Patent Description:
The present disclosure relates to an electrode for a secondary battery, and a secondary battery including the electrode, and more particularly, to a multilayer electrode formed by applying a slurry having different viscosity on an electrode current collector in which a plurality of through-holes are formed, and a method of manufacturing the same.

With the development of technology and demand for mobile devices, the demand for secondary batteries as an energy source has rapidly increased, and recently, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) has been realized. Among such secondary batteries, there is a high demand for lithium secondary batteries having high energy density, high discharge voltage, and output stability.

In general, a lithium secondary battery is manufactured by using a material capable of inserting and removing lithium ions as a negative electrode and a positive electrode and by charging an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode, and electrical energy is generated by oxidation and reduction reactions when lithium ions are inserted and desorbed from the positive electrode and the negative electrode.

In this case, the negative electrode and the positive electrode include an electrode mixture layer on the current collector of each electrode. For example, a slurry is prepared by mixing and stirring a binder, a solvent, and a conductive material and a dispersant as needed, in the electrode active material, and then, electrodes may be prepared by applying the slurry to a current collector of a metallic material, followed by being compressed and dried.

In the process of manufacturing such an electrode, the development of a high-capacity battery has been required by expanding application of a lithium secondary battery to an electric vehicle, etc., thus increasing the load on the electrode mixture layer. However, the increased volume and weight of the electrode mixture layer lowers the energy density of the entire secondary battery, and there is a problem that causes non-uniformity of the electrochemical reaction inside the electrode mixture layer. Moreover, when a current or voltage is applied, a concentration gradient of lithium ions in the electrode occurs. In the thick electrode mixture layer, this phenomenon is further exacerbated, causing deterioration of rapid charging characteristics.

Therefore, a method of obtaining the capacity of a secondary battery having a thick electrode mixture layer by laminating several layers of thin electrodes rather than thickly applying an electrode mixture layer on one current collector has been proposed. However, in this case, to preserve the movement of lithium ions, a current collector having pores having a specific porosity or higher or openings having a specific aperture ratio or higher is used. In addition, the current collector in which the pores or openings are formed may significantly reduce the weight of the entire secondary battery, and thus, the use in future is further expected.

However, when the slurry is applied during the electrode manufacturing process, there is a problem in that the slurry leaks to the opposite side of the coated surface, resulting in surface irregularity of the electrode mixture layer, and failing to form a uniform electrode mixture layer, due to the high porosity or aperture ratio. Secondary battery electrodes manufactured by applying two slurries on an electrod current collector are disclosed in <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>,.

The present invention provides an electrode for a secondary battery according to the subject-matter of independent claim <NUM>. Prefered embodiments of the electrode are defind in the dependent claims.

An aspect of the present disclosure is to provide a method of manufacturing an electrode for a secondary battery, in which processability may be secured by preventing leakage of a slurry in manufacturing an electrode including an electrode current collector in which a plurality of through-holes are formed, and thus, a uniform electrode mixture layer may be formed, and to provide an electrode for a secondary battery, manufactured by the method.

According to an aspect of the present disclosure, a method of manufacturing an electrode for a secondary battery includes preparing an electrode current collector in which a plurality of through-holes are formed, applying a first slurry including an electrode active material, a binder, and a conductive material to at least one surface of the electrode current collector, and applying a second slurry including an electrode active material, a binder, and a conductive material on the first slurry. Viscosity of the first slurry is greater than viscosity of the second slurry.

The viscosity of the first slurry may be 10000cp to 15000cp.

The viscosity of the second slurry may be 3000cp to 7000cp.

A solid content weight of the first slurry may be <NUM> to <NUM>% by weight.

A solid content weight of the second slurry may be <NUM> to <NUM>% by weight.

The first slurry may further include a thickener.

The second slurry may further include a thickener in a weight less than a weight of the thickener included in the first slurry.

The thickener included in the first slurry may be included in an amount of <NUM> to <NUM>% by weight, based on a total weight of the first slurry.

The thickener may be at least one selected from carboxy methyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC) and cellulose gum.

According to an aspect of the present disclosure, a secondary battery includes an electrode current collector in which a plurality of through-holes are formed, a first electrode mixture layer provided by coating at least one surface of the electrode current collector with a first slurry including an electrode active material, a binder, a conductive material, and a thickener, and a second electrode mixture layer provided by applying a second slurry including an electrode active material, a binder, and a conductive material on the first electrode mixture layer.

The second slurry may further include a thickener in a weight less than a weight of a thickener included in the first slurry.

The thickener included in the first slurry may be included in <NUM> to <NUM>% by weight, based on a total weight of the first slurry.

The thickener may be at least one selected from carboxy methyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC), ethyl hydroxylethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC) and cellulose gum.

Hereinafter, exemplary embodiments will be described with reference to various examples. However, the scope of the present invention is not limited to the embodiments described below.

An electrode for a secondary battery according to an exemplary embodiment and a method of manufacturing the same are provided. In detail, a multilayer electrode formed by applying a slurry having a different viscosity on an electrode current collector having a plurality of through-holes, and a method of manufacturing the same, are provided.

A method of manufacturing an electrode for a secondary battery is provided. The method of manufacturing an electrode for a secondary battery may include preparing an electrode current collector in which a plurality of through-holes are formed; applying a first slurry including an electrode active material, a binder, and a conductive material to at least one surface of the electrode current collector; and applying a second slurry including an electrode active material, a binder, and a conductive material on the first slurry. Viscosity of the first slurry is greater than viscosity of the second slurry. The electrode may be a negative electrode or a positive electrode.

In an exemplary embodiment, the current collector may be a current collector in a form in which a plurality of through-holes are perforated at a predetermined interval in a metal foil, and is not particularly limited as long as it has such a shape, but a metal foil in which a diameter of the through-hole is <NUM> to <NUM> and a pitch between the through-holes is <NUM> to <NUM> may be used.

Outside the above range, if the diameter of the through-holes is relatively too small or the average interval is relatively too large, it is difficult to have a required porosity, and thus it is difficult to manufacture, while if the average diameter of the through-holes is too large or if the average spacing between the through-holes is too small, the strength of the current collector itself may be relatively weak, and thus the support of the electrode mixture layer may be difficult.

The electrode for a secondary battery according to an exemplary embodiment may be a positive electrode or a negative electrode. Although not particularly limited, in the case of a positive electrode, a thin plate made of aluminum may be used as the current collector, and in the case of a negative electrode, a thin plate made of copper may be used as the current collector.

As described above, to form an electrode mixture layer on one surface of an electrode current collector in which a plurality of through-holes are formed, when a slurry including an electrode active material, a binder and a conductive material is applied, a phenomenon in which the slurry leaks through the through-holes may occur, and accordingly, a surface unevenness of the electrode mixture layer may occur, and problems such as contamination of a coater for applying the slurry may occur.

Accordingly, the method of manufacturing an electrode for a secondary battery may be provided. The method may include applying a first slurry including an electrode active material, a binder, and a conductive material to at least one surface of the electrode current collector; and applying a second slurry including an electrode active material, a binder, and a conductive material on the first slurry. In this case, viscosity of the first slurry is greater than viscosity of the second slurry.

To prevent leakage of the slurry through the through-holes, the first slurry may have a viscosity of <NUM> cp or higher, but if the viscosity is too high, it may be difficult to secure coating processability, and therefore, the first slurry may have, in detail, a viscosity of <NUM> cp to <NUM> cp.

To prepare a slurry having the above-mentioned viscosity, the solid content weight of the first slurry may be <NUM> to <NUM>% by weight. The solid content means the total amount of components excluding the solvent component from the slurry composition containing an electrode active material, a binder and a conductive material. In the case in which the solid content weight of the first slurry is less than <NUM>%, the viscosity is less than <NUM> cp, and thus, it is difficult to prevent the leakage of the slurry, whereas in the case in which the first slurry exceeds <NUM>%, the viscosity becomes too high, and there is a problem in which securing coating processability is difficult.

The second slurry may be <NUM> cp or less to secure processability. However, if it is less than 3000cp, since the viscosity is relatively too low, since there is a problem in which the coating processability is further reduced, the second slurry may have a viscosity of 3000cp to 7000cp.

To prepare a slurry having the above-described viscosity, the solid content weight of the second slurry may be <NUM> to <NUM>% by weight. In the case in which the solid content weight of the second slurry is less than <NUM>%, a viscosity of less than <NUM> cp is exhibited, which causes difficulty in securing coating processability.

According to another embodiment, a thickener may be additionally added to the first slurry to increase the viscosity of the first slurry. In addition, a thickener may be further added to the second slurry, as required. However, in this case, the thickener included in the second slurry may be included in a smaller weight than the thickener included in the first slurry. In addition, the types of thickeners included in the first slurry and the second slurry may be the same, or may be different.

The thickener is not particularly limited, and for example, may be one or more selected from carboxy methyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), and cellulose gum.

In addition, the thickener may be included in <NUM> to <NUM>% by weight, based on the total weight of the first slurry. If less than <NUM>% by weight, it is difficult to secure a viscosity that may prevent the leakage of the slurry, while if it is more than <NUM>% by weight, since the viscosity is relatively too high, there is a problem in which the coating processability is rather inhibited.

On the other hand, the electrode active materials included in the first slurry and the second slurry may be the same as or different from each other. When the electrode is a positive electrode, the positive electrode active material is not particularly limited, but for example, may be at least one selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium copper oxide, a compound having an olivine crystal structure, such as LiFePO<NUM>, LiMnPO<NUM>, LiCoPO<NUM>, LiNiPO<NUM>, or the like, vanadium oxide, and disulfide compounds.

When the electrode is a negative electrode, one or more selected from artificial graphite, natural graphite, soft carbon, hard carbon acetylene carbon black, ketjen black, carbon nanotube, carbon nanofiber, and silicon oxide may be used as the negative electrode active material.

The binder included in the first slurry and the second slurry may also be the same as or different from each other. The binder is a component that assists in the bonding of the active material and the conductive material or the like, and in the bonding to the current collector, and a material used as the binder is not particularly limited. For example, the material of the binder may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber (SBR), fluorine rubber, mussel protein, a polyacrylate-based binder, a polyolefin-based binder, or a silane-based binder. In detail, at least one selected from PVDF, SBR, mussel protein, a polyolefin-based binder, a polyacrylate-based binder and a silane-based binder may be used.

The conductive materials included in the first slurry and the second slurry may also be the same as or different from each other. The conductive material is a material to improve electronic conductivity, and is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, as the conductive material, graphite, such as natural graphite, artificial graphite or the like; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, summer black or the like; conductive fibers such as carbon fibers and metal fibers; metal powder such as carbon fluoride, aluminum and nickel powder, conductive whisker such as zinc oxide and potassium titanate, a conductive metal oxide such as titanium oxide, or a conductive material such as polyphenylene derivative, carbon nanotubes and graphene may be used.

The solvents included in the first slurry and the second slurry may also be the same as or different from each other. The type of the solvent is not particularly limited, and for example, may be at least one selected from acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylform amide, N-methyl-<NUM>-pyrrolidone (NMP), cyclohexane and water.

According to another embodiment, an electrode for a secondary battery manufactured according to the above method is provided. In detail, the electrode for a secondary electrode includes an electrode current collector in which a plurality of through-holes are formed; a first electrode mixture layer formed by coating a first slurry including an electrode active material, a binder, a conductive material, and a thickener on at least one surface of the electrode current collector; and a second electrode mixture layer formed by applying a second slurry including an electrode active material, a binder, and a conductive material on the first electrode mixture layer. A viscosity of the first slurry is greater than a viscosity of the second slurry.

As described above, according to an exemplary embodiment, the processability may be secured by preventing leakage of a slurry, and accordingly, an electrode for a secondary battery having a uniform electrode mixture layer may be manufactured.

Hereinafter, an exemplary embodiment of the present disclosure will be described in more detail with Examples. The following examples are intended to illustrate the present disclosure in more detail, but the present disclosure is not limited thereby.

As a negative electrode current collector, a copper thin plate having a thickness of <NUM> was prepared, and as a negative electrode active material on one surface of the copper thin plate, the first slurry including <NUM> parts by weight of graphite, <NUM> parts by weight of carboxymethyl cellulose as a thickener , <NUM> parts by weight of SBR binder, and <NUM> part by weight of carbon black as a conductive material, was applied by a slot die coating method. The solid content of the first slurry was <NUM>%, and the viscosity of the first slurry measured by Brookfield viscometer pin <NUM> at 30rpm was <NUM>,000cp.

Subsequently, a second slurry including <NUM> parts by weight of graphite, <NUM> part by weight of carboxymethyl cellulose as a thickener, <NUM> parts by weight of SBR binder, and <NUM> part by weight of carbon black as a conductive material was applied to the first slurry by a slot die coating method. The solid content of the second slurry was <NUM>%, and the second slurry had a viscosity of <NUM>,<NUM> cp.

Except that <NUM> parts by weight of graphite, <NUM> parts by weight of carboxymethyl cellulose as a thickener, <NUM> parts by weight of SBR binder, and <NUM> part by weight of carbon black as a conductive material were used as the negative electrode active material of the first slurry; the first and second slurries were applied in the same manner as in Example <NUM>. The solid content of the first slurry was <NUM>% and the viscosity thereof was 14000cp.

Except that <NUM> parts by weight of graphite, <NUM> parts by weight of carboxymethyl cellulose as a thickener, <NUM> parts by weight of SBR binder, and <NUM> part by weight of carbon black as a conductive material were used as the negative electrode active material of the first slurry; the first and second slurries were applied in the same manner as in Example <NUM>. The solid content of the first slurry was <NUM>% and the viscosity was 4867cp.

Except that <NUM> parts by weight of graphite, <NUM> parts by weight of carboxymethyl cellulose as a thickener, <NUM> parts by weight of SBR binder, and <NUM> part by weight of carbon black as a conductive material were used as the negative electrode active material of the first slurry; the first and second slurries were applied in the same manner as in Example <NUM>. The solid content of the first slurry was <NUM>% and the viscosity was <NUM> cp.

Images captured immediately after coating of the copper thin plates with the first and second slurries, prepared according to Examples <NUM> and <NUM>, and Comparative Examples <NUM> to <NUM>, and images of the copper thin plates captured after an elapse of <NUM> minutes after placing the copper thin plate in an oven, are illustrated in <FIG>. In Examples <NUM> and <NUM> of the present disclosure, it was confirmed that the leakage of the first slurry was relatively small, thereby ensuring processability.

As set forth above, according to exemplary embodiments, in manufacturing an electrode including an electrode current collector with a plurality of through-holes, processability may be secured by preventing leakage of a slurry, and thus, a uniform electrode mixture layer may be formed.

Claim 1:
An electrode for secondary battery comprising:
an electrode current collector in which a plurality of through-holes are formed;
a first electrode mixture layer including an electrode active material, a binder, a conductive material, and a thickener on at least one surface of the electrode current collector; and
a second electrode mixture layer including an electrode active material, a binder, and a conductive material on the first electrode mixture layer,
wherein the second electrode mixture layer comprises a thickener in a weight less than a weight of the thickener included in the first electrode mixture layer.