WO2018008955A1 - Negative electrode and secondary battery including same negative electrode - Google Patents

Abstract

The present invention relates to a negative electrode and a secondary battery including the same, comprising: a current collector; a first active material layer, which comprises a first active material particle and is disposed on the current collector; and a first pattern and a second pattern, which are alternately arranged on the first active material layer while being spaced from each other, wherein the first pattern comprises a first pattern active material particle, the second pattern comprises a second pattern active material particle, the first pattern is thicker than the second pattern, and the second pattern has a volume expansion rate larger than that of the first pattern.

Description

Secondary battery comprising a negative electrode and the negative electrode

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0083959, filed July 04, 2016 and Korean Patent Application No. 10-2017-0085056, filed July 04, 2017. All content disclosed in the literature of a patent application is included as part of this specification.

Technical Field

The present invention relates to a negative electrode and a secondary battery including the same, wherein the negative electrode may include a first active material layer, a first pattern, and a second pattern, and the thickness of the first pattern is greater than the thickness of the second pattern. Larger, the volume expansion rate of the second pattern is larger than the volume expansion rate of the first pattern.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and the most actively researched fields are power generation and storage using electrochemical reactions.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing. Recently, as the development and demand of portable devices such as portable computers, portable telephones, and cameras increases, the demand for secondary batteries as a source of energy is rapidly increasing, and these secondary batteries exhibit high energy density and operating potential, and have a cycle life. Many researches have been conducted on this long, low self-discharge rate lithium battery and are commercially available and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, and reciprocates positive and negative electrodes such that lithium ions from the positive electrode active material are inserted into a negative electrode active material such as carbon particles and are detached again when discharged. Since it plays a role of transmitting energy, charging and discharging becomes possible.

On the other hand, the amount of the active material in the negative electrode is one of several factors that determine the charge and discharge capacity of the battery. Thus, in order to fabricate high-capacity electrodes, negative electrode active materials have been loaded at high levels on current collector surfaces. However, in the case of an electrode loaded at a high level of the active material, wetting of the electrolyte solution to the active material layer is reduced, and lithium ions inserted into the active material layer or reacted with the active material are distributed too uniformly. Specifically, while the lithium ion concentration is high in the active material region near the surface of the active material layer directly in contact with the electrolyte, the lithium ion concentration in the active material layer region near the current collector may be too low. As a result, Li precipitates on the surface of the electrode, the capacity of the electrode decreases, and the rapid charge / discharge performance of the battery decreases.

In order to solve the problem, a method of increasing the porosity of the active material layer is used, but in order to realize the same level of capacity as the active material layer having a high porosity, a problem occurs in that the electrode thickness becomes thick.

Therefore, while maintaining a high capacity of the battery, the impregnation of the electrolyte solution can be improved, the distribution of lithium ions in the lubricant layer can be improved, the negative electrode that can improve the charge and discharge performance is required.

One problem to be solved by the present invention is to provide a negative electrode that can improve the impregnation of the electrolyte, while improving the charge and discharge performance of the battery, while maintaining a high capacity of the battery.

Another object of the present invention is to minimize the thickness of the electrode and improve the mechanical stability of the electrode while improving the distribution of lithium ions in the active material layer.

In order to solve the above problems, the present invention is a current collector; A first active material layer including first active material particles and disposed on the current collector; And a first pattern and a second pattern that are alternately spaced apart from each other on the first active material layer, wherein the first pattern includes first pattern active material particles, and the second pattern includes second pattern active material particles. And a thickness of the first pattern is greater than a thickness of the second pattern, and a volume expansion rate of the second pattern is greater than that of the first pattern.

In addition, the present invention provides a secondary battery including the negative electrode.

Since the negative electrode according to the present invention includes a form in which a part of the first active material layer is exposed to the electrolyte and the first pattern and the second pattern are spaced apart from each other, electrolyte wettability may be improved and distribution of lithium ions in the negative electrode may be improved. have. As a result, precipitation of Li on the surface of the cathode can be prevented, and the capacity and rapid charge / discharge performance of the electrode can be improved. In addition, by adjusting the configuration of the first pattern and the second pattern, it is possible to minimize the change in the thickness of the cathode or to improve the mechanical stability of the electrode.

1 is a schematic cross-sectional view of a negative electrode according to an embodiment of the present invention.

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

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

As used herein, the terms "comprise", "comprise" or "have" are intended to indicate that there is a feature, number, step, component, or combination thereof, that is, one or more other features, It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

1, the negative electrode according to an embodiment of the present invention is a current collector; A first active material layer including first active material particles and disposed on the current collector; And a first pattern and a second pattern that are alternately spaced apart from each other on the first active material layer, wherein the first pattern includes first pattern active material particles, and the second pattern includes second pattern active material particles. The thickness of the first pattern may be greater than the thickness of the second pattern, and the volume expansion rate of the second pattern may be greater than the volume expansion rate of the first pattern.

The current collector is conductive without causing chemical change in the secondary battery, and includes, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, on the surface of aluminum or stainless steel. The surface-treated with titanium, silver, etc. can be used.

According to an embodiment of the present invention, the first active material layer may be disposed on the current collector. In addition, the first pattern and the second pattern may be disposed on the first active material layer, respectively. Referring to FIG. 1, the first active material layer 210 may be evenly disposed on the current collector 100 without being spaced apart. The first pattern 220 and the second pattern 230 may be alternately spaced apart from each other on the first active material layer 210. Specifically, an uneven shape may be formed on the first active material layer by the first pattern and the second pattern.

In the case of a conventional negative electrode including a high-loaded active material layer having no uneven shape on the surface, the concentration of lithium ions is significantly reduced toward the current collector surface near the electrode surface, thereby degrading charge and discharge performance and battery capacity. Occurred. According to one embodiment of the present invention, according to the uneven shape formed by the first pattern and the second pattern, the contact area between the negative electrode and the electrolyte may increase, so that the electrolyte impregnation property can be improved, the charge and discharge performance of the battery This can be improved. Furthermore, the first loaded active material layer is exposed between the first pattern and the second pattern, so that the electrolyte can easily penetrate in the direction of the current collector, thereby further improving the electrolyte impregnation property, and the first active material layer, the first pattern, and the first pattern. Non-uniformity of the lithium ion distribution of the two patterns can be reduced.

The thickness of the first pattern may be greater than the thickness of the second pattern. Specifically, the thickness of the first pattern may be 1.1 times to 3 times greater than the thickness of the second pattern, and more specifically 1.2 times to 2 times.

The volume expansion rate of the second pattern may be greater than the volume expansion rate of the first pattern. The volume expansion rate may be calculated from an increase in thickness after one charge / discharge compared to the initial thickness of the first pattern or the second pattern. Specifically, the ratio of the amount of change in thickness increased after the first charge / discharge cycle with respect to the initial electrode thickness. At this time, the first charge-discharge cycle proceeds with CC-CV charging at 0.1C, 0.005V, 0.005C cut off, and discharges at CCC with 0.1C, 1.5V cut off.

More specifically, the volume expansion ratio is calculated by Equation 1 below, where A is the thickness of the first pattern or the second pattern before charging and discharging, and B may be the thickness of the first pattern or the second pattern after charging and discharging. .

[Equation 1]

Volume Expansion Rate = [(B-A) / A] × 100

The thickness can be measured with a micrometer, a mouse, or through a scanning electron microscope.

Even if the second pattern has a relatively large volume expansion ratio, since the thickness of the second pattern is relatively small, it is possible to prevent the thickness of the second pattern from being excessively larger than the thickness of the first pattern during charging and discharging. Therefore, the thickness of the cathode may not be excessively increased, and the first pattern may not be in contact with the neighboring first pattern, or excessive stress may not be applied to the first pattern. Therefore, excessive increase in battery thickness due to electrode expansion during charging can be prevented, and mechanical stability of the electrode can be ensured.

The first active material layer may include first active material particles, the first pattern may include the first pattern active material particles, and the second pattern may include the second pattern active material particles.

The composition of at least one of the first active material particles, the first pattern active material particles, and the second pattern active material particles may be different from the remaining composition.

According to an embodiment of the present invention, the first active material particles and the first pattern active material particles may be artificial graphite, and the second pattern active material particles may be natural graphite. Artificial graphite has a relatively good lithium absorption capacity compared to natural graphite. Therefore, by using artificial graphite as the first active material particles and the first pattern active material particles included in the first active material layer and the first pattern, which occupy most of the components located on the current collector, the charge and discharge characteristics of the battery can be improved. have. On the other hand, natural graphite has a higher lithium bonding amount than artificial graphite. Therefore, the capacity of the battery can be improved by using natural graphite as the second pattern active material particles included in the second pattern located on the electrode surface.

On the other hand, natural graphite has a large volumetric expansion ratio upon discharge relative to artificial graphite. Therefore, in the structure according to the embodiment of the present invention, even if the second pattern has a relatively large volume expansion ratio, since the thickness of the second pattern is relatively small, the thickness of the second pattern during charge and discharge may be It can be prevented from becoming too large than the thickness. Therefore, the thickness of the cathode may not be excessively increased, and the first pattern may not be in contact with the neighboring first pattern, or excessive stress may not be applied to the first pattern. Therefore, excessive increase in battery thickness due to electrode expansion during charging can be prevented, and mechanical stability of the electrode can be ensured. The effect may be further improved by alternately arranging the first pattern and the second pattern.

According to another embodiment of the present invention, similar to the above-described embodiment, the first active material particles are natural graphite, the first pattern active material particles and the second pattern active material particles are artificial graphite, the second pattern There is a difference in that the porosity of is smaller than the porosity of the first pattern.

By using the first active material particles included in the first active material layer, which occupies most of the components disposed on the current collector, as natural graphite, the capacity of the battery may be further improved. In addition, by using artificial graphite as the first pattern active material particles and the second pattern active material particles, the charge and discharge characteristics of the battery can be improved. Furthermore, since both the first pattern and the second pattern located on the surface of the cathode include artificial graphite, the artificial graphite and the electrolyte react primarily. Therefore, the charging performance of the negative electrode can be improved based on the excellent lithium absorption ability of artificial graphite, and at the same time, side reactions on the negative electrode surface due to the deposition of lithium ions can be minimized.

In addition, since the porosity of the second pattern is smaller than the porosity of the first pattern, the energy density may be improved by the second pattern, thereby improving the capacity of the battery. At the same time, since the porosity of the second pattern is smaller than the porosity of the first pattern, the volume expansion rate of the second pattern may be greater than the volume expansion rate of the first pattern. Even if the second pattern has a relatively large volume expansion ratio, since the thickness of the second pattern is relatively small, it is possible to prevent the thickness of the second pattern from being excessively larger than the thickness of the first pattern during charging and discharging. Therefore, the thickness of the cathode may not be excessively increased, and the first pattern may not be in contact with the neighboring first pattern, or excessive stress may not be applied to the first pattern. Therefore, excessive increase in battery thickness due to electrode expansion during charging can be prevented, and mechanical stability of the electrode can be ensured. Specifically, the porosity of the first pattern may be at least 5% greater than the porosity of the second pattern, more specifically, the porosity of the first pattern may be 23% to 35%, and the porosity of the second pattern is 18% to 30 May be%. The porosity can be calculated by the method of Equation 1 below.

[Equation 1]

Porosity = 1- [density of composition with voids / density of composition without voids]

According to another embodiment of the present invention, similar to the above-described embodiment, the first active material particles are artificial graphite, the first pattern active material particles and the second pattern active material particles are natural graphite, the second The difference is that the porosity of the pattern is smaller than the porosity of the first pattern.

By using artificial graphite as the first active material particles included in the first active material layer, which occupies most of the components disposed on the current collector, the charge and discharge characteristics of the battery may be further improved. At the same time, the capacity of the battery may be improved by using natural graphite as the first pattern active material particles included in the first pattern positioned on the electrode surface and the second pattern active material particles included in the second pattern.

In addition, since the porosity of the second pattern is smaller than the porosity of the first pattern, the energy density may be improved by the second pattern, thereby improving the capacity of the battery. At the same time, since the porosity of the second pattern is smaller than the porosity of the first pattern, the volume expansion rate of the second pattern may be greater than the volume expansion rate of the first pattern. Even if the second pattern has a relatively large volume expansion ratio, since the thickness of the second pattern is relatively small, it is possible to prevent the thickness of the second pattern from being excessively larger than the thickness of the first pattern during charging and discharging. Therefore, the thickness of the electrode may not be excessively increased, and the first pattern may not be in contact with the neighboring first pattern, or excessive stress may not be applied to the first pattern. Therefore, excessive increase in battery thickness due to electrode expansion during charging can be prevented, and mechanical stability of the electrode can be ensured. Specifically, the porosity of the first pattern may be at least 5% greater than the porosity of the second pattern, more specifically, the porosity of the first pattern may be 23% to 35%, and the porosity of the second pattern is 18% to 30 May be%. The porosity can be measured in the same manner as described above.

In embodiments of the present invention, the first active material layer, the first pattern, and the second pattern may each include a binder and a conductive material.

The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Various kinds of binder polymers such as sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers in which hydrogen thereof is replaced with Li, Na or Ca, or various copolymers can be used. Can be.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The negative electrode according to the embodiments of the present invention may be prepared by applying a slurry prepared by mixing an electrode mixture including an active material, a conductive material, and a binder to a solvent on a current collector, followed by drying and rolling. Specifically, after the first active material layer is formed on the current collector by the above method, the first pattern and the second pattern may be formed on the first active material layer. The first active material layer, the first pattern, and the second pattern may be used in combination with at least one of screen printing, inkjet, spray, gravure printing, thermal transfer, plate printing, intaglio printing, and offset printing. Can be. The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used.

More specifically, the slurry for forming the first active material layer may be applied, dried, and rolled on the current collector to form the first active material layer. Thereafter, after the pattern mask is disposed on the first active material layer, the second pattern forming slurry may be applied, dried, and rolled to selectively form a second pattern having a specific thickness on a portion of the first active material layer. Thereafter, the pattern mask may be removed, and another pattern mask may be disposed on a part of the first active material layer and the second pattern to form the first pattern. Thereafter, the slurry for forming the first pattern may be applied and dried, and then rolled to form a first pattern having a specific thickness. Thereafter, the pattern mask may be removed. The manufacturing method is not necessarily limited thereto, and in some cases, the first pattern and the second pattern may be formed using an etching process.

The first active material particles, the binder, and the conductive material of the first active material layer may be included in a weight ratio of 94 to 98: 2 to 4: 0.3 to 2, and the first pattern active material particles, the binder and the conductive material in the first pattern may be 94 to 98. 98: 2 to 4: 0.3 to 2 may be included, the second pattern active material particles, the binder and the conductive material in the second pattern may be included in a weight ratio of 94 to 98: 2 to 4: 0.3 to 2.

A secondary battery according to another embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode may be an electrode according to an embodiment of the present invention. .

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

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical change in the battery. For example, the positive electrode current collector is made of stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. Surface treated with nickel, titanium, silver, or the like may be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The cathode active material may be a cathode active material that is commonly used. Specifically, the cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium iron oxides such as LiFe ₃ O ₄ ; Lithium manganese oxides such as Li _{1 + c1} Mn _{2 - c1} O ₄ (0 ≦ _c1 ≦ 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , Cu ₂ V ₂ O _7, and the like; Formula _{LiNi 1 - c2 M c2 O 2} ( where, M is a least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, satisfies 0.01≤c2≤0.3) expressed in Ni-site type lithium nickel oxide; Formula _{LiMn 2 - c3 M c3 O 2} ( where, M is Co, Ni, Fe, Cr, Zn , and is at least one selected from the group consisting of Ta, satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO A lithium manganese composite oxide represented by ₈ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn ₂ O _{4 in} which Li in the formula is substituted with alkaline earth metal ions Although these etc. are mentioned, it is not limited only to these. The anode may be Li-metal.

The cathode active material layer may include a cathode conductive material and a cathode binder together with the cathode active material described above.

In this case, the cathode conductive material is used to impart conductivity to the electrode, and in the battery constituted, the cathode conductive material may be used without particular limitation as long as it has electron conductivity without causing chemical change. Specific examples thereof 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 powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used.

In addition, the positive electrode binder serves to improve adhesion between the positive electrode active material particles and the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used.

The separator separates the negative electrode from the positive electrode and provides a passage for lithium ions, and can be used without particular limitation as long as the separator is used as a separator in a secondary battery. In particular, it has a low resistance to ion migration of the electrolyte and an excellent ability to hydrate the electrolyte. It is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery, but are not limited thereto.

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

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1,2-dime Methoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, pyrion An aprotic organic solvent such as methyl acid or ethyl propionate can be used.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, may be preferably used as high-viscosity organic solvents because they have high dielectric constants to dissociate lithium salts well, such as dimethyl carbonate and diethyl carbonate. When the same low viscosity, low dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having a high electrical conductivity can be made, and thus it can be more preferably used.

The metal salt may be a lithium salt, the lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, is in the lithium salt anion ^{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 ^- can be used at least one member selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate 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 included.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, a medium-large device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system It can be used as a power source.

Hereinafter, preferred embodiments are provided to aid in understanding the present invention, but the above embodiments are merely illustrative of the present disclosure, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present disclosure. It is natural that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

Example  1: Preparation of Battery

(1) Preparation of Cathode

1) Formation of First Active Material Layer

Artificial graphite having an average particle diameter (D ₅₀ ) of 20.4 μm, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) were mixed at a weight ratio of 95.8: 1: 1.7: 1.5 to prepare 5 g of a mixture. It was. 28.9 g of distilled water was added to the mixture to prepare a negative electrode slurry. The negative electrode slurry was applied and dried to a copper current collector having a thickness of 20 μm. At this time, the temperature of the air circulated was 120 ° C. Thereafter, the rolling process was performed to form a first active material layer having a thickness of 50 μm.

2) formation of the second pattern

Natural graphite having an average particle diameter (D ₅₀ ) of the second pattern active material particles of 15 μm, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) in a weight ratio of 95.8: 1: 1.7: 1.5 5 g of the mixture was prepared by mixing. 28.9 g of distilled water was added to the mixture to prepare a negative electrode slurry. On the other hand, after placing a pattern mask on a part of the first active material layer, the negative electrode slurry was applied and dried. At this time, the temperature of the air circulated was 120 ° C. Thereafter, the pattern mask was removed and the rolling process was performed to form a second pattern having a thickness of 20 µm and a porosity of 25%.

3) formation of the first pattern

Artificial graphite having an average particle diameter (D ₅₀ ) of the first pattern active material particles having a particle size of 20 μm, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) in a weight ratio of 95.8: 1: 1.7: 1.5 5 g of the mixture was prepared by mixing. 28.9 g of distilled water was added to the mixture to prepare a negative electrode slurry. On the other hand, after placing a pattern mask on a part of the first active material layer and the second pattern, the negative electrode slurry was applied on the first active material layer, and then dried. At this time, the temperature of the air circulated was 120 ° C. Thereafter, the pattern mask was removed, and the rolling process was performed to form a first pattern having a thickness of 40 μm and a porosity of 25%.

4) drying and punching process

Thereafter, the current collector on which the first active material layer, the first pattern, and the second pattern were formed was dried in a vacuum oven at 130 ° C. for 12 hours, and then punched into a circle of 1.4875 cm ² to prepare a negative electrode.

(2) production of batteries

A battery was manufactured using a lithium metal thin film cut into a round shape of 1.7671 cm ² as a negative electrode, and using the prepared negative electrode as a positive electrode. Specifically, an electrode assembly was prepared by placing a separator of porous polyethylene between the anode and the cathode. Meanwhile, vinylene carbonate (VC) dissolved at 0.5% by weight was dissolved in a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume of 7: 3, and LiPF ₆ was dissolved (1 M concentration). An electrolyte solution was prepared. The electrolyte was injected into the electrode assembly to prepare a lithium coin half cell.

Example  2: manufacture of a battery

(1) Preparation of negative electrode and battery

The average particle size of 1 to the active material particles (D ₅₀₎ is 16㎛ of the natural graphite, the average particle size in the first pattern the active material particles (D ₅₀₎ is 20㎛ of the artificial graphite, the average particle size to the second pattern electrode active material particles (D ₅₀ A negative electrode and a battery were manufactured in the same manner as in Example 1, except that artificial graphite having 15.6 μm was used. At this time, the thickness of the first active material layer was 50 μm. In addition, the thickness of the first pattern was 40 µm and the porosity was 28%. In addition, the thickness of the second pattern was 20 µm and the porosity was 23%.

Example  3: manufacture of battery

(1) Preparation of negative electrode and battery

The average particle size of 1 to the active material particles (D ₅₀₎ is 20.4㎛ of the artificial graphite, the average particle size in the first pattern the active material particles (D ₅₀₎ is 13㎛ of the natural graphite, the average particle size to the second pattern electrode active material particles (D ₅₀ A negative electrode and a battery were manufactured in the same manner as in Example 1, except for using natural graphite having 16 μm). At this time, the thickness of the first active material layer was 50 μm. In addition, the thickness of the first pattern was 40 µm and the porosity was 28%. In addition, the thickness of the second pattern was 20 µm and the porosity was 23%.

Comparative example  1: Preparation of Battery

(1) Preparation of negative electrode and battery

A negative electrode and a battery were manufactured in the same manner as in Example 1, except that the thickness of the first pattern was 20 μm and the thickness of the second pattern was 40 μm.

Comparative example  2: manufacture of a battery

(1) Preparation of negative electrode and battery

A negative electrode and a battery were manufactured in the same manner as in Example 2, except that the thickness of the first pattern was 30 μm and the thickness of the second pattern was 30 μm.

Comparative example  3: manufacture of battery

(1) Preparation of negative electrode and battery

A negative electrode and a battery were manufactured in the same manner as in Example 3, except that the thickness of the first pattern was 20 μm and the thickness of the second pattern was 40 μm.

Experimental Example  1: volume of the first pattern and the first pattern Expansion rate , Electrode thickness change rate and cycle characteristics evaluation

Charge and discharge were performed for the batteries of Examples 1 to 3 and Comparative Examples 1 to 3 to evaluate the volume expansion rate, discharge capacity, initial efficiency, capacity retention rate, and electrode thickness change rate, which are described in Table 1 below.

Meanwhile, one cycle and two cycles were charged and discharged at 0.1C, and charging and discharging were performed at 0.5C from 3 cycles to 49 cycles. The 50 cycles were finished in the state of charging (with lithium in the negative electrode) and the capacity retention rate was evaluated.

Charging Conditions: CC (Constant Current) / CV (Constant Voltage) (5mV / 0.005C current cut-off)

Discharge condition: CC (constant current) condition 1.5 V

Discharge capacity (mAh / g) and initial efficiency (%) were derived through the result at the time of single charge / discharge. Specifically, the initial efficiency (%) was derived by the following calculation.

Initial efficiency (%) = (discharge capacity after 1 discharge / 1 charge capacity) x 100

The capacity retention rate and the electrode thickness change rate were derived by the following calculations, respectively.

Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

% Change in electrode thickness = (final electrode thickness change / initial electrode thickness) × 100

The volume expansion ratio of the first pattern or the second pattern is calculated by Equation 1 below, where A is the thickness of the first pattern or the second pattern before charge and discharge, and B is the thickness of the first pattern or the second pattern after charge and discharge. to be.

[Equation 1]

Volume Expansion Rate = [(B-A) / A] × 100

The thickness was confirmed by micrometer.

battery	Volume expansion rate (%) of the first pattern	% Volume expansion of second pattern	Discharge Capacity (mAh / g)	Initial Efficiency (%)	Capacity retention rate (%)	% Change in electrode thickness
Example 1	4	6	354	92.3	98.1	1.0
Example 2	3	5	364	94.4	95.8	1.5
Example 3	5	7	362	94	96.7	1.2
Comparative Example 1	4	6	354	91	95.0	2.0
Comparative Example 2	4	4.5	358	92	94.3	2.6
Comparative Example 3	5	7	355	90.4	94.6	2.4

Comparing Example 1, Comparative Example 1, Example 2, Comparative Example 2, Example 3 and Comparative Example 3, it can be seen that the electrode thickness change rate of the examples is relatively small, and the discharge capacity and the capacity retention ratio are relatively large. have. This is because the thickness of the second pattern having a relatively large volume expansion ratio is smaller than the thickness of the first pattern, and thus the anode thickness may be less changed when charging and discharging is repeated, and a portion of the first active material layer contacting with the electrolyte may be sufficiently secured. I think it is.

Claims (8)

1. Current collector;

   A first active material layer including first active material particles and disposed on the current collector; And

   It includes a first pattern and a second pattern alternately spaced apart from each other on the first active material layer,

   The first pattern includes the first pattern active material particles,

   The second pattern includes second pattern active material particles,

   The thickness of the first pattern is greater than the thickness of the second pattern,

   The volume expansion rate of the second pattern is greater than the volume expansion rate of the first pattern.
2. The method according to claim 1,

   The first active material particles and the first pattern active material particles are artificial graphite,

   The second pattern active material particles are natural graphite.
3. The method according to claim 1,

   The first active material particles are natural graphite,

   The first pattern active material particles and the second pattern active material particles are artificial graphite,

   The cathode of the second pattern is smaller than the porosity of the first pattern.
4. The method according to claim 3,

   The porosity difference between the porosity of the first pattern and the second pattern is 5% or more.
5. The method according to claim 1,

   The first active material particles are artificial graphite,

   The first pattern active material particles and the second pattern active material particles are natural graphite,

   The cathode of the second pattern is smaller than the porosity of the first pattern.
6. The method according to claim 5,

   The porosity difference between the porosity of the first pattern and the second pattern is 5% or more.
7. The method according to claim 1,

   The thickness of the first pattern is 1.1 to 3 times the thickness of the second pattern.
8. The negative electrode of any one of Claims 1-7;

   anode;

   A separator interposed between the anode and the cathode; And

   Secondary battery comprising an electrolyte.

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