KR20080038806A - Enhancement of electro-conductivity of conducting material in lithium ion battery - Google Patents

Abstract

A lithium secondary battery is provided to reduce electric resistance increment attendant on use of excess binder by treating a conducting material with UV-ozone, and thus increase discharge capacity. A lithium secondary battery includes a positive electrode and a negative electrode produced from electrode compositions for manufacturing the positive electrode or negative electrode of the lithium secondary battery, wherein the electrode composition comprises a positive electrode or negative electrode active material, a conducting material capable of providing electron movement routes to the positive electrode or negative electrode active material, and a binder. The conducting material is treated with ultraviolet ray-ozone.

Description

Lithium secondary battery including a conductive agent with improved electrical conductivity {enhancement of electro-conductivity of conducting material in lithium ion battery}

The present invention relates to the improvement of the electrical conductivity of the conductive material (conducting material) included in the electrode mixture in the production of the positive or negative electrode of a lithium secondary battery, by treating the material used as the conductive agent with UV-Ozone The present invention relates to increasing the discharge capacity of a lithium secondary battery by increasing the electrical conductivity of the conductive agent.

Today, various portable devices are used due to the development of the information and communication industry, and various types of batteries are used as an energy supply source for such portable devices. As technology development and demand for portable devices increase, the demand for secondary batteries is increasing as an energy source, and lithium secondary batteries having high energy density and voltage are commercially used among secondary batteries.

The lithium secondary battery uses an intercalation-deintercalation reaction of lithium ions during charging and discharging. The lithium secondary battery is composed of an anode using graphite as an active material in a basic configuration, a cathode using a lithium transition metal oxide as an active material, a separator, and an electrolyte of an organic solvent. Recently, tin or silicon-based composites having a larger capacity than graphite have attracted attention as a negative electrode active material.

However, since the positive electrode or the negative electrode active material of the lithium secondary battery is basically non-conductive, a conductive network is formed by coating a conductive agent on the surface of spherical active material particles to increase its conductivity.

Recently, silicon, which has attracted attention as a negative electrode active material of a lithium secondary battery, has a 4200 mA · h / g which is much higher than the maximum theoretical capacity of the conventional graphite-based active material, 372 mA · h / g, and thus has a limited capacity increase. It is attracting attention as a material that can replace the active material.

However, the silicon-based negative electrode active material has a large volume expansion of 200-300% during the occlusion-release reaction of lithium ions, so that the electrode mixture of the negative electrode applied during the continuous charging and discharging is detached from the copper film, which is the current collector, or the contact interface between the negative electrode active materials. As the charge and discharge cycle proceeds due to the increase in resistance due to the change in capacity, the capacity is drastically lowered, and thus the cycle life is shortened. Due to these problems, polyvinylidene fluoride, styrene-butadiene rubber, and the like, which are conventional binders for graphite-based negative electrode active materials, may have a desired effect. Hard to get In addition, when an excessive polymer is used as a binder to reduce the volume change during charging and discharging, the detachment of the active material from the current collector can be reduced, but the electrical resistance of the electrode mixture is increased by the polymer having the electrical insulation used as the binder. Reducing the amount of the active material relatively causes a problem of capacity reduction.

In connection with this, there have been attempts to use polyvinyl alcohol as a binder of an electrode of a lithium ion battery, and polyvinyl alcohol-based binders have superior adhesive strength as compared to conventional binders (Japanese Patent Application Laid-Open Nos. 1999-67216 and 2004-134206). ). However, polyvinyl alcohol does not uniformly apply the active material to the copper film, which is a current collector, and the desorption phenomenon between the electrode mixture and the current collector remains a problem.

Therefore, in a lithium ion battery using a silicon-based negative active material, an overweight binder is used to withstand a large volume change of the negative electrode active material during charge and discharge. This prevents an increase in electrical resistance and maintains charge and discharge efficiency. There is a need for the technology, a method for solving this problem has been developed to apply a new material as a conductive agent, or increase the dispersibility of the conductive agent to increase the contact area with the active material.

For example, Korean Patent Application Publication No. 2003-0013553 proposes the introduction of carbon nanotubes as a conductive agent, since sulfur, which is an insulator, cannot be used alone in manufacturing lithium / sulfur secondary batteries.

In addition, Korean Patent Application Publication No. 2005-0118864 discloses a planetary mixer for increasing the contact area between the negative electrode active material and the conductive material and achieving uniform mixing in a lithium secondary battery using carbon black as a conductive material. A method of manufacturing a lithium secondary battery by dispersing in a solvent using a mixer and then adding a binder is proposed.

On the other hand, Korean Patent No. 268,750 describes ozone treatment of carbon black as a positive electrode conductive agent of a lithium secondary battery, and Japanese Patent Laid-Open No. 2004-039443 discloses dispersibility by UV treatment of a conductive agent. A method of improving is disclosed.

However, the above-mentioned inventions do not mention the negative electrode conductive agent when the excess binder is used in the silicon-based negative electrode active material.

The present invention has been made in view of the above-mentioned conditions, and in the secondary battery using a carbon-based conductive agent, an increase in the case of using an excessive amount of binder by UV-Ozone treatment of the conductive agent. It is an object of the present invention to provide a secondary battery having a reduced electrical resistance and an increased discharge capacity.

Another object of the present invention is to provide a secondary battery by dramatically reducing the weight ratio of the conductive agent introduced in the conventional secondary battery by reducing the electrical resistance of the conductive agent by ultraviolet-ozone treatment of the carbon-based conductive agent.

The above and other objects of the present invention can be achieved by the present invention described below.

In order to achieve the above object, the present invention is prepared from an electrode mixture for manufacturing a positive electrode or a negative electrode of a lithium secondary battery comprising a positive electrode or a negative electrode active material, a conductive agent and a binder for providing a movement path of electrons to the positive or negative electrode active material It provides a lithium secondary battery comprising a positive electrode and a negative electrode, characterized in that the conductive agent is UV-ozone treated.

The electrode mixture may include 65 to 85% by weight of the positive electrode or negative electrode active material, 10 to 30% by weight of the binder and 0.1 to 5% by weight of the conductive agent.

Preferably, the electrode mixture may include 0.1 to 1% by weight of a conductive agent.

In addition, the conductive agent may be at least one selected from the group consisting of vapor growth carbon fiber (VGCF), natural graphite, artificial graphite, petroleum pitch, coal-based pitch and carbon nanotubes.

The negative active material may be one selected from the group consisting of silicon, silicon / graphite, and silicon oxide / graphite.

The binder may be one selected from the group consisting of a fluorine-based polymer, an aqueous polymer of styrene-butadiene rubber, and a polyvinyl alcohol polymer.

In particular, the present invention is 65 to 85% by weight of one negative electrode active material selected from the group consisting of silicon, silicon / graphite and silicon oxide / graphite; 0.1-5% by weight of conductive agent subjected to UV-ozone treatment of at least one selected from the group consisting of vapor growth carbon fiber (VGCF), natural graphite, artificial graphite, petroleum pitch, coal-based pitch and carbon nanotubes for 60 to 180 minutes ; And a negative electrode prepared from an electrode mixture comprising 10 to 30 wt% of a binder selected from the group consisting of a fluorine-based polymer, an aqueous polymer of styrene-butadiene rubber, and a polyvinyl alcohol polymer. do.

In this case, the conductive agent may be included in an amount of 0.1 to 1% by weight.

Hereinafter, the present invention will be described in detail.

The present invention is a lithium secondary battery consisting of a positive electrode / electrolyte / negative electrode as an electrode mixture for the production of the positive electrode or negative electrode, characterized in that for use as a conductive agent for providing electrical conductivity to the positive electrode or negative electrode active material UV-ozone treatment do.

In particular, the lithium secondary battery of the present invention is characterized in that a silicon compound such as lithium / silicon-graphite, lithium / silicon oxide-graphite is used as the negative electrode active material.

In addition, the conductive agent used in the lithium secondary battery of the present invention is a carbon-based conductive agent, carbon black, Vapor Grown Carbon Fiber (VGCF), single or multi-layered carbon nanotubes (single / multi-walled carbon nanotube) ) May be used alone or in combination.

In the present invention, the conductive agent is used after the ultraviolet-ozone treatment. The ultraviolet-ozone generating apparatus is used for the ultraviolet-ozone treatment, and the treatment time is preferably 60 to 180 minutes. As the treatment time increases, the electrical resistance of the electrode decreases, but there is no significant difference in the electrical resistance from the treatment time of 180 minutes or more. Therefore, ultraviolet-ozone treatment for 60 to 180 minutes is preferred for optimal reduction of electrical resistance. In particular, when the UV-ozone treatment time is 180 minutes, the VGCF can bring about evenly miscible with the silicon-based active material as compared with the 60-minute treatment.

Ultraviolet-ozone treatment disperses the conducting agent in a shallow and wide area such as petri-dish, and then evenly distributes the conducting agent in a UV-ozone generator for 20 minutes, and removes the conducting petri dish in which the conducting agent is dispersed. The agent is remixed and evenly dispersed and processed again in a UV-ozone generator. The above operation is repeated so that the conductive agent is evenly UV-ozone treated, and the sum of repeated UV-ozone treatment times is 60 to 180 minutes.

Ultraviolet-ozone treatment of the conductive agent firstly removes impurities scattered in the conductive agent to increase the purity of the conductive agent. Next, when mixed with an electrode active material and a binder as an electrode mixture, the dispersibility of a electrically conductive agent is improved. As an effect, when the content of the binder in the electrode mixture is increased, the electrical resistance of the electrode mixture may be increased by increasing the binder, which is an insulating material. The UV-ozone treated conductive agent has improved purity and dispersibility. The electrical resistance of the electrode mixture can be reduced.

In addition, although the conventional conductive agent was used in a weight ratio of 3 to 20% of the negative electrode or the positive electrode mixture, the conductive agent treated with the UV-ozone treatment of the present invention can reduce the amount of the conductive agent to within 5%, preferably within 1%. .

The present invention specifically comprises 65 to 85% by weight of one negative electrode active material selected from the group consisting of silicon, silicon / graphite and silicon oxide / graphite; 0.1 to 5 wt% of a conductive agent obtained by UV-ozone treatment of at least one selected from the group consisting of steam growth carbon fiber (VGCF), natural graphite, artificial graphite, petroleum pitch, coal-based pitch and carbon nanotubes for 60 to 180 minutes %; And a negative electrode prepared from an electrode mixture comprising 10 to 30 wt% of a binder selected from the group consisting of a fluorine-based polymer, an aqueous polymer of styrene-butadiene rubber, and a polyvinyl alcohol polymer. do.

Silicon-based negative electrode active materials such as silicon, silicon / graphite, or silicon oxide / graphite have a large volume change due to the absorption and desorption of lithium ions, thereby using an excessive amount of binder, thereby increasing the electrical resistance and decreasing the charge / discharge capacity of the battery. There is a problem. Electrode mixture for the preparation of the negative electrode of the present invention by using a carbon-based material, such as steam growth carbon fiber (VGCF), natural graphite, artificial graphite, petroleum pitch, coal-based pitch or carbon nanotubes UV-ozone treatment to use as a conductive agent Compared with the conductive agent, even a small amount of 0.1 to 5% by weight, more preferably 1% by weight or less, can achieve desired levels of electrical conductivity and charge and discharge capacity. Accordingly, the present invention provides a lithium secondary battery including a silicon-based negative electrode of silicon, silicon / graphite, or silicon oxide / graphite, which can obtain desirable electrical conductivity and charge / discharge capacity.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to Examples.

Example 1

VGCF as a conductive agent was dispersed in a petri dish shallowly and evenly, and then treated with an ultraviolet-ozone generator (UVO cleaner, 144AX-220, Jelight Company Inc, USA) for 20 minutes, and the petri dish with the conductive agent dispersed therein. After taking out, the conductive material was mixed again and dispersed, and then treated again in an ultraviolet-ozone generator. The above operation was repeated so that the sum of repeated UV-ozone treatment times was 180 minutes. The conductive agent and the polyvinyl alcohol (PVA) binder were mixed, coated on copper foil, and dried to obtain a "binder + conductor" film. The electrical resistance of the "binder + conductive" film was measured and the results are shown in Table 1 below.

Next, a negative electrode mixture was prepared by mixing 85% of a silicon-based negative active material as a weight ratio, 14.25% of a polyvinyl alcohol (PVA) having a polymerization degree of 3,000 or more as a binder, and 0.75% of the UV-ozone treated conductive agent VGCF, to prepare the negative electrode mixture. Was applied to a copper film as a negative electrode current collector to prepare a negative electrode. The resistance value of the negative electrode was measured and shown in Table 1 below.

 Example 2

Except for using acetylene black as the conductive agent, a conductive agent, a "binder + conductive" film and a negative electrode were prepared in the same manner as in Example 1. The electrical resistance of the "binder + conductive" film and the negative electrode was measured. The results are shown in Table 1 below.

Example 3

A conductive agent, a "binder + conductor" film and a negative electrode were prepared in the same manner as in Example 1 except that VGCF and a multilayer carbon nanotube were mixed 1: 1. The electrical resistance of the "binder + conductive" film and the negative electrode was measured. The results are shown in Table 1 below.

Comparative Example 1

The same method as in Example 1 was used except that VGCF without UV-ozone treatment was used as 5% of the total weight of the negative electrode mixture, and 85% silicon-based negative active material and 10% polyvinyl alcohol were used as the "binder + conductive agent". "Film and negative electrode were prepared. The electrical resistance of the "binder + conductive" film and the negative electrode was measured. The results are shown in Table 1 below.

Comparative Example 2

A "binder + conductor" film and a negative electrode were prepared in the same manner as in Comparative Example 1 except that acetylene black, which had not been subjected to UV-ozone treatment, was used as 5% of the total weight of the negative electrode mixture. The electrical resistance of the "binder + conductive" film and the negative electrode was measured. The results are shown in Table 1 below.

division Electrical resistance (Ω / sq.) Example 1 Binder + Challenger 5.18 x 10 ⁹ electrode 4.03 x 10 ² Example 2 Binder + Challenger 6.85 x 10 ⁹ electrode 8.03 x 10 ² Example 3 Binder + Challenger 2.79 x 10 ⁸ electrode 2.13 x 10 ² Comparative Example 1 Binder + Challenger 6.29 x 10 ¹⁰ electrode 3.67 x 10 ² Comparative Example 2 Binder + Challenger 9.54 x 10 ¹⁰ electrode 7.98 x 10 ²

In Examples 1 and 2, the weight ratio of the conductive agent was 0.75%, and the amount of the conductive agent was smaller than the weight ratio 5% in Comparative Examples 1 and 2, but as a result of measuring the electrical resistance of the manufactured negative electrode, the difference in electrical resistance was 10. The difference was not significant within%.

In addition, according to the results of confirming the effect of ultraviolet-ozone treatment using a conductive agent subjected to ultraviolet-ozone treatment in a weight ratio of 3% with respect to the negative electrode mixture and in the same manner as in Example 1, a film made by mixing a PVA binder and a conductive agent The surface electrical resistance of 4.68 x 10 ⁶ Ω / sq with UV-ozone treatment and 6.43 x 10 ⁸ Ω / sq without treatment. And the surface electrical resistance of the cathode is 1.31 x 10 Ω / sq., 3.08 x 10 ² Ω / sq. The UV-ozone treatment resulted in a reduction of the surface electrical resistance of about 10 ^1.5-2 .

According to the present invention, in the electrode mixture of the lithium secondary battery using the silicon-based negative active material and the polymer binder to which the carbon-based conductive agent treated with UV-ozone is treated, the impurities of the conductive agent are reduced by the ultraviolet-ozone treatment, and the conductive agent in the electrode mixture. Even if the amount of dispersion is increased and the amount of use thereof is greatly reduced compared to the conventional conductive agent, the contact area between the silicon-based negative active material and the conductive agent can be increased. Therefore, the electrical resistance of the electrode mixture can be reduced.

In addition, it is possible to use a silicon-based negative electrode active material and an excessive polymer binder. Therefore, according to the present invention, even when using a silicon-based negative active material, it is possible to reduce the volume expansion of the silicon-based active material due to the occlusion and release of lithium ions.

Although the present invention has been described with reference to the above-described embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and it is obvious that such changes and modifications belong to the appended claims. will be.

Claims (8)

A lithium secondary battery comprising a cathode and an anode prepared from an electrode mixture for preparing a cathode or an anode of a lithium secondary battery comprising a cathode or an anode active material, a conductive agent and a binder for providing electrons to the cathode or an anode active material. The lithium secondary battery, characterized in that the conductive agent is ultraviolet-ozone treatment. The method of claim 1, The electrode mixture is a lithium secondary battery comprising 65 to 85% by weight of the positive electrode or negative electrode active material, 10 to 30% by weight of the binder and 0.1 to 5% by weight of the conductive agent. The method of claim 2, The electrode mixture is a lithium secondary battery, characterized in that it comprises 0.1 to 1% by weight of a conductive agent. The method according to any one of claims 1 to 3, The conductive agent is a lithium secondary battery, characterized in that at least one selected from the group consisting of steam growth carbon fiber (VGCF), natural graphite, artificial graphite, petroleum pitch, coal-based pitch and carbon nanotubes.  The method according to any one of claims 1 to 3, The anode active material is a lithium secondary battery, characterized in that one selected from the group consisting of silicon, silicon / graphite and silicon oxide / graphite. The method according to any one of claims 1 to 3, The binder is a lithium secondary battery, characterized in that one kind selected from the group consisting of a fluorine-based polymer, an aqueous polymer of styrene-butadiene rubber and a polyvinyl alcohol polymer. 65 to 85% by weight of one negative electrode active material selected from the group consisting of silicon, silicon / graphite and silicon oxide / graphite; 0.1 to 5% by weight of a conductive agent subjected to UV-ozone treatment of at least one selected from the group consisting of VGCF, natural graphite, artificial graphite, petroleum pitch, coal pitch and carbon nanotube for 60 to 180 minutes ; And Lithium secondary, characterized in that it comprises a negative electrode prepared from an electrode mixture comprising 10 to 30% by weight of a binder selected from the group consisting of a fluorine-based polymer, an aqueous polymer of styrene-butadiene rubber and a polyvinyl alcohol polymer battery. The method of claim 7, wherein The conductive agent is a lithium secondary battery, characterized in that contained 0.1 to 1% by weight.