KR20100006396A - A forming method of electrode active material layer of a secondary battery developing electroconductivity and a secondary battery manufactured therefrom - Google Patents

Abstract

PURPOSE: A method for forming an electrode active material layer of a secondary battery is provided to prepare an electrode active material layer in which conductive agent particles are dispersed within a crosslinking binder resin, thereby minimizing the degradation of an electrode when volume expansion of the electrode active material layer is generated. CONSTITUTION: A method for forming an electrode active material layer of a secondary battery comprises the steps of: dispersing a conductive material(5) in a melt of a binder resin(3); crosslinking the binder resin within a range having the availability for solvent, and then preparing master batch type soluble crosslinking binder resin-conductive agent composite chips in which conductive agent particles are dispersed within a crosslinking binder resin; dispersing the master batch type soluble crosslinking binder resin-conductive agent composite chips and electrode active material particles(15) in a solvent, and then dissolving the soluble crosslinking binder resin of the composite chips to prepare an elelctrode active material slurry; and applying the elelctrode active material slurry on a substrate and drying the coated material.

Description

A method for forming an electrode active material layer of a secondary battery having improved conductivity and an electrode of a secondary battery manufactured therefrom.

The present invention relates to a method for forming an electrode active material layer of a secondary battery having improved conductivity and an electrode of a secondary battery manufactured therefrom.

In general, rechargeable batteries capable of charging and discharging are being actively researched by developing portable electronic devices such as cellular phones, notebook computers, and camcorders. Examples of such secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-hydrogen batteries, and lithium secondary batteries. Among them, lithium secondary batteries are considered the most promising and have high future prospects because they have superior operating voltage characteristics and energy density per unit weight compared to nickel-cadmium batteries or nickel-metal hydride batteries, which are widely used as power sources for electronic devices. .

The lithium secondary battery may be manufactured in various forms, and typical shapes include cylindrical and rectangular shapes mainly used in lithium ion batteries. Lithium polymer batteries, which are in the spotlight in recent years, are made of flexible materials and their shapes are relatively free. In addition, since the safety and light weight is excellent, it can be said that it is advantageous to slim and lighten portable electronic devices.

A lithium secondary battery typically includes a positive electrode having a positive electrode active material layer formed on at least one surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on at least one surface of a negative electrode current collector, and interposed between the positive electrode and the negative electrode to electrically insulate them. A separator is provided. The electrode (anode or cathode) active material layer may be formed by applying and drying the electrode active material slurry in which the electrode active material particles, the conductive agent particles, and the binder resin are dispersed in a solvent to the current collector, or the electrode active material. The slurry is applied and dried on top of a separate support, and then a film peeled from the support is formed by lamination onto a current collector.

Referring to FIG. 1, the microstructure of the electrode 20 having the electrode active material layer 13 formed on one surface of the current collector 11 according to the conventional method described above will be described. 15 are connected to each other and fixed to the current collector 11, and the conductive particles 5 having a fine size are not dispersed in the binder resin interior 3 but are only physically in point contact with the electrode active material particles 15. To act as a conductive agent.

However, when the battery is used for a long time, volume expansion of the electrode active material layer occurs, which causes a gap between the conductive agent particles and the electrode active material particles that are in point contact. The interaction between the conductive agent particles and the electrode active material particles is weakened, thereby lowering the ion conductivity of the electrode. In order to solve such a problem, increasing the content of the conductive agent decreases the content of the electrode active material particles so that the capacity of the secondary battery decreases.

Japanese Unexamined Patent Publication Nos. 1996-124560 and 1996-124562 disclose an electrode active material slurry obtained by dispersing an electron beam curable monomer and a polymer material, electrode active material particles, and conductive agent particles in a solvent, applying the same to a current collector, and then crosslinking the polymer material. The electrode active material layer formation method which improved the solvent resistance to electrolyte solution is disclosed. However, the conductive particles in the electrode active material layer formed by this manufacturing method also do not disperse the conductive agents in the crosslinked binder resin in the manufacturing process, and merely perform physical point contact with the electrode active material particles to perform the role of conductive agent. .

Meanwhile, in the method of forming the electrode active material layer, the ion conductivity of the formed electrode active material layer is uniformly maintained only when the conductive particles are well dispersed in the electrode active material slurry. However, in the case of using a conventional dispersing method in which the electrode active material particles, the conductive agent and the binder resin are added to the solvent at the same time and stirred and dispersed in the mixer, due to differences in particle sizes and specific gravity of the electrode active material particles and the conductive agent, The conductive particles are difficult to uniformly disperse in the slurry.

In order to improve this problem, Japanese Laid-Open Patent Publication No. 2003-173777 discloses a method of spray-drying an electrode active material slurry, and then adding a solvent therein and kneading the mixture, and then applying and drying the electrode active material layer to form an electrode active material layer. Is disclosed. In addition, Korean Unexamined Patent Application Publication No. 2000-6809 discloses a method of improving dispersibility of electrode active material and conductive particles in an electrode active material slurry through a specially designed dispersing device. However, these manufacturing methods require a special dispersing apparatus or are cumbersome in manufacturing process, and there is a limit in improving the dispersibility of the conductive particles in the electrode active material slurry.

The technical problem to be solved by the present invention is to solve the above problems, to produce an electrode active material layer in which the conductive particles are dispersed in the cross-linking binder resin to produce a volume expansion of the electrode active material layer according to the use of the battery for a long time In this case, the present invention provides a method of forming an electrode active material layer of a secondary battery capable of minimizing a decrease in ion conductivity of an electrode, and an electrode of a secondary battery manufactured therefrom.

In addition, another technical problem to be achieved by the present invention is to provide a method for forming an electrode active material layer of a secondary battery that improves the dispersibility of the conductive particles in a relatively simple method.

In order to achieve the above technical problem, a method of forming an electrode active material layer of a secondary battery according to the present invention includes dispersing a conductive agent in a melt of a binder resin (S1) (S2) dissolving the binder resin in a solvent. Cross-linking within a range having a step, and then preparing master batch soluble crosslinked binder resin-conductor composite chips in which the conductive agent is dispersed in the crosslinked binder resin (S3) and the master batch soluble crosslinked binder resin-conductor composite chips. Dispersing electrode active material particles in a solvent, and then dissolving the soluble crosslinked binder resin of the composite chips in the solvent to prepare an electrode active material slurry, and (S4) applying and drying the electrode active material slurry on a substrate. .

According to the forming method of the present invention, since the electrode active material layer in which the conductive agent particles are dispersed in the crosslinked binder resin can be produced, even when volume expansion of the electrode active material layer occurs due to battery use for a long time, It is possible to minimize the decrease in ion conductivity. That is, when the crosslinked binder resin is dissolved while the master batch soluble crosslinked binder resin-conductor composite chips are dispersed in the electrode active material slurry, the conductive particles are crosslinked in the electrode active material slurry because the binder particles have a strong binding force to the crosslinked binder resin. It is well mixed with the binder resin. Accordingly, the conductive particles are dispersed in the binder resin of the electrode active material layer formed of the electrode active material slurry to secure a conductive path with the electrode active material particles.

In addition, the soluble crosslinked binder resin is dissolved while the master batch soluble crosslinked binder resin-conductor composite chips are dispersed in the electrode active material slurry, and the conductive particles dispersed therein are released in the slurry, thereby providing a conductive agent. The dispersibility of the particles is improved. Accordingly, since the conductive particles are uniformly dispersed in the electrode active material layer formed using the electrode active material slurry, the ion conductivity of the electrode can be maintained uniformly.

In the method for forming an electrode active material layer of the secondary battery of the present invention, the conductive content of the master batch soluble crosslinked binder resin-conductor composite chip is preferably 10 to 80% by weight, and the master batch soluble crosslinked binder resin-conductive It is preferable that the average diameter of the first composite chip is 0.1 to 10 mm.

As described above, according to the forming method of the present invention, an electrode active material layer in which conductive particles are dispersed in a crosslinked binder resin may be manufactured. Accordingly, even when volume expansion of the electrode active material layer occurs using a battery for a long time, a decrease in ion conductivity of the electrode can be minimized. That is, the crosslinked binder resin is dissolved while the master batch soluble crosslinked binder resin-conductive composite chips are dispersed in the electrode active material slurry. At this time, since the conductive particles have a strong binding force to the crosslinked binder resin, they are well mixed with the crosslinked binder resin in the electrode active material slurry. Therefore, conductive agent particles are dispersed in the binder resin of the electrode active material layer formed of the electrode active material slurry to secure a conductive path with the electrode active material particles.

In addition, the soluble crosslinked binder resin is dissolved while the master batch soluble crosslinked binder resin-conductor composite chips are dispersed in the electrode active material slurry, and the conductive particles dispersed therein are released in the slurry, thereby providing a conductive agent. The dispersibility of the particles is improved. Accordingly, since the conductive agent particles are uniformly dispersed in the electrode active material layer formed by using the electrode active material slurry, the ion conductivity of the electrode can be maintained uniformly.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

The present invention relates to a method of forming an electrode active material layer using a conventional electrode active material slurry composed of binder resin, electrode active material particles, conductive particles and a solvent, wherein the conductive particles are pre-dispersed in a soluble crosslinked binder resin. It is characterized by using soluble crosslinked binder resin-conductor composite chips.

That is, as shown in Figure 2, the master batch soluble crosslinked binder resin-conductor composite chip 10 according to the present invention added to the electrode active material slurry is a plurality of conductive particles in the soluble crosslinked polymer resin (3) The fields 5 are dispersed. When the master batch soluble crosslinked binder resin-conductor composite chips are dispersed in a solvent together with the electrode active material particles, and then the soluble crosslinked binder resin of the composite chips is dissolved in a solvent to prepare an electrode active material slurry. When the crosslinked binder resin is dissolved in a state where the binder resin-conductor composite chips are dispersed in the electrode active material slurry, the conductive particles have a strong binding force to the crosslinked binder resin, so that they are well mixed with the crosslinked binder resin in the electrode active material slurry. do. Accordingly, the conductive particles are dispersed in the binder resin of the electrode active material layer formed of the electrode active material slurry to secure a conductive path with the electrode active material particles.

In addition, the soluble crosslinked binder resin is dissolved while the master batch soluble crosslinked binder resin-conductor composite chips are dispersed in the electrode active material slurry, and the conductive particles dispersed therein are released in the slurry, thereby providing a conductive agent. The dispersibility of the particles is improved.

The electrode active material layer forming method of the secondary battery according to the present invention will be described in detail as follows.

First, the conductive agent is dispersed in the melt of the binder resin (step S1).

That is, the binder resin is heated to melt above the melting point and melted, and then the conductive particles are dispersed in the melt of the binder resin by adding and stirring the conductive particles therein. In the method of forming the present invention, any conductive agent used in the electrode active material layer of the secondary battery may be used as the conductive agent. For example, acetylene black, carbon black, Ketjen black, graphite, and the like may be used alone or in combination thereof. It can use together 2 or more types. The content of the conductive particles may be controlled within a content range capable of sufficiently dispersing the conductive particles in the binder resin, for example, 10 to 80 weight based on the total weight of the master batch binder resin-conductive composite chip described below. % Can be added.

As the binder resin, any thermoplastic binder resin commonly used as a binder of the electrode active material particles can be used as long as it can be crosslinked by a known crosslinking method. For example, polyvinylidene fluoride and vinylidene fluoride-hexa Fluoropropylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyacetate Each may be used alone or in combination of two or more thereof.

Subsequently, the binder resin in the melt of the binder resin in which the conductive agent is dispersed is crosslinked within a range having solubility in a solvent, and then, master batch-type soluble crosslinked binder resin-conductive composite chips in which the conductive agent is dispersed in the crosslinking binder resin are prepared. do.

As described above, when the binder resin is crosslinked, the binding force of the conductive particles to the binder resin is enhanced. Accordingly, when the crosslinking binder resin is dissolved while the crosslinking master batch type soluble crosslinking binder resin-conductor composite chips described below are dispersed in the electrode active material slurry, the conductive particles are well mixed with the crosslinking binder resin in the electrode active material slurry. It becomes. The crosslinking of the binder resin may use a known polymer crosslinking method such as irradiating high energy such as radiation or light to the melt of the binder resin in which the conductive agent is dispersed, or adding a crosslinking agent such as a radical reagent or a peroxide compound. When the degree of crosslinking increases, the binder resin is not dissolved in a solvent and thus an electrode active material slurry cannot be prepared, so that the binder resin is crosslinked at low crosslinking so as to maintain solubility in the solvent. Since the degree of crosslinking degree for maintaining solubility in a solvent depends on the kind of binder resin and the solvent to be melt | dissolved, it should adjust suitably according to the kind and solvent of binder resin to select.

The melt in which the conductive agent is dispersed in the crosslinked binder resin is a master batch soluble crosslinked binder resin of cylindrical chips having a predetermined size and shape, for example, an average diameter of 0.1 to 10 mm, using a conventional chip manufacturing method such as cutting after extrusion. The conductive composite chip may be manufactured, and the shape and size of the chip and the method of manufacturing the chip may be variously selected by those skilled in the art within the scope of achieving the object of the present invention.

Subsequently, the master batch soluble crosslinked binder resin-conductor composite chips and electrode active material particles are dispersed in a solvent, and then the soluble crosslinked binder resin of the composite chips is dissolved in the solvent to prepare an electrode active material slurry (step S3). .

The method for dispersing the master batch soluble crosslinked binder resin-conductor composite chips and the electrode active material particles in a solvent may use various dispersion methods such as a dispersion method using a conventional mixer. The master batch soluble crosslinked binder resin-conductor composite chips dispersed in a solvent together with other components are dissolved in a solvent by soluble crosslinked binder resin constituting the composite chip over time or by heating. Are manufactured. As a solvent, any solvent may be used as long as it is used to form an electrode active material slurry and can dissolve the soluble crosslinking binder resin. For example, acetone or N-methyl pyrrolidone (NMP) may be used.

In addition to the master batch soluble crosslinked binder resin-conductor composite chips, the electrode active material slurry may contain a binder resin (or a soluble crosslinked binder resin having low crosslinking) and a conductive agent to the extent that does not impair the object of the present invention according to conventional methods. Of course, the particles can be added separately, respectively. The content of the total conductive particles in the electrode active material slurry including the conductive particles contained in the master batch soluble crosslinked binder resin-conductive composite chips can be controlled according to the content of the conductive material in the electrode active material layer which is typically formed. For example, it may be added to 1 to 20 parts by weight based on 100 parts by weight of the electrode active material particles. In addition, the content of the total binder resin in the electrode active material slurry including the binder resin contained in the master batch soluble crosslinked binder resin-conductor composite chips may be controlled according to the content of the binder resin in the electrode active material layer that is typically formed. For example, it may be added to 5 to 30 parts by weight based on 100 parts by weight of the electrode active material particles.

Then, the electrode active material slurry prepared by the above-described method is applied on a substrate and dried to form an electrode active material layer (step S4). The electrode active material layer is formed by directly applying it onto a substrate made of a current collector, such as a metal thin film, a mesh-type suspended metal, or a punched metal, and then drying, or a separate support such as a polyethylene terephthalate film or the like. After coating and drying on the substrate, the film peeled from the support may be formed by laminating on a current collector or the like. As the coating method of the electrode active material slurry, a conventional coating method known in the art may be used, and for example, dip coating, die coating, roll coating, comma coating or the like Various methods, such as a mixing method, can be used.

In the electrode active material layer forming method of the present invention, the electrode active material particles are not particularly limited, and conventional electrode active material particles known in the art may be used.

Non-limiting examples of the positive electrode active material particles of the electrode active material particles may be particles of lithium composite oxides such as lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or the like particles of the sulfur compound, negative electrode active material Non-limiting examples of particles may include lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, lithium adsorbents such as graphite (graphite) and the like.

The electrode of the secondary battery formed according to the above-described manufacturing method of the present invention includes a current collector and an electrode active material layer formed on at least one surface of the current collector and including a conductive agent, electrode active material particles, and a crosslinked binder resin, wherein the electrode active material particles These are connected and fixed to each other by a crosslinked binder resin, and the conductive agent is dispersed in the crosslinked binder resin. Referring to FIG. 3, which is an enlarged cross-sectional view of an electrode active material layer of a secondary battery electrode formed according to the method of the present invention, the binder resin 3 connects the electrode active material particles 15 to each other and is fixed to a current collector (not shown). The fine particles of conductive particles 5 are dispersed in the binder resin interior 3. Accordingly, conductivity is imparted to the binder resin itself to secure a conductive path with the active material particles.

Hereinafter, examples will be described in order to describe the present invention in more detail. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited by the embodiments described below. Embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

<Example>

100 weight% of carbon black was added to 100 weight part of melt melted by heating polyvinylidene fluoride, and it stirred, and the electrically conductive particle was disperse | distributed.

Subsequently, a peroxide crosslinking agent was added to the binder resin melt in which the conductive particles were dispersed and crosslinked, followed by melt extrusion and cutting to prepare cylindrical master batch soluble crosslinked binder resin-conductive composite chips having an average diameter of 3 mm. .

Then, 4 parts by weight of the prepared soluble crosslinking master batch binder resin-conductor composite chip and 92 parts by weight of the positive electrode active material particles of the lithium cobalt composite oxide, and 4 parts by weight of the total content of the binder resin and the conductive particles in the slurry. Separately, polyvinylidene fluoride and carbon black are added to N-methyl-2 pyrrolidone (NMP) to disperse, followed by heating and stirring to dissolve the soluble crosslinked binder resin and the separately added polyvinylidene fluoride in the solvent. A positive electrode active material slurry was prepared. The above-described positive electrode active material slurry was applied and dried on a thin film of aluminum (Al) of a positive electrode current collector having a thickness of 20 μm to form a positive electrode active material layer, and then roll press was performed.

Comparative Example

A master batch-type soluble crosslinked binder resin-conductor composite chip was prepared in the same manner as in Example, except that the content of the soluble crosslinked binder resin and the conductive agent was adjusted instead of the chip.

As a result of evaluating the dispersibility of the conductive particles in the positive electrode active material layer prepared according to the above-described Example and Comparative Example, it was found that the Example is superior to the comparative example.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments of the invention and, together with the description of the following preferred embodiments, serve to explain the principles of the invention.

1 is a cross-sectional view schematically showing a conventional secondary battery electrode having an electrode active material layer formed on one surface of a current collector and an enlarged cross-sectional view of the electrode active material layer,

2 is a schematic cross-sectional view of a master batch soluble crosslinked binder resin-conductor composite chip used in the electrode active material layer forming method of the present invention;

3 is an enlarged cross-sectional view of an electrode active material layer formed on a secondary battery electrode of the present invention.

Claims (13)

(S1) dispersing the conductive agent in the melt (melt) of the binder resin (S2) crosslinking the binder resin within a range having solubility in a solvent, and then preparing master batch soluble crosslinked binder resin-conductor composite chips in which a conductive agent is dispersed in the crosslinked binder resin. (S3) dispersing the master batch soluble crosslinked binder resin-conductor composite chips and electrode active material particles in a solvent, and then dissolving the soluble crosslinked binder resin of the composite chips in the solvent to prepare an electrode active material slurry; (S4) A method of forming an electrode active material layer of a secondary battery comprising applying and drying the electrode active material slurry on a substrate. The method of claim 1, The method of forming an electrode active material layer of a secondary battery, characterized in that the conductive agent content of the master batch soluble crosslinked binder resin-conductive composite chip is 10 to 80% by weight. The method according to claim 1 or 2, The binder resin may be polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene oxside, polyacrylonitrile, polymethyl methacrylate, polyacrylamide and A method for forming an electrode active material layer of a secondary battery, characterized in that any one selected from the group consisting of polyacetate or a mixture of two or more thereof. The method according to claim 1 or 2, The conducting agent is any one selected from the group consisting of acetylene black, carbon black, Ketjen black, graphite and mixtures thereof. The method according to claim 1 or 2, The method of forming an electrode active material layer of a secondary battery, characterized in that the average diameter of the master batch soluble crosslinked binder resin-conductor composite chip is 0.1 to 10mm. The method according to claim 1 or 2, The electrode active material particles are a method for forming an electrode active material layer of a secondary battery, characterized in that the positive electrode active material of a lithium composite oxide or a sulfur compound. The method according to claim 1 or 2, The electrode active material particles are any one negative electrode active material selected from the group consisting of lithium metal or lithium alloy, carbon, petroleum coke, activated carbon and graphite. Formation method of the active material layer. The method according to claim 1 or 2, The solvent is acetone or N-methyl pyrrolidone (NMP) electrode active material layer forming method, characterized in that. In the electrode of the secondary battery provided with a current collector and an electrode active material layer formed on at least one surface of the current collector and comprises a conductive agent, electrode active material particles and a crosslinked binder resin, The electrode active material particles are connected to and fixed to each other by a crosslinked binder resin, and the conductive agent is dispersed in the crosslinked binder resin. The method of claim 9, The crosslinked binder resin is polyvinylidene fluoride, (vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyacrylamide And a binder resin, which is any one selected from the group consisting of polyacetate or a mixture of two or more thereof, is crosslinked. The method of claim 9, The conductive material particles are any one selected from the group consisting of acetylene black, carbon black, Ketjen black, graphite and mixtures thereof. The method of claim 9, The electrode active material particles are electrodes of a secondary battery, characterized in that the positive electrode active material of a lithium composite oxide or a sulfur compound. The method of claim 9, The electrode active material particles are any one negative electrode active material selected from the group consisting of lithium metal or lithium alloy, carbon, petroleum coke, activated carbon and graphite. .

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