KR100528907B1 - Composition for electrode active material of lithium secondary battery - Google Patents

Abstract

The present invention discloses an electrode active material composition for a lithium secondary battery. The electrode active material composition includes an electrode active material, a conductive agent, a binder, and a solvent, wherein the binder is a result of polymerization of a composition containing a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer, and an amorphous polyethylene oxide. It is done.

In said formula, R <_1> is hydrogen or a methyl group.

When the electrode is formed from the electrode active material composition of the present invention, the following effects can be obtained. First, the interfacial adhesion between the components constituting the electrode active material composition can be improved to induce a decrease in interfacial resistance, thereby high current. Operation at density is possible. Second, by impregnating a large amount of organic electrolyte in the electrode, the ion conductivity is very excellent. In this way, the smooth movement of ions enables uniform electrode reaction, thereby improving the lifespan and capacity of the electrode. Third, since the electrode of the present invention has elasticity, it has a flexible structure. Therefore, it is easy to process into a desired shape.

Description

Composition of electrode active material for lithium secondary battery {Composition for electrode active material of lithium secondary battery}

The present invention relates to a composition for forming an electrode active material of a lithium secondary battery, and more particularly, has excellent ion conductivity characteristics and excellent interfacial adhesion between an electrode plate and an electrolyte, or between an electrode plate and an electrolyte or between an active material and a binder inside the electrode. The present invention relates to a composition used in forming an electrode active material of a lithium secondary battery having excellent charge and discharge characteristics by minimizing resistance.

Recently, with the development of electronic devices, especially portable electronic devices, secondary batteries used as driving power sources of such electronic devices have been remarkably developed. Among the known secondary batteries, lithium secondary batteries are attracting the most attention due to their high operating voltage, long life, high energy density, and the like.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), and the like are used for the positive electrode active material of the lithium secondary battery, and lithium metal, an alloy thereof, and a carbon material are used for the negative electrode active material. Etc. are used. As the electrolyte, an organic liquid electrolyte or a polymer solid electrolyte is used. However, when the organic liquid electrolyte is used as the electrolyte, there are many problems related to safety, such as a risk of leakage and breakage of the battery due to vaporization. In an effort to solve this problem, a polymer solid electrolyte is used instead of a liquid electrolyte.

Conventional lithium secondary batteries have a structure in which a cathode, a polymer electrolyte and an anode are sequentially stacked.

Looking at the conventional manufacturing method of the electrode, an electrode active material composition comprising an electrode active material, a binder, a conductive agent, a solvent and the like is applied on the current collector. The electrode is then completed by drying the resultant.

In the electrode active material composition described above, the binder not only has a great influence on the conductivity of the battery, but also acts as a large variable on the internal resistance during charging and discharging, which greatly affects the efficiency of the battery. Therefore, the binder should not basically act as a factor to increase the binding strength of the active material and the current collector, the active material and the conductive agent and to increase the internal resistance of the battery.

The technical problem to be achieved by the present invention is to provide an electrode active material composition of a lithium secondary battery containing a binder that can minimize the internal resistance between the electrode plate and the electrolyte or the active material and the binder.

In order to achieve the above technical problem, in the present invention, in the electrode active material composition for a lithium secondary battery comprising an electrode active material, a conductive agent, a binder and a solvent,

It provides a lithium secondary battery electrode active material composition characterized in that the binder is a result of the polymerization reaction of a composition comprising a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer, and an amorphous polyethylene oxide.

<Formula 1>

In said formula, R <_1> is hydrogen or a methyl group.

The present invention is characterized by using a product of a polymerization reaction of a hydrophobic trimethylolpropane derivative, a hydrophilic polymer, and an amorphous polyethylene oxide as a binder of the electrode active material composition.

The amorphous polyethylene oxide used in the present invention is a 100% amorphous polymer having a low glass transition temperature of about -110 ° C and excellent flexibility at room temperature. In particular, the ion conductivity of the crystalline polyethylene oxide is about 10 ^-6 S / cm, whereas the ion conductivity of the amorphous polyethylene oxide itself is 10 ^-4 S / cm, it is possible to greatly improve the ion conductivity of the electrode.

It is preferable that the molecular weight of the amorphous polyethylene oxide of the present invention is 1 × 10 ⁴ to 4 × 10 ⁴ , and if the molecular weight of the amorphous polyethylene oxide is out of the above range, the mechanical strength is improved, but the electrolyte moisture-impregnating ability is lowered, which is not preferable. .

As already mentioned, the binder of the present invention is formed by polymerizing a composition comprising a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer and an amorphous polyethylene oxide. In more detail, the binder comprises a homopolymer having a network structure formed by polymerizing a hydrophobic trimethylolpropane derivative represented by Formula 1, a hydrophilic polymer contained in the network structure of the homopolymer, and an amorphous polyethylene oxide.

In addition, the binder of the present invention comprises a copolymer of a network structure formed by copolymerization of a hydrophobic trimethylolpropane derivative represented by Formula 1 with a hydrophilic polymer, and an amorphous polyethylene oxide contained in the network structure, or represented by Formula 1 Consisting of a hydrophobic trimethylolpropane derivative, a hydrophilic polymer and an amorphous copolymer of amorphous polyethylene oxide.

Or a part of the homopolymer of the trimethylolpropane derivative of Formula 1 and the hydrophilic polymer and amorphous polyethylene oxide present between the network structure of the homopolymer,

The other part is composed of a structure in which the trimethylolpropane derivative represented by the formula (1) and the hydrophilic polymer are copolymerized, and the amorphous polyethylene oxide is present in the network structure of the copolymer of the trimethylolpropane derivative and the hydrophilic polymer,

The remaining part consists of a trimethylolpropane derivative represented by Formula 1, a ternary copolymer of a hydrophilic polymer and an amorphous polyethylene oxide.

It is preferable that the mixed weight ratio of the trimethylpropane derivative of Formula 1, the hydrophilic polymer, and the amorphous polyethylene oxide is 3: 6: 1 to 3: 4: 3. Here, when the content of the trimethylpropane derivative for the hydrophilic polymer and the amorphous polyethylene oxide exceeds the above range, the electrochemical properties of the electrode are lowered. On the other hand, when the content of the trimethylolpropane derivative is less than the above range, the mechanical strength of the electrode is lowered, which is not preferable.

The trimethylolpropane derivative is trimethylolpropane triacrylate (TMPTA) or trimethylolpropane trimethacrylate (TMPTMA), as can be seen from the formula (1).

The hydrophilic polymer is not particularly limited. Preference is given to using compounds of the formula (2). These include polyvinylpyrrolidone {poly (vinyl pyrrolidone)}, polyvinyl acetate {poly (vinylacetate)}, polyvinyl acrylate {poly (vinyl acrylate)}, polystyrene, polyacrylonitrile, Polyvinyl sulfone (poly (vinyl sulfone)) and the like.

In addition, the weight average molecular weight of the hydrophilic polymer is preferably 1 × 10 ⁴ to 1 × 10 ⁵ , among which polyvinylpyrrolidone having a weight basis molecular weight of 5 × 10 ⁴ is most preferred.

In the formula, R ₂ is selected from the 2-pyrrolidino carbonyl _{(2-pyrrolidinonyl), OCOCH 3} , OCOCH = CH 2, C 6 H 5, the group consisting of CN and SO ₂ CH = CH _2;

n is a number from 10 to 2000

The manufacturing process of the binder according to the present invention using TMPTA as a trimethylolpropane derivative and PVP as a hydrophilic polymer will be described according to three mechanisms.

According to the first mechanism, the polymerization initiator reacts with ultraviolet light or heat and decomposes to break carbon and carbon double bonds of TMPTA to form new active radicals. Since the TMPTA radicals activated by the polymerization initiator are metastable, they recombine to the linear chain structure of TMPTA to form a stable homopolymer of the network structure. The binder is completed by containing a hydrophilic polymer and amorphous polyethylene oxide in such a network structure.

According to the second mechanism, the TMPTA radicals activated by the polymerization initiator recombine with the PVP radicals and the amorphous polyethylene oxide radicals to form networked terpolymers.

According to a third mechanism, the TMPTA radicals activated by the polymerization initiator recombine with the PVP radicals to form a networked copolymer. The binder is completed by containing amorphous polyethylene oxide in this network structure.

The binder according to the present invention is prepared by the first mechanism, the second mechanism, the third mechanism or the three mechanisms simultaneously proceed as described above. However, since the TMPTA radical is metastable compared to the PVP radical, the homopolymerization reaction between the TMPTA radicals will be superior to the copolymerization reaction between the TMPTA radicals and the PVP radicals and the copolymerization reaction between the TMPTA radicals and the PVP radicals and amorphous polyethylene oxide radicals. It is expected that most of the binders produced according to the mechanism will be. In the binder having such a structure, the homopolymer of the hydrophobic and network-containing trimethylol propane derivative serves to bind the active material and the current collector or the active material and the conductive agent, and the hydrophilic polymer and the amorphous polyethylene evenly distributed in the homopolymer. Oxide plays a role of containing a large amount of electrolyte. Therefore, the binder of the present invention is very suitable for use as a binder for the electrode active material composition.

The electrode active material composition of the present invention contains an electrode active material, a conductive agent, a binder, and a solvent. Each component constituting the composition and its content will be described.

The content of the binder is preferably 5 to 20% by weight based on the total weight of the electrode active material composition. Here, when the content of the binder is less than 5% by weight, the binding force between the current collector and the active material is lowered, thereby reducing battery life and capacity. On the other hand, when the content of the binder exceeds 20% by weight, the specific gravity of the active material in the electrode is reduced, which is not preferable because the energy density of the battery is poor.

As the polymerization initiator, any conventional photopolymerization initiator or thermal polymerization initiator can be used. Especially, benzoin ethyl ether is mainly used as a photoinitiator, and azoisobutyronitrile is used mainly as a thermal polymerization initiator.

As the photopolymerization initiator of the present invention, it is preferable to use a substance which reacts to ultraviolet rays having a wavelength of 350 nm or more. This is because when the photopolymerization uses ultraviolet rays having a wavelength of less than 350 nm, the side reaction of TMPTA occurs before the photopolymerization initiator is decomposed by ultraviolet rays, and thus the object of the present invention cannot be achieved.

Since the content of the polymerization initiator has a great effect on the properties of the electrode, it is preferable to adjust the content within a predetermined range. The content of the preferred polymerization initiator is 0.5 to 20% by weight based on the weight of the trimethylolpropane derivative represented by the formula (1). If the content of the polymerization initiator is less than 0.5% by weight, the polymerization of the trimethylolpropane derivative, the copolymerization of the trimethylpropane derivative and the hydrophilic polymer, or the terpolymerization of the trimethylpropane derivative, the hydrophilic polymer and the amorphous polyethylene oxide may not proceed smoothly. This lowers the mechanical properties of the electrode. On the contrary, if the content of the polymerization initiator exceeds 20% by weight, it is not preferable because the unreacted polymerization initiator remains to lower the electrochemical properties of the electrode.

In the present invention, as the solvent, a non-aqueous solvent, particularly a non-aqueous solvent which is large in polarity with the dielectric constant and easily dissociated is used.

The non-aqueous solvent may be used as long as the phase separation property does not appear when mixed with the compound for forming the polymer matrix of Formulas 1 and 2, amorphous polyethylene oxide, and the like. Among them, propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone, 1,3-dioxolane (1,3-dioxolane), dimethoxyethane ( using at least one solvent selected from dimethoxyethane, dimethylcarbonate and diethylcarbonate, tetrahydrofuran (THF), dimethylsulfoxide and polyethyleneglycol dimethylether. It is preferable. And the content of the solvent is the usual level used in the lithium secondary battery.

Any conductive agent can be used as long as it is conventionally used in forming the electrode, and the content thereof is also at a normal level.

In some cases, the electrode active material composition of the present invention may further include an additive such as a plasticizer. The plasticizer forms pores in the electrode so that the electrolyte solution is easily moistened later. Specific examples thereof include dibutyl phthalate and N-methylpyrrolidone (NMP).

Hereinafter, a method of manufacturing an electrode according to the present invention will be described.

First, the electrode active material, the conductive agent, the trimethylolpropane derivative of the formula (1), the hydrophilic polymer, and the amorphous polyethylene oxide are added at a predetermined mixing weight ratio and mixed again.

A slurry is prepared by adding a binder-forming compound, that is, a trimethylolpropane derivative of Formula 1, a hydrophilic polymer, and a solvent for dissolving amorphous polyethylene oxide to the mixture.

A polymerization initiator is added to the slurry to form an electrode composition. The polymerization initiator is preferably added in this last step. If the polymerization initiator is added before the slurry forming step, the polymerization reaction occurs in advance due to the heat generated in the mixing process, and thus it is impossible to obtain a desired object.

The composition is applied and dried on the current collector. The method of applying the composition to the current collector is not particularly limited. In the present invention, the composition is applied using a doctor blade.

The electrode is completed by performing ultraviolet or thermal polymerization reaction on the resultant product.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Example

17.5 g of LiCoO ₂ and 1.7 g of a conductive agent were added to the clean glass jar, and the mixture was sufficiently mixed. To this, 4 g of PVP, 3 g of TMPTA, and 3 g of amorphous PEO are added, followed by 5 ml of EC / PC in a 1: 1 volume ratio and 6 g of butyl phthalate (DBP). This mixture was mixed well using a mixer. 0.2 g of AIBN was added to the mixture, followed by remixing.

The aluminum current collector was evenly spread over the Teflon substrate, and the slurry was cast to a thickness of about 200 μm using a doctor blade. After casting, it was dried to remove acetonitrile in the result. Then, a cathode was prepared by performing a thermal polymerization reaction on a hot plate at about 80 ° C. for 10 minutes.

18 g of MCMB and 1.2 g of a conductive agent were added to the clean glass bottle, and the mixture was sufficiently mixed. 4 g of PVP, 3 g of TMPTA, and 3 g of amorphous PEO were added, followed by 5 ml of EC / PC and 6 g of DBP in a 1: 1 volume ratio. This mixture was mixed well using a mixer. 0.2 g of AIBN was added to the mixture, followed by remixing to form a slurry.

The copper current collector was evenly spread over the Teflon substrate and then the slurry was cast to a thickness of about 200 μm using a doctor blade. After casting, it was dried to remove acetonitrile in the result. Subsequently, the anode was prepared by performing a thermal polymerization reaction on a hot plate at about 80 ° C. for 10 minutes.

4 g of PVP, 3 g of TMPTA, and 3 g of amorphous PEO were added to a clean glass bottle, and 2.5 ml of EC / PC and 6 g of DBP were added in a 1: 1 volume ratio. The mixture was sufficiently mixed using a mixer, and then 0.1 g of benzoin ethyl ether (BEE) was added and mixed sufficiently.

The mixture was cast on a Teflon substrate to a thickness of about 100 μm using a doctor blade. After casting, it was dried to remove the acetonitrile contained in the result. Thereafter, ultraviolet (350 nm) was irradiated to perform a photopolymerization reaction for about 5 minutes to complete the polymer electrolyte.

The polymer solid electrolyte was placed on both sides of the anode, and thermal polymerization was performed. Then, a cathode was disposed on the polymer electrolyte to complete a lithium ion polymer battery.

Comparative Example 1

A lithium ion polymer battery was completed in the same manner as in Example, except that amorphous polyethylene oxide was not used in the preparation of the cathode, anode, and polymer electrolyte.

Comparative Example 2

A lithium ion polymer battery was completed in the same manner as in Example, except that polyethylene oxide was used instead of amorphous polyethylene oxide when preparing the cathode, the anode, and the polymer electrolyte.

In order to evaluate the characteristics of the battery prepared according to the above method, charging and discharging were performed at 0.3 C using a maccor charger.

It was found that the battery manufactured according to the above example had a low charge voltage and a high discharge voltage as compared with the case of Comparative Examples 1-2. This means that the internal resistance of the cathode and anode electrodes of the embodiment is small, so that the electrode reaction occurs smoothly.

In addition, the capacity of the battery prepared according to the embodiment through the above-described charge and discharge test was (120) Wh / kg was better than that of Comparative Example 1-2 [110 Wh / kg].

On the other hand, the life characteristics of the lithium ion polymer battery prepared according to Examples and Comparative Examples 1-2 were investigated.

As a result, it was confirmed that the lithium ion polymer battery of Example was superior in life characteristics as in the case of Comparative Example 1-2.

When the electrode is formed from the electrode active material composition of the present invention, the following effects can be obtained.

First, the interfacial adhesion between the components constituting the electrode active material composition can be improved to induce a decrease in interfacial resistance. This enables operation at high current densities.

Second, by impregnating a large amount of organic electrolyte in the electrode, the ion conductivity is very excellent. In this way, the smooth movement of ions enables uniform electrode reaction, thereby improving the lifespan and capacity of the electrode.

Third, since the electrode of the present invention has elasticity, it has a flexible structure. Therefore, it is easy to process into a desired shape.

Claims (10)

In the electrode active material composition for lithium secondary batteries containing an electrode active material, a conductive agent, a binder and a solvent, The binder is a result of the polymerization reaction of a composition containing a trimethylolpropane derivative represented by the general formula (1), a hydrophilic polymer, and an amorphous polyethylene oxide. <Formula 1> In said formula, R <_1> is hydrogen or a methyl group. The method of claim 1, wherein the trimethylolpropane derivative represented by Formula 1 forms a homopolymer having a network structure (homopolymer), The hydrophilic polymer and the amorphous polyethylene oxide is present in the homopolymer of the network structure, the electrode active material composition for a lithium secondary battery. The method of claim 1, wherein the trimethylolpropane derivative represented by the formula (1) and the hydrophilic polymer is copolymerized to form a trimethylolpropane derivative-hydrophilic polymer copolymer having a network structure, An amorphous polyethylene oxide is present in the trimethylolpropane derivative-hydrophilic polymer copolymer of the network structure, the electrode active material composition for a lithium secondary battery. The electrode active material composition for a lithium secondary battery according to claim 1, wherein the trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer, and an amorphous polyethylene oxide are terpolymerized. The trimethylolpropane derivative represented by Formula 1 is a homopolymer having a network structure, and the hydrophilic polymer and the amorphous polyethylene oxide are present in the homopolymer of the network structure. , The other part is a trimethylolpropane derivative represented by the formula (1) and a hydrophilic polymer is copolymerized to form a trimethylolpropane derivative-hydrophilic polymer copolymer having a network structure, the amorphous polyethylene oxide is trimethylolpropane derivative-hydrophilic of the network structure Present in the copolymer of the polymer, The remaining part is a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer and an amorphous polyethylene oxide terpolymer is characterized in that the lithium secondary battery electrode active material composition. According to claim 1, wherein the hydrophilic polymer is a lithium secondary battery electrode active material composition, characterized in that the compound of formula (2). <Formula 2> In the formula, R ₂ is selected from the 2-pyrrolidino carbonyl _{(2-pyrrolidinonyl), OCOCH 3} , OCOCH = CH 2, C 6 H 5, the group consisting of CN and SO ₂ CH = CH _2; n is a number from 10 to 2000 2. The lithium secondary of claim 1, wherein the weight average molecular weight of the hydrophilic polymer is 1 × 10 ⁴ to 1 × 10 ⁵ , and the weight average molecular weight of amorphous polyethylene oxide is 1 × 10 ⁴ to 4 × 10 ⁴ . Battery electrode active material composition. The electrode active material composition for a lithium secondary battery according to claim 1, wherein the hydrophilic polymer is polyvinylpyrrolidone. The electrode active material composition of claim 1, wherein the mixed weight ratio of the trimethylolpropane derivative represented by Chemical Formula 1, the hydrophilic polymer, and the amorphous polyethylene oxide is 3: 6: 1 to 3: 4: 3. . The method of claim 1, wherein the binder is a lithium secondary battery electrode active material composition, characterized in that 5 to 20% by weight based on the total weight of the electrode active material composition.