KR101710225B1 - Manufacturing method of cathode for lithium secondary battery - Google Patents

Abstract

More particularly, the present invention relates to a method of manufacturing a positive electrode for a lithium secondary battery, which comprises applying a lithium iron phosphate compound containing a mixture of primary particles and secondary particles having different particle diameters on a positive electrode current collector, And separating the secondary particles to produce a dual coated anode.
A method of manufacturing a positive electrode according to the present invention includes the steps of forming a first cathode material layer containing first primary particles on a cathode current collector by magnetism and forming on the first cathode material layer a lithium iron phosphate compound The second anode material layer containing the secondary particles can be easily separated at a desired position by a simple method using magnetism.
Further, since the rolling on the second cathode material layer including the secondary particles can solve the problem of sticking to the roll during rolling, it is possible to improve the electrode processability

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a positive electrode for a lithium secondary battery,

The present invention relates to a method for producing a positive electrode for a lithium secondary battery, and more particularly, to a method for manufacturing a positive electrode for a lithium secondary battery, which comprises applying a lithium iron phosphate compound containing a mixture of primary particles and secondary particles, And separating the primary particles and the secondary particles to produce a double coated anode.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs, and electric vehicles further expand, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

Among the currently applied secondary batteries, the lithium secondary batteries developed in the early 1990s include a cathode made of a carbon material capable of absorbing and desorbing lithium ions, a cathode made of a lithium-containing oxide, and the like, and a lithium salt dissolved in an appropriate amount in a mixed organic solvent And a non-aqueous electrolytic solution.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium composite metal oxide (Li (Ni - Co - Al) O ₂ , Li (Ni - Co - Mn) O ₂ ) as the cathode active material of the lithium secondary battery, Among them, lithium cobalt oxide has a layered crystal structure, so that it is very easy to store and discharge lithium ions and is used in most lithium secondary batteries at present.

However, lithium cobalt oxide has not been environmentally friendly as a heavy metal, and cobalt as a raw material has been expensive, and research on a new cathode active material that can replace it has been continued. Spinel type lithium manganese oxide (LiMn ₂ O ₄ ) and olivine lithium iron phosphate compound (LiFePO ₂ ), which are inexpensive and highly stable, have been proposed as alternative cathode active materials.

Usually, one kind of the active material contained in the positive electrode is used, but two or more kinds of active materials are generally used. In this case, the active materials having different kinds are randomly applied onto the collector of each electrode. Various application methods have been studied in this regard.

Particularly, for example, a magnetic material such as iron, manganese, cobalt, samarium, and ferrite is included in the active material layer constituting the electrode to improve the bonding property between the electrode active material layers, There were efforts to try.

However, even in this case, the active materials are not applied to a desired level or easily separated from the positive electrode current collector, resulting in problems in adhesion and processability.

SUMMARY OF THE INVENTION The object of the present invention is to provide a positive electrode active material slurry containing a mixture of primary particles and secondary particles having different particle sizes of lithium iron phosphate compound on the positive electrode current collector, To a method for preparing a dual coated anode in a simple manner by easily separating the particles and secondary particles.

According to an aspect of the present invention, there is provided a method for manufacturing a lithium secondary battery, comprising: applying a slurry of a cathode active material containing a mixture of primary particles and secondary particles of a lithium iron phosphate compound on a cathode current collector; Sequentially forming a first cathode material layer including first primary particles and a second cathode material layer including secondary particles by disposing a magnetic material adjacent to the opposite side cathode current collector coated with the cathode active material slurry; And a step of pressing on the second cathode material layer.

Further, the present invention provides a positive electrode produced according to the above-described production method.

In addition, the present invention provides a lithium secondary battery including the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode.

According to the method for producing an anode according to an embodiment of the present invention, a positive electrode active material slurry containing a mixture of primary particles and secondary particles having different particle diameters of lithium iron phosphate compound on the positive electrode current collector is applied as a single layer, The primary particles and the secondary particles can be easily separated at a desired position.

In addition, since the dual coated anode can be easily manufactured by the separation of the primary particles and the secondary particles by the magnetic property, the simplicity of the electrode manufacturing process and the improvement of the productivity can be ensured, .

Further, since rolling on the cathode material layer including the secondary particles can solve the problem of being deposited on the roll during rolling, the electrode processability can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a schematic view illustrating a method of manufacturing an anode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

FIG. 1 schematically shows an embodiment of a method of manufacturing a positive electrode for a lithium secondary battery according to an embodiment of the present invention. It should be understood, however, that the description of the embodiments described hereinbelow and the constitutions depicted in the drawings are only exemplary of the present invention and are not intended to represent all of the inventive concepts of the present invention, It should be understood that there may be various equivalents and variations thereof.

1, a method of manufacturing an anode according to an embodiment of the present invention includes the steps of (i) forming a first primary particle 120 of a lithium iron phosphate compound and secondary particles 130 on a cathode current collector 110, Applying a slurry of the cathode active material comprising a mixture of the cathode active material slurry and the cathode active material slurry; (ii) a second cathode material layer including the first primary particles 120 and a second cathode material layer including the second particles 130 by disposing a magnetic material on the opposite side of the cathode current collector 110 coated with the cathode active material slurry, Sequentially forming a cathode material layer; And (iii) rolling on the second cathode material layer.

The lithium iron phosphate compound according to one embodiment of the present invention is an olivine-type lithium iron phosphate compound having not only high stability but also a metal reactive to a magnet or a magnetic field, and a cathode active material slurry containing the lithium iron phosphate compound When a magnet or a magnetic field is applied to the positive electrode current collector when the negative electrode current collector is coated on the positive electrode current collector, the magnetic field moves toward the magnetic field in response to the magnetic force.

The lithium iron phosphate compound may be represented by the following Formula 1:

Formula 1

Li _{1 + a} Fe _{1 - x} M _x (PO _{4 -b} ) X _b

In this formula,

M is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In,

X is at least one selected from F, S and N,

-0.5? A? + 0.5, 0? X? 0.5, and 0? B?

In particular, the lithium iron phosphate compound is preferably LiFePO ₄ .

In general, the primary particles of the lithium iron phosphate compound are nanoparticles, and when the anode is composed of the first primary particles, there is no problem of electrode adhesion, but there is a disadvantage in that the fast charge / discharge characteristics are inferior. In order to overcome such disadvantages, the first primary particles may be produced in a smaller size. In this case, however, the increase of the specific surface area may cause problems in the process of manufacturing the cathode slurry, for example, There may arise problems such as increase in electric conductivity and decrease in electric conductivity.

Therefore, in order to solve the problem of using only the first primary particles, the anode according to an embodiment of the present invention may include a lithium iron phosphate compound including the first primary particles and the secondary particles together.

According to one embodiment of the present invention, the secondary particles are secondary particles in which two or more second primary particles are aggregated, and may be porous particulate.

That is, the lithium iron phosphate compound composed of the secondary particles contained in the anode has a high porosity in the form of secondary particles in which the secondary primary particles are aggregated, and exhibits high electrical conductivity and density, which are advantages of the primary particles It is possible to satisfy all of the high process efficiency, which is an advantage of secondary particles.

However, the lithium iron phosphate compound composed of the secondary particles may cause a problem of adhesion as the size of the secondary primary particles decreases.

Accordingly, in the present invention, in order to improve the adhesive force, a first cathode material layer containing a lithium iron phosphate compound composed of first primary particles is formed on a cathode current collector, and a second cathode material layer containing second secondary particles on the first cathode material layer By constructing the second anode material layer, it is desired to improve the adhesive force between the cathode current collector and the first cathode material layer, and between the first cathode material layer and the second cathode material layer.

Further, according to an embodiment of the present invention, a slurry of a cathode active material containing a mixture of primary particles and secondary particles having different particle diameters of lithium iron phosphate compounds is coated on the cathode current collector by a single layer, The primary particles and the secondary particles can be easily separated from each other.

In addition, since the anode coated with a simple method can be easily manufactured by separating the primary particles and the secondary particles by the magnetism, simplicity and productivity of the electrode manufacturing process can be improved.

In addition, the method of manufacturing an anode according to an embodiment of the present invention can solve the problem of being deposited on a roll during rolling by performing rolling on the cathode material layer including the secondary particles, so that the electrode processability can be further improved .

The method of manufacturing an anode according to an embodiment of the present invention will now be described in detail. In step (i), the first primary particles 120 of the lithium iron phosphate compound and the secondary particles 130 And applying the slurry of the cathode active material containing the mixture.

According to an embodiment of the present invention, the first primary particles are composed of nanoparticles and have small particle diameters and are dense. Therefore, the primary particles can be easily moved by the magnetic force of a magnet, a magnetic field, or the like,

According to an embodiment of the present invention, it is preferable that an average particle diameter (D ₅₀ ) of the first primary particles contained in the first cathode material layer is 50 to 300 nm, and preferably 100 nm to 250 nm.

 If the average particle diameter of the first primary particles exceeds 300 nm, the adhesion between the positive electrode collector and the first cathode material layer and between the first cathode material layer and the second cathode material layer may be deteriorated.

In the present invention, the average particle diameter (D ₅₀ ) of the particles can be defined as the particle diameter at the 50% of the particle diameter distribution. The average particle diameter (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability.

The first primary particles include a step of mixing and reacting a lithium-containing precursor, an iron (Fe) -containing precursor and a phosphorus (P) -containing precursor, and spray-drying, firing and pulverizing a spray solution containing the obtained reaction product .

Specifically, the first primary particles are prepared by mixing a lithium-containing precursor, an iron (Fe) -containing precursor, and a phosphorus (P) -containing precursor in the presence of a hydrothermal (supercritical) The particles may be milled using conventional milling. At this time, the milling can be performed by using, for example, a flash jet or an Apex Mill.

The lithium-containing precursor may be any one selected from the group consisting of Li ₂ CO ₃ , Li (OH), Li (OH) .H ₂ O and LiNO ₃ , or a mixture of two or more thereof.

The iron (Fe) containing precursor may be a FeSO _4, FeSO ₄ and 7H ₂ O, FeC ₂ O ₄ and 2H ₂ O and FeCl any one selected from the group consisting of _2, or mixtures of two or more of these as a bivalent iron compound have.

The phosphorus-containing precursor may be any one selected from the group consisting of H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ and P ₂ O ₅ , or a mixture of two or more thereof.

The lithium-containing precursor, the iron-containing precursor and the phosphorus-containing precursor may be used in the form of an aqueous solution.

The calcination may be performed at 200 ° C to 700 ° C for 1 hour to 12 hours.

According to an embodiment of the present invention, it is preferable that the average particle size (D ₅₀ ) of the secondary particles is 10 μm to 30 μm.

When the average particle diameter of the secondary particles is less than 10 탆, problems may arise in the processability due to the rolling roll contamination during rolling. When the average particle diameter exceeds 30 탆, due to large average particles, Defects may occur, and there may be a problem of deterioration of electrode conductivity.

Therefore, when the average particle diameter of the secondary particles according to an embodiment of the present invention is in the range of 10 탆 to 30 탆, it is possible to reduce the amount of the binder to maintain electrode uniformity and fairness.

On the other hand, the average particle size (D ₅₀ ) of the second primary particles forming the secondary particles may be 50 nm to 200 nm, preferably 50 nm to 60 nm.

If the average particle diameter of the second primary particles is less than 50 nm, there is a problem that the adhesive strength is lowered. When the average particle diameter of the second primary particles exceeds 200 nm, the inherent material resistance of the lithium iron phosphate compound The electrode resistance is increased and the voltage may be lowered.

Meanwhile, the method for producing the secondary particles may include spray drying and firing a spray solution containing a lithium iron phosphate compound, a carbon precursor, and water in a spray chamber.

At this time, the method of preparing the lithium iron phosphate compound is not particularly limited, and may be prepared by using the first primary particle production method, or by conventional hydrothermal synthesis or supercritical synthesis.

According to one embodiment of the present invention, supercritical synthesis is performed by mixing a lithium-containing precursor, an iron-containing precursor, and a phosphorus-containing precursor to adjust the pH to about 5 to 7, The mixed solution is introduced into the reactor through a continuous process supercritical reactor at a constant rate, for example, at a temperature of about 300 ° C. to 450 ° C. and a pressure of 250 to 300 bar, and the lithium iron phosphate solution Can be manufactured.

According to an embodiment of the present invention, the secondary particles may be formed by a separate granulation process after the preparation of the second primary particles, but it is also possible to form the second primary particles through one process, Can be produced by a method of aggregating primary particles.

Hereinafter, a method of manufacturing a secondary particle according to an embodiment of the present invention will be described by taking a spray drying method as an example.

The method of manufacturing secondary particles according to an embodiment of the present invention may include spraying the spray liquid in a chamber provided in the spray drying equipment, and drying and then firing the spray liquid.

The spray drying apparatus may be a conventional spray drying apparatus, for example, an ultrasonic spray drying apparatus, an air nozzle spray drying apparatus, an ultrasonic nozzle spray drying apparatus, a filter expansion droplet generating apparatus or an electrostatic spray drying apparatus May be used, but is not limited thereto.

According to an embodiment of the present invention, the supply rate of the spray liquid into the chamber may be from 10 ml / min to 1000 ml / min. If the feed rate is less than 10 ml / min, the average particle size of the agglomerated second primary particles becomes small, which makes it difficult to form high-density secondary particles. When the feed rate exceeds 1000 ml / min, It is difficult to realize a desired high-rate characteristic because the particle size is large.

The spray liquid may be sprayed through a disk rotating at high speed in the chamber, and spraying and drying may be performed in the same chamber.

Further, in order to realize the average particle diameter and the internal porosity of the present invention, it may be possible to control spray drying conditions such as the flow rate of the carrier gas, the residence time in the reactor, and the internal pressure.

According to an embodiment of the present invention, the internal porosity of the secondary particles can be controlled by adjusting the drying temperature, and drying can be performed at a temperature of 20 to 300 ° C. However, in order to increase the density of the secondary particles, It is advantageous.

Further, the firing can be carried out at a temperature of 300 ° C to 800 ° C. The calcination may preferably be performed in an inert gas atmosphere such as Ar or N ₂ .

The mixing ratio of the first primary particles and the secondary particles of the lithium iron phosphate compound is preferably 5:95 to 30:70 by weight.

According to an embodiment of the present invention, a cathode active material slurry is prepared by mixing and stirring a solvent, a binder and a conductive agent, if necessary, with a mixture of the first primary particles and the secondary particles of the lithium iron phosphate compound, (Coating) on the substrate.

In addition, the viscosity of the cathode active material slurry including the mixture of the primary particles and the secondary particles of the lithium iron phosphate compound may affect the separation of the primary particles and the secondary particles due to magnetism.

The viscosity of the cathode active material slurry according to an embodiment of the present invention may be in the range of 7000 cps to 25000 cps, preferably 9000 cps to 23000 cps.

The viscosity measurement can be carried out in a conventional manner and can be measured, for example, using a Brookfield viscometer at temperatures between 10 ° C and 60 ° C.

The positive electrode current collector may be any metal that has high conductivity and can easily adhere to the slurry of the positive electrode active material and is not reactive in the voltage range of the battery.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode collector may be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface treated with carbon, nickel, titanium, silver or the like on the surface of aluminum or stainless steel. The cathode current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The binder is a component that assists in bonding of the active material to the conductive material and bonding to the current collector, and may be usually added in an amount of 1 to 30 wt% based on the total amount of the cathode active material slurry. Examples of such binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Sulphonated EPDM, styrene butadiene rubber (SBR) and fluororubber, or a mixture of two or more thereof.

The conductive material may typically be added in an amount of 0.05 to 5% by weight based on the total amount of the cathode active material slurry. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing side reactions with other elements of the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black (super-p), acetylene black; Carbon black such as Ketjen black, channel black, purne black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

In the method of manufacturing an anode according to an embodiment of the present invention, the step ii) includes disposing a magnetic material on the opposite side of the positive electrode current collector coated with the positive electrode active material slurry so that the first positive electrode And a second cathode material layer including a material layer and a secondary particle.

The magnetic material is preferably applied on the positive electrode collector before the positive electrode active material slurry applied on the positive electrode collector is dried, for example, about 5 to 10 minutes before the drying step is performed, preferably the positive electrode active material slurry is applied And can be disposed adjacent to the positive electrode collector.

The magnetic material used according to an embodiment of the present invention may be a permanent magnet, an electromagnet, or the like, or a method of applying a magnetic field may be used. Examples of the permanent magnet include a Ne-Fe-B magnet, an Sm-Co magnet, a neodymium magnet, an Fe-Al-Ni-Co magnet and an oxide magnet. The magnet may be a bulk magnet or a magnetic powder And is not particularly limited as long as it can attract magnet by a magnet tape or the like attached on a support tape.

According to an embodiment of the present invention, the first primary particles are composed of nanoparticles and have small particle diameters and are dense. Therefore, the first primary particles easily react due to magnetism such as a magnet or a magnetic field and move to a side on which the magnetic material is applied, Lt; / RTI >

On the other hand, since the secondary particles have an average particle diameter of 10 to 30 탆 and a particle size of about 10 to 60 times as large as that of the first primary particles, they are weak in magnetic properties relative to the primary particles, The first primary particles can be easily separated from the first primary particles.

That is, the first cathode material layer including the first primary particles 120 and the second cathode material layer including the secondary particles 130 can be sequentially formed on the cathode current collector by the magnetic material.

When the first cathode material layer and the second cathode material layer are formed on the cathode current collector, the magnetic material can be removed from the cathode current collector.

In the method of manufacturing an anode according to an embodiment of the present invention, the step (iii) may include a step of pressing on the second anode material layer.

The rolling may be carried out by a conventional method used in the art, for example, rolling on the second anode material layer using a roll press.

Generally, when a cathode material layer composed of only primary particles is formed on a positive electrode collector and then rolled, primary particles are too fine to be deposited on the roll during rolling, which is not preferable in terms of electrode processability.

However, according to an embodiment of the present invention, after forming a first cathode material layer including first primary particles, forming a second cathode material layer containing secondary particles, drying, and then performing rolling on the second cathode material layer The particles may not be deposited on the roll at the time of rolling according to the optimum size of the secondary particles contained in the second anode material layer, thereby improving the electrode processability.

In addition, the present invention can include a positive electrode produced by the above method.

According to an embodiment of the present invention, a cathode manufactured by the method includes a first cathode material layer including a lithium iron phosphate compound composed of first primary particles on a cathode current collector; And a second cathode material layer including a lithium iron phosphate compound composed of secondary particles formed by aggregating two or more second primary particles on the first cathode material layer.

According to an embodiment of the present invention, the thickness of the first cathode material layer may be 0.1 탆 to 10 탆, and the thickness of the second cathode material layer may be 30 탆 to 60 탆, preferably 50 탆 to 60 탆.

If the second anode material layer is too thick, there may be a problem that the first primary particles separated by the magnetic force are not moved due to the movement of the first primary particles. If the second anode material layer is too thin, Even if the primary particles and the secondary particles are separated due to the primary particles, the problem of the transferability of the secondary particles may be caused.

In addition, according to an embodiment of the present invention, a third cathode material layer including the first primary particles and the secondary particles may be further interposed between the first cathode material layer and the second cathode material layer. At this time, the content of the first primary particles in the third cathode material layer may decrease from the cathode current collector toward the second cathode material layer.

Meanwhile, a lithium secondary battery according to an embodiment of the present invention includes the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode.

As the negative electrode active material, a carbon material, lithium metal, silicon, or tin, in which lithium ions can be occluded and released, can be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

As the binder used for the cathode, those which can be commonly used in the art can be used as the anode. The negative electrode may be prepared by mixing and stirring the negative electrode active material and the additives, and then applying the negative electrode active material slurry to the current collector and compressing the negative electrode active material slurry.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Manufacturing example  1: lithium of the first primary particle Iron phosphate  Preparation of compounds

0.5 mol of iron sulfate (FeSO ₄揃 7H ₂ O), 0.55 mol of phosphoric acid (P ₂ O ₅ ), 1.5 wt% of an aqueous iron sulfate solution containing an antioxidant and 1.5 mol of lithium aqueous solution (LiOH 揃 H ₂ O) 7 was fed through a continuous process supercritical reactor at a temperature of about 375 to 450 ° C. and a pressure of 250 to 300 bar at a constant rate to prepare a LiFePO ₄ solution over a reaction time of several seconds .

The LiFePO ₄ solution was filtered to obtain LiFePO ₄ particles. Purity analysis by XRD analysis and primary particle analysis by SEM were performed. As a result, primary particles of LiFePO ₄ having an average particle diameter of 50 to 300 nm were obtained.

Washing the LiFePO ₄ was then subjected to re-slurry (reslurry) through the purified water, for the sucrose in the carbon precursor to the solution to ₄₁₀₀ parts by weight of LiFePO 4 By weight to obtain a spray solution. The spray solution containing the sucrose-added LiFePO ₄ solution was dried through a spray drier.

After drying, the LiFePO ₄ particles were pulverized using a flash jet or an Apex Mill, sieved, and fired at a temperature of about 700 캜 in an inert atmosphere of nitrogen atmosphere to prepare primary lithium iron phosphate compounds.

Manufacturing example  2: Lithium secondary particles Iron phosphate  Preparation of compounds

0.5 mol of iron sulfate (FeSO ₄揃 7H ₂ O), 0.55 mol of phosphoric acid (P ₂ O ₅ ), 1.5 wt% of an aqueous iron sulfate solution containing an antioxidant and 1.5 mol of lithium aqueous solution (LiOH 揃 H ₂ O) 7 was fed through a continuous process supercritical reactor at a temperature of about 375 to 450 ° C. and a pressure of 250 to 300 bar at a constant rate to prepare a LiFePO ₄ solution over a reaction time of several seconds .

The LiFePO ₄ solution was filtered to obtain LiFePO ₄ particles. Purity analysis by XRD analysis and primary particle analysis by SEM were performed. As a result, primary particles of LiFePO ₄ having an average particle diameter of 50 to 300 nm were obtained.

The washed LiFePO ₄ was reslurry through distilled water, and 4 parts by weight of sucrose as a carbon precursor to 100 parts by weight of LiFePO ₄ was added to the solution to obtain a spray solution. The spray solution containing the sucrose-added LiFePO ₄ solution was dried through a spray drier.

The spray liquid was supplied into a chamber of a spray drying equipment (Ain System product), sprayed in the chamber and dried. At this time, the spray drying conditions were as follows: the drying temperature was 130 ° C., the internal pressure was -20 mbar, the feeding rate was 30 ml / min, and the obtained precursor was fired in air at 800 ° C. to obtain an average particle size (D ₅₀ ) (LiFePO ₄ ) composed of secondary particles having an average particle diameter (D ₅₀ ) of 15 탆 formed by agglomeration of at least two second primary particles.

Example  1: Preparation of positive electrode

Step i) Whole house  Lithium on Iron phosphate  A cathode active material comprising a mixture of primary and secondary particles of a compound The slurry  Applying step

First primary particles and secondary particles of LiFePO ₄ prepared in Preparation Examples 1 and 2 were mixed at a weight ratio of 15:85. Then, 90 wt% of the mixture, 5 wt% of super-p as a conductive material, and polyvinylidene And 5 wt% of fluoride were mixed to prepare a cathode active material slurry.

The above-mentioned cathode active material slurry was applied to an aluminum (Al) thin film as a cathode current collector having a thickness of about 20 mu m.

step ii ) The anode Whole-house On the lower side  A magnetic material is disposed adjacent to the first magnetic particle to form a first Anode material layer  Secondary particles containing secondary particles The anode material layer  Sequentially forming step

Before the cathode active material slurry coating layer was completely dried, Ne-Fe-B based magnets were disposed adjacent to the cathode current collector on the opposite side of the slurry coating layer.

A first cathode material layer comprising LiFePO ₄ made of first primary particles on the cathode current collector by the magnet; And a second cathode material layer containing LiFePO ₄ composed of secondary particles formed by aggregating two or more second primary particles on the first cathode material layer, and then removing the magnetic material.

step iii ) The second Anode material layer  ( press ) Step

A double coated anode was prepared by performing rolling using a roll press on the second anode material layer formed in step ii) above.

Example  2 and 3

A double coated anode was prepared in the same manner as in Example 1 except that primary particles and secondary particles having an average particle size shown in Table 2 were mixed.

Example  4 and 5: Manufacture of lithium secondary battery

≪ Preparation of negative electrode &

As negative active material, 96.3% by weight of carbon powder, 1.0% by weight of super-p as a conductive material and 1.5% by weight and 1.2% by weight of SBR and carboxymethyl cellulose (CMC) as a binder were added to NMP as a solvent to prepare a negative electrode active material slurry . The negative electrode active material slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to produce a negative electrode, followed by roll pressing to produce a negative electrode.

≪ Production of lithium secondary battery >

Aqueous electrolyte was prepared by adding an organic solvent having a composition of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 3: 2: 5 (volume ratio) and 1.0M of LiPF ₆ .

After the polyolefin separator was interposed between the positive electrode and the negative electrode, the electrolyte solution was injected to prepare a lithium secondary battery.

Comparative Example  1: Preparation of positive electrode

LiFePO ₄ has a thickness composed of a first primary particles prepared in Preparation Example 1 to about the cathode current collector is aluminum (Al) thin film of 20㎛ 90% by weight, a super-p of 5% by weight as a conductive material, and 5% by weight of polyvinylidene fluoride as a binder were coated, dried at about 80 캜 for 20 minutes, To prepare a coated anode.

Comparative Example  2: Preparation of anode

LiFePO ₄ has a thickness made of the secondary particles prepared in Preparation Example 2 to the extent the positive electrode collector of aluminum (Al) film of 20㎛ 90% by weight, a super-p of 5% by weight as a conductive material, and 5% by weight of polyvinylidene fluoride as a binder were coated, dried at about 80 캜 for 20 minutes, To prepare a coated anode.

Comparative Example  3 to 5

A double coated anode was prepared in the same manner as in Example 1 except that primary particles and secondary particles having an average particle size shown in Table 2 were mixed.

Experimental Example  One

<Fairness>

In the preparation of the positive electrodes of Examples 1 to 3 and Comparative Examples 1 and 2, the degree of the particles on the rolls during rolling was visually checked to confirm the manufacturing processability, and the results are shown in Table 1 below. In Table 1, "O" indicates that the particles are hardly deposited on the roll at the time of rolling, and "X"

&Lt; Separation degree between first primary particle and secondary particle >

The degree of separation between the first primary particles and the secondary particles by magnetism was visually observed in the positive electrodes of Examples 1 to 3 and Comparative Examples 3 to 5, and "O", "Δ" and "X "Is shown in Table 2 below. In Table 2, "O" represents the case where the first primary particles and the secondary particles are mostly separated, "DELTA" indicates that the first primary particles and the secondary particles are separated but the mixed layer of the first primary particles and the secondary particles is somewhat , And "X" is a case where the first primary particles and the secondary particles are mostly not separated and remain on the cathode current collector in a mixed state of the first primary particles and the secondary particles.

The first anode material layer The second anode layer Fairness Example 1 Primary particle Secondary particle O Comparative Example 1 Primary particle X X Comparative Example 2 Secondary particle X O

Yes First primary particle D50 (nm) Secondary particles D50 (占 퐉) The degree of separation between primary and secondary particles Example 1 50 15 O Example 2 100 15 O Example 3 300 30 O Comparative Example 3 400 30 X Comparative Example 4 200 8 △ Comparative Example 5 400 40 X

As shown in Table 1, the slurry of the cathode active material including the mixture of the first primary particles and the secondary particles was applied and separated by the magnetic material as in Example 1, and the first cathode material layer and the second cathode material layer were sequentially , It can be confirmed that the rolled anode is superior in terms of processability without problems of transferring, compared with Comparative Examples 1 and 2 formed of a single layer.

As shown in Table 2, the degree of separation between the primary particles and the secondary particles according to the average particle diameters of the primary particles and the secondary particles was examined. As a result, the average particle size of the primary particles and the average It was confirmed that the degree of separation by the magnetic material was remarkably excellent.

By adjusting the average particle diameters of the first particles and the secondary particles from the Tables 1 and 2, it is possible to easily manufacture the anode coated with a double layer by a magnetic method by a single step process rather than a two-step process, Can be further improved.

110: positive electrode collector
120: Primary particle
130: secondary particle

Claims (21)

Applying a slurry of a cathode active material comprising a mixture of primary particles and secondary particles of a lithium iron phosphate compound on a cathode current collector;
Sequentially forming a first cathode material layer including first primary particles and a second cathode material layer including secondary particles by disposing a magnetic material adjacent to the opposite side cathode current collector coated with the cathode active material slurry; And
A step of pressing on the second anode material layer
/ RTI &gt;
Wherein the second cathode layer is positioned on the first cathode layer,
(D ₅₀ ) of the first primary particles is 50 nm to 300 nm,
Wherein an average particle diameter (D ₅₀ ) of the secondary particles is 10 탆 to 30 탆.
The method according to claim 1,
Wherein the magnetic material is disposed adjacent to the cathode current collector before the cathode active material slurry is dried.
The method according to claim 1,
Wherein the magnetic material is applied with a permanent magnet and an electromagnet, or a magnetic field is applied thereto.
The method of claim 3,
Wherein the permanent magnet is at least one selected from the group consisting of a Ne-Fe-B magnet, an Sm-Co magnet, a neodymium magnet, an Fe-Al-Ni-Co magnet and an oxide magnet. Way.
The method according to claim 1,
Wherein the secondary particles are aggregated with at least two second primary particles.
The method according to claim 1,
Wherein the lithium iron phosphate compound is represented by the following formula (1): &lt; EMI ID =
Formula 1
Li _{1 + a} Fe _{1 - x} M _x (PO _{4 -b} ) X _b
In this formula,
M is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In,
X is at least one selected from F, S and N,
-0.5? A? + 0.5, 0? X? 0.5, and 0? B?
The method according to claim 1,
Wherein the lithium iron phosphate compound is LiFePO ₄ .
delete delete 6. The method of claim 5,
Wherein an average particle diameter (D ₅₀ ) of the second primary particles is 50 nm to 200 nm.
The method according to claim 1,
Wherein the mixing ratio of the first primary particles to the secondary particles is from 5:95 to 30:70 by weight.
The method according to claim 1,
Wherein the viscosity of the cathode active material slurry is in the range of 7000 cps to 25000 cps.
The method according to claim 1,
The first primary particles include a step of mixing and reacting a lithium-containing precursor, an iron (Fe) -containing precursor and a phosphorus (P) -containing precursor, and spray-drying, firing and pulverizing a spray solution containing the obtained reaction product By weight based on the total weight of the positive electrode.
The method according to claim 1,
Wherein the secondary particles are prepared by spray drying and firing a spray solution containing a lithium iron phosphate compound, a carbon precursor and water in a spray chamber.
An anode prepared according to the method of claim 1.
16. The method of claim 15,
Wherein the anode comprises: a first cathode material layer comprising a lithium iron phosphate compound composed of first primary particles on a cathode current collector; And
And a second cathode material layer comprising a lithium iron phosphate compound composed of secondary particles formed by aggregating two or more second primary particles on the first cathode material layer.
17. The method of claim 16,
Further comprising a third cathode material layer including the first primary particles and the secondary particles between the first cathode material layer and the second cathode material layer.
18. The method of claim 17,
Wherein the content of the first primary particles in the third cathode material layer decreases from the cathode current collector toward the second cathode material layer.
17. The method of claim 16,
Wherein the thickness of the first cathode material layer is 0.1 占 퐉 to 10 占 퐉.
17. The method of claim 16,
Wherein the thickness of the second cathode material layer is 30 占 퐉 to 60 占 퐉.
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode of claim 15.

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