KR20240052661A - Anode and secondary battary - Google Patents

Abstract

The present invention relates to a current collector; A first negative electrode active material layer provided on the current collector; and a second negative electrode active material layer provided on the first negative electrode active material layer, wherein the first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment, and the second negative electrode active material layer includes artificial graphite in the form of secondary particles. and a method for manufacturing secondary batteries and negative electrodes for secondary batteries containing artificial graphite in the form of single particles.

Description

Anode and secondary battery{ANODE AND SECONDARY BATTARY}

This application claims the benefit of the filing date of Patent Application No. 10-2022-0132407 filed with the Korea Intellectual Property Office on October 14, 2022, the entire contents of which are incorporated into this specification.

The present invention relates to a negative electrode for a secondary battery and a secondary battery containing the same.

Secondary batteries are widely 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 from 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. Attempts have been made to add additives to the active material layer to improve battery performance. However, depending on the type of additive, some performance of the battery may be improved, but some performance may actually deteriorate. Accordingly, research is needed on the selection or combination of materials included in electrodes that can improve the required performance of secondary batteries.

The present invention seeks to provide a secondary battery anode with improved adhesion and expansion performance and a secondary battery containing the same.

One embodiment of the present invention is

house collector;

A first negative electrode active material layer provided on the current collector; and

It includes a second negative electrode active material layer provided on the first negative electrode active material layer,

The first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment,

The second negative electrode active material layer provides a negative electrode for a secondary battery including artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.

Another embodiment of the present invention provides a secondary battery including the negative electrode, positive electrode, and separator for the secondary battery.

Another embodiment of the present invention includes forming a first negative electrode active material layer on a current collector;

It includes forming a second negative electrode active material layer on the first negative electrode active material layer.

The first negative electrode active material layer includes isostatically treated natural graphite or natural graphite with a BET specific surface area of 1 m ² /g to 3 m ² /g,

A method of manufacturing a negative electrode for a secondary battery is provided, wherein the second negative electrode active material layer includes artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.

The negative electrode of the present invention uses artificial graphite in the form of secondary particles along with isostatically treated natural graphite and artificial graphite in the form of single particles in the negative electrode active material layer, so that the orientation within the electrode is relatively low and side reactions with the electrolyte are reduced. This can improve the expansion performance of the electrode. In addition, by forming isostatically treated natural graphite at the bottom of the negative electrode active material layer, the adhesion of the negative electrode active material layer can be maximized to provide an improved rapid charging effect.

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” the other 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 D50. D50 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, in the method of measuring the average particle diameter (D50) of the positive electrode active material, particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and measured at about 28 kHz. After irradiating ultrasonic waves with an output of 60 W, the average particle diameter (D50) corresponding to 50% of the volume accumulation in the measuring device can be calculated.

In this specification, descriptions referred to only as “active material layer” without the first and second expressions may be applied to both the first and second active material layers.

A negative electrode for a secondary battery according to an exemplary embodiment of the present specification includes a current collector; A first negative electrode active material layer provided on the current collector; and a second negative electrode active material layer provided on the first negative electrode active material layer, wherein the first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment, and the second negative electrode active material layer includes artificial graphite in the form of secondary particles. and artificial graphite in the form of single particles. In other words, the negative electrode for a secondary battery includes two layers of negative electrode active material, artificial graphite in the form of secondary particles, natural graphite subjected to isostatic pressure treatment, and artificial graphite in the form of single particles, and the natural graphite subjected to isostatic pressure treatment. By placing graphite at the bottom of the negative electrode active material layer, a negative electrode with excellent expansion performance and adhesion can be obtained.

A method of manufacturing a negative electrode for a secondary battery according to another embodiment includes forming a first negative electrode active material layer on a current collector; Forming a second negative electrode active material layer on the first negative electrode active material layer, wherein the first negative electrode active material layer is isostatically treated natural graphite or natural graphite having a BET specific surface area of 1 m ² /g to 3 m ² /g. It includes graphite, and the second negative electrode active material layer includes artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.

In this specification, “single particle” is a concept in contrast to secondary particles formed by agglomeration of tens to hundreds of primary particles, and means composed of 10 or less primary particles. Specifically, in the present invention, a single particle may be a single particle composed of one primary particle, or may be a particle in which several primary particles are aggregated.

In this specification, “primary particle” refers to the smallest unit of particle recognized when observing an active material through a scanning electron microscope, and “secondary particle” refers to a secondary structure formed by agglomerating tens to hundreds of primary particles. do.

In this specification, “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 observe this at greater magnification, you can see distinct areas where atoms form a lattice structure with a certain direction, and these are called 'crystal grains'. The size of the particles observed in XRD is defined as the grain size. The grain size can be quantitatively determined through the Scherrer equation using XRD data.

According to one embodiment of the present invention, the first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment. The isostatically treated natural graphite can be obtained through methods such as cold isostatic pressing (CIP). Specifically, spheronized granulated particles of which the size was adjusted through an airflow pulverizer were filled into a mold of a cold isostatic pressure molding device, the slopes of the mold were filled with water, and then cold pressed for 100 seconds at a molding pressure of 90 MPa. Perform isostatic pressure forming. Afterwards, the cold isostatically molded spheronized granulated particles are disintegrated. Isostatically treated natural graphite can be obtained by mixing 100 parts by weight of the disintegrated spheronized granulated particles with 5 parts by weight of pitch (solid pitch), a carbon coating material, and carbonizing the mixture for 24 hours at a temperature of 1,250°C and carbon coating it. However, the method for producing isostatically treated natural graphite is not limited to the above description.

As described above, when using a method such as cold isostatic pressing (CIP) to obtain isostatically treated natural graphite, pressure can be isotropically applied to the raw material particles from all directions. Therefore, the raw material particles in the spherical granulated particles have an advantage in that the internal voids are reduced and the specific surface area is reduced.

According to an exemplary embodiment of the present invention, as the first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment, the orientation within the electrode is relatively low, and side reactions with the electrolyte are reduced to improve the expansion performance of the electrode. and can increase the adhesion of the negative electrode active material layer.

According to one embodiment of the present invention, the BET specific surface area of the natural graphite may be 1 m ² /g to 3 m ² /g. By using natural graphite having a BET specific surface area in the above range, there is an advantage that the durability of the cell is improved. Specifically, if it exceeds 3 m ² /g, durability is reduced due to electrolyte side reactions, and if it is less than 1 m ² /g, it is difficult to implement and hinders electrolyte penetration. For example, it may be 1.2 m ² /g to 2.8 m ² /g, 1.2 m ² /g to 2.8 m ² /g, 1.2 m ² /g to 2.6 m ² /g, and 1.4 m ² /g to 2.4 m ² /g.

In this specification, the BET specific surface area can be measured, for example, by the BET (Brunauer-Emmett-Teller) measurement method using BELSORP (BET equipment) from BEL JAPAN using an adsorbed gas such as nitrogen.

According to one embodiment of the present invention, the average particle diameter (D50) of the isostatically treated natural graphite may be 6 ㎛ to 9 ㎛, 7 ㎛ to 9 ㎛, and 8 ㎛ to 9 ㎛. By using isostatically treated natural graphite having an average particle diameter (D50) in the above range, the effects of including isostatically treated natural graphite in the negative electrode active material layer (improved expansion performance of the electrode, increased adhesion of the negative electrode active material layer) are achieved. can be maximized.

The average particle diameter (D50) of the isostatically treated natural graphite can be adjusted through a pulverizing process using an airflow crusher device. Specifically, it can be obtained by preparing flaky graphite with an average particle diameter (D50) of 200 ㎛, grinding it by adjusting its size using an airflow grinder device, and pulverizing the flaky graphite into spheroids by subjecting it to a spheronization process. However, the method of obtaining natural graphite with isostatic pressure treatment and adjusted average particle diameter is not limited to the above description.

According to one embodiment of the present invention, the second negative electrode active material layer includes artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.

According to one embodiment of the present invention, the average particle diameter (D50) of the single particle form of artificial graphite may be 6 ㎛ to 9 ㎛, 7 ㎛ to 9 ㎛, and 8 ㎛ to 9 ㎛.

According to one embodiment of the present invention, the average particle diameter (D50) of the artificial graphite in the form of secondary particles may be 16 ㎛ to 22 ㎛.

In one embodiment of the present invention, in order to obtain artificial graphite in the form of single particles having an average particle diameter (D50) in the above range and artificial graphite in the form of particles, pulverization is performed using a jet mill, and heat treatment is performed after pulverization, etc. method can be used. Specifically, needle coke can be pulverized using a jet mill and then sieved to obtain powder with an adjusted size. Additionally, artificial graphite primary particles (or single particles) can be manufactured by heat treating (graphitizing) the powder at 3,000° C. for 20 hours under an inert argon (Ar) gas atmosphere, and the artificial graphite primary particles (only particles) and a binder such as petroleum pitch are added, and then heat treated at 1,000° C. or higher for 10 hours to obtain artificial graphite secondary particles in which the artificial graphite primary particles are agglomerated.

In one embodiment of the present invention, the OI (004/110) of the single particle type artificial graphite is 35 or less and 25 or less.

The OI (004/110) of the second negative electrode active material layer is a value obtained through X-ray diffraction analysis, and can be obtained using a general method of X-ray diffraction analysis, such as JIS K 0131-1996. The OI value of the cathode can be expressed as C004/C110, where C004 represents the characteristic diffraction peak area of the (004) crystal plane and C110 represents the characteristic diffraction peak area of the (110) crystal plane.

The OI (004/110) of the single-particle type artificial graphite of the second negative electrode active material layer is a value obtained through X-ray diffraction analysis, using a general method of X-ray diffraction analysis, such as an X-ray diffraction analyzer Bruker D4 Endeavor. It can be obtained by doing this. Additionally, the OI value of the cathode may be expressed as I004/I110, where I004 represents the characteristic diffraction peak area of the (004) crystal plane, and I110 represents the characteristic diffraction peak area of the (110) crystal plane.

These characteristics indicate the degree of orientation of graphite crystals in the second negative electrode active material layer. The larger the OI value, the higher the orientation of the graphite, and the lower the OI value, the lower the orientation. When the orientation of the graphite crystals is low, the expansion performance of the battery can be improved by expanding the battery at a random or non-random location rather than expanding only in a specific direction when charging the battery.

According to one embodiment of the present invention, the adhesive force of the first negative electrode active material layer to the current collector is 18 gF/cm or more. Since the negative electrode of the present invention is formed so that the first negative electrode active material layer and the current collector are in contact, the adhesive strength of the isostatically treated natural graphite, which is the material of the first negative electrode active material layer, is greater than the adhesive strength of the first negative electrode active material layer to the current collector. It will have an impact.

According to one embodiment of the present invention, the adhesion of the isostatically treated natural graphite included in the first negative electrode active material layer is 18 gF/cm or more. The adhesion of the isostatically treated natural graphite can be adjusted depending on the particle size distribution value.

In one embodiment of the present invention, the second negative electrode active material layer may include 30 to 90 parts by weight of artificial graphite in the form of secondary particles based on 100 parts by weight of the negative electrode active material. If the above range is satisfied, there is an advantage in improving the expansion performance and energy density of the battery.

In one embodiment of the present invention, the second negative electrode active material layer may include 10 to 30 parts by weight of artificial graphite in the form of single particles based on 100 parts by weight of the negative electrode active material. If the above range is satisfied, there is an advantage in improving the expansion performance and energy density of the battery.

According to an exemplary embodiment of the present specification, each of the negative electrode active material layers (the first negative electrode active material layer and the second negative electrode active material layer) includes the above-described isostatically treated natural graphite, artificial graphite in the form of secondary particles, and artificial graphite in the form of single particles. It may further contain negative electrode active materials other than graphite, and the type is not limited.

In one embodiment of the present specification, the amount of the negative electrode active material in 100 parts by weight of each 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. It may be included in an amount of 99.9 parts by weight or less, more preferably 98 parts by weight or more and 99.9 parts by weight or less.

According to a further embodiment of the present specification, the first negative electrode active material layer may further include a negative electrode binder in addition to isostatically treated natural graphite, and the second negative electrode active material layer may include artificial graphite in the form of secondary particles and single In addition to artificial graphite in particle form, it may further include an additional negative electrode binder.

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 include 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.

The negative electrode active material layer may further include a thickener such as Na-CMC (Sodium carboxymethyl cellulose), Li-CMC (Carboxymethyl cellulose lithium), and CNF (Cellulose nanofiber).

In an exemplary embodiment of the present specification, the thickness of the first and second negative electrode active material layers may be 5 ㎛ or more and 500 ㎛ or less, respectively.

According to an exemplary embodiment of the present specification, the thickness ratio of the first and second negative electrode active material layers (thickness of the first negative electrode active material layer:thickness of the second negative electrode active material layer) may be 3:7 to 5:5.

In an exemplary embodiment of the present specification, the negative electrode current collector may 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.

Additional embodiments of the present specification provide a secondary battery including a negative electrode, a positive electrode, and a separator according to the above-described embodiments.

In one embodiment of the present specification, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

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 μm, 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.

In one embodiment of the present specification, the positive electrode may include a lithium complex transition metal compound containing nickel (Ni) and cobalt (Co) as an active material. The lithium composite transition metal compound may further include at least one of manganese and aluminum. The lithium composite 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%.

In one embodiment, the amount of 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, it may be included in an amount of 98 parts by weight or more and 99.9 parts by weight or less.

According to a further embodiment of the present specification, the positive electrode active material layer according to the above-described embodiment may further include a positive electrode binder and a conductive material.

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 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the positive electrode active material layer, for example, preferably 0.3 parts by weight or more and 35 parts by weight or less, more preferably 0.5 parts by weight or more and 20 parts by weight or less. can be included.

The conductive material contained 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. may be included.

The positive electrode and the negative electrode can be manufactured according to a conventional manufacturing method of the positive electrode and negative electrode except for using the positive electrode 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 as described above.

The composition for forming the active material layer may further include a solvent. Specifically, the solvent may be a solvent commonly used in the art, including dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone ( acetone) or water, among which one type alone or a mixture of two or more types may be used. The amount of the solvent used is sufficient to dissolve or disperse the active 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 the production of positive and negative electrodes. Suffice. Alternatively, the positive electrode and the negative electrode may be manufactured by casting the composition for forming the active material layer on a separate support and then peeling off the support and laminating the film obtained on the current collector.

Additional embodiments of the present specification provide a method for manufacturing a negative electrode for a secondary battery according to the above-described embodiments.

The manufacturing method includes forming a first negative electrode active material layer on a current collector;

A method of manufacturing a negative electrode for a secondary battery comprising forming a second negative electrode active material layer on the first negative electrode active material layer,

The first negative electrode active material layer includes isostatically treated natural graphite or natural graphite with a BET specific surface area of 1 m ² /g to 3 m ² /g,

The second negative electrode active material layer may include artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.

A secondary battery according to an exemplary embodiment of the present invention includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, and may be a lithium secondary battery.

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 be preferably used because they easily dissociate lithium salts. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. If linear carbonates of the same low viscosity and low dielectric constant are 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 CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- One or more species selected from the group consisting of 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 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 secondary batteries according to embodiments of the present invention stably exhibit excellent discharge capacity, output characteristics, and cycle performance, they are 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 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 any 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.

Example 1

The average particle diameter (D50) is 9㎛, natural graphite isostatically treated at 80MPa pressure (adhesion: 19 gF/cm), SBR as a binder, CMC as a thickener, and carbon black as a conductive material at a ratio of 96:1:2:1. After weighing the weight ratio (natural graphite:SBR:CMC:carbon black), distilled water was added and mixed to prepare the first cathode slurry. Next, as the negative electrode active material, artificial graphite in the form of secondary particles with an average particle diameter (D50) of 18㎛, artificial graphite in the form of single particles (OI(004/110): 25) with an average particle diameter (D50) of 8.5㎛, and binder. SBR, CMC as a thickener, and carbon black as a conductive material have a weight ratio of 95:1:3:1 (artificial graphite (secondary particle artificial graphite: single particle artificial graphite = 80:20):SBR:CMC:carbon black). After weighing, distilled water was added and mixed to prepare a second cathode slurry. The prepared first negative electrode slurry was coated on a copper foil electrode current collector to form a first negative electrode active material layer, and the prepared second negative electrode slurry was coated on the surface of the first negative electrode active material layer to form a second negative electrode active material layer to prepare a negative electrode. At this time, the weight ratio (natural graphite:artificial graphite) of the natural graphite included in the first negative electrode active material layer and the artificial graphite included in the second negative electrode active material layer is 30:70, and the artificial graphite in the form of secondary particles The weight ratio (secondary particle: single particle) of the single particle type artificial graphite is 80:20.

Example 2

A negative electrode was manufactured in the same manner as in Example 1, except that isostatically treated natural graphite with an average particle diameter (D50) of 9㎛ and an adhesive force of 22 gF/cm was used.

Example 3

A cathode was manufactured in the same manner as in Example 1, except that natural graphite subjected to isostatic pressure treatment at 90 MPa was used.

Example 4

An anode was manufactured in the same manner as in Example 1, except that a mixing ratio of secondary particle artificial graphite and single particle artificial graphite was used as the anode active material of the second anode slurry at 70:30.

Comparative Example 1

A negative electrode was manufactured in the same manner as in Example 1, except that only the negative electrode active material layer containing artificial graphite in the form of secondary particles with a particle size (D50) of 18 μm was formed.

Comparative Example 2

A single-layer negative electrode active material layer is formed containing (mixed) artificial graphite in the form of secondary particles with a particle size (D50) of 18 ㎛ and artificial graphite in the form of single particles with a particle size (D50) of 18 ㎛. A negative electrode was manufactured in the same manner as in Example 1 except that.

Comparative Example 3

A single-layer negative electrode active material layer is formed containing (mixed) artificial graphite in the form of secondary particles with a particle size (D50) of 18㎛ and natural graphite that has not been isostatically treated with a particle size (D50) of 9㎛. A negative electrode was manufactured in the same manner as in Example 1 except that.

Comparative Example 4

A first negative electrode active material layer containing natural graphite that has not been subjected to isostatic pressure treatment and has a particle size (D50) of 9㎛; A negative electrode was manufactured in the same manner as in Example 1, except that a second negative electrode active material layer was formed including artificial graphite in the form of secondary particles with a particle size (D50) of 18 μm.

Comparative Example 5

As the anode active material layer, isostatically treated natural graphite with a particle size (D50) of 9㎛, artificial graphite in the form of secondary particles with a particle size (D50) of 18㎛, and artificial graphite in the form of single particles with a particle size (D50) of 9㎛. A negative electrode was manufactured in the same manner as in Example 1, except that a single layer of negative electrode active material containing (mixed) graphite was formed.

Comparative Example 6

A single-layer negative electrode active material layer is formed containing (mixed) artificial graphite in the form of secondary particles with a particle size (D50) of 18㎛ and artificial graphite in the form of single particles with a particle size (D50) of 9㎛. A negative electrode was manufactured in the same manner as in Example 1 except that.

Comparative Example 7

The negative electrode is formed by coating the surface of the copper foil electrode current collector with the second negative electrode slurry to form a second negative electrode active material layer, and the first negative electrode slurry is coated on the surface of the second negative electrode active material layer to form the first negative electrode active material layer. Then, a negative electrode was manufactured in the same manner as in Example 1.

The adhesion between the negative electrode active material layer of the manufactured negative electrode and the current collector and the cycle expansion performance of the battery manufactured using the negative electrode manufactured in the above Examples and Comparative Examples were measured and are shown in Table 1 below.

(1) Method of measuring adhesion of negative electrode active material layer (gF/cm): Each negative electrode manufactured in Examples and Comparative Examples was rolled, dried in a vacuum oven at 130°C for 8 hours, punched to a certain size, and then slided. After fixing it to the center of the glass using tape, the peeling strength was measured by peeling off the negative electrode current collector using a UTM (Universal Testing Machine).

(2) Cycle swelling performance (Swelling ratio(%)@30 ^th cycle(Charge)) Measurement method: LiCoO ₂ as the positive electrode active material, Li-435 (manufactured by Denka) as the conductive material, and binder and thickener at 96:2:2. A positive electrode slurry was prepared by mixing at a weight ratio (positive electrode active material: conductive material: binder + thickener) and adding N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was applied to aluminum foil, vacuum dried and rolled at about 130°C for 8 hours to prepare a positive electrode with an area of 1.7671 cm ² . At this time, the loading of the positive electrode was manufactured to be ~3.4mAh/cm ² . A polyethylene separator was interposed between the negative electrode prepared in Examples and Comparative Examples and the positive electrode prepared above, and then an electrolyte solution was injected to prepare a full-cell secondary battery using each negative electrode of Examples and Comparative Examples. The electrolyte solution is a non-aqueous electrolyte solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1:4, vinylene carbonate (VC) is added at 0.5% by weight based on the solvent, and LiPF6 is dissolved at 1M. Use what you ordered. The coin full-cell battery was charged and discharged at a charge range of SOC 0 to SOC 95, with the first cycle at 0.1C, the second cycle at 0.2C, and the third to 30th cycle at 0.5C. Afterwards, the swelling ratio was measured according to Equation 1 below.

[Equation 1]

Swelling ratio (%) = {(t2-t1)/t1} x 100

(The t1 is the thickness of the secondary battery negative electrode before the first charge and discharge cycle, and the t2 is the thickness of the secondary battery negative electrode after the 30th charge and discharge cycle.)

cathode Adhesion of negative electrode active material layer (gF/cm) Swelling ratio(%)@30 ^th cycle(Charge) First negative electrode active material layer
BET specific surface area of natural graphite
( ^m2 /g) Example 1 19 18 2.14 Example 2 22 18 2.12 Example 3 21 17 2.02 Example 4 20 17 2.14 Comparative Example 1 14 21 - Comparative Example 2 15 23 - Comparative Example 3 14 24 3.2 Comparative Example 4 16 21 3.2 Comparative Example 5 16 20 2.14 Comparative Example 6 15 20 - Comparative Example 7 15 21 2.14

As shown in Table 1, it was confirmed that the adhesion of the negative electrode active material layers of Examples 1 to 4 and the cycle expansion performance of the battery were superior to those of the negative electrode active material layers and the cycle expansion performance of the battery of Comparative Examples 1 to 7.

Claims (11)

house collector;
A first negative electrode active material layer provided on the current collector; and
It includes a second negative electrode active material layer provided on the first negative electrode active material layer,
The first negative electrode active material layer includes natural graphite subjected to isostatic pressure treatment,
The second negative electrode active material layer is a negative electrode for a secondary battery comprising artificial graphite in the form of secondary particles and artificial graphite in the form of single particles. The anode for a secondary battery according to claim 1, wherein the natural graphite has a BET specific surface area of 1 m ² /g to 3 m ² /g. The anode for a secondary battery according to claim 1, wherein the natural graphite has an average particle diameter (D50) of 6 ㎛ to 9 ㎛. The anode for a secondary battery according to claim 1, wherein the average particle diameter (D50) of the single particle form of artificial graphite is 6 ㎛ to 9 ㎛. The anode for a secondary battery according to claim 1, wherein the single particle artificial graphite has an OI (004/110) of 35 or less. The anode for a secondary battery according to claim 1, wherein the adhesive force of the first anode active material layer to the current collector is 18 gF/cm or more. The anode for a secondary battery according to claim 1, wherein the second anode active material layer includes 30 to 90 parts by weight of artificial graphite in the form of secondary particles based on 100 parts by weight of the anode active material. The anode for a secondary battery according to claim 1, wherein the second anode active material layer includes 10 to 30 parts by weight of the single particle form of artificial graphite based on 100 parts by weight of the anode active material. house collector;
A first negative electrode active material layer provided on the current collector; and
It includes a second negative electrode active material layer provided on the first negative electrode active material layer,
The first negative electrode active material layer includes natural graphite having a BET specific surface area of 1 m ² /g to 3 m ² /g,
The second negative electrode active material layer is a negative electrode for a secondary battery comprising artificial graphite in the form of secondary particles and artificial graphite in the form of single particles. A secondary battery comprising a cathode, an anode, and a separator according to any one of claims 1 to 9. Forming a first negative electrode active material layer on the current collector;
A method of manufacturing a negative electrode for a secondary battery comprising forming a second negative electrode active material layer on the first negative electrode active material layer,
The first negative electrode active material layer includes isostatically treated natural graphite or natural graphite with a BET specific surface area of 1 m ² /g to 3 m ² /g,
A method of manufacturing a negative electrode for a secondary battery, wherein the second negative electrode active material layer includes artificial graphite in the form of secondary particles and artificial graphite in the form of single particles.