KR20240015245A - Positive electrode and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a positive electrode active material, Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z =1) A positive electrode active material that has a layered structure containing both phases and includes lithium excess oxide doped with Sn and Cl, at least one selected from K and F, and can improve the performance of a lithium secondary battery containing the same. , a manufacturing method thereof, a positive electrode containing the same, and a lithium secondary battery.

Description

Cathode active material and manufacturing method thereof {POSITIVE ELECTRODE AND MANUFACTURING METHOD OF THE SAME}

The present invention relates to a positive electrode active material, a method of manufacturing the same, a positive electrode containing the same, and a lithium secondary battery.

A lithium secondary battery consists of four major components: an anode, a cathode, a separator, and an electrolyte. Among them, the positive electrode active material included in the positive electrode is a material that plays a major role in determining the capacity, output, and lifespan of the battery. In order for lithium secondary batteries to have high energy density, output, and lifespan, it is essential to improve the performance of cathode active materials, and for this reason, much research has been conducted recently to develop high-performance cathode active materials.

Lithium rich layered oxide, a type of positive electrode active material, is a mixed phase of Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni, Mn, Co) phase and has high operating voltage (>3.5V vs. Li/Li). ⁺ ) has the characteristic of providing a very large capacity of 250mAh/g. Accordingly, the lithium excess oxide is attracting attention as a low-cost, high-capacity positive electrode active material.

However, the lithium excess oxide has problems arising from its structural characteristic of mixing two phases. Specifically, when a battery containing the lithium excess oxide is driven under high voltage, there is a problem that irreversible capacity loss occurs in the first formation process and efficiency is reduced, and charge and discharge cycles are performed. During this process, there are problems such as voltage fading and O ₂ gas generation as it changes from a layered structure to a spinel structure to a rock salt structure.

Therefore, there is a need to secure technology to improve the performance and stability of the lithium excess oxide.

The problem to be solved by the present invention is to improve the performance and stability of lithium excess oxide and, as a result, to improve the performance of batteries containing it.

Additionally, the present invention aims to provide a method for manufacturing the positive electrode active material.

Additionally, the present invention aims to provide a positive electrode and a lithium secondary battery containing the positive electrode active material.

In order to solve the above problems, the present invention provides a positive electrode active material, a method for manufacturing the positive electrode active material, a positive electrode, and a lithium secondary battery.

(1) The present invention is a Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z=1) Provided is a positive electrode active material comprising lithium excess oxide having a layered structure containing both phases, wherein the lithium excess oxide is doped with at least one selected from K and F, Sn, and Cl.

(2) In the above (1), the present invention provides a positive electrode active material in which no secondary phase peak is observed at a diffraction angle (2θ) of 36.0˚ to 36.5˚ during X-ray diffraction (XRD) analysis. to provide.

(3) In the present invention, in (1) or (2) above, during X-ray diffraction (XRD) analysis, the secondary phase peak is not observed at a diffraction angle (2θ) of 44.0˚ to 44.5˚. Provides a phosphorus cathode active material.

(4) The present invention provides the positive electrode active material according to any one of (1) to (3) above, wherein the lithium excess oxide has a composition represented by the following formula (1).

[Formula 1]

Li(Li _a K _b Ni _c Co _d Mn _e Sn _f )O _2-gh Cl _g F _h

In Formula 1,

0.01≤a≤0.20, 0≤b≤0.04, 0≤c≤0.50, 0≤d≤0.05, 0.50≤e≤1.0, 0<f≤0.05, a+b+c+d+e+f=1 ,

0<g≤0.10, 0≤h≤0.06.

(5) The present invention provides the positive electrode active material according to any one of (1) to (4) above, wherein the lithium excess oxide is in the form of a single particle.

(6) The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the lithium excess oxide has an average particle diameter of 0.8 μm to 1.2 μm as measured from an SEM image.

(7) The present invention according to any one of (1) to (6) above, wherein the lithium excess oxide is doped with K, Sn, and Cl, and the weight ratio of Sn and K (Sn:K) is 1:0.75. A positive electrode active material having a ratio of 1:2.5 is provided.

(8) The present invention according to any one of (1) to (7) above, wherein the lithium excess oxide is doped with F, Sn, and Cl, and the weight ratio of Sn and F (Sn:F) is 1:0.05. To provide a positive electrode active material having a ratio of 1:0.3.

(9) The present invention includes the steps of (A) mixing lithium raw materials, transition metal raw materials, and doping element raw materials in an aqueous solvent to form a synthetic solution; and (B) drying the synthesis solution and then calcining, wherein the doping element raw material includes at least one selected from K and F, Sn, and Cl. ) provides a method for producing a positive electrode active material according to any one of the following.

(10) The present invention provides a method for producing a positive electrode active material according to (9) above, wherein the drying in step (B) is performed using a hot plate or a spray drying method.

(11) The present invention provides a method for producing a positive electrode active material according to (9) or (10), wherein the drying in step (B) is performed at a temperature of 100°C to 350°C.

(12) The present invention provides a method for producing a positive electrode active material according to any one of (9) to (11) above, wherein the baking in step (B) is performed at a temperature of 400°C to 1,000°C.

(13) The present invention according to any one of (9) to (12) above, wherein the firing in step (B) is carried out by first firing at a temperature of 400°C to 500°C and then at a temperature of 800°C to 1,000°C. A method for manufacturing a positive electrode active material that involves secondary firing is provided.

(14) The present invention provides a positive electrode containing the positive electrode active material according to any one of (1) to (8) above.

(15) The present invention provides a lithium secondary battery including the positive electrode according to (14) above.

The positive electrode active material of the present invention is Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z=1) It has a layered structure containing both phases, and includes lithium excess oxide doped with at least one selected from K and F, Sn, and Cl, and the performance of a lithium secondary battery containing it, for example, charging and discharging during the activation process. Capacity can be improved.

1 shows XRD data of the positive electrode active material of Examples 1 to 3 and Comparative Example 1 of the present invention.
Figure 2 is XRD data of the positive electrode active material of Example 2, Comparative Example 2, and Comparative Example 3 of the present invention.
Figure 3(A) is an SEM image of the positive electrode active material of Example 2, and Figure 3(B) is an SEM image of the positive electrode active material of Comparative Example 1.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

Terms or words used in the description and claims of the present invention should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately use the concept of the term to explain his or her invention in the best way. Based on the principle of definability, it must be interpreted with meaning and concept consistent with the technical idea of the present invention.

In this specification, 'single particle form' is a concept in contrast to the spherical secondary particle form formed by agglomeration of tens to hundreds of primary particles, and refers to a form consisting of 10 or less primary particles. Specifically, the 'single particle form' may be a single particle form consisting of one primary particle, or it may be a secondary particle form in which several primary particles are aggregated.

In this specification, 'primary particle' refers to the minimum unit of particle recognized when observing a positive electrode active material using a scanning electron microscope (SEM), and 'secondary particle' is a particle formed by agglomerating a plurality of primary particles. It means secondary structure.

In this specification, 'average particle diameter' is an average value obtained by obtaining SEM images of various parts of a sample using a scanning electron microscope (SEM), measuring the particle diameters of particles visible in the SEM image, and then averaging them.

positive electrode active material

The present invention simultaneously combines Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z=1) Provided is a positive electrode active material comprising lithium excess oxide having a layered structure, wherein the lithium excess oxide is doped with at least one selected from K and F, Sn, and Cl.

The inventors of the present invention believe that the positive electrode active material is Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z= 1) It contains lithium overoxide of a layered structure containing both phases, wherein the lithium overoxide is triple doped with K, Sn, and Cl, triple doped with F, Sn, and Cl, or quadruple doped with K, F, Sn, and Cl. The present invention was completed by finding that when doped, the charge/discharge capacity can be improved in the first formation process of a battery containing the positive electrode active material.

On the other hand, when the lithium excess oxide does not contain K or F, the formation of the secondary phase (Li(Ni _α Mn _2-α )O ₄ spinel phase) generated when doping only Sn and Cl is not controlled, resulting in battery failure. There is a problem that the charging and discharging capacity decreases in the first activation process. In addition, when the lithium excess oxide does not contain Sn and Cl, there is a problem of structural collapse due to O ₂ generated when lithium on Li ₂ MnO ₃ is desorbed during the first activation process of the battery.

According to the present invention, the positive electrode active material may not have a secondary phase peak observed at a diffraction angle (2θ) of 36.0˚ to 36.5˚ during X-ray diffraction (XRD) analysis. Additionally, according to the present invention, the positive electrode active material may not have a secondary phase peak observed at a diffraction angle (2θ) of 44.0˚ to 44.5˚ during X-ray diffraction (XRD) analysis. That is, the positive electrode active material does not have a secondary phase (Li(Ni _α Mn _2-α )O ₄ spinel phase) with a small capacity, and thus can provide a battery with excellent charge and discharge capacity.

According to the present invention, the lithium excess oxide may have a composition represented by the following formula (1). In this case, the charge/discharge capacity in the first formation process of a battery containing the positive electrode active material according to the present invention can be improved.

[Formula 1]

Li(Li _a K _b Ni _c Co _d Mn _e Sn _f )O _2-gh Cl _g F _h

In Formula 1,

0.01≤a≤0.20, 0≤b≤0.04, 0≤c≤0.50, 0≤d≤0.05, 0.50≤e≤1.0, 0<f≤0.05, a+b+c+d+e+f=1 ,

0<g≤0.10, 0≤h≤0.06.

The a may be 0.01, 0.05, 0.10, 0.12 or more, 0.18, or 0.20 or less.

The b may be 0, 0.01 or more, 0.03, or 0.04 or less.

The c may be 0, 0.10, 0.20 or more, 0.30, 0.40, or 0.50 or less.

The d may be 0, 0.01 or more, 0.02, 0.03, 0.04, or 0.05 or less. Specifically, d may be 0. That is, the lithium excess oxide may not contain expensive cobalt.

The e may be 0.50 or more, 0.60, 0.70, 0.80, 0.90, or 1.0 or less.

The f may be 0, 0.10, 0.20 or more, and 0.50 or less.

The g may be greater than 0, 0.02, 0.04 or more, and 0.10 or less.

The h may be 0 or more and 0.06 or less.

According to the present invention, the lithium excess oxide may be in the form of a single particle in order to improve the performance of a lithium secondary battery.

According to the present invention, the lithium excess oxide may have an average particle diameter measured from SEM images of 0.8 μm to 1.2 μm, specifically 0.9 μm to 1.1 μm. The average particle diameter is an average value obtained by obtaining SEM images of several parts of the sample using a scanning electron microscope (SEM), measuring the particle diameters of each particle visible in the SEM image, and then averaging them.

According to the present invention, the lithium excess oxide may be doped with K, Sn, and Cl. In this case, not only the charge and discharge capacity during the activation process of the battery including this, but also the efficiency during the activation process and the capacity during the initial charge and discharge after activation can all be improved. At this time, the weight ratio of Sn and K (Sn:K) may be 1:0.75 to 1:2.5. Specifically, the weight ratio of Sn and K may be 1:0.75 or more, 1:0.90 or more, 1:1.0 or less, and 1:2.5 or less. In this case, the capacity maintenance rate of the battery containing it can also be improved.

According to the present invention, the lithium excess oxide may be doped with F, Sn, and Cl. At this time, the weight ratio of Sn and F (Sn:F) may be 1:0.05 to 1:0.3. Specifically, the weight ratio of Sn and F may be 1:0.05 or more, 1:0.12 or more, 1:0.17 or less, and 1:0.30 or less. In this case, not only the charge/discharge capacity during the activation process of the battery including this, but also the initial charge/discharge efficiency after activation may be excellent.

According to the present invention, the lithium excess oxide may not contain expensive cobalt and can improve the performance of a lithium secondary battery without containing cobalt.

Method for producing positive electrode active material

The present invention includes the steps of (A) mixing lithium raw materials, transition metal raw materials, and doping element raw materials in an aqueous solvent to form a synthetic solution; and (B) drying the synthetic solution and then calcining the positive electrode according to the present invention, wherein the doping element raw material includes at least one selected from K and F, Sn, and Cl. A method for manufacturing an active material is provided.

(A) Step

Step (A) is a step of forming a synthetic solution by mixing lithium raw materials, transition metal raw materials, and doping element raw materials in an aqueous solvent.

In the step (A), in forming a lithium overoxide doped with at least one selected from K and F, Sn and Cl, Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤ x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z=1) It may be used to prepare a solution for simultaneously forming phases.

The aqueous solvent may be deionized water (DI water).

The lithium raw material may be a lithium raw material that can be used in the production of a positive electrode active material, such as lithium hydroxide, lithium carbonate, etc., but from the viewpoint of the purpose of the present invention, it may be preferable to use lithium acetate. , the lithium acetate may be lithium acetate dihydrate.

The transition metal raw material may include a nickel compound, a cobalt compound, a manganese compound, etc.

The nickel compound is a nickel raw material that can be used in the production of a positive electrode active material. For example, nickel sulfate, nitrate, etc. can be used as is, but from the viewpoint of the purpose of the present invention, it may be preferable to use nickel acetate, The nickel acetate may be nickel acetate tetrahydrate.

The cobalt compound is a cobalt raw material that can be used in the production of a positive electrode active material. For example, cobalt sulfate, nitrate, etc. can be used as is, but from the viewpoint of the purpose of the present invention, it may be preferable to use cobalt acetate, The cobalt acetate may be cobalt acetate tetrahydrate.

The manganese compound is a manganese raw material that can be used in the production of a positive electrode active material. For example, manganese sulfate, nitrate, etc. can be used as is, but from the viewpoint of the purpose of the present invention, it may be preferable to use manganese acetate, The manganese acetate may be manganese acetate tetrahydrate.

The doping element raw material includes at least one selected from K and F, Sn, and Cl, and may include a potassium compound, a fluorine compound, a tin compound, and a chlorine compound.

The potassium compound may be, for example, potassium acetate, potassium chloride (KCl), potassium fluoride (KF), etc., but is not limited thereto.

The fluorine compound may be, for example, NH ₄ F, LiF, NaF, KF, AlF _3, etc., but is not limited thereto.

The tin compound may be, for example, SnCl ₂ , SnO _{2 ,} etc., but is not limited thereto.

The chlorine compound may be, for example, SnCl ₂ , KCl, NaCl, MgCl _{2 ,} etc., but is not limited thereto.

The lithium raw material, transition metal raw material, and doping element raw material may be added in an amount such that the resulting lithium excess oxide has the composition represented by Chemical Formula 1.

The synthetic solution may further include a chelate. The chelate is added to prepare a synthetic solution of uniform composition, and may be, for example, citric acid, EDTA, PVP, EDA, SDS, etc., but is not limited thereto.

In order to improve solubility, mixing in step (A) is carried out at 25℃ or higher and 100℃ or lower, specifically, 25℃ or higher, 30℃ or higher, 35℃ or higher, 40℃ or higher, 45℃ or higher, 50℃ or higher, or 55℃ or higher. , may be 60°C or higher, 65°C or higher, 70°C or higher, 75°C or higher, or 80°C or higher, and may also be performed at a temperature of 100°C or lower, 95°C or lower, 90°C or lower, 85°C or lower, or 80°C or lower. It can be.

(B) step

Step (B) is a step of drying and then firing the synthetic solution.

The step (B) is a Li ₂ MnO ₃ phase structure, a Li ₂ MnO ₃ phase, and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y ≤0.1, 0.1≤z≤1.0, x+y+z=1), and the lithium excess oxide includes at least one selected from K and F, Sn and Cl. In order to obtain a positive electrode active material doped with , the synthesis solution may be dried and fired.

Drying in step (B) removes the solvent in the synthesis solution, Li ₂ MnO ₃ phase and LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤ 1.0, x+y+z=1) can be performed to obtain an intermediate for forming the phase simultaneously.

According to the present invention, the drying in step (B) may be performed using a hot plate or may be performed by a spray drying method. On the other hand, when the drying in step (B) is performed by spray drying, the intermediate is obtained in the form of a fine powder, so volumetric productivity is improved and handling can be advantageous.

According to the present invention, the drying in step (B) may be performed at a temperature of 100°C to 350°C to remove moisture.

When the drying in step (B) is performed by spray drying, the inlet temperature of the spray drying device is 100 ℃ or more and 220 ℃ or less, specifically, 100 ℃ or more, 110 ℃ or more, 120 ℃ or more, 130 ℃ or more, 140 ℃ or more. It may be adjusted to ℃ or higher, or 150℃ or higher, and 200℃ or lower, 190℃ or lower, 180℃ or lower, 170℃ or lower, 160℃ or lower, or 150℃ or lower.

According to the present invention, the calcination in step (B) is a step for obtaining a positive electrode active material by oxidizing the intermediate powder obtained by the drying, and may be performed at a temperature of 400°C to 1,000°C.

According to the present invention, the firing is performed at 450°C or higher, 500°C or higher, 550°C or higher, 600°C or higher, 650°C or higher, 700°C or higher, 750°C or higher, 800°C or higher, 850°C or higher, 900°C or higher, or 950°C or higher. It can be carried out at a temperature of ℃ or higher, and can also be carried out at a temperature of 1,000 ℃ or lower, 950 ℃ or lower, or 900 ℃ or lower.

Additionally, the firing may be carried out in a plurality of stages, such as primary firing and secondary firing, and in this case, the secondary firing may be performed at a higher temperature than the primary firing. Specifically, the firing in step (B) may be performed firstly at a temperature of 400°C to 500°C, followed by secondary firing at a temperature of 800°C to 1,000°C. At this time, in order to improve firing uniformity, the primary fired product obtained through the primary firing may be pulverized in a mortar, and then secondary firing may be performed.

The firing may be performed for 1 hour or more and 24 hours or less, and as specific examples, may be performed for 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more, and may also be performed for 24 hours or less, It may be performed for no more than 22 hours, no more than 20 hours, no more than 18 hours, no more than 16 hours, no more than 14 hours, or no more than 12 hours.

Additionally, when the firing is divided into a plurality of stages, such as primary firing and secondary firing, the secondary firing may be performed for a longer time than the primary firing. For example, the firing may be divided into primary firing for a period of time between 1 hour and 10 hours, and secondary firing for a period of between 8 hours and 24 hours.

anode

The present invention provides a positive electrode containing the above positive electrode active material.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

The positive electrode current collector may contain a highly conductive metal, and the positive electrode active material layer is easily adhered, but is not particularly limited as long as it is non-reactive within the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or an aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material layer may optionally include a conductive material and a binder as needed, along with the positive electrode active material. At this time, the positive electrode active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive electrode active material layer, and can exhibit excellent capacity characteristics within this range. there is.

The conductive material is used to provide conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. 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, thermal black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive tubes such as carbon nanotubes; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, conductive polymers such as polyphenylene derivatives may be used, and one of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1% to 15% by weight based on the total weight of the positive electrode active material layer.

The binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, and polymethylmethane. Crylate (polymethymethaxrylate), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene- Diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers whose hydrogens are substituted with Li, Na, or Ca, or various copolymers thereof Combinations, etc. may be mentioned, and one type of these may be used alone or a mixture of two or more types may be used. The binder may be included in an amount of 0.1% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

The positive electrode can be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode is prepared by dissolving or dispersing the positive electrode active material and optionally a binder, a conductive material, and a dispersant in a solvent, and the composition for forming a positive active material layer is applied to the positive electrode current collector and then dried. and rolling, or by casting the composition for forming the positive electrode active material layer on a separate support and then peeling from this support and laminating the film obtained on the positive electrode current collector.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and dimethylformamide. , DMF), acetone, or water, among which one type alone or a mixture of two or more types may be used. The amount of the solvent used is to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the application thickness and manufacturing yield of the slurry, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for subsequent positive electrode production. That's enough.

Lithium secondary battery

The present invention provides a lithium secondary battery including the positive electrode.

The lithium secondary battery includes the positive electrode; cathode; It may include a separator and an electrolyte interposed between the anode and the cathode. Additionally, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer located 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 changes in the battery. For example, it can be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The negative electrode active material layer may optionally include a binder and a conductive material along with the negative electrode active material.

As the negative electrode 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; Metallic compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; Metal oxides that can dope and undope lithium, such as SiO _β (0<β<2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite containing the above-described metallic compound and a carbonaceous material, such as a Si-C composite or Sn-C composite, may be used, and any one or a mixture of two or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Additionally, the carbon material may include both low-crystalline carbon and high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and high-crystalline carbon includes amorphous, plate-shaped, flaky, spherical, or fibrous natural graphite, artificial graphite, and Kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbonfiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived High-temperature fired carbon such as cokes is a representative example. The negative electrode active material may be included in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

The binder of the negative electrode active material layer is a component that assists bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on 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, and polytetra. Examples include fluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, and various copolymers thereof.

The conductive material of the negative electrode active material layer is a component to further improve the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples 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 fiber and metal fiber; fluorinated carbon; Metal powders such as 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.

The negative electrode is manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, onto a negative electrode current collector and drying the negative electrode active material layer, or by applying the composition for forming the negative electrode active material layer. It can be manufactured by casting on a separate support and then peeling from this support and laminating the obtained film onto the negative electrode current collector.

The separator separates the cathode from the anode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. In particular, it has low resistance to ion movement in the electrolyte and has an electrolyte moisturizing ability. Excellent is desirable. Specifically, porous polymer films, for example, porous polymer films made of polyolefin 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 may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

The electrolyte includes, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery. As a specific example, 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-based solvents such as dibutyl ether or tetrahydrofuran; Ketone-based solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC) ), carbonate-based solvents such as; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, branched or ring-structured hydrocarbon group having 2 to 20 carbon atoms and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane, etc. may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge/discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferable.

The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the anions of the lithium salt include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , 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 CO ₂ ^- , SCN ^- , and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- It may be at least one selected from the group consisting of, 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 may be used. The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trifluoroethylene for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexanoic 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. At this time, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

Since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and lifespan characteristics, it is used in portable devices such as mobile phones, laptop computers, and digital cameras, and hybrid electric vehicles. It is useful in the field of electric vehicles such as HEV) and electric vehicles (EV).

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

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

Accordingly, 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; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it can be used as a power source for one or more mid- to large-sized devices among power storage systems.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily perform it. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

Example

Example 1

Lithium acetate dihydrate (CH ₃ COOLi·2H ₂ O), nickel acetate tetrahydrate (Ni(CH3COO) ₂ ·4H ₂ O), and manganese acetate tetrahydrate (Mn(CH ₃ COO) ₂ in 80ml of deionized water (DI water). ·4H ₂ O), potassium acetate (CH ₃ COOK), and tin chloride (SnCl ₂ ) were added so that the molar ratio of lithium:potassium:nickel:manganese:tin was 57:1:12:29:1, and chelated. Citric acid was added so that the citric acid concentration was 0.64M, and then mixed with stirring at 80°C to form a synthetic solution. After stirring was sufficiently completed, spray drying was performed at an inlet temperature of 180°C of the spray drying device to obtain an intermediate. The obtained intermediate was first fired at 450°C for 5 hours to obtain a primary fired product, the primary fired product was pulverized in a mortar, and then secondary fired at 900°C for 12 hours to obtain a positive electrode active material (lithium). Excess oxide) was prepared.

Example 2

In Example 1, the same raw materials were added so that the molar ratio of lithium:potassium:nickel:manganese:tin was 57:1:12:27.5:2.5. , a positive electrode active material was prepared.

Example 3

Lithium acetate dihydrate (CH ₃ COOLi.2H ₂ O), nickel acetate tetrahydrate (Ni(CH3COO) _{2.4H 2} O), and manganese acetate tetrahydrate (Mn(CH3COO) _2.4H ) in 80 ml of deionized water (DI water). ₂ O) and tin chloride (SnCl ₂ ) were added so that the molar ratio of lithium: nickel: manganese: tin was 58:12:27.5:2.5, 0.015 mol of NH ₄ F was added, and citric acid was added so that the citric acid concentration was 0.64. After adding it to M, it was mixed with stirring at 80°C to form a synthetic solution. After stirring was sufficiently completed, spray drying was performed at an inlet temperature of 180°C of the spray drying device to obtain an intermediate. The obtained intermediate was first fired at 450°C for 5 hours to obtain a first fired product, the primary fired product was pulverized in a mortar, and then secondary fired at 900°C for 12 hours to prepare a positive electrode active material. did.

Comparative Example 1

Lithium acetate dihydrate (CH ₃ COOLi.2H ₂ O), nickel acetate tetrahydrate (Ni(CH3COO) _{2.4H 2} O) and manganese acetate tetrahydrate (Mn(CH3COO) _2.4H ) in 80 ml of deionized water (DI water). ₂ O) was added so that the molar ratio of lithium: nickel: manganese was 58:12:30, and mixed with stirring at 80 ° C. to form a synthetic solution, carried out in the same manner as in Example 1. , a positive electrode active material was prepared.

Comparative Example 2

In Example 1, potassium acetate was not added and the molar ratio of lithium: nickel: manganese: tin was added to 58:12:29:1. , a positive electrode active material was prepared.

Comparative Example 3

In Example 1, SnCl ₂ was not added and the molar ratio of lithium:potassium:nickel:manganese was added to 57:1:12:30, and was carried out in the same manner as Example 1. , a positive electrode active material was prepared.

Experiment example

Experimental Example 1: XRD analysis

For each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, after XRD measurement, the XRD data are shown in Figures 1 and 2.

At this time, the XRD was performed by collecting 2g to 3g of positive electrode active material particles from each of the positive electrode active material powders prepared in Examples 1 to 3 and Comparative Examples 1 to 3, and applying acceleration voltage using Cu-Kα line (wavelength 1.54 Å). Measurements were made using X-ray diffraction analysis in a 2θ range of 15° to 80° at a scan speed of 0.2°/sec at 40 kV/40 mA.

For reference, the small peak at 20~23˚ is the peak corresponding to the Li ₂ MnO ₃ phase, and the peak split into two in the 37.5~39˚ region is the (006) and (012) peak, respectively, and the peak in the 63~67˚ region. The peaks split into two are (018) and (110) peaks, respectively.

Referring to Figure 1, it can be seen that the positive electrode active materials of Examples 1 to 3 prepared according to the present invention formed lithium excess oxide containing both the Li ₂ MnO ₃ phase and the LiMO ₂ phase. In addition, since the splitting of the (006)/(012) peak and the (018)/(110) peak was clearly observed, it could be confirmed that lithium excess oxide with a layered structure was formed.

And, referring to Figure 2, in the positive electrode active material of Example 2 prepared according to the present invention, secondary phase peaks are not observed at 36.0 ~ 36.5 ˚ and 44.0 ~ 44.5 ˚, so secondary phase is not formed. You can check that it is not. Accordingly, it can be seen that when lithium excess oxide is triple doped with K, Sn, and Cl, the secondary phase generated when only Sn and Cl is doped is controlled.

Experimental Example 2: ICP analysis

After taking 0.1 g of each positive electrode active material prepared in the above Examples and Comparative Examples, 1 ml of hydrochloric acid was added and heated to dissolve the positive electrode active material. Afterwards, to promote the reaction, a small amount of hydrogen peroxide was added to completely dissolve the positive electrode active material to prepare a solution. Subsequently, the analysis sample was prepared by diluting the solution with deionized water to a total volume of 10 ml. Using an ICP device, the weight ratio of the constituent elements present in the analysis sample is measured, the composition of the positive electrode active material, the weight of the doping elements (ppm), the weight ratio of Sn and K (Sn:K), and the weight ratio of Sn and F. (Sn:F) is shown in Table 1 below.

division Furtherance Sn (ppm) Cl (ppm) K (ppm) F (ppm) Sn:K Sn:F Example 1 Li _1.14 K _0.02 Ni _0.24 Mn _0.58 Sn _0.02 O _1.96 Cl _0.04 2314 10 5505 - 1:2.38 - Example 2 Li _1.14 K _0.02 Ni _0.24 Mn _0.55 Sn _0.05 O _1.9 Cl _0.1 5926 29 5505 - 1:0.93 - Example 3 Li _1.16 Ni _0.24 Mn _0.55 Sn _0.05 O _1.84 Cl _0.1 F _0.06 5926 29 - 883 - 1:0.15 Comparative Example 1 Li _1.16 Ni _0.24 Mn _0.60 O ₂ - - - - - - Comparative Example 2 Li _1.16 Ni _0.24 Mn _0.58 Sn _0.02 O _1.96 Cl _0.04 2314 10 - - - - Comparative Example 3 Li _1.14 K _0.02 Ni _0.24 Mn _0.60 O ₂ - - 5505 - - -

As shown in Table 1, as a result of ICP analysis, it can be confirmed that the positive electrode active material, which is a lithium transition metal complex oxide, was prepared according to the adjusted molar ratio when forming the synthetic solution according to the Examples and Comparative Examples.

Experimental Example 3: Average particle size analysis

Each positive active material sample prepared in Example 2 and Comparative Example 1 was prepared, images of various parts of the sample were extracted using a scanning electron microscope (SEM), and the sizes of particles visible in the images were measured, respectively. The average value was calculated to obtain the average particle diameter.

Figure 3(A) is an SEM image of the positive electrode active material of Example 2, and Figure 3(B) is an SEM image of the positive electrode active material of Comparative Example 1.

division Average particle diameter (㎛) Example 2 1.0 Comparative Example 1 0.45

Experimental Example 4: Coin-type half-cell manufacturing and capacity characteristic evaluation

97.5% by weight of the positive electrode active material prepared in the above examples and comparative examples, 1.0% by weight of Super P as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone (NMP) solvent. A positive electrode slurry was prepared. The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode.

An electrode assembly was manufactured using a lithium metal electrode as a negative electrode and a porous polyethylene separator between the positive and negative electrodes. Place it inside the battery case and inject an electrolyte solution in which 1 M LiPF ₆ is dissolved in an organic solvent mixed with ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:4:3. A coin-type half cell was manufactured.

Using the coin-type half-cell containing the positive electrode active material of the above-prepared Examples and Comparative Examples, the battery was charged to 4.65V at 0.1C constant current at 45°C, and then discharged to 2.0V at 0.1C to perform an activation process (formation). This was performed, and the charging and discharging capacities at this time were measured.

Subsequently, the battery was charged to 4.25V at 0.1C constant current at 25°C, and then discharged to 2.5V at 0.1C to measure the initial charge and discharge capacity.

Then, after charging to 4.25V at 0.33C constant current at 25°C, one cycle of discharging to 2.5V at 0.33C was repeated for a total of 50 cycles of charging and discharging, and after measuring the charging and discharging capacity, The capacity maintenance rate was measured compared to the initial charge and discharge capacity.

The charging and discharging capacity and capacity maintenance rate measured at each stage are shown in Table 3 below.

division activation process Initial charge and discharge Capacity maintenance rate
(%) charging capacity
(mAh/g) discharge capacity
(mAh/g) efficiency
(%) charging capacity
(mAh/g) discharge capacity
(mAh/g) efficiency
(%) Example 1 308.88 260.82 84.44 201.79 182.33 90.36 - Example 2 315.73 267.49 84.72 206.22 187.05 90.70 93.82 Example 3 308.63 251.76 81.57 189.63 174.23 91.88 - Comparative Example 1 295.39 247.74 83.87 193.63 176.23 91.01 92.71 Comparative Example 2 305.54 256.81 84.05 193.98 176.95 91.22 91.43 Comparative Example 3 302.52 263.41 86.28 205.93 186.34 90.04 90.64

Referring to Table 3, the positive electrode active materials of Examples 1 to 3 prepared according to the present invention have a layered structure in which the lithium excess oxide simultaneously includes a Li ₂ MnO ₃ phase and a LiMO ₂ phase, and is selected from K and F. Since it is doped with one or more types of Sn and Cl, it can be confirmed that the charge and discharge capacity is excellent during the activation process of the battery containing it.

In particular, it can be seen that batteries containing the positive electrode active materials of Examples 1 and 2 doped with K, Sn, and Cl have excellent efficiency during the activation process and excellent capacity during initial charge and discharge after activation. In addition, it can be confirmed that the battery containing the positive electrode active material of Example 2, where the weight ratio of Sn and K is within the range of 1:0.9 to 1.0, has excellent capacity retention rate.

In addition, it can be seen that the battery containing the positive electrode active material of Example 3 doped with F, Sn, and Cl has excellent efficiency during initial charge and discharge after activation.

On the other hand, the positive electrode active material of Comparative Example 1 was not doped with one or more types selected from K and F, Sn, and Cl, and it was confirmed that the charge and discharge capacity of the battery containing it was reduced during the activation process.

As a result, the positive electrode active material of the present invention has a layered structure containing both the Li ₂ MnO ₃ phase and the LiMO ₂ phase, and includes lithium excess oxide doped with at least one selected from K and F, Sn and Cl, It can be seen that the performance of the lithium secondary battery containing it can be improved.

Claims (15)

A layer containing both the Li ₂ MnO ₃ phase and the LiMO ₂ (M=Ni _x Co _y Mn _z , 0≤x≤0.9, 0≤y≤0.1, 0.1≤z≤1.0, x+y+z=1) phase Contains lithium superoxide of the structure,
A positive electrode active material wherein the lithium excess oxide is doped with one or more types selected from K and F, Sn, and Cl. In claim 1,
A positive electrode active material in which a secondary phase peak is not observed at a diffraction angle (2θ) of 36.0˚ to 36.5˚ during X-ray diffraction (XRD) analysis. In claim 1,
A positive electrode active material in which no secondary phase peak is observed at a diffraction angle (2θ) of 44.0˚ to 44.5˚ during X-ray diffraction (XRD) analysis. In claim 1,
The lithium excess oxide is a positive electrode active material having a composition represented by the following Chemical Formula 1:
[Formula 1]
Li(Li _a K _b Ni _c Co _d Mn _e Sn _f )O _2-gh Cl _g F _h
In Formula 1,
0.01≤a≤0.20, 0≤b≤0.04, 0≤c≤0.50, 0≤d≤0.05, 0.50≤e≤1.0, 0<f≤0.05, a+b+c+d+e+f=1 ,
0<g≤0.10, 0≤h≤0.06. In claim 1,
The lithium excess oxide is a positive electrode active material in the form of a single particle. In claim 1,
The lithium excess oxide is a positive electrode active material having an average particle diameter of 0.8㎛ to 1.2㎛ as measured from SEM images. In claim 1,
The lithium excess oxide is doped with K, Sn and Cl,
A positive electrode active material in which the weight ratio of Sn and K (Sn:K) is 1:0.75 to 1:2.5. In claim 1,
The lithium excess oxide is doped with F, Sn and Cl,
A positive electrode active material in which the weight ratio of Sn and F (Sn:F) is 1:0.05 to 1:0.3. (A) mixing lithium raw materials, transition metal raw materials, and doping element raw materials in an aqueous solvent to form a synthetic solution; and
(B) drying the synthetic solution and then calcining it,
The method for producing a positive electrode active material according to claim 1, wherein the doping element raw material includes at least one selected from K and F, Sn, and Cl. In claim 9,
The drying in step (B) is performed using a hot plate or a spray drying method. In claim 9,
A method of producing a positive electrode active material, wherein the drying in step (B) is performed at a temperature of 100°C to 350°C. In claim 9,
A method for producing a positive electrode active material, wherein the calcination in step (B) is performed at a temperature of 400°C to 1,000°C. In claim 9,
The method of producing a positive electrode active material in which the sintering in step (B) is performed by first sintering at a temperature of 400°C to 500°C and then secondly sintering at a temperature of 800°C to 1,000°C. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 8. A lithium secondary battery including the positive electrode according to claim 14.