KR100889451B1 - Preparation method of electrode active material comprising nano particle with advanced dispersibility - Google Patents

Abstract

The present invention is a first step of mixing the electrode active material secondary particles formed by the aggregation of nano-sized primary particles and the powder having a Mohs hardness of 8 or more; And a second step of milling and dispersing the mixture of the first step in a dry state. It provides a method for producing a nanoparticle electrode active material including improved dispersibility. In addition, the present invention is an electrode active material in which the nano-sized primary particles are aggregated to form secondary particles, the electrode active material, characterized in that the powder having a Mohs hardness of 8 or more is distributed in the inner void or the outer surface of the secondary particles, and the electrode comprising the same; It provides a secondary battery.

The present invention can improve the dispersibility of the electrode active material powder by milling the electrode active material containing nanoparticles in a dry state with the particles of high hardness.

Secondary Battery, Electrode Active Material, Dispersibility, Milling

Description

Manufacturing method of electrode active material containing nanoparticles with improved dispersibility {PREPARATION METHOD OF ELECTRODE ACTIVE MATERIAL COMPRISING NANO PARTICLE WITH ADVANCED DISPERSIBILITY}

1 is a scanning electron microscope (SEM) photograph of a nano-sized Li ₄ Ti ₅ O ₁₂ material that is not dispersed.

2 is a nano-sized Li ₄ Ti ₅ O ₁₂ dispersed in carbon black and alumina according to the method of Example 1 SEM (Scanning Electron Microscope) picture of the material.

The present invention relates to a method for producing an electrode active material including nanoparticles, and to a method for improving dispersibility of an electrode active material during electrode production.

Recently, with the development of portable devices such as mobile phones, notebook computers, camcorders, etc., demand for secondary batteries such as Ni-MH (Ni-MH) secondary batteries and lithium secondary batteries is increasing. In particular, lithium secondary batteries using lithium and nonaqueous electrolytes have been actively developed due to the high possibility of realizing small, lightweight and high energy density batteries. Generally, a transition metal oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ is used as a cathode material of a lithium secondary battery, and lithium metal or carbon is used as an anode material. This is used, and a lithium secondary battery is comprised using the organic solvent which contains lithium ion as electrolyte between two electrodes.

Recently, nano-sized particles have begun to attract attention as electrode active materials of lithium secondary batteries. Examples of such materials include Si, SnO ₂ , Mn ₃ O ₄ , Fe ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ , CoO, Co ₃ O _4, etc., which are anode active materials, and LiCoO ₂ , LiMnO ₂ , LiNi _0.5 Mn _0.5 , which are cathode active materials. O ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li (MnNiCo) _1/3 O ₂ and the like, these nano-sized particles have the advantage of greater capacity or speed characteristics than the existing micron size active material. In spite of these advantages, since the size of the nanoparticles is much smaller than that of conventional materials, various problems occur when manufacturing electrodes using the same. In the general electrode manufacturing process, a slurry is prepared by dispersing a carbon black, which is a conductive material, and a binder, which is a high molecular material, in a solvent, and it is very difficult to mix carbon black and a binder when the size of the active material is reduced to nano size. Lose. This is because conventional mixers are designed to be suitable for mixing micron-sized active material particles, which makes it difficult to give enough energy to mix nanomaterials. In addition, when the size is reduced to nano size has a problem that the surface area is increased to increase the amount of the solvent required to produce a slurry (slurry) required for electrode production.

In general, nano-sized particles have a disadvantage that it is difficult to disperse them in a solvent because the surface area is large and the surface energy is high so that the particles adhere to each other. Therefore, in order to disperse these nano-sized particles in a solvent, attempts have been made to lower the surface energy of the particles by adding a surfactant to the solvent. However, the addition of these surfactants not only causes additional cost increase but also has a problem of lowering the adhesion of the resulting electrode.

In order to solve this problem, there is a technique of dispersing the active material, carbon black, binder, etc. of the nanoparticles in a solvent and then mixing them using a bead mill for milling them into beads of a small size. In this case, the slurry solution is not only buried in the ball that enters the bead mill, but it has to be replaced by abrasion of the ball. In addition, a large bead mill is required for mass production in a factory. It has the disadvantage of installing a lamp. In addition, when dispersed using a bead mill (bead mill) has a problem that the impact of the beads may collapse the structure of the active material itself may affect the resulting electrode properties.

In the present invention, it was found that by dispersing the electrode active material containing nanoparticles in a dry state with the particles of high hardness, it is possible to improve the dispersibility of the electrode active material powder.

Accordingly, an object of the present invention is to provide a method for dispersing an electrode active material including nanoparticles together with particles of high hardness in a dry state, an electrode active material prepared by the method, an electrode including the electrode active material and a secondary battery. do.

The present invention comprises a first step of mixing the electrode active material secondary particles formed by agglomeration of nano-sized primary particles and the powder having a Mohs hardness of 8 or more; And a second step of milling and dispersing the mixture of the first step in a dry state. It provides a method for producing a nanoparticle electrode active material including improved dispersibility.

The present invention also provides an electrode active material in which nano-sized primary particles are aggregated to form secondary particles, wherein the powder having a Mohs hardness of 8 or more is distributed in the inner voids or outer surfaces of the secondary particles.

The present invention also provides an electrode including the active material and a secondary battery provided with the electrode.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by milling in a dry state with a powder having an Mohs hardness of 8 or more in dispersing secondary active particles formed by agglomeration of nano-sized primary particles.

The method of the present invention

1) a first step of mixing the electrode active material secondary particles formed by agglomeration of nano-sized primary particles and the powder having a Mohs hardness of 8 or more; And

2) a second step of milling and dispersing the mixture of the first step in a dry state; It includes.

In the first step, the nano-sized electrode active material primary particles preferably have an average particle size in the range of 1 nm to 800 nm, and are not limited to specific ones as long as they are used as electrode active materials of secondary batteries. Typical examples include Si, SnO ₂ , Mn ₃ O ₄ , Fe ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ , CoO, Co ₃ O ₄ , LiCoO ₂ , LiMnO ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiMn ₂ O ₄ , LiNiO ₂ , Li (MnNiCo) _1/3 O _2, and the like.

Since the nano-sized primary particles have a high surface energy due to their large specific surface area, they tend to aggregate with each other in order to be stable. Therefore, as shown in FIG. 1, primary particles are aggregated to form large secondary particles. The secondary particles in which the primary particles are agglomerated may have a size in the range of 0.5 μm to 500 μm before the dispersion by the method of the present invention, and 0.1 μm in the average particle size after the dispersion by the method of the present invention. It may have a size in the range of ~ 200㎛. In the case of an electrode active material made of nanoparticles, due to its small size, it is often used as an active material by forming some aggregates artificially.However, according to the dispersion method of the present invention, dispersion of nanoscales in which nanoparticles are dispersed one by one is difficult. Rather, the dispersibility is improved to facilitate slurrying in the form of some aggregates.

Therefore, the present invention provides a method for milling and dispersing secondary particles, the primary particles are agglomerated in a dry state, at this time, it can be used with a powder of 50 nm to 100㎛ size of Mohs hardness 8 or more. Preferably, a powder having a size of 100 nm to 1 μm may be used. The powder having a Mohs hardness of 8 or more serves as a micro-sized ball during milling of the electrode active material.

As an example, when Al ₂ O ₃ powder is added during milling of nano sized Li ₄ Ti ₅ O ₁₂ powder, the Al ₂ O ₃ powder is interposed between the nano sized Li ₄ Ti ₅ O ₁₂ particles and mechanically It has the effect of milling to improve the dispersing properties and at the same time to crush the agglomerates produced by the cohesion between nano-size particles. At this time, the temperature inside the reactor is increased due to the mechanical energy, thereby removing the moisture.

Since the powder having a Mohs hardness of 8 or more is not recovered even after dispersion and is included in the electrode active material together, the powder is preferably electrochemically stable, and it is preferable that the material is high in hardness and inexpensive as described above. Non-limiting examples include SiO ₂ , ZrO ₂ , Al ₂ O ₃ , TiO ₂ , TiO ₂ , BaTiO ₃ , TiN, and the like. At this time, the mixing ratio of the powder having Mohs hardness of 8 or more is preferably in the range of 1% by weight to 20% by weight based on the total weight. If the amount of the powder is less than the above range, the effect of the present invention cannot be expected. If the amount of the powder exceeds the above range, the amount of the electrode active material decreases, which may adversely affect the electrochemical properties such as a decrease in capacity. to be.

The method of milling in a dry state in the second step is not limited to specific ones as long as it is known to those skilled in the art as a milling method using no balls or beads, and non-limiting examples thereof include mechanofusion mixer, henshel mixer, planetary mill, jar mill, etc.

In the mechanofusion mixer or henssel mixer used in the present invention, a blade having a specific shape in a vessel rotates at a high speed in a vessel without using a ball or the like to dry disperse the powder charged therein. As a device to make the impact energy applied to the active material is not so large, there is almost no collapse of the crystal structure of the active material. In addition, since it is dispersed in a dry state, there is also an advantage that the electrode active material can be used immediately after dispersion without further processing.

The milling in the dry state is preferably carried out for 30 minutes to 10 hours at a speed of 100 to 5000 rpm.

On the other hand, the method of the present invention may be to mix the conductive agent together in the first step.

The conducting agent used is not particularly limited as long as it is known to those skilled in the art as a material having excellent electrical conductivity, and non-limiting examples thereof include carbon black such as super P, Denka black, ketjenblack, acetylene black, or small particles of Timrex KS-. Artificial graphite or natural graphite such as KS-6 can be used. In the present invention, the mixing ratio of the conductive agent is preferably 0.1% to 20% by weight based on the total weight.

As described above, by further dispersing the conductive agent together with the active material by the method of the present invention, the conductive agent can be evenly distributed on the surface of the active material, thereby improving the conductivity.

In addition, since the particles of high hardness and carbonaceous material are distributed on the surface of the secondary particles of the nanoparticle electrode active material, the affinity with the slurry solvent may be improved by improving the surface properties of the electrode active material.

In the present invention, by treating the electrode active material containing the nanoparticles in a simple method, it can be provided in an easy state for electrode production. This treatment can be applied regardless of the material properties of the nanoparticles and has the advantage of low additional process cost. In addition, the advantages of the method described in the present invention are as follows.

1) Since the particles treated by the method of the present invention are well dispersed in the surface of the particles, the surface properties of the particles are improved, so that the mixing is easy, the dispersion is excellent, and the conductivity of the electrode is excellent.

2) The amount of solvent required for slurry production can be reduced.

3) The wettability of the nanoparticles is improved due to the change in the surface properties of the nanoparticles.

4) Unlike conventional milling, there is an advantage that the structure of the nano-sized active material does not collapse.

In the electrode active material according to the present invention, nano-sized primary particles are aggregated to form secondary particles, and powders having a Mohs hardness of 8 or more may be distributed in the inner voids or the outer surfaces of the secondary particles. In addition, the electrode active material may be one in which a conductive agent is further distributed on the surface, and the secondary particles formed by agglomeration of nano-sized primary particles by the method of the present invention are mixed with a powder having a Mohs hardness of 8 or more and dried. It may be milled and dispersed in the state.

As described above, when the powder and / or the conductive agent having a Mohs hardness of 8 or more are distributed on the outer surface of the secondary particles, the surface properties of the secondary particles, which are nanoparticle aggregates, are improved, so that the wettability of the particles is improved and the solvent of the electrode slurry is improved. Also, the effect of improving the affinity can be expected.

The primary particles of the electrode active material may have a size of an average particle diameter of 1 nm to 800 nm, and the secondary particles in which the primary particles are aggregated may have a size of 0.1 μm to 200 μm.

According to the present invention, an electrode including a material which improves dispersibility by milling in a dry state together with a powder having a Mohs hardness of 8 or more can be manufactured by a method known to those skilled in the art. For example, in addition to using the material as an active material according to the present invention, the electrode may further use a conductive agent for providing electrical conductivity and a binder that enables adhesion between the material and the current collector. The paste was prepared by adding and stirring a conductive agent in a weight ratio of 1 to 30 wt% and a binder in a weight ratio of 1 to 10% with respect to the electrode active material prepared by the above method, and then adding the mixture to a dispersion solvent. It is applied to the current collector, compressed and dried to prepare a laminate electrode.

The conducting agent generally uses carbon black. Products currently marketed as conductive agents include acetylene black series (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (Armak Company ), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by MMM).

Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) or copolymers thereof, cellulose, and the like, and representative examples of the dispersant are isopropyl alcohol and N-methylpyrrolidone. (NMP), acetone and the like.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the paste of the material is easily adhered and is not reactive in the voltage range of the battery. Representative examples include meshes, foils, and the like, such as aluminum or stainless steel.

On the other hand, when the material in which the conductive agent is dispersed together by the method of the present invention is used as the electrode active material, it can be reduced by the amount of the conductive agent dispersed with the active material in the amount of the conductive agent generally added during electrode production.

The present invention also provides a secondary battery comprising the electrode of the present invention. The secondary battery of the present invention can be produced using a method known in the art, and is not particularly limited. For example, the separator may be placed between the positive electrode and the negative electrode to add a nonaqueous electrolyte. In addition, the electrode, the separator and the nonaqueous electrolyte and, if necessary, other additives, may be those known in the art.

In addition, a porous separator may be used as a separator in manufacturing a battery of the present invention, and for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

The nonaqueous electrolyte of the secondary battery that can be used in the present invention may include a cyclic carbonate and / or a linear carbonate. Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), and the like. Examples of the linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), and the like. In addition, the nonaqueous electrolyte of the secondary battery of the present invention contains a lithium salt together with the carbonate compound. Specific examples of lithium salts include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ .

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited thereto.

Example 1

5 wt% of carbon black and 5 wt% of alumina particles were mixed in a Li ₄ Ti ₅ O ₁₂ powder having a primary particle size of 500 nm, and then, the mixture was milled for 1 hour at 1500 rpm using a mechanofusion mixer. The secondary particle size before milling had an average particle diameter of 15 mu m and was dispersed about 5 mu m after milling. At this time, even in the case of particles finely dispersed on a nano scale by the dispersion treatment, the particles themselves have a cohesive force to some extent, so that small particles may be aggregated together to form secondary particles. It has a size on the order of μm. The shape of the material obtained by the milling is shown in FIG. 2. It was found that the small carbon particles were evenly distributed on the surface of the Li ₄ Ti ₅ O ₁₂ powder.

When the electrode was prepared using the above materials, the amount of NMP, which is a solvent required for slurry production, was reduced by about 20 to 30% compared to that of Comparative Example 1. That is, the amount of NMP required to have a viscosity similar to that of Comparative Example 1 is small. In general, the carbon black added during slurry production is composed of agglomerates of fine particles and has a large number of open pores therein, and thus shows a low density, and when mixed with a solvent, the solvent enters the pores. The result is more than the amount of solvent required for the operation. However, in the case of the electrode active material dispersed by the present invention, the amount of carbon black administered during the slurry production is reduced by the amount of carbon black dispersed together, and the carbon black dispersed together with the electrode active material is dispersed in a small amount to the surface of the active material. Since it is evenly dispersed in not only excellent wettability, but also no pores, the amount of solvent consumed can be reduced.

In addition, the non-uniform aggregates were not visually observed in the manufactured electrode, indicating that the mixing characteristics were significantly improved.

Comparative Example 1

An electrode was manufactured in the same manner as in Example 1, except that Li ₄ Ti ₅ O ₁₂ , which was not dispersed, was used.

The shape of the particle | grains before a dispersion process is shown in FIG. The size of the Li ₄ Ti ₅ O ₁₂ primary particles is about 500 nm, it can be seen that they are aggregated to form large particles. In the case where the dispersion treatment was not carried out, the agglomeration of the active materials was excessive when the slurry was prepared, so that the surface of the electrode was uneven and had an uneven shape.

The present invention can improve the dispersibility of the electrode active material powder by milling the electrode active material containing nanoparticles in a dry state with the particles of high hardness.

In the present invention, by treating the electrode active material containing the nanoparticles by a simple method to improve dispersibility, it can be provided in an easy state for manufacturing the electrode, which can be applied regardless of the material properties of the nanoparticles, and the cost is low Holding In addition, it is possible to improve the wettability of the nanoparticles due to changes in the surface properties of the particles.

Claims (16)

Primary particles having an average particle diameter of 1 nm to 800 nm are formed by agglomeration , and secondary electrode particles having a first average particle diameter are selected from the group consisting of SiO ₂ , ZrO ₂ , Al ₂ O ₃ , BaTiO ₃ , and TiN. A first step of mixing a powder having a Mohs hardness of 8 or more; And Including a second step of milling and dispersing the mixture of the first step in a dry state, Method of producing a nanoparticle electrode active material dispersed so as to have a second average particle diameter smaller than the first average particle diameter . delete The method of claim 1, wherein the secondary particles before dispersion have a first average particle diameter of 0.5 μm to 500 μm. The method of claim 1, wherein the secondary particles after dispersion have a second average particle diameter of 0.1 μm to 200 μm. The method of claim 1, wherein the powder having a Mohs hardness of 8 or more has a size of 50 nm to 100 μm. delete The method of claim 1, wherein the mixing amount of the powder having a Mohs hardness of 8 or more is in the range of 1 wt% to 20 wt% of the total weight of the mixture. The method according to claim 1, wherein the milling in the dry state is performed for 30 minutes to 10 hours at a speed of 100 to 5000 rpm. The method according to claim 1, wherein the conductive agent is mixed together in the first step. The method of claim 9, wherein the amount of the conductive agent added is in the range of 0.1 wt% to 20 wt% based on the total weight of the mixture. An electrode active material in which primary particles having an average particle diameter of 1 nm to 800 nm are aggregated to form secondary particles having an average particle size of 0.1 μm to 200 μm, and are composed of SiO ₂ , ZrO ₂ , Al ₂ O ₃ , BaTiO ₃ , and TiN. Electrode active material, characterized in that the powder of at least one Mohs hardness of 8 or more selected from the group is distributed in the inner void or the outer surface of the secondary particles. The electrode active material according to claim 11, wherein a conductive agent is further distributed on the surface. delete At least one Mohs hardness selected from the group consisting of SiO ₂ , ZrO ₂ , Al ₂ O ₃ , BaTiO ₃ , TiN, and secondary particles having an average particle diameter formed by aggregation of primary particles having an average particle diameter of 1 nm to 800 nm. 8 or more powder and mixed and, during the milling, the dispersion in the dry state is less than on the first average particle size of the second average particle size is a characteristic of the electrode active material so as to have distributed. An electrode comprising the electrode active material of any one of claims 11, 12 or 14. A secondary battery having the electrode of claim 15.

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