KR102203636B1 - A cathode active material comprising lithium transition metal oxide, a method for manufacturing the same, and a lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material including lithium transition metal oxide particles, a method of manufacturing the same, and a lithium secondary battery including the same. The positive electrode active material according to the present invention has excellent electrolyte impregnation property due to the hydrophilic functional group introduced into the conductive layer, so that ion diffusion in the positive electrode is fast, and high rate charging and discharging is possible. Therefore, when this is applied to a battery, there is an effect of improving the rate characteristics of the battery. In addition, since deterioration of the positive electrode active material is delayed, there is an effect of improving life characteristics.
In addition, the positive electrode active material according to the present invention has high dispersibility and affinity for a solvent, so that it is uniformly dispersed in the solvent when preparing the positive electrode slurry, thereby preventing the positive electrode active material from being unevenly distributed.

Description

A cathode active material comprising lithium transition metal oxide, a method for manufacturing the same, and a lithium secondary battery including the same}

The present invention relates to a positive electrode active material including lithium transition metal oxide particles, a method of manufacturing the same, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life, and low self-discharge rate are It is commercialized and widely used.

Carbon materials are mainly used as negative active materials of such lithium secondary batteries, and use of lithium metal, sulfur compounds, silicon compounds, and tin compounds is also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material. In addition, lithium-containing manganese oxides such as LiMnO _{2 in a} layered crystal structure and LiMn ₂ O _{4 in a} spinel crystal structure, and lithium-containing nickel oxide (LiNiO The use of ₂ ) is also being considered. LiCoO ₂ is currently widely used because of its excellent physical properties such as excellent cycle characteristics, but it is low in safety, and is expensive due to the resource limitation of cobalt as a raw material, and there is a limit to using it in large quantities as a power source in fields such as electric vehicles.

LiNiO ₂ is difficult to apply to the actual mass production process at a reasonable cost due to the characteristics of its manufacturing method, and lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have a disadvantage of poor cycle characteristics.

Accordingly, recently, a method of using lithium transition metal phosphate as a positive electrode active material has been studied. Lithium transition metal phosphate is largely divided into Nasicon structure Li _x M ₂ (PO ₄ ) ₃ and Olivine structure LiMPO ₄ , and is researched as a material with superior high temperature safety compared to existing LiCoO ₂ Has become. Currently, Li ₃ V ₂ (PO ₄ ) ₃ is known among the nasicon-structured compounds, and LiFePO ₄ and Li(Mn, Fe)PO ₄ are the most widely studied among the olivine-structured compounds.

Among the compounds of the olivine structure, LiFePO ₄ in particular has a voltage of ~3.5 V and a high volume density of 3.6 g/cm ³ compared to lithium, and is a material having a theoretical capacity of 170 mAh/g, and has excellent high temperature stability compared to cobalt (Co). However, since Fe is used as a raw material, it is highly likely to be applied as a cathode active material for lithium secondary batteries in the future.

However, LiFePO ₄ is low, the case of using LiFePO ₄ as a positive electrode active material is electrically conductive, there is a problem that the internal resistance of the battery increases. This increases the polarization potential when the battery circuit is closed, thereby reducing the battery capacity. In order to compensate for these shortcomings and improve the rate-limiting characteristics of LiFePO ₄ , methods of coating a thin carbon film on the particles have been developed as a method for increasing electronic conductivity along with controlling the particle size for improving ion conductivity.

In order to solve this problem, some prior art techniques such as Japanese Patent Application Laid-Open No. 2001-110414 propose a technique of adding a conductive material to an olivine-type metal phosphate to improve conductivity.

However, when the surface of LiFePO ₄ is treated with carbon (C), the surface of the particles becomes hydrophobic, causing a problem in that dispersibility in the solvent is inferior when preparing a slurry. In order to solve this problem, it is necessary to increase the amount of the solvent. When the amount of the solvent is increased, cracks are caused in the pores generated by the evaporation of the solvent during the drying process, and problems such as non-uniformity of the electrode and a decrease in conductivity occur. This mixing problem corresponds to the initial process of battery manufacturing and has a profound effect on all battery processes and characteristics of the battery.

In addition, when the hydrophobicity of the particle surface is increased, impregnation into the electrolyte solution is lowered, so that the diffusion of ions is reduced, and the deterioration of the electrode active material is accelerated.

Accordingly, the present invention aims to solve the above-described problems.

A first object of the present invention is to improve the performance characteristics of a lithium secondary battery containing the positive electrode active material by improving the conductivity of a positive electrode active material containing lithium transition metal phosphate.

In addition, the second object of the present invention is to improve the impregnation property of a positive electrode containing a lithium transition metal phosphate.

In addition, it is a third object to improve the dispersibility and affinity of the positive electrode active material with respect to the solvent so that the positive electrode slurry can be uniformly dispersed in the solvent. It will be easily understood that other objects and advantages of the present invention can be realized by the means shown in the claims and combinations thereof.

The present invention relates to a positive electrode active material for solving the above technical problem, a method of manufacturing the positive electrode active material, and a positive electrode for an electrochemical device including the positive electrode active material.

A first aspect of the present invention includes a lithium transition metal oxide represented by the following Formula 1, wherein the lithium transition metal oxide includes a form of a primary particle or a form of a secondary particle in which two or more primary particles are aggregated, or both. And, in the primary particle and/or secondary particle, at least a part of the surface is covered with a conductive layer, the conductive layer comprises a carbon material, wherein the conductive layer is characterized in that a hydrophilic functional group is introduced. , Is the positive active material:

[Formula 1]

Li _{1 + a} M1 _{1 - x} M2 _x (PO _4-b )D _b

In Equation 1 above

M1 is at least one element selected from Fe, Mn, Co, Ni, Cu, Zn and Mg, M2 is one or more elements selected from any one of groups 2 to 15, excluding element M1, and D is F , At least one selected from the group consisting of S and N, and -0.5≦a≦+0.5, 0≦x≦0.5, and 0≦b≦1.

In a second aspect of the present invention, in the first aspect, the positive electrode active material further includes a hollow core portion inside the secondary particle.

In addition, in the third aspect of the present invention, in the second aspect, the diameter of the hollow core portion is 4 μm to 10 μm.

In the fourth aspect of the present invention, in the first to third aspects, the hydrophilic functional group is chemically bonded to a carbon material, and in the group consisting of -COOH, -OH and -COO ^- M ⁺ (M is a metal) It is one or more selected.

In the fifth aspect of the present invention, in the fourth aspect, the M is at least one selected from the group consisting of Li, B, and Al.

A sixth aspect of the present invention is that in any one of the first to fifth aspects, the average particle diameter of the primary particles is in the range of 10 nm to 500 nm.

A seventh aspect of the present invention is that in any one of the first to sixth aspects, the average particle diameter of the secondary particles is in the range of 15 μm to 20 μm.

An eighth aspect of the present invention is that in any one of the first to seventh aspects, the thickness of the conductive layer is 5 nm to 100 nm.

In the ninth aspect of the present invention, according to any of the first to eighth aspects, the conductive layer covers 70% or more of the surface area of the primary particles.

In any one of the first to ninth aspects of the present invention, M1 is Fe, and M2 is Al, Mg, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, It is one or more selected from the group consisting of Zn and Y.

An eleventh aspect of the present invention is that in any one of the first to tenth aspects, the lithium iron phosphate includes LiFePO ₄ .

In addition, the present invention relates to a method of manufacturing the positive electrode active material according to the present invention.

In a twelfth aspect of the present invention, the method of preparing the positive electrode active material comprises the steps of preparing lithium transition metal phosphate primary particles having an olivine crystal structure (S10); Preparing a first mixture by mixing the primary particles and the solvent obtained in the step (S10) (S20); Spray drying the first mixture (S30); Firing the resultant product of (S30) to obtain secondary particles formed by agglomeration of the primary particles (S40); Preparing a second mixture by mixing the secondary particles obtained in (S40), the carbon precursor, the hydrophilic functional group providing source, and the solvent (S50); And heat-treating the second mixture (S60).

In the thirteenth aspect of the present invention, in the twelfth aspect, the (S10) is performed through the following steps:

(S10a) preparing a slurry including a raw material and an alkalizing agent; And

(S10b) reacting the slurry under supercritical or subcritical conditions to synthesize lithium transition metal phosphate primary particles, wherein the raw material includes a lithium-containing precursor and a transition metal-containing precursor.

In a fourteenth aspect of the present invention, in the twelfth or thirteenth aspect, the carbon precursor is a saccharide.

In a fifteenth aspect of the present invention, in the fourteenth aspect, the saccharide is a compound containing a C _n H _2n cycloalkane ring having 3 to 6 carbon atoms.

In any one of the 12th to 15th aspects of the present invention, at least one of the first and second mixtures further comprises a cellulose-based dispersant.

A seventeenth aspect of the present invention is that in any one of the 12th to 16th aspects, spray drying is performed at 20°C to 350°C in the step (S30).

In an eighteenth aspect of the present invention, in any one of the 12th to 17th aspects, the firing in the step (S40) is performed at 700°C to 800°C.

In any one of the twelfth to eighteenth aspects of the present invention, the heat treatment in step (S60) is performed at 250°C to 500°C.

In addition, a twentieth aspect of the present invention is a positive electrode for an electrochemical device including the positive electrode active material according to any one of the first to eleventh aspects.

The positive electrode active material according to the present invention has excellent electrolyte impregnation property due to the hydrophilic functional group introduced into the conductive layer, so that ion diffusion in the positive electrode is fast, and high rate charging and discharging is possible. Therefore, when this is applied to a battery, there is an effect of improving the rate characteristics of the battery. In addition, since deterioration of the positive electrode active material is delayed, there is an effect of improving life characteristics.

In addition, the positive electrode active material according to the present invention has high dispersibility and affinity for a solvent, so that it is uniformly dispersed in the solvent when preparing the positive electrode slurry, thereby preventing the positive electrode active material from being unevenly distributed.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description of the present invention to be described later. It is limited only to and should not be interpreted.
1 is a schematic cross-sectional view of a primary particle of a lithium transition metal oxide according to an embodiment of the present invention.
2 is a process flow diagram schematically showing a method of manufacturing a positive active material according to an embodiment of the present invention.
3 is a comparison of the batteries of Example 2 and Comparative Example 2 by confirming the capacity decrease according to the C-rate.
4 is a diagram illustrating charging and discharging characteristics of the batteries of Example 2 and Comparative Example 2.
5 is a diagram showing the resistance increase rate and capacity retention rate for the cells of Example 3 and Comparative Example 3.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor shall appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be. Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and do not represent all the technical ideas of the present invention, so that they can be replaced at the time of application It should be understood that there may be various equivalents and variations.

The present invention relates to a positive electrode active material containing a lithium transition metal phosphate.

The positive electrode active material according to an embodiment of the present invention includes a lithium transition metal phosphate represented by the following Formula 1, wherein the lithium transition metal phosphate is in the form of primary particles or secondary particles formed by agglomeration of the primary particles or It includes both forms.

[Formula 1]

Li _{1 + a} M1 _{1 - x} M2 _x (PO _4-b )D _b

In the above formula, M1 is at least one element selected from the group consisting of Fe, Mn, Co, Ni, Cu, Zn and Mg,

M2 is one or more elements selected from elements belonging to groups 2 to 15, and is not M1,

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

-0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1.

In general, since lithium transition metal phosphate, particularly LiFePO _4, has low electrical conductivity, when it is used as a positive electrode active material, the internal resistance of the battery increases. Accordingly, when the battery circuit is closed, the polarization potential is increased, thereby reducing the battery capacity.

Thus, the present invention is devised to solve the above problem. That is, the positive electrode active material according to an embodiment of the present invention includes the lithium transition metal phosphate, and the lithium transition metal phosphate is in the form of primary particles, or secondary particles formed by agglomeration of two or more primary particles or Both of these. Further, in the present invention, the lithium transition metal phosphate is characterized in that at least a part of its surface is covered with a conductive layer into which a hydrophilic functional group is introduced. According to a specific embodiment of the present invention, the lithium transition metal phosphate primary particle has at least a part of its surface covered with a conductive layer. 1 is a diagram showing primary particles of lithium iron phosphate, which is a lithium transition metal phosphate according to a specific embodiment of the present invention, schematically showing that the surface of lithium iron phosphate is covered with a conductive layer into which a hydrophilic functional group is introduced. . In Fig. 1, the symbol M represents a metal.

In the present invention, the conductive layer includes a carbon material, and the carbon material is carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal, activated carbon polyphenylene derivative, natural Graphite, artificial graphite, Super-P, Acetylene Black, Ketjen Black, Channel Black, Finace Black, Lamp Black, Thermo Black, Denka Black, Aluminum Powder, Nickel Powder, Zinc Oxide, Gallium Titanate and Titanium Oxide It may be any one selected from the group consisting of, or a mixture of two or more of them.

Alternatively, the conductive layer may be formed by carbonization of a carbon precursor such as sugar. In a specific embodiment of the present invention, the saccharide may be a compound including a C _n H _2n cycloalkane ring having 3 to 6 carbon atoms.

Specific examples of the saccharides include glucose, fructose, galactose, sucrose, maltose, and lactose. The saccharide may be any one or a mixture of two or more selected from these.

According to a specific embodiment of the present invention, the conductive layer may cover 70% or more, 80% or more, or 90% or more of the surface area of the primary particles.

In a specific embodiment of the present invention, the thickness of the conductive layer may be 5nm to 100nm, or 5nm to 50nm. If the above range is satisfied, there is no obstacle to the movement of lithium ions, and the synergistic effect of electrical conductivity is excellent.

In the present invention, the conductive layer is characterized in that a hydrophilic functional group is introduced.

In a specific embodiment of the present invention, a hydrophilic functional group may be introduced by the hydrophilization surface treatment. The hydrophilization surface treatment is not limited in any way as long as it is to introduce a hydrophilic group to the surface, and for example, an oxidation treatment in which an oxygen-containing functional group such as a carboxyl group, a carbonyl group, or an alcohol group is introduced may be mentioned. The oxidation treatment method is a surface treatment method of an inorganic material, and may be selected and used as necessary from among methods known in other fields. Further, according to a specific embodiment of the present invention, the functional group may be in the form of a metal salt in which a metal ion is ionic bonded. The metal ion may be Li ⁺ , B ⁺ or Al ⁺ , but is not particularly limited thereto.

By introducing the hydrophilic functional group, impregnation of the electrolyte solution is increased, so that ion diffusivity of the lithium transition metal phosphate can be improved, and deterioration of the active material particles is delayed, thereby improving cycle characteristics.

In addition, when preparing the slurry for forming the positive electrode active material layer, dispersibility in the solvent is improved, thereby reducing the tendency of the positive electrode active material particles to be aggregated or localized.

According to a specific embodiment of the present invention, the positive electrode active material may further include a hollow core portion inside the secondary particles of lithium transition metal phosphate.

When the lithium transition metal phosphate has the form of secondary particles, if there is no hollow core inside the particles, a spring back phenomenon may occur when manufacturing a positive electrode using the lithium transition metal phosphate.

In the present specification, a spring back phenomenon refers to an elastic phenomenon that attempts to recover to its original state when the pressure is removed after deforming by applying pressure to an object.

When manufacturing a positive electrode by coating and rolling the positive electrode active material according to the present invention on a current collector, when the secondary particles of the lithium transition metal phosphate are dense, the springback phenomenon to recover to the spherical secondary particle phenomenon of the original shape May appear, which may result in voids (gaps) between the particles and the particles. Due to the generation of voids, the adhesion of the positive electrode active material to the current collector may be reduced, leading to desorption of active material particles, and the formed voids may act as resistance, thereby reducing electronic conductivity.

In order to solve the above problem, such as a decrease in binding force, a method of increasing the amount of the binder may be considered, but when the amount of the binder increases, the resistance increases and the voltage decreases.

Therefore, the lithium transition metal phosphate secondary particles according to an embodiment of the present invention intentionally weaken the mechanical strength by forming a hollow inside the particles, so that the secondary particles may collapse during the rolling process and become primary particles. . Accordingly, since the springback phenomenon is reduced, adhesion and process efficiency can be improved.

In the positive electrode active material according to an embodiment of the present invention, the diameter of the hollow core portion is 4 μm to 10 μm, preferably 6 μm to 10 μm.

In the present invention, when the diameter of the hollow core portion satisfies the above range, the springback phenomenon does not occur excessively and the disintegration rate of the secondary particles is lowered, so that the processability and productivity are not lowered.

In the present invention, the measurement of the diameter of the hollow core portion is not particularly limited, but may be measured, for example, by electron microscopy (SEM).

In addition, according to a specific embodiment of the present invention, the specific surface area (BET) of the positive electrode active material particles is preferably 30 m ² /g or less, preferably 10 m ² /g to 30 m ² /g. If it is out of the above range, there is a concern about a decrease in adhesion.

On the other hand, in the present invention, in order to exhibit excellent electrical conductivity, stability of crystal structure, and high bulk density even when secondary particles collapse and return to primary particles during manufacture of the positive electrode, primary particles in a crystallized state are used. It is preferred to use to form secondary particles. That is, it is preferable that the primary particles each independently have an olivine-type crystal structure.

In addition, in order to facilitate return to the primary particles while the secondary particles are collapsed, the primary particles are aggregated by physical bonds such as Van der Waals attraction rather than chemical bonds such as covalent bonds or ionic bonds, thereby forming secondary particles. It is desirable to form.

According to a specific embodiment of the present invention, in the lithium transition metal oxide, M1 is Fe, and M2 is Al, Mg, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. It may be one or more selected from the group consisting of. Specifically, the lithium transition metal phosphate may be lithium iron phosphate (LiFePO ₄ ).

In an embodiment of the present invention, the average particle diameter (D ₅₀ ) of the secondary particles is preferably in the range of 15 μm to 20 μm. When the average particle diameter of the secondary particles exceeds 20 μm, the amount of the binder for maintaining the desired electrode adhesion increases due to the increase in the specific surface area of the positive electrode active material, which may cause problems such as a decrease in electrode conductivity. . Conversely, if the average particle diameter is too small, such as less than 15 μm, process efficiency cannot be exhibited. In particular, in consideration of uniform mixing of the slurry for forming an active material layer and smoothness of the electrode surface, it is preferable to have an average particle diameter of 15 µm to 20 µm.

In addition, the average particle diameter (D ₅₀ ) of the primary particles of the lithium transition metal oxide is in the range of 10 nm to 500 nm, preferably 100 nm to 400 nm.

If the average particle diameter of the primary particles is too small, such as less than 10 nm, manufacturing is not easy and process efficiency cannot be exhibited. If the average particle diameter of the primary particles exceeds 500 nm, the formability of the lithium transition metal oxide particles decreases, and it is difficult to control granulation. Difficult problems can arise.

In the present invention, the average particle diameter (D ₅₀ ) of the particles can be defined as the particle diameter based on 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. In general, the laser diffraction method can measure a particle diameter of about several mm from a submicron region, and high reproducibility and high resolution results can be obtained.

Next, a method of manufacturing the positive electrode active material according to the present invention will be described.

According to an embodiment of the present invention, in the positive electrode active material, secondary particles of lithium transition metal phosphate particles may be formed by a separate granulation process after manufacturing the primary particles. Alternatively, it may be produced by a method of agglomerating the primary particles while generating the primary particles. Hereinafter, a method of manufacturing a positive electrode active material according to the former method will be described.

According to an embodiment of the present invention, the positive active material may be obtained through a manufacturing method including the following steps (S10) to (S40):

(S10) preparing lithium transition metal phosphate primary particles having an olivine crystal structure;

(S20) preparing a first mixture by mixing the primary particles obtained in step (S10) and a solvent;

(S30) spray drying the first mixture;

(S40) firing the resultant product of (S30) to obtain secondary particles formed by agglomeration of the primary particles;

(S50) preparing a second mixture by mixing the secondary particles obtained in (S40), a carbon precursor, a hydrophilic functional group providing source, and a solvent; And

(S60) heat-treating the second mixture.

It is preferable that the primary particles obtained in step (S10) each independently have an olivine crystal structure. The method of preparing the primary particles is not limited in its kind, and for example, a solid phase method, a coprecipitation method, a hydrothermal method, a supercritical hydrothermal synthesis method, or the like may be used. In a specific embodiment of the present invention, the step (S10) may be performed by a method of supercritical hydrothermal synthesis.

In a specific embodiment of the present invention, the preparation of the primary particles by the supercritical hydrothermal synthesis method may be performed by the following method.

First, a slurry is prepared by mixing a raw material and an alkalizing agent (S10a). In some cases, the slurry may further contain an appropriate additive such as an antioxidant.

In a specific embodiment of the present invention, a lithium-containing precursor and a transition metal-containing precursor are included as raw materials in the step (S10).

The lithium-containing precursor may be Li ₂ CO _{3 ,} Li(OH), Li(OH)·H ₂ O, LiNO ₃ , and the like. In a specific embodiment of the present invention, when lithium hydroxide is used as a lithium-containing precursor, it may serve to increase alkalinity as well as a lithium source.

The transition metal-containing precursor may be a commonly used precursor containing a transition metal, and in the case of preparing lithium iron phosphate (LiFePO ₄ ) according to a specific embodiment of the present invention, iron (Fe)-containing precursor and phosphorus (P) It contains a containing precursor.

According to a specific embodiment of the present invention, when the lithium transition metal phosphate is LiFePO ₄ , the iron (Fe)-containing precursor is a compound having a divalent valence of iron, which is FeSO ₄ , FeC ₂ O ₄ ·2H ₂ O, FeCl ₂ , Or a mixture of two or more of them may be used. In addition, the phosphorus (P)-containing precursor is an ammonium salt, such as H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , P ₂ O ₅ , or a mixture of two or more of them.

In a specific embodiment of the present invention, the alkalinizing agent is an alkali metal hydroxide (NaOH, KOH, etc.), alkaline earth metal hydroxide (Ca(OH) ₂ , Mg(OH) _2, etc.), ammonia compounds (ammonia water, ammonium nitrate, etc.) ) Or a mixture thereof.

In a specific embodiment of the present invention, the lithium-containing precursor, the transition metal-containing precursor, and/or the alkalizing agent may be added in the form of an aqueous solution.

Next, the slurry prepared above is reacted under supercritical or subcritical conditions to synthesize primary particles. According to a specific embodiment, in (S10b), lithium transition metal phosphate primary particles are obtained by injecting the slurry into a continuous process supercritical reactor and performing a supercritical or subcritical reaction.

In a specific embodiment of the present invention, the reaction of the supercritical reactor may be carried out under conditions of a pressure of 180 bar to 550 bar and a temperature of 200° C. to 700° C.

In some cases, after completing the step (S10), impurity salts that may remain in the primary particles obtained before step (S20) (e.g., NH ₄ NO ₃ ), ionic impurities (e.g. For example, it may be subjected to a washing process to remove the decomposed NO ₃ ^- , SO ₄ ^2-, etc.) from the metal precursor.

When the lithium transition metal phosphate primary particles are obtained through the (S10), the primary particles are then added to a solvent and mixed to prepare a first mixture (S20).

As the solvent that can be used in the above process, at least one or more solvents selected from a polar solvent and a non-polar solvent may be used. Examples of the polar solvent include water and ethanol. Moreover, as a non-polar solvent, benzene, methylene chloride, etc. are mentioned, for example. Considering the safety aspect, it is advantageous to use water.

In an embodiment of the present invention, the total solid content (TSC) in the first mixture is 10% to 40%. Here, by adjusting the content ratio of the solid content, the internal porosity of the secondary particles can be adjusted. In order to form a hollow inside the secondary particles, the total solid content (TSC) may preferably be 10% to 30% or 10 to 20%.

In the present invention, "solid content (TSC)" refers to a value obtained by converting a solid substance remaining by evaporating a solvent into a percentage based on the total weight of the first mixture.

In addition, in the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the mixture may further include a cellulose-based dispersant to increase dispersibility. The cellulose-based dispersant may be a cellulose crab dispersant commonly used in the art, for example, any one selected from the group consisting of carboxy methyl cellulose, carboxy ethyl cellulose, amino ethyl cellulose, and oxyethyl cellulose, or two of them. It may contain a mixture of more than one species.

The dispersant may be used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the lithium transition metal phosphate primary particles.

If necessary, after performing the step (S10) and before performing the step (S20), a process (S11) of calcining the synthesized lithium transition metal phosphate primary particles under a temperature condition of 600°C to 1200°C may be further performed. . The adhesion between the crystals may be improved while growing crystals of the lithium transition metal phosphate particles through the calcination process.

Next, the first mixture obtained in (S20) is dried and the particles are compounded (S30). The particles are dried through this step, and at the same time, secondary particles formed by agglomeration of the primary particles are obtained. The step (S30) may be performed by various methods known in the art, such as spray drying, fluidized bed drying, and vibration drying, among the above methods, in particular, spray drying such as rotational spray drying may produce secondary particles in a spherical shape. It is preferable because it can increase the bulk density.

When the step (S30) is performed by the method of spray drying, for example, after supplying the first mixture (spray liquid) of (S20) into the spray chamber, the spray liquid is spray dried in the chamber. . According to a specific embodiment of the present invention, the spray liquid is sprayed through a disk rotating at high speed in the chamber, and at this time, spraying and drying may be performed in the same chamber.

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. In addition, the spray drying may be a temperature condition of 110 to 140°C, -30 mbar to 10 mbar, and a flow rate of 35 ml/min to 60 ml/min.

In one embodiment of the present invention, the spray drying temperature may be important to control the size of the hollow of the secondary particles. According to an embodiment of the present invention, the spray drying can be performed in about 4 to 20 minutes.

Next, the lithium phosphate secondary particles obtained through (S30) are calcined (S40). The sintering may be performed at a temperature of 600°C to 800°C. In addition, the firing process may be preferably performed in an inert gas atmosphere such as Ar or N ₂ .

Next, a second mixture is prepared by mixing the secondary particles calcined in (S40), a carbon precursor, and a source for providing a hydrophilic functional group in a solvent (S50).

The solvent used in (S50) may refer to the type of solvent used in the (S20) process, and the same or different solvents may be used.

Examples of carbon precursors that can be used in this step include saccharides that can be dissolved in a polar solvent, and additionally PVDF, PE-based polymers, coke, and the like may be further included. In addition, in a specific embodiment of the present invention, 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 of them.

In a specific embodiment of the present invention, the hydrophilic functional group providing source is a metal salt containing a metal functional group, and specifically, one selected from the group consisting of salts of metal ions such as Li ⁺ , B ⁺ and Al ⁺ That's it. For example, the metal salt is Mg ₂ B ₂ O ₅ , CaAlB ₃ O _{7 ,} Borate such as Li ₆ B ₄ O ₉ , boron nitrate (BN), lithium borate, lithium aluminate, lithium hydroxide, It is one selected from aluminum carbonate and aluminum hydroxide, or a mixture of two or more.

In addition, in the method of manufacturing a positive electrode active material according to an embodiment of the present invention, the second mixture may further include a cellulose-based dispersant to increase dispersibility. The cellulose-based dispersant may be a cellulose crab dispersant commonly used in the art, for example, any one selected from the group consisting of carboxy methyl cellulose, carboxy ethyl cellulose, amino ethyl cellulose, and oxyethyl cellulose, or two of them. It may contain a mixture of more than one species.

The dispersant may be used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the lithium transition metal phosphate secondary particles.

Next, the second mixture is heat-treated (S60). In one embodiment of the present invention, the heat treatment may be performed at about 250°C to 500°C. In addition, the heat treatment may be performed under an inert gas atmosphere such as argon or helium or under a nitrogen gas atmosphere. The reduction of the metal of the metal salt is prevented through the heat treatment, so that secondary particles with high purity can be obtained.

As described above, the positive electrode active material according to the present invention can be obtained by the method described above, and the obtained positive electrode active material is a lithium transition metal oxide, and at least a part of the surface of at least one of the primary particles and the secondary particles is introduced with a hydrophilic functional group. It is covered with a conductive layer.

On the other hand, in a specific embodiment of the present invention, the carbon precursor and the hydrophilic functional group providing source may be added together with the primary particles to the first mixture of (S20) (alternative 1). In this case, the first mixture may be spray-dried to form secondary particles, and then the resultant may be fired at a temperature of 600°C to 800°C to obtain a positive electrode active material. The firing may be preferably carried out in an inert gas atmosphere such as Ar or N ₂ . In the case of alternative 1, since the heat treatment is performed simultaneously with firing, it is not necessary to proceed with the heat treatment step of (S60).

In addition, the present invention provides a positive electrode comprising the lithium transition metal phosphate.

According to an embodiment of the present invention, the positive electrode may include forming a positive electrode mixture layer by applying and drying a positive electrode slurry in which a positive electrode active material, a binder, and a conductive material are mixed on a positive electrode current collector; And rolling the positive electrode mixture layer.

According to an embodiment of the present invention, the rolling may be performed by a conventional method used in the art, such as, for example, a roll press.

The positive electrode active material includes the lithium transition metal phosphate particles described above, preferably includes lithium iron phosphate particles, and more preferably lithium iron phosphate secondary particles.

According to an embodiment of the present invention, when the positive electrode active material is applied to the positive electrode, the secondary particles may be crushed by roll pressing during the rolling process, so that the shape of the secondary particles may disappear and become primary particles.

According to an embodiment of the present invention, the thickness of the positive electrode mixture layer before and after the rolling may be different from each other. According to an embodiment of the present invention, the thickness of the positive electrode mixture layer after rolling may be thinner than the thickness of the positive electrode mixture layer before rolling. For example, the thickness of the positive electrode mixture layer before rolling may be 80 μm to 200 μm, and the thickness of the positive electrode mixture layer after rolling may be 20 μm to 80 μm.

In addition, the thickness of the positive electrode mixture layer after rolling may be as thin as 45 μm to 70 μm than the thickness of the positive electrode mixture layer before rolling, but is not limited thereto.

Meanwhile, the binder is a component that assists in bonding of an active material and a conductive material and bonding to a current collector, and may be generally added in an amount of 1 to 30% by weight based on the total amount of the positive electrode slurry. Examples of such a binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), It may be any one selected from the group consisting of sulfonated EPDM, styrene butadiene rubber (SBR), and fluorine rubber, or a mixture of two or more of them.

The conductive material may be typically added in an amount of 0.05 to 5% by weight based on the total weight of the positive electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing side reactions with other elements of the battery. Graphite such as natural graphite or artificial graphite; Carbon black (super-p), acetylene black; Carbon blacks such as Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Summer Black; Conductive fibers such as carbon fibers and metal fibers; 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 may 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.

In the negative electrode, as a negative electrode active material, a carbon material, lithium metal, silicon, tin, or the like, through which lithium ions can be inserted and released, may be used. Preferably, a carbon material may be used, and both low crystalline carbon and high crystalline carbon may be used as the carbon material. As low crystalline carbon, soft carbon and hard carbon are typical, and high crystalline carbon is natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber High-temperature calcined carbons such as (mesophase pitch based carbon fiber), meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes are typical.

The binder used for the negative electrode may be one that can be commonly used in the art like the positive electrode. The negative electrode may be prepared by mixing and stirring the negative electrode active material and the additives to prepare a negative electrode active material composition, and then coating and compressing the negative electrode active material composition on a current collector to prepare a negative electrode.

In addition, the separator is a conventional porous polymer film used as a separator, for example, polyolefin such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. A porous polymer film made of a polymer-based polymer may be used alone or by stacking them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is limited thereto. It is not.

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

Hereinafter, examples will be described in detail to illustrate the present invention in detail. However, the embodiments according to the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Example One

In a mixture of 0.5 mol of iron sulfate (FeSO ₄ ㆍ7H ₂ O), 0.55 mol of phosphoric acid (P ₂ O ₅ ) and an aqueous iron sulfate solution containing an antioxidant, and 1.5 mol of an aqueous lithium solution (LiOH · H ₂ O), the pH was 5.5 to Ammonia water was added so as to be 7 to prepare a slurry. The temperature of the continuous process supercritical reactor is adjusted to about 375 to 450°C, the pressure is controlled to a pressure of 250 to 300 bar, and the slurry is introduced at a constant rate, and a lithium iron phosphate LiFePO ₄ solution is prepared through a reaction time of several seconds. Was prepared. The obtained LiFePO ₄ solution was filtered to obtain lithium iron phosphate primary particles. Purity analysis through XRD analysis and primary particle analysis through SEM were performed on the obtained result. As a result, lithium iron phosphate primary particles having an average particle diameter of 50 to 300 nm were obtained.

The primary particles obtained above were added to distilled water to prepare a first mixture (spray liquid). The prepared first mixture was supplied into a chamber of a spray drying equipment, and dried by spraying in the chamber. At this time, the spray drying conditions were adjusted to a drying temperature of 130° C., an internal pressure of -20 mbar, and a flow rate of 45 ml/min. As a result of the spray drying, lithium iron phosphate secondary particles were obtained. The secondary particles were formed by aggregation of primary particles. Next, the obtained primary particles (lithium iron phosphate) were calcined in a reducing atmosphere (N ₂ ) of 700° C./10 hr.

Next, a second mixture was prepared by adding the secondary particles, borate (Mg ₂ B ₂ O ₅ ) and sucrose obtained in the above process in an amount of 10 parts by weight based on 100 parts by weight of the lithium iron phosphate secondary particles, respectively. It was heat-treated at °C. The heat treatment was performed in a nitrogen gas (N ₂ ) atmosphere. The heat treatment was performed for about 2 hours.

Lithium iron phosphate secondary particles were obtained through the above process. The lithium iron phosphate secondary particles are configured in a form in which a conductive layer covers at least a part of the surfaces of the primary particles and the secondary particles, and the conductive layer is a hydrophilic functional group introduced therein.

Example 2

Lithium iron phosphate secondary particles obtained in Example 1 were used as a positive electrode active material. The secondary particles, conductive material (carbon black), and binder (SBR/CMC, 70:30 weight ratio) were added to DI water at a weight ratio of 90: 5: 5, respectively, and mixed to prepare a positive electrode mixture, and the prepared positive electrode mixture was As a positive electrode current collector, a 20 μm thick aluminum foil was coated with a thickness of 60 μm and dried to prepare a positive electrode. As the negative electrode, a lithium metal thin film (thickness 160 μm) was used. After manufacturing an electrode assembly by interposing a separator (a separator made of polyethylene, thickness: 20 μm) between the negative electrode and the positive electrode, an organic solvent containing 3 wt% of LiPF ₆ 1M and VC (Vinyl Carbonate, additive) : Methyl ethyl carbonate = 2:1 volume ratio) as an electrolyte to prepare a coin cell.

Example 3

Lithium iron phosphate secondary particles obtained in Example 1 were used as a positive electrode active material. The secondary particles, conductive material (carbon black), and binder (SBR/CMC, 70:30 weight ratio) were added to DI water at a weight ratio of 90: 5: 5, respectively, and mixed to prepare a positive electrode mixture, and the prepared positive electrode mixture was As a positive electrode current collector, a 20 μm thick aluminum foil was coated with a thickness of 60 μm and dried to prepare a positive electrode.

Next, artificial graphite, carbon black, carboxymethylcellulose, and methyl acrylate were mixed with water in a weight ratio of 95.8:1:1.2:2 to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil (Cu-foil) with a thickness of 14 μm to form a thin electrode plate, dried at 135 for 3 hours or more, and then pressed to prepare a negative electrode.

After manufacturing an electrode assembly by interposing a separator (a separator made of polyethylene, thickness: 20 μm) between the negative electrode and the positive electrode, the electrode assembly was accommodated in a battery case, and a concentration of LiPF ₆ 1M and a VC (Vinyl Carbonate, additive) were added. A full cell was prepared using an organic solvent (Ethylene carbonate: Methyl ethyl carbonate = 2:1 volume ratio) contained in 3wt% as an electrolyte.

Comparative example One

In a mixture of 0.5 mol of iron sulfate (FeSO ₄ ㆍ7H ₂ O), 0.55 mol of phosphoric acid (P ₂ O ₅ ) and an aqueous iron sulfate solution containing an antioxidant, and 1.5 mol of an aqueous lithium solution (LiOH · H ₂ O), the pH was 5.5 to Ammonia water was added so as to be 7 to prepare a slurry. The temperature of the continuous process supercritical reactor is adjusted to about 375 to 450°C, the pressure is controlled to a pressure of 250 to 300 bar, and the slurry is introduced at a constant rate, and a lithium iron phosphate LiFePO ₄ solution is prepared through a reaction time of several seconds. Was prepared. The obtained LiFePO ₄ solution was filtered to obtain lithium iron phosphate primary particles. Purity analysis through XRD analysis and primary particle analysis through SEM were performed on the obtained result. As a result, lithium iron phosphate primary particles having an average particle diameter of 50 to 300 nm were obtained.

The primary particles obtained above were added to distilled water to prepare a first mixture (spray liquid). The prepared first mixture was supplied into a chamber of a spray drying equipment, and dried by spraying in the chamber. At this time, the spray drying conditions were adjusted to a drying temperature of 130° C., an internal pressure of -20 mbar, and a flow rate of 45 ml/min. As a result of the spray drying, lithium iron phosphate secondary particles were obtained. The secondary particles were formed by aggregation of primary particles. Next, the obtained primary particles (lithium iron phosphate) were calcined in a reducing atmosphere (N ₂ ) of 700° C./10 hr.

Comparative example 2

Lithium iron phosphate secondary particles obtained in Comparative Example 1 were used as a positive electrode active material. The secondary particles, conductive material (carbon black), and binder (SBR/CMC, 70:30 weight ratio) were added to DI water at a weight ratio of 90: 5: 5, respectively, and mixed to prepare a positive electrode mixture, and the prepared positive electrode mixture was As a positive electrode current collector, a 20 μm thick aluminum foil was coated with a thickness of 60 μm and dried to prepare a positive electrode. As the negative electrode, a lithium metal thin film (thickness 160 μm) was used. After manufacturing an electrode assembly by interposing a separator (a separator made of polyethylene, thickness: 20 μm) between the negative electrode and the positive electrode, an organic solvent containing 3 wt% of LiPF ₆ 1M and VC (Vinyl Carbonate, additive) : Methyl ethyl carbonate = 2:1 volume ratio) as an electrolyte to prepare a coin cell.

Comparative example 3

Lithium iron phosphate secondary particles obtained in Comparative Example 1 were used as a positive electrode active material. The secondary particles, conductive material (carbon black), and binder (SBR/CMC, 70:30 weight ratio) were added to DI water at a weight ratio of 90: 5: 5, respectively, and mixed to prepare a positive electrode mixture, and the prepared positive electrode mixture was As a positive electrode current collector, a 20 μm thick aluminum foil was coated with a thickness of 60 μm and dried to prepare a positive electrode.

Next, artificial graphite, carbon black, carboxymethylcellulose, and methyl acrylate were mixed with water in a weight ratio of 95.8:1:1.2:2 to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil (Cu-foil) with a thickness of 14 μm to form a thin electrode plate, dried at 135 for 3 hours or more, and then pressed to prepare a negative electrode.

After manufacturing an electrode assembly by interposing a separator (a separator made of polyethylene, thickness: 20 μm) between the negative electrode and the positive electrode, the electrode assembly was accommodated in a battery case, and a concentration of LiPF ₆ 1M and a VC (Vinyl Carbonate, additive) were added. A full cell was prepared using an organic solvent (Ethylene carbonate: Methyl ethyl carbonate = 2:1 volume ratio) contained in 3wt% as an electrolyte.

Electrolyte Impregnation Property evaluation

Two positive electrodes prepared in Example 2 and Comparative Example 2 were prepared, and then one drop of polycarbonate was added thereto, and then the time until completely absorbed by moisture was measured. The results are summarized in Table 1 below.

Moisture absorption time (sec) Example 2-1 450 Example 2-2 460 Comparative Example 2-1 540 Comparative Example 2-2 640

In the case of the anodes of Examples 2-1 and 2-2, the time taken to completely absorb the dropped polycarbonate was less than 500 seconds, but the anodes of Comparative Examples 2-1 and 2-2 took 500 seconds to absorb Exceeded.

Battery characteristic evaluation

Discharge rate characteristics

Charging and discharging were performed for the batteries of Example 2 and Comparative Example 2 while changing a constant current from 0.1 to 5. The results are shown in FIG. 3. In FIG. 3, the black line is for the battery of Example 2, and the red line is for the battery of Comparative Example 2. According to this, it was confirmed that the battery of Example 2 has superior discharge rate according to the same moisture absorption time (24hr@coin half cell: wetting time of the battery) compared to the battery of Comparative Example 2.

Capacity characteristics

The batteries of Example 2 and Comparative Example 2 were charged with a constant current at 0.1C to 4.2V and then discharged at 0.1C to 2.5V with a constant current to confirm charge/discharge characteristics. The results are shown in FIG. 4. In FIG. 4, the black line is for the battery of Example 2, and the red line is for the battery of Comparative Example 2. Accordingly, it was confirmed that the battery of Example 2 has superior capacity characteristics compared to the battery of Comparative Example 2.

Room temperature life characteristics

The cells of Example 3 and Comparative Example 3 were charged with a constant current at 1.0C to 4.2V, and then charged and discharged at 1.0C at a constant current to 2.5V, and the ratio of the amount of discharge to the initial capacity and the rate of increase in resistance were measured. It is shown in Figure 5. In FIG. 5, the black line is for the battery of Example 3, and the red line is for the battery of Comparative Example 3. Accordingly, it was confirmed that the battery of Example 3 had a lower resistance increase rate and higher capacity retention compared to the battery of Comparative Example 3, resulting in excellent room temperature lifespan characteristics.

Claims (20)

delete delete delete delete delete delete delete delete delete delete delete (S10) preparing lithium transition metal phosphate primary particles having an olivine crystal structure;
(S20) preparing a first mixture by mixing the primary particles obtained in step (S10) and a solvent;
(S30) spray drying the first mixture;
(S40) firing the resultant product of (S30) to obtain secondary particles formed by agglomeration of the primary particles;
(S50) preparing a second mixture by mixing the secondary particles obtained in (S40), a carbon precursor, a hydrophilic functional group providing source, and a solvent; And
(S60) heat-treating the second mixture; and
The source of the hydrophilic functional group of (S40) is Mg ₂ B ₂ O ₅ , CaAlB ₃ O _7, Li ₆ B ₄ O ₉ , boron nitrate (BN), lithium borate, lithium aluminate, lithium hydroxide, aluminum carbonate And one selected from among aluminum hydroxide, or a mixture of two or more,
The lithium transition metal phosphate of (S10) is a method for producing a positive electrode active material for a secondary battery is represented by the following formula:
[Formula 1]
Li _1+a M1 _1-x M2 _x (PO _4-b )D _b
In Formula 1
M1 is at least one element selected from Fe, Mn, Co, Ni, Cu, Zn and Mg, M2 is one or more elements selected from any one of groups 2 to 15, excluding element M1, and D is F , At least one selected from the group consisting of S and N, and -0.5≦a≦+0.5, 0≦x≦0.5, and 0≦b≦1.
The method of claim 12,
The step (S10) is (S10a) preparing a first slurry comprising a raw material and an alkalizing agent; And (S10b) reacting the first slurry under supercritical or subcritical conditions to synthesize primary particles of lithium transition metal phosphate,
In the step (S10a), the raw material is a method of manufacturing a cathode active material for a secondary battery that includes a lithium-containing precursor and a transition metal-containing precursor.
The method of claim 12,
The carbon precursor is a method of manufacturing a positive electrode active material for a secondary battery, characterized in that the sugar.
The method of claim 14,
The saccharide is a method for producing a positive electrode active material for a secondary battery that is a compound containing a C _n H _2n cycloalkane ring having 3 to 6 carbon atoms.
The method of claim 12,
At least one of the first mixture and the second mixture further comprises a cellulose-based dispersant. The method of manufacturing a positive electrode active material for a secondary battery.
The method of claim 12,
Spray drying in the step (S30) is a method of producing a positive electrode active material for a secondary battery, characterized in that performed at 20 ℃ to 350 ℃.
The method of claim 12,
The method for producing a positive electrode active material for a secondary battery, characterized in that the firing in the step (S40) is carried out at 700 ℃ to 800 ℃.
The method of claim 12,
The method of manufacturing a positive electrode active material for a secondary battery, characterized in that the heat treatment in step (S60) is performed at 250 ℃ to 500 ℃. delete

Images