Negative electrode composition, method for producing the same, negative electrode slurry, negative electrode, and lithium secondary battery

Abstract

This application relates to a negative electrode composition containing a silicon-based active material, a conductive material, a binder, and a pH adjuster, having a pH of 5 or more and 7 or less, a negative electrode slurry containing the same, a negative electrode, a lithium secondary battery, and a method for manufacturing the negative electrode composition. The negative electrode composition provides the advantage of achieving excellent adhesion by adjusting the pH of the entire negative electrode composition, and also provides the advantage of solving the problems of the silicon-based active material.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0184166, filed with the Korean Intellectual Property Office on December 26, 2022, and Korean Patent Application No. 10-2023-0189478, filed with the Korean Intellectual Property Office on December 22, 2023, and all of its content is incorporated herein by reference.

[0002] This application relates to a negative electrode composition, a method for manufacturing the same, a negative electrode slurry, a negative electrode, and a lithium secondary battery.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the fields of power generation and energy storage using electrochemical reactions are among the most actively studied areas.

[0004] Currently, secondary batteries are representative examples of electrochemical devices using such electrochemical energy, and their usage areas are increasingly expanding.

[0005] As technology development and demand related to mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and as the negative electrode active material, silicon-based particles with a large discharge capacity can be used.

[0007] In particular, with the recent demand for high-density energy batteries, research has been actively conducted on methods to increase the capacity by using both Si / C and SiOx, which are silicon-based compounds with a capacity more than 10 times greater than that of graphite-based materials, as the negative electrode active material. In the case of silicon-based compounds, which are high-capacity materials, they offer the advantage of having a larger capacity compared to conventionally used graphite. However, hydrogen gas can be generated by surface oxidation reactions during the production and storage of silicon-based compound-containing electrode compositions or slurries, which poses problems such as explosion hazards and a decrease in phase stability.

[0008] Although various methods have been discussed to solve the above problems, there are limitations in their application because they can conversely reduce the performance of the battery. Therefore, there are still limitations in the commercialization of negative electrodes containing silicon-based compounds.

[0009] Therefore, additional research is needed on negative electrode compositions that contain silicon-based compounds and can reduce the generation of hydrogen gas from the silicon-based compounds in order to improve the above-mentioned problems.

Summary of the Invention

Problems to be Solved by the Invention

[0010] The purpose of this application is to provide a negative electrode composition, a method for manufacturing the same, a negative electrode slurry, a negative electrode, and a lithium secondary battery in which the hydrogen ion concentration (pH) is adjusted by a pH regulator in order to solve the above problems.

Means for Solving the Problems

[0011] One embodiment of this specification provides a negative electrode composition containing a silicon-based active material, a conductive material, a binder, and a pH regulator, with a pH of 5 or more and 7 or less when measured at 25°C.

[0012] In another embodiment, a negative electrode slurry containing the negative electrode composition and a solvent is provided.

[0013] In another embodiment, a negative electrode is provided that includes a negative electrode current collector layer; and a negative electrode active material layer in which the negative electrode slurry is applied to one or both surfaces of the negative electrode current collector layer.

[0014] Finally, a lithium secondary battery is provided that includes a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either one of the first electrode or the second electrode is the negative electrode.

Advantages of the Invention

[0015] The negative electrode composition according to one embodiment of the present invention provides the effect of preventing the generation of hydrogen gas due to a surface oxidation reaction during the production or storage of the negative electrode composition and the negative electrode slurry containing the same by adjusting the hydrogen ion concentration (pH) of the entire negative electrode composition. Thereby, the phase stability of the negative electrode composition and the negative electrode slurry containing the same can be improved, and the explosion risk due to the generation of hydrogen gas can be reduced.

[0016] By using the negative electrode composition according to another embodiment of the present invention, it is possible to ensure the process safety and stability for future negative electrodes and lithium secondary batteries containing the same.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] Before explaining the present invention, first, several terms will be defined.

[0019] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise specified to the contrary, it does not exclude other components, but may further include other components.

[0020] In this specification, "p to q" means a range of "p or more and q or less".

[0021] In this specification, when a polymer includes a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer includes a monomer, this is interpreted in the same way as the polymer including the monomer as a monomer unit.

[0022] In this specification, unless otherwise specified as "homopolymer", the term "polymer" is understood to be used in a broad sense including copolymers.

[0023] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC) using various degrees of polymerization of monodisperse polystyrene polymers (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, unless otherwise specified, the molecular weight means the weight-average molecular weight.

[0024] Hereinafter, with reference to the drawings, a detailed description will be given so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention may be realized in various different forms and is not limited to the following description.

[0025] <Negative electrode composition> One embodiment of this specification is characterized by a negative electrode composition in which the negative electrode active material includes a silicon-based active material and a pH regulator is included to control the pH to 5 or more and 7 or less.

[0026] The negative electrode composition according to the above-described embodiment can prevent the generation of hydrogen gas from the negative electrode active material by adjusting the pH of the entire negative electrode composition with a pH adjuster, and can improve stability when used in the negative electrode in the future.

[0027] Specifically, the negative electrode composition can prevent oxidation of the negative electrode active material (particularly, silicon particles) in the negative electrode composition by controlling the overall pH in the range of 5 or more and 7 or less with a pH adjuster.

[0028] In one embodiment of the present specification, the pH adjuster may include one or more selected from the group consisting of fumaric acid, glutaric acid, oxalic acid, malonic acid, succinic acid, maleic acid, palmitic acid, tartaric acid, formic acid, acetic acid, glycolic acid, sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, sulfonic acid, aminosulfonic acid, lithium hydroxide, and sodium hydroxide, but is not limited thereto as long as the desired range of hydrogen ion concentration can be easily achieved.

[0029] In one embodiment of the present specification, the pH adjuster may be used alone or in combination of two or more different substances.

[0030] In one embodiment of the present specification, the negative electrode active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0031] In another embodiment of the present specification, the negative electrode active material may be contained in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0032] In one embodiment of the present specification, the negative electrode active material may include one or more selected from the group consisting of silicon-based active materials and carbon-based active materials.

[0033] In one embodiment of the present specification, the negative electrode active material may consist of a silicon-based active material and a carbon-based active material.

[0034] In this specification, the silicon-based active material has a capacity 10 times or more higher than that of the carbon-based active material. Thus, when the silicon-based active material is applied to the negative electrode, it is possible to realize a negative electrode having a high level of energy density even with a thin thickness as compared with the case where the carbon-based active material is used alone.

[0035] In another embodiment of this specification, when the negative electrode active material is composed of a silicon-based active material and a carbon-based active material, the composition ratio of the silicon-based active material to the carbon-based active material may be in the range of 2:98 to 30:70.

[0036] The negative electrode active material according to the above-described embodiment has a carbon-based active material as a main component, and can further provide an effect of less volume expansion of the active material during charge and discharge, less swelling, and excellent conductive connectivity of the negative electrode.

[0037] In one embodiment of this specification, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may include 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0038] In one embodiment of this application, the silicon-based active material may use only pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean including pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range when based on 100 parts by weight of the total silicon-based active material as described above.

[0039] In another embodiment, the silicon-based active material may include 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, or may include 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0040] In this specification, the negative electrode composition containing the silicon-based active material within the above-described content range is significant in that, despite the large amount of the silicon-based active material, the amount of hydrogen gas generated from the silicon-based active material is remarkably small by adjusting the pH of the negative electrode composition with a pH adjuster.

[0041] In other embodiments of this specification, both the conductive material and the binder contained in the negative electrode composition relate to the negative electrode composition, and can be respectively referred to as a negative electrode conductive material; and a negative electrode binder.

[0042] The negative electrode composition according to the above-described embodiment uses the silicon-based active material within the above range, and by using a specific conductive material and binder that can suppress the volume expansion rate during the charging and discharging processes, even when contained within the above range, it does not deteriorate the performance of the negative electrode and has the characteristic of excellent output characteristics in charging and discharging.

[0043] In one embodiment of this specification, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0044] In this specification, the silicon-based active material may exist, for example, in a crystalline or amorphous form. Specifically, the silicon particles of the silicon-based active material may preferably be spherical particles, but are not limited thereto.

[0045] In this specification, in the case of SiO2 where x in SiOx is 2, it is not included, and this SiO2 does not react with lithium ions and cannot store lithium. Therefore, x is preferably within the range of the above-described embodiment.

[0046] In this specification, the silicon-based active material may be Si / C or Si composed of a composite of Si and C.

[0047] In this specification, two or more kinds of the silicon-based active materials may be mixed and used.

[0048] In one embodiment of this specification, the carbon-based active material may include one or more selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0049] In one embodiment of this specification, the conductive material may be 0.03 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0050] In another embodiment of this specification, the conductive material may be contained in an amount of 0.03 parts by weight or more and 40 parts by weight or less, preferably 0.05 parts by weight or more and 30 parts by weight or less, more preferably 0.5 parts by weight or more and 25 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0051] In one embodiment of this specification, the conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a sheet-shaped conductive material, and a linear conductive material.

[0052] In one embodiment of this specification, the conductive material may include a dot-shaped conductive material and a linear conductive material.

[0053] In this specification, the dot-shaped conductive material means a dot-shaped or spherical conductive material that can be used to improve the conductivity of the negative electrode, does not cause a chemical change, and has conductivity. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may include carbon black and / or artificial graphite in terms of realizing high conductivity and excellent dispersibility.

[0054] In this specification, the sheet-like conductive material can play a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity and suppressing the interruption of the conductive path due to volume expansion. The sheet-like conductive material can be represented as a plate-like conductive material or a bulk conductive material. As an example of the sheet-like conductive material, it may include at least any one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-like graphite.

[0055] In this specification, the linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube units. Specifically, here, the "bundle type" refers to a bundle-like or rope-like secondary shape in which a plurality of carbon nanotube units are arranged side by side or intertwined with substantially the same orientation of the axis in the length direction of the carbon nanotube unit, unless otherwise specified. The carbon nanotube unit has a cylindrical shape with a nanosize diameter and an sp 2 bonding structure. At this time, depending on the angle and structure of the curling of the graphite sheet, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotube can be uniformly dispersed during the manufacture of the negative electrode compared to the entangled type carbon nanotube, can smoothly form a conductive network in the negative electrode, and can improve the conductivity of the negative electrode.

[0056] In other embodiments of this specification, the conductive material may be a negative electrode conductive material.

[0057] In this specification, the negative electrode conductive material is applied to the negative electrode and has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material, it serves to make contact between silicon-based active materials with a very large volume expansion of the negative electrode during charging and discharging, whereas the positive electrode conductive material serves as a buffer with a buffering role during rolling and also serves to impart some conductivity. Therefore, the negative electrode conductive material and the positive electrode conductive material have different configurations and roles from each other.

[0058] In one embodiment of this specification, the binder may be 2 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0059] In another embodiment of this specification, the binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or may be 2 parts by weight or more, 5 parts by weight or more, 10 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0060] In another embodiment of this specification, the binder may be a negative electrode binder.

[0061] In one embodiment of this specification, the weight average molecular weight of the binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0062] According to the above-described embodiments, by satisfying the weight average molecular weight of the binder within the above-described range, it has the characteristics of excellent mechanical strength, high intermolecular interaction, and excellent binding force of the binder. Also, when the above range is satisfied, the viscosity of the binder can be selected within a suitable range. Therefore, when using this to manufacture a negative electrode, it has the characteristic of excellent coating property.

[0063] In one embodiment of the present specification, the binder is an aqueous binder, and the aqueous binder may include one or more selected from the group consisting of carboxymethyl cellulose-based and its derivatives containing a polymer resin having at least one carboxyl group, polyacrylic acid (PAA) - based, polyvinyl alcohol (PVA) - based, polyacrylonitrile (PAN) - based, and polyacrylamide (PAM) - based.

[0064] In another embodiment of the present specification, the aqueous binder may be a polymer containing one or more monomers selected from the group consisting of (meth) acrylamide, (meth) acrylic acid, and (meth) acrylonitrile.

[0065] In the present specification, a polymerization initiator is used to produce the binder. As an example of the polymerization initiator, ammonium persulfate may be used, but it is not limited thereto.

[0066] In the present specification, when the binder contains a plurality of compounds having a specific ratio (expressed in parts by weight or weight ratio), it may mean that each compound (for example, acrylamide, acrylic acid, acrylonitrile) is included as a monomer of the binder polymer.

[0067] In the present specification, when the binder contains a plurality of compounds as monomers, the monomer with the highest content can be regarded as representative and named a "monomer" - based compound.

[0068] In the present specification, the term "(meth) acrylic" may mean methacrylic and / or acrylic.

[0069] In the present specification, when two or more binder materials are used to produce a copolymer having two or more monomers, as long as it belongs to the aqueous binder, the ratio of each monomer is not particularly limited.

[0070] <Negative electrode slurry> One embodiment of the present invention provides a negative electrode slurry containing the aforementioned negative electrode composition and solvent.

[0071] In another embodiment of the present invention, the solvent may include those known in the art. For example, the solvent may be water (e.g., distilled water) or NMP, but is not limited thereto.

[0072] In some cases, the viscosity of the negative electrode slurry can be controlled within a suitable range by appropriately adjusting the average particle size (D50) of the silicon-based active material or the specific surface area of the particles. When the viscosity of the negative electrode slurry is controlled within a suitable range, the dispersion of the components in the slurry (e.g., conductive material, binder, silicon-based active material, carbon-based active material, etc.) can be improved. Thereby, the contact area between the components can be improved, the conductive network can be sustained, the capacity retention rate can be increased, and the non-uniformity phenomenon of the current density during charging and discharging can also be prevented.

[0073] In some cases, the viscosity of the negative electrode slurry can be adjusted to be 5000 cps to 6000 cps. When the above-mentioned viscosity range is satisfied, it has excellent storage stability, and in the future, when the negative electrode slurry is coated on one or both sides of the negative electrode current collector layer, it has excellent coating properties.

[0074] <Negative electrode> One embodiment of the present specification provides a negative electrode including a negative electrode current collector layer; and a negative electrode active material layer coated with the aforementioned negative electrode slurry on one or both sides of the negative electrode current collector layer.

[0075] In this specification, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Also, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0076] In another embodiment of this specification, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0077] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0078] <Lithium secondary battery> One embodiment of the present invention is a lithium secondary battery including a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either one of the first electrode or the second electrode is the negative electrode described above.

[0079] Specifically, the first electrode may be the negative electrode described above and the second electrode may be a positive electrode, or the first electrode may be a positive electrode and the second electrode may be the negative electrode described above.

[0080] In this specification, as the positive electrode, a known positive electrode material may be used as long as it does not deviate from the scope of the present invention.

[0081] Specifically, the lithium secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0082] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0083] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0084] The positive electrode active material may be a commonly used positive electrode active material. Specifically, examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; lithium iron oxides such as LiFe3O4; the chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; the chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3) of Ni-site type lithium nickel oxide; the chemical formula LiMn 2-c3 M c3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1), or a lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include, but are not limited to, LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li-metal.

[0085] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0086] At this time, the positive electrode conductive material is used to impart conductivity to the positive electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone, or a mixture of two or more may be used.

[0087] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0088] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte and excellent in electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0089] Examples of the electrolyte 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.

[0090] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0091] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone (NMP), 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, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0092] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, at an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so it can be more preferably used.

[0093] As the metal salt, a lithium salt may be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0094] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide (HMPA), nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, improve the discharge capacity of the battery, etc.

[0095] One embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the lithium secondary battery having high capacity, high rate characteristics, and cycle characteristics, they 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.

[0096] Figure 1 is a photograph of a state in which a negative electrode composition according to an embodiment of the present application has been stored in a battery pouch for a certain period of time, and Figure 2 is a photograph of a state in which an electrode composition according to the prior art has been stored in a battery pouch for a certain period of time. Both Figure 1 and Figure 2 are the same in that they are stored under high temperature conditions (about 60 °C) for a certain period of time (about 24 hours). However, it can be confirmed that in Figure 1, the generation of hydrogen gas is small and there is almost no expansion, while in Figure 2, the expansion is intense due to the generation of a large amount of hydrogen gas.

[0097] <Method for manufacturing negative electrode composition> One embodiment of the present invention provides a method for manufacturing a negative electrode composition including a step of mixing a silicon-based active material; a conductive material; a binder; and a pH adjuster, and adjusting the negative electrode composition to a pH of 5 or more and 7 or less during the mixing step or after the completion of the mixing step (for example, when a uniform mixture is achieved) by the pH adjuster.

[0098] In the present specification, the silicon-based active material; the conductive material; the binder; and the pH adjuster are as described above.

[0099] <Method for manufacturing lithium secondary battery> One embodiment of the present invention provides a method for manufacturing a lithium secondary battery including a step of mixing the negative electrode composition and a solvent to produce a negative electrode slurry; a step of applying the negative electrode slurry to one or both sides of an electrode current collector layer; and a step of drying the electrode current collector layer coated with the negative electrode slurry, wherein the negative electrode composition, the solvent, the negative electrode current collector layer, and the application are as described above.

[0100] In the present specification, drying uses a known method such as air drying.

[0101] In the present specification, steps such as rolling applied after the above steps are as known in the art.

[0102] [Examples] The following presents preferred embodiments to facilitate the understanding of the present invention. However, the following embodiments are merely illustrative of the present description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims.

[0103] Production Example. Production of an Aqueous Binder <Production Example 1> In a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, acrylamide (Acryl amide, 50% aqueous solution) and AA (acrylic acid, 80% aqueous solution) were mixed at a molar ratio of 6:4 and reacted at 80 °C for 5 hours to produce an aqueous polymer (polyacrylamide polymer, in aqueous solution state).

[0104] Next, an aqueous solution of NaOH with a concentration of 0.1 mol / L (M) was dropped into the aqueous polymer to produce an aqueous binder with a pH of 7.8.

[0105] Example. Production of a Negative Electrode Slurry <Example 1> Si with a D50 of 5.2 μm was used as the negative electrode active material, and three types of carbon black (product name: Super C65, Timcal), artificial graphite (product name: SFG6L, Timcal), and SWCNT were used as the conductive materials. Using the aqueous binder produced in Production Example 1 as the binder, Si:C65:SFG6L:SWCNT:binder = 80:3:8.5:0.5:8 (by weight ratio) was mixed to prepare a negative electrode composition. To this, 1 M oxalic acid (pH adjuster) was added so that the final pH of the electrode composition became 5.2.

[0106] Next, water was added as a solvent, and the water content was adjusted so that the viscosity of the obtained negative electrode slurry was 5000 cps to 6000 cps in consideration of coatability, viscosity, and solid content.

[0107] <Example 2> Si with a D50 of 5.2 μm was used as the negative electrode active material, and three types of conductive materials, carbon black (product name: Super C65, Timcal), artificial graphite (product name: SFG6L, Timcal), and SWCNT, were used. Using the aqueous binder produced in Production Example 1, they were mixed so that Si:C65:SFG6L:SWCNT:binder = 80:3:8.5:0.5:8 (based on weight ratio) to prepare a negative electrode composition. To this, 0.0001 M sulfuric acid (pH adjuster) was added so that the final pH of the electrode composition became 5.5.

[0108] Next, water was added as a solvent, and the water content was adjusted considering coating property, viscosity, and solid content. The viscosity of the obtained negative electrode slurry was adjusted to be 5000 cps to 6000 cps.

[0109] <Example 3> A negative electrode slurry was produced in the same manner as in Example 1, except that a mixture of artificial graphite (QCG-N2, Shanshan):Si = 90:10 was used as the negative electrode active material.

[0110] <Example 4> A negative electrode slurry was produced in the same manner as in Example 1, except that a mixture of artificial graphite:SiC (SD5100A, Sila nano) = 90:10 was used as the negative electrode active material.

[0111] <Comparative Example 1> Si with a D50 of 5.2 μm was used as the negative electrode active material, and three types of conductive materials, carbon black (product name: Super C65, Timcal), artificial graphite (product name: SFG6L, Timcal), and SWCNT, were used. Using the aqueous binder produced in Production Example 1 as the binder, they were mixed so that Si:C65:SFG6L:SWCNT:binder = 80:3:8.5:0.5:8 (based on weight ratio) to prepare a negative electrode composition.

[0112] Next, water was added as a solvent, and the water content was adjusted so that the viscosity of the obtained negative electrode slurry fell within the range of 5000 cps to 6000 cps considering coating property, viscosity, and solid content (however, pH of the electrode composition state = 7.4).

[0113] <Comparative Example 2> A negative electrode slurry was produced in the same manner as in Comparative Example 1 except that a mixture of artificial graphite (QCG-N2, Shanshan Co., Ltd.):Si = 90:10 was used as the negative electrode active material (however, pH of the electrode composition state = 7.6).

[0114] <Comparative Example 3> A negative electrode slurry was produced in the same manner as in Comparative Example 1 except that a mixture of artificial graphite:SiC = 90:10 was used as the negative electrode active material (however, pH of the electrode composition state = 7.5).

[0115] <Comparative Example 4> In Comparative Example 1, a negative electrode slurry was produced in the same manner as in Comparative Example 1 except that 0.0001 M nitric acid was further added so that the final pH of the electrode composition became 4.2.

[0116] <Comparative Example 5> In Comparative Example 1, a negative electrode slurry was produced in the same manner as in Comparative Example 1 except that 100% natural graphite was used.

[0117] Experimental Example <Experimental Example 1: Evaluation of Hydrogen Gas Generation Amount> The negative electrode slurries of Examples 1 to 4 and Comparative Examples 1 to 5 were stored at a temperature of 60°C for 1 day, and the hydrogen gas generation amount was measured.

[0118] Specifically, the hydrogen gas generation amount can be obtained by putting 5 g of each negative electrode slurry into a pouch with a size of 9 cm × 9 cm, sealing it, leaving it in a constant temperature chamber at 60°C for 24 hours, collecting the gas generated in the pouch, and performing quantitative analysis by GC / MS.

[0119] <Experimental Example 2: Manufacture of Battery and Evaluation of Battery Characteristics> The negative electrode slurries of Examples 1 to 4 and Comparative Examples 1 to 5 were each coated on a copper foil with a thickness of 18 μm and dried, and an active material layer with a thickness of 50 μm was formed on one side of the copper foil, and then punched into a circular shape with a diameter of 14Φ (mm) to manufacture a test electrode (negative electrode). A metal lithium foil with a thickness of 0.3 mm was used as the positive electrode. A porous polyethylene sheet with a thickness of 0.1 mm was used as the separator. Further, as the electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1, in which LiPF6 was dissolved at a concentration of about 1 mol / L as a lithium salt, was used.

[0120] The negative electrode, positive electrode, separator, and electrolytic solution were sealed in a stainless steel container to manufacture an evaluation coin cell with a thickness of 2 mm and a diameter of 32 mm. The coin cell was charged at a constant current of 0.05C until the voltage reached 0.01V, and discharged at a constant current of 0.05C until the voltage reached 1.0V to obtain the initial (discharge) capacity. Then, the cycle characteristics were carried out in the same voltage range as above at a constant current of 0.2C to perform a capacity retention rate test, and the results are shown in Table 1 below.

[0121]

Table 1

[0122] As shown in Table 1 above, it can be seen that the batteries (Examples 1 to 4) using the negative electrode slurry whose pH of the electrode composition satisfies the range of 5 or more and 7 or less by the pH adjuster have less hydrogen gas generation amount and are excellent in cycle capacity retention rate compared with Comparative Examples 1 to 4.

[0123] Specifically, in the case of Comparative Example 4 where the pH of the electrode composition is less than 5, although the hydrogen gas generation amount is low, the capacity retention rate is very low despite using Si as the negative electrode active material. Also, in the cases of Comparative Examples 1 to 3 where the pH of the binder exceeds 7, it can be seen that they are not suitable as the negative electrode composition in that the hydrogen gas generation amount is 28,000 μL or more even though the capacity retention rate is as high as 80% or more.

[0124] In Comparative Example 5, the electrode active material is composed of graphite, and although the capacity retention rate and the amount of hydrogen gas generation are good, since the initial capacity is less than 400 mAh / g, it is not suitable for manufacturing a high-capacity battery and is judged to be unsuitable.

Claims

1. A negative electrode active material containing a silicon-based active material; a conductive material; a binder; and a pH adjuster, A negative electrode composition having a pH of 5 or more and 7 or less when measured at 25°C.

2. The negative electrode composition according to claim 1, wherein the pH adjuster contains one or more selected from the group consisting of fumaric acid, glutaric acid, oxalic acid, malonic acid, succinic acid, maleic acid, palmitic acid, tartaric acid, formic acid, acetic acid, glycolic acid, sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, sulfonic acid, aminosulfonic acid, lithium hydroxide, and sodium hydroxide.

3. The negative electrode composition according to claim 1, wherein the negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

4. The negative electrode composition according to claim 1, wherein the negative electrode active material further contains a carbon-based active material.

5. The negative electrode composition according to claim 1, wherein the silicon-based active material contains one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys.

6. The negative electrode composition according to claim 1, wherein the silicon-based active material contains one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and contains 70 parts by weight or more of the SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

7. The negative electrode composition according to claim 4, wherein the carbon-based active material contains one or more selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

8. The negative electrode composition according to claim 1, wherein the conductive material contains one or more selected from the group consisting of a dot-shaped conductive material, a sheet-shaped conductive material, and a linear conductive material.

9. The binder is an aqueous binder, The negative electrode composition according to claim 1, wherein the aqueous binder contains one or more selected from the group consisting of carboxymethyl cellulose-based and its derivatives containing a polymer resin having at least one carboxyl group, polyacrylic acid (PAA: polyacrylic acid) - based, polyvinyl alcohol (PVA: polyvinyl alcohol) - based, polyacrylonitrile (PAN: polyacrylonitrile) - based, and polyacrylamide (PAM: polyacrylamide) - based.

10. A negative electrode slurry containing the negative electrode composition according to any one of claims 1 to 9 and a solvent.

11. A negative electrode current collector layer; and A negative electrode active material layer in which the negative electrode slurry according to claim 10 is applied to one or both surfaces of the negative electrode current collector layer Including, a negative electrode.

12. A lithium secondary battery including a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, A lithium secondary battery, wherein either one of the first electrode or the second electrode is the negative electrode according to claim 11.

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