KR20210080051A - Positive electrode material for secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode material for a secondary battery, which is a lithium composite transition metal oxide containing nickel, cobalt and manganese, wherein the particles of the lithium composite transition metal oxide contain a coating element inside the particles, and a concentration change rate represented by the following formula 1 (concentration change rate = │A-B│/A X 100) is 20% or less and a powder rolling density is less than 3 g/cc when the average concentration of the coating element in the 1 μm region from the particle surface to the center direction is A, and the average concentration of the coating element in the 1 μm region from the particle center to the particle surface direction is B.

Description

A cathode material for a secondary battery and a lithium secondary battery comprising the same {POSITIVE ELECTRODE MATERIAL FOR SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a cathode material for a secondary battery and a lithium secondary battery including the same.

Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

In a lithium secondary battery, an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are intercalated/deintercalated from the positive electrode and the negative electrode. Electric energy is produced by a reduction reaction with

As a cathode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _{4 ,} etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. were used. . Among them, lithium cobalt oxide (LiCoO ₂ ) has the advantage of high operating voltage and excellent capacity characteristics, and is widely used, and is applied as a positive electrode active material for high voltage. However, there is a limit to mass use as a power source in fields such as electric vehicles due to an increase in the price of cobalt (Co) and unstable supply, and the need to develop a cathode active material that can replace it has emerged.

Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') in which a part of cobalt (Co) is substituted with nickel (Ni) and manganese (Mn) has been developed. In order to control problems such as electrolyte decomposition and increased surface resistance that may occur when NCM-based lithium composite transition metal oxide comes into contact with electrolyte, a surface coating of NCM-based lithium composite transition metal oxide has been introduced. However, the NCM-based lithium composite transition metal oxide is in the form of secondary particles in which primary particles are agglomerated, and the secondary particles are broken during electrode rolling, exposing parts that are not surface-coated and causing side reactions with the electrolyte. It became a problem. Accordingly, there is still a need to develop a technology capable of minimizing the deterioration of battery performance caused by particle breakage while maintaining the existing level of rolling in order to improve the electrode energy density.

Korean Patent No. 1785266

In the cathode material of NCM-based lithium composite transition metal oxide, the present invention controls the density of the particles so that the coating element can penetrate to the inside of the particles during the coating process, so that the coating inside is not coated due to particle breakage during rolling. An object of the present invention is to provide a cathode material for a secondary battery capable of improving a side reaction with an electrolyte that occurs when the part is exposed and deterioration of battery performance caused by the side reaction.

The present invention is a lithium composite transition metal oxide containing nickel, cobalt and manganese, wherein the particles of the lithium composite transition metal oxide contain a coating element inside the particle, and the coating element in the 1 μm region from the particle surface to the center direction When the average concentration of A is A, and the average concentration of the coating element in the 1 μm region from the particle center to the particle surface direction is B, the concentration change rate expressed by the following formula 1 is 20% or less, and the powder rolling density is It provides a cathode material for a secondary battery of less than 3 g/cc.

[Equation 1]

Concentration change rate = │A-B│/A X 100

In addition, the present invention provides a positive electrode for a secondary battery including the positive electrode material and a lithium secondary battery including the same.

According to the present invention, it is possible to provide a cathode material of an NCM-based lithium composite transition metal oxide in which a coating element penetrates to the inside of the particles during coating by controlling the density of particles. Accordingly, even if particle breakage occurs during rolling, the surface of the coated primary particles is exposed, so that the side reaction with the electrolyte and the deterioration of battery performance resulting therefrom can be improved when the portion that is not coated therein is exposed.

1 is a cross-sectional composition analysis photograph of a cathode material prepared according to Example 1. FIG.
2 is a cross-sectional composition analysis photograph of a cathode material prepared according to Comparative Example 1. FIG.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

<For secondary battery cathode material >

The present invention is a lithium composite transition metal oxide containing nickel, cobalt and manganese, wherein the particles of the lithium composite transition metal oxide contain a coating element inside the particle, and the coating element in the 1 μm region from the particle surface to the center direction When the average concentration of A is A, and the average concentration of the coating element in the 1 μm region from the particle center to the particle surface direction is B, the concentration change rate expressed by the following formula 1 is 20% or less, and the powder rolling density is It provides a cathode material for a secondary battery of less than 3 g/cc.

[Equation 1]

Concentration change rate = │A-B│/A X 100

The lithium composite transition metal oxide is an NCM-based lithium composite transition metal oxide including nickel (Ni), cobalt (Co) and manganese (Mn). The lithium composite transition metal oxide is more preferably a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide in which the content of nickel (Ni) is 50 mol% or more in the total content of metals excluding lithium (Li), and , more preferably, the nickel (Ni) content may be 60 mol% or more, and more preferably 80 mol% or more. Since the content of nickel (Ni) in the total content of the metal excluding lithium (Li) of the lithium composite transition metal oxide satisfies 50 mol% or more, it may be possible to secure a higher capacity.

The lithium composite transition metal oxide may be represented by the following formula (1).

[Formula 1]

Li _a Ni _1-bcd Co _b Mn _c Q _d O _2+δ

In the above formula, Q is any one or more elements selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 1.0≤a≤1.5, 0<b≤0.5, 0<c≤0.5, 0≤d≤0.1, 0<b+c+d≤0.5, -0.1≤δ≤1.0.

In the lithium composite transition metal oxide of Formula 1, Li may be included in an amount corresponding to a, that is, 1.0≤a≤1.5. If a is less than 1.0, there is a fear that the capacity may decrease, and if it exceeds 1.5, the particles are sintered in the firing process, so it may be difficult to manufacture the positive active material. Considering the remarkable effect of improving the capacity characteristics of the positive electrode active material according to the control of the Li content and the balance of sinterability during the preparation of the active material, Li may be more preferably included in a content of 1.1≤a≤1.2.

In the lithium composite transition metal oxide of Formula 1, Ni may be included in a content corresponding to 1-(b+c+d), for example, 0.5≤1-(b+c+d)<1. When the content of Ni in the lithium composite transition metal oxide of Formula 1 is 0.5 or more, an amount of Ni sufficient to contribute to charging and discharging is secured, thereby achieving high capacity. More preferably, Ni may be included as 0.60≤1-(b+c+d)≤0.99.

In the lithium composite transition metal oxide of Formula 1, Co may be included in an amount corresponding to b, that is, 0<b≤0.5. When the content of Co in the lithium composite transition metal oxide of Formula 1 exceeds 0.5, there is a risk of cost increase. Considering the significant effect of improving capacity characteristics according to the inclusion of Co, Co may be included in a content of 0.05≤b≤0.2 more specifically.

In the lithium composite transition metal oxide of Formula 1, Mn may be included in a content corresponding to c, that is, 0<c≤0.5. If c in the lithium composite transition metal oxide of Formula 1 exceeds 0.5, there is a risk that the output characteristics and capacity characteristics of the battery are rather deteriorated, and the Mn may be included in a content of 0.05≤c≤0.2 more specifically.

In the lithium composite transition metal oxide of Formula 1, Q may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and Q may be included in a content corresponding to d, that is, 0≤d≤0.1.

The lithium composite transition metal oxide may be secondary particles in which primary particles are aggregated. In the present invention, the 'primary particle' refers to a primary structure of a single particle, and the 'secondary particle' refers to the physical between the primary particles without intentional aggregation or assembly process for the primary particles constituting the secondary particles. Alternatively, it refers to an aggregate in which primary particles are aggregated with each other by chemical bonding, that is, a secondary structure.

The lithium composite transition metal oxide of the present invention may have a powder rolling density of less than 3 g/cc, more preferably a rolling density of 2.5 to 2.95 g/cc, and still more preferably 2.7 to 2.9 g/cc. In the present invention, the powder rolling density is a value calculated by measuring the thickness when the pressure is 2000 kgF by putting 5 g powder into a cylindrical mold with an inner diameter of 2 cm, and applying pressure to a cylinder with an outer diameter of 2 cm.

Rolling is performed to improve the electrode energy density. Conventionally, if there is a lot of fine powder during rolling, the surface of primary particles that are not surface-coated is exposed, and a side reaction with the electrolyte occurs, resulting in deterioration of battery performance. has been known to do However, in the present invention, when the powder rolling density is less than 3 g/cc, that is, when the particle density is controlled to be low, the coating element penetrates to the inside of the particles, thereby suppressing the occurrence of side reactions with the electrolyte, and the battery It relates to a cathode material that can bring performance improvement. More specifically, in the case of the present invention, in which the powder rolling density is less than 3 g/cc to control the generation of fine powder to be relatively large during rolling, the coating element can be uniformly distributed not only on the particle surface but also on the inside of the particle, and from the particle surface to the center When the average concentration of the coating element in the region of 1 μm in the direction is A and the average concentration of the coating element in the region of 1 μm in the direction from the particle center to the surface of the particle is denoted as B, the concentration change rate expressed by the following formula 1 This 20% or less can be satisfied.

[Equation 1]

Concentration change rate = │A-B│/A X 100

The cathode material of the present invention may have a fine powder generation rate of 25% or more, more preferably 25 to 35%, and still more preferably 25 to 30%, as defined below. In the present invention, the fine powder generation rate refers to the particle size distribution (PSD) analysis result after rolling by putting 3 g powder into a metal cylindrical mold with an inner diameter of 2 cm and pressing it with a metal cylinder with an outer diameter of 2 cm at a pressure of 9 tons. ) to the area ratio of the newly formed area. It can be determined that the larger the value of the occurrence rate of fine powder, the more the generation of fine powder according to rolling, and the more the generation of fine powder, the lower the particle density. By satisfying the range of the fine powder production rate, the particle density is low, so that the coating element can effectively penetrate to the inside of the particle.

The coating element is not particularly limited, and those typically used as a coating element for a cathode material for a secondary battery may be applied without limitation. For example, the coating element may be at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

The cathode material of the present invention controls the particle density so that the coating element can penetrate not only the particle surface but also the inside to be evenly distributed, and from the particle center to the concentration of the coating element in the 1 μm region from the particle surface to the center direction. The rate of change of the concentration of the coating element in the 1 μm region in the surface direction satisfies 20% or less. More preferably, the concentration change rate may be 0.01 to 15%, and more preferably, the concentration change rate may be 0.01 to 10%. In addition, the concentration change rate of the coating element from the particle center to the particle surface direction may be 20% or less, and more preferably, the concentration change rate from the particle center to the particle surface direction may be 0.01 to 10%.

In the present invention, the particle internal distribution of the coating element is a value measured through NANO-SIMS analysis on a cross-section sample of the cathode material.

The cathode material according to the present invention may be prepared by, for example, controlling the temperature and stirring speed in the co-precipitation reaction of the precursor, and controlling the pH to a specific value or less to lower the density of the fired product, but is not particularly limited thereto. .

As described above, since the coating element satisfies the concentration change rate as described above and is uniformly distributed to the inside of the particle, even if particle breakage occurs during rolling, the surface of the coated primary particle is exposed, so that the portion that is not coated inside is exposed. It is possible to improve a side reaction with the generated electrolyte and deterioration of battery performance resulting therefrom.

<Anode and lithium secondary battery>

According to another embodiment of the present invention, there is provided a positive electrode for a secondary battery and a lithium secondary battery including the positive electrode material as described above.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector and including the positive electrode material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may have a thickness of typically 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase adhesion of the positive electrode material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

In addition, the positive electrode material layer may include a conductive material and a binder together with the above-described positive electrode material.

In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples 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 powders 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, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the cathode material layer.

In addition, the binder serves to improve adhesion between the positive electrode material particles and the adhesive force between the positive electrode material and the positive electrode 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, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, and styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the cathode material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above-described positive electrode material. Specifically, the cathode material and optionally, the composition for forming a cathode material layer including a binder and a conductive material may be coated on a cathode current collector, and then dried and rolled. In this case, the types and contents of the cathode material, the binder, and the conductive material are as described above.

The solvent may be a solvent commonly used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for subsequent positive electrode manufacturing. Do.

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

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

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. In addition, the lithium secondary battery may optionally 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, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 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 strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, 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 negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite, Kish graphite (Kish) in amorphous, plate-like, flaky, spherical or fibrous shape graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

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

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is normally used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

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

The organic solvent may be used without any 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, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based 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 and the like may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

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 may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imine One or more additives such as dazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the positive electrode material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

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 battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example One

After putting 4 liters of distilled water in a coprecipitation reactor (capacity 20L), maintaining a temperature of 50° C., and adding 100 ml of 28 wt% ammonia aqueous solution, NiSO ₄ , CoSO ₄ , MnSO ₄ Nickel: Cobalt: Manganese molar ratio of 0.6 A 3.2 mol/L concentration of a transition metal solution mixed to :0.2:0.2 was continuously added to the reactor at 300 ml/hr, and a 28 wt% aqueous ammonia solution was added to the reactor at 42 ml/hr. The speed of the impeller was stirred at 400 rpm, and 40% by weight of sodium hydroxide solution was used to maintain the pH so that the pH was maintained at 10.0. The precursor particles were formed by co-precipitation reaction for 24 hours. The precursor particles were separated, washed, and dried in an oven at 130° C. to prepare a precursor.

_{Ni 0} synthesized by co-precipitation reaction _{. 6} Co _{0 . 2} Mn _{0 .2} (OH) ₂ precursor mixture so that the Li ₂ CO ₃ and Li / Me mole ratio of 1.05 (Ni, Co, Mn), and heat-treated for 5 hours in the atmosphere _{750 ℃ LiNi 0.6 Co 0.2 Mn 0.2} O 2 A lithium composite transition metal oxide was synthesized. The synthesized lithium composite transition metal oxide was pulverized, mixed with B(OH)3 so that the B content was 1000 ppm based on the total lithium composite transition metal oxide, and then heat-treated at 400° C. for 5 hours to prepare a B-coated cathode material. .

Example 2

A cathode material was prepared in the same manner as in Example 1, except that the pH was maintained at 9.0 during the precursor co-precipitation reaction.

comparative example One

A cathode material was prepared in the same manner as in Example 1, except that the pH was maintained at 11.0 during the precursor co-precipitation reaction.

comparative example 2

A cathode material was prepared in the same manner as in Example 1, except that the pH was maintained at 12.0 during the precursor co-precipitation reaction.

[ Experimental example One: powder Measurement of rolling density and fine powder generation]

Powder rolling density and fine powder generation rate of the positive electrode materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. Powder rolling density is a value calculated by putting 5 g powder into a cylindrical mold with an inner diameter of 2 cm, applying pressure to a cylinder with an outer diameter of 2 cm, and measuring the thickness when the pressure is 2000 kgF. The fine powder generation rate is the area newly formed compared to the particle size distribution (PSD) before rolling in the particle size distribution (PSD) analysis result after rolling by putting 3 g powder into a metal cylindrical mold with an inner diameter of 2 cm and pressing it with a metal cylinder with an outer diameter of 2 cm at a pressure of 9 tons It is a calculated value of the area ratio of The results are shown in Table 1 below.

Powder rolling density (g/cc) Differentiation rate (%) Example 1 2.89 28.8 Example 2 2.75 28.0 Comparative Example 1 3.09 15.27 Comparative Example 2 3.12 16.77

Referring to Table 1, the positive electrode materials of Examples 1 and 2 had a powder rolling density of less than 3 g/cc and a fine powder generation rate of 25% or more, and the positive electrode materials of Comparative Examples 1 and 2 had a rolling density of 3 g/cc or more, It can be seen that the differential generation rate is less than 25%.

[ Experimental example 2: cathode material Section composition analysis]

NANO-SIMS cross-sectional composition analysis was performed on the cross-sectional samples of the cathode materials prepared in Example 1 and Comparative Example 1, and the coating composition permeated into the secondary particles was confirmed. The results are shown in FIGS. 1 and 2 .

1 is a cross-sectional composition analysis photograph of the positive electrode material according to Example 1, ^{it can be seen that the positive electrode material according to the present invention has a coating element 11} B evenly distributed to the inside of the secondary particles. On the other hand, FIG. 2 is a cross-sectional composition analysis photograph of the positive electrode material according to Comparative Example 1, ^{and it can be confirmed that the coating element 11} B is distributed only on the surface of the secondary particles.

[ Experimental example 3: High temperature storage evaluation]

Each of the positive electrode material, carbon black conductive material, and PVdF binder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was mixed in an N-methylpyrrolidone solvent in a weight ratio of 96:2:2 to prepare a positive electrode composite material. Then, it was coated on one side of an aluminum current collector, dried at 100° C., and then rolled to prepare a positive electrode.

As the negative electrode, lithium metal was used.

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

For each lithium secondary battery half-cell prepared as described above, it is charged (termination current 1/20C) to 0.7C and 4.2V in CCCV mode at 25°C, and high temperature at 60°C for 4 weeks After saving, discharge it with a constant current of 0.5C until it becomes 3.0V. Capacity retention and resistance change were measured. The results are shown in Table 2.

Capacity retention rate (%) Resistance change (%) Example 1 95.7 143.7 Example 2 93.4 144.7 Comparative Example 1 87.3 190.1 Comparative Example 2 85.2 187.5

Referring to Table 2, in the case of Examples 1 and 2, the rolling density was lower than that of Comparative Examples 1 and 2, and despite the occurrence of fine powder, it was confirmed that the capacity retention rate was improved during high temperature storage and the resistance change rate was reduced. have.

Claims (8)

It is a lithium composite transition metal oxide containing nickel, cobalt and manganese,
The particles of the lithium composite transition metal oxide contain a coating element inside the particle, and the average concentration of the coating element in a 1 μm region from the particle surface to the center direction is A, and a 1 μm region from the particle center to the particle surface direction When the average concentration of the coating element in is B, the concentration change rate represented by the following formula 1 is 20% or less,
A cathode material for a secondary battery having a powder rolling density of less than 3 g/cc:
[Equation 1]
Concentration change rate = │AB│/AX 100
According to claim 1,
The powder rolling density is a cathode material for a secondary battery of 2.7 to 2.9 g / cc.
According to claim 1,
The coating element is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr.
According to claim 1,
The lithium composite transition metal oxide particles are secondary particles in which primary particles are aggregated. A cathode material for a secondary battery.
According to claim 1,
The lithium composite transition metal oxide is a cathode material for a secondary battery represented by the following Chemical Formula 1:
[Formula 1]
Li _a Ni _1-bcd Co _b Mn _c Q _d O _2+δ
In the above formula, Q is any one or more elements selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 1.0≤a≤1.5, 0<b≤0.5, 0<c≤0.5, 0≤d≤0.1, 0<b+c+d≤0.5, -0.1≤δ≤1.0.
According to claim 1,
A cathode material for a secondary battery having a differential generation rate of 25% or more defined as follows:
[Difference rate]
In the particle size distribution (PSD) analysis result after rolling, 3g powder was put into a metal cylindrical mold with an inner diameter of 2cm and pressurized with a metal cylinder with an outer diameter of 2cm at a pressure of 9ton, the area ratio of the newly formed area compared to the particle size distribution (PSD) before rolling .
A positive electrode for a secondary battery comprising the positive electrode material according to any one of claims 1 to 6.
A lithium secondary battery comprising the positive electrode according to claim 7.

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