KR20220063043A - Binder for anode of secondary battery, anode of secondary battery, and secondary battery - Google Patents

Abstract

The present invention relates to a binder for a negative electrode of a secondary battery having excellent adhesion and elasticity and capable of suppressing the volume change of a negative electrode active material, a negative electrode of a secondary battery, and a secondary battery.

Description

Binder for negative electrode of secondary battery, negative electrode of secondary battery, and secondary battery

The present invention relates to a binder for a negative electrode of a secondary battery, a negative electrode for a secondary battery, and a secondary battery.

BACKGROUND ART A secondary battery is in the spotlight as a power source for not only small electronic devices such as portable computers, portable telephones, and cameras, but also large electronic devices such as electric vehicles and power storage devices.

The negative electrode of the secondary battery includes a current collector and an anode active material layer, wherein the anode active material layer includes an anode active material.

Specifically, as the negative electrode active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of insertion/desorption of lithium have been applied, and silicon, tin, silicon-tin alloy, etc. Research to use it as an active material is also ongoing.

However, as the discharge capacity of the negative active material increases, the volume change due to charging and discharging is severe, thereby weakening the adhesion of the negative electrode and reducing the lifespan of the secondary battery.

In this regard, in order to secure the lifespan of the secondary battery, a binder having elasticity enough to withstand the volume change of the anode active material and capable of suppressing the volume change is required. In addition, a binder with high elasticity is required also in order to ensure fairness at the time of manufacturing a negative electrode.

An object of the present invention is to provide a binder for a negative electrode, which has enough elasticity to withstand a change in the volume of an anode active material while improving processability, and can ultimately secure the lifespan of a secondary battery.

Specifically, in one embodiment of the present invention, in 100% by weight of the repeating unit of the main chain copolymer, 50 to 60% by weight of the first repeating unit derived from the (meth)acrylamide-based monomer, and the second repeating unit derived from the unsaturated carboxylic acid-based monomer 20 to 35 wt%, and a main chain copolymer comprising 10 to 20 wt% of a third repeating unit derived from a nitrile-based monomer, comprising a crosslinked polymer crosslinked through poly(alkylene glycol) di(meth)acrylate A binder for a negative electrode of a secondary battery is provided.

In other embodiments of the present invention, the method for producing the binder for the negative electrode of the one embodiment, the negative electrode including the negative electrode mixture layer and the negative electrode current collector comprising the negative electrode binder and the negative electrode active material of the one embodiment, and the negative electrode It provides a secondary battery comprising.

The binder for a negative electrode of a secondary battery of one embodiment has elasticity enough to withstand a change in the volume of the negative active material while improving processability, and furthermore, it is possible to suppress a change in the volume of the negative active material, and ultimately, the lifespan of the secondary battery can be obtained

In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

In addition, the terminology used herein is used only to describe exemplary embodiments, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.

Also in the present invention, when it is said that each layer or element is formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may additionally be formed between each layer, on the object, on the substrate.

Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Binder for negative electrode of secondary battery

In one embodiment of the present invention, in 100% by weight of the repeating unit of the main chain copolymer, 50 to 60% by weight of the first repeating unit derived from the (meth)acrylamide-based monomer, 20 to 35% by weight of the second repeating unit derived from the unsaturated carboxylic acid-based monomer Weight %, and the main chain copolymer comprising 10 to 20 wt% of a third repeating unit derived from a nitrile-based monomer is a secondary battery comprising a crosslinked polymer crosslinked via poly (alkylene glycol) di (meth) acrylate A binder for an anode is provided.

The binder for the negative electrode of one embodiment includes a cross-linked polymer cross-linked through poly(alkylene glycol) di(meth) acrylate in which the type and content of the repeating unit are each controlled to a specific range and the copolymer has a long chain. do.

This cross-linked polymer has excellent adhesion and has elasticity enough to withstand the volume change of the anode active material due to a loose cross-linked structure (loose network), and further exhibits an effect of suppressing the volume change of the anode active material. Accordingly, the negative electrode binder of the present invention can improve processability during electrode manufacturing, and has excellent durability, thereby ultimately securing the lifespan of the secondary battery.

Hereinafter, the binder for the negative electrode of the embodiment will be described in detail.

first repeat unit

The first repeating unit is derived from a (meth)acrylamide-based first monomer. Specifically, the first repeating unit corresponds to a structural unit of a copolymer formed by adding a (meth)acrylamide-based first monomer during polymerization.

When the first repeating unit is included in the cross-linked polymer, the binder for the negative electrode of the embodiment may exhibit high adhesive strength and an effect of suppressing the swelling of the active material containing silicone.

The (meth)acrylamide-based first monomer is acrylamide, n-methylol acrylamide, n-butoxymethyl acrylamide, methacrylamide, n-methylol methacrylamide, and n-butoxymethyl methacryl It may be at least one selected from the group consisting of amides. For example, acrylamide may be used as the (meth)acrylamide-based first monomer.

The first repeating unit may be included in an amount of 50 to 60% by weight, or 54 to 60% by weight of the total weight (100% by weight) of the main chain copolymer repeating unit. That is, when preparing the cross-linked polymer, the first monomer may be used in an amount of 50 to 60% by weight, or 54 to 60% by weight of the total weight (100% by weight) of the monomer.

If the content of the first repeating unit is less than 50% by weight, there may be a problem in that the adhesive strength is significantly reduced. In addition, since the adhesive strength tends to decrease even when the content of the first repeating unit exceeds 60% by weight, it is preferable to satisfy the above range.

second repeat unit

The second repeating unit is derived from an unsaturated carboxylic acid-based second monomer. Specifically, the second repeating unit corresponds to a structural unit of a copolymer formed by adding the above-described second monomer during polymerization.

When the second repeating unit is included in the cross-linked polymer, the adhesive strength of the negative electrode binder according to the embodiment may be improved due to the hydrophilicity of the carboxylic acid.

The unsaturated carboxylic acid-based second monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid, , for example, acrylic acid.

The second repeating unit may be included in an amount of 20 to 35% by weight based on the total weight (100% by weight) of the main chain copolymer repeating unit. That is, when preparing the cross-linked polymer, the second monomer may be used in an amount of 20 to 35 wt% based on the total weight (100 wt%) of the monomer.

If the content of the second repeating unit is less than 20% by weight, the adhesive strength of the binder may decrease, and if it exceeds 35% by weight, the content of the first and third repeating units is relatively out of the above-described range, so that each repeating unit No synergistic effect can be obtained by

third repeat unit

The third repeating unit is derived from a nitrile-based third monomer. Specifically, the third repeating unit corresponds to a structural unit of the copolymer formed by adding the above-described third monomer during polymerization.

When the third repeating unit is included in the crosslinked polymer, the negative electrode binder of the embodiment may have improved chemical resistance of the electrolyte in the electrode due to the hydrophobicity of the nitrile type.

The nitrile-based third monomer may be at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide. For example, it may be acrylonitrile.

The third repeating unit may be included in an amount of 10 to 20% by weight based on the total weight (100% by weight) of the main chain copolymer repeating unit. That is, when preparing the cross-linked polymer, the third monomer may be used in an amount of 10 to 20 wt% based on the total weight (100 wt%) of the monomer.

If the content of the third repeating unit is less than 10% by weight, the effect on the chemical resistance of the electrolyte cannot be expected, and if it exceeds 20% by weight, phase separation occurs due to its hydrophobicity, and polymer polymerization may not proceed normally.

Meanwhile, the content of the third repeating unit among the repeating units is more preferably the same as the content of the second repeating unit or less than the content of the second repeating unit in terms of improving adhesion. Specifically, the weight ratio of the third repeating unit derived from the nitrile monomer to 100 parts by weight of the second repeating unit derived from the unsaturated carboxylic acid monomer is 28 parts by weight or more, or 30 parts by weight or more, and 100 parts by weight or less, 70 parts by weight part or less, or 50 parts by weight or less.

crosslinking agent

In the present invention, poly (alkylene glycol) di (meth) acrylate is included as a crosslinking agent of the main chain copolymer including the first to third repeating units. In this case, 'poly(alkylene glycol) di(meth) acrylate' is used as a generic term for poly(alkylene glycol) diacrylate and poly(alkylene glycol) di(meth) acrylate.

The poly (alkylene glycol) di (meth) acrylate has a long chain structure consisting of a polyalkylene glycol repeating unit between two (meth) acrylate functional groups, and the main chain copolymer is crosslinked to form a loose network ( loose network) can form a cross-linked structure. Accordingly, the binder prepared by using poly(alkylene glycol) di(meth) acrylate as a crosslinking agent has excellent flexibility and can effectively suppress volume expansion of the negative electrode active material.

The poly(alkylene glycol)di(meth)acrylate may have a number average molecular weight of 500 to 1000 g/mol, or 700 to 1000 g/mol. When the number average molecular weight is less than 500 g/mol, the poly(alkylene glycol) chain length is not sufficient, so it is difficult to form a loose cross-linked network structure, and thus the elasticity and flexibility of the binder may be reduced. In addition, poly (alkylene glycol) di (meth) acrylate having a number average molecular weight of more than 1000 g/mol has low solubility in water used as a solvent, so that the crosslinking agent is not uniformly dissolved during binder polymerization. , whereby the binder in a uniform form may not be polymerized.

On the other hand, the number average molecular weight of poly(alkylene glycol) di(meth) acrylate can be measured using size exclusion chromatography (SEC). For example, it can be measured with a PL-GPC instrument (manufactured by Agilent) using a column of PLgel 10㎛ Mixed-B (manufactured by Agilent), and 1,2,4-TCB (1,2,4-Trichlorobenzene) is used as a mobile phase Therefore, it can be measured under the conditions of a temperature of 125° C. and a flow rate of 1 ml/min. Specifically, the sample is dissolved in 1,2,4-TCB at a concentration of 10mg/10mL, and then supplied in an amount of 200μL, and a polystyrene standard (molecular weight is 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / The number average molecular weight (Mn) can be confirmed using a calibration curve formed using 9 types of 4,000,000 / 10,000,000).

The poly(alkylene glycol) di(meth) acrylate may be poly(ethylene glycol) diacrylate (PEGDA), and/or poly(ethylene glycol) dimethacrylate (PEGDMA). Specifically, the poly(alkylene glycol) di(meth) acrylate may be poly(ethylene glycol) dimethacrylate having a number average molecular weight of 500 to 1000 g/mol.

The poly(alkylene glycol)di(meth)acrylate is included in an amount of 0.5 to 3% by weight, preferably 1 to 3% by weight, based on 100% by weight of the main chain copolymer. That is, when preparing the cross-linked polymer, the poly (alkylene glycol) di (meth) acrylate is 0.5 to 100% by weight of a monomer mixture including a (meth) acrylamide-based monomer, an unsaturated carboxylic acid-based monomer, and a nitrile-based monomer 3% by weight, or 1 to 3% by weight.

If the content of poly(alkylene glycol)di(meth)acrylate is less than 0.5% by weight based on 100% by weight of the main chain copolymer, a loose cross-linked network structure is not sufficiently formed, thereby reducing the flexibility of the binder and the effect of suppressing volume expansion of the negative active material. can't get

Conversely, when the content of poly(alkylene glycol)di(meth)acrylate exceeds 3% by weight based on 100% by weight of the main chain copolymer, the adhesive performance of the binder is significantly reduced, and the main chain polymer and crosslinking agent in the electrode mixture during battery operation Phase separation occurs between the electrodes to make the adhesive force on the electrode surface non-uniform, and cracks or detachment may occur in the electrode mixture due to the imbalance in the adhesive force, and furthermore, a battery short circuit may occur.

aqueous solvent

In addition, an aqueous solvent, ie, water, may be added to the binder for the negative electrode of the embodiment in addition to the above-described cross-linked polymer.

The aqueous solvent may be used in an amount of about 50 to about 1,000 parts by weight, specifically, about 200 to about 800 parts by weight, based on 100 parts by weight of the crosslinked polymer, in terms of stability and viscosity control of the crosslinked polymer. For example, in the total amount (100% by weight) of the binder for the negative electrode of the embodiment, it may be used so that the total solid content (TSC) is adjusted to about 10 to about 50%.

When the aqueous solvent is used too little, there may be a problem that the stability of the cross-linked polymer particles is reduced, and if the solvent is used too much, the viscosity may decrease and the adhesive force of the binder may be weakened, and thus the battery There may be a problem that the overall performance is deteriorated.

Method for manufacturing a binder for a negative electrode of a secondary battery

In another embodiment of the present invention, in the presence of poly (alkylene glycol) di (meth) acrylate and a polymerization initiator, polymerizing a monomer mixture to prepare a cross-linked polymer; including, a binder for a negative electrode of a secondary battery provides a method for manufacturing

This may be a method of manufacturing the binder for the negative electrode of the above-described embodiment.

Specifically, the monomer mixture contains 50 to 60% by weight of a meth)acrylamide-based monomer, 20 to 35% by weight of an unsaturated carboxylic acid-based monomer, and 10 to 20% by weight of a nitrile-based monomer, based on the total weight (100% by weight) of the monomer mixture. includes

In the preparation method, the poly(alkylene glycol)di(meth)acrylate used as a crosslinking agent is included in an amount of 0.5 to 3% by weight or less, more preferably 1 to 3% by weight based on 100% by weight of the monomer mixture.

If the content of poly(alkylene glycol)di(meth)acrylate is less than 0.5% by weight based on 100% by weight of the monomer mixture, a loose network-type crosslinked structure cannot be sufficiently formed to obtain flexibility of the binder and the effect of suppressing volume expansion of the negative active material. can't Conversely, when the content of poly(alkylene glycol)di(meth)acrylate exceeds 3% by weight based on 100% by weight of the monomer mixture, the adhesive performance of the binder is significantly reduced, and between the main chain polymer and the crosslinking agent in the electrode mixture when the battery is driven Phase separation occurs on the surface of the electrode, resulting in non-uniform adhesion on the surface of the electrode, and cracks or detachment may occur in the electrode mixture due to this imbalance in adhesion, and furthermore, a battery short circuit may occur.

Hereinafter, the manufacturing method of the one embodiment will be described in detail, but a description overlapping with the above will be omitted.

polymerization

The method for polymerizing the monomer mixture in the method for producing the binder for the negative electrode of the secondary battery of the present invention is not particularly limited, and for example, solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, etc. can be As polymerization reaction, addition polymerization, such as ionic polymerization, radical polymerization, and living radical polymerization, can be used.

The polymerization may be carried out by single polymerization or multi-stage polymerization. Here, single polymerization refers to a method in which used monomers are put into a single reactor and polymerized at the same time, and multistage polymerization refers to a method in which used monomers are sequentially polymerized in two or more stages.

In addition, the polymerization may be carried out in the presence of a polymerization initiator in a solution containing the above-described aqueous solvent.

The polymerization temperature and polymerization time of the polymerization step for preparing the cross-linked polymer may be appropriately determined according to the case. For example, the polymerization temperature may be about 35 °C to about 90 °C, and the polymerization time may be about 0.5 hours to about 20 hours.

polymerization initiator

As the polymerization initiator usable during the polymerization, an inorganic or organic peroxide may be used, for example, a water-soluble initiator including potassium persulfate, sodium persulfate, ammonium persulfate, and the like may be used.

Anode for lithium secondary battery

In still other embodiments of the present invention, there is provided a negative electrode mixture including the binder for the negative electrode and the negative electrode active material of the above-described embodiment, and a negative electrode including a negative electrode mixture layer including the negative electrode mixture and a negative electrode current collector .

Except for the negative electrode binder of the embodiment, the negative electrode active material used for the negative electrode mixture and the negative electrode, the negative electrode current collector, etc. may each include generally known components.

cathode

The binder for the negative electrode of the embodiment may be included in an amount of 1% to 10% by weight, specifically 1% to 5% by weight of the total weight (100% by weight) of the negative electrode mixture. When this is satisfied, the content of the negative active material may be relatively increased, and the discharge capacity of the negative electrode may be further improved.

On the other hand, since the binder for a negative electrode of one embodiment has excellent properties in binding force and mechanical properties, etc., when a graphite-based negative electrode active material is used as the negative electrode active material of the negative electrode mixture, as well as a negative electrode active material having a higher capacity than that is used, the negative electrode The binding force between the active material and the negative electrode active material, between the negative electrode active material and the negative electrode current collector, etc. can be maintained, and expansion of the negative electrode active material can be suppressed by its own mechanical properties.

Since the binder for the negative electrode of one embodiment is suitable to be applied not only with the graphite-based negative active material but also with the negative active material having a higher capacity than that, in one embodiment of the present invention, the type of the negative electrode active material is not particularly limited.

Specifically, as the negative active material, carbon such as non-graphitizable carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , metal oxides such as Bi ₂ O ₅ ; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; Lithium titanium oxide and the like can be used.

The negative electrode current collector is generally made to have a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens.

The negative electrode is manufactured by coating the negative electrode mixture including the negative electrode active material and the binder on the negative electrode current collector, drying and rolling, and, if necessary, may be prepared by further adding a conductive material, a filler, and the like.

The conductive material is used to impart conductivity to the negative electrode, and any electronically conductive material can be used as long as it does not cause chemical change in the battery of which it is configured, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black , carbon-based materials such as carbon fibers; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

The filler is optionally used as a component for suppressing the expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. A fibrous material such as glass fiber or carbon fiber may be used.

anode

The positive electrode includes a positive active material, and the positive 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 manganese oxides such as Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; LiNi _x Mn _2-x O ₄ A lithium manganese composite oxide having a spinel structure; LiMn ₂ O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; Although Fe2 _{(MoO4)3 etc. are} mentioned, It is not limited only to these.

The positive electrode current collector is generally made to have a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver, etc. may be used on the surface of the surface-treated. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, sheet, foil, net, porous body, foam body, and non-woven body are possible.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

A generally known binder may be used for the positive electrode. Representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, Polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like may be used, but is not limited thereto.

The negative electrode and the positive electrode may be prepared by mixing an active material and a binder, in some cases, a conductive material, a filler, and the like in a solvent to prepare a slurry-like electrode mixture, and applying the electrode mixture to each electrode current collector. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein.

secondary battery

In another embodiment of the present invention, a secondary battery including the negative electrode of the embodiment described above is provided. Such a secondary battery, a positive electrode; electrolyte; and a negative electrode, and may be implemented as a lithium secondary battery.

The lithium secondary battery may be manufactured by impregnating an electrode assembly including a positive electrode, a separator, and a negative electrode with a non-aqueous electrolyte.

The positive electrode and the negative electrode are the same as described above.

In the case of the separator, any one commonly used in lithium batteries may be used as it separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. That is, a low-resistance to ion movement of the electrolyte and excellent electrolyte moisture content may be used. For example, it may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for lithium ion batteries, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and optionally single-layer or multi-layer structure can be used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and the like.

However, when a solid electrolyte other than the non-aqueous electrolyte is used, the solid electrolyte may also serve as a separator.

The non-aqueous electrolyte may be a liquid electrolyte including a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate , gamma-butylolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane Aprotic organic solvents such as derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used. can

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ions A polymer containing a sexually dissociating group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4 phenyl lithium borate, and the like can be used.

In addition, for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (fluoro-ethylene) carbonate), propene sultone (PRS), and fluoro-propylene carbonate (FPC) can be further included.

The lithium secondary battery according to the present invention may be used not only in a battery cell used as a power source for a small device, but also as a unit battery in a medium/large battery module including a plurality of battery cells.

Hereinafter, preferred embodiments are presented to help the understanding of the invention. However, the following examples are only for illustrating the invention, and do not limit the invention thereto.

<Reference example>

In order to confirm the monomer composition having excellent adhesion performance, a copolymer of a (meth)acrylamide-based monomer, an unsaturated carboxylic acid-based monomer, and a nitrile-based monomer without a crosslinking agent was prepared as in Reference Examples 1 to 8 below, and the adhesion performance was evaluated. .

Reference Example 1

(1) Preparation of binder

To a monomer mixture of acrylamide (AAM, 60 g), acrylic acid (AA, 33 g), and acrylonitrile (AN, 16 g), ammonium persulfate (0.5 g) as a polymerization initiator and water (700 g) as a solvent were added. and mixed.

The mixture was polymerized at 70° C. for about 8 hours to prepare the binder of Reference Example 1 including an uncrosslinked copolymer.

(2) Preparation of negative electrode

A 1.5% CMC aqueous solution (90 g) and a conductive material (carbon black, Super C65, 3 g) were stirred for 1 hour to prepare a conductive material dispersion.

Artificial graphite (Zichen's GT, 150g), natural graphite (BTR's AGP8, 50g), silicone-based active material (BTR's DMSO, 30g), distilled water (20g), and Example prepared in (1) in the conductive material dispersion liquid The negative electrode slurry of Example 1 was prepared by adding the binder (0.5 g) of No. 1 and stirring for 30 minutes.

The slurry of Example 1 was coated on the cross section at a loading amount of 10.8 mg/cm ² per side on a 20 μm thick copper foil, dried, and rolled to a total thickness of 90 μm to obtain the negative electrode of Reference Example 1 did

Reference Examples 2 to 8

A binder and a negative electrode were prepared in the same manner as in Reference Example 1, except that the content of each monomer was changed as shown in Table 1 below. In Table 1 below, the content of each monomer is the content (% by weight) in 100% by weight of the total monomer.

Adhesion evaluation of binders

When the negative electrode active material layer of the negative electrode of each reference example is adhered to a glass substrate in a constant temperature chamber at 25° C., and the negative electrode is pulled at a peeling rate of 5 mm/min and a peeling angle of 180°, the negative electrode from the glass substrate The force at which the anode active material layer was peeled was measured.

monomer Reference Example 1 Reference Example 2 Reference Example 3 Reference Example 4 Reference Example 5 Reference Example 6 Reference Example 7 Reference Example 8 monomer
Furtherance AAM (%) 55 55 55 60 60 60 65 65 AA (%) 40 35 30 30 20 10 10 20 AN(%) 5 10 15 10 20 30 25 15 Adhesion (gf/cm) 22 34 41 29 31 22 24 11

Referring to Table 1 above, in the monomer mixture, the (meth)acrylamide-based monomer, the unsaturated carboxylic acid-based monomer, and the nitrile-based monomer are respectively 50 to 60% by weight, 20 to 35% by weight, and 10 to 20% by weight. It can be seen that the satisfactory binders of Reference Examples 2 to 5 exhibit excellent adhesion.

<Example>

Example 1

(1) Preparation of binder

acrylamide (AAM, 54 g), acrylic acid (AA, 30 g), and acrylonitrile (AN, 15 g) as monomers; Ammonium persulfate (0.5 g) as polymerization initiator; Poly(ethylene glycol) methacrylate (PEGDMA, number average molecular weight 700 g/mol, 1 g) as a crosslinking agent was added to 600 g of water as a solvent and mixed.

The mixture was polymerized at 70° C. for about 8 hours to prepare the binder of Example 1 having a solid content of 13%.

(2) Preparation of negative electrode

A 1.5% CMC aqueous solution (90 g) and a conductive material (carbon black, Super C65, 3 g) were stirred for 1 hour to prepare a conductive material dispersion.

Artificial graphite (Zichen's GT, 150g), natural graphite (BTR's AGP8, 50g), silicone-based active material (BTR's DMSO, 30g), distilled water (20g), and the example prepared in (1) in the conductive material dispersion liquid The negative electrode slurry of Example 1 was prepared by adding the binder (0.5 g) of No. 1 and stirring for 30 minutes.

The slurry of Example 1 was coated on both sides with a loading amount of 10.8 mg/cm ² per side on a 20 μm thick copper foil, dried, and rolled to a total thickness of 90 μm to obtain the negative electrode of Example 1 did

(3) Preparation of lithium secondary battery

The negative electrode is used as a working electrode, a lithium metal sheet having a thickness of 150 μm is used as a reference electrode, and a polyethylene separator (thickness: 20 μm, porosity: 40%) is inserted between the working electrode and the reference electrode. A lithium secondary battery was manufactured in the form of a 2032 half-cell according to a conventional manufacturing method after putting it in a container, injecting an electrolyte, and other matters.

As the electrolyte, a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) (EC:PC:DEC=3:2:5 weight ratio) was dissolved in LiPF ₆ so as to have a concentration of 1.3M, and an additive fluoroethylene carbonate (FEC) of 10% by weight based on the total weight of the electrolyte was added.

Examples 2 to 3 and Comparative Examples 1 to 3

Binders, negative electrodes, and lithium secondary batteries of Examples 2 to 4 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the composition of the monomer and crosslinking agent was changed as shown in Table 2 during binder preparation.

In Table 2 below, the content of each monomer is the content (% by weight) in 100% by weight of the total monomer, and the content of the crosslinking agent is the content (% by weight) used relative to 100% by weight of the total monomer.

Monomer (wt%) Crosslinking agent (wt%) AAM AA AN PEGDMA Comparative Example 1 55 30 15 0 Example 1 54 30 15 One Example 2 54 29 15 2 Example 3 54 29 14 3 Comparative Example 2 53 29 14 4 Comparative Example 3 64 19 14 3

<Experimental example>

The negative electrodes and lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated under the following conditions, respectively, and the results are recorded in Table 3 below.

Experimental Example 1: Evaluation of the adhesive strength of the binder

In a constant temperature chamber at 25° C., when the negative electrode active material layer of each negative electrode is adhered to a glass substrate, and the negative electrode is pulled at a peeling rate of 5 mm/min and a peeling angle of 180°, the negative electrode of the negative electrode from the glass substrate The force at which the active material layer was peeled was measured.

Experimental Example 2: Performance evaluation of lithium secondary batteries

(1) Charging/discharging efficiency

In a constant temperature chamber at 25°C, CC/CV discharge was performed three times from 1.5V to 5mV at 0.1C, and CC/CV discharge was performed at 1C after CC charging. The charge/discharge efficiency was calculated by converting the CC section discharge capacity to a percentage of the total discharge capacity.

(2) Capacity retention rate

Charging and discharging were repeated at 25° C. with a standard charge/discharge current density of 0.2C/0.2C, a final charge voltage of 4.25 V, and a final discharge voltage of 2.5 V, and the capacity retention rate was calculated according to Equation 1 below.

[Equation 1]

Capacity retention rate (%) = (discharge capacity in the nth cycle/discharge capacity in the first cycle)*100

Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Comparative Example 3 Binder adhesion (gf/cm) 41 42 44 48 12 13 3 ^rd cycle charge/discharge efficiency (%) 98.84 98.87 98.67 98.71 - 98.60 10 ^th cycle capacity retention rate (%) 91.9 93.6 94.0 93.4 - 91.2 20 ^th cycle capacity retention rate (%) 79.2 86.8 86.2 88.1 - 79.8

In the above experiment, the battery of Comparative Example 2 was short-circuited during the test, so that battery performance data could not be obtained.

Referring to Table 3, the binders of Examples 1 to 3 have excellent adhesive strength, and exhibit elasticity to withstand the volume change of the negative electrode active material when used as a negative binder of a secondary battery due to a loose cross-linked structure, and further, the negative active material It can be confirmed that by suppressing the volume expansion of the electrode, the durability of the electrode is increased and excellent cycle performance is exhibited.

Claims (13)

Among 100% by weight of the repeating unit of the main chain copolymer, 50 to 60% by weight of the first repeating unit derived from the (meth)acrylamide-based monomer, 20 to 35% by weight of the second repeating unit derived from the unsaturated carboxylic acid-based monomer, and the nitrile-based monomer-derived A binder for a negative electrode of a secondary battery, wherein the main chain copolymer including 10 to 20 wt% of the third repeating unit includes a crosslinked polymer crosslinked via poly(alkylene glycol) di(meth)acrylate.
According to claim 1,
The poly (alkylene glycol) di (meth) acrylate has a number average molecular weight of 500 to 1000 g / mol,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The poly (alkylene glycol) di (meth) acrylate is poly (ethylene glycol) diacrylate, and / or poly (ethylene glycol) dimethacrylate,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The poly (alkylene glycol) di (meth) acrylate is contained in an amount of 0.5 to 3% by weight based on 100% by weight of the main chain copolymer,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The weight ratio of the third repeating unit derived from the nitrile-based monomer to 100 parts by weight of the second repeating unit derived from the unsaturated carboxylic acid-based monomer is 28 to 100 parts by weight,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The (meth)acrylamide-based monomer is composed of acrylamide, n-methylol acrylamide, n-butoxymethyl acrylamide, methacrylamide, n-methylol methacrylamide, and n-butoxymethyl methacrylamide. At least one selected from the group,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The unsaturated carboxylic acid-based monomer is at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The nitrile-based monomer is at least one selected from the group consisting of acrylonitrile, methacrylonitrile, and allyl cyanide,
A binder for a negative electrode of a secondary battery.
According to claim 1,
The (meth)acrylamide-based monomer is acrylamide, the unsaturated carboxylic acid-based monomer is acrylic acid, and the nitrile-based monomer is acrylonitrile,
A binder for a negative electrode of a secondary battery.
In the presence of poly (alkylene glycol) di (meth) acrylate and a polymerization initiator, polymerizing a monomer mixture to prepare a cross-linked polymer;
The monomer mixture comprises 50 to 60% by weight of a (meth)acrylamide-based monomer, 20 to 35% by weight of an unsaturated carboxylic acid-based monomer, and 10 to 20% by weight of a nitrile-based monomer,
A method of manufacturing a binder for a negative electrode of a secondary battery.
11. The method of claim 10,
The poly (alkylene glycol) di (meth) acrylate is contained in an amount of 0.5 to 3% by weight based on 100% by weight of the monomer mixture,
A method of manufacturing a binder for a negative electrode of a secondary battery.
A negative electrode mixture layer comprising the binder for the negative electrode of claim 1 and the negative electrode active material; and
comprising a negative electrode current collector,
negative electrode of the secondary battery.
comprising the negative electrode of claim 12,
secondary battery.