KR20150025047A - Hollow lithium transition metal oxide particles, preparation method thereof, and cathode active material for lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to hollow lithium transition metal oxide particles and to a method for producing the same. The hollow lithium transition metal oxide particles include lithium transition metal oxide particles consisting of secondary particles produced by cohering two or more primary particles, wherein a hollow core unit is included in each secondary particle. The hollow lithium transition metal oxide particles according to an embodiment of the present invention consist of secondary particles produced by cohering primary particles and respectively have a hollow part therein. When the same is applied to a positive pole, the secondary particles are rolled so that the hollow parts are destroyed and the secondary particles are broken. Accordingly, a spring back phenomenon is decreased, and adhesion and processability can be improved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow lithium transition metal oxide particle, a method for producing the same, and a cathode active material for a lithium secondary battery comprising the same. BACKGROUND ART [0002] Hollow lithium transition metal oxide particles,

The present invention relates to a hollow lithium transition metal oxide particle, a method for producing the same, and a cathode active material for a lithium secondary battery comprising the hollow lithium transition metal oxide particle.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

As a negative electrode active material of such a lithium secondary battery, a carbon material is mainly used, and use of lithium metal, a sulfur compound, a silicon compound, a tin compound and the like is also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and a lithium- ₂ ) is also considered.

Although LiCoO ₂ has excellent physical properties such as excellent cycle characteristics and is widely used at present, it is low in safety, is expensive due to the resource limit of cobalt as a raw material, and has a limitation in using it as a power source for fields such as electric vehicles. LiNiO ₂ is difficult to apply to actual mass production process at a reasonable cost due to its characteristics depending on the production method thereof, and lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have poor cycle characteristics.

Recently, a method of using a lithium transition metal phosphate as a cathode active material has been studied. Lithium transition metal phosphates are classified into Nasicon structure Li _x M ₂ (PO ₄ ) ₃ and Olivine structure LiMPO ₄ , which are superior to conventional LiCoO ₂ . Li ₃ V ₂ (PO ₄ ) ₃ is known among the nasicon compounds, and LiFePO ₄ and Li (Mn, Fe) PO ₄ are the most widely studied compounds of the olivine structure.

Among the above olivine structures, LiFePO ₄ has a high capacity density of ~3.5 V vs. 3.6 g / cm ³ and a theoretical capacity of 170 mAh / g, which is superior to that of cobalt (Co) Fe is used as a raw material, it is highly likely to be applied to a cathode active material for a lithium secondary battery in the future.

However, such LiFePO ₄ has the following problems, and thus has a practical limit.

First, since LiFePO ₄ has a low electron conductivity, there is a problem that when LiFePO ₄ is used as a cathode active material, the internal resistance of the battery increases. As a result, the polarization potential is increased at the time of closing the battery circuit, thereby reducing the battery capacity.

Second, since LiFePO ₄ has a lower density than a conventional cathode active material, there is a limitation that the energy density of the battery can not be sufficiently increased.

Thirdly, since the olivine crystal structure in the state of lithium removal is very unstable, there is a problem in that the movement path of the portion where lithium disappears from the crystal surface is blocked, and the loading / desorption rate of lithium is delayed.

Accordingly, a technique has been proposed in which the crystal diameter of olivine is reduced to nano-level to shorten the travel distance of lithium ions to increase the discharge capacity.

However, when the electrode is manufactured using the olivine particles having such a fine particle size, the spring back phenomenon easily causes the separation from the positive electrode current collector, and a large amount of binder should be used to reduce such desorption .

However, when a large amount of binder is used, there may arise a problem that the resistance increases and the voltage decreases, and the mixing time of the slurry is prolonged and the process efficiency is lowered.

Accordingly, the present invention has been made in order to solve the above problems.

A first aspect of the present invention is to provide a hollow lithium transition metal oxide particle having improved adhesion strength so as to minimize separation of a cathode active material from a cathode current collector and capable of improving electrode processability in the production of an anode.

A second object of the present invention is to provide a process for preparing the hollow lithium transition metal oxide particles.

A third object of the present invention is to provide a cathode active material comprising the hollow lithium transition metal oxide particles.

A fourth object of the present invention is to provide a positive electrode comprising the positive electrode active material and a method of manufacturing the positive electrode.

A fifth aspect of the present invention is to provide a lithium secondary battery including the positive electrode.

In order to solve the above problems, the present invention provides a lithium transition metal oxide particle represented by the following Chemical Formula 1, wherein the lithium transition metal oxide particle is composed of secondary particles formed by aggregation of two or more primary particles, There is provided a hollow lithium transition metal oxide particle comprising a hollow core portion:

Formula 1

Li _{1 + a} M _{1 - x} M 2 _x (PO _{4 -b} ) X _b

In this formula,

M1 represents at least one element selected from Fe, Mn, Co, Ni, Cu, Zn and Mg;

M2 represents at least one element selected from the elements selected from Groups 2 to 15 except for M1,

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

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

In addition, the present invention provides a method for preparing a spraying composition comprising: (i) supplying a spraying liquid containing a lithium transition metal oxide, a carbon precursor and water into a spraying chamber; And (ii) spray-drying and firing the spray liquid in the chamber. The present invention also provides a method for producing hollow lithium transition metal oxide particles.

The present invention also provides a cathode active material comprising the hollow lithium transition metal oxide particles.

The present invention also provides a positive electrode comprising the positive electrode active material.

In addition, the present invention provides a method for manufacturing a lithium secondary battery, comprising: forming a cathode active material coating layer on a cathode current collector by coating and drying a cathode active material composition comprising the hollow lithium transition metal oxide particles, a binder, and a conductive material; And rolling the cathode active material coating layer.

Further, the present invention provides a lithium secondary battery comprising the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode.

According to one embodiment of the present invention, the hollow lithium transition metal oxide particles are formed of secondary particles in which two or more primary particles are aggregated, and a hollow is formed in the hollow lithium transition metal oxide particles, Since the secondary particles collapse as the hollow collapses, the springback phenomenon is reduced, thereby improving the adhesion and the processability.

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 cross-sectional view of a hollow lithium transition metal oxide particle according to an embodiment of the present invention.
2 is a cross-sectional SEM photograph of the hollow lithium iron phosphate (LiFePO ₄ ) particles prepared in Example 1 of the present invention.
3 is a cross-sectional SEM photograph of the anode (Example 2) including the hollow lithium iron phosphate oxide (LiFePO ₄ ) prepared in Example 1 of the present invention.
4 shows a cross-sectional SEM photograph (Comparative Example 2) of a positive electrode containing lithium iron phosphate (LiFePO ₄ ) produced in Comparative Example 1 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.

A hollow lithium transition metal oxide particle according to an embodiment of the present invention includes a lithium transition metal oxide particle represented by the following formula (1), wherein the lithium transition metal oxide particle is a secondary particle formed by aggregation of two or more primary particles And may include a hollow core portion within the secondary particle:

Formula 1

Li _{1 + a} M _{1 - x} M 2 _x (PO _{4 -b} ) X _b

In this formula,

M1 represents at least one element selected from Fe, Mn, Co, Ni, Cu, Zn and Mg;

M2 represents at least one element selected from the elements selected from Groups 2 to 15 except for M1,

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

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

1, a hollow lithium transition metal oxide particle according to an embodiment of the present invention includes secondary particles formed by aggregation of two or more primary particles, and a hollow core portion is formed inside the secondary particles .

The lithium transition metal oxide may include secondary particles composed of primary particles of several tens nanometers to several hundreds of nanometers.

In general, when the lithium transition metal oxide particles are in the form of agglomerated secondary particles of two or more primary particles, in the case of the lithium transition metal oxide particles, the secondary particles are spring back when applied to the anode, A phenomenon may occur.

Here, the spring back phenomenon refers to an elastic phenomenon in which an object is deformed by applying pressure and then restored to its original state when the pressure is removed.

That is, when a cathode is prepared by coating and rolling a cathode active material composition containing a lithium-transition metal oxide particle on a cathode current collector, if secondary particles of the lithium-transition metal oxide after rolling are dense, A springback phenomenon to be recovered by the particle phenomenon may occur, which may cause a gap (gap) between the particle and the particle. Due to the occurrence of such pores, the adhesion with the positive electrode current collector is reduced, so that desorption can occur. As a result, the gap acts as a resistor and the electrode conductivity can be weakened.

In order to solve such a problem, a large amount of binder should be used. However, when a large amount of binder is used, the resistance may increase and the voltage may decrease.

The hollow lithium transition metal oxide particles according to an embodiment of the present invention are formed into hollows so that when the hollow lithium transition metal oxide particles are rolled in application to the anode, the hollow lithium transition metal oxide particles collapse, So that the shape of the secondary particles is lost and can be converted into primary particles. Accordingly, the spring back phenomenon is reduced, thereby improving the adhesive force and the process efficiency.

That is, the hollow lithium transition metal oxide particle according to an embodiment of the present invention includes a hollow core portion having a shape of secondary particles in which two or more primary particles are aggregated, and thus has high electrical conductivity and density, which are advantages of primary particles It is possible to improve the adhesive force and satisfy all of the high process efficiency, which is an advantage of the secondary particles.

Therefore, when the hollow lithium transition metal oxide particles according to an embodiment of the present invention are used, the capacity, lifetime characteristics and energy density of the electrode and the battery can be maximized.

In the hollow lithium transition metal oxide particle according to one embodiment of the present invention, it is preferable that the diameter of the hollow core portion is 4 탆 to 10 탆, preferably 6 탆 to 10 탆.

If the diameter of the hollow core portion is less than 4 탆, springback phenomenon occurs after the rolling process of the electrode, so that the adhesion force with the positive electrode current collector is decreased to cause desorption, and when the diameter exceeds 10 탆, Which can lead to problems in fairness and productivity.

In addition, according to an embodiment of the present invention, the measurement of the diameter of the hollow core portion is not particularly limited, but may be measurable by, for example, an electron microscope (SEM).

The lithium transition metal oxide according to an embodiment of the present invention is an olivine structure and may be an oxide represented by the above formula (1).

Further, the lithium transition metal compound may preferably be a lithium iron phosphate represented by the following formula (2), more preferably LiFePO ₄ :

(2)

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 average particle diameter (D ₅₀ ) of the hollow lithium transition metal oxide particles is preferably in the range of 15 탆 to 20 탆.

According to an embodiment of the present invention, the average particle size (D ₅₀ ) of the primary particles is preferably in the range of 10 nm to 500 nm, preferably 100 nm to 400 nm.

If the average particle size of the primary particles is too small, the processability is not feasible. If the average particle size is more than 500 nm, the formability of the lithium transition metal oxide particles is deteriorated. A difficult problem may arise.

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 lithium transition metal oxide particle according to an embodiment of the present invention may be a secondary particle in which two or more primary particles are aggregated, and may be a porous particle.

When the lithium transition metal oxide particles are in the form of primary particles and used as a positive electrode active material of a lithium secondary battery, there is no problem of electrode adhesion, but the lithium secondary battery has a disadvantage in that the rapid charge / discharge characteristics are inferior. In order to overcome such disadvantages, the diameter of the primary particles may be reduced to a smaller diameter. In this case, however, the increase of the specific surface area causes problems in the process of manufacturing the anode 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 such primary particles, the lithium transition metal oxide particles according to one embodiment of the present invention may be in the form of secondary particles in which two or more primary particles are aggregated.

In addition, in the lithium transition metal oxide particle according to an embodiment of the present invention, a carbon coating layer may be further formed on the primary particles.

When the carbon coating layer is further included, the carbon coating layer may be coated so as to surround the primary particles of the lithium transition metal oxide particles.

According to an embodiment of the present invention, by forming a carbon coating layer on the primary particles, the electric conductivity can be further improved.

The carbon coating layer preferably includes a saccharide. The saccharide may include any one selected from the group consisting of glucose, fructose, galactose, sucrose, maltose, and lactose, or a mixture of two or more thereof.

The thickness of the carbon coating layer may be 5 nm to 100 nm, preferably 5 nm to 50 nm. If the thickness of the carbon coating layer is less than 5 nm, the effect of increasing the electrical conductivity due to the carbon coating layer may be insignificant. On the other hand, when the thickness of the carbon coating layer is more than 100 nm, the resistance of the lithium ion mobility may be increased and the resistance may increase.

According to an embodiment of the present invention, the lithium transition metal oxide particles preferably have a specific surface area (BET) of 30 m 2 / g or less, and preferably 6 m 2 / g to 30 m 2 / g.

If the specific surface area of the lithium transition metal oxide particle is out of the above range, the adhesion of the electrode may deteriorate. If the specific surface area of the lithium transition metal oxide particle is out of the above range, an increase in the initial irreversible capacity Which is undesirable.

According to an embodiment of the present invention, the specific surface area of the lithium-transition metal oxide particles can be measured by a BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by a BET 6-point method by a nitrogen gas adsorption / distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

Meanwhile, in order to exhibit excellent electrical conductivity, stability of crystal structure, and high bulk density even when the secondary particles are disintegrated in the production of the electrode and returned to the primary particle formation in the present invention, the primary particles in the crystallized state are used To form secondary particles. That is, it is preferable that the primary particles each independently have an olivine-type crystal structure.

In view of facilitating the return to the primary particles as the secondary particles are collapsed, the primary particles are aggregated by physical bonding such as van der Waals force rather than chemical bonding such as covalent bond or ionic bond, .

The method for preparing lithium transition metal oxide particles according to an embodiment of the present invention includes the steps of (i) supplying a spray liquid containing a lithium transition metal oxide, a carbon precursor, and water into a spray chamber; And (ii) spray drying and firing the spray liquid in the chamber.

According to one embodiment of the present invention, in the cathode active material, the secondary particles of the lithium-transition metal oxide particles may be formed by a separate granulation process after the primary particles are produced. Also, it can be produced by a method of producing primary particles through one process and coagulating the primary particles.

Hereinafter, a method of preparing a lithium-transition metal oxide particle according to an embodiment of the present invention will be described by taking a spray-drying method as an example.

 The method for producing the lithium-transition metal oxide particle according to an embodiment of the present invention will be described in detail. In the step (i), the spray liquid containing the lithium-transition metal oxide, the carbon precursor and water may be supplied into the atomizing chamber have.

Specifically, the lithium transition metal oxide may be an oxide of Formula 1, preferably a compound of Formula 2, more preferably LiFePO ₄ .

The lithium transition metal oxide may be prepared by a method commonly used in the art, for example, by mixing a lithium-containing precursor and a transition metal-containing precursor.

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.

On the other hand, the transition metal-containing precursor may be a conventionally used precursor containing a transition metal, and it preferably contains a precursor containing iron (Fe) and a precursor containing phosphorus (P).

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.

In addition, an alkalizing agent may be further added to adjust the pH of the lithium transition metal oxide precursor. The alkalizing agent may be any one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides and ammonia compounds, or a mixture of two or more thereof.

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 lithium transition metal oxide may be used in an amount of 5 to 40 parts by weight based on 100 parts by weight of water.

Further, according to an embodiment of the present invention, the supply rate of the spray liquid into the chamber may be 20 kg / hour to 50 kg / hour.

According to an embodiment of the present invention, in the step (i), the spray liquid may further include a carbon coating layer on the primary particles by including a carbon precursor together with lithium transition metal oxide and water.

The carbon precursor according to an embodiment of the present invention is preferably a saccharide, and the saccharide may be any one selected from the group consisting of glucose, fructose, galactose, sucrose, maltose and lactose, or a mixture of two or more thereof Can be used.

The carbon precursor may be used in an amount of 2 to 40 parts by weight based on 100 parts by weight of the lithium transition metal oxide.

The step (ii) is a step of spray drying the sprayed liquid in the chamber and then firing it.

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.

According to one embodiment of the present invention, in the hollow lithium transition metal oxide particle, in order to form a hollow, the total solid content (TSC) of the lithium transition metal oxide is 10% to 40% May be 10% to 20%, more preferably 10% to 15%.

In the present invention, "solid content (TSC)" means a solid material remaining after evaporating moisture, that is, a hollow lithium transition metal oxide obtained after drying, in the total weight of the spray liquid containing the lithium transition metal oxide and water Means a value obtained by converting a particle into a percentage.

According to an embodiment of the present invention, when the solid content is less than 10%, the average particle size of the secondary particles may be small and the productivity may be low. When the solid content is more than 40%, the average particle size of the secondary particles is increased, There may be limitations in productivity.

In order to realize the total solid content of the lithium-transition metal oxide particles, it may be possible to control spray drying conditions such as flow rate of carrier gas, residence time in the reactor and internal pressure.

Also, the spray drying temperature may be important to control the size of the hollow in accordance with an embodiment of the present invention. According to one embodiment of the present invention, the spray drying can be performed at a temperature range of 20 ° C to 350 ° C for about 4 minutes to 20 minutes.

Further, the firing can be carried out at a temperature of 700 ° C to 800 ° C. The calcination may preferably be performed in an inert gas atmosphere such as Ar or N ₂ .

The present invention provides a cathode active material comprising the hollow lithium transition metal oxide particles.

The present invention also provides a positive electrode comprising the positive electrode active material.

According to an embodiment of the present invention, there is provided a method for manufacturing a lithium secondary battery, comprising: forming a positive electrode active material coating layer by coating a positive electrode active material composition prepared by mixing the hollow lithium transition metal oxide particles, a binder and a conductive material on a positive electrode current collector; And rolling the cathode active material coating layer.

According to one embodiment of the present invention, the rolling can be carried out in a conventional manner used in the art, for example, using a roll press.

Since the hollow lithium transition metal oxide particles used as the cathode active material according to an embodiment of the present invention are rolled on the secondary particles in the form of secondary particles, So that the electrode fairness can be improved.

According to one embodiment of the present invention, the hollow lithium transition metal oxide particles are hollow, so that when the lithium transition metal oxide particles are applied to an anode, hollows of the hollow lithium iron phosphate particles, As the secondary particles collapse as they collapse, the shape of the secondary particles may disappear and become primary particles.

Thus, according to an embodiment of the present invention, the thickness of the cathode active material coating layer before and after the rolling may be different from each other.

According to an embodiment of the present invention, the thickness of the cathode active material coating layer after rolling may be thinner than the thickness of the cathode active material coating layer before rolling. For example, the thickness of the cathode active material coating layer before rolling may be 80 占 퐉 to 200 占 퐉, and the thickness of the cathode active material coating layer after rolling may be 20 占 퐉 to 80 占 퐉.

On the other hand, 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 composition. Examples of such binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 weight of the cathode active material composition. 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.

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 preparing a negative electrode active material composition by mixing and stirring the negative electrode active material and the additives, applying the negative electrode active material composition to the current collector, and compressing the negative electrode active material composition to produce a negative electrode.

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 can 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.

≪ Preparation of Hollow Lithium Transition Metal Oxide Particles >

Example  One

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 produce lithium iron phosphate LiFePO ₄ Solution.

The LiFePO ₄ solution was filtered to obtain LiFePO ₄ particles. Purity analysis by XRD analysis and primary particle analysis by SEM were performed.

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.

At this time, the spray drying conditions were as follows: the drying temperature was 110 ° C, the internal pressure was -20 mbar, and the slurry feed rate was 40 kg / hr. After the particles were sieved, they were dried in an inert atmosphere of nitrogen (0.1 L / And then fired at a temperature of ± 3 ° C to obtain hollow LiFePO ₄ particles.

The hollow LiFePO ₄ particles are composed of secondary particles having an average particle diameter (D ₅₀ ) of 15 μm formed by aggregation of two or more primary particles having an average particle diameter (D ₅₀ ) of 50 to 300 nm, and have a diameter of about 10 μm A hollow core portion was included. Also, the total solid content (TSC) of the LiFePO ₄ was about 15%.

Comparative Example  One

Except that the total solid content (TSC) of LiFePO ₄ was about 41% and the drying temperature was 95 캜, LiFePO ₄ having no hollow was obtained.

≪ Preparation of positive electrode &

Example  2

As the positive electrode active material, the hollow LiFePO ₄ produced in Example 1 , 5 wt% of super-p as a conductive material, and 5 wt% of polyvinylidene fluoride as a binder were mixed to prepare a cathode active material composition.

The cathode active material composition was applied to an aluminum (Al) thin film as a cathode current collector having a thickness of about 20 mu m and dried at about 130 DEG C for 20 minutes to form a cathode active material coating layer. The positive electrode was prepared by rolling on the positive electrode active material coating layer using a roll press.

Comparative Example  2

A positive electrode was prepared in the same manner as in Example 2 except that LiFePO ₄ prepared in Comparative Example 1 was used as the positive electrode active material.

Room  1: Measurement of the thickness of the cathode active material coating layer before and after rolling

In Example 2 and Comparative Example 2, the thickness of the cathode active material coating layer before and after rolling in the cathode production process was measured and shown in Table 1 below.

Yes Before rolling
Thickness (占 퐉) of the cathode active material coating layer After rolling
Thickness (占 퐉) of the cathode active material coating layer Example 2 95 50 Comparative Example 2 95 55

As can be seen from Table 1, the positive electrode of Example 2 using the positive electrode active material containing hollowed LiFePO ₄ had a thickness of 95 탆 before rolling and a thickness of 50 탆 after rolling, % ≪ / RTI > to < RTI ID = 0.0 > 50% < / RTI >

On the other hand, the cathode of Comparative Example 2 using a cathode active material containing no LiFePO ₄ without hollow was 55 μm thick after rolling, and the thickness of the cathode increased by 5 μm compared to the anode of Example 2.

As a result of the above thickness, it can be predicted that, in the case of Comparative Example 2, since the positive electrode active material does not contain a hollow, the springback phenomenon can easily occur when the positive electrode active material is applied to the positive electrode.

Experimental Example  2: Adhesive strength measurement

Adhesion of the positive electrode prepared in Example 2 and Comparative Example 2 was measured. Adhesion measurements were carried out using a known 180 ^o peel test. The results are shown in Table 2 below.

Yes Primary particle
D50 (nm) Secondary particle
D50 (占 퐉) Hollow diameter
(탆) Adhesion (gf) Example 2 50 to 300 15 10 60 Comparative Example 2 100 to 200 15 X 10

As can be seen from the above Table 2, in the case of the anode including the hollow lithium transition metal oxide particles of Example 2 having an average particle diameter of the primary particles and the secondary particles of Table 2 and having a hollow diameter of 10 탆, Is 60 gf, which is six times higher than that of Comparative Example 2 in which no hollow is formed.

Experimental Example  3: SEM  Microscope pictures

Sections of the particles of the hollow LiFePO ₄ particles prepared in Example 1 were confirmed by SEM micrographs, and the results are shown in FIG.

2 (a) is a cross-sectional view of a hollow LiFePO ₄ particle. FIG. 2 (b) is a partial enlargement of the hollow LiFePO ₄ particle, in which secondary particles agglomerated by two or more primary particles, As shown in FIG. The diameter of the hollow was measured through a SEM micrograph of FIG. 2 (a), and the diameter of the hollow was observed to be about 10 탆.

SEM micrographs of the positive electrodes prepared in Example 2 and Comparative Example 2 were confirmed, and the results are shown in FIGS. 3 and 4, respectively.

3 (a) is a cross-sectional view of a positive electrode (Example 2) obtained by applying a positive electrode active material composition containing a hollow LiFePO ₄ having a hollow diameter of 10 탆 prepared in Example 1 on a positive electrode collector and rolling, 3 (b) is an enlarged view of a part of FIG. 3 (a). FIG.

FIG. 4 (b) showing a cross-section of the Comparative Example anode after the anode active material composition, which hollow contains the LiFePO ₄ made of a non-formed secondary particles prepared in 1 rolled by applying on a positive electrode collector (Comparative Example 2) 4 (b) is an enlarged view of a portion of Fig. 4 (a).

 At this time, the black part of the SEM photograph shows a gap between the particle and the particle due to the spring back phenomenon.

As can be seen from Figs. 3 and 4, in the case of Fig. 3, it can be seen that in the hollow LiFePO ₄ of Example 1, after rolling, the secondary particles collapse and the shape of the spherical shape changes.

In contrast, in the case of FIG. 4, it can be seen that the spherical shape of the secondary particles remains after the rolling, and the void (black portion) due to the springback phenomenon between the secondary particles and the particles is found.

Therefore, in the case of Example 2, it is predicted that the occurrence of pores due to the springback phenomenon is reduced as compared with Comparative Example 2, thereby improving the adhesion and the processability with the cathode current collector.

Claims (26)

1. A lithium secondary battery comprising: a lithium transition metal oxide particle represented by the following formula (1)
The lithium transition metal oxide particles are composed of secondary particles formed by aggregation of two or more primary particles,
A hollow lithium transition metal oxide particle including a hollow core portion in the secondary particle;
Formula 1
Li _{1 + a} M _{1 - x} M 2 _x (PO _{4 -b} ) X _b
In this formula,
M1 represents at least one element selected from Fe, Mn, Co, Ni, Cu, Zn and Mg;
M2 represents at least one element selected from the elements selected from Groups 2 to 15 except for M1,
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 diameter of the hollow core portion is 4 占 퐉 to 10 占 퐉.
The method according to claim 1,
Wherein the average particle size (D ₅₀ ) of the primary particles is in the range of 10 nm to 500 nm.
The method according to claim 1,
Wherein the average particle diameter (D ₅₀ ) of the hollow lithium transition metal oxide particles is in the range of 15 탆 to 20 탆.
The method of claim 1,
The hollow lithium transition metal oxide particle according to claim 1, further comprising a carbon coating layer on the primary particle.
6. The method of claim 5,
Wherein the carbon coating layer has a thickness of 5 nm to 100 nm.
The method of claim 5,
Wherein the carbon coating layer comprises a saccharide. The hollow lithium transition metal oxide particle according to claim 1, wherein the carbon coating layer comprises a saccharide.
8. The method of claim 7,
Wherein the saccharide includes any one selected from the group consisting of glucose, fructose, galactose, sucrose, maltose and lactose, or a mixture of two or more thereof.
The method according to claim 1,
Wherein the lithium transition metal oxide is lithium iron phosphate represented by the following formula (2): < EMI ID =
(2)
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?
10. The method of claim 9,
Wherein the lithium transition metal oxide is LiFePO ₄ .
The method of claim 1,
Wherein the secondary particles have a specific surface area of 30 m < 2 > / g or less.
i) supplying a spray liquid comprising a lithium transition metal oxide, a carbon precursor and water into a spray chamber; And
ii) spray drying and firing the spray liquid in the chamber
≪ / RTI > wherein the hollow lithium transition metal oxide particles have an average particle size of less than 100 nm.
13. The method of claim 12,
Wherein the lithium transition metal oxide has a total solid content (TSC) of 10% to 40%.
13. The method of claim 12,
Wherein the spray drying is performed at a temperature ranging from 20 ° C to 350 ° C.
13. The method of claim 12,
Wherein the calcination is carried out at a temperature of 700 ° C to 800 ° C.
13. The method of claim 12,
Wherein the carbon precursor is a saccharide. ≪ RTI ID = 0.0 > 11. < / RTI >
17. The method of claim 16,
Wherein the saccharide comprises any one selected from the group consisting of glucose, fructose, galactose, sucrose, maltose and lactose, or a mixture of two or more thereof.
13. The method of claim 12,
Wherein the carbon precursor is used in an amount of 2 to 40 parts by weight based on 100 parts by weight of the lithium transition metal oxide.
13. The method of claim 12,
Wherein the lithium transition metal oxide is a lithium iron phosphate represented by the following formula (2): < EMI ID =
(2)
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?
A positive electrode active material comprising the hollow lithium transition metal oxide particles of claim 1.
An anode comprising the cathode active material of claim 20.
Forming a cathode active material coating layer on the cathode current collector by coating and drying the cathode active material composition comprising the hollow lithium transition metal oxide particles of the first aspect, the binder and the conductive material; And
The step of rolling the cathode active material coating layer
And a cathode.
23. The method of claim 22,
Wherein after the rolling, the hollow lithium transition metal oxide particles are collapsed to form secondary particles, thereby forming primary particles.
24. The method of claim 23,
Wherein the thickness of the cathode active material coating layer before rolling and after rolling is different from each other.
25. The method of claim 24,
Wherein the thickness of the cathode active material coating layer after rolling is thinner than the thickness of the cathode active material coating layer before rolling.
A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode according to claim 21.

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