KR101122938B1 - Preparation method of electrode active material particle - Google Patents

Abstract

The present invention comprises a first step of dispersing the electrode active material powder in a solvent in which the binder is dissolved; A second step of partially evaporating the solvent in the dispersion; Applying a centrifugal force to the obtained product to form an aggregate in which the electrode active material powder and the binder are aggregated to a predetermined size; And a fourth step of forming the granulated electrode active material particles by heat treating the aggregated particles. It provides a method for producing a granulated electrode active material particles, including the electrode active material particles prepared by the above method, the electrode and the secondary battery comprising the electrode active material.

According to the present invention, the electrode active material particles are pasted using a binder and a solvent, and then granulated and heat treated by applying centrifugal force thereto, thereby producing granulated electrode active material particles through a relatively simple method.

Electrode active material, granulation, centrifugal force, secondary battery

Description

Method for producing electrode active material particles {PREPARATION METHOD OF ELECTRODE ACTIVE MATERIAL PARTICLE}

1 is a SEM (Scanning Electron Microscope) photograph of the electrode active material particles prepared by the method of Example 1. (200x magnification)

2 is a SEM (Scanning Electron Microscope) photograph of the electrode active material particles prepared by the method of Example 1. (2000x magnification)

3 is a charge and discharge curve of a lithium ion battery prepared by the method of Example 1.

The present invention relates to a method for producing a granulated electrode active material particles for secondary batteries.

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.

In general, the electrode active material is usually a powdery substance, and the powdery substance is dispersed in a solvent together with a conductive agent and a binder to be slurry, and then the electrode is manufactured by applying a powder onto a current collector such as a metal. At this time, when the particle shape of the powder used as the electrode active material is non-uniform, the formability of the electrode is not good, there is a problem that the performance of the manufactured electrode is lowered. Particularly, when the shape of the active material particles is not spherical but includes a sharp part, the formability of the electrode may not be good, and a separator or the like contacting the electrode may be minutely torn after fabrication of the battery. In addition, the charge density of the surface is increased at the sharp part of the particles, when using such an active material as a negative electrode material, there is a problem that a dendrite crystal of lithium can be formed during charging. This problem becomes even more important when used as an electrode material for a battery for a hybrid electric vehicle (HEV), which requires high power and energy.

Therefore, in order to reduce the problems caused by the morphology of the particles, the electrode active material particles are generally coarsened. In the conventional granulation process, mixing with a material such as pitch, resin, etc., which acts as a binder and making it into a monolith, carbonizing it at a relatively low temperature of about 400 ~ 500 ℃, milling the monolith The granulated particles are prepared by pulverizing to form granulated particles, followed by coating the surface with a coating material and carbonizing at a high temperature of 1000 ° C. or higher. However, this process has the disadvantage of being complicated, time-consuming and expensive.

In the present invention, it was found that the electrode active material particles may be pasted using a binder and a solvent, and then granulated and heat treated by applying centrifugal force to prepare granulated electrode active material particles by a relatively simple method.

Accordingly, an object of the present invention is to provide a method for producing granulated electrode active material particles, an electrode active material prepared by the above method, an electrode including the electrode active material, and a secondary battery having the electrode.

The present invention comprises a first step of dispersing the electrode active material powder in a solvent in which the binder is dissolved; A second step of partially evaporating the solvent in the dispersion; Applying a centrifugal force to the obtained product to form an aggregate in which the electrode active material powder and the binder are aggregated to a predetermined size; And a fourth step of forming the granulated electrode active material particles by heat treating the aggregated particles. It provides a method for producing a granulated electrode active material particles including, and an electrode active material prepared by the method.

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

Hereinafter, the present invention will be described in detail.

<Method of producing granulated electrode active material particles>

The present invention can produce a granulated electrode active material particles through a relatively simple method, as described above

1) a first step of dispersing the electrode active material powder in a solvent in which the binder is dissolved;

2) a second step of partially evaporating the solvent in the dispersion;

3) a third step of applying a centrifugal force to the obtained product to form agglomerated aggregates of the electrode active material powder and the binder to a certain size; And

4) a fourth step of forming the granulated electrode active material particles by heat-treating the aggregated particles;

This is done through.

In the present invention, the binder is not particularly limited as long as it is a tacky material so as to increase the bonding force between the particles of the electrode active material having a non-uniform shape, and non-limiting examples thereof include petroleum pitch, coal pitch, furan resin, phenol resin, gelatin, Cellulose, and the like.

The amount of the binder is preferably in the range of 5% by weight to 50% by weight relative to the weight of the solvent of the first step. If the amount of the binder is too small, the cohesion between the particles of the electrode active material may not be as desired in the subsequent granulation process, and if the amount of the binder is too large, the ratio of the binder to the active material is too large, as an electrode active material There is a risk of deterioration of characteristics.

In the present invention, the solvent serves to provide sufficient fluidity to the paste so that the electrode active material and the binder can be uniformly mixed, and is not particularly limited as long as it is a general solvent known to those skilled in the art, and a non-limiting example is tetrahydrofuran (THF). , Acetone, ethanol, water, methanol, benzene, phenol, cyclohexane, toluene, pyridine, quinoline and the like.

The amount of the solvent is preferably in the range of 50% by weight to 500% by weight based on the weight of the electrode active material. If the amount of solvent is too small, it is difficult to expect uniform mixing because it does not give sufficient fluidity to the electrode active material and the binder. If the amount of solvent is too large, too much time and energy is required to evaporate the solvent in the second step. Can be consumed.

In the present invention, the second step of partially evaporating the solvent in the dispersion prepared in the first step, which can be used for all methods known to those skilled in the art, such as heating or spontaneous evaporation.

However, the residual amount of the solvent after the evaporation is preferably 1% by weight to 20% by weight relative to the weight of the electrode active material, and more preferably 0.5% by weight to 20% by weight. In the case where the solvent is completely removed to become dry, it is preferable that the bonding force between the particles becomes weak and the particles cannot be granulated, so that the solvent is partially removed to maintain a wet and sticky paste state.

In addition, when too much solvent is left and the fluidity is large, it is easy to be dispersed without being bound between particles in the granulation step, so that the solvent needs to be sufficiently evaporated to a high concentration in order to maintain the shape of the granulated particles. have.

In the third step, a strong centrifugal force is applied to the mixture of the electrode active material, the binder, and the solvent in which the solvent is partially removed, and in this process, the electrode active material particles are bound to each other by the binder by the centrifugal force. To form a close assembly. Non-limiting examples of the apparatus used to apply the centrifugal force at this time is a henshel mixer, mechanofusion mixer, v-mixer, w-type mixer, QMY type quick mill. The centrifugal force is preferably applied at 100 to 5000 rpm for 5 to 30 hours.

The size of the particles of the electrode active material granulated by applying the centrifugal force as described above may be adjusted according to the residual amount of the solvent (ie, the viscosity of the paste), rpm during the granulation. That is, when the residual amount of solvent is small and the adhesion between the particles is weak, the particle size tends to be small, and even when the rpm during granulation is increased, the particle size tends to be small.

In the fourth step, the bonding strength may be strengthened by heat-treating the granulated particles in the third step. That is, when the heat treatment in the reducing atmosphere, the binder such as pitch or resin is carbonized, the particles of the electrode active material may be strongly bonded by carbon, when the heat treatment in air, the binder reacts with oxygen to carbon dioxide Since it is burned, only the particles of the electrode active material may be bonded to each other.

Therefore, the heat treatment may be carried out in a reducing atmosphere or air, the heat treatment temperature is preferably 500 ℃ to 1000 ℃.

On the other hand, the electrode active material that can be assembled by the method of the present invention is not only carbon-based negative electrode active material such as graphite-based material, coke, or hard carbon, but also Si, SnO ₂ , 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 can be applied to the negative electrode or positive electrode active material, and is not particularly limited to the above examples Instead, the method of the present invention can be applied to any electrode active material having a non-uniform particle shape.

When preparing the electrode active material particles assembled by the method of the present invention, there are the following advantages.

① It is easy to control the size of granulated particles by controlling the manufacturing conditions properly.

② The assembly process is simple and the cost is low.

<Production of Electrode and Secondary Battery>

According to the present invention, an electrode including the assembled material as an electrode active material can be prepared 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. However, the binder at the time of manufacturing an electrode is different from the binder used at the time of manufacturing the said granulated electrode active material particle | grains.

The paste was prepared by adding and stirring a conductive agent in a weight ratio of 1 to 30% by weight 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 stirring the mixture. After coating, compressing and drying, the laminate electrode is manufactured.

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.

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 non-aqueous electrolyte and, if necessary, other additives may be used as 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

After dissolving 5 g of carbon pitch in 500 g of THF as a solvent, 100 g of hard carbon (Kureha Chemical Industry) having an average particle size of about 10 μm was added and uniformly dispersed. The dispersion was heated to evaporate to a state where the THF solvent remained about 20% of the initial volume to form a paste state. The paste was mixed and granulated by centrifugal force at 1000 rpm for 1 hour using a henshel mixer. Then, the granulated hard carbon particles were obtained by carbonizing the carbon pitch by heat treatment at 1000 ° C. for 1 hour in an N ₂ atmosphere.

As shown in Figure 1, after granulation, it was found that the hard carbon particles had a uniform and nearly spherical shape.

Figure 2 is an enlarged photo of Figure 1, it can be seen that the small particles agglomerate with each other to form a large particle, it was found that the granulation was well made.

The electrode material was used as a cathode, lithium metal foil was used as an anode, and 1 mol of LiPF ₆ -EC: DMC (volume ratio 1: 2) was used as an electrolyte, and a porous polypropylene membrane was used as a separator. The battery was produced and the charge / discharge experiment was performed. The charging and discharging conditions were charged and discharged at a constant current of 0.1 C, and constant voltage charging was performed at 5 mV during charging.

3 shows a charge / discharge curve of a lithium ion battery including the assembled hard carbon as a negative electrode active material. It can be seen that the initial charge and discharge efficiency is about 74% and the discharge capacity is about 260 mAh / g. Compared with the case of Comparative Example 1 below it can be seen that the increase in charge and discharge efficiency.

Comparative Example 1

Using the same hard carbon as in Example 1, but using a non-assembled hard carbon as a negative electrode material, a lithium secondary battery was prepared in the same manner as in Example 1, the charge and discharge experiments were performed in the same manner.

As a result of the charge and discharge test of the secondary battery prepared in Comparative Example 1, the initial efficiency was about 72%, the discharge capacity was about 250mAh / g was expressed.

According to the present invention, the electrode active material particles are pasted using a binder and a solvent, and then granulated and heat treated by applying centrifugal force thereto, thereby producing granulated electrode active material particles through a relatively simple method.

According to the method of the present invention, it is easy to control the size of the granulated particles, there is an advantage that the assembly process is simple and low cost.

Claims (11)

A first step of dispersing the electrode active material powder in a solvent in which the binder is dissolved; A second step of partially evaporating the solvent in the dispersion; Applying a centrifugal force to the obtained product to form an aggregate in which the electrode active material powder and the binder are aggregated to a predetermined size; And a fourth step of forming the granulated electrode active material particles by heat treating the aggregated particles. Method for producing a granulated electrode active material particles, including. The method according to claim 1, wherein the binder is at least one selected from the group consisting of petroleum pitch, coal pitch, furan resin, phenol resin, gelatin, and cellulose. The method of claim 1, wherein the amount of the binder is in the range of 5% to 50% by weight relative to the weight of the solvent in the first step. The method according to claim 1, wherein the solvent is at least one selected from the group consisting of tetrahydrofuran (THF), acetone, ethanol, water, methanol, benzene, phenol, cyclohexane, toluene, pyridine, quinoline. The method of claim 1, wherein the amount of the solvent in the first step is in the range of 50% to 500% by weight based on the weight of the electrode active material. The method of claim 1, wherein the residual amount of the solvent after evaporation in the second step is in the range of 0.5% to 20% by weight based on the weight of the electrode active material. The method according to claim 1, wherein the means for applying the centrifugal force in the third step is one selected from the group consisting of a henssel mixer, a mechanofusion mixer, a v-mixer, a w-type mixer, and a qmy type quick mill. The method of claim 1, wherein the third step is centrifugal force applied for 5 to 30 hours at 100 to 5000 rpm. Electrode active material An electrode active material in which primary particles are bonded by a binder or a residual material after heat treatment of the binder to form secondary particles, wherein the electrode active material prepared by the method of any one of claims 1 to 8. An electrode comprising the electrode active material of claim 9. A secondary battery having the electrode of claim 10.

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