KR102086533B1 - Positive electrode active material for secondary battery and secondary battery comprising the same - Google Patents

Abstract

In the present invention, a secondary structure comprising a lithium iron phosphate primary structure is assembled, the primary structure has a ratio (TD / BD ratio) of true density (TD) and bulk density (BD) on the surface 10 Carbon black having a dibutyl phthalate oil absorption of 100 ml / 100g to 450 ml / 100g; And a conductive layer including carbon, wherein the conductive layers are connected to each other to form a conductive path in the secondary structure, and thus have a good electrical conductivity, thereby improving a cathode active material for a secondary battery, and the same. Provided is a secondary battery comprising.

Description

Positive electrode active material for secondary battery and secondary battery comprising same {POSITIVE ELECTRODE ACTIVE MATERIAL FOR SECONDARY BATTERY AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a positive electrode active material for a secondary battery and a secondary battery including the same having excellent electrical conductivity, which can improve output characteristics when a battery is applied.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

However, lithium secondary batteries have a problem in that their lifespan drops rapidly as they are repeatedly charged and discharged. In particular, this problem is more serious at high temperatures. This is due to the phenomenon that the electrolyte is decomposed or the active material is deteriorated due to moisture or other effects in the battery, and the internal resistance of the battery is increased.

Accordingly, the positive electrode active material for lithium secondary batteries currently being actively researched and developed is LiCoO ₂ having a layered structure. LiCoO ₂ is most commonly used due to its excellent lifespan characteristics and charge and discharge efficiency. However, LiCoO ₂ has a low structural stability, and thus, LiCoO ₂ has a limitation in being applied to high capacity battery technology.

As a cathode active material to replace this, lithium manganese composite metal oxide, lithium iron phosphate compound, lithium nickel composite metal oxide and the like have been developed. Among them, lithium iron phosphate (LiFePO ₄ ) having an olivinic structure has a high volume density of 3.6 g / cm 3, generates a high potential of 3.4 V, and has a high theoretical capacity of about 170 mAh / g. In addition, LiFePO ₄ in the initial state contains one electrochemically undoped Li for each Fe atom, and thus is a promising material as a cathode active material for secondary batteries. Furthermore, since LiFePO ₄ contains iron, which is a resource that is abundant and inexpensive, it is less expensive than LiCoO ₂ , LiNiO ₂ , or LiMn ₂ O ₄ described above, and is less toxic to the environment. In addition, LiFePO ₄ has a low electrical conductivity, and usually has a form of a secondary structure in which primary structures are assembled, resulting in a problem of low output characteristics due to large interfacial resistance between primary structures.

Accordingly, a method of surface coating of LiFePO ₄ with a carbon-based material has been proposed. However, since the coating efficiency of the carbon-based material itself is low, the effect of improving the electrical conductivity according to the surface treatment of the carbon-based material is not sufficient.

Japanese Patent Registration No. 5111369 (2012.10.19 registration)

The first technical problem to be solved by the present invention is to provide a cathode active material for a secondary battery and a method of manufacturing the same, which has an excellent electrical conductivity by the formation of an electric pass in the active material and can improve the output characteristics when the battery is applied. .

In addition, a second technical problem to be solved by the present invention is to provide a secondary battery positive electrode and a lithium secondary battery containing the positive electrode active material.

According to an embodiment of the present invention for solving the above problems, it is a secondary structure formed by agglomeration of a particulate primary structure containing lithium iron phosphate, the primary structure on the surface, the bulk density for true density Carbon black having a ratio of 10 to 20 and a dibutyl phthalate oil absorption of 100 ml / 100g to 450 ml / 100g; And a conductive layer including carbon, wherein the conductive layers are connected to each other in the secondary structure to form a conductive path.

According to another embodiment of the present invention, preparing a composition for forming a positive electrode active material by mixing the primary structure, the carbon precursor and the carbon black particles containing lithium iron phosphate in a solvent; Spray drying the composition for forming the cathode active material and then heat-treating the carbon black, wherein the ratio of the bulk density to the true density is 10 to 20, and the dibutyl phthalate oil absorption amount is 100 ml / 100g to 450 ml / 100g. It provides a method for producing a cathode active material for a secondary battery.

According to another embodiment of the present invention, a cathode for a secondary battery including the cathode active material and a lithium secondary battery including the same are provided.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The cathode active material for a secondary battery according to the present invention may exhibit excellent electrical conductivity by forming a conductive path inside the active material. As a result, the output characteristics can be improved when the battery is applied.

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in the drawings. It should not be construed as limited.
1 is a graph showing the Raman spectroscopic analysis results of the positive electrode active material prepared in Example 1 and Comparative Examples 2, 3.
2 is a graph evaluating output characteristics of a battery including the cathode active material of Example 1. FIG.
3 is a graph evaluating output characteristics of a battery including the cathode active material of Comparative Example 1. FIG.

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 are not to be construed as being limited to the common or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meanings and concepts corresponding to the technical idea of the present invention based on the principle that the present invention.

A cathode active material for a secondary battery according to an embodiment of the present invention,

It is a secondary structure formed by aggregation of a particulate primary structure containing lithium iron phosphate,

The primary structure is a carbon black having a bulk density ratio of 10 to 20, and dibutyl phthalate oil absorption amount of 100 ml / 100g to 450 ml / 100g on the surface; And a conductive layer comprising carbon,

The conductive layers are connected to each other in the secondary structure to form a conductive path.

As described above, in the positive electrode active material containing lithium iron phosphate, a conductive layer is formed on the surface of the particulate primary structure containing lithium iron phosphate, and the conductive layers formed on each primary structure are connected to each other to form an active material. By forming a three-dimensional conductive path in the secondary structure, the electrical conductivity in the active material is improved, the resistance can be reduced to exhibit excellent output characteristics in the battery application.

In the present invention, 'primary structure' means a single particle structure, and 'secondary structure' means a physical or chemical bond between the primary structures without the intentional agglomeration or assembly process for the primary structure constituting the secondary structure. By means the aggregates aggregated between the primary structures.

Specifically, the cathode active material for a secondary battery according to an embodiment of the present invention is a secondary structure in which a particulate primary structure including lithium iron phosphate is aggregated through a physical / chemical bond, and each of the primary structures is a surface. Together with the highly structured carbon black on the phase, there is a conductive layer comprising carbon produced by pyrolysis of the carbon precursor.

In the conductive layer, the carbon black may be acetylene black, ketjen black, channel black, furnace black, lamp black, or summer black, and may include a mixture of two or more of these. Specifically, the carbon black may be a furnace black produced by oil combustion, more specifically, by thermally decomposing aromatic liquefied hydrocarbons in a reactor.

Furnace black is made of ketjen black, which is made from ethylene heavy oil, channel black, which is quenched and precipitated after burning the raw material gas, and thermal black, which is produced by periodically repeating combustion and pyrolysis of gaseous raw materials, especially acetylene gas. Compared with other carbon blacks such as acetylene black, the primary structure of the carbon black on the secondary structure is highly structured, and exhibits excellent conductivity and dispersibility. Accordingly, when the primary structure of lithium iron phosphate is surface-treated with the carbon black, it not only shows excellent conductivity per se, but also easily forms a conductive path in the secondary structure of the positive electrode active material by forming a uniform conductive layer. .

More specifically, the furnace black is a high abrasion furnace black (HAP), super abrasion furnace black (SAP) or semi-super abrasion furnace black having excellent strength characteristics , Hard carbon (ISAF), and the like, and may include any one or a mixture of two or more thereof.

Specifically, the carbon black may have a ratio (TD / BD ratio) of true density (TD) and bulk density (BD) of 10 to 20, and dibutyl phthalate oil absorption amount of 100 ml / 100g to 450 ml / 100g. .

In the present invention, the true density of the carbon black is measured by using a Pycnometer (AccuPycII 1340), the bulk density (bulk density) in terms of the density of the particle itself except the pores in the porous solid It is different from. Accordingly, the internal structure of the carbon black can be predicted from the TD / BD ratio. If the TD / BD ratio is too large, the content of the primary structure in the carbon black is low, which may lower the capacity characteristics of the battery, and also the TD / BD ratio. When too small, there exists a possibility that the dispersibility of carbon black may fall. Considering the remarkable effect of the improvement effect of the ratio of the bulk density and the true density, the TD / BD ratio of the carbon black usable in the present invention may be more specifically 10 to 15.

More specifically, the carbon black is 0.1 g / cm ³ under the conditions that meet the above TD / BD ratio Bulk density to 0.2 g / cm ³ and 1.9 g / cm ³ To 2.0 g / cm ³ . Even more specifically, it may have a bulk density of 0.15 g / cm ³ to 0.18 g / cm ³ and a true density of 1.9 g / cm ³ to 1.96 g / cm ³ .

In addition, the carbon black may have a dibutyl phthalate (DBP) adsorption of 100 ml / 100g to 450 ml / 100g.

In the present invention, the DBP oil absorption is a measure of the voids of the secondary structure in which the primary structures of carbon black are aggregated, and indicate how well the primary structures in the carbon black are connected. In general, the greater the DBP oil absorption, the better the conductivity. However, when the DBP oil absorption is too large, there is a fear that the conductivity is lowered. Carbon black usable in the present invention can exhibit excellent conductivity and dispersibility by exhibiting the DBP oil absorption in the above range due to its unique structure. More specifically, the carbon black may have a DBP oil absorption of 170 ml / 100g to 350 ml / 100g, and more specifically 190 ml / 100g to 250 ml / 100g.

The carbon black used in the present invention simultaneously satisfies the above-mentioned bulk density and true density ratio and DBP oil absorption conditions, thereby exhibiting excellent conductivity in itself, and excellent in surface treatment of the primary structure of the active material. It is possible to form a surface treatment layer having a uniform thickness by showing acidity, and as a result, it is easy to form a conductive path in the secondary structure.

In addition, the carbon black is a secondary structure formed by agglomeration of the primary structure, and specifically, may be a secondary structure formed by agglomeration of a primary structure having an average particle diameter (D ₅₀ ) of 10 nm to 80 nm.

As such, the carbon black usable in the present invention may exhibit more excellent conductivity by having a highly developed structure. In particular, when used in the manufacturing of the electrode of the lithium secondary battery, the reactivity can be improved by increasing the electron supply at the three-phase interface between the positive electrode active material and the electrolyte. If the average particle diameter of the primary structure of carbon black is less than 10 nm under the conditions satisfying the above TD / BD ratio, there is a fear that the dispersibility is greatly reduced due to the aggregation of the carbon black. In addition, when the average particle diameter of the primary structure exceeds 80 nm, the dispersibility itself is difficult to form a uniform surface treatment layer during the surface treatment of the lithium iron phosphate primary structure, as a result, the conductive path in the active material secondary structure Can be difficult to form. More specifically, considering the remarkable influence of the average particle diameter of the primary structure of the carbon black on the conductivity and dispersibility, the average particle diameter (D ₅₀ ) of the primary structure of the carbon black may be 20nm to 35nm.

In addition, the average particle diameter (D ₅₀ ) of the primary structure of carbon black can be defined as the particle size at 50% of the particle size distribution. In addition, the average particle diameter (D ₅₀ ) of the carbon black can be measured using, for example, a laser diffraction method, more specifically, after dispersing the primary structure of the carbon black in a solvent. After introducing into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) and irradiating an ultrasonic wave of about 28 kHz with an output of 60 W, the average particle diameter (D ₅₀ ) at 50% of the particle size distribution in the measuring device was measured. Can be calculated.

The carbon black may satisfy the above conditions of the average particle diameter and have a specific surface area (SSA) of 30 m ² / g to 200 m ² / g.

As such, since the primary structure has a small size and the BET specific surface area of the secondary structure has a highly developed structure, excellent conductivity can be exhibited. More specifically, the carbon black may have a specific surface area of 40 m ² / g to 90 m ² / g.

In the present invention, the specific surface area of the carbon black is measured by the BET method, and specifically, it can be calculated from the nitrogen gas adsorption amount under the liquid nitrogen temperature (77 K) using BELSORP-mino II manufactured by BEL Japan. .

In addition, the carbon black is 1330 cm ^-1 to 1370 cm ^- with respect to the peak height (I _G ) of the band of 1550 cm ^-1 to 1620 cm ^-1 obtained by Raman spectroscopy using a laser of 532 nm wavelength of the Raman spectral spectrum. the ratio of the peak (I _D) of the height of the ^first band (I ratio of _D / I _G) may be greater than 1.

Raman spectroscopy is a method for analyzing the structure of carbon black, which is useful for analyzing the surface state of carbon black. The peak present in the region near the wavenumber of 1580 cm ⁻¹ in the Raman spectrum of carbon black is called a G band, which is a peak indicating sp 2 bond of carbon black, indicating a carbon crystal without structural defects. On the other hand, the peak present in the region near the wave number 1360 cm ^-1 in the Raman spectrum is called the D band, which is a peak indicating sp3 bond of carbon black, and increases when an atomic bond composed of sp2 bond is broken and becomes sp3 bond. Such a D-band is a so increased when the disorder (disorder) to the defect (defect) present in the carbon black is to be created, up to a peak intensity (I _D) of D-band of the maximum peak intensity (I _G) of G-band The ratio I _D / I _G can be calculated to quantitatively assess the degree of disorder to defect generation.

G band in Raman spectrum of the carbon black in the present invention may be a peak existing in a wave number region of 1550 cm ^-1 to 1620 cm ^-1, D band is in the range of wave number 1330 cm ^-1 to 1370cm ^-1 May be a peak. The wave ranges for the G and D bands correspond to a range that can be shifted according to the laser light source used in the Raman analysis. The Raman value used in the present invention is not particularly limited, but may be measured at a laser wavelength of 532 nm using DXR Raman Microscope (Thermo Electron Scientific Instruments LLC).

In general, the larger the ratio of the G band peak integral value to the D band peak integral value, the higher the amount of amorphous carbon or the poorer crystallinity of the carbon black. However, in the present invention, the specific surface area is increased and highly structured. The crystallinity is good while the above average value of I _D / I _G is shown.

In addition, the carbon black may control the content of metal impurities in the carbon black through the impurity control in the manufacturing process or the purification process after production, specifically, the purity may be 99.5% or more.

As an example, a lithium secondary battery degrades its life characteristics as components deteriorate due to various causes. One of the main causes is due to incorporation of metal impurities in a battery into a battery. Specifically, metal impurities such as iron (Fe) contained in the conductive material are dissolved in the electrolyte by reacting at an operating voltage range of about 3.0V to 4.5V of the lithium secondary battery, and the dissolved metal impurities are in the form of metal at the negative electrode. Is reprecipitated. The precipitated metal penetrates the separator and shorts with the positive electrode, causing a low voltage failure, and deteriorating the capacity characteristics and life characteristics of the secondary battery, thereby preventing its function as a battery. Therefore, it is important to prevent the incorporation of impurities, particularly metal impurities, in the application of the secondary battery of the conductive material. Accordingly, the carbon black usable in the present invention may be carbon black having high purity in the above range in which the content of metal impurities is removed to the maximum.

In the present invention, the content of impurities in the carbon black, in particular metal impurities, may be determined by using magnetic, X-ray diffraction (XRD), differential thermal analysis (DTA), differential scanning. Differential Scanning Calorimetry (DSC), Modulated Differential Scanning Calorimetry (MDSC), Thermogravimetric Analysis (TGA), Thermogravimetric-infrared (TG-IR) Analysis and Melting Point Analysis or identification may be accomplished by including one or more thermal assays, including measurements. Specifically, the content of metal impurities in carbon black can be measured through the main peak intensity of the metal impurities obtained by X-ray diffraction (XRD).

In addition, the carbon black may be surface treated to increase dispersibility when forming the surface treated layer.

Specifically, the carbon black imparts hydrophilicity by introducing an oxygen-containing functional group on the surface of the carbon black by oxidation treatment; Alternatively, hydrophobicity may be imparted by fluorination treatment or siliconization treatment on carbon black. The carbon black may be coated with a phenol resin or subjected to mechanical / chemical treatment. For example, when the carbon black is oxidized, it may be performed by heat treating the carbon black at 500 ° C. to 700 ° C. for about 1 to 2 hours in air or under an oxygen atmosphere. However, if the surface treatment for the carbon black is excessive, since the electrical conductivity and strength characteristics of the carbon black itself may be greatly deteriorated, it may be desirable to control properly.

In addition, the carbon black may be included in an amount of 0.1% to 10% by weight based on the total weight of the positive electrode active material. If the carbon black content is less than 0.1% by weight, the formation of a conductive path in the positive electrode active material is not sufficient, and if the carbon black content is more than 10% by weight, the capacity may decrease due to the relative decrease of the lithium iron phosphate content in the positive electrode active material. There is.

On the other hand, in the positive electrode active material for secondary battery according to an embodiment of the present invention, the carbon is produced by the thermal decomposition of an organic carbon precursor such as sucrose, conductive on the surface of the primary structure together with the carbon black Form a layer.

The carbon may be included in an amount of 1% by weight to 5% by weight based on the total weight of the positive electrode active material. If the carbon content is less than 1% by weight, the formation of a conductive path in the positive electrode active material is not sufficient. If the carbon content is more than 5% by weight, the capacity may decrease due to the relative decrease of the lithium iron phosphate content in the positive electrode active material.

The conductive layer including carbon black and carbon as described above may be formed on the entire surface of the primary structure of the active material, or may be partially formed. In addition, when the conductive layer is partially formed, there may be a plurality of conductive layers formed locally on the surface of the primary structure of lithium iron phosphate.

Specifically, when the conductive layer is partially formed, it may be formed for a surface area of 30% or more and less than 100% of the total surface area of the lithium iron phosphate primary structure. When the conductive layer formation area is less than 30%, it may be difficult to form a conductive path by connecting conductive layers in the active material secondary structure. More specifically, it may be formed for a surface area of 40% to 99.9%.

In addition, the conductive layer is preferably formed to an appropriate thickness in consideration of the diameter of the primary structure of lithium iron phosphate to determine the capacity of the positive electrode active material. Specifically, the conductive layer may be formed in an average thickness ratio of 0.01 to 0.1 with respect to the radius of the primary structure of lithium iron phosphate. If the thickness ratio of the conductive layer is less than 0.01, the improvement effect due to the formation of the conductive layer may be insignificant, and if the thickness ratio exceeds 0.1, there is a concern that the capacity decreases due to the relatively decrease in the content of lithium iron phosphate in the active material. More specifically, the conductive layer may be formed with an average thickness ratio of 0.05 to 0.1 with respect to the radius of the primary structure of lithium iron phosphate.

In the present invention, the particle size of the primary structure of lithium iron phosphate and the thickness of the conductive layer can be measured through particle cross-sectional analysis using a focused ion beam (fib).

On the other hand, in the positive electrode active material for a secondary battery according to the present invention, the lithium iron phosphate may specifically have an olivine crystal structure, and more specifically may include a compound of formula (1):

[Formula 1]

LiFe _1-x M _x P _a O ₄

In Chemical Formula 1,

M is Al, Mg, Ni, Co, Mn, Ga, Cu, V, Ce, Y, Zn, In, Mn, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir and Any one or two or more elements selected from the group consisting of V,

0 ≦ x <1, more specifically 0 ≦ x <0.05,

a is 0.910 to 1, more specifically 0.955 to 1.

Further, when in the formula 1 a is at least 0.910 less than 1, the lithium phosphate cheolnae phosphorus molar ratio is reduced more than in the lithium iron phosphate having a single oxidation state of Fe ^{2 +} and becomes Fe ^{3 +} coexist, the conventional Fe ^{2 +} Excellent electrical conductivity and ion conductivity due to lithium ion diffusion can be improved. As a result, despite the decrease in the phosphorus content, the IR drop phenomenon during charging and discharging is suppressed without structural change, and the discharge profile is improved to improve the energy density of the battery. In addition, it is possible to maximize battery efficiency and capacity by leveling the efficiency of the positive electrode active material to the level of the negative electrode active material having a relatively low operating efficiency. In this case, more specifically, in Formula 1, a may be 0.910 to 0.999, and more specifically, 0.955 to 0.995.

A cathode active material for a secondary battery according to an embodiment of the present invention having the above structure is a secondary structure in which a primary structure having a conductive layer on its surface is assembled. Specifically, an average particle diameter of the primary structure of lithium iron phosphate is increased. It may be from 100nm to 500nm.

In addition, the cathode active material may have an average particle diameter (D ₅₀ ) of 1.5 ㎛ to 30 ㎛, BET specific surface area of 0.5 m ² / g to 25 m ² / g.

If the average particle diameter (D ₅₀ ) of the positive electrode active material is less than 1.5 μm or the BET specific surface area exceeds 25 m ² / g, there is a fear that the dispersibility of the positive electrode active material in the active material layer and the resistance in the electrode are increased due to the aggregation between the positive electrode active materials, In addition, when the average particle diameter (D ₅₀ ) exceeds 30 µm or the BET specific surface area is less than 0.5 m ² / g, there is a fear that the dispersibility and capacity of the positive electrode active material itself decrease. In addition, the positive electrode active material according to an embodiment of the present invention may exhibit excellent capacity and charge and discharge characteristics by simultaneously accelerating the average particle diameter and the BET specific surface area conditions. More specifically, the cathode active material may have an average particle diameter (D ₅₀ ) of 3 μm to 20 μm and a BET specific surface area of 1.0 m ² / g to 20 m ² / g.

In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material may be defined as the particle size at 50% of the particle size distribution. In the present invention, the average particle diameter (D ₅₀ ) of the core is, for example, electron microscope observation using a scanning electron microscopy (SEM), a field emission scanning electron microscopy (FE-SEM), or the like. Or, it can be measured using a laser diffraction method. In the measurement by the laser diffraction method, more specifically, the core was dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to irradiate an ultrasonic wave of about 28 kHz at an output of 60 W. after that, it is possible to calculate the average particle diameter (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

In addition, in the present invention, the specific surface area of the positive electrode active material is measured by the Brunauer-Emmett-Teller (BET) method, specifically BELSORP-mino II, manufactured by BEL Japan, under liquid nitrogen temperature (77K). It can calculate from nitrogen gas adsorption amount.

In addition, the cathode active material according to an embodiment of the present invention has a peak height (I _G ) of a band of 1550 cm ^-1 to 1620 cm ^-1 obtained by Raman spectroscopy using a laser of 532 nm wavelength in the Raman spectral spectrum. The ratio of the peak height I _D (ratio of I _D / I _G ) of the band 1330 cm ⁻¹ to 1370 cm ⁻¹ may be 0.85 or more, specifically 0.85 to 0.9, and more specifically 0.85 to 0.87 have.

In addition, the cathode active material according to an embodiment of the present invention may have a tap density of 0.5 g / cc or more, or 0.5 g / cc to 2.5 g / cc. By having a high tap density in the above range, high capacity characteristics can be exhibited. More specifically, it may have a tap density of 0.7 g / cc to 2.5 g / cc. In the present invention, the tap density of the positive electrode active material can be measured using a conventional tap density measuring device, and specifically, can be measured using a powder tester manufactured by Seishin.

The cathode active material according to an embodiment of the present invention comprises the steps of preparing a composition for forming a cathode active material by mixing a particulate primary structure, a carbon precursor and carbon black containing lithium iron phosphate in a solvent; It may be prepared by a manufacturing method comprising the step of spray drying the positive electrode active material forming composition for heat treatment. In this case, the carbon black has a ratio of true density and bulk density of 10 to 20, and dibutyl phthalate oil absorption of 100 to 450 ml / 100 g, which is the same as described above.

More specifically, a composition for forming a cathode active material is prepared by mixing a primary structure containing lithium iron phosphate, a carbon precursor, carbon black, and a solvent.

In this case, the lithium iron phosphate, the primary structure including the same, and carbon black are the same as described above, and may be mixed in an appropriate amount in consideration of the content of the materials in the positive electrode active material.

In addition, the carbon precursor is thermally decomposed by subsequent heat treatment to form a conductive layer on the surface of the first structure together with carbon black.

 The carbon precursor may be a saccharide, more specifically monosaccharides such as glucose or fructose; Disaccharides such as sucrose, lactose and maltose; Or polysaccharides such as galactose, starch, dextrin or cellulose, and any one or a mixture of two or more thereof may be used.

The carbon precursor may be used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the primary structure. If the content of the carbon precursor is less than 1 part by weight, the formation of the conductive layer in the final cathode active material is not sufficient, and if it exceeds 10 parts by weight, the capacity may decrease due to the relative decrease of the lithium iron phosphate content in the cathode active material.

In addition, the solvent is water; An organic solvent including any one or both selected from the group consisting of a ketone solvent and an alcohol solvent; Or it may be a mixture of the organic solvent and water, more specifically it may be water.

The solvent subsequently affects the size of the droplets formed during spray drying. Specifically, since the size of the droplets may vary depending on the surface tension and density of the composition for forming the positive electrode active material, the type and content of the organic solvent are considered. It is desirable to determine. Specifically, the organic solvent may be included in an amount such that the composition for forming the positive electrode active material has an appropriate viscosity. Specifically, the organic solvent may be used in an amount such that the viscosity of the composition for forming the positive electrode active material is 50 cps to 2500 cps, more specifically 100 cps to 2000 cps. Can be.

In addition, additives such as a primary structure including lithium iron phosphate in the composition for forming the positive electrode active material and a dispersant for increasing the dispersibility of carbon black or a binder for increasing the binding force of carbon black to the primary structure may be further added. It may be.

In this case, the dispersant and the binder used are carbonized in a subsequent firing step, thereby not adversely affecting battery performance.

In addition, the mixing of the primary structure, carbon black and water containing the lithium iron phosphate may be performed according to a conventional mixing process. Specifically, an ultrasonic disperser, a stirring disperser, a high speed rotary shear disperser, a mill disperser, a high pressure jet disperser, etc. are mentioned.

Next, the cathode active material is prepared by spray-drying and heat-treating the composition for forming the cathode active material prepared above.

The spray drying is performed by spraying the solvent under a high temperature atmosphere to instantly blow off the solvent to simultaneously treat the surface of the carbon black and agglomerate the surface-treated primary structures to the primary structure containing lithium iron phosphate and thereby secondary structure. Get up.

In addition, it is possible to promote aggregation and fixation of the primary structure through the heat treatment process after the spraying process.

In addition, the spraying and heat treatment process may be performed under an inert atmosphere such as nitrogen or argon or under vacuum.

In the cathode active material prepared by the above-described manufacturing method, after the primary structure of lithium iron phosphate constituting the cathode active material is surface treated with a conductive layer of carbon black, the cathode active material is aggregated onto the secondary structure, thereby forming a conductive path in the active material particles. do. As a result, the output characteristics of the battery may be improved by increasing the electrical conductivity and decreasing the resistance in the active material.

According to another embodiment of the present invention provides a cathode and a lithium secondary battery comprising the cathode active material.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium on a surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In addition, in the positive electrode for a secondary battery according to an embodiment of the present invention, the positive electrode active material layer is a compound capable of reversible intercalation and deintercalation of ordinary lithium together with the positive electrode active material described above (lithiated intercal). Ration compound) (hereinafter, simply referred to as "second positive electrode active material").

Specifically, the second cathode active material may be a cathode active material of a metal such as cobalt, manganese, nickel or aluminum, and a lithium composite metal oxide containing lithium (hereinafter, simply referred to as “second lithium composite metal oxide”).

More specifically, the second positive electrode active material is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O Etc.), lithium-cobalt-based oxides (e.g., LiCoO _2, etc.), lithium-nickel-based oxides (e.g., LiNiO _2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi _{1 - Y} Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ (where, 0 <Z <2) and the like), lithium-nickel-cobalt-based oxide (for example, LiNi _{1- Y} Co _Y O ₂ (here, 0 <Y <1) and the like, lithium-manganese-cobalt-based oxide (eg, LiCo _1-Y Mn _Y O ₂ (here, 0 <Y <1), LiMn _{2 - z} Co _z O ₄ (here, 0 <Z <2) and the like, lithium-nickel-manganese-cobalt-based oxides (eg, Li (Ni _P Co _Q Mn _R ) O ₂ (here, 0 <P <1, 0 <Q <1, 0 <R <1, P + Q + R = 1) or Li (Ni _P Co _Q Mn _R ) O ₄ (where 0 <P <2, 0 <Q <2, 0 <R <2, P + Q + R = 2), or lithium-nickel-cobalt-transition metal (M) oxide (for example, Li (Ni _P Co _Q Mn _R M _S ) O ₂ (here, M is atoms of Al, Fe, V, Cr, Ti, Ta, Mg , and selected from the group consisting of Mo, and P, Q, R and S are each independent element Rate, 0 <P <1, 0 <Q <1, 0 <R <1, 0 <S <1, P + Q + R + S = 1), etc.), and any one or two of them may be used. Mixtures of the above may be used. In addition, the second cathode active material may be doped by tungsten (W), boron (B), aluminum (Al), or the like. Among these, the second cathode active material may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or lithium nickel manganese cobalt oxide (eg, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O _2. , LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , or LiNi _{0 . 8} Mn _{0 . 1} Co _{0 . 1} O _2), or lithium nickel cobalt aluminum oxide _{(e.g., LiNi 0. 8 Co 0.} 15 Al 0. 05 O 2 , etc.) and the like, wherein in that it can increase the capacity characteristics of the battery, and reliability The second cathode active material is LiNi _0.6 Mn _0.2 Co _0.2 O ₂ , LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , LiNi _{0 . 7} Mn _{0 . 15} Co _{0 . 15} O ₂ , LiNi _{0 . 8} Mn _{0 . 1} Co _{0 . 1} O ₂ or mixtures thereof.

The second cathode active material may be included in an amount of 99 wt% or less, specifically 70 wt% or less, and more specifically 1 wt% to 50 wt%, based on the total weight of the cathode active material layer. More specifically, it may be included in the same amount (weight ratio of 50:50) or higher with the positive electrode active material according to an embodiment of the present invention under conditions satisfying the above-described content range.

In addition, the cathode active material layer may optionally further include at least one of a conductive material and a binder.

In this case, the conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material may be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the cathode active material layer.

In addition, the binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or more of these may be used. The binder may be included in an amount of 1 wt% to 30 wt% with respect to the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except using the positive electrode active material described above. Specifically, by applying the composition for forming a positive electrode active material layer containing at least one selected from the second positive electrode active material, a binder and a conductive material together with the positive electrode active material on a positive electrode current collector, and then drying and rolling Can be prepared. In this case, the type and content of the cathode active material, the second cathode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the coating thickness of the slurry, the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during the application for the production of the positive electrode. Do.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

At this time, the operating voltage of the lithium secondary battery may be 2.0V to 4.6V. This is because it is possible to operate at a relatively high voltage as the stability of the battery is improved due to the structural stability of the positive electrode active material including a lithium excess composite metal oxide of the formula (1). More specifically, the lithium secondary battery according to an embodiment of the present invention may be a high voltage driving battery of 2.5V to 4.6V, and more specifically, it may be a high voltage driving battery of 2.5V to 4.35V.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium, such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular for ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte solution and excellent in electrolytic solution moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge / discharge performance of a battery, and low viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the cathode active material according to the present invention may exhibit excellent battery stability and life characteristics even under high temperature and high voltage conditions due to the excellent stability of the cathode active material. Accordingly, the present invention is useful for portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicle fields such as hybrid electric vehicles (HEVs).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example 1: Preparation of positive electrode active material

After mixing 2 parts by weight of the furnace black and 10 parts by weight of sucrose shown in Table 1 to 100 parts by weight of a particulate primary structure (average particle diameter: 300 nm) containing LiFePO ₄ having an olivine crystal structure, The resulting mixture was dispersed for 10 minutes using an ultrasonic disperser to prepare a composition for forming a cathode active material. Subsequently, after filling the spray dryer with the composition for positive electrode active material formation prepared, it spray-dried at the temperature of 125 degreeC. The resulting powder was calcined at 700 ° C. for 5 hours in a nitrogen atmosphere to obtain a positive electrode active material on the secondary structure in which a conductive layer containing furnace black and carbon was formed on the surface of the primary structure (the carbon in the positive electrode active material). Content = 3.5% by weight).

Example 2: Preparation of Cathode Active Material

LiFeP _{0 . A} positive electrode active material was prepared in the same manner as in Example 1, except that a particulate primary structure including ₉₈₅ O ₄ was used.

Comparative Example 1: Preparation of Cathode Active Material

Without using the furnace black, a cathode active material on a secondary structure in which a primary structure containing LiFePO ₄ (average particle size: 300 nm) was assembled was used.

Comparative Example 2: Preparation of Cathode Active Material

Except for using the acetylene black shown in Table 1 in place of the furnace black in Example 1 was carried out in the same manner as in Example 1 to obtain a positive electrode active material.

Comparative Example 3: Preparation of Cathode Active Material

Except for using the ketjen black shown in Table 1 in place of the furnace black in Example 1 was carried out in the same manner as in Example 1 to obtain a positive electrode active material.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Kinds Furnace Black
(Super-P Li) - Acetylene black Ketchen Black
(EC-600JD) Primary structure average particle diameter (D ₅₀ , nm) 32 - 36 35 True density (g / cm ³ ) 1.95 - 1.95 2.038 Bulk Density (g / cm ³ ) 0.16 - 0.08 0.11 Specific surface area
(SSA, m ² / g) 65 - 65 1300 DBP oil absorption (ml / 100g) 190 - 165 495 Metal Impurities & Contents Fe, 5 ppm - Fe, 4 ppm Fe, 5 ppm

Preparation Example 1: Fabrication of Lithium Secondary Battery

A lithium secondary battery was manufactured using the cathode active materials prepared in Example 1, respectively.

In detail, the positive electrode active material, the carbon black conductive material, and the PVdF binder prepared in Example 1 were mixed in a ratio of 92: 3: 5 by weight in an N-methylpyrrolidone solvent (viscosity: 5000 mPa). S) was prepared, applied to an aluminum current collector, dried at 130 ° C., and then rolled to prepare a positive electrode.

In addition, as a negative electrode active material, natural graphite, carbon black conductive material, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 95: 1: 1: 2. A negative electrode was prepared by preparing a composition for forming a negative electrode and applying the same to a copper current collector.

An electrode assembly was manufactured between the positive electrode and the negative electrode manufactured as described above through a separator of porous polyethylene, the electrode assembly was placed in a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3/4/3) It was.

[Production Example 2]

A lithium secondary battery was manufactured by the same method as in Preparation Example 1, except that the cathode active material prepared in Example 2 was used instead of the cathode active material prepared in Example 1.

[Production Example 3]

The cathode active material prepared in Example 1 and LiNi _{0 . 6} Co _{0 . 2} Mn _{0 .} A cathode active material composition, a carbon black conductive material, and a PVdF binder, which contain a second positive electrode active material of ₂ O ₂ mixed at a weight ratio of 5: 5, are mixed in an N-methylpyrrolidone solvent at a ratio of 92: 3: 5 by weight. To prepare a composition for forming a positive electrode (viscosity: 5000 mPa · s), which was applied to an aluminum current collector, dried at 130 ° C., and rolled to prepare a positive electrode.

A lithium secondary battery was manufactured by the same method as in Preparation Example 1, except that the positive electrode prepared above was used.

Experimental Example 1

Raman spectroscopy was performed on the cathode active materials prepared in Examples 1 and Comparative Examples 2 and 3 and carbon black used in the preparation of the cathode active materials. The results are shown in FIG. 1 and Table 2 below.

1 is a graph showing the results of Raman spectroscopy for the positive electrode active material prepared in Comparative Examples 1 to 3.

Example 1 Comparative Example 2 Comparative Example 3 Cathode active material Combination E @ I _D (cm ^-1 ) 1345-1360 1361 1347 Combination E @ I _G (cm ^-1 ) 1605 1605 1605 I _D / I _G ratio 0.85-0.87 0.848 0.839 Carbon black I _D / I _G ratio > 1.0 ND ND

In Table 2, ND means not measured.

[ Experimental Example  2]

The cathode active material prepared in Example 1 was observed with a transmission electron microscope (TEM).

As a result, it was confirmed that the primary structure of lithium iron phosphate having a conductive layer of carbon black on the surface was aggregated to form a secondary structure. In addition, it was confirmed that the conductive layer formed on the surface of the primary structure is connected to the conductive layer of the adjacent primary structure to form a three-dimensional conductive path.

 Experimental Example 3

Coin cells (using a negative electrode of Li metal) prepared by using the positive electrode active materials in Example 1 and Comparative Example 1 were charged at 25 ° C. with a constant current (CC) of 3.8 V until 3.8 V, and then 3.8 V The battery was charged at a constant voltage (CV), and charged for the first time until the charging current became 0.05C. After leaving for 20 minutes and discharged to 2.5V with a constant current of 4C to evaluate the output characteristics. The results are shown in FIGS. 2 and 3.

As a result of the experiment, the battery containing the positive electrode active material of Example 1 showed significantly better output characteristics than the battery containing the positive electrode active material of Comparative Example 1, which is an aggregate of LFP primary structures in which conductivity was not secured.

Claims (18)

delete delete delete delete delete delete delete delete delete delete delete delete Preparing a composition for forming a cathode active material by mixing a particulate primary structure including lithium iron phosphate, a carbon precursor, and carbon black in a solvent; And
Spray drying the composition for forming the positive electrode active material and then performing heat treatment to prepare a positive electrode active material of a secondary structure including agglomerated particulate primary structures including lithium iron phosphate,
The primary structure is to include a conductive layer containing carbon black and carbon on the surface, the conductive layer is to be connected to each other in the secondary structure to form a conductive path,
The carbon black has a ratio of bulk density to true density of 10 to 20, and dibutyl phthalate oil absorption amount of 100 ml / 100g to 450 ml / 100g, the method for producing a positive electrode active material for secondary batteries.
The method of claim 13,
Wherein the carbon precursor comprises at least any one selected from the group consisting of monosaccharides, disaccharides and polysaccharides.
The method of claim 13,
The carbon precursor is used in an amount of 1 part by weight to 10 parts by weight with respect to 100 parts by weight of the primary structure.
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