Process for preparing an electrode composition or composition with magnetic properties, mixture and composition obtained by means of said process and said electrode

Abstract

A process for preparing a polymeric composition for forming a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode or for exhibiting magnetic properties, to such a polymeric composition obtained by means of this process, to a mixture which is a precursor of the composition, obtained by means of a first mixing step of the process, and to this electrode. The process for preparing this composition comprises: a) hot-mixing, via the melt process and without solvent, at least one active material, a binder-forming polymeric phase and a sacrificial polymeric phase so as to obtain a mixture, and b) at least partially eliminating said sacrificial polymeric phase so as to obtain said composition which comprises the active material(s) according to a weight fraction greater than 80%. The sacrificial phase is used in step a) according to a weight fraction in the mixture being greater than or equal to 15%.

Claims

1. A process for preparing a polymeric composition, the process comprising: 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 molten mixture, and b) at least partially eliminating said sacrificial polymeric phase to obtain said polymeric composition which comprises the at least one active material according to a weight fraction greater than 80%, wherein 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%, wherein said binder-forming polymeric phase comprises at least one noncrosslinked elastomer chosen from a group consisting of hydrogenated butadiene/acrylonitrile copolymers (HNBR), ethylene/acrylate/maleic anhydride terpolymers, and mixtures thereof, said polymeric composition being devoid of a crosslinking agent, wherein said sacrificial polymeric phase is eliminated in step b) via a thermal decomposition, and wherein the polymeric composition forms a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode, or exhibits magnetic properties.

2. The process as claimed in claim 1, wherein 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, wherein said sacrificial polymeric phase is used in step a) in the form of granules having a number-average size greater than 1 mm, and wherein 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 claim 1, wherein said sacrificial polymeric phase has 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, wherein 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 claim 1, wherein said at least one elastomer is used in said mixture according to a weight fraction of between 1% and 12%.

7. The process as claimed in claim 1, wherein said active material(s) is (are) present in said polymeric 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 LiMPO.sub.4 coated with carbon, a lithiated titanium oxide of formula Li.sub.4Ti.sub.5O.sub.12, oxides of formula LiCoO.sub.2, LiMnO.sub.4 or LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.4, or graphite, and fillers comprising porous carbon for supercapacitor electrodes.

8. The process as claimed in claim 1, wherein said polymeric 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.

9. The process as claimed in claim 1, wherein the process comprises, between steps a) and b), a step of fashioning by calendering said mixture obtained in step a), and wherein said polymeric composition obtained in step b) is formed from a sheet having a thickness of between 50 m and 150 m.

10. A polymeric composition forming a lithium-ion or sodium-ion battery electrode or a supercapacitor electrode or exhibiting magnetic properties, wherein said polymeric composition is made by the process of claim 1, the polymeric composition comprises: at least one active material according to a weight fraction greater than 80%; a binder-forming polymeric phase; and a sacrificial polymeric phase according to a weight fraction greater than or equal to 0.001%, wherein said polymeric composition derives from a molten mixture of said at least one active material, said binder-forming polymeric phase and said sacrificial polymeric phase, in which said sacrificial polymeric phase has been partially eliminated, wherein said polymeric composition is devoid of a solvent in which said at least one active material, said binder-forming polymeric phase and said sacrificial polymeric phase are dissolved or dispersed, and wherein said binder-forming polymeric phase comprises at least one noncrosslinked elastomer chosen from a group consisting of hydrogenated butadiene/acrylonitrile copolymers (HNBR), ethylene/acrylate/maleic anhydride terpolymers, and mixtures thereof, said polymeric composition being devoid of a crosslinking agent.

11. A polymeric molten mixture usable for forming a precursor of said polymeric composition as claimed in claim 10, wherein said polymeric molten mixture is obtained by hot-mixing, by a melt process and without solvent, said at least one active material, said binder-forming polymeric phase and said sacrificial polymeric phase, and wherein said polymeric molten mixture 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%.

12. The polymeric molten mixture as claimed in claim 11, wherein said binder-forming polymeric phase is homogeneously dispersed in said sacrificial polymeric phase which is continuous, or else forms a co-continuous phase with the latter.

13. A lithium-ion or sodium-ion battery electrode or supercapacitor electrode, wherein it comprises the polymeric composition as claimed in claim 10.

14. The electrode as claimed in claim 13, wherein said polymeric 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 polymeric composition according to a weight fraction of between 1% and 10%.

15. The process as claimed in claim 1, wherein said at least one noncrosslinked elastomer is chosen from the group consisting of hydrogenated butadiene/acrylonitrile copolymers (HNBR), ethylene-ethyl acrylate-maleic anhydride terpolymers, and mixtures thereof.

16. The process as claimed in claim 1, wherein said binder-forming polymeric phase consists of said at least one noncrosslinked elastomer.

17. The polymeric composition as claimed in claim 10, wherein said at least one noncrosslinked elastomer is chosen from the group consisting of hydrogenated butadiene/acrylonitrile copolymers (HNBR), ethylene-ethyl acrylate-maleic anhydride terpolymers and mixtures thereof.

18. The polymeric composition as claimed in claim 10, wherein said binder-forming polymeric phase consists of said at least one noncrosslinked elastomer.

19. The process as claimed in claim 7, wherein said at least one active material is a magnetic inorganic filler chosen from the group consisting of ferrites, said polymeric composition exhibiting magnetic properties.

20. The process as claimed in claim 7, wherein said at least one active material is an active inorganic filler 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 LiMPO.sub.4 coated with carbon, a lithiated titanium oxide of formula Li.sub.4Ti.sub.5O.sub.12, oxides of formula LiCoO.sub.2, LiMnO.sub.4 or LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.4, said polymeric composition forming a lithium-ion battery electrode.

Description

EXAMPLE 1

According to the Invention

(1) A composition 1 of magnetic material was prepared according to the following formulations (expressed as weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for composition 1 obtained after this extraction.

(2) TABLE-US-00001 TABLE 1 Before After extraction extraction % by % by % by % by Composition 1 weight volume weight volume Binder: HNBR (Zetpol 2010L) 4 12.5 5 22 Active material: Ferrites (NK-132) 76 44.3 95 78 Sacrificial polymer: Polyethylene 20 43.2 0 0 carbonate (QPAC25)

(3) Composition 1 was prepared using an internal mixer at 60 C. The HNBR and a part of the polyethylene carbonate were first added in order to obtain a plasticized molten mixture. The magnetic fillers were then gradually added with regular addition of the remaining polyethylene carbonate, until a homogeneous mixture was obtained.

(4) The mixture obtained was then calendered in the form of a sheet before placing it in an oven at 230 C. under air for 15 min. Finally, the resulting product was placed in a press at 150 C. in order to re-densify the material forming this composition 1.

(5) During the heat treatment, the elimination of the polyethylene carbonate was measured by difference in weight: 100% of the polyethylene carbonate initially incorporated into the mixture was thus decomposed. This results in a decrease in density of composition 1 from 3 g/cm.sup.3 to 2.4 g/cm.sup.3. After redensification, a density of 3.7 g/cm.sup.3 was obtained.

(6) Contrary to the prior art set out in the preamble, it will be noted that this process for preparing composition 1 does not require the surface functionalization of the magnetic fillers, which can be used as they are for the magnetic fields that they generate in the final product by virtue of the high amounts of fillers (weight content of 95%) and of the redensification of the material after extraction of the sacrificial polymer.

(7) It will also be noted that this process makes it possible to obtain a strong magnetic field in one direction, by virtue of the presence of a relatively high content of sacrificial phase in the molten mixture (weight content of 20%) and of the fluidity of the mixture. Once the fillers have been added and oriented, this extraction and redensification make it possible to preserve this orientation and to increase the density and therefore the intensity of the field emitted.

EXAMPLE 2

According to the Invention

(8) A cathode composition 2 for a 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 the extraction.

(9) TABLE-US-00002 TABLE 2 Before After extraction extraction % by % by % by % by Composition 2 weight volume weight volume Binder: HNBR (Zetpol 2010L) 4.9 10.4 7.5 20.8 Conductive filler: Carbon black 4.9 5.3 7.5 10.6 (C-Nergy C65) Sacrificial polymer: Polyethylene 34.2 50 0 0 carbonate (QPAC25) Active material: CLiFePO.sub.4 56 34.3 85 68.6 (Life power P2)

(10) Composition 2 was prepared using an internal mixer at 70 C. The HNBR and a part of the polyethylene carbonate were first added in order to obtain a plasticized molten mixture. The inorganic fillers were then gradually added with regular addition of the remaining polyethylene carbonate, until a homogeneous mixture was obtained.

(11) The mixture obtained was then calendered in the form of a sheet in order to compress it under a press at 170 C. for 15 min. Finally, a step of decomposition of the sacrificial polymer in an oven under air at 230 C. for 15 min was carried out. During the heat treatment, the elimination of the polyethylene carbonate was measured by difference in weight: 100% of the polyethylene carbonate initially incorporated into the mixture was thus decomposed. This resulted in a decrease in density of the electrode from 2.0 g/cm.sup.3 to 1.3 g/cm.sup.3 and in a volume porosity of 50%.

(12) It will be noted that the resulting composition 2, which stems from a molten mixture comprising more than 30% by weight of sacrificial phase and which comprises 85% by weight of active material, may be directly usable as a cathode. Indeed, this composition 2 was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity achieved of 115 mAh per gram of cathode was obtained (without including the weight of the current collector), which corresponds to a capacity of 135 mAh per gram of CLiFePO.sub.4.

EXAMPLE 3

According to the Invention

(13) A cathode composition 3 for a lithium-ion battery was prepared according to the following formulations (expressed in weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for composition 3 obtained after this extraction.

(14) TABLE-US-00003 TABLE 3 Before After extraction extraction % by % by % by % by Composition 3 weight volume weight volume Binder: HNBR (Zetpol 2010L) 5.7 12.5 7.5 20.8 Conductive filler: Carbon black 5.7 6.4 7.5 10.6 (C-Nergy C65) Sacrificial polymer: Polypropylene 11.9 20 0 0 carbonate (low molar mass) Sacrificial polymer: Polypropylene 11.9 20 0 0 carbonate (high molar mass) Active material: CLiFePO.sub.4 64.8 41.1 85 68.6 (Life power P2)

(15) Composition 3 was prepared using an internal mixer at 80 C. The HNBR and the high-molar-mass polypropylene carbonate were first added in order to obtain a plasticized molten mixture. The inorganic fillers were then gradually added with regular addition of the low-molar-mass polypropylene carbonate (preheating of the material to approximately 60 C. may be necessary in order to reduce the viscosity thereof and to facilitate the addition), until a homogeneous mixture was obtained.

(16) The mixture obtained was then calendered in the form of a sheet in order to compress it under a press at 170 C. for 15 min. Finally, a step of decomposition of the sacrificial polymer in an oven under air at 230 C. for 45 min was carried out. During the heat treatment, the elimination of the polypropylene carbonates was measured by difference in weight: 100% of the polypropylene carbonates initially incorporated into the mixture was thus decomposed. This resulted in a decrease in density of the electrode from 2.1 g/cm.sup.3 to 1.6 g/cm.sup.3 and in a volume porosity of 40%.

(17) It will be noted that the resulting composition 3, which stems from a molten mixture comprising more than 20% by weight of sacrificial phase and which comprises 85% by weight of active material, may be directly usable as a cathode. Indeed, it was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity achieved of 123 mAh per gram of cathode was obtained (without including the weight of the current collector), which corresponds to a capacity of 145 mAh per gram of CLiFePO.sub.4.

EXAMPLE 4

According to the Invention

(18) A cathode composition 4 for a lithium-ion battery was prepared according to the following formulations (expressed as weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for composition 4 obtained after this extraction.

(19) TABLE-US-00004 TABLE 4 Before After extraction extraction % by % by % by % by Composition 4 weight volume weight volume Binder: Ethylene-ethyl acrylate 3.4 7.6 5 15.3 (Lotader 5500) Conductive filler: Carbon black 3.4 3.7 5 7.5 (C-Nergy C65) Sacrificial polymer: Polypropylene 30.9 50.4 0 0 carbonate (QPAC40) Active material: CLiFePO.sub.4 62.3 38.3 90 77.2 (Life power P2)

(20) Composition 4 was prepared using a twin-screw extruder equipped with three gravimetric metering devices, with a side feeder, with a gear pump and with a flat die. The various starting materials were distributed in these various gravimetric metering devices. During the extrusion, the flow rates of the metering devices were regulated so as to obtain the desired composition 4. The starting materials were dispersed and homogenized by the melt process in the twin-screw extruder using a specific screw profile. The gear pump and the flat die at the end of the extruder served to form the mixture obtained in the form of a film directly deposited on a current collector. The film thus obtained was subsequently heat treated at 230 C. for 60 min, under air, in order to obtain the final composition 4.

(21) During the heat treatment, the elimination of the polypropylene carbonate was measured by difference in weight: 100% of the polypropylene carbonate incorporated into the mixture was thus decomposed. This resulted in a decrease in density of the electrode from 2.0 g/cm.sup.3 to 1.4 g/cm.sup.3 and in a volume porosity of 50%.

(22) The resulting composition 4, which stems from a molten mixture comprising more than 30% by weight of sacrificial phase and which comprises 90% by weight of active material, may be directly usable as a cathode. Indeed, it was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity attained of 123 mAh per gram of cathode was obtained (without including the weight of the collector), which corresponds to a capacity of 136 mAh per gram of CLiFePO.sub.4.

EXAMPLE 5

According to the Invention

(23) A cathode composition 5 for a lithium-ion battery was prepared according to the following formulations (expressed as weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for composition 5 obtained after this extraction.

(24) TABLE-US-00005 TABLE 5 Before After extraction extraction % by % by % by % by Composition 5 weight volume weight volume Binder: Ethylene-ethyl acrylate 3.4 7.7 5 15.8 (Lotader 5500) Conductive filler: Carbon black 3.4 3.8 5 7.7 (C-Nergy C65) Sacrificial polymer: Polypropylene 30.9 51.2 0 0 carbonate (QPAC40) Active material: Li.sub.4Ti.sub.5O.sub.12 62.3 37.3 90 76.5 (EXM 1979)

(25) Composition 5 was prepared using a twin-screw extruder equipped with three gravimetric metering devices, with a side feed, with a gear pump and with a flat die. The various starting materials were distributed into these various gravimetric measuring devices. During the extrusion, the flow rates of the measuring devices were regulated so as to obtain the desired composition 5. The starting materials were dispersed and homogenized by the melt process in the twin-screw extruder using a specific screw profile. The gear pump and the flat die at the end of the extruder served to form the mixture obtained in the form of a film directly deposited on a current collector. The film thus obtained was then heat treated at 230 C. for 60 min, under air, in order to obtain the final composition 5.

(26) During the heat treatment, the elimination of the polypropylene carbonate was measured by difference in weight. 100% of the polypropylene carbonate incorporated into the mixture was thus decomposed. This resulted in a decrease in density of the electrode from 2.1 g/cm.sup.3 to 1.4 g/cm.sup.3 and in a volume porosity of 50%.

(27) The resulting composition 5, which stems from a molten mixture comprising more than 30% by weight of sacrificial phase and which comprises 90% by weight of active material, may be directly usable as a cathode. Indeed, it was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity attained of 135 mAh per gram of cathode was obtained (without including the weight of the collector), which corresponds to a capacity of 150 mAh per gram of Li.sub.4Ti.sub.5O.sub.12.

EXAMPLE 6

According to the Invention

(28) A cathode composition 6 for a lithium-ion battery was prepared according to the following formulations (expressed as weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for composition 6 obtained after this extraction.

(29) TABLE-US-00006 TABLE 6 Before After extraction extraction % by % by % by % by Composition 6 weight volume weight volume Binder: HNBR (Zetpol 2010L) 3.75 7.1 7.5 20.8 Conductive filler: Carbon black 3.75 3.6 7.5 10.6 (C-Nergy C65) Sacrificial polymer: Polyethylene 50 65.8 0 0 carbonate (QPAC25) Active material: CLiFePO.sub.4 42.5 23.5 85 68.6 (Life power P2)

(30) Composition 6 was prepared using an internal mixer at 70 C. The HNBR and a part of the polyethylene carbonate were first added in order to obtain a plasticized molten mixture. The inorganic fillers were then gradually added with regular addition of the remaining polyethylene carbonate, until a homogeneous mixture was obtained.

(31) The mixture obtained was then calendered in the form of a sheet in order to compress it under a press at 170 C. for 15 min. Finally, a step of decomposition of the sacrificial polymer in an oven under air at 240 C. for 30 min was carried out. During the heat treatment, the elimination of the polyethylene carbonate was measured by difference in weight: 100% of the polyethylene carbonate initially incorporated into the mixture was thus decomposed. This resulted in a volume porosity of 66%.

(32) The resulting composition 6, which stems from a molten mixture comprising 50% by weight of sacrificial phase and which comprises 85% by weight of active material, may be directly usable as a cathode. Indeed, it was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity attained of 109 mAh per gram of cathode was obtained (without including the weight of the current collector), which corresponds to a capacity of 128 mAh per gram of CLiFePO.sub.4.

(33) This electrode was, moreover, compressed after degradation of the sacrificial phase, the resulting product still having the same final formulation as composition 6 and likewise being directly usable as a cathode. It was characterized as previously in a button cell against Li metal, with a current equivalent to a charge and discharge rate of C/5 being fixed, and a maximum discharge capacity attained of 106 mAh per gram of cathode was obtained (without including the weight of the collector), which corresponds to a capacity of 124 mAh per gram of CLiFePO.sub.4.

(34) It will be noted that the very high (50%) weight content of sacrificial phase used in the molten mixture advantageously makes it possible to render this mixture very fluid and to achieve very low electrode thicknesses (50 m).

(35) It will 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 energy density which is acceptable for the electrode.

Control Example not in Accordance with the Invention

(36) A control cathode composition for a lithium-ion battery was prepared according to the following formulations (expressed as weight and volume fractions), for the mixture before extraction of the sacrificial polymer and for the control composition obtained after this extraction.

(37) TABLE-US-00007 TABLE 7 Before After extraction extraction % by % by % by % by Control composition weight volume weight volume Binder: HNBR (Zetpol 2010L) 6.75 17.1 7.5 20.8 Conductive filler: Carbon black 6.75 8.8 7.5 10.6 (C-Nergy C65) Sacrificial polymer: Polyethylene 10 17.6 0 0 carbonate (QPAC25) Active material: CLiFePO.sub.4 76.5 56.5 85 68.6 (Life power P2)

(38) The control composition was prepared using an internal mixer at 70 C. The HNBR and the polyethylene carbonate were first added in order to obtain a plasticized molten mixture. A part of the inorganic fillers was then gradually added. The remainder of the inorganic fillers had to be added on an open mixer. This is because complete addition of the fillers in the internal mixer leads to a phenomenon of scorching due to abrasion.

(39) The mixture obtained was then calendered in the form of a sheet in order to compress it under a press at 170 C. for 15 min. Because of the high viscosity of the mixture, it was only possible to obtain a thickness of 280 m, in comparison with the 50 m to 150 m obtained under normal circumstances with the process of the invention.

(40) Finally, a step of decomposition of the sacrificial polymer in an oven under air at 230 C. for 20 min was carried out. During the heat treatment, the elimination of the polyethylene carbonate was measured by difference in weight: 100% of the polyethylene carbonate initially incorporated into the mixture was thus decomposed. This resulted in a volume porosity of only 17.6%.

(41) The control composition obtained was characterized in a button cell against Li metal. By fixing a current equivalent to a charge and discharge rate of C/5, a maximum discharge capacity attained of 26 mAh per gram of cathode was obtained (without including the weight of the current collector), which corresponds to a capacity of 30 mAh per gram of CLiFePO.sub.4.

(42) It will be noted that this control composition, which stems from a molten mixture containing only 10% by weight of sacrificial phase, contrary to the amounts of at least 15% required in the molten mixtures of the present invention, is very difficult to use.

(43) Furthermore, this very sparingly porous control composition (porosity of less than 20% by volume) does not provide effective electrochemical results because of the insufficient access of the electrolyte to the active material which results therefrom (see the maximum discharge capacity of only 26 mAh per gram of cathode), in particular contrary to example 2 according to the invention characterized by the same final weight content of active material (85%), but also by the incorporation of a much higher weight content of sacrificial phase (more than 30%) which provides a maximum discharge capacity of 115 mAh per gram of cathode.