Solvent-free cathode for lithium-ion secondary battery

Abstract

A method (100) for preparing a cathode for a secondary battery, comprising mixing (102) an active material and a conductive material with an electron beam-curable prepolymer to obtain a solvent-free mixture made of the active material, the conductive material, and the prepolymer, passing the solvent-free mixture through a wet powder tableting device, polymerizing (108) the prepolymer with an electron beam to obtain a polymerized active layer on a metallic foil, pressing (110) the polymerized active layer on the metallic foil at room temperature to increase the density of the polymer active layer. A composition for preparing a cathode for a secondary battery, the composition comprising an active material, a conductive material, and an electron beam-curable prepolymer, the composition being free of solvent. A cathode made of the composition and a secondary battery comprising the cathode.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to cathodes of secondary batteries, and more particularly to cathodes of lithium-ion secondary batteries. BACKGROUND

[0002] Cathodes of secondary batteries can be produced using a wet powder sheeting process (hereinafter MPS). The concept is to make a coating of cathode material on aluminum or copper using a three-roll mill. The main advantage of this process is that it allows to process powders with very low solvent content (typically between 15-20% by weight). In the MPS process, the first step is to mix the dry powder with a solvent. Due to the low amount of solvent, the mixture does not form a homogeneous smooth paste.

[0003] Typically, N-methyl-2-pyrrolidone (hereinafter NMP) is used as solvent. However, in order to improve the environmental performance (NMP is a toxic substance) and in order to reduce the energy consumption of the cathode formation process, alternatives to NMP are being sought.

[0004] Water has been tested as a replacement for NMP. However, the active material can react with water and a resistive layer can be formed on the active material, thereby reducing the performance of the cathode. SUMMARY

[0005] Therefore, according to an embodiment of the present disclosure, a method for manufacturing a cathode of a secondary battery is provided. The method comprises:

[0006] - mixing an active material and a conductive material with an electron beam-curable prepolymer to obtain a solvent-free mixture made of the active material, the conductive material and the prepolymer;

[0007] - passing the solvent-free mixture between a first roll and a second roll to apply a layer of the solvent-free mixture on the second roll;

[0008] - passing the layer of the solvent-free mixture between the second roll and a third roll carrying a metallic foil to transfer the layer of the solvent-free mixture onto the metallic foil;

[0009] - polymerizing the prepolymer with an electron beam, thereby obtaining a polymerized active layer on the metallic foil;

[0010] - pressing the polymerized active layer on the metallic foil at room temperature to increase the density of the polymer active layer;

[0011] - cutting the metallic foil to obtain the cathode.

[0012] By providing such a method, a cathode can be produced without using NMP. Moreover, this cathode production is solvent-free, i.e. there is no step of removing the solvent in the production method. Since the removal of the solvent is usually performed at a temperature higher than ambient temperature, the method of the present disclosure allows to reduce the energy consumption.

[0013] Pre-polymer refers to a mixture of monomers that will form a polymer upon irradiation with an electron beam.

[0014] Non-limiting examples of metallic foils are aluminum foils, copper foils.

[0015] As a non-limiting example, the pressing step can be performed at 0.5 ton / cm (ton / cm).

[0016] The increase of the density of the polymeric active layer allows to reduce the IV resistance.

[0017] The active material, the conductive material and the electron beam-curable pre-polymer are mixed together. There is no need for a pre-mixing of the active material and the conductive material.

[0018] It can be understood that, during the cutting of the metallic foil, the polymeric active layer is also cut.

[0019] As a non-limiting example, the absorbed dose can be 60 kGy (kilo Gray).

[0020] As a non-limiting example, the metallic foil can have a speed equal to or less than 10 m / s (meter / second).

[0021] In some embodiments, the total content of active material in the solvent-free mixture can be equal to or greater than 80 mass%, preferably equal to or greater than 85 mass%, more preferably equal to or greater than 90 mass%.

[0022] In some embodiments, the pre-polymer can comprise an acrylic resin.

[0023] Non-limiting examples of acrylic resins can be aliphatic polyurethane acrylates, epoxy acrylates, methacrylates or acrylates.

[0024] In some embodiments, the pre-polymer can comprise methacrylates.

[0025] In some embodiments, the pre-polymer can comprise methacrylates and a lithiated monomer having acrylate functionality.

[0026] The lithiated monomer having acrylate functionality allows to further reduce the IV resistance by providing lithium in the cathode.

[0027] In some embodiments, the pre-polymer can consist of methacrylates and a lithiated monomer having acrylate functionality.

[0028] In some embodiments, the lithiumated monomer having acrylate-based functionality can be lithium bis(trifluoromethylsulfonyl)imido methacrylate.

[0029] In some embodiments, the content of lithium bis(trifluoromethylsulfonyl)imido methacrylate in the prepolymer can be equal to or less than 20 mass%.

[0030] In some embodiments, the active material can be a lithium-containing complex oxide.

[0031] Non-limiting examples of lithium-containing complex oxide active materials are LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi x Co (1-x) O2, LiNi x Co y Mn (1-x-y) O2 (0 < x < 1 and 0 < y < 1), Li2Mn3NiO8, LiNiCoMnO2.

[0032] In some embodiments, the conductive material can be carbon.

[0033] Non-limiting examples of carbon conductive materials are acetylene black, Ketjen black.

[0034] The present disclosure also relates to a composition for preparing a cathode for a secondary battery, the composition comprising an active material, a conductive material, and an electron beam-curable prepolymer, the composition being free of solvent.

[0035] In some embodiments, the total content of active material in the solvent-free mixture can be equal to or greater than 80 mass%, preferably equal to or greater than 85 mass%, more preferably equal to or greater than 90 mass%.

[0036] In some embodiments, the active material can be a lithium-containing complex oxide.

[0037] Non-limiting examples of lithium-containing complex oxide active materials are LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi x Co (1-x) O2, LiNi x Co y Mn (1-x-y) O2 (0 < x < 1 and 0 < y < 1), Li2Mn3NiO8, LiNiCoMnO2.

[0038] In some embodiments, the prepolymer can comprise an acrylic resin.

[0039] Non-limiting examples of acrylic resins can be aliphatic polyurethane acrylates, epoxy acrylates, methacrylates or acrylates.

[0040] In some embodiments, the prepolymer can include methacrylates.

[0041] In some embodiments, the prepolymer can include methacrylates and a lithiated monomer having acrylate functionality.

[0042] In some embodiments, the prepolymer can consist of methacrylates and a lithiated monomer having acrylate functionality.

[0043] In some embodiments, the lithiated monomer having acrylate functionality can be lithium bis(trifluoromethylsulfonyl)imide methacrylate.

[0044] In some embodiments, the content of lithium bis(trifluoromethylsulfonyl)imide methacrylate in the prepolymer can be equal to or less than 20 mass%.

[0045] In some embodiments, the conductive material can be carbon.

[0046] Non-limiting examples of carbon conductive materials are acetylene black, ketjen black.

[0047] The present disclosure relates to a cathode for a secondary battery prepared from the above composition by the above method.

[0048] The present disclosure relates to a secondary battery including the above cathode.

[0049] The above elements can be combined with other elements in the specification, unless otherwise contradicted by context.

[0050] It should be understood that the foregoing Summary of the Invention and the following Detailed Description are merely exemplary and explanatory, and are not restrictive of the disclosure as claimed.

[0051] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 A flow chart showing a method according to embodiments of the present disclosure; and

[0054] Figure 2 A wet powder tableting device is shown. DETAILED DESCRIPTION

[0055] Exemplary embodiments of the present disclosure will now be described in detail with reference to the drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. Reference Example

[0056] Figure 1 A flowchart of a method 100 for manufacturing a cathode 30 for a secondary battery according to an embodiment of the present disclosure is shown.

[0057] In a mixing step 102, the active material and the electrically conductive material are mixed with the electron beam-curable prepolymer to obtain a solvent-free mixture 20 made of said active material, electrically conductive material and prepolymer.

[0058] The solvent-free mixture 20 is then introduced into a wet powder sheeting (MPS) device 12 as shown in Figure 2

[0059] The MPS device 12 comprises three rollers, a first roller 14, a second roller 16 and a third roller 18, the second roller 16 being arranged between the first roller 14 and the third roller 18. The first roller 14 has a speed VI, the second roller 16 has a speed V2 and the third roller 18 has a third speed V3, with VI < V2 < V3.

[0060] During a first passing step 104, the solvent-free mixture 20 is passed between the first roller 14 and the second roller 16, thereby applying a layer 22 of the solvent-free mixture 20 on the second roller 16.

[0061] During a second passing step 106, said layer 22 of the solvent-free mixture 20 is passed between the second roller 16 and the third roller 18 carrying the metallic foil 24, thereby transferring the layer 22 of the solvent-free mixture 20 onto the metallic foil 24.

[0062] During a polymerizing step 108, the prepolymer is polymerized with an electron beam 26, thereby obtaining a polymerized active layer 28 on the metallic foil 24.

[0063] During a pressing step 110, said polymerized active layer on the metallic foil is pressed at room temperature, for example between two rollers 30, to increase the density of the polymer active layer.

[0064] During a cutting step 112, the metallic foil 24 is cut to obtain the cathode 30.

[0065] Example 1

[0066] In example 1, in the mixing step 102, the active material is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 ​O2, the conductive material is acetylene black, and the prepolymer is a methacrylate (EBECRYL 151, Allnex®). The active material, the conductive material and the prepolymer are mixed together to obtain a solvent-free mixture 20. The content of active material is 90 mass%, the content of conductive material is 3 mass% and the content of prepolymer is 7 mass%.

[0067] The mixing step 102 is performed in a mixer (mixing device), for example a household food processor with a bowl capacity of 3 L (liters) and an impeller radius of 80 mm (millimeters). Two diametrically opposed blades are offset from each other by a vertical distance of about 16 mm. The mixer is operated at a constant speed of 1650 rpm (revolutions per minute), which corresponds to a tip speed of 13.8 m / s (meters per second). The mixing step 102 is performed for 10 minutes.

[0068] The solvent-free mixture 20 is then introduced into a wet powder sheeting (MPS) device 12 as shown in Figure 2 .

[0069] In a first passing step 104, the solvent-free mixture 20 is passed between a first roller 14 and a second roller 16, thereby applying a layer 22 of the solvent-free mixture on the second roller 14.

[0070] During a second passing step 106, the layer 22 of the solvent-free mixture 20 is passed between the second roller 16 and a third roller 18 carrying a metallic foil 24, thereby transferring the layer 22 of the solvent-free mixture 20 onto the metallic foil 24. The metallic foil 24 can have a speed of 10 m / s.

[0071] In this embodiment, the metallic foil 24 can be an aluminum foil with a thickness of 12 pm (micrometers).

[0072] During a polymerization step 108, the prepolymer is polymerized with an electron beam 26, thereby obtaining a polymerized active layer 28 on the metallic foil 24. The absorbed dose is equal to 60 kGy. The absorbed dose is monitored by the exposure time, the exposure area, the machine voltage and the current.

[0073] During a pressing step 110, the polymerized active layer 28 is pressed on the metallic foil 24, for example between two rollers 30, to increase the density of the polymer active layer.

[0074] Before pressing, the polymerized active layer 28 has a density equal to 1.67 g / cm 3 , and after pressing at room temperature with two rollers at a pressure of 0.5 tons / cm, the polymerized active layer 28 has a density equal to 2.63 g / cm 3 .

[0075] During the cutting step 112, the metallic foil 24 and the polymerized active layer 28 are cut to obtain the cathode 30.

[0076] Other non-limiting examples of electron beam-curable prepolymers are aliphatic polyurethane acrylates (Genomer 4212, Rahn®) and acrylates (DSM, Agisyn®).

[0077] Example 2

[0078] Example 2 was prepared using the same method as for the preparation of Example 1.

[0079] The active material was LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, the conductive material was acetylene black, and the electron beam-curable prepolymer was a mixture of methacrylates and lithium bis(trifluoromethylsulfonyl)imide methacrylate (LiMTFSI).

[0080] The content of the active material was 90 mass%, the content of the conductive material was 3 mass%, and the content of the prepolymer was 7 mass%. The content of LiMTFSI in the prepolymer was 10 mass%.

[0081] Example 3

[0082] Example 3 was similar to Example 2, except that the content of LiMTFSI in the prepolymer was 15 mass%.

[0083] Example 4

[0084] Example 4 was similar to Example 2, except that the content of LiMTFSI in the prepolymer was 20 mass%.

[0085] IV resistance

[0086] The IV resistance (internal resistance) of the battery cell including the cathode 30 was measured using a test cell.

[0087] In the test cell, the anode was made of 98.8% by mass of graphite (as an active material), 0.7% by mass of styrene-butadiene rubber, and 0.5% by mass of carboxymethyl cellulose (as a binder).

[0088] In the test cell, the separator was a polyethylene film type and the electrolyte was EC: DMC (1:1 by volume), and 1 mol / L (moles per liter) of LiPF6.

[0089] The measurement of the IV resistance is as follows. A charging device for battery cells is used, for example TOSCAT-3300 K (TOYO System Co). The temperature is set to 25°C and the state of charge (SOC) of the battery cell is set to 60%.

[0090] The charging / discharging of the cell is as follows:

[0091] - discharging at 0.33 C for 10 s and charging at 0.33 C for 10 s;

[0092] - discharging at 1 C for 10 s and charging at 0.33 C for 30 s;

[0093] - discharging at 3 C for 10 s and charging at 0.33 C for 90 s;

[0094] - discharging at 5 C for 10 s and charging at 0.33 C for 150 s;

[0095] - discharging at 8 C for 10 s and charging at 0.33 C for 240 s.

[0096] Between each discharging / charging cycle, there is a 10 minute rest before the next step.

[0097] The voltage drop during each discharge is measured and the average IV resistance can be calculated from the voltage drop.

[0098] For examples 1 to 4, the IV resistance is given in table 1 below.

[0099] Table 1

[0100]

[0101] As can be seen from table 1, for the methyl methacrylate alone or for mixtures of LiMTFSI with methyl methacrylate up to 20 mass% of the prepolymer, the internal resistance is reduced to 3.82 The lower the IV resistance, the better the cathode 30.

[0102] Throughout the specification, unless otherwise specified, the term "comprising" is to be understood as synonymous with "including" or "comprising at least". Furthermore, any ranges presented in the specification, including the claims, are to be understood as including the end values, unless otherwise specified. The specific values of the recited elements are to be understood as within acceptable manufacturing or industry tolerances known to those skilled in the art, and any use of the terms "substantially" and / or "approximately" and / or "generally" is to be understood as falling within such acceptable tolerances.

[0103] If any of the standards of national, international or other standard bodies (such as ISO, etc.) are cited, such citation is intended to refer to the standard defined by the national or international standard body at the priority date of the present specification. Any subsequent substantial change to these standards is not intended to alter the scope and / or definition of the present disclosure and / or claims.

[0104] While the present disclosure has been described herein with reference to particular embodiments thereof, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

[0105] The specification and examples are intended to be exemplary only, with the true scope of the present disclosure being indicated by the following claims.

Claims

1. A method (100) for manufacturing a cathode (30) for a secondary battery, the method comprising: - The active material and the conductive material are mixed with an electron beam curable prepolymer (102) to obtain a solvent-free mixture (20) made of the active material, the conductive material and the prepolymer. - Pass the solvent-free mixture (20) between the first roller (14) and the second roller (16) (104) to apply a layer (22) of the solvent-free mixture (20) on the second roller (16). - Pass the layer (22) of the solventless mixture (20) between the second roller (16) and the third roller (18) carrying the metallic foil (24) (106) to transfer the layer (22) of the solventless mixture (20) onto the metallic foil (24); - The prepolymer is polymerized (108) with an electron beam (26) to obtain an active layer (28) polymerized on a metallic foil (24). - The polymerized active layer (28) is pressed (110) on a metallic foil (24) at room temperature to increase the density of the polymer active layer (28); - Cut (112) the metallic foil (24) to obtain the cathode (30). The prepolymers mentioned above include methacrylates and lithium-ionized monomers with acrylate functionality. The lithium monomer having acrylate functionality is lithium bis(trifluoromethanesulfonyl)imide methacrylate.

2. The method (100) according to claim 1, wherein the total content of active materials in the solvent-free mixture (20) is equal to or greater than 80% by mass.

3. The method (100) according to claim 1, wherein the total content of active materials in the solvent-free mixture (20) is equal to or greater than 85% by mass.

4. The method (100) according to claim 1, wherein the total content of active materials in the solvent-free mixture (20) is equal to or greater than 90% by mass.

5. The method (100) according to claim 1, wherein the content of lithium bis(trifluoromethanesulfonyl)imide methacrylate in the prepolymer is equal to or less than 20% by mass.

6. A composition for preparing a cathode (30) for a secondary battery, said composition comprising an active material, a conductive material, and an electron beam-curable prepolymer, said composition being solvent-free. The prepolymer comprises methacrylates and lithium monomers having acrylate functionality, wherein the lithium monomer having acrylate functionality is lithium bis(trifluoromethanesulfonyl)imide methacrylate.

7. The composition according to claim 6, wherein the total content of the active material in the solvent-free mixture is equal to or greater than 80% by mass.

8. The composition according to claim 6, wherein the total content of the active material in the solvent-free mixture is equal to or greater than 85% by mass.

9. The composition according to claim 6, wherein the total content of the active material in the solvent-free mixture is equal to or greater than 90% by mass.

10. The composition according to claim 6, wherein the content of lithium bis(trifluoromethanesulfonyl)imide in the prepolymer is equal to or less than 20% by mass.

11. The composition according to claim 6, wherein the conductive material is carbon.

12. A cathode (30) for use in a secondary battery, which is made from the composition according to claim 6 by means of any one of claims 1 to 5.

13. A secondary battery, comprising the cathode according to claim 12.

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