KR20240046048A - Cathode composition, cathode and secondary battery - Google Patents

Abstract

The present invention provides a first positive electrode active material in the form of a single particle; a second positive electrode active material having a particle size larger than that of the first positive electrode active material and a particle strength of 150 Mpa or more; bookbinder; and a positive electrode composition containing a conductive material, and a positive electrode and secondary battery containing the same.

Description

Cathode composition, cathode and secondary battery {CATHODE COMPOSITION, CATHODE AND SECONDARY BATTERY}

This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0125359 filed with the Korea Intellectual Property Office on September 30, 2022, the entire contents of which are incorporated into this specification.

The present invention relates to positive electrode compositions, positive electrodes, and secondary batteries.

Secondary batteries are universally applied not only to portable devices but also to electric vehicles (EVs) and hybrid vehicles (HEVs) that are driven by an electrical drive source.

These secondary batteries not only have the primary advantage of being able to dramatically reduce the use of fossil fuels, but also have the advantage of not generating any by-products due to energy use, so they are attracting attention as a new energy source to improve eco-friendliness and energy efficiency.

Generally, secondary batteries include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Additionally, electrodes such as positive electrodes and negative electrodes may have an electrode active material layer provided on a current collector.

As the utilization of secondary batteries increases, various battery performances are required. For example, attempts are being made to apply silicon-based active materials to negative electrodes to develop high-capacity batteries, but silicon-based active materials have a major problem of initial irreversibility. Attempts have been made to adjust the components of the positive or negative electrode or add additives to improve battery performance, but the wrong combination of materials may have a negative effect on the performance of the final battery. Accordingly, research on improving battery performance according to the combination of anode or cathode materials is necessary.

The present invention provides a cathode composition and cathode that not only provides irreversible capacity of the cathode when used with a cathode using a silicon-based active material, but also realizes an electrode with high energy density and improves the problem of gas generation due to reaction with an electrolyte solution. and a secondary battery including the same.

One embodiment of the present invention includes a first positive electrode active material in the form of a single particle; a second positive electrode active material having a particle size larger than that of the first positive electrode active material and a particle strength of 150 Mpa or more; bookbinder; and a conductive material.

Another embodiment of the present invention is a current collector; and a positive electrode active material layer provided on the current collector and containing the positive electrode composition according to the above-described embodiment.

Another embodiment of the present invention provides a secondary battery including an anode, a cathode, and a separator according to the above-described embodiment.

According to another embodiment of the present invention, the negative electrode includes a silicon-based active material.

According to the embodiments described in this specification, not only high density but also low efficiency can be achieved by using a first positive electrode active material in the form of single particles together with a second positive electrode active material with high particle strength as the positive electrode active material. Specifically, because it has low efficiency characteristics, it can provide irreversible capacity of the cathode when used with a cathode using a silicon-based active material. In addition, the first and second cathode active materials can suppress the generation of fine powder due to particle breakage during rolling, thereby preventing an increase in specific surface area and improving the problem of gas generation due to reaction with the electrolyte solution. In addition, since problems during rolling can be improved as described above, the rolling density can be increased, thereby not only realizing high energy density, but also improving rapid charging performance by reducing the anode thickness.

Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein. 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.

In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or It should be understood that this does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

Additionally, when a part of a layer, etc. is said to be “on” or “on” another part, this includes not only cases where it is “right above” another part, but also cases where there is another part in between. Conversely, when a part is said to be “right on top” of another part, it means that there is no other part in between. In addition, being “on” or “on” a standard part means being located above or below the standard part, and it necessarily means being “on” or “on” the direction opposite to gravity. no.

In this specification, particle size means the average particle size expressed as D ₅₀ . D ₅₀ can be defined as the particle size based on 50% of the particle size distribution and can be measured using 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 approximately 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.

In this specification, 'primary particle' refers to a particle that does not appear to have grain boundaries when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

In this specification, 'secondary particles' are particles formed by agglomerating the primary particles.

In this specification, single particle is a term used to distinguish from positive electrode active material particles in the form of secondary particles formed by the agglomeration of tens to hundreds of primary particles commonly used in the past, and consists of one primary particle. It is a concept that includes single particles and aggregate particles of 10 or less primary particles.

In this specification, when referring to 'particle', it may mean that any one or all of single particles, secondary particles, and primary particles are included.

The positive electrode composition according to an exemplary embodiment of the present specification includes a first positive electrode active material in the form of a single particle; a second positive electrode active material having a particle size larger than that of the first positive electrode active material and a particle strength of 150 Mpa or more; bookbinder; and conductive materials.

In this specification, the first positive electrode active material in the form of single particles may be referred to as a small particle diameter positive electrode active material for convenience, and the second positive electrode active material having a particle size larger than the first positive electrode active material and a particle strength of 150 Mpa or more may be referred to as a large diameter positive electrode active material. You can.

In the above embodiment, by using a single particle form as a small-diameter positive electrode active material, the lithium pathway can be lengthened and efficiency can be reduced. In addition, by applying single particles with excellent rolling density, a high-density electrode can be realized, and by applying single particles with excellent tap density, the rolling rate can be improved and the generation of fine powder due to particle breakage can be suppressed. According to one example, the first positive electrode active material has a tap density of 2 g/cc or more, for example, 2 g/cc or more and 30 g/cc or less. According to one example, the first positive electrode active material has a rolling density of 3 g/cc or more, for example, 3 g/cc or more and 30 g/cc or less.

The tap density is the apparent density of particles obtained by vibrating under certain conditions, and can be measured using a tap density tester (KYT-5000, Seishin). The rolling density can be measured as the rolling density when rolling with a force of 2,000 kgf/cm ² using a powder resistance characteristic device HPRM-1000 (HAN TECH CO.).

In the above embodiment, the second positive electrode active material has a larger particle size than the first positive electrode active material and a particle strength of 150 Mpa or more. The particle strength of the second positive electrode active material may preferably be 180 Mpa or more. The higher the particle strength of the second positive electrode active material is, the more advantageous it is, but for example, it may be 600 Mpa or less.

The particle strength refers to the force when the particle is destroyed by increasing the compression force after placing the particle on the plate, and can be measured using a Micro Compression Testing Machine (Shimadzu, MCT-W500).

According to one embodiment, the particle strength of the first positive electrode active material is 150 Mpa or more, preferably 180 Mpa or more and less than 250 Mpa. If the particle strength of the first positive electrode active material is 250 Mpa or more, rolling characteristics may be inferior.

According to one embodiment, the second positive electrode active material may be in the form of secondary particles, in which case the particle size of the secondary particles is larger than the single particle particle size of the first positive electrode active material. Even when the second positive electrode active material is a secondary particle, the particle strength is over 150 Mpa as described above. Therefore, even during rolling of an electrode mixed with the first positive electrode active material in the form of single particles, particle breakage is alleviated and the generation of fine powder is suppressed, thereby suppressing the gas. Occurrence is improved. The particle strength of the large-diameter positive electrode active material can be adjusted by controlling firing conditions, such as firing time or temperature, when manufacturing the positive electrode active material.

According to one embodiment, D ₅₀ of the first positive electrode active material may be 1 ㎛ to 10 ㎛, and D ₅₀ of the second positive electrode active material may be 8 ㎛ to 20 ㎛. The second positive electrode active material may have a particle size larger than the first positive electrode active material by 3 ㎛ to 15 ㎛, for example, 5 ㎛ to 10 ㎛. When the difference in particle size between the first and second positive electrode active materials is 3 to 15㎛, particle breakage is improved, which is advantageous in improving fine powder and gas generation.

According to one embodiment, the weight ratio of the first positive electrode active material and the second positive electrode active material may be 1:9 to 9:1, specifically 3:7 to 7:3. In particular, when the content of the first and second positive electrode active materials is 3:7 to 7:3, the rolling characteristics of the electrode are improved, which is advantageous in implementing a high-density electrode.

According to one embodiment, the first cathode active material and the second cathode active material may each include a lithium composite transition metal compound containing nickel (Ni) and cobalt (Co). The lithium composite transition metal compound may further include at least one of manganese and aluminum. The lithium complex transition metal compound may contain 80 mol% or more of nickel among metals other than lithium, for example, 80 mol% or more and less than 100 mol%. For example, the lithium composite transition metal compound is Li _a Ni _(1-xy) Co _x M1 _y M2 _w O ₂ (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one metal selected from Mn or Al, and M2 is one or more metal elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo) It may be a positive electrode active material represented by .

According to one embodiment, one or both of the first and second positive electrode active materials may further include a cobalt oxide layer provided on at least a portion of the surface. The cobalt raw material of the cobalt oxide layer may contain lithium cobalt oxide by reacting with residual lithium on the surface of the active material. In this case, it can have the effect of reducing residual lithium on the surface of the active material and can have the effect of improving output due to the excellent lithium ion conductivity of lithium cobalt oxide. Additionally, the cobalt oxide layer can reduce side reactions with the electrolyte solution by existing on the surface of the active material.

According to a further embodiment of the present specification, the positive electrode binder may serve to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material particles and the positive electrode current collector. The anode binder may be those known in the art, and non-limiting examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), and polyvinylidene fluoride (PVDF). Alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene. -Propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc., of which one type alone or a mixture of two or more types may be used. .

The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer, for example, preferably 0.3 to 35 parts by weight, more preferably 0.5 to 20 parts by weight. can be included.

The conductive material included in the positive electrode active material layer is used to provide conductivity to the electrode, and can be used without particular restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, etc., of which one type alone or a mixture of two or more types may be used.

Specifically, in one embodiment, the conductive material is a single-walled carbon nanotube (SWCNT); and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the composition for the positive electrode active material layer, for example, preferably 0.3 parts by weight or more and 1.5 parts by weight or less, more preferably 0.5 parts by weight or more and 1.2 parts by weight or less. can be included.

According to a further embodiment of the present specification, a current collector; and a positive electrode active material layer provided on the current collector and containing the above-described positive electrode composition. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

According to one embodiment, the fine powder having a particle size of 1 μm or less in the positive electrode active material layer is 5 vol% or less, preferably 3 vol% or less, and more preferably 1 vol% or less based on 100 vol% of the positive electrode active material layer. . The fine powder content in the positive electrode active material layer can be measured using a laser diffraction method by heat-treating the rolled electrode in an air atmosphere at 500°C for 5 hours to remove the conductive material and binder, and then obtaining only the positive electrode active material. For example, after dispersing lithium composite transition metal oxide powder or cathode active material powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g. Microtrac MT 3000) and irradiated with ultrasonic waves at about 28 kHz with an output of 60 W. , it can be measured by obtaining a volume cumulative particle size distribution graph and then determining the volume accumulation amount of 1 ㎛ or less.

The positive electrode active material in 100 parts by weight of the positive electrode active material layer is 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight. It may contain more than 99.9 parts by weight and less than 99.9 parts by weight.

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, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , surface treated with silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 1 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.

Additional embodiments of the present specification provide a secondary battery including an anode, a cathode, and a separator according to the above-described embodiments.

The negative electrode may include a current collector and a negative electrode active material layer provided on the current collector.

According to one embodiment, the negative electrode includes a silicon-based active material.

The silicon-based active material containing SiO _x (0≤x<2) may be a silicon-based composite particle including SiO _x (0<x<2) and pores.

The SiO _x (0<x<2) corresponds to a matrix within the silicon-based composite particles. The SiO _x (0<x<2) may be in a form containing Si and SiO ₂ , and the Si may be in a phase. That is, x corresponds to the number ratio of O to Si included in the SiO _x (0<x<2). When the silicon-based composite particles include the SiO _x (0<x<2), the discharge capacity of the secondary battery can be improved.

The silicon-based composite particle may further include at least one of an Mg compound and a Li compound. The Mg compound and Li compound may correspond to a matrix within the silicon-based composite particle.

The Mg compound and/or Li compound may be present inside and/or on the surface of the SiO _x (0<x<2). The initial efficiency of the battery may be improved by the Mg compound and/or Li compound.

The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg ₂ SiO ₄ and MgSiO ₃ . The Mg silicide may include Mg ₂ Si. The Mg oxide may include MgO.

In one embodiment of the present specification, the Mg element may be included in an amount of 0.1% by weight to 20% by weight, or may be included in an amount of 0.1% by weight to 10% by weight based on a total of 100% by weight of the silicon-based active material. Specifically, the Mg element may be included in an amount of 0.5% to 8% by weight or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon-based active material, so the volume change of the silicon-based active material can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li ₂ SiO ₃ , Li ₄ SiO ₄ and Li ₂ Si ₂ O ₅ . The Li silicide may include Li ₇ Si ₂ . The Li oxide may include Li ₂ O.

In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate is expressed as Li _a Si _b O _c (2≤a≤4, 0<b≤2, 2≤c≤5), and can be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the silicon-based composite particle in the form of at least one type of lithium silicate selected from the group consisting of Li ₂ SiO ₃ , Li ₄ SiO ₄ , and Li ₂ Si ₂ O ₅ , and the amorphous lithium silicate may be Li It may be in the form of _a Si _b O _c (2≤a≤4, 0<b≤2, 2≤c≤5), but is not limited to the above form.

In one embodiment of the present specification, the Li element may be included in an amount of 0.1% by weight to 20% by weight, or may be included in an amount of 0.1% by weight to 10% by weight based on a total of 100% by weight of the silicon-based active material. Specifically, the Li element may be included in an amount of 0.5% by weight to 8% by weight, and more specifically, it may be included in an amount of 0.5% by weight to 4% by weight. When the above range is satisfied, the Li compound can be included in an appropriate amount in the silicon-based active material, so the change in volume of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

The content of the Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (about 0.01 g) of the negative electrode active material is accurately separated, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Then, using an induced plasma luminescence spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of the standard solution (5 mg/kg) prepared using the standard solution (5 mg/kg) is measured at the unique wavelength of the Mg element or Li element, and a standard calibration curve is prepared. . Afterwards, the pretreated sample solution and blank sample are introduced into the device, the intensity of each is measured to calculate the actual intensity, the concentration of each component is calculated compared to the calibration curve prepared above, and then converted so that the sum of all becomes the theoretical value. The Mg element or Li element content of the manufactured silicon-based active material can be analyzed.

In one embodiment of the present specification, a carbon layer may be provided on the surface and/or inside the pores of the silicon-based composite particle. By the carbon layer, conductivity is imparted to the silicon-based composite particles, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery containing a negative electrode active material containing the silicon-based composite particles can be improved. The total weight of the carbon layer may be 5% to 40% by weight based on a total of 100% by weight of the silicon-based composite particles.

In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

The average particle diameter (D ₅₀ ) of the silicon-based active material may be 2 ㎛ to 15 ㎛, specifically 3 ㎛ to 12 ㎛, and more specifically 4 ㎛ to 10 ㎛. When the above range is satisfied, side reactions between the silicon-based composite particles and the electrolyte solution are controlled, and the discharge capacity and initial efficiency of the battery can be effectively implemented.

In this specification, the average particle size (D ₅₀ ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters ranging from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

According to an exemplary embodiment of the present specification, the negative electrode slurry may further include an additional negative electrode active material in addition to the silicon-based active material described above.

As the additional negative active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include 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, lithium titanium oxide, and lithium vanadium oxide; A composite containing the above metallic compound and a carbonaceous material, such as a Si-C composite or SnC composite; Carbon-based active materials, etc. may be mentioned, 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.

In one embodiment of the present invention, the weight ratio of the silicon-based active material and the additional negative electrode active material contained in the negative electrode slurry may be 1:99 to 90:10, and specifically 1:99 to 50:50.

In one embodiment of the present specification, the carbon-based active material can be used without particular limitation, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake-shaped, spherical or fibrous natural graphite and artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). , hard carbon, mesophase pitch carbide, and calcined coke. The graphite may be natural graphite, graphite graphite, or a mixture thereof. Based on 100 parts by weight of the total negative electrode active material included in the negative electrode active material layer, the carbon-based active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less.

In one embodiment of the present specification, the amount of the negative electrode active material in 100 parts by weight of the negative electrode active material layer is 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or more. It may be included in an amount of no more than 98 parts by weight and no more than 99.9 parts by weight.

According to a further embodiment of the present specification, the negative electrode active material layer may further include a negative electrode binder in addition to the silicon-based active material and the carbon-based active material.

The negative electrode binder may serve to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material particles and the negative electrode current collector. As the cathode binder, those known in the art can be used, and non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, poly Acrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and their hydrogen is replaced by Li, Na or Ca, etc. It may include at least one selected from the group consisting of materials, and may also include various copolymers thereof.

The negative electrode binder may be included in an amount of 0.1 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode active material layer, for example, preferably 0.3 parts by weight or more and 20 parts by weight or less, more preferably 0.5 parts by weight or more and 10 parts by weight or less. can be included.

The negative electrode active material layer may not contain a conductive material, but may further include a conductive material if necessary. The conductive material included in the negative electrode active material layer is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, Paneth black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, 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 content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

In one embodiment of the present specification, the thickness of the negative electrode active material layer may be 10 μm or more and 500 μm or less.

In one embodiment, the negative electrode current collector can be any conductive material without causing chemical changes in the battery, and is not particularly limited. For example, the current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, can be used as a current collector. The thickness of the current collector may be 1㎛ to 500㎛, but the thickness of the current collector is not limited thereto.

The positive electrode and the negative electrode can be manufactured according to a conventional positive electrode and negative electrode manufacturing method, except for using the positive and negative electrode active materials described above. Specifically, it can be manufactured by applying a composition for forming an active material layer containing the above-described active material and, optionally, a binder and a conductive material onto a current collector, followed by drying and rolling. At this time, the types and contents of the positive and negative electrode active materials, 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 active material, conductive material, and binder in consideration of the application thickness and manufacturing yield of the composition, and to have a viscosity that can exhibit excellent thickness uniformity when applied for the production of positive and negative electrodes. Suffice. As another method, the positive and negative electrodes may be manufactured by casting the composition for forming the active material layer on a separate support and then laminating the film obtained by peeling from the support on a current collector.

The separator separates the cathode from the anode and provides a passage for lithium ions. It can be used without particular restrictions as long as it is normally used as a separator in 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. In addition, 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 electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethyl. Toxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxoran, formamide, dimethylformamide, dioxoran, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid. Triesters, trimethoxy methane, dioxoran derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyropionate, propionic acid. Aprotic organic solvents such as ethyl may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can easily dissociate lithium salts, so they can be preferably used. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. If the same low-viscosity, low-dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte with high electrical conductivity can be made and can be used more preferably.

The metal salt may be a lithium salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte solution. For example, anions of the lithium salt include F-, Cl-, I-, NO ₃ -, N(CN) ) ₂ -, BF ₄ -, ClO ₄ -, PF ₆ -, (CF ₃ ) ₂ PF ₄ -, (CF ₃ ) ₃ PF ₃ -, (CF ₃ ) ₄ PF ₂ -, (CF ₃ ) ₅ PF- , (CF ₃ ) ₆ P-, CF ₃ SO ₃ -, CF ₃ CF ₂ SO ₃ -, (CF ₃ SO ₂ ) ₂ N-, (FSO ₂ ) ₂ N-, CF ₃ CF ₂ (CF ₃ ) ₂ CO-, (CF ₃ SO ₂ ) ₂ CH-, (SF ₅ ) ₃ C-, (CF ₃ SO ₂ ) ₃ C-, CF ₃ (CF ₂ ) ₇ SO ₃ -, CF ₃ CO ₂ -, CH ₃ One or more species selected from the group consisting of CO ₂ -, SCN-, and (CF ₃ CF ₂ SO ₂ ) ₂ N- may be used.

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.

A further embodiment of the present invention provides a battery module including the above-described lithium secondary battery as a unit cell and a battery pack including the same. Since the battery module and battery pack include the secondary battery with high capacity, high rate characteristics, and cycle characteristics, they are medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. It can be used as a power source.

Since the lithium secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, it is used not only in portable devices such as mobile phones, laptop computers, and digital cameras, but also in electric vehicles, hybrid electric vehicles, and plug-in devices. - It can be used as a power source for medium to large-sized devices selected from the group consisting of hybrid electric vehicles and power storage systems. For example, the battery module or battery pack may include 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, preferred embodiments are presented to aid understanding of the present invention. However, the above examples are merely illustrative of the present description, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, It is natural that such variations and modifications fall within the scope of the attached patent claims.

Examples 1 to 3

A positive electrode was manufactured by coating, drying, and rolling a positive electrode active material layer on a positive electrode current collector. As a composition for manufacturing the positive electrode active material layer, a Ni-based positive electrode active material (Li _1.0 Ni _0.84 Co _0.08 Mn _0.08 O ₂ ) having a cobalt oxide layer on a portion of the particle surface, a conductive material (CNT), and a binder (PVDF) are prepared at 97 A positive electrode slurry was prepared by adding it to methylpyrrolidone (NMP) solvent at a weight ratio of 1:2 (the solid content of the positive electrode slurry is included in 70 parts by weight of the total positive electrode slurry).

The positive electrode slurry prepared above was applied on an Al current collector, dried at high temperature, and rolled at room temperature to produce a positive electrode.

Here, the positive electrode active material is a first positive electrode active material having the D ₅₀ , tap density, and rolling density of single particles in Table 1 below and the particle strength in Table 2, and a second positive electrode active material having the D ₅₀ and particle strength in Table 2 below. Included in a weight ratio of 6:4.

Tap density, rolling density, and particle strength were prepared in the following manner.

* Tap density: A 300 cc container was filled with 10 g of the positive electrode active material obtained in Example 1 and Comparative Example 1, and then vibrated under certain conditions to measure the apparent density of the obtained particles. Specifically, the tap density of the lithium transition metal oxide particles was measured using a tap density tester (KYT-5000, Seishin).

* Rolling density: The rolling density of the positive electrode active material (die area: 2.3 cm ² ) was measured using a powder resistance characteristic device HPRM-1000 (HAN TECH CO.) at a force of 2,000 kgf/cm ² each.

* Particle strength: After placing the particles on the plate, the compression force was increased using a Micro Compression Testing Machine (Shimadzu, MCT-W500) and the force when the particles were broken was measured, which was used as the particle strength value.

The negative electrode current collector contains SiO and graphite (SiO-based active material is included in 5 parts by weight of the total negative electrode active material), conductive material (carbon black), binder (SBR), and thickener (CMC) in the ratio of 96:1:2: A negative electrode slurry was prepared by adding it to distilled water solvent at a weight ratio of 1 (the solid content of the negative electrode slurry is included in 50 parts by weight of the total negative electrode slurry).

The anode slurry prepared above was applied on a Cu current collector, dried at high temperature, and rolled at room temperature to produce a cathode.

The anode and cathode were stacked with a separator in between, and an electrolyte (1M LiPF ₆ , ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (volume ratio 3/7), vinylene carbonate (VC)/propane sultone (PS, propane) A lithium secondary battery was manufactured by injecting sultone (containing 3 parts by weight and 1.5 parts by weight, respectively, based on 100 parts by weight of electrolyte).

The electrode density, rolling rate, and degree of fine dust generation of the positive electrode, and the 0.1 C efficiency and degree of gas generation of the lithium secondary battery are shown in Table 2 below.

Electrode density, rolling rate, degree of fine powder generation, and degree of gas generation were measured by the following methods.

* Electrode density: Electrode weight / (electrode thickness * electrode area)

- Electrode weight: Slurry weight excluding aluminum foil weight

- Electrode thickness: Slurry layer thickness excluding aluminum foil thickness

* Rolling rate: [(Thickness before rolling - aluminum foil thickness) - (Thickness after rolling - aluminum foil thickness)] / (Thickness before rolling - aluminum foil thickness)

* Generation of fine powder: The positive electrode active material obtained by heat-treating the rolled electrode in an air atmosphere at 500°C for 5 hours was obtained by using Microtrac MT 3000 to obtain a volume particle size distribution graph, and then the volume accumulation of less than 1 ㎛ was obtained.

* Gas generation: The manufactured cell was charged with constant current/constant voltage (CC/CV) to 4.2V at 0.33C (0.05C-cut) and stored at high temperature (60℃) for 8 weeks. The amount of gas generated was measured using gas chromatography (gc). Measured using agilent 7890b).

Comparative Example 1

The same procedure as Example 1 was carried out, except that secondary particles rather than single particles were used as the first positive electrode active material, and single particles with a strength of 149 Mpa were used as the first positive electrode active material. The first positive electrode active material, which is a secondary particle, has the secondary particle D ₅₀ , tap density, and rolling density shown in Table 1 below.

Comparative Example 2

The same procedure as Example 1 was performed, except that secondary particles with a strength of 121 Mpa were used as the second positive electrode active material, and single particles with a strength of 149 Mpa were used as the first positive electrode active material.

Comparative Example 3

The same procedure as Example 1 was carried out, except that secondary particles with a strength of 121 Mpa were used as the second positive electrode active material.

Single particle of the first positive electrode active material of Example 1 First positive electrode active material secondary particles of Comparative Example 1 D ₅₀ (㎛) 4 4 Tap density (g/cc) 2.4 1.6 Rolling density (g/cc) 3.3 2.4

As shown in Table 1, it can be confirmed that single particles have higher tap density and rolling density than secondary particles even if D ₅₀ is the same.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 D ₅₀ (㎛)
(2nd cathode active material/1st cathode active material) 12/4 12/4 12/4 12/4 12/4 12/4 Particle strength (Mpa)
(2nd cathode active material/1st cathode active material) 269/181 168/181 232/181 269/149 121/149 121/181 Electrode density (g/cc) 3.49 3.48 3.51 3.32 3.41 3.33 Rolling rate (%) 27.8 28.6 27.9 35.6 26.5 27.1 Fine powder (particles with a particle diameter of 1㎛ or less) generated (vol%) 0.34 4.7 0.31 11.7 8.5 7.6 0.1 C efficiency (%) 88.3 91.2 88.1 92.8 92.5 91.4 Gas generation (@ 8 weeks) 0.58 0.77 0.52 1.13 0.99 0.95

Since the first cathode active materials of Example 1 and Comparative Example 1 are single particles and secondary particles, respectively, a difference in tap density of the first cathode active materials occurs as shown in Table 1, and as a result, the first cathode active materials coated with the same loading amount Because the coating thickness of the positive electrode active material layer varies before rolling, a difference in rolling rate occurs when rolling to the final target thickness. That is, when single particles are used as the first positive electrode active material as in Example 1, the tap density is excellent and the coating thickness of the first positive electrode active material layer is thin, so the rolling rate for rolling to the target thickness can be improved.

In Examples 2 and 3, compared to Example 1, the particle sizes of the first and second positive electrode active materials were the same, but the particle strengths were different. The second cathode active material of Examples 2 and 3 has a different particle strength from the second cathode active material of Example 1, was manufactured under different firing conditions from those of Example 1, and had a higher tab than the second cathode active material of Example 1. The density is relatively low, so there is a slight difference in rolling rate.

As shown in Table 2, it was confirmed that in Examples 1 to 3, less fine powder was generated, efficiency was low, and gas generation was greatly reduced compared to Comparative Examples 1 to 3.

Comparative Example 1 corresponds to the case where secondary particles were used as the first positive electrode active material. Compared to the case where single particles were used, the tap density was relatively low, and rolling was not performed properly, resulting in fine powder and gas compared to Examples 1 to 3. You can see that this happens a lot.

Comparative Examples 2 and 3 correspond to cases where the particle strength of the second positive electrode active material is less than 150Mpa, and the particle strength of the second positive electrode active material is weak and cracking occurs during rolling, resulting in more fine powder and gas than Examples 1 to 3. You can check that.

Claims (12)

A first positive electrode active material in the form of a single particle;
a second positive electrode active material having a particle size larger than that of the first positive electrode active material and a particle strength of 150 Mpa or more;
bookbinder; and
A positive electrode composition containing a conductive material. The positive electrode composition according to claim 1, wherein the second positive electrode active material is in the form of secondary particles. The positive electrode composition of claim 1, wherein the first positive electrode active material has a D ₅₀ of 1 ㎛ to 10 ㎛, and the second positive electrode active material has a D ₅₀ of 8 ㎛ to 20 ㎛. The positive electrode composition of claim 1, wherein the first positive electrode active material has a tap density of 2 g/cc or more. The positive electrode composition of claim 1, wherein the first positive electrode active material has a rolling density of 3 g/cc or more. The positive electrode composition according to claim 1, wherein the particle strength of the first positive electrode active material is 150 Mpa or more. The cathode composition according to claim 1, wherein a weight ratio of the first cathode active material and the second cathode active material is 1:9 to 9:1. house collector; and a positive electrode active material layer provided on the current collector and containing the positive electrode composition according to any one of claims 1 to 7. The positive electrode according to claim 8, wherein the fine powder having a particle diameter of 1 ㎛ or less in the positive electrode active material layer is 5 vol% or less based on 100 vol% of the positive electrode active material layer. A secondary battery comprising an anode, a cathode, and a separator according to claim 8. The secondary battery according to claim 10, wherein the negative electrode includes a silicon-based active material. The secondary battery of claim 11, wherein the negative electrode further includes a carbon-based active material.