KR20210156575A - Manufacturing method of positive electrode additives, positive electrode additives and positive electrode comprising the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a positive electrode additive capable of increasing the stability of an excessive lithium transition metal oxide upon exposure to air, to a positive electrode additive having excellent stability upon exposure to air, and to a positive electrode comprising the same. The method for manufacturing a positive electrode additive comprises the steps of: preparing an excessive lithium transition metal oxide represented by chemical formula 1, Li_xM_yO_z; and forming a coating layer containing boron on a surface of the excessive lithium transition metal oxide through a liquid phase sintering process after mixing the excessive lithium transition metal oxide and boron-containing raw material. The positive electrode additive includes the excessive lithium transition metal oxide represented by the chemical formula 1 with the coating layer containing boron formed on a surface thereof, and when exposed for five days under a relative humidity of 15 to 25% and a temperature of 25℃, the weight change rate of Li_2CO_3 is 1 wt% or less. In the chemical formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2 =< x =< 6, 0.5 =< y =< 2, and 2 =< z =< 4.

Description

A positive electrode additive manufacturing method, a positive electrode additive, and a positive electrode comprising the same

The present invention relates to a method for manufacturing a positive electrode additive, a positive electrode additive, and a positive electrode comprising the same.

In recent years, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used.

Graphite is mainly used as a negative electrode material for a lithium secondary battery, but since graphite has a small capacity per unit mass of 372 mAh/g, it is difficult to increase the capacity of the lithium secondary battery. Accordingly, in order to increase the capacity of a lithium secondary battery, as a non-carbon-based negative electrode material having a higher energy density than graphite, a negative electrode material that forms an intermetallic compound with lithium, such as silicon, tin, and their oxides, has been developed and used. However, in the case of such a non-carbon-based negative electrode material, although the capacity is large, the initial efficiency is low, the lithium consumption during the initial charge/discharge is large, and there is a problem that the irreversible capacity loss is large.

In this regard, a method for overcoming the irreversible capacity loss of the negative electrode by using a material that can provide a lithium ion source or storage for the positive electrode material and exhibits electrochemical activity after the first cycle so as not to degrade the overall performance of the battery is studied. , has been proposed. Specifically, as a sacrificial cathode material or an irreversible additive (or overdischarge inhibitor), for example, Li ₆ CoO ₄ (hereinafter, L6C) A method of applying a lithium transition metal oxide containing an excess of lithium to the cathode is known. have.

_{However, the lithium transition metal oxide is phase-separated into LiOH, Li 2} CO _3, etc. due to a chemical reaction with _{CO 2} and H ₂ O in the atmosphere in a battery manufacturing environment using an existing cathode material, thereby preparing a slurry composition for manufacturing an electrode This may result in increased viscosity or gelation of the composition. That is, darithium oxide such as L6C has a problem in that stability when exposed to air is not good. As a result, when the composition for forming the active material layer is applied, it is difficult to uniformly apply the composition, which may cause a problem in which the characteristics of the battery are deteriorated.

Accordingly, a technology for forming a coating layer on the lithium transition metal oxide is being developed, and the conventional coating technology adopts a method of coating a material to be coated by dry mixing. In the case of this method, the process cost is low and convenient, so it is generally used. However, there is a limit in improving the stability when exposed to the atmosphere because the coating is not well made to the surface of the primary particles inside the secondary particles.

Therefore, there is a need for a coating technology that can improve stability when exposed to air while maintaining the unique properties of dalithium transition metal oxide.

The present invention is to provide a positive electrode additive manufacturing method capable of increasing the stability when exposed to air, a positive electrode additive having excellent stability when exposed to air, and a positive electrode comprising the same will be.

The present invention comprises the steps of preparing a darithium transition metal oxide represented by the following formula (1); and forming a coating layer containing boron on the surface of the lithium transition metal oxide through a liquid phase sintering process after mixing the britium transition metal oxide and boron-containing raw material; .

[Formula 1]

Li _x M _y O _z

In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.

In addition, the present invention includes a darithium transition metal oxide represented by the following Chemical Formula 1 on which a coating layer containing boron is formed on the surface, and when exposed for 5 days under a relative humidity of 15% to 25% and a temperature of 25°C, Li ₂ A positive electrode additive having a weight change rate of _{CO 3 of 1 wt% or less is provided.}

[Formula 1]

Li _x M _y O _z

In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.

And, the present invention provides a positive electrode including the positive electrode additive.

The positive electrode additive manufactured according to the manufacturing method of the present invention includes a coating layer formed through a liquid phase sintering process, and hardly undergoes phase separation even when exposed to the air, so it has excellent stability when exposed to air, and gelation when preparing a slurry composition for manufacturing a battery can be prevented from becoming Accordingly, deterioration of battery performance can also be prevented.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.

Hereinafter, the present invention will be described in more detail.

Anode additive manufacturing method

The positive electrode additive manufacturing method of the present invention includes the steps of preparing a darithium transition metal oxide represented by the following Chemical Formula 1; and forming a coating layer containing boron on the surface of the britium transition metal oxide through a liquid phase sintering process after mixing the lithium transition metal oxide and the boron-containing raw material.

[Formula 1]

Li _x M _y O _z

In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.

Hereinafter, the method for manufacturing the positive electrode additive of the present invention will be described in detail step by step.

(1) preparing a darithium transition metal oxide

Step (1) is a step of preparing a darithium transition metal oxide represented by the following formula (1).

[Formula 1]

Li _x M _y O _z

In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.

According to the method for manufacturing a positive electrode additive of the present invention, specifically, the lithium transition metal oxide may be at least one selected from among _{Li 6} CoO ₄ , Li ₅ FeO ₄ , Li ₅ MnO ₄ and Li ₂ NiO _{2 .} More specifically, the lithium transition metal oxide may be _{Li 6} CoO _{4 .} In this case, while preventing the irreversible capacity loss of the negative electrode, it is also possible to prevent deterioration of the battery performance.

The lithium transition metal oxide represented by Chemical Formula 1 may be prepared by mixing a lithium-containing raw material and a transition metal-containing raw material, followed by heat treatment.

As the lithium-containing raw material, at least one selected from lithium oxide (Li ₂ O), lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and hydrates thereof may be used.

As the transition metal-containing raw material, at least one selected from oxides, hydroxides, oxyhydroxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, phosphates, and hydrates thereof containing M may be used. can

For example, when M is Co, as the cobalt-containing raw material, cobalt oxide such as cobalt oxide (CoO), _{cobalt hydroxide such as cobalt hydroxide (Co(OH) 2} ), cobalt oxyhydroxide, cobalt sulfate, cobalt nitrate , cobalt acetate, cobalt carbonate, cobalt oxalate, cobalt citrate, cobalt halide, cobalt phosphate, and at least one selected from hydrates thereof may be used. Specifically, as the cobalt-containing raw material, CoO, Co ₃ O ₄ , Co(OH) ₂ , Co(OH) ₃ , Co(NO ₃ ) ₂ ·xH ₂ O(1≤x≤7), Co(COOCH) ₃ ) _2, etc. can be used.

When mixing the above raw materials, a moisture scavenger may be optionally further added. The moisture scavenger may include citric acid, tartaric acid, glycolic acid or maleic acid, and a mixture of one or more of these may be used.

The heat treatment may be performed at a temperature of 600° C. to 750° C. for 1.5 hours to 12 hours. In this case, a lithium transition metal oxide suitable for a liquid phase sintering process may be prepared. That is, the particles forming the lithium transition metal oxide may have a size and distribution suitable for the liquid phase sintering process. In addition, the lithium transition metal oxide prepared according to the above method may have a form of secondary particles in which a plurality of primary particles (10 μm to 20 μm) are aggregated. The secondary particles may have a spherical or grape cluster shape.

(2) forming a coating layer containing boron on the surface of the britium transition metal oxide through a liquid phase sintering process after mixing the britium transition metal oxide and boron-containing raw material

Step (2) is a step of preparing a britium transition metal oxide including a coating layer containing boron on the surface through a liquid phase sintering process.

According to the liquid phase sintering process, densification is performed in a state in which the liquid phase is present in the molded body at the sintering temperature, so that the densification of the particles can be improved. In addition, according to the liquid phase sintering process, it is possible to uniformly coat the particle surface of the lithium transition metal oxide. Accordingly, the positive electrode additive prepared according to the present invention is a darithium transition metal oxide uniformly coated with a coating layer containing boron, and may have excellent atmospheric stability and moisture stability.

According to the cathode additive manufacturing method of the present invention, the boron-containing raw material may include at least one selected from boron oxide, boron hydroxide, and lithium boron oxide. The boron-containing raw material is specifically, B ₂ O ₃ , B(OH) ₃ , Li ₃ BO ₃ , It _{may be at least one selected from Li 2} B ₄ O ₇ and LiBO ₂ , and preferably, at least one selected from B ₂ O ₃ , B(OH) ₃ and Li ₃ BO ₃ . In this case, due to the melting point of the boron-containing raw materials and particle characteristics in a solid state, the coating layer may be uniformly formed.

According to the method for manufacturing a positive electrode additive of the present invention, the content of the boron-containing raw material may be 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the darithium transition metal oxide. Specifically, the content of the boron-containing raw material may be specifically, 0.5 parts by weight to 5 parts by weight, more specifically, 1.5 parts by weight to 5 parts by weight based on 100 parts by weight of the britium transition metal oxide. When the content of the boron-containing raw material is within the above range, the entire surface of the darithium transition metal oxide can be uniformly coated without a boron-containing raw material that is not consumed, so that the atmospheric stability and moisture stability of the prepared positive electrode additive are improved can do it

According to the method for manufacturing the positive electrode additive of the present invention, the liquid phase sintering process may be performed at a temperature of 90°C to 500°C. Specifically, the temperature of the liquid phase sintering process may be 250 °C to 400 °C, 250 °C to 350 °C, or 300 °C to 350 °C. When the liquid phase sintering process temperature is within the above range, it is possible to densely form a coating layer containing boron on the surface of the britium transition metal oxide without causing decomposition of the britium transition metal oxide represented by Chemical Formula 1, etc.

According to the positive electrode additive manufacturing method of the present invention, the liquid phase sintering process may be performed for 0.5 to 6 hours. Specifically, the liquid phase sintering process time may be 0.5 hours to 5.5 hours, 2 hours to 5.5 hours, or 4 hours to 5.5 hours. When the liquid phase sintering process time is within the above range, a coating layer containing boron may be uniformly and densely formed on the surface of the lithium transition metal oxide.

According to the positive electrode additive manufacturing method of the present invention, the liquid phase sintering process raises the temperature from room temperature to 90° C. to 500° C. for 0.1 hour to 1 hour, and then maintains the temperature at 90° C. to 500° C. for 0.2 hour to 5 hours. and may be performed. In this case, a coating layer containing boron is uniformly and densely formed on the surface of the britium transition metal oxide by inducing coating by osmotic force without causing decomposition of britium transition metal oxide or loss of boron-containing raw material. can do it In addition, there is an advantage in that it is easy to control the thickness of the coating film to improve atmospheric stability. Accordingly, atmospheric stability and moisture stability of the prepared positive electrode additive may be improved.

On the other hand, when the temperature is raised from room temperature to 90°C to 500°C, the temperature may be increased at a constant rate.

According to the method for manufacturing the positive electrode additive of the present invention, the liquid phase sintering process may be performed under a pressure of 0.1 MPa to 10 MPa. Specifically, the liquid phase sintering process may be performed under a pressure of 0.1 MPa to 5 MPa or 1 MPa to 5 MPa.

The liquid phase sintering process involves a phase change process in which the boron-containing raw material changes from a solid to a liquid phase. In the case of narrowing, an osmosis force acts between the gaps, and the boron-containing raw material in a liquid phase changed in the liquid phase in the liquid phase sintering process receives the osmotic force to permeate between the lithium transition metal oxide particles. Accordingly, when the pressure during the liquid phase sintering process is within the above range, there is an advantage in that the coating layer can be formed very homogeneously on the surfaces of all particles of the darithium transition metal oxide, that is, even the surfaces of the primary particles.

According to the method for manufacturing the positive electrode additive of the present invention, the liquid phase sintering process may be performed in a vacuum or an inert atmosphere to increase reaction efficiency and suppress side reactions. Preferably, the liquid phase sintering process may be performed in a vacuum atmosphere.

The thickness of the coating layer of the positive electrode additive prepared according to the present invention may be 100 nm to 1 μm. Specifically, the coating layer of the positive electrode additive may have a thickness of 100 nm to 500 nm. When the thickness of the coating layer of the positive electrode additive is within the above range, atmospheric stability and moisture stability of the positive electrode additive may be improved.

anode additive

The positive electrode additive of the present invention includes a darithium transition metal oxide represented by the following Chemical Formula 1 on which a coating layer containing boron is formed on the surface, and when exposed for 5 days under a relative humidity of 15% to 25% and a temperature of 25°C, Li _{The weight change rate of 2} CO ₃ is 1% by weight or less.

[Formula 1]

Li _x M _y O _z

In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.

According to the present invention, the positive electrode additive is prepared according to the method for producing the positive electrode additive, and is a darithium transition metal oxide uniformly coated with a coating layer containing boron, and is included in the positive electrode active material layer to be used in a secondary battery, It is possible to prevent deterioration of battery performance. Specifically, the positive electrode additive prepared according to the present invention has excellent stability when exposed to the air, and thus it is possible to prevent gelation during the preparation of the slurry composition for manufacturing the battery, and thus, it is possible to prevent deterioration of the battery performance.

According to the present invention, the lithium transition metal oxide may be, specifically, at least one selected from _{Li 6} CoO ₄ , Li ₅ FeO ₄ , Li ₅ MnO ₄ and Li ₂ NiO _{2 .} More specifically, the lithium transition metal oxide may be _{Li 6} CoO _{4 .} In this case, while preventing the irreversible capacity loss of the negative electrode, it is also possible to prevent deterioration of the battery performance.

anode

The positive electrode of the present invention includes the positive electrode additive.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the current collector, and the positive electrode active material layer includes the positive electrode additive and the positive electrode active material.

The positive active material may _{include a layered compound such as lithium cobalt oxide (LiCoO 2} ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; lithium iron oxides such as LiFe ₃ O _{4 ;} Lithium manganese oxide, such as Formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3) Ni site-type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO ₈ (herein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) lithium manganese composite oxide; It may be at least one selected _{from LiMn 2} O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion.

The positive electrode 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, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase adhesion of the positive 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, a non-woven body.

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

At this time, the positive electrode 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 has electronic conductivity without causing chemical change. 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 or a mixture of two or more thereof may be used.

In addition, the positive electrode binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active 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, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, 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 secondary battery includes the positive electrode; cathode; a separator interposed between the anode and the cathode; and electrolytes.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer includes a negative electrode active material, and as the negative electrode active material, reversible intercalation and deintercalation of lithium is possible compounds 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 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, amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite (Kish) 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.

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, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 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 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, a nonwoven body.

The anode active material layer may include an anode conductive material and an anode binder together with the anode active material described above.

The negative electrode conductive material and the negative electrode binder may be the same as those described above for the positive electrode.

The separator separates the anode and the anode and provides a passage for lithium ions to move, and it can be used without any particular limitation as long as it is normally used as a separator in a secondary battery. Excellent is preferred. 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 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.

Examples of the electrolyte may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing a lithium secondary battery.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, 1,2-dime ethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant and thus well dissociate lithium salts. If the same low-viscosity, low-dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, which can be more preferably used.

A lithium salt may be used as the metal salt, and the lithium salt is a material readily soluble in the non-aqueous electrolyte. For example, as an anion of the lithium salt ^{, F -} , Cl ^- , I ^- , NO ₃ ^- , N(CN ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ At least one selected from the group consisting of _{CO 2} ^— , SCN ^— and (CF ₃ CF ₂ SO ₂ ) ₂ N ^{— may be used.}

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, 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 jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included.

As described above, since the lithium secondary battery containing the positive electrode additive manufactured according to the present invention is inhibited from deterioration of electrochemical performance, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles, HEV) and the like are useful in the field of electric vehicles.

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 several different forms and is not limited to the embodiments described herein.

Examples and Comparative Examples

Example 1

Li ₂ O and CoO were put into a dry mixer (hantech, 3D shaking mixer) at a molar ratio of 3:1 and mixed at 500 rpm for 30 minutes. A _{mixture of Li 2} O and CoO was charged into an alumina sagger and heat-treated at 700° C. for 5 hours under _{N 2} atmosphere to prepare _{Li 6} CoO _{4 .}

300 parts by weight of the Li ₆ CoO _{4 and 15 parts by weight of B 2} O ₃ (Sigma-Aldrich) were put into a dry mixer (hantech, 3D shaking mixer) and mixed at 500 rpm for 30 minutes. After the mixture was charged into a 12.7 cm (0.5 inch) Inconel die, the temperature was increased at a constant rate from room temperature to 300° C. for 30 minutes in a vacuum atmosphere under a pressure of 3 MPa by hot pressing, and then 300 for 5 hours. Through a liquid phase sintering process of sintering while maintaining a temperature of °C, _{Li 6} CoO ₄ (anode additive 1) having a _{B 2} O ₃ coating layer formed on the surface was prepared.

Example 2

_{When performing the liquid phase sintering process, B 2} O on the surface in the same manner as in Example 1, except that the temperature was increased at a constant rate from room temperature to 350° C. for 30 minutes, and the temperature was maintained at 350° C. for 5 hours. _{3 Li 6} CoO ₄ (positive electrode additive 2) formed with a coating layer was prepared.

Comparative Example 1

Li ₆ CoO ₄ was prepared _{using Li 2} O and CoO.

300 parts by weight of Li ₆ CoO _{4 and 15 parts by weight of B 2} O ₃ were put into a dry mixer and mixed at 500 rpm for 30 minutes. The mixture was heat-treated at 500° C. for 5 hours _{to prepare a B 2} O ₃ coating layer formed _{on the surface of Li 6} CoO ₄ (anode additive 3).

Comparative Example 2

_{Li 6} CoO ₄ (positive electrode additive 4) having a _{B 2} O ₃ coating layer formed on the surface was prepared in the same manner as in Comparative Example 1, except that the heat treatment temperature was 550° C.

Experimental example: air stability evaluation

In order to evaluate the atmospheric stability of positive electrode additives 1 to 4, positive electrode additives 1 to 4 were exposed for 5 days under a relative humidity of 15 to 25% and a temperature of 25°C.

Hereinafter, positive electrode additive 1 exposed for 5 days as positive electrode additive 4, positive electrode additive 2 exposed for 5 days as positive electrode additive 5, positive electrode additive 3 exposed for 5 days as positive electrode additive 6, and positive electrode exposed for 5 days Additive 4 will be referred to as positive electrode additive 8.

Experimental Example 1: Evaluation of the degree of phase separation

When the positive electrode additives 1 to 4 were exposed for 5 days at a relative humidity of 15 to 25% and a temperature of 25° C., the phase separation in the positive electrode additive was analyzed using an X-ray diffraction analyzer (Bruker AXS GmbH, D8). Specifically, after obtaining the X-ray diffraction pattern data of the positive electrode additives 1 to 8 using the X-ray diffraction analysis device, the main phase of the positive electrode additive and the atmospheric exposure were separated using the Rietveld analysis method, which is a quantitative analysis tool. Quantification of the formed secondary phase (Li ₂ CO _{3 ) was performed.}

The degree of phase separation (phase separation due to a chemical reaction with _{CO 2} and H ₂ O in the atmosphere) that occurred when exposed for 5 days at a relative humidity of 15 to 25% and a temperature of 25 ° C. _{Specifically, the change in weight percent of Li 2} CO ₃ is shown in the table below. 1 is shown.

Change in weight % of Li ₂ CO ₃ Anode Additive 1 -> Anode Additive 5 0 wt% -> 0.21 wt% Anode Additive 2 -> Anode Additive 6 0 wt% -> 0.20 wt% Anode Additive 3 -> Anode Additive 7 0 wt% -> 1.3 wt% Anode Additive 4 -> Anode Additive 8 0 wt% -> 1.8 wt%

Experimental Example 2: Evaluation of initial charging capacity

A composition for forming a positive electrode was prepared by mixing positive electrode additive 1, carbon black conductive material, and PVdF binder in a N-methylpyrrolidone solvent in a ratio of 97.5:1.5:1 by weight, applied to an aluminum current collector, and dried (70°C) was rolled to prepare a positive electrode. Cathode was used as the lithium metal, using that contains 1M of LiPF ₆ electrolytic solution in EC / DMC / DEC mixing volume ratio = 1/2/1 of a solvent, and by using porous polyethylene separator, a coin-type half-cell ( coin half-cell) 1 was prepared.

Using positive electrode additives 2 to 8 instead of positive electrode additive 1, respectively, coin-type half-cells 2 to 8 were prepared in the same manner as above.

For each coin-type half-cell prepared as described above, in CCCV mode at 25° C., it was charged until 0.1C and 4.25V, and was discharged at a constant current of 0.51 until it became 2.5V, and a charge-discharge experiment was conducted. , the initial charging capacity and the initial charging capacity reduction rate are shown in Table 1 below.

Initial charge capacity change Initial charge capacity reduction rate (%) Anode Additive 1 -> Anode Additive 5 689mAh/g -> 671mAh/g 2.61 Anode Additive 2 -> Anode Additive 6 730mAh/g -> 711mAh/g 2.60 Anode Additive 3 -> Anode Additive 7 770mAh/g -> 698mAh/g 9.35 Anode Additive 4 -> Anode Additive 8 710mAh/g -> 650mAh/g 8.45

Referring to Table 1, the positive electrode additives 1 and 2 manufactured through the liquid phase sintering process according to the manufacturing method of the present invention have a B ₂ O ₃ coating layer formed uniformly and densely on the surface, so that the phase separation almost proceeds even when exposed to atmospheric conditions. I could confirm that it wasn't. On the other hand, it was confirmed that the positive electrode additives 3 and 4 prepared through the general firing process exhibited 6 times more phase separation than the positive electrode additives 1 and 2 when exposed to atmospheric conditions. _{This is because, according to the general firing process, a B 2} O ₃ coating layer is formed while a gaseous phase, not a liquid phase, is deposited on the surface of the darium transition metal oxide, so there is a limit to uniformly and densely forming the coating layer.

In addition, referring to Table 2, the positive electrode additives 1 and 2 prepared according to the manufacturing method of the present invention hardly undergo phase separation even when exposed to atmospheric conditions, so there is little difference in the initial charging capacity with the positive electrode additives 5 and 6 It was confirmed that there is no (the initial charge capacity reduction rate is small). On the other hand, it was confirmed that the positive electrode additives 3 and 4 manufactured through the general firing process undergoes a lot of phase separation when exposed to atmospheric conditions, so that the initial charge capacity reduction rate is large.

Accordingly, it can be seen that the positive electrode additive manufactured according to the manufacturing method of the present invention has excellent stability when exposed to air, including the coating layer containing boron formed through the liquid phase sintering process.

Claims (13)

Preparing a darithium transition metal oxide represented by the following Chemical Formula 1; and
A cathode additive manufacturing method comprising: mixing the britium transition metal oxide and a boron-containing raw material, and then forming a coating layer containing boron on the surface of the britium transition metal oxide through a liquid phase sintering process:
[Formula 1]
Li _x M _y O _z
In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.
According to claim 1,
The lithium transition metal oxide is Li ₆ CoO ₄ , Li ₅ FeO ₄ , Li ₅ MnO ₄ and Li ₂ NiO _{2 At} least one selected from the cathode additive manufacturing method.
According to claim 1,
The boron-containing raw material is a cathode additive manufacturing method comprising at least one selected from boron oxide, boron hydroxide, and lithium boron oxide.
According to claim 1,
The content of the boron-containing raw material is 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the lithium transition metal oxide.
According to claim 1,
The liquid phase sintering process is a cathode additive manufacturing method that is performed at a temperature of 90 ℃ to 500 ℃.
According to claim 1,
The liquid phase sintering process is a positive electrode additive manufacturing method that is performed for 0.5 to 6 hours.
According to claim 1,
The liquid phase sintering process is performed by increasing the temperature from room temperature to 90° C. to 500° C. for 0.1 hour to 1 hour, and then maintaining the temperature of 90° C. to 500° C. for 0.2 hour to 5 hours.
According to claim 1,
The liquid phase sintering process is a positive electrode additive manufacturing method that is performed under a pressure of 0.1 MPa to 10 MPa.
According to claim 1,
The liquid phase sintering process is a positive electrode additive manufacturing method that is performed in a vacuum or an inert atmosphere.
According to claim 1,
The thickness of the coating layer is 100nm to 1㎛ a positive electrode additive manufacturing method.
Containing a darithium transition metal oxide represented by the following formula (1) on the surface of which a coating layer containing boron is formed,
A positive electrode additive having a weight change rate of _{Li 2} CO ₃ of 1% by weight or less when exposed for 5 days under a relative humidity of 15% to 25% and a temperature of 25°C:
[Formula 1]
Li _x M _y O _z
In Formula 1, M is at least one selected from Co, Fe, Mn, and Ni, and 2≤x≤6, 0.5≤y≤2, and 2≤z≤4.
12. The method of claim 11,
The lithium transition metal oxide is Li ₆ CoO ₄ , Li ₅ FeO ₄ , Li ₅ MnO ₄ and Li ₂ NiO _{2 At} least one positive electrode additive selected from.
A positive electrode comprising the positive electrode additive according to claim 11 .