Negative electrode, method for manufacturing negative electrode, secondary battery, and method for manufacturing secondary battery

Abstract

The present invention relates to: a negative electrode comprising a first negative electrode active material and a second negative electrode active material, wherein the first negative electrode active material contains ethylene carbonate; a method for manufacturing the negative electrode; a secondary battery; and a method for manufacturing the secondary battery.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0055339, filed with the Korean Intellectual Property Office on May 8, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a negative electrode, a method of manufacturing the same, a secondary battery related thereto, and a method of manufacturing the secondary battery, wherein the negative electrode has a first negative electrode active material layer and a second negative electrode active material layer, and the first negative electrode active material layer adjacent to the current collector contains ethylene carbonate. Background Art

[0005] In recent years, with the increase in the development of and demand for mobile devices, the demand for secondary batteries as an energy source has rapidly increased. Accordingly, various studies have been conducted on batteries that can meet various requirements. In particular, as a power source for such devices, active research has been conducted on lithium secondary batteries having a high energy density and excellent life and cycle performance.

[0006] A lithium secondary battery refers to a battery including an electrolytic solution containing lithium ions in an electrode assembly, the electrode assembly including a positive electrode containing a positive electrode active material capable of intercalating / deintercalating lithium ions, a negative electrode containing a negative electrode active material capable of intercalating / deintercalating lithium ions, and a microporous separator disposed between the positive electrode and the negative electrode.

[0007] When the electrode assembly is formed, the electrode assembly is placed in a case, and then the electrolytic solution is injected into the case so that the electrode assembly is impregnated with the electrolytic solution. At this time, the electrolytic solution wets the negative electrode, thereby increasing the lithium ion mobility in the negative electrode.

[0008] However, when the loading amount of the negative electrode active material layer in the negative electrode is set high to increase the energy density of the negative electrode, it is difficult for the electrolytic solution to easily move into the negative electrode, resulting in a significant decrease in the electrolytic solution wettability of the negative electrode. When the electrolytic solution wettability decreases, an SEI layer cannot be uniformly formed on the surface of the negative electrode, resulting in non-uniform negative electrode performance and deteriorating the life and stability of the secondary battery. In addition, the low electrolytic solution wettability reduces the efficiency of the manufacturing process.

[0009] Generally, the negative electrode active material layer is formed into two layers to improve the electrolytic solution wettability. However, only by this method, there are limitations in improving the electrolytic solution wettability of the negative electrode active material layer adjacent to the current collector.

[0010] Therefore, in the present specification, a negative electrode capable of significantly improving the wettability of an electrolyte, a method for manufacturing the negative electrode, a secondary battery, and a method for manufacturing the secondary battery will be described. Summary of the Invention

[0011] Technical problem

[0012] One aspect of the present invention provides a negative electrode capable of improving the wettability of an electrolyte and a method for manufacturing the same.

[0013] Another aspect of the present invention provides a secondary battery with improved electrolyte wettability and a method for manufacturing the same.

[0014] Technical solution

[0015] According to an embodiment of the present invention, there is provided a negative electrode including a current collector and a negative electrode active material layer, the negative electrode active material layer having a first negative electrode active material layer disposed on the negative electrode current collector and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the first negative electrode active material layer contains ethylene carbonate.

[0016] According to another embodiment of the present invention, there is provided a method for manufacturing a negative electrode, the method including forming a first negative electrode active material layer on a negative electrode current collector by a first negative electrode slurry containing ethylene carbonate, and forming a second negative electrode active material layer by a second negative electrode slurry, wherein the second negative electrode active material layer is disposed on the first negative electrode active material layer.

[0017] According to another embodiment of the present invention, there is provided a secondary battery including a negative electrode, a positive electrode, a separator, and an electrolyte, wherein the negative electrode includes a negative electrode current collector, a first negative electrode active material layer disposed on the negative electrode current collector, and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the first negative electrode active material layer contains ethylene carbonate.

[0018] According to another embodiment of the present invention, there is provided a method for manufacturing a secondary battery, the method including manufacturing an electrode assembly having the negative electrode, positive electrode, and separator of the above embodiments, and impregnating the electrode assembly in an electrolyte.

[0019] Advantageous effects

[0020] The negative electrode according to the present invention includes a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer adjacent to the current collector contains ethylene carbonate. Therefore, when the electrolyte penetrates into the negative electrode in the secondary battery, the ethylene carbonate becomes a liquid phase, and the ethylene carbonate that has become a liquid phase also turns the surrounding adjacent ethylene carbonate into a liquid phase. Due to the continuous change of ethylene carbonate, a wetting path that allows the electrolyte to easily penetrate into the negative electrode can be formed, significantly improving the wettability of the electrolyte. In addition, the ionic conductivity of ethylene carbonate is high, which can increase the mobility of lithium ions in the negative electrode and uniformly form a SEI layer on the surface of the negative electrode. Description of the Drawings

[0021] Figure 1 is a schematic diagram of a negative electrode according to an embodiment of the present invention. Detailed Description

[0022] It should be understood that the words or terms used in the description and claims of the present invention should not be construed as being limited to the meanings defined in a common dictionary. It should be further understood that based on the principle that the inventor can appropriately define the meanings of the words or terms to best explain the present invention, the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant field and technical concept of the present invention.

[0023] The terms used herein are for the purpose of describing specific exemplary embodiments only and are not intended to limit the present invention. Unless otherwise clearly specified in the context, the singular forms of the terms may include the plural forms.

[0024] It should be further understood that when the terms "comprising", "including" or "having" are used in this specification, they indicate the presence of the stated features, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0025] In this specification, unless otherwise noted, "%" refers to weight %.

[0026] In this specification, the "specific surface area" is measured by the BET method. Specifically, Belsorp-mini II of BEL Japan Co., Ltd. can be used to calculate from the nitrogen adsorption amount at liquid nitrogen temperature (77K).

[0027] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% cumulative volume in the particle size distribution curve of the particles. The average particle size (D 50 ) can be measured by, for example, the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters, thereby obtaining highly reproducible and high-resolution results.

[0028] In this specification, the porosity can be determined by the following method. The manufactured secondary battery is disassembled and taken apart, and then ion milling is performed on the negative electrode to determine the cross-sectional thickness of each of the first negative electrode active material layer and the second negative electrode active material layer using SEM, and the bulk volume of each of the first negative electrode active material layer and the second negative electrode active material layer is derived from the thickness. After that, the second negative electrode active material layer is scraped off and removed to measure the weight of the first negative electrode active material layer and the weight of the second negative electrode active material layer, and then their respective loadings (mass / area) are calculated. After that, the weight of each layer is divided by the density of the negative electrode active material of each layer to obtain the true volume. After that, the porosity of each layer is calculated by [(bulk volume - true volume) / bulk volume]×100.

[0029] Hereinafter, the present invention will be described in detail.

[0030] 1. Negative electrode

[0031] The negative electrode according to one embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer has a first negative electrode active material layer disposed on the negative electrode current collector and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the first negative electrode active material layer may contain ethylene carbonate.

[0032] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the negative electrode current collector. Specifically, transition metals with good carbon adsorption such as copper and nickel can be used as the negative electrode current collector.

[0033] The negative electrode may include a negative electrode active material layer. The negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector. The loading of the negative electrode active material layer may be 50 mg / 25 m 2 to 600 mg / 25 m 2 , specifically 400 mg / 25 cm 2 to 600 mg / 25 cm 2 . The above loading is higher than that of a typical negative electrode active material layer.

[0034] Refer to Figure 1, the negative electrode active material layer may include a first negative electrode active material layer 210 and a second negative electrode active material layer 220. The first negative electrode active material layer 210 may be disposed on the negative electrode current collector 100, specifically, may be in contact with the negative electrode current collector 100. The second negative electrode active material layer 220 may be disposed on the first negative electrode active material layer 210, and the first negative electrode active material layer 210 may be disposed between the second negative electrode active material layer 220 and the negative electrode current collector 100. Since the first negative electrode active material layer 210 and the second negative electrode active material layer 220 are formed from slurries prepared separately, an interface may exist between the first negative electrode active material layer 210 and the second negative electrode active material layer 220.

[0035] Each of the first negative electrode active material layer and the second negative electrode active material layer may include a negative electrode active material. The negative electrode active material may be a commonly used negative electrode active material in the art, and its type is not particularly limited. The negative electrode active material of the first negative electrode active material layer and the negative electrode active material of the second negative electrode active material layer may be the same or different.

[0036] The negative electrode active material may be at least one of a carbon-based active material and a silicon-based active material. As carbon-based active material particles, one or more selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesophase carbon microspheres may be used. In particular, when artificial graphite is used, the rate performance can be improved. As the silicon-based active material, one or more selected from the group consisting of SiO X (0 ≤ X <2), Si-C composite materials, and Si-Y alloys (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, and combinations thereof) may be used.

[0037] Each of the first negative electrode active material layer and the second negative electrode active material layer may further include a binder. The binder of the first negative electrode active material layer and the binder of the second negative electrode active material layer may be the same or different. The binder is used to ensure the adhesion force between the negative electrode active materials or between the negative electrode active material and the current collector. Any binder commonly used in the art may be used, and its type is not particularly limited.

[0038] The binder may be, for example, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, carboxymethyl cellulose (CMC), styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used.

[0039] Each of the first negative electrode active material layer and the second negative electrode active material layer may further contain a conductive material. The conductive material may be a conductive material commonly used in the art, and there is no particular limitation on its type. The conductive materials of the first negative electrode active material layer and the second negative electrode active material layer may be the same or different.

[0040] There is no particular limitation on the conductive material as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxides; conductive materials such as polyphenylene derivatives, etc.

[0041] The loading amount of the first negative electrode active material layer may be 50 mg / 25 cm 2 to 400 mg / 25 cm 2 specifically 100 mg / 25 cm 2 to 300 mg / 25 cm 2 more specifically 150 mg / 25 cm 2 to 250 mg / 25 cm 2 . The above loading amount is similar to that of a typical negative electrode active material. When the second negative electrode active material layer is added, a negative electrode active material layer with a loading amount higher than that of a typical negative electrode active material is formed. In the present invention, since the first negative electrode active material layer contains ethylene carbonate, the problem of reduced electrolyte wettability is solved, so that the overall loading amount of the negative electrode active material can be high.

[0042] The first negative electrode active material layer may contain ethylene carbonate. Ethylene carbonate is in a solid phase at room temperature, making it advantageous to include it in the first negative electrode active material layer. In addition, when the negative electrode is immersed in the electrolyte, the solid-phase ethylene carbonate turns into a liquid phase. The liquid-phase ethylene carbonate serves as an electrolyte wetting path and forms pores in the first negative electrode active material layer, thereby significantly improving the electrolyte wettability of the negative electrode. Additionally, ethylene carbonate has a high ionic conductivity, which can increase the mobility of lithium ions in the negative electrode and can uniformly form a SEI layer on the surface of the negative electrode. This results in an improvement in the lifespan and stability of the secondary battery.

[0043] The content of the ethylene carbonate in the first negative electrode active material layer may be 0.5 wt% to 15 wt%, specifically 2 wt% to 10 wt%, and more specifically 3 wt% to 6 wt%. When the above range is satisfied, the effect of improving electrolyte wettability can be maximized.

[0044] The second negative electrode active material layer may not contain ethylene carbonate. In this case, the ratio of the negative electrode active material in the second negative electrode active material layer can be increased, and the thickness of the second negative electrode active material layer can be reduced, thereby improving the energy density.

[0045] 2. Method for manufacturing a negative electrode

[0046] A method for manufacturing a negative electrode according to another embodiment of the present invention includes forming a first negative electrode active material layer on a negative electrode current collector through a first negative electrode paste containing ethylene carbonate, and forming a second negative electrode active material layer through a second negative electrode paste, where the second negative electrode active material layer may be disposed on the first negative electrode active material layer. The correspondingly manufactured negative electrode may be the same as the negative electrode described above. The ethylene carbonate, the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer are the same as those described in the above embodiments regarding the negative electrode, and thus the description thereof will be omitted.

[0047] Each of the first negative electrode paste and the second negative electrode paste may contain a negative electrode active material and a solvent. Additionally, each of the first negative electrode paste and the second negative electrode paste may further contain a binder and a conductive material. The negative electrode active material, the binder, and the conductive material are the same as those described in the above embodiments, and thus the description thereof will be omitted.

[0048] The solvent may be, for example, water; amide-based polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexanediol; polyols such as glycerol, trimethylolpropane, pentaerythritol, and sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyrolactone, and ε-propiolactone. Any one of them and mixtures of two or more thereof can be used.

[0049] The first negative electrode paste may contain ethylene carbonate. The first negative electrode paste may be formed by mixing and stirring a negative electrode active material and ethylene carbonate in a solvent. In some cases, based on the negative electrode active material and the ethylene carbonate, a binder and / or a conductive material may also be mixed and stirred. On the other hand, the second negative electrode paste may not contain ethylene carbonate. Specifically, the second negative electrode paste may be formed by mixing and stirring the negative electrode active material in a solvent. In some cases, based on the negative electrode active material, a binder and / or a conductive material may also be mixed and stirred.

[0050] When preparing the first negative electrode paste, ethylene carbonate is contained in the first negative electrode paste, and the ethylene carbonate may be in a solid phase. Since ethylene carbonate is contained in the first negative electrode paste in a solid phase rather than a liquid phase, the process can be simplified. Specifically, when ethylene carbonate is in a liquid phase, it is difficult to weigh ethylene carbonate and prepare the paste. Therefore, it is preferable to use ethylene carbonate present in a solid phase when preparing the paste.

[0051] The content of ethylene carbonate in the solid component of the first negative electrode paste may be 0.5% by weight to 15% by weight, specifically 2% by weight to 10% by weight, and more specifically 3% by weight to 6% by weight. When the above range is satisfied, the effect of improving the wettability of the electrolyte can be maximized.

[0052] The first negative electrode active material layer and the second negative electrode active material layer may be manufactured by the following method, but are not limited thereto.

[0053] As a first method, the first negative electrode paste may be applied onto the negative electrode current collector and dried to form the first negative electrode active material layer, and then the second negative electrode paste may be applied onto the first negative electrode active material layer and dried to form the second negative electrode active material layer. The rolling process may be carried out immediately after the drying of the first negative electrode paste and immediately after the drying of the second negative electrode paste, or the rolling process may be carried out only after the drying of the second negative electrode paste.

[0054] As a second method, the first negative electrode paste and the second negative electrode paste may be sequentially applied onto the negative electrode current collector, dried, and then rolled to form the first negative electrode active material layer and the second negative electrode active material layer.

[0055] 3. Secondary battery

[0056] A secondary battery according to another embodiment of the present invention includes a negative electrode and an electrolyte, wherein the negative electrode may include a negative electrode current collector, a first negative electrode active material layer disposed on the negative electrode current collector, and a second negative electrode active material layer disposed on the first negative electrode active material layer, and wherein the first negative electrode active material layer may include ethylene carbonate. The negative electrode current collector and the second negative electrode active material layer are the same as the current collector and the second negative electrode active material layer of the negative electrode in the above embodiment regarding the negative electrode, and thus the description thereof will be omitted.

[0057] Similar to the negative electrode of the above embodiment, the negative electrode includes a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer. However, different from the negative electrode of the above embodiment, the difference lies in that the ethylene carbonate contained in the first negative electrode active material layer is in a liquid phase.

[0058] Before the negative electrode is immersed in the electrolyte, the ethylene carbonate contained in the negative electrode is in a solid phase. When manufacturing the secondary battery, when the negative electrode is immersed in the electrolyte, the ethylene carbonate is dissolved by the electrolyte and becomes a liquid phase. The liquid-phase ethylene carbonate dissolves the adjacent solid-phase ethylene carbonate, and such a reaction chain occurs. Eventually, the ethylene carbonate contained in the negative electrode inside the manufactured secondary battery exists in a liquid phase. Accordingly, the liquid-phase ethylene carbonate serves as an electrolyte wetting path and forms pores in the first negative electrode active material layer, thereby significantly improving the electrolyte wettability of the negative electrode. In addition, ethylene carbonate has a high ionic conductivity, so that the lithium ion mobility in the negative electrode can be improved, and an SEI layer can be uniformly formed on the surface of the negative electrode. This results in an improvement in the life and stability of the secondary battery.

[0059] Both the first negative electrode active material layer and the second negative electrode active material layer contain pores. The porosity of the first negative electrode active material layer can be 1% to 5% higher than that of the second negative electrode active material layer, specifically 2% to 3%. The pores may contain an electrolyte or the liquid-phase ethylene carbonate inside. When forming the first negative electrode active material, there is solid-phase ethylene carbonate, and since a large number of pores are generated in the first negative electrode active material layer when the ethylene carbonate becomes liquid-phase, there may be a difference in porosity.

[0060] The positive electrode may include a positive electrode active material. The positive electrode active material may be a positive electrode active material commonly used in the art. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO 2 ) and lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; lithium iron oxide, such as LiFe 3 O 4 ; lithium manganese oxide represented by the formula Li 1+ c1 Mn 2-c1 O 4 (0≤c1≤0.33), LiMnO 3 , LiMn 2 O 3 , or LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 O 8 , V 2 O 5 and Cu 2 V 2 O 7 ; Ni-site type lithium nickel oxide represented by the formula LiNi 1-c2 M c2 O 2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≤y2≤0.3); lithium manganese composite oxide represented by the formula LiMn 2-c3 M c3 O 2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, 0.01≤c3≤0.1) or the formula Li 2 Mn 3 MO 8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn 2 O 4, where a part of Li in the formula is replaced by alkaline earth metal ions, etc.; but not limited thereto. The positive electrode may be Li metal.

[0061] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used without particular limitation as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having a high moisture-holding capacity for the electrolyte and a low resistance to the movement of electrolyte ions is preferred. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof. A typical porous nonwoven fabric can also be used, for example, a nonwoven fabric formed of high melting point glass fibers, polyethylene terephthalate fibers, etc. A coated separator containing a ceramic component or a polymer material can also be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0062] The electrolyte may contain a non-aqueous organic solvent and a lithium salt.

[0063] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate can be used.

[0064] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be preferably used because it is a high-viscosity organic solvent and has a high dielectric constant to dissociate lithium salts well. When such a cyclic carbonate is mixed with a linear carbonate having a low viscosity and a low dielectric constant such as dimethyl carbonate and diethyl carbonate at an appropriate ratio, an electrolyte having a high conductivity can be prepared, and thus such a combination is more preferably used.

[0065] More preferably, the organic solvent may contain ethylene carbonate. When the electrolyte contains ethylene carbonate, the phenomenon that ethylene carbonate present in the first negative electrode active material layer diffuses excessively into the electrolyte due to the concentration difference can be suppressed, which can increase the residual amount of ethylene carbonate in the first negative electrode active material layer, thereby further improving the above effects.

[0066] As the metal salt, a lithium salt can be used. The lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, as the anion of the lithium salt, one or more selected from the group consisting of the following can be used: 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 (CF2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - 、and (CF 3 CF 2 SO 2 ) 2 N - 。

[0067] In the electrolyte, in order to improve the life performance of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, on the basis of the above electrolyte components, one or more additives may be further included. For example, a haloalkyl carbonate compound such as difluoroethyl carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, diglyme, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidone, N,N-substituted imidazoline, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc.

[0068] 4. Method for manufacturing a secondary battery

[0069] A method for manufacturing a secondary battery according to another embodiment of the present invention may include: manufacturing an electrode assembly having a negative electrode, a positive electrode, and a separator, and immersing the electrode assembly in an electrolyte. The negative electrode is the same as the negative electrode in the above embodiment regarding the negative electrode. In addition, the positive electrode, the separator, and the electrolyte are the same as the positive electrode, separator, and electrolyte in the above embodiment regarding the secondary battery, and thus the description thereof will be omitted.

[0070] In the electrode assembly, the separator is disposed between the negative electrode and the positive electrode and serves to electrically disconnect the negative electrode and the positive electrode. Even when a plurality of negative electrodes and positive electrodes are provided, the negative electrode and the positive electrode are alternately stacked and insulated from each other with the separator disposed therebetween.

[0071] When the electrode assembly is manufactured, the electrode assembly is placed in a case, and then the electrolyte is injected so that the electrode assembly is immersed in the electrolyte. As a result, the solid-phase ethylene carbonate contained in the negative electrode becomes a liquid phase. The liquid-phase ethylene carbonate and the pores formed when the solid-phase ethylene carbonate becomes a liquid phase make it easier for the electrolyte to penetrate into the negative electrode.

[0072] The electrolyte is the same as the electrolyte in the above embodiment. Specifically, the electrolyte contains an organic solvent, and the organic solvent may contain ethylene carbonate.

[0073] According to still another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The secondary battery included in the battery module and the battery pack has high capacity, high rate performance, and cycle performance, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0074] Hereinafter, the present invention will be described in more detail with reference to specific embodiments.

[0075] Examples and comparative examples

[0076] Example 1. Fabrication of negative electrode and secondary battery

[0077] (1) Fabrication of negative electrode

[0078] Artificial graphite as a negative electrode active material, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders, Super P as a conductive material, and solid-phase ethylene carbonate are mixed and stirred in water as a solvent to prepare a first negative electrode slurry. In the first negative electrode slurry, the weight ratio of the negative electrode active material, the binder, the conductive material, and the ethylene carbonate is 91:4:1:4.

[0079] On the other hand, artificial graphite as a negative electrode active material, CMC and SBR as binders, and Super P as a conductive material are mixed and stirred in water as a solvent to prepare a second negative electrode slurry. In the second negative electrode slurry, the weight ratio of the negative electrode active material, the binder, and the conductive material is 95:4:1.

[0080] The first negative electrode slurry is applied to both sides of a copper current collector having a thickness of 8 μm and dried. At this time, the temperature of the circulating air is 80°C to 110°C. Thereafter, the second negative electrode slurry is applied to the first negative electrode slurry and dried. At this time, the temperature of the circulating air is 80°C to 110°C.

[0081] Thereafter, the copper current collector on which the first negative electrode slurry and the second negative electrode slurry in a dry state are present is roll-pressed, and then dried in a vacuum oven at 60°C for 24 hours to fabricate a negative electrode.

[0082] In the negative electrode, the loading amount of the first negative electrode active material layer is 200 mg / 25 cm 2 , and the ethylene carbonate is contained in the first negative electrode active material layer at 4 wt%. The loading amount of the second negative electrode active material layer is about 250 mg / 25 cm2 to 300 mg / 25 cm 2 , so the loading amount of the entire negative electrode active material layer is 450 mg / 25 cm 2 to 500 mg / 25 cm 2 .

[0083] (2) Fabrication of secondary battery

[0084] Mix Li[Ni 0.8 Co 0.1 Mn 0.1 O 2 , carbon black and PVDF in a non-aqueous solvent to prepare a positive electrode paste, and then apply the positive electrode paste on both sides of a current collector, dry, and then roll-press to form a positive electrode including a positive electrode active material layer. In the positive electrode active material layer, the contained Li[Ni 0.8 Co 0.1 Mn 0.1 O 2 is 95 wt%, carbon black (conductive material) is 2.5 wt%, and PVDF is 2.5 wt%.

[0085] Use porous polyethylene coated with PVDF as the separator.

[0086] Place the positive electrode on one side of the separator, and place the negative electrode on the other side, and then laminate to form an electrode assembly. At this time, roll-laminate the electrode assembly under the conditions of 80 °C and 5 kgf / cm.

[0087] The electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) with a concentration of 1.0 M in an organic solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3:7.

[0088] Accommodate the fabricated electrode assembly in a pouch-type battery case, and inject the electrolyte therein to fabricate a secondary battery.

[0089] In the secondary battery, the porosity of the first negative electrode active material layer is 30%, and the porosity of the second negative electrode active material layer is 28%. In addition, the ethylene carbonate exists in the liquid phase in the negative electrode.

[0090] Example 2: Fabrication of negative electrode and secondary battery

[0091] Fabricate the negative electrode and secondary battery in the same manner as in Example 1, except that the content of ethylene carbonate introduced into the first negative electrode paste is adjusted so that the first negative electrode active material layer contains 6 wt% of ethylene carbonate.

[0092] Example 3: Manufacture of negative electrode and secondary battery

[0093] The negative electrode and the secondary battery were manufactured in the same manner as in Example 1, except that the content of ethylene carbonate introduced into the first negative electrode paste was adjusted so that the first negative electrode active material layer contained 2% by weight of ethylene carbonate.

[0094] Comparative Example 1: Manufacture of negative electrode and secondary battery

[0095] The negative electrode and the secondary battery were manufactured in the same manner as in Example 1, except that ethylene carbonate was not introduced when preparing the first negative electrode paste.

[0096] Experimental example 1: Evaluation of the life performance (capacity retention rate) and resistance of a secondary battery

[0097] For the secondary batteries of each example and comparative example, the charging range was set to SOC 0% to SOC 95% (2.5V to 4.2V), and then for the first cycle, charging and discharging were performed at a current rate of 0.2C to measure the discharge capacity of the battery. For the second cycle, charging was performed at a current rate of 0.5C to SOC 50%, and then discharging was performed at 2.5C for 10 seconds. From the 3rd to the 100th cycle, charging and discharging were performed at a current rate of 0.5C, and then the capacity retention rate of the battery was determined. Based on the discharge capacity of the third cycle being 100%, the capacity retention rate was evaluated by the discharge capacity of the 100th cycle. The results are shown in Table 1. In addition, the resistance was calculated by dividing the voltage drop that occurred after the 100th cycle by the applied current (DCIR measurement method), and the results are shown in Table 1.

[0098] Capacity retention rate = (Discharge capacity after the 100th cycle / Discharge capacity after the 3rd cycle) × 100

[0099] [Table 1]

[0100] Capacity retention rate (%) Resistance (Ω) Example 1 93.7 5.2 Example 2 93.4 4.9 Example 3 92.4 6.5 Comparative example 1 89.1 8.9

[0101] Symbol description

[0102] 100: Current collector

[0103] 210: First negative electrode active material layer

[0104] 220: Second negative electrode active material layer

Claims

1. A negative electrode for a secondary battery containing an electrolyte, the negative electrode comprising: A negative electrode current collector; and A negative electrode active material layer, the negative electrode active material layer comprising a first negative electrode active material layer disposed on the negative electrode current collector and a second negative electrode active material layer disposed on the first negative electrode active material layer, Wherein the first negative electrode active material layer contains ethylene carbonate, and when the negative electrode is immersed in the electrolyte, the solid-phase ethylene carbonate becomes a liquid phase.

2. The negative electrode according to claim 1, wherein the content of ethylene carbonate in the first negative electrode active material layer is 0.5 wt% to 15 wt%.

3. The negative electrode according to claim 1, wherein the content of ethylene carbonate in the first negative electrode active material layer is 3 wt% to 6 wt%.

4. The negative electrode according to claim 1, wherein the loading amount of the first negative electrode active material layer is 50 mg / 25 m 2 to 400 mg / 25 m 2 .

5. The negative electrode according to claim 1, wherein the loading amount of the negative electrode active material layer is 50 mg / 25 m 2 to 600 mg / 25 m 2 .

6. A method of manufacturing the negative electrode according to any one of claims 1-5, the method Comprising: Forming a first negative electrode active material layer on a negative electrode current collector by a first negative electrode paste containing ethylene carbonate; And Forming a second negative electrode active material layer by a second negative electrode paste, Wherein the second negative electrode active material layer is disposed on the first negative electrode active material layer.

7. The method according to claim 6, wherein the content of ethylene carbonate in the solid component of the first negative electrode paste is 0.5 wt% to 15 wt%.

8. The method according to claim 6, wherein the ethylene carbonate is in a solid phase.

9. A secondary battery, the secondary battery comprising: The negative electrode according to any one of claims 1-5; a positive electrode; a separator; and an electrolyte, Wherein the negative electrode comprises: A negative electrode current collector; A first negative electrode active material layer disposed on the negative electrode current collector; and A second negative electrode active material layer disposed on the first negative electrode active material layer, Wherein the first negative electrode active material layer contains ethylene carbonate.

10. The secondary battery according to claim 9, wherein the first negative electrode active material layer contains pores, and the porosity of the first negative electrode active material layer is 1% to 5% higher than the porosity of the second negative electrode active material layer.

11. The secondary battery according to claim 9, wherein the ethylene carbonate is in a liquid phase.

12. The secondary battery according to claim 9, wherein the electrolyte contains an organic solvent, and the organic solvent contains ethylene carbonate.

13. A method of manufacturing a secondary battery, the method Comprising: Manufacturing an electrode assembly, the electrode assembly comprising the negative electrode, positive electrode and separator according to claim 1; And Immersing the electrode assembly in an electrolyte.

14. The method according to claim 13, wherein the electrolyte contains an organic solvent, and the organic solvent contains ethylene carbonate.

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