KR20240104013A - Negative electrode composition, methode for preparing thereof, negative electrode slurry, negative electrode and lithium secondary battery - Google Patents

Abstract

This application covers silicon-based active materials; conductive materials; bookbinder; and a negative electrode composition containing a pH regulator and 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 of manufacturing the negative electrode composition.
The negative electrode composition provides the advantage of achieving excellent binding force by adjusting the pH of the entire negative electrode composition, while also providing the advantage of solving the problems of silicon-based active materials.

Description

NEGATIVE ELECTRODE COMPOSITION, METHODE FOR PREPARING THEREOF, NEGATIVE ELECTRODE SLURRY, NEGATIVE ELECTRODE AND LITHIUM SECONDARY BATTERY}

This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0184166 filed with the Korea Intellectual Property Office on December 26, 2022, the entire contents of which are incorporated herein by reference.

This application relates to a negative electrode composition, a method for producing the same, a negative electrode slurry, a negative electrode, and a lithium secondary battery.

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

Currently, secondary batteries are a representative example of electrochemical devices that use such electrochemical energy, and their use area is gradually expanding.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, research is being actively conducted on methods for manufacturing a high-density electrode with a higher energy density per unit volume.

Generally, a secondary battery consists of an anode, a cathode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions from the positive electrode, and silicon-based particles with a large discharge capacity may be used as the negative electrode active material.

In particular, in response to the recent demand for high-density energy batteries, research is being actively conducted on ways to increase capacity by using silicon-based compounds such as Si/C or SiOx, which have a capacity more than 10 times greater than graphite-based materials, as anode active materials. there is. In the case of silicon-based compounds, which are high-capacity materials, they provide a large capacity advantage compared to conventionally used graphite, but when manufacturing and storing electrode compositions or slurries containing silicon-based compounds, hydrogen gas may be generated due to surface oxidation reaction, Accordingly, there are problems with the risk of explosion and deterioration of phase stability.

In order to solve the above problems, various methods are being discussed, but there are limits to their application in that they can reduce battery performance, so there are still limits to the commercialization of negative electrodes containing silicon-based compounds.

Therefore, in order to improve the above-mentioned problems, additional research is needed on a cathode composition that includes a silicon-based compound and can simultaneously reduce hydrogen gas generation from the silicon-based compound.

In order to solve the above problems, the present application seeks to provide a negative electrode composition in which the hydrogen ion concentration (pH) is adjusted by a pH adjuster, a method for manufacturing the same, a negative electrode slurry, a negative electrode, and a lithium secondary battery.

An exemplary embodiment of the present specification includes a negative electrode active material including a silicon-based active material; conductive materials; bookbinder; and a pH adjuster, and has a pH of 5 or more and 7 or less when measured at 25°C.

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

In another embodiment, 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 sides of the negative electrode current collector layer.

Finally, the first electrode; second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the negative electrode.

The anode composition according to an exemplary embodiment of the present invention adjusts the hydrogen ion concentration (pH) of the entire anode composition to prevent the generation of hydrogen gas due to a surface oxidation reaction when manufacturing or storing the anode composition and the anode slurry containing the same. Provides a preventive effect. As a result, the phase stability of the negative electrode composition and the negative electrode slurry containing it can be improved, and the risk of explosion due to hydrogen gas generation can be reduced.

By using a negative electrode composition according to another embodiment of the present invention, process safety and stability for the negative electrode and lithium secondary battery containing the same can be secured in the future.

Figure 1 is a photograph of a negative electrode composition according to an exemplary embodiment of the present application after a certain period of time has passed after being stored in a pouch.
Figure 2 is a photograph of a prior art negative electrode composition after a certain period of time has passed after being stored in a pouch.

Before explaining the present invention, some terms are first defined.

In this specification, when a part “includes” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

In this specification, 'p to q' means a range of 'p to q or less'.

In this specification, the fact that a polymer contains a certain monomer as a monomer unit 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 contains a monomer, this is interpreted the same as saying that the polymer contains a monomer as a monomer unit.

In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers, unless specified as 'homopolymer'.

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are determined by using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization for molecular weight measurement as standard materials, and using gel permeation chromatography (Gel Permeation Chromatography). ; It is the polystyrene conversion molecular weight measured by GPC). In this specification, molecular weight means weight average molecular weight unless otherwise specified.

Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the following description.

<Cathode composition>

One embodiment of the present specification is characterized by a negative electrode composition in which the negative electrode active material includes a silicon-based active material and the pH is controlled to be 5 or more and 7 or less by including a pH adjuster.

The negative electrode composition according to the above embodiment can control the pH of the entire negative electrode composition through a pH adjuster, prevent the generation of hydrogen gas from the negative electrode active material, and improve stability when used in a negative electrode in the future.

Specifically, the overall pH of the anode composition can be controlled to a range of 5 to 7 using a pH adjuster, thereby preventing oxidation of the anode active material (particularly, silicon particles) in the anode composition.

In one embodiment of the present specification, the pH adjuster includes 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, It may include one or more selected from the group consisting of nitric acid, sulfonic acid, aminosulfonic acid, lithium hydroxide, and sodium hydroxide, but is not limited thereto, as long as the hydrogen ion concentration in the desired range can be easily achieved.

In an exemplary embodiment of the present specification, one type of pH adjuster may be used alone, or two or more different substances may be used in combination.

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.

In another embodiment of the present specification, the negative electrode active material may include 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and 95 parts by weight. or less, preferably 90 parts by weight or less.

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.

In one embodiment of the present specification, the negative electrode active material may be made of a silicon-based active material and a carbon-based active material.

In this specification, the silicon-based active material has a capacity more than 10 times higher than the carbon-based active material, and accordingly, when the silicon-based active material is applied to the negative electrode, a high level even with a thin thickness is achieved compared to when the carbon-based active material is used alone. It is possible to implement a cathode with high energy density.

In another embodiment of the present specification, when the negative electrode active material is made of a silicon-based active material and a carbon-based active material, the composition ratio between the silicon-based active material and the carbon-based active material may be within the range of 2:98 to 30:70.

The negative electrode active material according to the above embodiment contains a carbon-based active material as a main component, so the volume expansion of the active material is small during charging and discharging, so swelling is small and the negative electrode has excellent conductive connectivity.

In one embodiment of the present 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 the SiOx (based on 100 parts by weight of the silicon-based active material) x=0) may be included in an amount of 70 parts by weight or more.

In an exemplary embodiment of the present application, only pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as a silicon-based active material means that pure Si particles (SiOx (x=0)) that are not combined with other particles or elements are within the above range, based on 100 parts by weight of the total silicon-based active material as described above. It may mean including.

In another embodiment, the silicon-based active material may contain at least 70 parts by weight, preferably at least 80 parts by weight, and more preferably at least 90 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material. It may contain 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

In the present specification, the negative electrode composition containing the silicon-based active material in the above content range, despite having a large amount of silicon-based active material, has a significantly small amount of hydrogen gas generated from the silicon-based active material by adjusting the pH of the negative electrode composition with a pH adjuster. It is meaningful.

In another embodiment of the present specification, the conductive material and binder contained in the negative electrode composition are all for the negative electrode composition, and each includes a negative electrode conductive material; and a cathode binder.

The anode composition according to the above embodiment uses a silicon-based active material in the above range, and uses a specific conductive material and binder that can control the volume expansion rate during the charging and discharging process, so even if it contains the above range, the performance of the anode deteriorates. It has excellent output characteristics during charging and discharging.

In one embodiment of the present 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 alloy.

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

In this specification, the case of SiO ₂ where x is 2 in the SiOx is not included, and SiO ₂ does not react with lithium ions and cannot store lithium. Therefore, x is preferably within the range of the above embodiment.

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

In this specification, two or more types of silicon-based active materials may be mixed and used.

In one embodiment of the present 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.

In one embodiment of the present specification, the conductive material may be in an amount of 0.03 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the anode composition.

In another embodiment of the present specification, the conductive material is present 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, based on 100 parts by weight of the anode composition. It may contain less than one part by weight.

In one embodiment of the present specification, the conductive material is a point-shaped conductive material; Planar conductive material; And it may include one or more selected from the group consisting of linear conductive materials.

In one embodiment of the present specification, the conductive material may include a point-shaped conductive material and a linear conductive material.

In this specification, the point-shaped conductive material refers to a point-shaped or spherical conductive material that can be used to improve conductivity in the cathode and has conductivity without causing chemical changes. Specifically, the dot-shaped conductive material is natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Parness black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, It may be at least one selected from the group consisting of potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black and/or artificial graphite in terms of realizing high conductivity and excellent dispersibility.

In this specification, the planar conductive material may serve to improve conductivity by increasing surface contact between silicon particles within the cathode and at the same time suppress disconnection of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk-type conductive material. Examples of the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

In this specification, the linear conductive material may be a carbon nanotube. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the 'bundle type' herein means, unless otherwise stated, a bundle in which a plurality of carbon nanotube units are arranged side by side or entangled with the longitudinal axis of the carbon nanotube units in substantially the same orientation. It refers to a secondary shape in the form of a bundle or rope. The carbon nanotube unit has a graphite sheet in the shape of a cylinder with a nano-sized diameter and an sp ² bond structure. At this time, the characteristics of a conductor or semiconductor can be displayed depending on the angle and structure at which the graphite surface is rolled. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed when manufacturing a cathode, and can smoothly form a conductive network within the cathode, improving the conductivity of the cathode.

In another embodiment of the present specification, the conductive material may be a negative conductive material.

In this specification, the negative electrode conductive material is applied to the negative electrode and has a completely separate configuration from the positive electrode conductive material applied to the positive electrode. In other words, in the case of the negative electrode conductive material, it serves to hold the contact point between silicon-based active materials whose volume expansion of the negative electrode is very large due to charging and discharging, while the positive conductive material acts as a buffer and retains some conductivity when rolled. Since they play a role in providing energy, the composition and role of the cathode conductive material and the anode conductive material are different from each other.

In one embodiment of the present specification, the binder may be in an amount of 2 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the anode composition.

In another embodiment of the present specification, the binder may include 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the anode composition. It may be more than 5 parts by weight, or more than 10 parts by weight.

In another embodiment of the present specification, the binder may be a negative binder.

In one embodiment of the present 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.

According to the above embodiment, the weight average molecular weight of the binder satisfies the above-mentioned range, thereby providing excellent mechanical strength and high interaction between molecules, so that the binder has excellent binding power. In addition, when the above range is satisfied, the viscosity of the binder can be selected in an appropriate range, and when a cathode is manufactured using this, it has excellent coating properties.

In an exemplary embodiment of the present specification, the binder is an aqueous binder, and the aqueous binder is a carboxymethyl cellulose-based and derivative thereof containing a polymer resin having at least one carboxyl group, a polyacrylic acid (PAA: polyacrylic acid)-based, It may include one or more selected from the group consisting of polyvinyl alcohol (PVA), polyacrylonitrile (PAN), and polyacryl amide (PAM).

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

In this specification, a polymerization initiator is used to prepare the binder, and ammonium persulfate may be used as an example of the polymerization initiator, but is not limited thereto.

In this specification, the fact that the binder includes a plurality of compounds having a specific ratio (expressed in parts by weight or weight ratio) means that each compound (e.g., acrylamide, acrylic acid, acrylonitrile) is included as a monomer of the binder polymer. can do.

In the present specification, the binder includes a plurality of compounds as monomers, and the monomer with the highest content is regarded as the representative, and may be referred to as a “monomer”-based compound.

As used herein, the term “(meth)acrylic” may mean methacrylic and/or acrylic.

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

<Cathode slurry>

One embodiment of the present invention provides a cathode slurry containing the above-described cathode composition and solvent.

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

In some cases, the viscosity of the negative electrode slurry can be controlled to an appropriate range by appropriately adjusting the average particle diameter (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 to an appropriate range, the dispersion of components (e.g., conductive material, binder, silicon-based active material, carbon-based active material, etc.) in the slurry can be improved. Accordingly, the contact area between the components is improved, so that the conductive network can be maintained, the capacity maintenance rate can be increased, and current density unevenness during charging and discharging can also be prevented.

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

<Cathode>

An exemplary embodiment of the present specification includes a negative electrode current collector layer; and a negative electrode active material layer in which the negative electrode slurry described above is applied to one or both sides of the negative electrode current collector layer.

In this specification, the negative electrode current collector layer generally has a thickness of 1㎛ to 100㎛. This negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

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

However, the thickness may vary depending on the type and purpose of the cathode used and is not limited to this.

<Lithium secondary battery>

One embodiment of the present invention includes a first electrode; second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the negative electrode described above.

Specifically, the first electrode may be the above-described cathode and the second electrode may be the anode, or the first electrode may be the anode and the second electrode may be the above-described cathode.

In this specification, known positive electrode materials can be used as the positive electrode as long as they do not deviate from the scope of the present invention.

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, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, detailed description will be omitted.

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

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , surface treated with nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3㎛ to 500㎛, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium iron oxide such as LiFe ₃ O ₄ ; Lithium manganese oxide with the formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , etc.; 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 ; Chemical 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 satisfies 0.01≤c2≤0.3). Ni site-type lithium nickel oxide; Chemical 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, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO lithium manganese composite oxide represented by ₈ (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); Examples include LiMn ₂ O ₄ in which part of Li in the chemical formula is replaced with an alkaline earth metal ion, but it is not limited to these. The anode may be Li-metal.

The positive electrode active material layer may include the positive electrode active material described above, a positive conductive material, and a positive electrode binder.

At this time, the positive electrode conductive material is used to provide conductivity to the positive electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, conductive polymers such as polyphenylene derivatives may be used, and one of these may be used alone or a mixture of two or more may be used.

Additionally, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion 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, carboxymethylcellulose (CMC), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer. , or various copolymers thereof, etc., of which one type alone or a mixture of two or more types may be used.

The separator separates the cathode from the anode and provides a passage for lithium ions. It can be used without particular restrictions as long as it is normally used as a separator in secondary batteries. In particular, it has low resistance to ion movement in the electrolyte and has an electrolyte moisture capacity. Excellent is desirable. Specifically, porous polymer films, for example, porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these. A laminated structure of two or more layers may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. In addition, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

The electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1, 2-dimethoxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxoran, formamide, dimethylformamide, dioxoran, acetonitrile, nitromethane, methyl formate, acetic acid Methyl, phosphoric acid triester, trimethoxy methane, dioxoren derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, pyropionic acid Aprotic organic solvents such as methyl and ethyl propionate can be used.

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

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

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trifluoroethylene for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexanoic acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida. One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may be further included.

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. The battery module and battery pack include the lithium secondary battery with high capacity, high rate characteristics, and cycle characteristics, and are therefore medium to large-sized batteries selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. It can be used as a power source for devices.

Figure 1 is a photograph taken a certain time after being stored in a battery pouch containing a negative electrode composition according to an exemplary embodiment of the present application, and Figure 2 is a photograph taken after a certain time has passed after being stored in a battery pouch containing an electrode composition according to the prior art. This is a picture of the condition. Both Figures 1 and 2 are the same in that they are stored for a certain period of time (about 24 hours) under high temperature conditions (about 60°C). However, in Figure 1, there is almost no expansion due to low generation of hydrogen gas, and in Figure 2, a large amount of hydrogen gas is stored. It can be seen that the swelling is severe due to the occurrence.

<Method for producing anode composition>

One embodiment of the present invention includes a silicon-based active material; conductive materials; Provided is a method for manufacturing a negative electrode composition comprising the step of mixing a binder and a pH adjusting agent, wherein the negative electrode composition is adjusted to pH 5 or higher and pH 7 or lower in the middle of the mixing step through the pH adjusting agent, or the mixing step is terminated. (For example, when achieving a homogeneous mixture), the anode composition can then be adjusted to pH 5 or more and pH 7 or less.

In this specification, the silicon-based active material; conductive materials; bookbinder; and the pH adjuster is the same as described above.

<Manufacturing method of lithium secondary battery>

One embodiment of the present invention includes preparing a negative electrode slurry by mixing the negative electrode composition and a solvent; Applying the negative electrode slurry to one or both sides of an electrode current collector layer; and drying the electrode current collector layer to which the negative electrode slurry is applied. The negative electrode composition, the solvent, the negative electrode current collector layer, and the application are as described above.

In this specification, drying uses known methods such as air drying.

In this specification, steps such as rolling applied after the above steps are known in the art.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the above examples are merely illustrative of the present description, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, It is natural that such variations and modifications fall within the scope of the attached patent claims.

Manufacturing example. Preparation of water-based binder

<Manufacturing Example 1>

In a reactor equipped with a stirrer, thermometer, reflux cooler, and nitrogen gas inlet pipe, acryl amide (50% aqueous solution) and AA (acrylic acid, 80% aqueous solution) were mixed at a molar ratio of 6:4, An aqueous polymer (polyacrylamide polymer, aqueous solution) was prepared by reacting at 80°C for 5 hours.

Then, an aqueous NaOH solution of 0.1 molar concentration (M) was added dropwise to the aqueous polymer to prepare an aqueous binder with pH = 7.8.

Example. Preparation of cathode slurry

<Example 1>

As a negative electrode active material, Si with d50 = 5.2㎛ was used, as a conductive material, carbon black (product name: Super C65, Timcal), artificial graphite (product name: SFG6L, Timcal), and three types of SWCNT were used, and as a binder, the product prepared above was used. Using the water-based binder prepared in Example 1, a negative electrode composition was prepared by mixing Si: C65: SFG6L: SWCNT: binder = 80: 3: 8.5: 0.5: 8 (based on weight ratio). Here, 1M oxalic acid (pH adjuster) was added so that the final pH of the electrode composition was 5.2.

Then, water was added as a solvent, and the water content was adjusted so that the viscosity of the obtained cathode slurry was 5000 cps to 6000 cps, taking into account coating properties, viscosity, and solid content.

<Example 2>

Si with d50 = 5.2㎛ 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 conductive materials, and in Preparation Example 1 Using the prepared water-based binder, a negative electrode composition was prepared by mixing Si:C65:SFG6L:SWCNT:binder = 80:3:8.5:0.5:8 (based on weight ratio). Here, 0.0001M sulfuric acid (pH adjuster) was added so that the final pH of the electrode composition was 5.5.

Then, water was added as a solvent, and the water content was adjusted considering coating properties, viscosity, and solid content. The viscosity of the obtained cathode slurry was adjusted to be 5000 cps to 6000 cps.

<Example 3>

A negative electrode slurry was prepared in the same manner as in Example 1, except that a mixture of artificial graphite (QCG-N2, Shanshan Company):Si=90:10 was used as the negative electrode active material.

<Example 4>

A negative electrode slurry was prepared 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.

<Comparative Example 1>

Si with d50 = 5.2㎛ was used as the negative electrode active material, three types of carbon black (product name: Super C65, Timcal), artificial graphite (product name: SFG6L, Timcal) and SWCNT were used as the conductive material, and as a binder, a production example was prepared. Using the water-based binder prepared in 1, a negative electrode composition was prepared by mixing Si:C65:SFG6L:SWCNT:binder = 80:3:8.5:0.5:8 (based on weight ratio).

Then, water was added as a solvent, and the water content was adjusted so that the viscosity of the obtained cathode slurry was within the range of 5000 cps to 6000 cps, taking into account coating properties, viscosity, and solid content. (However, the pH of the electrode composition was = 7.4)

<Comparative Example 2>

A negative electrode slurry was prepared in the same manner as Comparative Example 1, except that a mixture of artificial graphite (QCG-N2, Shanshan Company): Si = 90: 10 was used as the negative electrode active material. (However, pH of the electrode composition = 7.6)

<Comparative Example 3>

A negative electrode slurry was prepared in the same manner as 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 = 7.5)

<Comparative Example 4>

In Comparative Example 1, a negative electrode slurry was prepared in the same manner as Comparative Example 1, except that 0.0001M nitric acid was additionally added so that the final pH of the electrode composition was 4.2.

<Comparative Example 5>

In Comparative Example 1, a negative electrode slurry was prepared in the same manner as Comparative Example 1, except that 100% natural graphite was used.

Experiment example.

<Experimental Example 1: Evaluation of hydrogen gas generation>

The cathode slurries of Examples 1 to 4 and Comparative Examples 1 to 5 were stored at a temperature of 60°C for one day and the amount of hydrogen gas generated was measured.

Specifically, the amount of hydrogen gas generated was measured by sealing 5 g of cathode slurry in each 9 cm It can be obtained by quantitative analysis.

<Experimental Example 2: Battery manufacturing and battery characteristic evaluation>

The negative electrode slurries of Examples 1 to 4 and Comparative Examples 1 to 5 were each coated on copper foil with a thickness of 18㎛ and dried, and an active material layer with a thickness of 50㎛ was formed on one side of the copper foil, and was formed into a circle with a diameter of 14Φ (mm). A test electrode (cathode) was manufactured by punching. Metal lithium foil with a thickness of 0.3 mm was used as the anode. A porous polyethylene sheet with a thickness of 0.1 mm was used as a separator. In addition, as an electrolyte, LiPF ₆ as a lithium salt was dissolved at a concentration of about 1 mol/L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1.

The cathode, anode, separator, and electrolyte were sealed in a stainless steel container to prepare a coin cell for evaluation 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. Afterwards, the cycle characteristics were 0.2C. The capacity retention rate test was conducted at a constant current in the same voltage range as above, and the results are shown in Table 1 below.

Experiment
detail Example
One Example
2 Example
3 Example
4 Comparative Example 1 Comparative example
2 Comparative Example 3 Comparative example
4 Comparative example
5 note H ₂ gas generation (μL) 120 150 62 95 86,200 28,000 38,000 42 5 Capacity maintenance rate (%) 86 83 80 85 84 81 84 55 91 30 cycle Initial capacity (mAh/g) 3450 3470 680 480 3300 630 460 3460 370

As shown in Table 1, the battery (Examples 1 to 4) using a negative electrode slurry as a pH adjuster satisfying the pH of the electrode composition within the range of 5 to 7 had a higher amount of hydrogen gas generated compared to Comparative Examples 1 to 4. It can be seen that the cycle capacity maintenance rate is excellent at the same time.

Specifically, in the case of Comparative Example 4, where the pH of the electrode composition was less than 5, the amount of hydrogen gas generated was low, but the capacity retention rate was very low despite using Si as the negative electrode active material. In addition, in the case of Comparative Examples 1 to 3 in which the pH of the binder exceeds 7, it can be seen that even though the capacity retention rate is as high as 80% or more, the amount of hydrogen gas generated is more than 28,000 μL, so it is not suitable as a negative electrode composition.

In addition, in Comparative Example 5, the electrode negative material was made of graphite, and the capacity retention rate and hydrogen gas generation amount were good, but the initial capacity was less than 400 mAh/g, so it was judged to be unsuitable for manufacturing high-capacity batteries.

Claims (12)

A negative electrode active material containing a silicon-based active material; conductive materials; bookbinder; And a pH adjuster,
A negative electrode composition having a pH of 5 or more and 7 or less when measured at 25°C. In claim 1,
The pH adjusting agent includes 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, A negative electrode composition comprising at least one selected from the group consisting of lithium hydroxide and sodium hydroxide. In claim 1,
The negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition. In claim 1,
The negative electrode composition further includes a carbon-based active material. In claim 1,
A negative electrode composition wherein the silicon-based active material includes one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloy. In claim 1,
The silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the SiOx (x=0) is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material. A cathode composition comprising: In claim 4,
A negative electrode composition wherein the carbon-based active material includes at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon. In claim 1,
A negative electrode composition wherein the conductive material includes at least one selected from the group consisting of a point-shaped conductive material, a planar conductive material, and a linear conductive material. In claim 1,
The binder is an aqueous binder,
The water-based binder is a polymer resin having at least one carboxyl group, such as carboxymethyl cellulose and its derivatives, polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyacrylonitrile. A negative electrode composition comprising at least one selected from the group consisting of (PAN: polyacrylonitrile) and polyacrylamide (PAM: polyacryl amide). A negative electrode slurry comprising the negative electrode composition according to any one of claims 1 to 9 and a solvent. Negative current collector layer; and
A negative electrode including a negative electrode active material layer coated with the negative electrode slurry according to claim 10 on one or both sides of the negative electrode current collector layer. first electrode; second electrode; A lithium secondary battery comprising a separator and an electrolyte provided between the first electrode and the second electrode,
A lithium secondary battery, wherein either the first electrode or the second electrode is the negative electrode according to claim 11.