KR102657451B1 - Positive electrode material for secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is a bimodal cathode material comprising a first cathode active material as a small particle and a second cathode active material as an opposing cathode, wherein the first and second cathode active materials include nickel (Ni), cobalt (Co), and It is a lithium composite transition metal oxide containing manganese (Mn), consists of single particles, and is used for secondary batteries in which a coating layer containing boron (B) is formed on the particle surfaces of the first and second positive electrode active materials. It is about cathode materials.

Description

Cathode material for secondary batteries and lithium secondary batteries containing the same {POSITIVE ELECTRODE MATERIAL FOR SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

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

Recently, with the rapid spread of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for secondary batteries that are small, lightweight, and relatively high capacity is rapidly increasing. In particular, lithium secondary batteries are lightweight and have high energy density, so they are attracting attention as a driving power source for portable devices. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are actively underway.

Lithium secondary batteries are oxidized when lithium ions are intercalated/deintercalated from the positive and negative electrodes when an organic electrolyte or polymer electrolyte is charged between the positive and negative electrodes, which are made of active materials capable of intercalation and deintercalation of lithium ions. Electrical energy is produced through a reduction reaction.

Cathode active materials for lithium secondary batteries include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. were used. Among these, lithium cobalt oxide (LiCoO ₂ ) has the advantages of high operating voltage and excellent capacity characteristics, so it is widely used and is applied as a high-voltage positive electrode active material. However, due to the rising price and unstable supply of cobalt (Co), there are limits to its mass use as a power source in fields such as electric vehicles, and the need to develop a positive electrode active material that can replace it has emerged.

Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') was developed in which part of cobalt (Co) was replaced with nickel (Ni) and manganese (Mn). However, conventionally developed NCM-based lithium composite transition metal oxides are generally in the form of secondary particles in which primary particles are aggregated, have low particle strength, and have a high content of lithium by-products, resulting in a large amount of gas generation during cell operation and low stability. There was a problem with falling. As such, the previously developed NCM-based lithium composite transition metal oxide had limited stability, especially when applied to high-voltage batteries. In addition, in order to increase the capacity per unit volume of the electrode, it is necessary to increase the rolling density. Conventionally developed NCM-based lithium composite transition metal oxides had problems with increased resistance and gas generation due to severe particle breakage during rolling. .

Accordingly, there is still a need to develop cathode materials of NCM-based lithium composite transition metal oxides that improve particle breakage during rolling, improve rolling density, and improve stability.

Korean Patent Publication No. 2014-0018685

The present invention seeks to provide a cathode material of NCM-based lithium composite transition metal oxide in which crack generation and particle breakage of the cathode active material by rolling are improved. Anodes and lithium secondary batteries for secondary batteries with reduced electrode and interface resistance, improved adhesion, reduced cell resistance, improved lifespan characteristics, and reduced gas generation by reducing crack generation and particle breakage of NCM-based lithium composite transition metal oxide anode materials. It is intended to provide.

The present invention is a bimodal cathode material comprising a first cathode active material as a small particle and a second cathode active material as an opposing cathode, wherein the first and second cathode active materials include nickel (Ni), cobalt (Co), and It is a lithium composite transition metal oxide containing manganese (Mn), consists of single particles, and is used for secondary batteries in which a coating layer containing boron (B) is formed on the particle surfaces of the first and second positive electrode active materials. A cathode material is provided.

Additionally, the present invention provides a positive electrode and a lithium secondary battery containing the above positive electrode material.

The cathode material according to the present invention can reduce the occurrence of cracks and particle breakage of the cathode active material due to rolling. By using the cathode material with improved crack generation and particle breakage according to the present invention, it is possible to reduce the electrode and interface resistance of the cathode for secondary batteries, improve adhesion, reduce cell resistance and lifespan characteristics of lithium secondary batteries. It can improve and reduce gas generation. In addition, the cathode material of NCM-based lithium composite transition metal oxide according to the present invention can secure excellent stability and can be applied to high-voltage lithium secondary batteries.

Figure 1 is a graph measuring the electrode resistance of each positive electrode manufactured using the positive electrode materials of Examples and Comparative Examples.
Figure 2 is a graph measuring the interfacial resistance of each positive electrode manufactured using the positive electrode materials of Examples and Comparative Examples.
Figure 3 is a graph measuring the adhesion of each positive electrode manufactured using the positive electrode materials of Examples and Comparative Examples.
Figure 4 is a graph measuring the cell resistance of each lithium secondary battery manufactured using the cathode materials of Examples and Comparative Examples.
Figure 5 is a graph showing the high-temperature lifespan characteristics of each lithium secondary battery manufactured using the cathode materials of Examples and Comparative Examples.
Figure 6 is a graph showing the high-temperature storage characteristics of each lithium secondary battery manufactured using the cathode materials of Examples and Comparative Examples.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. At this time, the terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately define the concept of the term in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

< cathode material >

The cathode material for a secondary battery of the present invention is a bimodal cathode material containing a first cathode active material that is small particles and a second cathode active material that is an opposing cathode material, and the first cathode active material and the second cathode active material are nickel (Ni) and cobalt. It is a lithium complex transition metal oxide containing (Co) and manganese (Mn), and consists of a single particle, and a coating layer containing boron (B) on the particle surfaces of the first and second positive electrode active materials. This is formed.

The first and second positive electrode active materials are lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn), that is, NCM-based lithium composite transition metal oxides. The lithium composite transition metal oxide may have a nickel (Ni) content of 70 mol% or more, more preferably 80 mol% or more, of the total transition metal content. It may be possible to secure high capacity by satisfying the nickel (Ni) content of 70 mol% or more among the total transition metal content of the lithium composite transition metal oxide.

More specifically, the first positive electrode active material and the second positive electrode active material according to an embodiment of the present invention may be a lithium composite transition metal oxide represented by the following Chemical Formula 1.

[Formula 1]

Li _p Ni _{1 -(x1+y1+z1)} Co _x1 Mn _y1 M ^a _z1 O _{2 +δ}

In the above formula, M ^a is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, Cr, Ba, Sr and Ca, 1≤p≤1.3, 0<x1≤0.5, 0<y1≤0.5, 0≤z1≤0.1, -0.1≤δ≤1.

In the lithium composite transition metal oxide of Formula 1, Li may be included in a content corresponding to p, that is, 1≤p≤1.3. If p is less than 1, there is a risk that the capacity may decrease, and if it exceeds 1.3, the strength of the fired positive electrode active material increases, making pulverization difficult, and the amount of gas generated may increase due to an increase in Li by-products. Considering the effect of improving the capacity characteristics of the positive electrode active material by controlling the Li content and the sinterability balance when manufacturing the active material, Li may be more preferably included in an amount of 1.0≤p≤1.1.

In the lithium composite transition metal oxide of Formula 1, Ni may be included in an amount corresponding to 1-(x1+y1+z1), for example, 0<1-(x1+y1+z1)≤0.9. More preferably, Ni may be included as 0.4≤1-(x1+y1+z1)≤0.9, and even more preferably as 0.7≤1-(x1+y1+z1)≤0.9.

In the lithium composite transition metal oxide of Formula 1, Co may be included in an amount corresponding to x1, that is, 0<x1≤0.5. If the Co content in the lithium composite transition metal oxide of Formula 1 exceeds 0.5, there is a risk of increased cost. Considering the significant effect of improving capacity characteristics due to the inclusion of Co, Co may be specifically included in an amount of 0.2≤x1≤0.4.

In the lithium composite transition metal oxide of Formula 1, Mn may be included in an amount corresponding to y1, that is, 0<y1≤0.5. Mn can improve the stability of the positive electrode active material and, as a result, improve the stability of the battery. More specifically, the Mn may be included in an amount of 0.05≤y1≤0.2.

In the lithium composite transition metal oxide of Formula 1, M ^a may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ^a may be included in a content corresponding to z1, that is, 0≤z1≤0.1. there is.

The first positive electrode active material and the second positive electrode active material may be lithium composite transition metal oxides of the same composition, or may be lithium composite transition metal oxides of different compositions.

The cathode material for secondary batteries of the present invention is bimodal, comprising a first cathode active material that is small particles with a relatively small average particle diameter (D ₅₀ ) and a second cathode active material that is small particles with a relatively large average particle diameter (D ₅₀ ). It is an anode material of In the case of a bimodal positive electrode material that is a mixture of large and small particle positive electrode active materials as in the present invention, the empty space between particles of the large positive positive active material can be filled with the small particle positive active material, allowing for more dense filling. It is possible, and the energy density of the anode can be increased.

In the present invention, the average particle size (D ₅₀ ) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. For example, the method for measuring the average particle diameter (D ₅₀ ) of the positive electrode active material is to disperse the particles of the positive electrode active material in a dispersion medium and then introduce them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) to measure about After irradiating 28 kHz ultrasonic waves with an output of 60 W, the average particle diameter (D ₅₀ ) corresponding to 50% of the volume accumulation in the measuring device can be calculated.

The average particle diameter (D ₅₀ ) ratio of the first positive electrode active material and the second positive electrode active material may be 1:1.5 to 1:8, and more preferably, the average particle diameter (D ₅₀ ) of the first positive electrode active material and the second positive electrode active material is The ratio may be 1:1.6 to 1:5, more preferably 1:2 to 1:3.5. By satisfying the average particle diameter (D ₅₀ ) ratio of the first and second positive electrode active materials within the above range, the voids between the positive electrode active material particles are more effectively reduced, the filling density is increased, and the pressure acting according to the particle size is optimized. Particle breakage can be reduced during rolling, and the capacity per anode volume can be effectively improved.

The average particle diameter (D ₅₀ ) of the first positive electrode active material may be 2 to 8 ㎛, more preferably 4 to 7 ㎛, and even more preferably 4 to 6 ㎛.

The average particle diameter (D ₅₀ ) of the second positive electrode active material may be 12 to 20 μm, more preferably 12 to 18 μm, and even more preferably 12 to 15 μm.

The first positive electrode active material and the second positive active material may be mixed at a weight ratio of 1:9 to 5:5, more preferably 1:9 to 4:6, more preferably 2:8 to 3: It can be mixed at a weight ratio of 7. By mixing the first positive electrode active material, which is a small particle, and the second positive electrode active material, which is an opposing particle, within the above range, the energy density of the positive electrode can be increased, the pressure applied according to the particle size can be optimized to reduce particle breakage during rolling, and high capacity and excellent quality can be achieved. Thermal stability can be ensured and side reactions with the electrolyte solution can be suppressed.

The first and second positive electrode active materials are made of single particles, that is, primary particles, not in the form of aggregated secondary particles. In the present invention, 'primary particle' refers to the primary structure of a single particle, and 'secondary particle' refers to the physical bond between primary particles without an intentional agglomeration or assembly process for the primary particles constituting the secondary particle. Alternatively, it refers to an aggregate of primary particles aggregated together by chemical bonds, that is, a secondary structure. By using single particles as both the first positive electrode active material, which is small particles, and the second positive electrode active material, which is small particles, the particle strength can be improved and the occurrence of cracks and particle breakage of the positive electrode active material due to rolling can be reduced. , side reactions with the electrolyte can be reduced, the amount of gas generated during cell operation can be reduced, and excellent stability can be ensured.

As described above, the first and second positive electrode active materials composed of single particles may be formed by overheating at a temperature of 960°C or higher. The first positive electrode active material and the second positive electrode active material are overheated to form a single particle, and the crystal size may be 180 nm or more. More preferably, the first positive electrode active material and the second positive electrode active material may have a crystal size of 200 to 250 nm, more preferably 200 to 240 nm.

In the present invention, 'particles' refer to micro-scale grains, and when observed enlarged, they can be distinguished as 'grains' that have a crystal form of tens of nanoscale. If you enlarge this further, you can see distinct areas where atoms form a lattice structure in a certain direction. These are called 'crystallites', and the size of the particles observed in XRD is defined by the size of the crystal grains. . Crystallite size can be measured using peak broadening of XRD data, and can be quantitatively calculated using the Scherrer equation.

As described above, when the crystal size satisfies 180 nm or more, particle strength can be improved and the occurrence of cracks and particle breakage of the positive electrode active material due to rolling can be more effectively reduced.

A coating layer containing boron (B) is formed on the surface of the particles of the first and second positive electrode active materials. A coating layer containing boron (B) is formed on the surface of both the small particle first positive electrode active material and the small particle second positive electrode active material, thereby improving particle strength and effectively preventing cracks and particle breakage of the positive electrode active material due to rolling. It can be reduced.

Next, a method for manufacturing a cathode material for a secondary battery of the present invention will be described, but the method is not particularly limited to the following manufacturing method.

The first and second positive electrode active materials of the present invention are formed by mixing a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a lithium raw material and overheating at a temperature of 960°C or higher to form single particles. Forming a (single particle) lithium complex transition metal oxide; And mixing the single particle lithium complex transition metal oxide with a boron (B) coating source and heat treating it to form a boron (B)-containing coating layer on the particle surface.

The first positive electrode active material, which is a small particle, and the second positive electrode active material, which is an opposing particle, can be manufactured and mixed, respectively, to produce a bimodal positive electrode material of the present invention.

The precursor may be purchased and used as a commercially available positive electrode active material precursor, or may be manufactured according to a method for producing a positive electrode active material precursor well known in the art.

For example, the precursor may be prepared by co-precipitation reaction by adding an ammonium cation-containing complex former and a basic compound to a transition metal solution containing nickel-containing raw materials, cobalt-containing raw materials, and manganese-containing raw materials.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ . 2Ni(OH) ₂ ㆍ4H ₂ O, NiC ₂ O ₂ ㆍ2H ₂ O, Ni(NO ₃ ) ₂ ㆍ6H ₂ O, NiSO ₄ , NiSO ₄ ㆍ6H ₂ O, fatty acid nickel salt, nickel halide or these It may be a combination, but is not limited to this.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) _{2.4H 2} O , Co(NO ₃ ) ₂ ㆍ6H ₂ O, CoSO ₄ , Co(SO ₄ ) ₂ ㆍ7H ₂ O, or a combination thereof, but is not limited thereto.

The manganese-containing raw material may be, for example, manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically Mn ₂ O ₃ , MnO ₂ , Mn ₃ Manganese oxides such as O ₄ and the like; Manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, dicarboxylic acid manganese salt, manganese citrate, fatty acid manganese salt; It may be manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

The transition metal solution is a mixture of nickel-containing raw materials, cobalt-containing raw materials, and manganese-containing raw materials in a solvent, specifically water, or an organic solvent that can be uniformly mixed with water (for example, alcohol, etc.). It may be manufactured by adding a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and a manganese-containing raw material.

The ammonium cation-containing complex forming agent is, for example, NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , NH ₄ CO ₃ Or it may be a combination thereof, but is not limited thereto. Meanwhile, the ammonium cation-containing complex former may be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that is uniformly miscible with water.

The basic compound may be a hydroxide of an alkali metal or alkaline earth metal such as NaOH, KOH, or Ca(OH) ₂ , a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, and in this case, the solvent may be water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that is uniformly miscible with water.

The basic compound is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution is 11 to 13.

Meanwhile, the coprecipitation reaction may be performed at a temperature of 40°C to 70°C in an inert atmosphere such as nitrogen or argon.

Particles of nickel-cobalt-manganese hydroxide are generated through the above process and precipitated in the reaction solution. The precipitated nickel-cobalt-manganese hydroxide particles can be separated and dried according to a conventional method to obtain a nickel-cobalt-manganese precursor. The precursor is a secondary particle formed by agglomerating primary particles.

Next, the precursor and the lithium raw material are mixed and overheated at a temperature of 960° C. or higher to form a single particle NCM-based lithium composite transition metal oxide.

The lithium raw material may include lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium source is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH·H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ It may be COOLi, or Li ₃ C ₆ H ₅ O ₇ , and any one or a mixture of two or more of these may be used.

In order to form the single particle NCM-based lithium composite transition metal oxide, the overheating temperature is preferably 960°C or higher, more preferably 970 to 1050°C, and even more preferably 980 to 1000°C. You can. The oversaturation can be performed for 10 to 30 hours, and more preferably for 20 to 26 hours. The overheating may be performed in an oxygen atmosphere or an air atmosphere, and more preferably in an oxygen atmosphere. By over-tempering in this way, single particle NCM-based lithium composite transition metal oxide can be formed, and the single particle NCM-based lithium composite transition metal oxide has improved particle strength, preventing particle breakage during rolling. It is suppressed, side reactions with the electrolyte can be reduced, the amount of gas generated during cell operation can be reduced, and excellent stability can be ensured. If the overheating temperature is less than 960°C, it cannot be converted into single particles, and the primary particles exist as lithium composite transition metal oxides in the form of aggregated secondary particles, which may reduce particle strength and stability.

Next, the single particle NCM-based lithium composite transition metal oxide and the boron (B) coating source are mixed and heat treated to form a boron (B)-containing coating layer on the particle surface.

The boron (B) coating source is B ₄ C, B ₂ O ₃ , BF ₃ , H ₃ BO ₃ , (C ₃ H ₇ O) ₃ B, (C ₆ H ₅ O) ₃ B, [CH ₃ (CH ₂ ) ₃ O] ₃ B, C ₁₃ H ₁₉ O ₃ , C ₆ H ₅ B(OH) ₂ , and B ₂ F ₄ It may include at least one selected from the group consisting of.

The boron (B) coating source may be dry mixed with the lithium composite transition metal oxide and then heat treated at 500 to 750° C. to form a boron (B)-containing coating layer. The heat treatment can be more preferably performed at 600 to 700°C.

The bimodal cathode material of the present invention can be manufactured by mixing the first cathode active material, which is a small particle, and the second cathode active material, which are particles prepared as described above. However, it is not necessarily limited to the above manufacturing method, and any manufacturing method that can implement the configuration and effects of the present invention can be applied without limitation.

<Cathode and secondary battery>

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

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

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , surface treated with nickel, titanium, silver, etc. can be used. 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 positive electrode 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.

Additionally, the cathode material layer may include a conductive material and a binder along with the previously described cathode material.

At this time, the conductive material is used to provide conductivity to the electrode, and can be used without particular restrictions in the battery being constructed as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; 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 typically be included in an amount of 1 to 30% by weight based on the total weight of the cathode material layer.

Additionally, the binder serves to improve adhesion between positive electrode active material particles and 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, and 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 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 1 to 30% by weight based on the total weight of the cathode material layer.

The positive electrode can be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode material described above. Specifically, it can be manufactured by applying the cathode material layer-forming composition containing the above-described cathode material and, optionally, a binder and a conductive material onto a cathode current collector, followed by drying and rolling. At this time, the types and contents of the cathode material, binder, and conductive material are the same as described above.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or Water, etc. may be used, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used is sufficient to dissolve or disperse the cathode material, conductive material, and binder in consideration of the application thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied for subsequent anode production. do.

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

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

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, 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.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode 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 material layer optionally includes a binder and a conductive material along with the negative electrode active material. As an example, the negative electrode material layer is formed by applying a negative electrode forming composition containing a negative electrode active material and optionally a binder and a conductive material on a negative electrode current collector and drying it, or by casting the negative electrode forming composition on a separate support. , it can also be manufactured by laminating a film obtained by peeling from this support onto a negative electrode current collector.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. 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, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. 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 carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch. High-temperature calcined carbon such as derived cokes is a representative example.

Additionally, the binder and conductive material may be the same as those previously described for the positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for 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, and in particular, it can be used for ion movement in the electrolyte. It is desirable to have low resistance and excellent electrolyte moisturizing ability. 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 a ceramic component or polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

In addition, electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, and are limited to these. It doesn't work.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether-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 Carbonate-based solvents such as PC); Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or ring-structured hydrocarbon group 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 charging and discharging performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferable. In this case, excellent electrolyte performance can be obtained by mixing cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9.

The lithium salt can be used without particular restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of 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.

As described above, the lithium secondary battery containing the cathode material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity maintenance rate, and is therefore widely used in portable devices such as mobile phones, laptop computers, digital cameras, and hybrid electric vehicles ( It is useful in electric vehicle fields such as hybrid electric vehicle (HEV).

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

The battery module or battery pack is a power tool; 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 any 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 implement it. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

Example One

Cathode active material precursor N _{0. 8} Co _{0 . 1} Mn _0.1 (OH) ₂ (D ₅₀ = 4.5㎛) was added to the Henschel mixer (20L) so that the lithium source LiOH had a Li _/ M(Ni,Co,Mn) molar ratio of 1.045, and stirred at the center at 300rpm for 20 minutes. Mixed. The mixed powder was placed in an alumina crucible with a size of 330 mm x 330 mm, and calcined at 960°C for 10 hours in an oxygen atmosphere to prepare single particle lithium composite transition metal oxide. Thereafter, the lithium composite transition metal oxide powder was ground using a mortar, and 0.1 parts by weight of H ₃ BO ₃ was mixed with 100 parts by weight of the lithium composite transition metal oxide. The mixed mixture was heat-treated at 295°C for 5 hours in an air atmosphere to prepare a first positive electrode active material (D ₅₀ = 6㎛).

Additionally, the positive electrode active material precursor Ni _{0 . 8} Co _{0 . 1} Mn _0.1 (OH) ₂ (D ₅₀ = 12.5㎛) was added to the Henschel mixer (20L) so that the lithium source LiOH had a Li _/ M (Ni, Co, Mn) molar ratio of 1.055, and stirred at 300 rpm in the center for 20 minutes. Mixed. The mixed powder was placed in an alumina crucible with a size of 330 mm x 330 mm, and calcined at 980°C for 10 hours in an oxygen atmosphere to prepare single particle lithium composite transition metal oxide. Thereafter, the lithium composite transition metal oxide powder was ground using a mortar, and 0.1 parts by weight of H ₃ BO ₃ was mixed with 100 parts by weight of the lithium composite transition metal oxide. The mixed mixture was heat-treated at 295°C for 5 hours in an air atmosphere to prepare a second positive electrode active material (D ₅₀ = 14㎛).

A bimodal positive electrode material was prepared by mixing the first and second positive electrode active materials at a weight ratio of 2:8.

Example 2

A cathode material was manufactured in the same manner as in Example 1, except that the first and second cathode active materials were mixed at a weight ratio of 3:7.

Comparative example One

Cathode active material precursor Ni _{0 . 8} Co _{0 . 1} Mn _0.1 (OH) ₂ (D ₅₀ = 4.5㎛) was added to the Henschel mixer (20L) so that the lithium source LiOH had a Li _/ M(Ni,Co,Mn) molar ratio of 1.045, and stirred at the center at 300rpm for 20 minutes. Mixed. The mixed powder was placed in an alumina crucible measuring 330mmx330mm, and calcined at 780°C for 10 hours in an oxygen atmosphere to prepare lithium composite transition metal oxide. Thereafter, the lithium composite transition metal oxide powder was ground using a mortar, and 0.1 parts by weight of H ₃ BO ₃ was mixed with 100 parts by weight of the lithium composite transition metal oxide. The mixed mixture was heat-treated at 295°C for 5 hours in an air atmosphere to prepare a first positive electrode active material (D ₅₀ = 4.5 ㎛).

Additionally, the positive electrode active material precursor Ni _{0 . 8} Co _{0 . 1} Mn _0.1 (OH) ₂ (D ₅₀ = 12.5㎛) was added to the Henschel mixer (20L) so that the lithium source LiOH had a Li _/ M (Ni, Co, Mn) molar ratio of 1.055, and stirred at 300 rpm in the center for 20 minutes. Mixed. The mixed powder was placed in an alumina crucible measuring 330mmx330mm and calcined at 800°C for 10 hours in an oxygen atmosphere to prepare lithium composite transition metal oxide. Thereafter, the lithium composite transition metal oxide powder was ground using a mortar, and 0.1 parts by weight of H ₃ BO ₃ was mixed with 100 parts by weight of the lithium composite transition metal oxide. The mixed mixture was heat-treated at 295°C for 5 hours in an air atmosphere to prepare a second positive electrode active material (D ₅₀ = 12.5 ㎛).

A bimodal positive electrode material was prepared by mixing the first and second positive electrode active materials at a weight ratio of 2:8.

Comparative example 2

A cathode material was manufactured in the same manner as in Example 1, except that H ₃ BO ₃ was not added when producing the first and second cathode active materials.

Comparative example 3

A cathode material was manufactured in the same manner as in Example 1, except that Mo ₂ O ₃ was added instead of H ₃ BO ₃ when producing the first and second cathode active materials and heat treatment was performed.

Comparative example 4

A cathode material was manufactured in the same manner as in Example 1, except that the first cathode active material prepared in Comparative Example 1 was used as the first cathode active material.

Comparative example 5

A cathode material was manufactured in the same manner as in Example 1, except that the second cathode active material prepared in Comparative Example 1 was used as the second cathode active material.

[ Experiment example 1: Particle shape and crystal size of positive electrode active material]

The particle shapes of the first and second positive electrode active materials prepared in Example 1 and Comparative Example 1 were observed, and the crystal sizes were measured. The particle shape was observed using SEM photographs, and the average value of crystal size was calculated by measuring XRD.

Single particle? Crystal size (nm) First positive electrode active material Second positive active material First positive electrode active material Second positive active material Example 1 O O 200 230 Comparative Example 1 X X 100 140

Referring to Table 1, the first and second positive electrode active materials prepared in Example 1 by overheating at 960°C and 980°C, respectively, were formed as single particles and had a crystal size of 200 nm or more. On the other hand, the first and second positive electrode active materials of Comparative Example 1, which were fired at 780°C and 800°C, respectively, were in the form of secondary particles rather than single particles, and had a crystal size of less than 180nm.

[ Experiment example 2: Particle breakage evaluation]

The degree of particle breakage when the cathode materials of Examples 1 to 2 and Comparative Examples 1 to 5 were rolled at 7,000 kgf was evaluated. The degree of particle breakage was evaluated through the Num% D ₁₀ change in PSD (Particle Size Distribution), and the results are shown in Table 2.

D ₁₀ (㎛) before rolling D ₁₀ (㎛) after rolling △D ₁₀ (㎛) Example 1 4.28 3.12 1.16 Example 2 4.12 3.07 1.05 Comparative Example 1 3.23 1.25 1.98 Comparative example 2 4.25 1.36 2.89 Comparative Example 3 4.22 1.41 2.81 Comparative example 4 3.15 1.23 1.92 Comparative Example 5 3.02 1.03 1.99

Referring to Table 2, in the case of the cathode materials of Examples 1 to 2, the increase in D ₁₀ after rolling was significantly smaller than that of Comparative Examples 1 to 5. Through this, it can be seen that the occurrence of particle breakage during rolling of the cathode materials of Examples 1 and 2 was significantly reduced compared to the cathode materials of Comparative Examples 1 and 5.

[ Experiment example 3: Electrode resistance and interface resistance]

Each of the cathode materials, carbon black conductive material, and PVdF binder prepared in Examples 1 to 2 and Comparative Examples 1 to 5 were mixed in a weight ratio of 96.5:1.5:2 in N-methylpyrrolidone solvent to form a cathode composite. (viscosity: 5000 mPa·s) was prepared, applied to one side of an aluminum current collector, dried at 130°C, and rolled to produce a positive electrode.

For each positive electrode manufactured in Examples 1 to 2 and Comparative Examples 1 to 5, the thickness of the electrode layer (positive electrode composite) and the interface layer were determined by inputting the total thickness of the positive electrode and the thickness of the current collector using a device called a multi probe. Electrode resistance and interface resistance were measured using the calculated and measured values. The results are shown in Figures 1 and 2.

Referring to Figures 1 and 2, it can be seen that the electrode resistance and interface resistance of the positive electrodes manufactured using the positive electrode materials of Examples 1 and 2 were reduced compared to the positive electrodes manufactured using the positive electrode materials of Comparative Examples 1 and 5. You can.

[ Experiment example 4: Adhesion evaluation]

For each positive electrode manufactured as in Experimental Example 3, the adhesion of the electrode was measured using a TXA universal testing machine (UTM). The measurement method involved attaching an anode punched to a width of 10x150 mm on a slide glass with double-sided tape. Afterwards, in order to make the attachment surface uniform, a sample was manufactured by pressing it using a roller with a load of 2kg. The manufactured sample was placed in the measuring part of the adhesive force meter and peeled at an angle of 90 degrees. The measurement results are shown in Figure 3. indicated.

Referring to Figure 3, it can be seen that the adhesion of the positive electrodes manufactured using the positive electrode materials of Examples 1 and 2 was improved compared to the positive electrodes manufactured using the positive electrode materials of Comparative Examples 1 and 5.

[ Experiment example 5: Battery resistance evaluation]

The positive electrode material, carbon black conductive material, and PVdF binder prepared in Examples 1 to 2 and Comparative Examples 1 to 5 were mixed in a weight ratio of 96.5:1.5:2 in N-methylpyrrolidone solvent to prepare a positive electrode composite. The positive electrode was manufactured by applying it to one side of an aluminum current collector, drying it at 130°C, and then rolling it.

Lithium metal was used as the cathode.

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

For each lithium secondary battery half cell manufactured as described above, the voltage before the start of discharge and the voltage 60 seconds after the start of discharge were measured after discharging 50% of the discharge capacity measured at 25°C in a fully charged state. The cell resistance was measured by dividing the difference by the discharge current. The results are shown in Figure 4.

Referring to FIG. 4, it can be seen that the cell resistance of the lithium secondary batteries manufactured using the cathode materials of Examples 1 and 2 was reduced compared to the lithium secondary batteries manufactured using the cathode materials of Comparative Examples 1 and 5. .

[ Experiment example 6: High temperature life characteristics]

For each lithium secondary battery half cell manufactured as in Experimental Example 5, it was charged at 45°C in CCCV mode at 0.5C and until 4.25V (end current 1/20C), with a constant current of 0.5C. The high-temperature lifespan characteristics were evaluated by measuring the capacity retention rate when the battery was discharged to 2.5V and charged and discharged 30 times. The results are shown in Figure 5.

Referring to Figure 5, it can be seen that the lithium secondary batteries manufactured using the cathode materials of Examples 1 and 2 have improved high-temperature lifespan characteristics compared to the lithium secondary batteries manufactured using the cathode materials of Comparative Examples 1 and 5. .

[ Experiment example 7: High temperature storage characteristics]

For each lithium secondary battery half cell manufactured as in Experimental Example 5, it was charged with 100% SOC, disassembled, electrodes were placed in an aluminum pouch, and stored at 60°C for 4 weeks to measure the amount of gas generated. As a result, is shown in Figure 5.

Referring to FIG. 6, the amount of gas generated in the lithium secondary battery manufactured using the cathode materials of Examples 1 and 2 was significantly reduced when stored at high temperature compared to the lithium secondary battery manufactured using the cathode material of Comparative Examples 1 and 5. You can check that.

Claims (11)

It is a bimodal positive electrode material containing a first positive electrode active material that is elementary particles and a second positive electrode active material that is an opposing particle,
The first and second positive electrode active materials are lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn), and are made of single particles,
The first and second positive electrode active materials have a crystal size of 180 nm or more,
A cathode material for a secondary battery in which a coating layer containing boron (B) is formed on the particle surfaces of the first and second cathode active materials.
delete According to paragraph 1,
The cathode material for a secondary battery wherein the average particle diameter (D ₅₀ ) ratio of the first cathode active material and the second cathode active material is 1:1.5 to 1:8.
According to paragraph 1,
The first positive electrode active material is a positive electrode material for a secondary battery having an average particle diameter (D ₅₀ ) of 2 to 8 μm.
According to paragraph 1,
The second positive electrode active material is a positive electrode material for a secondary battery having an average particle diameter (D ₅₀ ) of 12 to 20 μm.
According to paragraph 1,
A cathode material for a secondary battery in which the first cathode active material and the second cathode active material are mixed at a weight ratio of 2:8 to 3:7.
According to paragraph 1,
The lithium composite transition metal oxide is a cathode material for secondary batteries in which the nickel (Ni) content of the total transition metal content is 70 mol% or more.
According to paragraph 1,
The first cathode active material and the second cathode active material are cathode materials for secondary batteries represented by the following formula (1).
[Formula 1]
Li _p Ni _{1 -(x1+y1+z1)} Co _x1 Mn _y1 M ^a _z1 O _{2 +δ}
In the above formula, M ^a is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, Cr, Ba, Sr and Ca, 1≤p≤1.3, 0<x1≤0.5, 0<y1≤0.5, 0≤z1≤0.1, -0.1≤δ≤1.
According to paragraph 1,
A cathode material for a secondary battery in which the first cathode active material and the second cathode active material are formed by overheating at a temperature of 960° C. or higher.
A positive electrode for a secondary battery comprising the positive electrode material according to any one of claims 1 and 3 to 9.
A lithium secondary battery comprising the positive electrode according to claim 10.