Solvent-free electrode manufacturing method and electrode
Patent Information
- Application Number
- JP2024509358
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2021-08-19
- Filing Date
- 2022-08-17
- Publication Date
- 2025-06-09
AI Technical Summary
Existing methods for producing battery electrodes require high energy inputs and use binders like PTFE or PVDF, which are electrochemically unstable for anodes, leading to irreversible deterioration reactions and reduced mechanical stability.
A dry powder mixture using a polyamide binder, such as sericin, is applied under mechanical forces to form fibrils, enabling high mechanical stability and specific capacity without irreversible reactions.
The method produces electrodes with high mechanical stability and specific capacity, ensuring stable operation as anodes in lithium-ion batteries without undesirable deterioration.
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Abstract
Description
[Technical field]
[0001] A method for producing an electrode without solvent is provided, which allows the production of an electrode having high mechanical stability and offering a high specific capacity. Moreover, this method allows the production of an electrode that can be used as an anode in lithium-ion batteries without unstable operation accompanied by undesirable irreversible degradation reactions. Furthermore, an electrode having the above-mentioned advantages is provided. Furthermore, a use of the electrode according to the invention is proposed. [Background technology]
[0002] In the production of battery electrodes, layers 50-100 μm thick must be applied at high orbital speeds to metal current collectors. This is routinely done by wet-chemical roll-to-roll coating from a suspension of active material in aqueous or organic solvents. In the prior art, CMC / SBR or PVDF are often used as anode binders in such wet-chemical, i.e. solvent-based, methods. Numerous alternatives have been described in scientific publications, including polyamides such as the polypeptide sericin. However, wet-chemical methods have the disadvantage that for the production of electrodes (e.g. anodes), high energy inputs are required both for the dispersion of the material (e.g. active material) and for the drying of the produced battery electrode layers.
[0003] The production of electrode layers by solvent-free, i.e. dry manufacturing methods, constitutes an energetic advantage. For this purpose, a dry powder mixture formed from active material, conductive additives and a suitable binder must be converted into a mechanically loadable layer. In these conventional methods, polytetrafluoroethylene (PTFE) is usually used as a binder, since it is known to form fibrils under the action of shear forces (see, for example, WO 2018 / 210723 A1). However, a disadvantage of PTFE as a binder for electrode materials in dry chemical methods is that in the case of lithium-ion batteries, PTFE may only be used as a binder for the cathode. The reason for this is that PTFE as a binder for anodes with an anode potential close to 0 V (Li / Li+) is electrochemically unstable and causes undesirable irreversible degradation reactions during operation.
[0004] As an alternative to the use of PTFE for the manufacture of electrode layers in dry chemical processes, the use of PVDF and polyolefins is known (see, for example, US 7 883 553 B2). However, the disadvantage of using these binders is that in order to ensure sufficient mechanical stability of the manufactured electrode layers, the proportion of binder must be high, at the expense of the achievable capacity of the electrode. Also, processability is much more difficult in the case of these binders.
[0005] In the production of electrodes by dry processes which are advantageous from an energy point of view, the prior art has not disclosed binders for anodes which can be used in low proportions in order to ensure, on the one hand, high mechanical stability of the produced anodes and, on the other hand, to enable high capacities of the produced anodes. Summary of the Invention [Problem to be solved by the invention]
[0006] On this basis, the object of the present invention is to provide a method for producing an electrode without solvent and, moreover, to provide an electrode which overcomes the drawbacks known in the prior art, in particular, it is possible to provide an electrode which has high mechanical stability, offers a high specific capacity and allows a stable operation without undesirable or irreversible degradation reactions when used as an anode in a lithium-ion battery. [Means for solving the problem]
[0007] This object is achieved by a method having the features of claim 1, an electrode having the features of claim 12 and a use having the features of claim 15. The dependent claims present advantageous embodiments.
[0008] According to the present invention there is provided a method for producing an electrode in a solvent-free manner, said method comprising or consisting of the following steps: a) providing a dry powder mixture for producing an electrode, said mixture comprising or consisting of: At least one active material for an electrode; At least one conductive additive, and at least one binder; and b) applying a mechanical force to the powder mixture such that a dry film is formed from the dry powder mixture; At least one binder is characterized in that it comprises or consists of a polyamide suitable for forming fibrils under the action of a mechanical force.
[0009] The term "dry powder mixture" means a powder mixture that does not contain a solvent (e.g., does not contain water). The term "polyamide" is understood to mean a molecule with repeating peptide bonds (-CO-NH bonds), i.e., the term is understood to include a polypeptide or a protein.
[0010] At least one binder of the dry powder mixture provided in step a) may already be present partially fibrillated. For example, the dry powder mixture may be mechanically sheared during its provision, so that fibrils are partially generated from the at least one binder. This powder mixture may then be used in step b) for the formation of a dry film (optionally after a new grinding), where due to the mechanical forces acting, further fibrils are generated from the binder.
[0011] The mechanical forces acting on the dry powder mixture in the present method in particular comprise or consist of compressive and shear forces.
[0012] It was found that this dry chemical method allows the production of electrodes characterized by high mechanical stability, even with a very low proportion of binder in the dry powder mixture. The option of using a low proportion of binder allows the resulting battery electrode layer to have a high specific capacity. Furthermore, electrodes produced by this dry chemical method using polyamide-based binders have the advantage, compared to electrodes produced using PTFE-based binders, of a stable operation without undesirable irreversible degradation reactions when used as negative electrodes in lithium-ion batteries.
[0013] The method of the invention is characterized in that the polyamide comprises or consists of a polypeptide, which is preferably a polypeptide suitable for forming a β-sheet secondary structure under the action of a mechanical force. Whether a polypeptide is suitable for forming fibrils under the action of a mechanical force may depend on whether it is suitable for forming a β-sheet secondary structure under the action of a mechanical force. The polypeptide is preferably a silk polypeptide (particularly a silk protein), and it is particularly preferred that the silk polypeptide (particularly a silk protein) is selected from the group consisting of sericin, fibroin, spider silk polypeptide (particularly a spider silk protein) and combinations thereof. In particular, the silk polypeptide (or silk protein) is sericin, preferably non-hydrolyzed sericin. The advantage of non-hydrolyzed sericin is that the molecular chain length (i.e. molecular weight) of the polypeptide is longer than in the case of hydrolyzed sericin, whereby fibril formation is possible in the first place or, in the method of the invention, longer fibrils are produced, which increases the mechanical stability of the produced electrode.
[0014] Upon application of a mechanical force to the powder mixture of step b), the at least one binder of the dry powder mixture preferably at least partially forms fibrils, the formed fibrils increasing the mechanical stability of the produced electrode layer.
[0015] The at least one binder of the dry powder mixture may be present in the dry powder mixture in a concentration of 0.1% to 10% by weight, preferably 1% to 5% by weight, based on the total weight of the powder mixture. The lower the concentration (or percentage) of binder in the dry powder mixture, and the correspondingly higher the relative percentage of active material, the higher the specific capacity of the electrode provided by this method.
[0016] At least one active material of the dry powder mixture may be an anode active material, preferably an active material selected from the group consisting of carbon, silicon, combinations thereof, and composites thereof, with carbon being particularly selected from the group consisting of graphite, non-graphitized carbon, and combinations thereof.
[0017] Alternatively, at least one active material of the dry powder mixture is a cathode active material, preferably LiCoO2, LiNiO2, LiFePO4, LiMnO2, LiMn2O4, Li2Mn3NiO8, Li4Ti5O 12 , Li2FeSiO4, Na2S, Na3V2(PO4) 3、 NaFePO4, Na2FePO4F, NaNiMnO2, Na2TiO7, NaTi2(PO4)3, LiNi 1-x Co x O2 (wherein x ranges from 0 to 1), LiNi x Co y Mn z O2 (in the formula, x+y+z=1), LiNi x Co y Al z O2 (wherein x+y+z=1), Na x MnO2, where x is in the range of 0.5 to 1, and combinations thereof.
[0018] The at least one active material of the dry powder mixture can be present in the dry powder mixture in a concentration, in percent relative to the total weight of the powder mixture, of 60% to 99% by weight, preferably 76% to 97% by weight, particularly preferably 86% to 96% by weight, very particularly preferably 91% to 95% by weight, in particular 92% to 94% by weight. The higher the concentration (or proportion) of the active material in the dry powder mixture, the higher the achievable specific capacity of the electrode provided by this method.
[0019] At least one conductive additive of the dry powder mixture can be present in the dry powder mixture in a concentration in percent relative to the total weight of the powder mixture of 1% to 35% by weight, preferably 1% to 20% by weight, particularly preferably 1.5% to 10% by weight, very particularly preferably 2% to 5% by weight, in particular 2% to 4% by weight. The lower the concentration (or proportion) of the conductive additive in the dry powder mixture, the higher the proportion of active material and the greater the achievable specific capacity of the electrode that can be produced by this method. The concentration range is 2% to 4% by weight. The percentage in this case represents the optimum value of the electrical conductivity on the one hand and the achievable capacity on the other hand.
[0020] At least one conductive additive of the dry powder mixture comprises or consists of carbon, preferably selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, carbon fibers, graphene, and combinations thereof.
[0021] The dry powder mixture is preferably free of at least one material selected from the group consisting of PTFE, PVDF, carboxymethylcellulose, styrene-butadiene rubber and polyolefins.
[0022] A preferred embodiment of the method is characterized in that step b) of the method comprises or consists of applying the dry powder mixture to a calendar nip, which is formed by a first rotating roller and a second rotating roller, the second rotating roller having a higher rotation speed than the first roller. A dry film is then formed in the calendar nip. The resulting dry film is conveyed onto the first rotating roller. The ratio of the rotation speed of the second rotating roller to the first rotating roller is in the range of 10:1 to 2:1 (optionally in the range of 9:1 to 3:1). The diameters of the rollers may be the same. It is important that the rotation speeds of the two rollers, i.e. the rotation speeds of the respective surfaces of the two rollers in the calendar nip, are different.
[0023] The distance from the first rotating roller to the second rotating roller can be set so that the calendar nip has a width in the range of 10 μm to 200 μm, preferably in the range of 20 μm to 100 μm, particularly preferably in the range of 40 μm to 60 μm.
[0024] In a preferred embodiment of the method, step b) comprises disposing the dry-film on a flat electrical conductor (e.g., a metal foil), which forms a stack of electrodes on the flat electrical conductor.
[0025] According to the invention there is also provided an electrode comprising: a) a dry film comprising or consisting of at least one active material for an electrode, at least one conductive additive, and at least one binder; and b) optionally, a flat electrical conductor onto which the dry-film is disposed; or consisting of At least one binder is characterized in that it comprises or consists of a polyamide which is present in the dry film at least partially in the form of fibrils.
[0026] The electrode according to the invention has high mechanical stability and is suitable for providing a high specific capacity due to the low proportion of binder, and when used as the anode of a lithium-ion battery, it allows a stable operation without undesirable irreversible degradation reactions.
[0027] The fibrils in the electrode can have diameters in the range of >0 nm to <1 μm as measured by scanning electron microscopy. The advantage of this small diameter is that the fibrils expose a large surface area relative to their volume, allowing for a high binding effect for active materials or conductive additives and increasing mechanical stability.
[0028] In a preferred embodiment, the electrode has been produced by the method of the present invention. Thus, the electrode of the present invention may have features which arise necessarily due to the implementation of the method of the present invention.
[0029] Finally, it is proposed to use the electrode of the invention in a lithium ion battery, preferably as the anode of a lithium ion battery.
[0030] The objects of the present invention will be described in detail below with reference to the following figures and examples, without being limited to the embodiments of the present invention. [Brief description of the drawings]
[0031] [Figure 1] An example of the method of the present invention is shown diagrammatically. To produce an electrode layer (dry film) 1, a dry powder mixture 2 is introduced into the calendar nip 3 between a first roller 4 and a second roller 5. The first roller rotates at a first rotation speed v1, and the second roller rotates at a second rotation speed v2, which is faster than the first rotation speed v1. Due to the short distance between the two rollers 4,5 and the different rotation speeds v1,v2, pressing and shear forces are applied to the dry powder mixture, forming a dry film 1 with binder fibrils. After passing through the calendar nip 3, the dry film 1 is guided over the first roller 4, which can then be applied to a flat conductor (e.g., a metal film). [Diagram 2] Electron microscopy images of the electrode layer produced by the method of the invention are shown, in which it is clear that the polyamide forms fibrils with diameters in the submicron range in the binder (polypeptide sericin) due to the action of mechanical forces during the method. The formed fibrils increase the mechanical stability of the electrode layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Example 1 - An embodiment of the method of the present invention The polypeptide sericin is added to the mixture of active material and conductive additive to form a dry mixture. The proportion of sericin in this dry mixture is 3% by weight, in this case, relative to the total weight of the composition. The dry mixture is ground in an XV mill to form a dry powder mixture 2.
[0033] A mechanical force is applied to the dry powder mixture 2 to introduce the dry powder mixture 2 into a calender nip 3 consisting of a first roller 4 and a second roller 5 to form a dry film. The first roller 4 rotates at a first rotation speed v1, and the second roller 5 rotates at a second rotation speed v2 that is faster than the first rotation speed v1. In this case, the rotation speed v 2: The ratio of v1 was 2:1. Thus, the dry powder mixture 2 was pressed and oriented to form a dry film 1, and the dry film 1 was transported onto a first roller 4. The dry film 1 thus formed is an electrode.
[0034] The dry-film 1 can then be transferred from the first roller 4 to a flat conductor (e.g., a metal foil) (not shown in FIG. 1) to form a laminate, resulting in a dry-film (electrode film) adhered to the flat conductor.
[0035] When this laminate was used in a lithium-ion battery cell, it was confirmed that the dry film (electrode film) not only had excellent mechanical stability but also had a high specific capacity due to the low binder content.When this laminate was used as the anode of a lithium-ion battery cell, it was found that stable operation of the battery cell was possible using such an anode and that there were no undesirable or irreversible degradation reactions during the operation of such a battery.
[0036] Example 2 - Evidence of fibrils in electrodes according to the invention An image of the electrode prepared in Example 1 was taken with an electron microscope (see FIG. 2).
[0037] This image shows that fibrils were formed in the electrode. The polypeptide sericin used as a binder in the dry powder mixture alone appears to be the source of fibril formation. The formed fibrils are responsible for the high mechanical stability of the electrode layer. [Explanation of symbols]
[0038] List of reference symbols 1: electrode layer (or dry film); 2: Dry powder mixture; 3: calendar nip between the first roller and the second roller; 4: First roller; 5: second roller; v 1: The rotation speed of the first roller (v1 <v2); v 2:: The rotational speed of the second roller (v2>v1).
Claims
1. A method for manufacturing an electrode without a solvent, comprising: a) providing a dry powder mixture for manufacturing the electrode, said mixture comprising: at least one active material for the electrode, at least one conductive additive, and at least one binder; and b) applying mechanical force to said powder mixture to form a dry film from said dry powder mixture, characterized in that said at least one binder comprises a polyamide suitable for forming fibrils under the action of mechanical force.
2. The method according to claim 1, characterized in that said polyamide comprises a polypeptide.
3. The at least one binder of said dry powder mixture: i) forms fibrils at least partially by the action of said mechanical force on said powder mixture in step b), and / or ii) is present in said dry powder mixture in a concentration of 0.1% to 10% by weight based on the total weight of said powder mixture, The method according to claim 1 or 2, characterized thereby.
4. The at least one active material of said dry powder mixture: i) is an active material of the anode, or ii) is an active material of the cathode, The method according to claim 1 or 2, characterized thereby.
5. The at least one active material of said dry powder mixture is present in said dry powder mixture in a concentration of 60% to 99% by weight based on the total weight of said powder mixture, The method according to claim 1 or 2, characterized thereby.
6. The at least one conductive additive of said dry powder mixture is present in said dry powder mixture in a concentration of 1% to 35% by weight based on the total weight of said powder mixture, The method according to claim 1 or 2, characterized thereby.
7. The at least one conductive additive of said dry powder mixture comprises carbon, The method according to claim 1 or 2, characterized thereby.
8. Said dry powder mixture does not contain at least one material selected from the group consisting of PTFE, PVDF, carboxymethyl cellulose, styrene-butadiene rubber and polyolefin, The method according to claim 1 or 2, characterized thereby.
9. The method according to claim 1 or 2, characterized in that step b) comprises applying the dry powder mixture to a calendar nip formed by a first rotating roller and a second rotating roller, the second rotating roller having a higher rotational speed than the first rotating roller, and the dry film being formed within the calendar nip.
10. The method according to claim 9, characterized in that the distance from the first rotating roller to the second rotating roller is set such that the calendar nip has a width in the range of 10 μm to 200 μm.
11. The method according to claim 1 or 2, characterized in that step b) comprises placing the dry film on a flat conductor.
12. A dry film comprising at least one active material for an electrode, at least one conductive additive, and at least one binder, An electrode, characterized in that the at least one binder comprises a polyamide present in the dry film at least partially in the form of fibrils.
13. The electrode according to claim 12, characterized in that the fibrils have a diameter in the range greater than 0 nm and less than 1 μm as measured by a scanning electron microscope.
14. A method of using the electrode according to claim 12 or 13 in a lithium-ion battery.