Method for producing a rechargeable battery, and rechargeable battery

Abstract

The invention relates to a method for producing a rechargeable battery (2), which has at least one lithium-ion cell (4) in which a first electrode is arranged (12) that has a first active material layer (22), and in which lithium-ion cell an electrolyte (10) is introduced, wherein to produce the first electrode (12) a first material strip (30) is produced from which the first electrode (12) is separated during a separating process, and wherein the first material strip (30) is produced by mixing in a first suspension that has a first active material, applying the first suspension onto a first metal film (18) to form the first active material layer (22) and forming a first polymer coating (26) as a first intermediate layer between the first active material and the electrolyte (10).

Description

[0001] Description

[0002] Method for producing an accumulator and accumulator

[0003] The invention relates to a method for producing a rechargeable battery. The invention also relates to a rechargeable battery.

[0004] Lithium-ion batteries are widely used as electrical energy storage devices. They are also used in the automotive sector, among other applications, and are primarily used as drive or traction batteries for powering hybrid or electric vehicles.

[0005] A lithium-ion battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. There are many different designs regarding their exact structure. However, what all of them have in common is that the lithium-ion battery contains free and therefore mobile lithium ions—that is, lithium ions that can freely migrate back and forth through the electrolyte between the negative and positive electrodes.

[0006] A possible process for producing a lithium-ion battery is outlined, for example, in “Heimes, Heiner Hans; Kampker, Achim; Lienemann, Christoph; Locke, Marc; Offermanns, Christian; Michaelis, Sarah; Rahimzei, Ehsan (2018): Production process of a lithium-ion battery cell, Frankfurt am Main, PEM of RWTH Aachen and VDMA Eigendruck”.

[0007] The invention is based on the object of providing an advantageous method for producing an accumulator and an advantageously designed accumulator.

[0008] This object is achieved by a method having the features of patent claim 1 and by a battery having the features of patent claim 10. The advantages and preferred embodiments cited with regard to the method are also transferable to the battery, and vice versa. Advantageous embodiments with expedient further developments of the invention are specified in the dependent patent claims.

[0009] The method according to the invention, described in more detail below, serves to produce a rechargeable battery according to the invention, which is designed as a lithium-ion rechargeable battery. Such a rechargeable battery comprises at least one lithium-ion cell. For a variety of applications, however, a corresponding rechargeable battery comprises several lithium-ion cells, with the lithium-ion cells typically being of similar design. In some cases, the rechargeable battery is then designed as a so-called drive or traction battery for powering a hybrid or electric vehicle.

[0010] A corresponding lithium-ion cell, also referred to as a cell for short, has a first electrode with a first active material layer. The lithium-ion cell also expediently has a second electrode and a separator. Furthermore, an electrolyte, in particular an electrolyte solution, is introduced into the lithium-ion cell.

[0011] To produce the first electrode and thus also to produce the accumulator, according to the invention, a first material strip is first produced, from which the first electrode is then separated during a separation process. The first material strip is produced by mixing a first suspension containing a first active material, by applying the first suspension to a first metal foil to form the first active material layer, and by forming a first polymer coating as a first intermediate layer between the first active material and the electrolyte.

[0012] This intermediate layer serves, at least in the finished cell or battery, as a so-called passivation layer. According to the prior art, a comparable passivation layer is formed from the electrolyte during a so-called formation process. At least in the case of the negative electrode, this is then also referred to as Solid Electrolyte Interphase (SEI). The intermediate layer, however, is formed according to the invention before the so-called formation process and in particular before the so-called cell assembly. The intermediate layer is preferably formed as a purely organic layer. In this case, it contains, in particular, no metallic component.

[0013] A further advantageous process variant is one in which a first monomer or monomer material is introduced into the first suspension to form the first polymer coating. This occurs in particular before the first suspension is applied to the first metal foil. According to another advantageous process variant, the first monomer is sprayed onto the active material layer to form the first polymer coating. This typically occurs after the first suspension is applied to the first metal foil.

[0014] In some applications, the first monomer is introduced into the first suspension to form the first polymer coating, which occurs in particular before the first suspension is applied to the first metal foil. Furthermore, the first monomer or another monomer is sprayed onto the active material layer to form the first polymer coating, which occurs in particular after the first suspension is applied to the first metal foil. If another monomer is sprayed on, the first polymer coating in its finished state typically comprises two different layers formed by different polymers.

[0015] If the formation of a first polymer coating is intended which, in the finished state, has two different layers, this is formed in a further alternative embodiment by spraying the first monomer onto the active material layer, which occurs in particular after the application of the first suspension to the first metal foil, and by subsequently spraying on the further monomer.

[0016] Regardless of which of the previously described process variants is used, styrene, an acrylate, or a sulfonate is preferably used as the first monomer. Styrene, an acrylate, or a sulfonate is also preferably used for the additional monomer, if another monomer is used.

[0017] If spraying as described above is intended, it is expedient to spray a solution in which the first monomer or the further monomer is dissolved in a solvent. This solvent is, for example, a fluorinated or non-protic solvent. Preferably, it is an electrolyte solvent, i.e., a solvent contained in the cell's electrolyte.

[0018] The electrolyte of the cell thus preferably contains at least one solvent, in particular an organic solvent. Examples of solvents used, in particular as electrolyte solvents, include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, acetonitrile, glutaronitrile, adiponitrile, pimelonitrile, gamma-butyrolactone, gamma-valerolactone, dimethoxyethane, 1,3-dioxalane, methyl acetate, and / or mixtures thereof.

[0019] In addition, the electrolyte expediently contains at least one lithium salt (also known as a "lithium conducting salt"). Examples of such lithium salts include LiAsF6, LiCIO4, LiSbF6, LiPtCl6, Li(CF3)SO3 (LiTf), LiC(SO2CF3)3, or a phosphate-based lithium salt, e.g., LiFePO4. B. LiPF6, LiPF3(CF3)3 (LiFAP), and LiPF4(C2O4) (LiTFOB) - a borate-based lithium salt - e.g. LiBF4, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiDFOB), LiB(C2O4)(C3O4) (LiMOB), Li(C2F5BF3) (LiFAB), and Li2B12Fi2 (LiDFB),L - and / or a lithium salt of sulfonylimides - e.g. LiN(SO2CF3)2 (LiTFSI) and UN(SO2C2F5)2 (LiBETI) - are used. A particularly preferred lithium conducting salt is LiPF6 (lithium hexafluorophosphate) or mixtures thereof.

[0020] As already explained above, the first suspension is applied to the first metal foil to form the first active material layer. This then produces a first coated metal foil. If the first electrode is to serve as the negative electrode in the finished cell or accumulator, graphite or silicon, for example, is used as the active material for the active material layer. If the first electrode is to serve as the positive electrode in the finished cell or accumulator, an NMC (lithium nickel manganese cobalt oxide), LFP (lithium iron phosphate), or NCA (lithium nickel cobalt aluminum oxide) is used as the active material for the active material layer. Alternatively, so-called next-generation electrode materials, in particular next-generation cathode materials, or high-voltage spinels such as LNMO (lithium nickel manganese oxide) are used.

[0021] Independently of this, the first suspension is then applied to the first metal foil to form the first active material layer, producing the first coated metal foil. Preferably, a voltage is then further applied to the first coated metal foil to form the first polymer coating. This applies in particular if the first monomer and / or another monomer is sprayed onto the active material layer to form the first polymer coating. The applied voltage then increases the diffusion / migration of the monomer to or onto the surface of the active material layer.

[0022] Further preferably, dry room conditions are specified for the formation of the first polymer coating. Typically, a relative humidity of less than or equal to 10% is specified, and in particular, a relative humidity of less than or equal to 10% is specified. The use of a protective gas is preferably avoided. Furthermore, no special pressure conditions are preferably specified. This means that the prevailing pressure is in the range of normal pressure.

[0023] Independently of this, polymerization is induced to form the first polymer coating. Depending on the application, this occurs, for example, by spraying a radical initiator such as a peroxodisulfate, a benzyl peroxide, or an azobisisobutyronitrile. Alternatively or additionally, a heat treatment is performed.

[0024] According to the method described above, to produce the first electrode and thus also to produce the accumulator, the first material strip is first produced, from which the first electrode is then cut out during the cutting process. Such a material strip, from which electrodes are cut out during a cutting process, is also referred to as an “electrode coil.” Essentially, this is a coated film that is typically held in wound form. Previously, only a one-sided coating for the first material strip was described. Depending on the application, however, the method according to the invention can produce a first material strip that is coated on two sides, i.e., on an upper side and on an underside. The coatings on the upper side and the underside are preferably of the same type.

[0025] As previously mentioned, a lithium-ion cell typically has a second electrode in addition to the first electrode. Depending on whether the first electrode serves as the negative electrode or the positive electrode in the finished cell, the second electrode then serves as the positive electrode or the negative electrode, respectively.

[0026] A further typical variant of the method is then that for producing the accumulator, the second electrode is produced by producing a second material strip from which the second electrode is separated during a separation process. In this case, the second material strip is preferably produced by mixing a second suspension comprising a second active material, by applying the second suspension to a second metal foil to form the second active material layer, and by forming a second polymer coating as a second intermediate layer between the second active material and the electrolyte. In this case, the second material strip is preferably produced in a manner as previously described for the first material strip.

[0027] The advantages and further developments described above in connection with the method according to the invention can also be transferred analogously to the accumulator according to the invention described above and vice versa.

[0028] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the schematic drawings, in which:

[0029] Fig. 1 is a simplified representation of an accumulator with several lithium-ion cells,

[0030] Fig. 2 is a simplified sectional view of one of the lithium-ion cells of the accumulator, and

[0031] Fig. 3 is a simplified representation of a plant for producing the accumulator.

[0032] Corresponding parts are provided with the same reference numerals in all figures.

[0033] A method described below as an example serves to manufacture a rechargeable battery 2, which is designed as a lithium-ion rechargeable battery 2. In many applications, such a rechargeable battery 2 comprises several uniformly designed lithium-ion cells 4, or cells 4 for short. The corresponding cells 4 are then typically interconnected in the rechargeable battery 2 via a connection device 6 in a manner not shown in detail. This is indicated in Fig. 1.

[0034] In any case, such a rechargeable battery 2 comprises at least one cell 4, and a possible embodiment of such a cell 4 is shown in Fig. 2 in a simplified sectional view. It comprises a cell housing 8 filled with an electrolyte 10, more precisely an electrolyte solution 10. A first electrode 12 and a second electrode 14 are arranged in the electrolyte solution 10. The electrodes 12, 14 are separated by a separator 16.

[0035] According to Fig. 2, both electrodes 12, 14 have in common a structure with a metal foil 18, 20, an active material layer 22, 24 and a polymer coating 26, 28. The polymer coatings 26, 28 serve as a so-called passivation layer, at least in the finished cell 4 or in the finished accumulator 2.

[0036] The two electrodes 12, 14 are manufactured in an analogous manner in the exemplary embodiment, with different materials typically being used for the electrodes 12, 14. The manufacture of the first electrode 12, which has a first metal foil 18, a first active material layer 22, and a first polymer coating 26, is described below as an example. The manufacture of the second electrode 14, which has a second metal foil 20, a second active material layer 24, and a first polymer coating 28, can then be derived from this.

[0037] To produce the first electrode 12 and thus also to produce the accumulator 2, a first material strip 30 is first produced. This is indicated in Fig. 3. The first electrode 12 is then cut out of the first material strip 30 in a cutting process (not shown).

[0038] Such a separation process is also called singulation and is described, for example, in “Heimes, Heiner Hans; Kampker, Achim; Lienemann, Christoph; Locke, Marc; Offermanns, Christian; Michaelis, Sarah; Rahimzei, Ehsan (2018): Production process of a lithium-ion battery cell, Frankfurt am Main, PEM of RWTH Aachen and VDMA Eigendruck”.

[0039] To produce the first material strip 30, a first suspension comprising a first active material is first mixed. The first suspension is then applied to the first metal foil 18 to form the first active material layer 22. This step is indicated in Fig. 3 by an application unit 32. After application, drying takes place by means of a drying unit 34 as shown in Fig. 3. Subsequently, a first solution containing a first monomer is sprayed on. This step is indicated in Fig. 3 by a first spray head 36. Next, a radical initiator is sprayed on using a second spray head 38, and finally, a heat treatment is carried out using a heating unit 40.

[0040] In the exemplary embodiment, the polymerization of the first monomer is stimulated by the radical initiator and the heat treatment. In an alternative embodiment, the polymerization is induced solely by spraying a radical initiator or solely by heat treatment. According to Fig. 3, a voltage is also applied to the first metal foil 32 by means of a voltage unit 42. The applied voltage then increases the diffusion / migration of the first monomer on the surface of the first active material layer 22. In an alternative embodiment, the specification of a voltage is omitted.

[0041] According to a further alternative embodiment, the use of several monomers is provided, which are sprayed in one or more solutions in one or more spraying processes.

[0042] According to a further alternative embodiment, drying by means of the drying unit 34 is omitted.

[0043] Using the previously described process, an artificial passivation layer in the form of a polymer coating is now formed. The additional steps required for this are integrated, as shown in Fig. 3, into an existing roll-to-roll processing process, namely the "coating" process described in "Heimes, Heiner Hans; Kampker, Achim; Lienemann, Christoph; Locke, Marc; Offermanns, Christian; Michaelis, Sarah; Rahimzei, Ehsan (2018): Production process of a lithium-ion battery cell, Frankfurt am Main, PEM of RWTH Aachen University and VDMA Eigendruck."

[0044] In an alternative embodiment, the polymer coating is formed in an additional roll-to-roll processing process. This additional roll-to-roll processing process is then preferably carried out after a drying process or a calendering process.

[0045] List of reference symbols

[0046] accumulator

[0047] Lithium-ion cell

[0048] interconnection device

[0049] Cell housing

[0050] Electrolyte first electrode second electrode

[0051] Separator first metal foil first metal foil first active material layer second active material layer first polymer coating second polymer coating first material band

[0052] Application unit

[0053] Drying unit first spray head second spray head

[0054] Heating unit

[0055] voltage unit

Claims

Patent claims Method for producing an accumulator (2) which has at least one lithium-ion cell (4) in which a first electrode (12) is arranged, which has a first active material layer (22), and in which an electrolyte (10) is introduced, wherein for producing the first electrode (12) a first material strip (30) is produced, from which the first electrode (12) is cut out in the course of a cutting process, and wherein the first material strip (30) is produced by - a first suspension is mixed which comprises a first active material, - the first suspension is applied to a first metal foil (18) to form the first active material layer (22) and - a first polymer coating (26) is formed as a first intermediate layer between the first active material and the electrolyte (10). The method according to claim 1, wherein the first polymer coating (26) is formed as a purely organic coating. The method according to claim 1 or 2, wherein a first monomer is introduced into the suspension to form the first polymer coating (26). The method according to one of claims 1 to 3, wherein a first monomer is sprayed onto the first active material layer (22) to form the first polymer coating (26). The method according to claim 4, wherein a solution comprising the first monomer and an electrolyte solvent is sprayed onto the first active material layer (26) to form the first polymer coating (26). The method according to claim 4 or 5, wherein the first suspension is applied to the first metal foil (18) to form the first active material layer (26), thereby producing a first coated metal foil, and wherein a voltage is applied to the first coated metal foil to form the first polymer coating (26). The method according to any one of claims 1 to 6, wherein dry room conditions are specified for the formation of the first polymer coating (26). The method according to claim 7, wherein a relative humidity of less than or equal to 10% is specified for the formation of the first polymer coating (26).Method according to one of claims 1 to 8, wherein to produce the accumulator (2) a second electrode (14) is produced which is arranged in the at least one lithium-ion cell (4), wherein to produce the second electrode (14) a second material strip is produced, from which the second electrode (14) is cut out in the course of a cutting process, and wherein the second material strip is produced in that. - a second suspension is mixed which comprises a second active material, - the second suspension is applied to a second metal foil (20) to form the second active material layer (24) and - a second polymer coating (28) is formed as a second intermediate layer between the second active material and the electrolyte (10). The accumulator (2) is produced by a method according to one of the preceding claims.

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