METHOD FOR PRODUCE AN ELECTRODE OR COMPOSITION WITH MAGNETIC PROPERTIES AND MIXTURE PRODUCED BY SAYEN METHOD AND SAYEN ELECTRODE

Description

[0001] The present invention relates to a method for preparing a polymeric composition, particularly one suitable for use as a lithium-ion, sodium-ion, or supercapacitor battery electrode, or for exhibiting magnetic properties; such a composition obtained by this method; a precursor mixture of this composition obtained by a first mixing step of this method; and this lithium-ion or supercapacitor battery electrode. The invention is applicable to all polymeric compositions comprising a very high charge content (advantageously greater than 80% by mass or 60% by volume) and a controlled porosity depending on the chosen application, the charge being, for example, an active inorganic material for a lithium-ion or sodium-ion battery electrode, porous carbon for a supercapacitor electrode, or a magnetic inorganic charge.

[0002] Several processes for manufacturing materials with high filler content have already been described in the literature.

[0003] For example, with regard to magnetic charges, a solvent-based process is generally used to mix the various components (e.g., magnetic charge, surfactant, compatibilizer, binder) to obtain a dispersion or slurry. Once dried, this slurry yields the magnetic material, as described, for example, in US-A1-2011 / 0018664. After coating this dispersion, a magnetic field is applied to orient the magnetic charges. The resulting coated film is then dried, cut into the desired shape, and finally sintered to obtain the final material. For these magnetic applications, a dense material is preferred to achieve the highest possible corresponding magnetic field.

[0004] The same type of process is found in the field of batteries, where electrodes are most often obtained using an organic or aqueous solvent method. This method involves a step of dissolving or dispersing the various electrode components, including a polymer binder, in the solvent, followed by a spreading step on a metallic collector, and finally a solvent evaporation step. This method, described for example in US-B2-7 235 332 using an organic solvent, results in high porosity in the material due to the space occupied by the solvent. This porosity is necessary for the electrode to be impregnated by an electrolyte, which enables its operation.

[0005] These known coating processes present numerous environmental and safety drawbacks when potentially toxic or flammable organic solvents are used. Indeed, significant quantities of these solvents must be evaporated. When using aqueous solvents, known coating processes must include thorough drying of the electrode before its use in a lithium-ion battery cell.

[0006] Furthermore, it is difficult to control the porosity of the material coated by solvent evaporation and, in general, the solvent limits the possibilities of formulation and addition of additives in the composition, particularly due to its migration during drying and high molar masses which are difficult to solvate, as in the field of paints.

[0007] It is therefore highly desirable to implement a process that avoids the use of solvents and allows control of the porosity of the resulting composition.

[0008] Another known process, primarily for incorporating high levels of magnetic charge into materials, involves injecting a paste containing the filler and a thermosetting resin precursor into a mold, as described, for example, in document US-A1-2006 / 0280921, followed by curing the paste. The resulting magnetic materials exhibit a high concentration of magnetic charges bound by a three-dimensional network. However, once crosslinked, these materials are no longer processable and have the drawback of generally requiring long processing times due to the resin reaction. Furthermore, this type of process is highly dependent on the flow of the thermosetting precursors through the inter-grain porosity (Darcy's law) and therefore on the viscosity of these precursors.Here too, high molar masses cannot be used due to excessive viscosity, nor can complex formulations be employed given the additive filtration phenomena induced by the fillers. Furthermore, this injection molding process presents a mold sealing problem when operating at high pressures. Finally, it is impossible with this process to control the porosity and therefore the density of the final material.

[0009] It is now known that continuous processes, such as those commonly used for thermoplastics (e.g., extrusion, mixing, injection molding), can be used to rapidly melt-process materials. However, the filler content achieved to date varies depending on the mineral fillers used. These processes, which melt-mix the fillers and disperse them in a binder, generate high viscosities and cause abrasion of the binder by the high concentration of mineral fillers. Furthermore, it is still impossible to control the density of the resulting materials. Indeed, only dense materials inherent to melt-processing can be obtained, without porosity control.

[0010] Regarding the incorporation of magnetic fillers, US-A1-2011 / 017939 describes the production of materials by melting with an elastomeric binder, where a magnetic filler mass content of only 88% is achieved in the best-case scenario. To achieve mass contents exceeding 90% using such a process, it is generally necessary to functionalize the filler to improve its compatibility with the binder, using a coupling agent that modifies the filler's surface before mixing with the binder. However, this functionalization significantly increases the overall cost and complexity of the process. Furthermore, no control over porosity, and therefore density, is possible with these known melt-process methods.For example, US-A1-2011 / 074531 describes the melt-processing of materials containing a magnetic charge volume fraction greater than 80%, via functionalization of the charge surface with an epoxy oligomer, the use of a low molecular weight polymer chain (4 to 12 kmol / g) containing a labile amine hydrogen allowing crosslinking with the epoxy function, and the addition of a pentaerythritol-type additive and a fatty acid.

[0011] A major drawback of these melt incorporation processes of high levels of magnetic charges lies in the need to functionalize the surface of the charge and to use a binder with a low molar mass, typically less than 15 kmol / g, to avoid the problems induced by high molar masses and without compatibilizing of the surface of the charge, which include a considerable increase in viscosity and therefore in pressures associated with the process and significant abrasion of the equipment and raw materials in contact generated by the unfunctionalized charge due to its high concentration.

[0012] It is also known to use melt processes to prepare battery electrodes, although major difficulties are encountered in the specific case of lithium-ion batteries, due to the fact that the mass percentages of active material required for sufficient electrode capacity in lithium-ion batteries must be equal to or greater than 85%. However, at such active material percentages, the viscosity of the polymer mixture becomes very high, leading to risks of overheating of the mixture and loss of mechanical cohesion after processing.

[0013] Lithium-ion batteries consist of at least two faradic electrodes with opposite polarities: the anode (usually graphite) and the cathode (usually a transition metal oxide). Between these electrodes is a separator made of electrical insulation soaked in an aprotic electrolyte based on Li+ cations, which ensures ionic conductivity. The active material in a lithium-ion battery electrode allows for the reversible insertion and removal of lithium within the electrode, and the higher the mass fraction of this active material, the greater the electrode's capacity. The electrode must also contain an electrically conductive compound, such as carbon black, and a polymeric binder to provide sufficient mechanical cohesion.A lithium-ion battery is thus based on the reversible exchange of lithium ions between the anode and the cathode during the charging and discharging of the battery, and it has a high energy density for a very low mass thanks to the physical properties of lithium.

[0014] As examples of melt-process preparation of electrodes specifically for lithium-ion batteries, we can cite in particular the two documents US-A1-2013 / 0183577 and US-A1-2013 / 0244098, both filed in the name of the Applicant, which respectively present cathode and anode compositions for this battery. Each of these compositions is characterized by the presence of a cross-linked elastomeric binder and a non-volatile organic compound usable in the electrolyte solvent. This organic compound is present in the composition in a reduced mass fraction (typically less than 5%) and may be a carbonate of at least one olefin, e.g., ethylene carbonate.

[0015] However, the processes presented in these last two documents do not allow control of the porosity of the electrode obtained.

[0016] US-B1-7 820 328 attempted to address this problem by using, in conjunction with a polymeric binder and a conductive dilution charge, a small mass fraction of at most 5% of a thermally decomposed sacrificial polymer to obtain an electrode incorporating an active material in a mass fraction greater than 90%, but without an example of an embodiment detailing the process used (which can be implemented indifferently with or without solvent).

[0017] A major drawback of the process presented in this latter document lies in the difficulty of implementing the electrodes if they were obtained by melting, as well as in their electrochemical capacity which may prove insufficient in a lithium-ion battery.

[0018] One aim of the present invention is therefore to design a melt manufacturing process which remedies these drawbacks by allowing in particular control of the porosity of the compositions obtained according to the applications intended, with incorporation of a very high mass percentage of fillers typically greater than 80%, without the need for functionalization of these fillers.

[0019] This goal is achieved in that the Applicant has just discovered, surprisingly, that if an active material and additives comprising a polymeric binder and a continuous sacrificial polymeric phase are mixed hot by melting without solvent evaporation so that the mass fraction of this phase in the resulting mixture is equal to or greater than 15%, then a polymeric composition is obtained that can be used to constitute an electrode for a lithium-ion, sodium-ion or supercapacitor battery or to exhibit magnetic properties, with improved plasticity and fluidity during the implementation of the melted mixture despite the very high mass percentage of active material(s) in the composition, and controlled porosity of the composition is obtained according to the desired application, giving it, as the case may be, satisfactory electrode capacity or magnetic field properties.

[0020] A method for preparing, according to the invention, a polymeric composition usable for forming an electrode of a lithium-ion, sodium-ion or supercapacitor battery, or for exhibiting magnetic properties, thus comprises the following steps: a) hot, melt-mixing, solvent-free mixing of at least one active substance, a binder-forming polymeric phase, and a sacrificial polymeric phase to obtain a mixture, and b) at least partial removal of said sacrificial polymeric phase to obtain said composition comprising the active substance(s) in a mass proportion exceeding 80% and this process according to the invention is such that said sacrificial polymeric phase is used in step a) in a mass fraction in said mixture which is equal to or greater than 15%.

[0021] Preferably, said sacrificial polymeric phase is used in step a) in a mass fraction in said mixture which is inclusively between 20% and 80%.

[0022] It should be noted that the process of the invention makes it possible to incorporate, directly in the melt process and by conventional plastic transformation techniques, very high cumulative charge levels in the compositions obtained, exceeding 80% by mass or 60% by volume, which give high performance to electrochemical cells incorporating electrodes made up of these compositions.

[0023] The Applicant was thus able to produce by melting materials usable as is according to the chosen application which, after shaping and removal of the sacrificial phase, contain these very high levels of fillers without prior modification of the surface of the fillers or use of a coupling agent.

[0024] It should also be noted that this process allows control of the porosity within the composition by adjusting the amount of sacrificial phase introduced according to the intended application. This control is achieved by controlling the size, quantity, and morphology of the pores, and can even eliminate porosity altogether by using a continuous sacrificial phase carefully selected for its specific characteristics in relation to this melt-melting process and the chosen application. For example, an open porosity with dimensions less than 20 µm can be desirable for applications such as electrodes used to sorb an electrolyte. Depending on the application, the composition's porosity can be controlled (density / magnetism trade-off), reduced, or even eliminated by compression to obtain a denser material. Indeed, depending on the application, it is possible to either decrease the density for an equivalent magnetic field or increase the magnetic field for a given volume by increasing the density.To obtain electrodes, the material can also be compressed to control its porosity.

[0025] Furthermore, the mixing, dispersion, and homogeneous distribution of the binder-forming phase, the sacrificial phase, and the active ingredient(s) are ensured during the melt process. Crosslinking of the binder-forming phase is possible to optimize the mechanical properties and cohesion of the composition, but is not necessary if future processing is planned.

[0026] It should also be noted that the process according to the invention provides short implementation times, typical of conventional plastics processing such as extrusion for example, and that the suitability for improved implementation of the compositions of the invention is maintained thereafter as long as no crosslinking has been carried out.

[0027] According to another feature of the invention, said sacrificial polymer phase can be used in step a) in the form of medium-sized granules in a number greater than 1 mm (i.e., not nanoparticles), and step a) is carried out in an internal mixer or in an extruder without macro-separation of phases between the binder-forming phase and the sacrificial polymer phase in said mixture, wherein the binder-forming phase is dispersed homogeneously in the sacrificial polymer phase which is continuous, or forms a co-continuous phase with the latter.

[0028] It should be noted that the sacrificial phase can be extracted by simple thermal decomposition or by any other process that allows its extraction without affecting the rest of the mixture. The sacrificial phase can also be directly extracted as it exits the die by decompression when using volatile compounds. It is preferable to use as the sacrificial material one or more polymers that leave little or no residue upon decomposition. However, if such a polymer, compatible with the final application, is chosen as the sacrificial phase, its extraction can be controlled, leaving a portion of the sacrificial phase in the resulting composition.

[0029] According to one embodiment of the invention, the sacrificial polymer phase is eliminated substantially without residue or not in step b) via thermal decomposition, the sacrificial phase having a thermal decomposition temperature at least 20°C lower than the thermal decomposition temperature of the binder-forming phase. In this case, this sacrificial phase is preferably based on at least one sacrificial polymer selected from among the carbonate polyalkenes, preferably carbonate polyethylenes and / or carbonate polypropylenes (other polymers known to have a clear thermal degradation temperature may nevertheless also be used).

[0030] According to another embodiment of the invention, said sacrificial polymer phase is removed substantially without residue or not in step b) via solvent extraction and is based on at least one liquid-extractable sacrificial polymer preferably chosen from the group consisting of polyethylene glycols, polypropylene glycols and their mixtures (note that other liquid-extractable polymer bases, aqueous or organic, are also usable).

[0031] It should be noted that in order to control the implementation, the integrity of the final composition, and its porosity, it is necessary to carefully select the binder polymer(s) - sacrificial polymer(s) pair and to proceed with the mixing process, making informed choices regarding the tools used (e.g., screw profile in the case of extrusion), the proportions of additives, any compatibilizers, etc. Indeed, as explained above, it is necessary to avoid macro-separation of phases during implementation between the binder phase and the sacrificial phase (pure, undispersed polymer(s) larger than a few tens of µm).

[0032] It should also be noted that photoacid generators can be used as additives to aid the decomposition of sacrificial phases, e.g., for polypropylene carbonate (see the article by Cupta M., Jayachandran P., Khol P., "Photoacid generators for catalytic decomposition of polycarbonate," Journal of Applied Polymer Science, 2007, Vol. 105, pp. 2655-2662). The use of these photoacids makes it possible to lower the degradation temperatures after cathode incorporation, in particular. They are therefore useful, although not essential to the invention.

[0033] As active ingredient(s) usable in the process of the invention and present in the composition obtained in step b) in a mass fraction preferably equal to or greater than 85%, a filler chosen from the group consisting of: may be used, depending on the application sought. all inorganic magnetic charges known to those skilled in the art, such as Fe₂O₃ ferrites and magnetic materials of the Nd-Fe-B, Sm-Fe-N type or cobalt-based such as SmCo, in particular, active inorganic charges suitable for lithium insertion / deinsertion for lithium-ion battery electrodes, including lithia-coated polyanionic compounds or complexes such as a lithia-coated carbon-based phosphate of a metal M of formula LiMPO₄ (e.g., C-LiFePO₄), a lithia-coated titanium oxide of formula Li₄Ti₅O₁₂, or any other active material known to those skilled in the art for cathodes (e.g., LiCoO₂, LiMnO₄, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O₄) or anodes (e.g., graphite), and charges comprising porous carbon for electrodes of supercapacitors.

[0034] Electrically conductive mineral fillers can be added in conjunction with others, for example in the electrodes for lithium-ion, sodium-ion or supercapacitor batteries, but also alone in highly conductive applications, for conductivities exceeding 1 S / cm. Examples include conductive carbon black, but also graphite, graphene, carbon nanofibers, carbon nanotubes and mixtures thereof.

[0035] As a binder polymer(s) ensuring the cohesion of the composition after processing, all polymer bases can be used, provided they are suitable for melt processing and, as mentioned previously, compatible with the chosen sacrificial phase. Examples include polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, and elastomers.

[0036] According to the invention, the binder-forming phase comprises at least one crosslinked or non-crosslinked elastomer, which is used in the mixture in a mass fraction of between 1% and 12% and is selected from the group consisting of hydrogenated butadiene-acrylonitrile copolymers (HNBR), ethylene-acrylate copolymers, polyisoprenes, and mixtures thereof. However, it is preferable to use a binder that ensures continuity of elastic properties over a temperature range from approximately -20°C to 80°C, hence the preferential use of elastomers such as HNBR or ethylene-acrylate copolymers, in particular.

[0037] Specific additives can be added to the compositions of the invention to improve or optimize their manufacturing process. Compounds that promote binder crosslinking, as well as co-agents that aid in crosslinking and its homogenization, can also be added. Examples include organic peroxides as crosslinking agents and triallyl cyanurate as a co-agent. Other compounds that promote binder crosslinking, such as photoinitiators or sulfur compounds (typical of rubber crosslinking by vulcanization), can also be used. Alternatively, chemical reactions of bifunctional compounds on the dangling chains of the binder, such as maleic anhydride, epoxide, acid, alcohol, amine, amide, or ester groups, can be used, provided that a reaction on the dangling groups leads to the formation of crosslinks between polymer chains and, consequently, to binder crosslinking.Crosslinking ensures the cohesion of the composition depending on the nature of the binder. As indicated above, it should be noted that the use of a crosslinking agent and co-agent is useful but not necessary for the invention, and depends directly on the intended application and the need to maintain the composition's workability (in the case of a non-crosslinked composition) or not to maintain it (in the case of a crosslinked composition).

[0038] Advantageously, the composition obtained in step b) may have a volume porosity of between 30% and 70% and is suitable for use as an electrode in a lithium-ion, sodium-ion or supercapacitor battery.

[0039] According to another feature of the invention, the process may include between steps a) and b) a shaping step by calendering said mixture obtained in step a), and said composition obtained in step b) is formed of a sheet of thickness between 50 µm and 150 µm.

[0040] According to another aspect of the invention concerning the case where the elimination of said sacrificial polymeric phase is only partial, a polymeric composition according to the invention which is usable to constitute an electrode of lithium-ion, sodium-ion battery or supercapacitor or to exhibit magnetic properties, is such that the composition is obtained by said process of the invention as defined above and may have said sacrificial phase in a mass fraction equal to or greater than 0.001% and for example between 0.01% and 10%.

[0041] According to yet another aspect of the invention, a polymeric mixture according to the invention which is usable to constitute a precursor of this composition (e.g. an electrode precursor) is such that this mixture is obtained by step a) of said process of the invention and comprises said sacrificial polymeric phase in a mass fraction in this mixture equal to or greater than 15% and preferably inclusively between 20% and 80%.

[0042] As indicated above, this mixture of the invention is further such that said binder-forming phase is dispersed homogeneously in said sacrificial polymeric phase which is continuous, or forms a co-continuous phase with the latter.

[0043] A lithium-ion, sodium-ion or supercapacitor battery electrode according to the invention (e.g. a cathode or an anode) is such that it comprises a polymeric composition according to the invention as defined above.

[0044] Advantageously, this electrode may be such that said composition further comprises an electrically conductive charge selected from the group consisting of carbon black, graphite, expanded graphite, carbon fibers, carbon nanotubes, graphene and mixtures thereof, said electrically conductive charge being present in the composition in a mass fraction between 1% and 10%.

[0045] It should be noted that the invention described herein can be applied to fields other than those mentioned above that require high levels of inorganic (metallic, magnetic, or other) charge and possibly control of the porosity of the resulting composition, such as, for example, insulating screens between two diamagnetic materials. By replacing the magnetic charges with electrically conductive charges, materials with very high electrical conductivities (greater than 1 S / cm) can also be produced by melt casting, porous or non-porous depending on the desired application. Controlled and finely dispersed porosity allows for thermal or acoustic insulation while maintaining a high charge level. For example, it is advantageous to obtain high electrical conductivity combined with thermal insulation in the context of the Seebeck or Peltier effect and a thermoelectric generator.

[0046] Other features, advantages and details of the present invention will become apparent from the following description of several examples of embodiments of the invention, given by way of illustration and not limitation, in comparison with a "control" example not in accordance with the invention.

[0047] In the case of using mineral feedstocks for energy storage applications, the resulting compositions were electrochemically characterized. To do this, 14 mm diameter discs were punched out and placed in a glove box under an inert atmosphere. Button cells with lithium metal as the counter electrode were mounted in the glove box to prepare half-cells. The electrolyte used (supplied by Solvionic) was 1M LiPF6 in EC / DMC at 1V / 1V. The cells thus assembled were characterized on a Biologic VMP3 galvanostatic bench at different charge and discharge rates. Measurements were primarily performed at C / 5. Example 1 according to the invention :

[0048] A composition 1 of magnetic material was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the composition 1 obtained after this extraction. Table 1 : Before extraction After extraction Composition 1 % mass % volume % mass % volume Binder: HNBR (Zetpol 2010L) 4 12,5 5 22 Active ingredient: Ferrites (NK-132) 76 44,3 95 78 Sacrificial polymer: Polyethylene carbonate (QPAC25) 20 43,2 0 0

[0049] Composition 1 was prepared using an internal mixer at 60°C. First, HNBR and some of the polyethylene carbonate were added to obtain a plasticized molten mixture. Then, the magnetic fillers were gradually added, with the remaining polyethylene carbonate added regularly, until a homogeneous mixture was obtained.

[0050] The resulting mixture was then calendered into a sheet before being placed in an oven at 230°C under air for 15 minutes. Finally, the resulting product was placed in a press at 150°C to redensify the material forming this composition 1.

[0051] During heat treatment, the removal of polyethylene carbonate was measured by mass difference: 100% of the polyethylene carbonate initially incorporated into the mixture was decomposed. This led to a decrease in the density of composition 1 from 3 g / cm³ to 2.4 g / cm³. After redensification, a density of 3.7 g / cm³ was obtained.

[0052] Unlike the prior art described in the preamble, it should be noted that this process for preparing composition 1 does not require the surface functionalization of the magnetic charges, which can be used as is for the magnetic fields they generate in the final product thanks to the high quantities of charges (mass rate of 95%) and the redensification of the material after extraction of the sacrificial polymer.

[0053] It should also be noted that this process makes it possible to obtain an intense magnetic field in one direction, thanks to the presence of a relatively high proportion of sacrificial phase in the molten mixture (20% by mass) and the fluidity of the mixture. Once the charges are added and oriented, this extraction and redensification process maintains this orientation and increases the density, and therefore the intensity, of the emitted field. Example 2 according to the invention :

[0054] A composition 2 of cathode for lithium-ion battery was prepared according to the following formulations, for the mixture before extraction of the sacrificial polymer and for composition 2 obtained after extraction. Table 2 : Before extraction After extraction Composition 2 % mass % volume % mass % volume Binder: HNBR (Zetpol 2010L) 4,9 10,4 7,5 20,8 Conductive filler: Carbon black (C-Nergy C65) 4,9 5,3 7,5 10,6 Sacrificial polymer: Polyethylene carbonate (QPAC25) 34,2 50 0 0 Active material: C-LiFePO 4 ("Life power P2") 56 34,3 85 68,6

[0055] Composition 2 was prepared using an internal mixer at 70°C. First, HNBR and some of the polyethylene carbonate were added to obtain a plasticized molten mixture. Then, the mineral fillers were gradually added, with the remaining polyethylene carbonate added regularly, until a homogeneous mixture was obtained.

[0056] The resulting sheet mixture was then calendered and compressed under pressure at 170°C for 15 minutes. Finally, the sacrificial polymer was decomposed in an air oven at 230°C for 15 minutes. During the heat treatment, the removal of polyethylene carbonate was measured by mass difference: 100% of the polyethylene carbonate initially incorporated into the mixture was decomposed. This resulted in a decrease in the electrode density from 2.0 g / cm³ to 1.3 g / cm³ and a volumetric porosity of 50%.

[0057] It should be noted that the resulting composition 2, which is derived from a molten mixture comprising more than 30% by mass of sacrificial phase and 85% by mass of active material, can be used directly as a cathode. Indeed, this composition 2 was characterized as a button cell against Li metal. By setting a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 115 mAh per gram of cathode (excluding the mass of the current collector) was obtained, which corresponds to a capacity of 135 mAh per gram of C-LiFePO4. Example 3 according to the invention :

[0058] A lithium-ion battery cathode composition 3 was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the composition 3 obtained after this extraction. Table 3 : Before extraction After extraction Composition 3 % mass % volume % mass % volume Binder: HNBR (Zetpol 2010L) 5,7 12,5 7,5 20,8 Conductive filler: Carbon black (C-Nergie C65) 5,7 6,4 7,5 10,6 Sacrificial polymer: Polypropylene carbonate (low molar mass) 11,9 20 0 0 Sacrificial polymer: Polypropylene carbonate (high molar mass) 11,9 20 0 0 Active material: C-LiFePO 4 ("Life Power P2") 64,8 41,1 85 68,6

[0059] Composition 3 was prepared using an internal mixer at 80°C. First, HNBR and high molecular weight polypropylene carbonate were added to obtain a plasticized molten mixture. Then, the mineral fillers were gradually added, with regular addition of low molecular weight polypropylene carbonate (preheating the material to approximately 60°C may be necessary to reduce its viscosity and facilitate addition), until a homogeneous mixture was obtained.

[0060] The resulting sheet mixture was then calendered and compressed under pressure at 170°C for 15 minutes. Finally, the sacrificial polymer underwent decomposition in an air oven at 230°C for 45 minutes. During this heat treatment, the removal of polypropylene carbonates was measured by mass difference: 100% of the polypropylene carbonates initially incorporated into the mixture were decomposed. This resulted in a decrease in electrode density from 2.1 g / cm³ to 1.6 g / cm³ and a volumetric porosity of 40%.

[0061] It should be noted that the resulting composition 3, which is derived from a molten mixture comprising more than 20% by mass of sacrificial phase and 85% by mass of active material, can be used directly as a cathode. Indeed, it has been characterized as a button cell against Li metal. By setting a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 123 mAh per gram of cathode (not including the mass of the current collector) was obtained, which corresponds to a capacity of 145 mAh per gram of C-LiFePO4. Example 4 according to the invention :

[0062] A composition 4 of cathode for lithium-ion battery was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the composition 4 obtained after this extraction. Table 4 : Before extraction After extraction Composition 4 % mass % volume % mass % volume Binder: Ethylene-ethyl acrylate (Lotader 5500) 3,4 7,6 5 15,3 Conductive filler: Carbon black (C-Nergie C65) 3,4 3,7 5 7,5 Sacrificial polymer: Polypropylene carbonate (QPAC40) 30,9 50,4 0 0 Active material: C-LiFePO4 ("Life Power P2") 62,3 38,3 90 77,2

[0063] Composition 4 was prepared using a twin-screw extruder equipped with three gravimetric feeders, a side feeder, a gear pump, and a flat die. The different raw materials were distributed among these various gravimetric feeders. During extrusion, the feeder flow rates were adjusted to obtain the desired composition 4. Using a specific screw profile, the raw materials were dispersed and homogenized by melting in the twin-screw extruder. The gear pump and the flat die at the extruder end were used to shape the resulting mixture into a film, which was then deposited directly onto a current collector. The film was then heat-treated at 230°C for 60 minutes in air to obtain the final composition 4.

[0064] During heat treatment, the removal of polypropylene carbonate was measured by mass difference: 100% of the polypropylene carbonate incorporated in the mixture was decomposed. This led to a decrease in electrode density from 2.0 g / cm³ to 1.4 g / cm³ and a volumetric porosity of 50%.

[0065] The resulting composition 4, which is derived from a molten mixture comprising more than 30% by mass of sacrificial phase and 90% by mass of active material, can be used directly as a cathode. Indeed, it has been characterized in a button cell versus Li metal cell. By setting a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 123 mAh per gram of cathode (excluding the collector mass) was obtained, which corresponds to a capacity of 136 mAh per gram of C-LiFePO4. Example 5 according to the invention :

[0066] A lithium-ion battery cathode composition 5 was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the composition 5 obtained after this extraction. Table 5 : Before extraction After extraction Composition 5 % mass % volume % mass % volume Binder: Ethylene-ethyl acrylate (Lotader 5500) 3,4 7,7 5 15,8 Conductive filler: Carbon black (C-Nergie C65) 3,4 3,8 5 7,7 Sacrificial polymer: Polypropylene carbonate (QPAC40) 30,9 51,2 0 0 Active ingredient: Li 4 Ti 5 O 12 (EXM 1979) 62,3 37,3 90 76,5

[0067] Composition 5 was prepared using a twin-screw extruder equipped with three gravimetric feeders, a side feeder, a gear pump, and a flat die. The different raw materials were distributed among these various gravimetric feeders. During extrusion, the feeder flow rates were adjusted to obtain the desired composition 5. Using a specific screw profile, the raw materials were dispersed and homogenized by melting in the twin-screw extruder. The gear pump and the flat die at the extruder end were used to shape the resulting mixture into a film, which was then deposited directly onto a current collector. The film was then heat-treated at 230°C for 60 minutes in air to obtain the final composition 5.

[0068] During heat treatment, the removal of polypropylene carbonate was measured by mass difference: 100% of the polypropylene carbonate incorporated in the mixture was decomposed. This led to a decrease in electrode density from 2.1 g / cm³ to 1.4 g / cm³ and a volumetric porosity of 50%.

[0069] The resulting composition 5, which is derived from a molten mixture comprising more than 30% by mass of sacrificial phase and 90% by mass of active material, can be used directly as a cathode. Indeed, it has been characterized as a button cell against Li metal. By setting a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 135 mAh per gram of cathode (excluding the collector mass) was obtained, which corresponds to a capacity of 150 mAh per gram of Li₄Ti₅O₁₂. Example 6 according to l'invention :

[0070] A composition 6 of cathode for lithium-ion battery was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the composition 6 obtained after this extraction. Table 6 : Before extraction After extraction Composition 6 % mass % volume % mass % volume Binder: HNBR (Zetpol 2010L) 3,75 7,1 7,5 20,8 Conductive filler: Carbon black (C-Nergy C65) 3,75 3,6 7,5 10,6 Sacrificial polymer: Polyethylene carbonate (QPAC25) 50 65,8 0 0 Active material: C-LiFePO 4 ("Life power P2") 42,5 23,5 85 68,6

[0071] Composition 6 was prepared using an internal mixer at 70°C. First, HNBR and some of the polyethylene carbonate were added to obtain a plasticized molten mixture. Then, the mineral fillers were gradually added, with the remaining polyethylene carbonate added regularly, until a homogeneous mixture was obtained.

[0072] The resulting sheet mixture was then calendered and compressed under pressure at 170°C for 15 minutes. Finally, the sacrificial polymer was decomposed in an air oven at 240°C for 30 minutes. During this heat treatment, the removal of polyethylene carbonate was measured by mass difference: 100% of the polyethylene carbonate initially incorporated into the mixture was decomposed. This resulted in a volumetric porosity of 66%.

[0073] The resulting composition 6, which is a molten mixture comprising 50% by mass of sacrificial phase and 85% by mass of active material, can be used directly as a cathode. Indeed, it has been characterized as a button cell against Li metal. By applying a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 109 mAh per gram of cathode (excluding the mass of the current collector) was obtained, which corresponds to a capacity of 128 mAh per gram of C-LiFePO4.

[0074] Furthermore, this electrode was compressed after degradation of the sacrificial phase, the resulting product having the same final formulation as composition 6 and also being directly usable as a cathode. It was characterized as before as a button cell against Li metal, by fixing a current equivalent to a charge and discharge rate of C / 5, and a maximum discharge capacity of 106 mAh per gram of cathode (not including the collector mass) was obtained, which corresponds to a capacity of 124 mAh per gram of C-LiFePO4.

[0075] It should be noted that the very high mass ratio of sacrificial phase (50%) used in the molten mixture advantageously makes this mixture very fluid and allows very small electrode thicknesses (50 µm) to be achieved.

[0076] It should also be noted that the final compression makes it possible to reduce the very high porosity (66%) of composition 6, in order to have an acceptable energy density for the electrode. Example "control" not conforming to the invention :

[0077] A "control" composition of lithium-ion battery cathode was prepared according to the following formulations (expressed in mass and volume fractions), for the mixture before extraction of the sacrificial polymer and for the "control" composition obtained after this extraction. Table 7 : Before extraction After extraction "Control" composition % mass % volume % mass % volume Binder: HNBR (Zetpol 2010L) 6,75 17,1 7,5 20,8 Conductive filler: Carbon black (C-Nergy C65) 6,75 8,8 7,5 10,6 Sacrificial polymer: Polyethylene carbonate (QPAC25) 10 17,6 0 0 Active material: C-LiFePO 4 ("Life power P2") 76,5 56,5 85 68,6

[0078] The "control" composition was prepared using an internal mixer at 70°C. First, HNBR and polyethylene carbonate were added to obtain a plasticized molten mixture. Then, a portion of the mineral fillers was gradually added. The remaining mineral fillers had to be added to an open mixer because adding all the fillers to the internal mixer would cause abrasion and scorching.

[0079] The resulting mixture was then calendered into a sheet before being compressed under pressure at 170°C for 15 minutes. Due to the high viscosity of the mixture, a thickness of only 280 µm could be obtained, compared to the 50 µm to 150 µm normally obtained with the process of the invention.

[0080] Finally, a decomposition step of the sacrificial polymer was implemented in an air oven at 230°C for 20 minutes. During the heat treatment, the removal of polyethylene carbonate was measured by mass difference: 100% of the polyethylene carbonate initially incorporated into the mixture was decomposed. This resulted in a volumetric porosity of only 17.6%.

[0081] The "control" composition obtained in a button cell against Li metal was characterized. By fixing a current equivalent to a charge and discharge rate of C / 5, a maximum discharge capacity of 26 mAh per gram of cathode (not including the mass of the current collector) was obtained, which corresponds to a capacity of 30 mAh per gram of C-LiFePO4.

[0082] It should be noted that this "control" composition, which is derived from a molten mixture containing only 10% by mass of sacrificial phase, contrary to the quantities of at least 15% required in the molten mixtures of the present invention, is very difficult to implement.

[0083] Moreover, this "control" composition with very low porosity (porosity of less than 20% by volume) does not provide efficient electrochemical results due to insufficient access of the electrolyte to the resulting active material (see the maximum discharge capacity of only 26 mAh per gram of cathode), in particular unlike example 2 according to the invention characterized by the same final mass percentage of active material (85%) but by the incorporation of a significantly higher mass percentage of sacrificial phase (more than 30%) which provides a maximum discharge capacity of 115 mAh per gram of cathode.

Claims

1. A process for preparing a polymeric composition usable for forming a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode or for exhibiting magnetic properties, the process comprising the following steps: a) hot-mixing, by a melt process and without solvent, at least one active material, a binder-forming polymeric phase and a sacrificial polymeric phase to obtain a mixture, and b) at least partially eliminating said sacrificial polymeric phase to obtain said composition which comprises the active material(s) according to a weight fraction greater than 80%, characterized in that said sacrificial polymeric phase is used in step a) according to a weight fraction in said mixture which is greater than or equal to 15%.

2. The process as claimed in claim 1, characterized in that said sacrificial polymeric phase is used in step a) according to a weight fraction in said mixture which is inclusively between 20% and 80%.

3. The process as claimed in claim 1 or 2, characterized in that said sacrificial polymeric phase is used in step a) in the form of granules having a number-average size greater than 1 mm, and in that step a) is carried out in an internal mixer or in an extruder without macrophase separation between said binder-forming polymeric phase and said sacrificial polymeric phase in said mixture, in which said binder-forming phase is homogeneously dispersed in said sacrificial polymeric phase which is continuous, or else forms a co-continuous phase with the latter.

4. The process as claimed in one of claims 1 to 3, characterized in that said sacrificial polymeric phase is eliminated in step b) via a thermal decomposition, said sacrificial polymeric phase having a thermal decomposition temperature which is at least 20°C below a thermal decomposition temperature of said binder-forming phase.

5. The process as claimed in claim 4, characterized in that said sacrificial polymeric phase is based on at least one sacrificial polymer chosen from polyalkene carbonates, preferably polyethylene carbonates and / or polypropylene carbonates.

6. The process as claimed in one of claims 1 to 3, characterized in that said sacrificial polymeric phase is eliminated in step b) via an extraction with a solvent and is based on at least one liquid-extractable sacrificial polymer preferably chosen from the group consisting of polyethylene glycols, polypropylene glycols and mixtures thereof.

7. The process as claimed in one of the preceding claims, characterized in that said binder-forming phase comprises at least one crosslinked or noncrosslinked elastomer, which is used in said mixture according to a weight fraction of between 1% and 12% and which is preferably chosen from the group consisting of hydrogenated butadiene / acrylonitrile copolymers (HNBR), ethylene / acrylate copolymers, polyisoprenes and mixtures thereof.

8. The process as claimed in one of the preceding claims, characterized in that said active material(s) is (are) present in said composition obtained in step b) according to a weight fraction preferably greater than or equal to 85%, and is (are) chosen from the group consisting of: - magnetic inorganic fillers, such as ferrites, - active inorganic fillers capable of allowing lithium insertion / deinsertion for lithium-ion battery electrodes, comprising lithiated polyanionic compounds or complexes such as a lithiated metal M phosphate of formula LiMPO4 coated with carbon, a lithiated titanium oxide of formula Li4Ti5O12, oxides of formula LiCoO2, LiMnO4 or LiNi1 / 3Mn1 / 3Co1 / 3O4, or graphite, and - fillers comprising porous carbon for supercapacitor electrodes.

9. The process as claimed in one of the preceding claims, characterized in that said composition obtained in step b) has a volume porosity between 30% and 70% and is suitable for forming a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode.

10. The process as claimed in one of the preceding claims, characterized in that the process comprises, between steps a) and b), a step of fashioning by calendering said mixture obtained in step a), and in that said composition obtained in step b) is formed from a sheet having a thickness of between 50 µm and 150 µm.

11. A polymeric composition usable for forming a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode or for exhibiting magnetic properties, characterized in that said composition is obtained by means of a process as claimed in one of claims 1 to 10 and exhibits said sacrificial polymeric phase according to a weight fraction greater than or equal to 0.001% and for example between 0.01% and 10%, and in that said binder-forming polymeric phase comprises at least one crosslinked or noncrosslinked elastomer which is used in said mixture according to a weight fraction of between 1% and 12% and which is chosen from the group consisting of hydrogenated butadiene / acrylonitrile copolymers (HNBR), ethylene / acrylate copolymers and mixtures thereof.

12. A polymeric mixture usable for forming a precursor of said composition as claimed in claim 11, characterized in that said mixture is obtained via step a) of the process as claimed in one of claims 1 to 10 and comprises said sacrificial polymeric phase according to a weight fraction in said mixture greater than or equal to 15% and preferably inclusively of between 20% and 80%.

13. The mixture as claimed in claim 12, characterized in that said binder-forming phase is homogeneously dispersed in said sacrificial polymeric phase which is continuous, or else forms a co-continuous phase with the latter.

14. A lithium-ion or sodium-ion battery electrode or supercapacitor electrode, characterized in that it comprises a polymeric composition as claimed in claim 11.

15. The electrode as claimed in claim 14, characterized in that said composition also comprises an electrically conducting filler chosen from the group consisting of carbon black, graphite, expanded graphite, carbon fibers, carbon nanotubes, graphene and mixtures thereof, said electrically conducting filler being present in said composition according to a weight.