol-formaldehyde plastic (PF); polyamide (PA); polyamide-imide (PAI); polyaryl ether ketone (PAEK) polyether ether ketone (PEEK); cis 1,4-polybutadiene (PBD); trans 1,4-polybutadiene (PBD); poly 1-butene (PB); polybutylene terephthalate (PBT); polycaprolactam; polycarbonate (PC); polycarbonate / acrylonitrile butadiene styrene (PC / ABS); poly 2,6-dimethyl-1,4-phenylene ether (PPE); polydicyclopentadiene (PDCP); polyester (PL); polyether ether ketone (PEEK); polyetherimide (PEI); polyethylene (PE, LDPE, MDPE, HDPE, UHDPE); polyethylenechlorinates (PEC); poly (ethylene glycol) (PEG); polyethylene hexamethylene dicarbamate (HDPE); polyethylene oxide (PEO); polyethersulfone (PES); polyethylene sulphide (PES); polyethylene terephthalate (PET); phenolics (PF); poly hexamethylene adipamide (PHMA); poly hexamethylene sebacamide (PHMS); polyhydroxyethyl methacrylate (HEMA); polyimide (PI such as KAPTON); polyisobutylene (PM); polyketone (PK); polylactic acid (PLA); poly methyl methacrylate (PMMA); poly methyl pentene (PMP); poly m-methyl styrene (PMMS); poly p-methyl styrene (PPMS); polyoxymethylene (POM); poly pentamethylene hexamethylene dicarbamate (PPHD); poly m-phenylene; isophthalamide (PMIA); polyphenylene oxide (PPO); poly p-phenylene sulphide (PPS); poly p-phenylene terephthalamide (PPTA); polyphthalamide (PTA); polypropylene (PP); poly propylene oxide (PPDX); poly styrene (PS); polysulfone (PSU); poly tetrafluoroethylene (PTFE); poly (trimethylene terephthalate) (PTT); polyurethane (PU); polyvinyl butyral (PVB); polyvinyl chloride (PVC); polyvinylidene chloride (PVDC); polyvinylidene fluoride (PVDF); poly vinyl methyl ether (PVME); poly (vinyl pyrrolidone) (PVP) silicone (SI); styrene-acrylonitrile resin (SAN); thermoplastic elastomers (TPE); thermoplastic polymers (TP); and urea-formaldehyde (UF). 6. A method of manufacturing a secondary battery according to one of claims 1 to 5, characterized in that it further comprises a step of incorporating an electrolyte, preferably after polymerization of the resin. 7. A method of manufacturing a secondary battery according to one of claims 1 to 6, characterized in that the battery core is deposited by successive impressions on the substrate of: - a first current collector; a first electrode; an electrode separator; a second electrode of sign opposite to the first electrode; a second current collector. 8. Secondary battery, advantageously lithium-ion type, obtained according to the method of one of claims 1 to 7. 9. Flexible secondary battery according to claim 8. 10. Use of the secondary battery according to claim 8 or 9, in the textile field.