JP2014505341A - Electrode manufacturing method - Google Patents

Abstract

  A method for manufacturing an electrode of an electrochemical cell having a metal substrate, particularly a negative electrode, the method comprising: treating the metal substrate by ultraviolet irradiation; and using the organic acid to treat the metal substrate. Processing steps.

Description

  The entire contents of the priority application DE 10 2011 011 154.9 are hereby incorporated by reference.

  The present invention relates to a method for producing an electrode of an electrochemical cell, in particular a negative electrode. The electrochemical cell is preferably available for driving an electric motor, preferably a vehicle with a hybrid drive, and / or in a “plug-in” mode.

  Electrochemical cells, especially lithium secondary batteries, are used as energy storage devices in mobile information devices such as mobile phones, tools, or vehicles with electric and hybrid drives due to their high energy density and large capacity. . In these various areas of use of electrochemical cells, in particular cells used to drive automobiles, electrochemical cells must meet high demands. That is, the largest possible capacitance and energy density that is stable over a number of charge / discharge cycles at the smallest possible weight.

  The lifetime of an electrochemical cell often depends on the aging of the electrodes, in particular the aging of the negative electrode. In an aging process, an electrochemical cell loses its capacity and power. This process is performed on a more or less large scale in most conventional electrochemical cells and depends greatly on the usage conditions (temperature, storage conditions, state of charge, etc.), but the quality of the material and the manufacturing process of the electrochemical cell Depends on the processing inside. Therefore, when an extremely pure material is processed with high quality, an electrochemical cell having a very long life can be obtained. The electrochemical cell hardly degrades over a relatively long period of time and only slightly loses capacity and power.

  Since the physical or chemical limits are often set for the purity of the materials used, eg based on the synthesis process, the battery manufacturer's preferential goal is as described in US Pat. By optimizing the electrode manufacturing method, it is always to obtain an electrochemical cell of higher quality and thus longer life.

  In particular, the adhesion of the electrochemically active material to the surface of the metal substrate contributes decisively to the quality of the electrochemical cell. It is known from the prior art that the adhesion of the electrochemically active material to the metal substrate surface is decisively improved by corona treatment, ie etching of the metal substrate surface with chromium sulfate. A major drawback of this method is that the use of chromium sulfate, which is highly toxic to the human body and the environment and is highly toxic for further processing in electrochemical cells, is an unacceptable contamination.

European Patent Application Publication No. 20000692

  Accordingly, in light of the prior art, the object of the present invention is to provide an optimized method for producing electrodes, in particular negative electrodes, of long-life electrochemical cells.

  According to the invention, this problem is solved by the teachings of the independent claims. Preferred further configurations of the invention are the subject of the subclaims.

  In order to solve this problem, as will be described in detail below, there is provided a method for producing an electrode of an electrochemical cell, in particular a negative electrode, which depends on ultraviolet irradiation and the use of organic acids. Has processing of metal substrate.

  The advantage of the method according to the present invention is that it allows an environmentally friendly and reliable cleaning of the metal substrate, thereby improving the adhesion of the electrochemically active material to the surface of the metal substrate, in particular, reducing the lifetime of the electrochemical cell. To be long.

  An “electrochemical cell” is understood to be any kind of device for the electrical storage of energy. This concept defines in particular primary or secondary type electrochemical cells, but also defines other forms of energy storage devices such as capacitors. Preferably, in the present invention, an electrochemical cell is understood to be a lithium ion cell.

  The concept of “negative electrode” means that the electrode emits electrons when connected to a load such as an electric motor (Verbraucher). Therefore, the negative electrode here is the anode. Correspondingly, the concept of “positive electrode” means that the electrode accepts electrons when connected to a load such as an electric motor. Therefore, the positive electrode here is the cathode.

  The electrode manufactured by the method according to the present invention, that is, the positive electrode and / or the negative electrode has at least one metal substrate and at least one electrochemically active material.

  The concept of “electrochemically active material” is understood to be a material suitable for the storage and release of ions, in particular cations, preferably lithium ions.

  In one embodiment, the electrochemically active material is a cathode active material.

  In a preferred embodiment, the electrochemically active material is an anode active material. The anode active material preferably contains carbon.

  In one embodiment, the electrode produced by the method according to the invention has at least one further additive in addition to the metallic substrate and the electrochemically active material, which preferably increases the conductivity. Additives, such as carbon-based additives such as carbon black, and / or redox activity that reduces, preferably minimizes and preferably prevents electrochemical active material destruction during overcharge of electrochemical cells Additive.

  The concept of “metal substrate” preferably relates to the members known as “electrode carrier” and “collector” of an electrochemical cell. In the present invention, the metal substrate is suitable for the application of the active material, and generally has metallic properties, preferably completely metallic properties.

  Preferably, the metallic substrate is at least partly configured as a foil, as a network or as a web, and preferably comprises copper or an alloy containing copper.

  The method according to the invention preferably comprises treating the surface of a metal substrate, in particular a metal substrate, with an organic acid, in particular at least partly, for applying an electrochemically active material at time intervals. Washing, preferably washing thoroughly.

  The concept of “time interval” is the start or end of treatment, particularly at least partial cleaning of a metal substrate, in particular treatment with an organic acid on the surface of the metal substrate, and a metal substrate treated with an electrochemically active material. It is understood that there is a time difference dt> 0 between the start of application to The treatment, in particular at least partial cleaning of the metal substrate with an organic acid, is performed prior to application of the electrochemically active material to the treated metal substrate. The time difference dt between the treatment, in particular the at least partial cleaning of the metal substrate with an organic acid and the application of the electrochemically active material to the treated, in particular at least partially cleaned collector, is preferably dt = up to 3 hours, preferably up to 2 hours, preferably up to 1 hour.

  In a preferred embodiment, treatment, in particular at least partial cleaning of the metal substrate, in particular treatment with an organic acid on the surface of the metal substrate, and treatment of the electrochemically active material, in particular at least partially cleaned metal. The time difference from application to the substrate is 30 to 40 minutes, preferably 35 minutes (± 2 minutes).

  This treatment, in particular at least partial cleaning of the metal substrate, in particular treatment with an organic acid on the surface of the metal substrate, and application of an electrochemically active material to the treated, particularly at least partially cleaned metal substrate The time difference between the first and the second is an advantage that a particularly effective cleaning is possible in which metal substrates, in particular up to 50% of contaminants on their surface, particularly preferably up to 100% of contaminants are removed. Have

  Between the cleaning of the metal substrate using the organic acid and the application of the electrochemically active material, further steps such as a drying step may be performed for further processing the surface of the metal substrate.

  The concept of “organic acid” is a compound having an acidic group O═X—OH, that is, a compound having a central atom (X) and having an OH group by a single bond between the central atom X and the oxygen atom O of the OH group. It is understood to be a compound having a further oxygen atom by a double bond to the central atom X. The central atom X is bonded to an oxygen atom by the formation of a double bond, and at the same time, it is bonded to the oxygen atom O of the OH group by the formation of a single bond. Can be selected from the group of Preferably, the central atom X is selected from the group of carbon, sulfur, phosphorus, silicon, with carbon being particularly preferred.

  Furthermore, the central atom X is a component of an organic substituent selected from alkyl or aryl substituents which may have additional heteroatoms in addition to carbon and hydrogen atoms, preferably nitrogen, oxygen, sulfur or phosphorus. It is bonded to some further atom, preferably a carbon atom. The use of the term “organic acid” in the singular does not preclude a mixture of different organic acids.

  When the organic acid is configured as a “solid acid”, ie as an acid that exists as a solid under standard conditions (25 ° C., 1031 bar), it is preferred to dissolve the acid in a suitable solvent before use. Preferably, the water content of the organic acid and / or solvent is less than 20%, preferably less than 10%, preferably less than 5%, preferably less than 2%, particularly preferably 1% or more. Few. Preferably, the organic acid is selected so that it decomposes upon UV irradiation or temperature rise. Preferably, the decomposition product produced upon UV irradiation is at least partially gaseous. A preferred decomposition product is, for example, carbon dioxide or water.

  In one embodiment, the organic acid is selected from acetic acid, succinic acid, fumaric acid, citric acid, maleic acid, oxalic acid, lactic acid, pyruvic acid, formic acid, oxalosuccinic acid, oxaloacetic acid, oxalic acid or mixtures thereof. .

  In a preferred embodiment, the organic acid contains oxalic acid (also called ethanedioic acid), optionally in addition to further components.

  The use of organic acids, in particular oxalic acid, has the advantage that the organic acid can be decomposed, for example by heating or UV irradiation. The organic acid decomposition products thus obtained are generally carbon dioxide and water, and can be easily removed. In addition, handling of organic acids is generally easier and less dangerous than handling of chromium sulfate used, for example, in corona etching. This is particularly useful in the context of “clean room” conditions that exist during the manufacture of electrochemical cells.

  In one particularly preferred embodiment, the organic acid is configured as “anhydrous” oxalic acid. This is available as a product under CAS number 144-62-7. Here, “anhydrous” means that the water content of oxalic acid is 1% or less.

  In a further particularly preferred embodiment, the organic acid is configured as “anhydrous” oxalic acid and is at least partially dissolved in NMP (N-methyl-2-pyrrolidone). The moisture content of NMP is preferably less than 100 ppm, preferably less than 60 ppm, preferably less than 30 ppm, preferably less than 10 ppm, and NMP is a pollutant containing amines in the so-called “Battery Quality”. Exist almost without.

  The use of organic acid anhydrides, especially oxalic anhydride, can be used at least in part, particularly efficiently and easily, especially when the metal substrate, especially the contaminants on its surface, are configured as a copper foil, Preferably it has the advantage of being completely removed. Contaminants on the surface of the metal substrate can occur through storage, transportation, packaging or during manufacture of the metal substrate. Contaminants can negatively affect, for example, the adhesion of the electrochemically active material to the metal substrate surface. Thereby, the electrochemical cell will “age over time” earlier, or the function of the metal substrate, ie the acceptance or emission of electrons from or into the electrochemically active material will be compromised. This becomes apparent, for example, in the form of an increase in the internal resistance of the electrochemical cell and the accompanying loss of capacity or power.

In one embodiment, the metallic substrate is or comprises copper or a copper-containing foil, in particular a copper foil. The surface of the copper foil collector can be contaminated by fat-containing and / or oily substances, in particular beef tallow or dust particles, during its manufacture, for example in a rolling or cutting process. In addition, copper-containing foils, in particular copper foil surfaces, when relatively long in contact with ambient air, are at least partially passivated by ambient air, in particular through oxidation, to form a passive film, In one embodiment, it has copper (I) Cu ₂ O and is also considered a contaminant. Therefore, it is advantageous to use an organic acid having an organic substituent. Because organic fat-containing and / or oily substances are also at least partly, preferably completely soluble in organic acids, according to the chemical principle “Similar solvates well” (similia similibus solvuntur) This is because it can be removed from the surface of the metal substrate. A further advantage of using organic acids is that in one embodiment the passivating coating with copper (I) Cu ₂ O can be at least partially, preferably completely removed. Preferably, the metal substrate surface treated in this way, in particular at least partially cleaned, no longer reacts with organic acids.

In a particularly preferred embodiment, the metallic substrate is configured as a foil containing copper, in particular a copper foil, the surface of which contains fat-containing and / or oily substances, in particular beef tallow, and / or at least Partially at least partially contaminated by a passive coating with copper (I) oxide Cu ₂ O, treated at least partly, preferably completely with an organic acid, preferably oxalic anhydride, in particular at least partly In particular, the contaminants are preferably completely removed, i.e. washed.

  The concepts “cleaned” and “cleaned” preferably indicate that up to 50%, preferably up to 70%, and preferably up to 100% of contaminants have been removed from the metal substrate surface, but at least preferably each time. 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90% 95% of the contaminant has been removed from the metal substrate surface.

  The concept of “treatment” and “treat” is preferably that up to 50%, preferably up to 70%, preferably up to 100% of the metal surface has been in contact with an organic acid, in particular wetted with an organic acid, however Preferably at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85 It is understood that the surface of the%, 90%, 95% metal substrate has been in contact with an organic acid, and in particular has been wetted with an organic acid.

  In one embodiment, the metal substrate surface is moistened with an organic acid by spraying the organic acid onto the metal substrate surface.

  In a further embodiment, wetting the metallic substrate surface with an organic acid is performed by pouring the organic acid onto the metallic surface.

  In a further embodiment, moistening the metal substrate surface with an organic acid is performed by an organic acid bath of the metal substrate.

  In a further embodiment, the metal substrate surface is moistened with an organic acid using a device such as a roller whose surface is moistened with an organic acid. At this time, the organic acid is at least partially transferred from the device surface to the metal substrate surface when the metal substrate surface contacts the device surface.

  In a further embodiment, the treatment of the metal substrate surface with an organic acid is performed by vapor deposition of the metal substrate with a vapor comprising or consisting of an organic acid. This allows for a particularly homogeneous treatment of the surface, in particular with virtually no wetting effect (Benetzungseffekt). This treatment is preferably carried out at a temperature of at least 85 ° C., 100 ° C., 150 ° C. A vapor stream is used for this treatment, which, with pressure, impinges on the surface to be treated, thereby providing a mechanical cleaning effect. This pressure is in each case preferably at least 1 bar, 2 bar, 5 bar, 10 bar, 25 bar, 50 bar, 100 bar, 200 bar or 500 bar. However, the pressure or the ambient pressure on the metal substrate may be less than 1 bar. The cross section of the vapor stream has a surface AD, which corresponds to at least the surface AO of the surface to be treated. However, this cross-section AD corresponds to a fraction A of the surface AO (Br = teil) f (AD = f * AO), preferably f is the lowest or highest and f = 0.5; 0.25; 0.1; 05 is also possible and preferable. The cross section of the steam flow is preferably and in each case has a substantially rectangular parallelepiped, strip or line profile.

  The treatment of the metal substrate, in particular its cleaning, is preferably carried out with plasma, in particular with a plasma flow, in particular when the ambient pressure of the metal substrate is between 0.05 bar and 1 bar. Plasma is partially or completely a gas composed of free charge carriers such as ions or electrons, and is generated, for example, by electrical treatment of the gas in an alternating electric field in a plasma facility available as a product. The plasma can be generated using oxygen or organic acids. At this time, the temperature can be arbitrarily selected, and is particularly the atmospheric temperature. Soft or gentle cleaning is performed.

  It is possible and preferred that the organic acid and in particular the vapor stream comprising the organic acid and the surface to be treated can be moved with respect to each other, preferably at a constant speed, in order to obtain a particularly homogeneous result. Preferably, for example, the surface to be treated is moved relative to the organic acid (or vapor stream) or the organic acid (or vapor stream) is moved relative to the surface to be treated.

  In one embodiment, further steps are performed following the step of wetting the metal substrate surface. In this step, the organic acid is uniformly dispersed on the surface of the metal substrate using a mechanical process such as vibration.

  In one embodiment, the homogenous dispersion of the organic acid on the metal substrate surface is performed simultaneously with wetting the metal substrate surface with the organic acid.

  In one embodiment, the method includes mechanical cleaning of the metal substrate surface, which can be performed by polishing using, for example, a brush or fiber device. The mechanical cleaning step can be performed before, during or after wetting the metal substrate surface with the organic acid before wetting the metal substrate surface with the organic acid.

  In a preferred embodiment, the step of wetting the metal substrate surface with an organic acid, the step of uniformly dispersing the organic acid on the metal substrate surface, and the step of mechanically cleaning the metal surface are combined into one step. The This can be done, for example, by a vapor stream with an organic acid or by the use of a movable brush. The brush is continuously moistened with organic acid from a stock container filled with organic acid, and releases the organic acid onto the metal substrate by contacting the metal substrate surface. At this time, the movable brush performs, for example, a circular movement on the surface of the metal substrate, whereby the organic acid is uniformly dispersed on the surface of the metal substrate. This is simultaneously mechanically cleaned by optionally applying pressure to the metal substrate surface with a brush.

  The time that the organic acid stays on the surface of the metal substrate is preferably up to 30 seconds, up to 5 minutes, preferably up to 30 minutes, preferably up to 60 minutes, preferably up to 2 hours. However, this time may be longer or shorter.

  Furthermore, the method according to the present invention comprises treating the metal substrate with ultraviolet light.

  In one embodiment, the ultraviolet treatment of the metal substrate is performed before the treatment with the organic acid.

  In a further embodiment, the ultraviolet treatment of the metal substrate is performed after the treatment with an organic acid.

  In a preferred embodiment, the ultraviolet treatment of the metal substrate is performed before and after the treatment with the organic acid.

  In a preferred embodiment, the electrochemically active material is irradiated with ultraviolet light in addition to the metal substrate.

  Irradiation of the ultraviolet light to the electrochemically active material is performed immediately before applying the electrochemically active material to the metal substrate or at a time interval.

  The ultraviolet treatment of the metal substrate and the electrochemically active material is advantageous for adhesion of the electrochemically active material to the surface of the metal substrate. By the ultraviolet irradiation, organic contaminants on the metal substrate surface due to oxidation are at least partially removed. At this time, decomposition products such as carbon dioxide and water are generated. Therefore, the surface of the metal substrate is at least partially cleaned by the ultraviolet irradiation, and the adhesion force of the surface of the metal substrate is at least partially improved.

  A further advantage of the UV treatment of the metal substrate is that the organic acid applied to the surface of the metal substrate is at least partially removed by UV irradiation, preferably completely removed by decomposition of the organic acid. It is particularly advantageous if a decomposition product having mild volatility, for example a gas such as carbon dioxide, is produced during the irradiation with ultraviolet rays. Furthermore, water may be generated as a decomposition product upon irradiation with ultraviolet rays. These degradation products can be easily removed in further ways or are not harmful in the electrochemical cell.

  Suitable as the ultraviolet irradiation source is, for example, a mercury vapor lamp such as a low-pressure mercury lamp or an ultraviolet light emitting diode. The ultraviolet light is an electromagnetic beam having a wavelength of 1 nm to 380 nm.

  Preferably, the method comprises the step of drying the metal substrate, ie reducing or removing the liquid adsorbed on the metal substrate surface, in particular water. The drying step can be performed before and / or after treatment with ultraviolet light. Furthermore, the drying step can be carried out before and / or before and / or after treatment with the organic acid.

  Preferably, the method according to the present invention comprises the step of coating the surface of a metal substrate treated with ultraviolet radiation and / or an organic acid, preferably with an electrochemically active material which has also been treated with ultraviolet radiation. It is also advantageous if the coating is followed by further treatment with UV radiation.

  In one embodiment, the electrochemical cell according to the present invention has at least one electrode produced by the method according to the present invention, and the electrode, preferably the negative electrode, has a metal substrate, The metal substrate preferably contains copper and is configured as a foil, the entire surface of which is preferably up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 100% electrical. Coated with a chemical active material, preferably material-connected, wherein the electrochemical active material contains carbon, preferably selected from crystalline graphite, earthy graphite, “hard carbon”, or mixtures thereof. doing.

  In a further embodiment of the electrochemical cell, a bonding agent that can further improve the adhesion between the electrochemically active material and the metallic substrate is included. Preferably, such a bonding agent comprises a polymer, preferably a fluorinated polymer, preferably polyvinylidene fluoride, which is Kynar®, Solef®, Kureha® or Dyneon ( Registered trademark).

FIG. 3 schematically shows an embodiment of the method according to the invention.

  An embodiment of the electrode manufacturing method according to the present invention includes the following steps.

  A metal substrate, preferably a copper metal collector or a metal collector containing copper is prepared (11). Next, the surface of the metal substrate, particularly the metal substrate, is treated by ultraviolet irradiation (12). An organic acid, in particular oxalic acid, is provided (21) and subsequently at least partially dissolved in NMP (22). Steps (11) and / or (12) can be performed in parallel with steps (21) and / or (22). However, the steps (11) and / or (12) may be performed independently of the steps (21) and / or (22) or at different times. For example, after steps (11) and (21) have already been performed, step (22) can be performed, and then step (12) can be performed for the first time.

  An organic acid dissolved in NMP, preferably oxalic anhydride dissolved in NMP, is applied to the surface of the metal substrate that has been subjected to UV treatment (30).

  The organic acid dissolved in NMP applied in step (30) is at least partially removed from the metal substrate surface (40). Advantageously, step (30) is performed with a time interval relative to step (40). Thereby, more effective cleaning becomes possible.

  In step (40), the surface of the metal substrate cleaned with the organic acid is treated with ultraviolet irradiation.

  An electrochemically active material, particularly an electrochemically active material for the anode is prepared (71), and the electrochemically active material is treated with ultraviolet irradiation. Steps (71) and (72) can be performed at arbitrary points in time. However, it is particularly advantageous if step (72) is performed without a time interval with respect to step (60). Step (60) includes a coating of the metal substrate, particularly its treated surface, treated in previous steps (12), (30), (40) and (50).

  In step (60), the metal substrate coated with the electrochemically active material is treated with ultraviolet irradiation (80). Step (80) is an optional step.

11 Steps for preparing a metal substrate, preferably a copper metal collector or a metal collector containing copper 12 Steps for treating the surface of a metal substrate, in particular a metal substrate, by UV irradiation 21 Steps for preparing an organic acid, in particular oxalic acid 22 Step of dissolving oxalic acid at least partially in NMP 30 Step of applying an organic acid dissolved in NMP, preferably oxalic anhydride dissolved in NMP, onto the surface of a metal substrate that has been subjected to UV treatment 40 Applying in step 30 The organic acid dissolved in NMP is removed at least partially from the surface of the metallic substrate 50. The surface of the metallic substrate washed with the organic acid in Step 40 is treated with ultraviolet irradiation 60. Steps 12, 30 , 40 and 50 treated metal substrates, in particular their treated Step 71 for coating the surface Step 71 for preparing an electrochemically active material, particularly for the anode 72 Step for treating the electrochemically active material with UV irradiation 80 Metal coated with the electrochemically active material in Step 60 The step of processing the substrate made by ultraviolet irradiation

Claims (8)

In a method for producing an electrode of an electrochemical cell having a metal substrate, particularly a negative electrode,
Treating the metal substrate with ultraviolet radiation; and
Treating the metal substrate with an organic acid;
A method characterized by comprising:   The method according to claim 1, characterized in that the metallic substrate comprises copper, preferably as a foil containing copper or as a copper foil.   The method according to claim 1, wherein the ultraviolet irradiation of the metal substrate is performed before or after, or before and after the treatment of the metal substrate with an organic acid.   The method according to claim 1, wherein the organic acid is configured as oxalic anhydride.   The method according to claim 4, wherein the oxalic anhydride is dissolved in NMP.   The treatment of the metal substrate with an organic acid is performed 30 to 40 minutes before coating of the electrochemically active material on the metal substrate. the method of.   The method of claim 6, wherein the electrochemically active material is treated with ultraviolet irradiation. In a method for cleaning an electrode of an electrochemical cell, particularly a metal substrate of a negative electrode,
Treating the metal substrate with ultraviolet radiation; and
Treating the metal substrate with an organic acid;
A method characterized by comprising:

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