KR20220170622A - Manufacturing method of positive electrode active material - Google Patents

Abstract

The present invention relates to a manufacturing method of positive electrode active materials which uses crystalline compounds represented by chemical formula 1 which is reacted with lithium byproducts remaining in lithium transition metal oxide to form a coating layer having high lithium ion conductivity to minimize lithium byproducts capable of remaining on a surface of a positive electrode active material and to improve capacities and outputs of batteries. The manufacturing method comprises a step which mixes and heat-treats lithium transition metal oxide and the crystalline compounds represented by chemical formula 1 described in the present specification to form a coating layer containing boron and aluminum on the lithium transition metal oxide.

Description

Manufacturing method of cathode active material {MANUFACTURING METHOD OF POSITIVE ELECTRODE ACTIVE MATERIAL}

The present invention relates to a method for manufacturing a cathode active material for a lithium secondary battery.

As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Among these 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.

As a cathode active material of a lithium secondary battery, a lithium transition metal such as lithium cobalt oxide such as LiCoO ₂ , lithium nickel oxide such as LiNiO ₂ , lithium manganese oxide such as LiMnO ₂ or LiMn ₂ O ₄ , and lithium iron phosphate oxide such as LiFePO ₄ Oxides have been developed, and more recently, two or more transitions such as Li[Ni _a Co _b Mn _c ]O ₂ , Li[Ni _a Co _b Al _c ]O ₂ , Li[Ni _a Co _b Mn _c Al _d ]O ₂ . A lithium composite transition metal oxide containing a metal has been developed and is widely used.

Lithium by-products such as LiOH and Li ₂ CO ₃ that are not reacted during the manufacturing process may be present in the cathode active material of the lithium secondary battery. In order to minimize such lithium by-products, conventionally, aluminum oxide, boron oxide, or a mixture thereof, which reacts with lithium by-products to form a coating layer, is used as a coating material, and lithium aluminum oxide and/or lithium boron oxide are formed on the surface of the positive electrode active material. A coating layer containing was formed. However, when aluminum oxide, boron oxide, or a mixture thereof is used as a coating material, lithium byproducts still exist, and aluminum boron oxide, aluminum oxide, or boron oxide having low lithium ion conductivity as a byproduct, for example, LiAl ₅ O ₈ , LiB ₃ O ₅ , Al ₂ O ₃ , B ₂ O ₃ , etc. are generated, so that the capacity and output of the battery are not improved and the resistance increase rate is high.

Accordingly, there is a need for a method for manufacturing a positive electrode active material including a coating layer capable of improving the output and resistance increase rate of a battery.

An object of the present invention is to provide a method for manufacturing a cathode active material capable of forming a coating layer having high lithium ion conductivity on the surface of the cathode active material.

The present invention is a method for producing a cathode active material comprising mixing and heat-treating a lithium transition metal oxide and a crystalline compound represented by Formula 1 to form a coating layer containing boron and aluminum on the lithium transition metal oxide. provides

[Formula 1]

Al _x B _y O _z

In Formula 1,

x, y, z are integers greater than or equal to 2;

The present invention minimizes lithium by-products that may remain on the surface of a positive electrode active material by using a crystalline compound represented by Formula 1 capable of forming a coating layer having high lithium ion conductivity by reacting with lithium by-products remaining in a lithium transition metal oxide. In addition, it is possible to improve the output and resistance increase rate of the battery.

1 is a view showing an XRD graph of Al ₄ B ₂ O ₉ used in Example 1 and an XRD graph of AlBO ₃ used in Comparative Example 1;
2 is a SEM image of the cathode active material prepared in Example 1.

The terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but one or more other features or It should be understood that the presence or addition of numbers, steps, components, or combinations thereof is not precluded.

In this specification, the term “on” means not only the case where a certain component is formed directly on top of another component, but also the case where a third component is interposed between these components.

In the present specification, the primary particle refers to the smallest unit particle observed when measuring with a scanning electron microscope (SEM). Secondary particles refer to an aggregate, that is, a secondary structure, in which primary particles are aggregated by physical or chemical bonding between primary particles without intentional aggregation or assembling of the primary particles constituting the secondary particles.

In the present specification, the single particle form is a concept in contrast to the form of spherical secondary particles formed by aggregation of tens to hundreds of primary particles prepared by the conventional method, and each particle is independently and / or separated phase ), or may include a form in which 2 to 10 particles are attached to each other, or the form in which they are separated and / or dispersed from each other to form.

In the present specification, a crystalline compound is a crystalline solid (crystalline solid) and is a concept in contrast to an amorphous compound and a noncrystalline compound in which atoms are arranged in no order.

Cathode active material manufacturing method

When the present inventors use a compound represented by Chemical Formula 1 and a crystalline solid as a coating material that reacts with lithium by-products to remove lithium by-products, a coating layer having high lithium ion conductivity is formed, thereby improving the output and resistance increase rate of the battery. It was found that it could be done and the present invention was completed. That is, when the present inventors use the crystalline compound represented by Formula 1, the lithium ion conductivity is higher than when the coating layer is formed using an amorphous compound AlBO ₃ or a mixture of Al(OH) ₃ and H ₃ BO ₃ Li -It was found that more Al-BO solid solution was formed. And, when using the crystalline compound represented by Formula 1, it was found that by-products such as aluminum oxide and boron oxide having low lithium ion conductivity, such as Al ₂ O ₃ and B ₂ O ₃ , were not generated.

Hereinafter, a method for manufacturing a cathode active material according to the present invention will be described in detail.

The method for manufacturing a positive electrode active material according to the present invention includes mixing a lithium transition metal oxide and a crystalline compound represented by Formula 1 and heat-treating to form a coating layer containing boron and aluminum on the lithium transition metal oxide. do.

[Formula 1]

Al _x B _y O _z

In Formula 1,

x, y, z are integers greater than or equal to 2;

According to the present invention, x, y, z may be 2≤x≤20, 2≤y≤8, and 2≤z≤36, respectively.

The x, y, and z may be values such that the sum of the oxidation numbers of the compound represented by Chemical Formula 1 calculated according to the oxidation numbers of Al, B, and O is zero. For example, if the oxidation number of Al is +3, the oxidation number of B is +3, and the oxidation number of O is -2, x, y, z are (+3)×x + (+3)×y + (-2 ) × z = 0, and specifically, for example, x may be 4, B may be 2, and y may be 9 ((+3) × 4 + (+3) × 2 + (- 2)×9 = 0).

According to the present invention, the crystalline compound represented by Chemical Formula 1 may be at least one selected from Al ₄ B ₂ O ₉ , Al ₁₈ B ₄ O ₃₃ and Al ₆ B ₈ O ₂₁ , and improve the output and resistance increase rate. In , the crystalline compound represented by Chemical Formula 1 may be Al ₄ B ₂ O ₉ , Al ₁₈ B ₄ O ₃₃ , or a combination thereof.

According to the present invention, the crystalline compound represented by Formula 1 is 0.1 part by weight to 5.0 parts by weight, specifically 0.1 part by weight to 1.0 part by weight, more specifically 0.1 part by weight based on 100 parts by weight of the lithium transition metal oxide. It may be added in parts to 0.5 parts by weight. When the content of the crystalline compound represented by Formula 1 is within the above range, excessive capacity reduction of the positive electrode active material after coating can be prevented, and coating coverage on the surface of the positive electrode active material is optimized, resulting in high coating efficiency.

According to the present invention, in the crystalline compound represented by Formula 1, the aluminum contained in the crystalline compound represented by Formula 1 is 100 ppm to 10,000 ppm, specifically 100 ppm to 5,000 ppm, more specifically, compared to the lithium transition metal oxide. As may be added to be 500ppm to 1,500ppm. When the amount of aluminum included in the crystalline compound represented by Formula 1 is within the above range, not only the effect of improving the resistance increase rate, but also the effect of improving the capacity may be realized.

According to the present invention, the lithium transition metal oxide may have a composition represented by Formula 2 below. In addition, the lithium transition metal oxide may be in the form of secondary particles in which primary particles are aggregated or in the form of single particles.

[Formula 2]

Li _1+a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 2,

M ¹ is at least one selected from Mn and Al;

M ² is at least one selected from W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb;

0≤a≤0.3, 0.60≤b≤1.0, 0≤c≤0.40, 0≤d≤0.40, 0≤e≤0.3, b+c+d+e=1.

The lithium transition metal oxide may be prepared through a method known in the art. For example, a lithium transition metal oxide may be prepared by mixing a precursor for a cathode active material (eg, a transition metal hydroxide, a transition metal oxyhydroxide, etc.) and a lithium-containing raw material and firing them.

The mixing of the lithium transition metal oxide and the crystalline compound represented by Chemical Formula 1 may be dry mixing.

According to the present invention, the heat treatment may be performed at 500 °C to 900 °C, specifically at 600 °C to 800 °C. When the heat treatment temperature is within the above range, it is possible to prevent the coating material from melting and being substituted into the positive electrode active material and from changing the crystal of the positive electrode active material itself, and coating efficiency can be increased.

And, the heat treatment may be performed under an oxygen atmosphere. Specifically, the heat treatment may be performed under an oxygen atmosphere having an oxygen concentration of 95 vol% to 99 vol%. In this case, there is an advantage in that the surface of the positive electrode active material is uniformly coated without changing the state of the coating material as the heat treatment proceeds while maintaining a high-concentration oxygen state.

According to the present invention, the heat treatment may be performed for 1 hour to 24 hours, specifically, 5 hours to 15 hours. When the heat treatment time is within the above range, it is advantageous in terms of economy and coating efficiency.

In the cathode active material prepared according to the present invention, a coating layer made of a compound (Li-Al-BO solid solution) containing boron and aluminum having high lithium ion conductivity is formed on a lithium transition metal oxide, and when applied to a battery, the coating layer is The output and resistance increase rate can be improved. On the other hand, the coating layer made of a compound (Li-Al-BO solid solution) containing boron and aluminum having high lithium ion conductivity is aluminum oxide or boron oxide having low lithium ion conductivity, for example, Al ₂ O ₃ , B ₂ O It may be one that does not include ₃ , etc.

anode

In addition, the present invention provides a positive electrode including a positive electrode active material layer including the positive electrode active material. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including the positive electrode active material.

The positive current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , those surface-treated with silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 μm to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The positive active material layer may include a conductive material and a binder together with the positive active material according to the present invention described above.

The cathode active material may be included in an amount of 80 parts by weight to 99 parts by weight, more specifically, 85 parts by weight to 98 parts by weight based on 100 parts by weight of the total weight of the cathode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

The conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or 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 whiskers 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 of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1 part by weight to 30 parts by weight based on 100 parts by weight of the total weight of the cathode active material layer.

The binder serves to improve adhesion between particles of the positive electrode active material and adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or in a mixture of two or more of them. The binder may be included in an amount of 1 part by weight to 30 parts by weight based on 100 parts by weight of 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 for using the positive electrode active material according to the present invention. Specifically, the positive electrode active material and, optionally, a positive electrode mixture prepared by dissolving or dispersing a binder and a conductive material in a solvent may be coated on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active 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, N-methylpyrrolidone (NMP), acetone, etc. Among them, one type alone or a mixture of two or more types may be used. The amount of the solvent is enough to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the positive electrode material, and to have a viscosity capable of exhibiting excellent thickness uniformity during subsequent coating for manufacturing the positive electrode. Suffice.

Alternatively, the positive electrode may be manufactured by casting the positive electrode mixture on a separate support and then laminating a film obtained by peeling from the support on a positive electrode current collector.

lithium secondary battery

In addition, the present invention can manufacture an electrochemical device including the anode. The electrochemical device may be specifically a battery, a capacitor, and the like, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is the same as described above, so a detailed description is omitted, Hereinafter, only the remaining configurations will be described in detail.

In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member 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 anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed 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 _β (0<β<2), SnO ₂ , vanadium oxide, and 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 of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. 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 representative.

The negative electrode active material may be included in an amount of 80 parts by weight to 99 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 part by weight to 10 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluorocarbons, roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 parts by weight or less, preferably 5 parts by weight or less, based on 100 parts by weight of the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

For example, the negative electrode active material layer is prepared by coating a negative electrode composite prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent on a negative electrode current collector and drying the negative electrode composite, or by drying the negative electrode composite. It can be produced by casting on a support and then laminating a film obtained by peeling from the support on a negative electrode current collector.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement. Anything that is normally used as a separator in a lithium secondary battery can be used without particular limitation, especially for the movement of ions in the electrolyte. It is preferable to have low resistance to the electrolyte and excellent ability to absorb the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

In addition, the electrolyte used in the present invention includes organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

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 includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether 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, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Among them, carbonate-based solvents are preferred, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high permittivity that can increase the charge and discharge performance of batteries, 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, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, 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 , LiAlO 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 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 within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid 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 further included. In this case, the additive may be included in an amount of 0.1 part by weight to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicles 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 battery pack may include a 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 one or more medium or large-sized devices among power storage systems.

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

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit cell in a medium-large battery module including a plurality of battery cells.

Hereinafter, examples will be described in detail to explain the present invention in detail. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Examples and Comparative Examples

Example 1

After mixing 30 g of LiNi _0.88 Co _0.06 Mn _0.06 O ₂ and 0.038 g of Al ₄ B ₂ O ₉ , which is a crystalline compound, in a mixer (mixing so that the aluminum content is 500 ppm relative to LiNi _0.88 Co _0.06 Mn _0.06 O ₂ ), 600 ° C. Heat treatment was performed in an oxygen atmosphere for 10 hours to prepare a cathode active material having a coating layer containing a Li-Al-BO solid solution on the lithium transition metal oxide.

An XRD graph of Al ₄ B ₂ O ₉ used in Example 1 is shown in FIG. 1 , and an SEM image of the cathode active material prepared in Example 1 is shown in FIG. 2 .

Example 2

After mixing 30 g of LiNi _0.87 Co _0.065 Mn _0.065 O ₂ and 0.038 g of Al ₄ B ₂ O ₉ , a crystalline compound, in a mixer (mixing so that the aluminum content is 500 ppm relative to LiNi _0.87 Co _0.065 Mn _0.065 O ₂ ), 600 ° C. Heat treatment was performed in an oxygen atmosphere for 10 hours to prepare a cathode active material having a coating layer containing a Li-Al-BO solid solution on the lithium transition metal oxide.

Example 3

Mixing 30 g of LiNi _0.87 Co _0.065 Mn _0.065 O ₂ , a lithium transition metal oxide used in preparing the cathode active material in Example 2, and 0.033 g of Al ₁₈ B ₄ O ₃₃ , a crystalline compound, in a mixer (compared to LiNi _0.87 Co _0.065 Mn _0.065 O ₂ ) mixed so that the content of aluminum is 500 ppm), and then heat-treated for 10 hours in an oxygen atmosphere at 600 ° C. to prepare a cathode active material having a coating layer containing a Li-Al-BO solid solution on the lithium transition metal oxide.

Comparative Example 1

LiNi _0.88 Co _0.06 Mn _0.06 O ₂ , which is a lithium transition metal oxide used in preparing the cathode active material in Example 1, was used as a cathode active material without any treatment.

Comparative Example 2

After mixing 30 g of LiNi _0.88 Co _0.06 Mn _0.06 O ₂ , a lithium transition metal oxide used in the preparation of the cathode active material in Example 1, and 0.038 g of AlBO ₃ , an amorphous compound, in a mixer, heat treatment was performed in an oxygen atmosphere at 600° C. for 10 hours. A positive electrode active material having a coating layer including Al ₂ O ₃ , B ₂ O ₃ and a Li-Al-BO solid solution on a lithium transition metal oxide was prepared.

An XRD graph of AlBO ₃ used in Comparative Example 2 is shown in FIG. 1 .

Comparative Example 3

30 g of LiNi 0.88 Co 0.06 Mn 0.06 O 2 , 30 g of LiNi _0.88 Co _0.06 Mn _0.06 O ₂ , 0.043 g of Al(OH) ₃ , and 0.017 g of H ₃ BO ₃ , which are lithium transition metal oxides used in the preparation of the cathode active material in Example 1, were mixed in a mixer, and then mixed at 600° C. under an oxygen atmosphere. Heat treatment was performed for 10 hours to prepare a cathode active material having a coating layer including Al ₂ O ₃ , B ₂ O ₃ and a Li-Al-BO solid solution on the lithium transition metal oxide.

Comparative Example 4

LiNi _0.87 Co _0.065 Mn _0.065 O ₂ , which is a lithium transition metal oxide used in preparing the cathode active material in Example 2, was used as a cathode active material without any treatment.

Experimental example

Experimental Example 1: Evaluation of Battery Characteristics

Lithium secondary batteries were manufactured using the cathode active materials prepared in Examples and Comparative Examples, and each lithium secondary battery was evaluated for charge/discharge capacity, capacity retention rate at high temperature, and resistance increase rate.

Specifically, a positive electrode slurry was prepared by mixing each of the positive electrode active materials prepared in Examples and Comparative Examples, a carbon black conductive material, and a PVdF binder in a NMP solvent at a weight ratio of 97.5:1.0:1.5. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode. Meanwhile, a Li metal disk was used as an anode active material. An electrode assembly was prepared by interposing a separator between the positive electrode and the negative electrode prepared above, and then placed inside a battery case, and then an electrolyte was injected into the case to prepare a lithium secondary battery. At this time, a lithium secondary battery was prepared by injecting an electrolyte in which 1M LiPF ₆ was dissolved in an organic solvent of EC/EMC/DMC (3/3/4, vol%) as an electrolyte.

The lithium secondary battery prepared as described above was charged with a constant current at 25° C. at a current of 0.1C until the voltage reached 4.25V, and then discharged at a constant current of 0.1C until the voltage reached 2.5V. Table 1 shows the charge capacity, discharge capacity, charge/discharge efficiency, and DCIR.

In addition, one charge/discharge cycle is performed at 45°C in the range of 2.5 to 4.25V, charging with a current of 0.2C until the voltage reaches 4.25V, and then discharging at a constant current of 0.2C until the voltage reaches 2.5V. After repetition, 0.5C charge / 1.0C discharge was repeated 30 times in one cycle from the second time to measure the capacity of the lithium secondary battery. In particular, the ratio of the 31st cycle capacity to the 2nd cycle capacity was used as the capacity retention rate, Table 1 shows. In addition, the resistance at high temperature was measured by measuring the voltage drop for 60 seconds after the start of discharge in each cycle and dividing it by the applied current value. In particular, the increase rate of the 31st cycle resistance value against the 2nd cycle resistance value 1.

coating material charge capacity
(mAh/g) discharge capacity
(mAh/g) charge/discharge efficiency
(%) DCIR
(Ω) capacity retention rate
(%) resistance increase rate
(%) Example 1 Al ₄ B ₂ O ₉ 229.6 201.4 87.7 15.9 96.5 128.8 Example 2 Al ₄ B ₂ O ₉ 229.4 199.9 87.1 17.4 98.0 131.2 Example 3 Al ₁₈ B ₄ O ₃₃ 229.4 199.6 87.0 17.6 98.0 133.6 Comparative Example 1 - 229.7 201.6 87.7 17.1 96.9 138.3 Comparative Example 2 Al(OH) ₃ , H ₃ BO ₃ 229.9 201.3 87.6 17.1 96.5 136.4 Comparative Example 3 AlBO ₃ 229.6 201.3 87.8 16.2 96.7 134.1 Comparative Example 4 - 227.5 197.1 86.6 19.3 97.9 135.4

Experimental Example 2: Evaluation of lithium byproduct present in cathode active material

5 g of each of the cathode active materials of Example 1 and Comparative Examples 1 to 3 were put into 100 g of distilled water, mixed for 5 minutes, and then filtered. After filtering, the amount of Li ₂ CO ₃ and LiOH dissolved in distilled water was measured by a titration method (using 0.1N HCl) using a pH meter, and these are shown in Table 2. In addition, the ratio of Li ₂ CO ₃ (wt%) to LiOH (wt%) (Li ₂ CO ₃ /LiOH) is shown in Table 2 below.

Li ₂ CO ₃
(weight%) LiOH
(weight%) Li ₂ CO ₃ /LiOH Example 1 0.362 0.250 1.45 Comparative Example 1 0.554 0.173 3.20 Comparative Example 2 0.424 0.180 2.36 Comparative Example 3 0.453 0.125 3.62

Referring to Table 1, batteries including the cathode active materials of Examples 1 to 3 in which a coating layer was formed on a lithium transition metal oxide using the crystalline compound Al ₄ B ₂ O ₉ or Al ₁₈ B ₄ O ₃₃ are Compared to Comparative Examples 1 to 4, it can be confirmed that the initial resistance and resistance increase rate are significantly lower, and in the case of Examples 2 and 3 compared to Comparative Example 4, it can be seen that they have high charge and discharge capacity and high capacity retention rate. This is because when the coating layer is formed by reacting the crystalline compound with the residual lithium on the surface of the lithium transition metal oxide, more compounds (Li-Al-BO solid solution) having excellent lithium ion conductivity are generated compared to Comparative Examples 1 to 3. In addition, this is because by-products such as Al ₂ O ₃ and B ₂ O ₃ do not exist in the coating layers of the cathode active materials of Examples 1 to 3.

Referring to Table 2, it can be seen that the residual lithium carbonate content of Example 1 in which a coating layer was formed on the lithium transition metal oxide using the crystalline compound Al ₄ B ₂ O ₉ was significantly lower than that of Comparative Examples 2 and 3. there is. This is because the residual lithium carbonate reacts with the crystalline compound Al ₄ B ₂ O ₉ to form a coating layer.

In conclusion, when preparing the cathode active material, by using the crystalline compound represented by Formula 1 capable of forming a coating layer having high lithium ion conductivity by reacting with the lithium by-product remaining in the lithium transition metal oxide, the remaining surface of the cathode active material It can be seen that not only can minimize lithium by-products that can occur, but also can improve the capacity and output of the battery.

Claims (10)

Forming a coating layer containing boron and aluminum on the lithium transition metal oxide by mixing and heat-treating a lithium transition metal oxide and a crystalline compound represented by Formula 1 below; manufacturing method of a cathode active material comprising:
[Formula 1]
Al _x B _y O _z
In Formula 1,
x, y, z are integers greater than or equal to 2;
The method of claim 1,
wherein x, y, and z are 2≤x≤20, 2≤y≤8, and 2≤z≤36, respectively.
The method of claim 1,
The crystalline compound represented by Chemical Formula 1 is at least one selected from Al ₄ B ₂ O ₉ , Al ₁₈ B ₄ O ₃₃ and Al ₆ B ₈ O ₂₁ Method for producing a cathode active material.
The method of claim 1,
The method for producing a positive electrode active material in which the crystalline compound represented by Formula 1 is added in an amount of 0.1 part by weight to 5.0 parts by weight based on 100 parts by weight of the lithium transition metal oxide.
The method of claim 1,
The method for producing a positive electrode active material in which the crystalline compound represented by Formula 1 is added so that aluminum contained in the crystalline compound represented by Formula 1 is 100 ppm to 10,000 ppm relative to the lithium transition metal oxide.
The method of claim 1,
The heat treatment is a method for producing a cathode active material that is performed at 500 ° C to 900 ° C.
The method of claim 1,
The heat treatment is a method for producing a cathode active material that is performed at 600 ° C to 800 ° C.
The method of claim 1,
The heat treatment is a method for producing a positive electrode active material to be performed for 1 hour to 24 hours.
The method of claim 1,
The heat treatment is a method for producing a positive electrode active material to be performed for 5 hours to 15 hours.
The method of claim 1,
The method for producing a positive electrode active material in which the lithium transition metal oxide has a composition represented by Formula 2 below:
[Formula 2]
Li _1+a Ni _b Co _c M ¹ _d M ² _e O ₂
In Formula 2,
M ¹ is at least one selected from Mn and Al;
M ² is at least one selected from W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb;
0≤a≤0.3, 0.60≤b≤1.0, 0≤c≤0.40, 0≤d≤0.40, 0≤e≤0.3, b+c+d+e=1.

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