KR102283795B1 - Negative electrode active material layer for rechargeable lithium battery, preparing the same, and rechargeable lithium battery - Google Patents

Abstract

It relates to a negative active material layer for a lithium secondary battery comprising a binder including a negative active material including a silicon-based active material and a carbon-based active material, and a polyacrylic acid amine salt having a hydroxyl group, a manufacturing method thereof, and a lithium secondary battery including the same.

Description

Anode active material layer for lithium secondary battery, manufacturing method thereof, and lithium secondary battery

The present invention relates to an anode active material layer for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery.

Non-aqueous electrolyte secondary batteries, including lithium ion secondary batteries, are widely used as power sources for portable devices such as notebook computers (Note PCs) and mobile phones. are flocking

As a negative electrode material (negative electrode active material) of such a non-aqueous electrolyte secondary battery, in addition to lithium metal or lithium alloy, graphite carbon materials such as natural graphite or artificial graphite capable of insertion/desorption of Li ions, that is, a carbon-based active material, etc. are used.

In recent years, a further improved high-capacity is required for miniaturized and multifunctional mobile device batteries, and new negative electrode active materials are being considered instead of carbon-based active materials (eg, graphite carbon materials) widely used as negative electrode active materials. there is.

Although tin (Sn) alloy, silicon (Si) alloy, silicon (Si) oxide, lithium (Li) nitride, etc. are attracting attention as novel negative electrode active materials, at this point in time, any of the new negative electrode materials has charge/discharge cycle characteristics that are the same as those of conventional anode materials. Compared to graphitic carbon materials, it is inferior.

Since the carbon-based active material has a layered structure, Li ions are intercalated and desorbed between layers during charging and discharging, so expansion/contraction at the time of insertion/desorption of Li ions is small.

On the other hand, the novel negative electrode material, particularly the silicon-based active material, has a more complex structure than the carbon-based active material, and at the same time has a large amount of Li ions inserted/desorbed per unit mass during charging and discharging. For this reason, the silicon-based active material expands/contracts accompanying charging and discharging, and as a result, in a charge/discharge cycle that repeats expansion/contraction, the connection between the silicon-based active materials is cut. In addition, the silicon-based active material isolated from other silicon-based active materials has lower electronic conductivity and cannot participate in charging and discharging.

For this reason, the silicon-based active material is inferior in charge-discharge cycle characteristics compared to the carbon-based active material.

Accordingly, efforts are being made to develop a negative electrode for a lithium secondary battery that includes a silicon-based active material and has excellent cycle characteristics.

The present invention provides an anode active material layer for a lithium secondary battery capable of improving cycle characteristics of a lithium secondary battery while including a silicon-based active material as an anode active material, a manufacturing method thereof, and a lithium secondary battery comprising the same .

One embodiment of the present invention provides an anode active material layer for a lithium secondary battery comprising a binder including a polyacrylic acid amine salt having a hydroxyl group and a negative active material including a silicon-based active material and a carbon-based active material.

Another embodiment of the present invention comprises the steps of applying a slurry comprising a silicon-based active material, a carbon-based active material, and a polyacrylic acid amine salt having a hydroxyl group on a current collector, and drying the slurry on the current collector at a temperature of 150° C. or higher It provides a method of manufacturing a negative active material layer for a lithium secondary battery comprising the step of.

The polyacrylic acid amine salt having a hydroxyl group may be prepared by mixing polyacrylic acid and an amine compound in a weight ratio of 1:1.

The amine compound may be tris(hydroxymethyl)aminomethane or ethanolamine.

The polyacrylic acid amine salt having a hydroxyl group may have a network structure.

The silicon-based active material may be included in an amount of 3% by mass to 80% by mass based on the total mass of the negative active material.

The silicon-based active material is Si, SiO _m , a Si-C composite, a Si-Q alloy, or a combination thereof (wherein m is 0<m≤2, and Q is an alkali metal, alkaline earth metal, group 13 to group 16 element) , a transition metal, a rare earth element, or a combination thereof, and Si is excluded from Q).

The carbon-based active material may be artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or a combination thereof.

The negative active material layer for a lithium secondary battery may further include a conductive material.

Another embodiment of the present invention provides a lithium secondary battery including a negative electrode including the negative electrode active material layer, a positive electrode, and a separator layer.

The negative active material layer for a lithium secondary battery according to the present invention can improve the cycle life of the lithium secondary battery while including the silicon-based active material.

1 is a side cross-sectional view schematically showing the configuration of a lithium secondary battery according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

In the present specification, unless otherwise defined as "substitution", at least one hydrogen in the compound is a C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30 alkynyl group, C1 to C10 alkylsilyl group, C3 to C30 cycloalkyl group , C6 to C30 aryl group, C1 to C30 heteroaryl group, C1 to C10 alkoxy group, silane group, alkylsilane group, alkoxysilane group, amine group, alkylamine group, arylamine group or means substituted with a halogen group.

As used herein, "hetero" refers to an atom selected from the group consisting of N, O, S and P, unless otherwise defined.

As used herein, unless otherwise defined, the term "alkyl group" refers to a "saturated alkyl group" or at least one alkenyl group that does not contain any alkenyl or alkynyl groups. Or it is meant to include all of the "unsaturated alkyl (unsaturated alkyl) group" containing an alkynyl group. The "alkenyl group" refers to a substituent in which at least two carbon atoms form at least one carbon-carbon double bond, and the "alkynyl group" refers to a substituent in which at least two carbon atoms form at least one carbon-carbon triple bond. it means. The alkyl group may be branched, straight-chain or cyclic.

The alkyl group may be a C1 to C20 alkyl group, specifically, a C1 to C6 lower alkyl group, a C7 to C10 intermediate alkyl group, or a C11 to C20 higher alkyl group.

For example, a C1 to C4 alkyl group means that there are 1 to 4 carbon atoms in the alkyl chain, which are methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl and t-butyl. It indicates that it is selected from the group consisting of.

Typical alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, ethenyl, propenyl, butenyl, cyclopropyl, cyclobutyl, cyclo a pentyl group, a cyclohexyl group, and the like.

"Aromatic group" means a substituent in which all elements of a cyclic substituent have p-orbitals, and these p-orbitals form a conjugate. Specific examples include an aryl group and a heteroaryl group.

"Aryl group" includes a single ring or a fused ring, ie, a plurality of ring substituents that divide adjacent pairs of carbon atoms.

"Heteroaryl group" refers to an aryl group including a hetero atom selected from the group consisting of N, O, S and P in the aryl group. When the heteroaryl group is a fused ring, each ring may include 1 to 3 heteroatoms.

Unless otherwise defined herein, "copolymerization" may mean block copolymerization, random copolymerization, graft copolymerization or alternating copolymerization, and "copolymer" means block copolymer, random copolymer, graft copolymer or alternating copolymer. It can mean amalgamation.

In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. Throughout the specification, like reference numerals are assigned to similar parts. When a part, such as a layer, film, region, plate, etc., is "on" or "on" another part, it includes not only the case where it is "directly on" another part, but also the case where there is another part in between. Conversely, when we say that a part is "just above" another part, we mean that there is no other part in the middle.

(Composition of lithium secondary battery)

First, referring to FIG. 1 , the configuration of the lithium secondary battery 10 according to the present invention, that is, a positive electrode, a negative electrode including a negative electrode active material layer, and a separator layer will be described.

The lithium secondary battery 10 includes a positive electrode 20 , a negative electrode 30 , and a separator layer 40 .

The charging reached voltage (oxidation-reduction potential) of the lithium secondary battery 10 may be, for example, 4.3V (vs.Li/Li ⁺ ) or more and 5.0V or less, for example, 4.5V or more and 5.0V or less.

The form of the lithium secondary battery 10 is not specifically limited. That is, the lithium secondary battery 10 may have any shape, such as a cylindrical shape, a prismatic shape, a laminate type, or a button type.

anode

The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22 .

The current collector 21 may be any conductor as long as it is a conductor, and may be, for example, aluminum, stainless steel, or nickel-coated steel.

The positive electrode active material layer 22 may include at least a positive electrode active material, and may further include a conductive material and a binder.

The positive active material is, for example, a solid solution oxide containing lithium, but is not particularly limited as long as it is a material capable of electrochemically occluding and releasing lithium ions.

The solid solution oxide is, for example, Li _a Mn _x Co _y Ni _z O ₂ (1.150≤a≤1.430, 0.45≤x≤0.6, 0.10≤y≤0.15, 0.20≤z≤0.28), LiMn _x Co _y Ni _z O ₂ (0.3≤x≤0.85, 0.10≤y≤0.3, 0.10≤z≤0.3), LiMn 1 .5 Ni 0 .5 O 4 , but the like, and the like.

The conductive material may be, for example, carbon black such as KETJEN BLACK and acetylene black, natural graphite, artificial graphite, etc., but is not particularly limited as long as it is intended to increase the conductivity of the positive electrode.

The binder is, for example, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber (acrylonitrile-) butadiene rubber, fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, cellulose nitrate, etc. may be used, but the positive electrode active material and conductive material is not particularly limited as long as it can be bound on the current collector 21 .

The positive electrode active material layer 22 is produced, for example, by the following manufacturing method.

First, a positive electrode mixture is prepared by dry mixing a positive electrode active material, a conductive material, and a binder.

Next, the positive electrode mixture is dispersed in a suitable organic solvent to form a positive electrode mixture slurry, the positive electrode mixture slurry is applied on the current collector 21 , dried, and rolled to form a positive electrode active material layer.

cathode

The negative electrode 30 includes a current collector 31 and an anode active material layer 32 .

The current collector 31 may be any conductor as long as it is a conductor, and may be, for example, copper, aluminum, stainless steel, or nickel-plated steel, but is not limited thereto.

The anode active material layer 32 includes an anode active material and a binder.

The negative active material may include a silicon-based active material and a carbon-based active material.

The silicon-based active material includes silicon (atoms) and is a material capable of electrochemically occluding and releasing lithium ions.

Examples of the silicon-based active material include, but are not limited to, fine particles of a silicon group, fine particles of a silicon compound, and the like.

The silicon compound is not particularly limited as long as it is used as an anode active material of a lithium secondary battery.

The silicon compound may include, for example, Si, a Si-C composite, silicon oxide, a silicon alloy, or a combination thereof, but is not limited thereto.

The silicon oxide may be expressed as, for example, SiO _n (0<n≤2).

The silicon alloy is a Si-Q alloy (Q is an alkali metal, an alkaline earth metal, a group 13 to 16 element, a transition metal, a rare earth element, or a combination thereof, except for Si in Q), such as a Si-Ti-Ni alloy , Si-Al-Fe alloy, Si-Fe alloy, and the like, but is not limited thereto.

Meanwhile, the carbon-based active material includes carbon (atoms) and is a material capable of electrochemically occluding and releasing lithium ions at the same time.

The carbon-based active material may include, for example, a graphite active material, such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite, but is not limited thereto.

Meanwhile, the content of the silicon-based active material in the negative active material is not particularly limited, but may be included in an amount of 3 mass% to 80 mass% based on the total mass of the negative active material. When content of the said silicon-type active material is in the said range, the improvement effect of cycle life becomes more remarkable.

The binder includes a polyacrylic acid amine salt having a hydroxyl group.

In general, the binder used in the negative electrode active material layer is different from the lithium polyacrylate salt, but the polyacrylic acid amine salt used in the negative electrode active material layer according to an embodiment has high flexibility and binding force, so that the silicon-based active material is expanded and This is because the shrinkage can be tracked and, therefore, the connection between the silicon-based active materials can be maintained. As a result, the cycle life of the lithium secondary battery 10 may be improved.

Furthermore, since the amine constituting the polyacrylic acid amine salt has a hydroxyl group, the binding strength and flexibility of the polyacrylic acid amine salt are further improved, and as a result, the cycle life of the lithium secondary battery 10 is further improved.

As the amine has more hydroxyl groups, binding strength and flexibility may be further improved.

In addition, the hydroxyl group may form a single bond with a hydrocarbon group constituting the amine. That is, the polyacrylic acid amine salt may include an amine having a hydrocarbon group, and the hydrocarbon group may form a single bond with a hydroxyl group.

In this case, the hydroxyl groups of the amine are bonded to each other, so that the polyacrylic acid amine salt has a more three-dimensional structure, that is, a network structure. Accordingly, the binding strength and flexibility of the polyacrylic acid amine salt are further improved, and further, the cycle life of the lithium secondary battery 10 is further improved.

The polyacrylic acid amine salt may be, for example, an amino alcohol salt of polyacrylic acid prepared through a neutralization reaction by mixing polyacrylic acid and an amine compound in a weight ratio of 1:1.

Specific examples of the amine compound include, but are not limited to, tris (hydroxymethyl) aminomethane or ethanolamine.

The negative electrode active material layer 32 is manufactured, for example, by the following manufacturing method.

First, a negative electrode mixture is prepared by dry mixing the negative electrode active material and the binder. That is, the negative electrode mixture may include a silicon-based active material, a carbon-based active material, and a polyacrylic acid amine salt having a hydroxyl group.

Next, the negative electrode mixture is dispersed in a suitable solvent to form a negative electrode mixture slurry, the negative electrode mixture slurry is applied on the current collector 31, dried, and rolled to form the negative electrode active material layer 32 do.

The drying temperature is not particularly limited as long as it is a temperature applied to the negative electrode active material layer of the lithium secondary battery, but is preferably 150°C or higher, for example 150°C or higher and 200°C or lower.

The drying may be carried out under an inert atmosphere or vacuum. The gas constituting the inert atmosphere may include, for example, N ₂ gas, Ar gas, and the like, but is not limited thereto.

When the negative electrode mixture slurry is dried at a temperature of 150° C. or more and 200° C. or less, cycle characteristics of the lithium secondary battery 10 may be further improved. This is considered to be because, when the negative electrode mixture slurry is dried at a temperature of 150° C. or more and 200° C. or less, a dehydration reaction occurs between the carboxyl group of acrylic acid and the amine, thereby forming an amide bond. Since the amide bond is formed, the flexibility and binding force of the polyacrylic acid amine salt having a hydroxyl group are further improved, and the expansion and contraction of the silicon-based active material can be more efficiently followed.

On the other hand, when the negative electrode mixture slurry is dried at a temperature of more than 200° C., the carboxyl group of acrylic acid may be decomposed, and the binding force of the polyacrylic acid amine salt having a hydroxyl group may be reduced.

The negative active material layer may further include a conductive material. The conductive material is the same as described above for the positive electrode.

separator layer

The separator layer 40 includes a separator and an electrolyte.

The separator is not particularly limited, and any separator may be used as long as it is used as a separator for a lithium secondary battery.

As the separator, it is preferable to use a porous membrane or a nonwoven fabric that exhibits excellent high-rate discharge performance, alone or in combination.

As a resin constituting the separator, for example, a polyolefin-based resin represented by polyethylene, polypropylene, etc., polyethylene terephthalate, polybutylene terephthalate, etc. Representative polyester resins, PVDF, vinylidene fluoride (VDF)-hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether (par fluorovinyl ether) copolymer, vinylidene fluoride- Tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer , vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoro propylene copolymer, vinylidene fluoride-tetrafluoroethylene- and a hexafluoropropylene copolymer, a vinylidene fluoride-ethylene (ethylene)-tetrafluoroethylene copolymer, and the like, but is not limited thereto.

The non-aqueous electrolyte may be used without any particular limitation as long as it is the same as the conventional non-aqueous electrolyte that can be used in a lithium secondary battery.

The non-aqueous electrolyte has a composition in which an electrolyte salt is contained in a non-aqueous solvent.

The non-aqueous solvent is, for example, a cyclic carbonate ester such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, etc. ); cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate, and methyl butyric acid; Tetrahydrofuran or a derivative thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl diglyme, etc. of ethers; nitriles such as acetonitrile and benzonitrile; Dioxolane or a derivative thereof; ethylene sulfide (ethylene sulfide), sulfolane (sulfolane), sultone (sultone) or a derivative thereof may be mentioned alone or a mixture of two or more thereof, but is not limited thereto.

In addition, the electrolyte salt is, for example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF _{6 -x} (C _n F _2n+1 ) _x [provided that 1<x<6, n=1 or 2], LiSCN , LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , one of lithium (Li), sodium (Na), or potassium (K) such as KSCN Inorganic ionic salts containing, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ), LiC ( CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H- ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N -benzoate, (C ₂ H ₅ ) ₄ N-phthalate, stearyl sulfonic acid lithium, octyl sulfonic acid lithium, dodecyl benzene sulphonic acid lithium, etc. An ionic salt etc. are mentioned, Although these ionic compounds can be used individually or in mixture of 2 or more types, it is not limited to this.

On the other hand, the concentration of the electrolyte salt may be the same as the non-aqueous electrolyte used in the conventional lithium secondary battery, and there is no particular limitation. For example, a non-aqueous electrolyte containing a suitable lithium compound (electrolyte salt) at a concentration of 0.8 mol/L to 1.5 mol/L may be used.

Meanwhile, various additives may be further added to the non-aqueous electrolyte.

The additive includes, for example, a negative electrode action additive, an anode action additive, an ester-based additive, a carbonic acid ester-based additive, a sulfuric acid ester-based additive, a phosphoric acid ester-based additive, a boric acid ester-based additive, an acid anhydride-based additive, and an electrolyte system additives, and the like, but are not limited thereto.

Any one of these may be added to the non-aqueous electrolyte, and a plurality of types of additives may be added to the non-aqueous electrolyte.

(Method for manufacturing lithium secondary battery)

Hereinafter, a method of manufacturing the lithium secondary battery 10 will be described.

Preparation of anode

The anode 20 is manufactured as follows.

First, a mixture of a positive active material, a conductive material, and a binder is dispersed in a solvent (eg, N-methyl-2-pyrrolidone) to form a slurry.

Then, the slurry is applied on the current collector 21 and dried to form the positive electrode active material layer 22 .

In addition, the method of the said application|coating is not specifically limited.

As a method of application, for example, a knife coater (knife coater) method, a gravure coater (gravure coater) method, etc. may be used, but is not limited thereto.

Each of the following application steps is also performed by the same method.

Then, using a press machine, the positive electrode active material layer 22 is pressed to a packing density ^{of 1.0 g/cm 3} to 5.0 g/cm ^{3 .}

Accordingly, the anode 20 is manufactured.

Preparation of the cathode

The negative electrode 30 is also manufactured in the same manner as the positive electrode 20 .

First, a mixture of a negative active material and a binder is dispersed in a solvent (eg, N-methyl-2-pyrrolidone) to form a slurry.

Then, the slurry is applied on the current collector 31 and dried to form the negative electrode active material layer 32 .

As for the temperature at the time of drying, 150 degreeC or more, for example, 150 degreeC or more and 200 degrees C or less are preferable.

Then, using a press machine, the negative electrode active material layer 32 is pressed to a packing density ^{of 0.5 g/cm 3} to 3.0 g/cm ^{3 .}

Accordingly, the negative electrode 30 is manufactured.

Manufacturing of lithium secondary batteries

Next, by placing the separator between the positive electrode 20 and the negative electrode 30, an electrode structure is manufactured.

Then, the electrode structure is processed into a desired shape (eg, cylindrical, prismatic, laminated, buttoned, etc.) and inserted into a container of the corresponding shape.

Next, an electrolyte solution is injected into the container, and the electrolyte solution is impregnated into each pore in the separator.

Accordingly, a lithium secondary battery is manufactured.

Hereinafter, the aspects of the present invention described above through examples will be described in more detail. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

( Example )

Example 1: Preparation of lithium secondary battery

(Manufacture of silicon-based active material)

First, a silicon-based active material (silicon-based alloy) was prepared using the gas atomization method with reference to the method described in Japanese Patent Laid-Open No. 2001-297757.

Specifically, a molten metal was formed by high-frequency melting of 60 mass% of Si powder, 20 mass% of Al powder, and 20 mass% of Fe powder in an argon atmosphere.

Then, the molten metal was poured into the tundish, and a trickle of the molten metal was formed through a thin hole formed in the bottom of the tundish.

Then, high-pressure argon gas was sprayed on the molten metal trickle to pulverize the molten metal.

The powder becomes a silicon-based active material (silicon-based alloy).

The cooling rate was 103°C/sec to 105°C/sec according to the distance between the secondary arms of the dendrite of aluminum-4 mass% copper alloy solidified under the same conditions. In other words, cooling was performed at a cooling rate sufficiently faster than 100° C./sec.

On the other hand, heat treatment was not performed.

(Preparation of binder (polyacrylic acid amine salt having a hydroxyl group))

Polyacrylic acid and tris hydroxymethyl aminomethane were neutralized 1:1 on a monomer basis to prepare a polyacrylic acid amine salt.

(Preparation of slurry for negative electrode)

Then, the silicon-based alloy Si-Al-Fe alloy (silicon-based active material), artificial graphite (carbon-based active material), acetylene black (conductive material), and polyacrylic acid amine salt having the hydroxyl group in the ratio of 45.5:45.5:1.0:8.0 The mixture was mixed in a mass ratio to prepare a negative electrode mixture.

Then, water was added to the negative electrode mixture to adjust the viscosity suitable for application, to prepare a negative electrode mixture slurry (slurry for negative electrode).

(Production of cathode)

The negative electrode mixture slurry (slurry for negative electrode) is applied to one side of a copper foil, dried for 15 minutes with a blow dryer set at 80° C., rolled, and vacuum dried at 150° C. for 6 hours, negative electrode active material A negative electrode comprising a layer was prepared. The packing density of the negative active material layer was 1.50 g/cm ³ .

(Manufacture of anode)

The solid solution oxide _{.15 Li 1 .20 Mn 0 .55 Co} 0 .10 Ni 0 O 2, ketjen black (KETJEN BLACK), and polyvinylidene fluoride 96: 2 were mixed in a mass ratio of 2, to prepare a positive electrode material mixture , The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode mixture slurry (slurry for positive electrode).

Then, the positive electrode mixture slurry (slurry for positive electrode) is uniformly coated on an aluminum foil, dried for 15 minutes with a blow dryer set at 80° C., rolled, and vacuum dried at 100° C. for 6 hours, the positive electrode A positive electrode including an active material layer was manufactured. The packing density of the positive active material layer was 3.0 g/cm ³ .

(Manufacture of coin cell)

The positive electrode was cut to a diameter of 13 mm and the negative electrode to a diameter of 15.5 mm, and a separator composed of a polyethylene microporous film having a diameter of 19 mm and a thickness of 25 μm was placed between the positive electrode and the negative electrode, and accommodated in a CR2032 coin cell battery case.

Next, a non-aqueous electrolyte solution containing 1.5 M of LiPF ₆ added to the battery case (a mixed solution of ethylene carbonate (EC)/diethyl carbonate (DEC)/fluoroethylene carbonate (FEC)=10/70/20 (volume ratio))) was injected and sealed to prepare a lithium secondary battery.

Example 2: Preparation of lithium secondary battery

The same treatment as in Example 1 was performed, except that ethanolamine was used instead of tris hydroxymethyl aminomethane when the polyacrylic acid amine salt having a hydroxyl group was prepared.

Example 3: Preparation of lithium secondary battery

The same treatment as in Example 1 was performed, except that the vacuum drying temperature was changed to 100°C instead of 150°C during the preparation of the negative electrode.

Example 4: Preparation of lithium secondary battery

As the silicon-based active material, the same treatment as in Example 1 was performed, except that silicon oxide (SiO) was used instead of the silicon-based alloy.

comparative example 1: Preparation of lithium secondary battery

The same treatment as in Example 1 was performed, except that polyacrylic acid was used instead of the polyacrylic acid amine salt having a hydroxyl group as a binder when the slurry for the negative electrode was prepared.

comparative example 2: Preparation of lithium secondary battery

When preparing the slurry for the negative electrode, polyacrylic acid was used instead of the polyacrylic acid amine salt having a hydroxyl group as a binder, and when the negative electrode was prepared, the same treatment as in Example 1 was used, except that the vacuum drying temperature was changed to 100°C instead of 150°C. .

comparative example 3: Preparation of lithium secondary battery

As the silicon-based active material, the same treatment as in Comparative Example 1 was performed, except that silicon oxide (SiO) was used instead of the silicon-based alloy.

Evaluation 1: Peel strength (adhesion) evaluation

The negative electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were cut into a rectangle having a width of 25 mm and a length of 100 mm.

Next, the active material side was stuck to the glass plate as an adherend side using a double-sided tape, and it was used as a sample for a peeling strength test.

The sample for the peel strength test was mounted on a peel tester (Shimadzu Corporation, SHIMAZU EZ-S), and the peel strength at 180° C. was measured, and the results are shown in Table 1 below.

It can be said that the binding force and flexibility of a binder are so large that the peeling strength is large.

Evaluation 2: Evaluation of cycle characteristics

The lithium ion secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were charged to 4.2V at a constant current of 1It=5mA at 25°C, and charged until 1/50It=0.1mA at a constant voltage of 4.2V. After that, there was a pause of 10 minutes, and discharge was performed at a constant current of 1 It until it became 2.75 V.

The discharge capacity at this time was taken as the discharge capacity at one cycle, the charge/discharge cycle was repeated 100 times, and the percentage (cycle characteristics) of the discharge capacity at 100 cycles to the discharge capacity at one cycle was calculated. , the results are shown in Table 1 below.

in the anode active material layer
bookbinder Silicon-based active material Carbon-based active material in the anode active material layer: Silicon-based active material in the anode active material layer (mass ratio) Heat treatment temperature (℃) Peel strength (mN/mm) Cycle Characteristics (%) Comparative Example 1 polyacrylic acid Si alloy 50:50 150 19 61 Comparative Example 2 polyacrylic acid Si alloy 50:50 100 17 57 Comparative Example 3 polyacrylic acid SiO 50:50 150 17 58 Example 1 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 50:50 150 29 74 Example 2 polyacrylic acid + ethanolamine Si alloy 50:50 150 22 66 Example 3 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 50:50 100 25 70 Example 4 Polyacrylic acid + tris hydroxymethyl aminomethane SiO 50:50 150 24 68

From Table 1, it can be seen that Examples 1 to 4 have higher peel strength and better cycle characteristics than Comparative Examples 1 to 3.

Tris hydroxymethyl aminomethane possesses a side chain with a hydroxyl group, and at the same time, the side chain is long.

Accordingly, since tris hydroxymethyl aminomethane has a more three-dimensional structure, the anode active material can be bound with a stronger binding force and at the same time have high flexibility.

For this reason, the polyacrylic acid amine salt prepared from tris hydroxymethyl aminomethane has a high peel strength and can improve the cycle characteristics of a lithium secondary battery.

Moreover, Example 1 had higher peeling strength than Example 2, and was the most excellent in cycling characteristics. This is because tris hydroxymethyl aminomethane has more side chains having a hydroxyl group than ethanolamine, and thus has high flexibility and binding force.

In addition, the peel strength improved as the heat treatment temperature was higher, which is thought to be because dehydration reaction occurs in the salt containing an amino group and a carboxyl group, and an amide bond is partially formed.

In addition, comparing Example 4 and Comparative Example 3, even when silicon oxide was used as a silicon-based active material, when a polyacrylic acid amine salt having a hydroxyl group was used as a binder, a polyacrylic acid amine salt having no hydroxyl group was used as a binder. It can be seen that the peel strength and cycle characteristics are superior to those of the case.

Example 5 to 8: Preparation of lithium secondary battery

The same treatment as in Example 1 was performed except that the mass ratio of the carbon-based active material and the silicon-based active material was changed as shown in Table 2 below.

comparative example 4 to 7: Preparation of a lithium secondary battery

The same treatment as in Comparative Example 1 was performed except that the mass ratio of the carbon-based active material and the silicon-based active material was changed as shown in Table 2 below.

in the anode active material layer
bookbinder Silicon-based active material Carbon-based active material in the anode active material layer: Silicon-based active material in the anode active material layer (mass ratio) Heat treatment temperature (℃) Peel strength (mN/mm) Cycle Characteristics (%) Comparative Example 4 polyacrylic acid Si alloy 99:1 150 13 79 Comparative Example 5 polyacrylic acid Si alloy 97:3 150 13 75 Comparative Example 1 polyacrylic acid Si alloy 50:50 150 19 61 Comparative Example 6 polyacrylic acid Si alloy 20:80 150 25 55 Comparative Example 7 polyacrylic acid Si alloy 10:90 150 26 54 Example 5 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 99:1 150 23 80 Example 6 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 97:3 150 24 79 Example 1 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 50:50 150 29 74 Example 7 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 20:80 150 33 60 Example 8 Polyacrylic acid + tris hydroxymethyl aminomethane Si alloy 10:90 150 33 56

From Table 2, when comparing Examples and Comparative Examples in which the mass ratio of the silicon-based active material and the carbon-based active material is the same, it can be confirmed that the peel strength and cycle characteristics of the Examples are better than those of the Comparative Examples at any mass ratio. .

In particular, when the silicon-based active material is contained in an amount of 3% by mass to 80% by mass relative to the total mass of the negative active material, the difference between Examples and Comparative Examples becomes significant.

As mentioned above, although preferred embodiment of this invention was described in detail, referring an accompanying drawing, this invention is not limited to this example. It is clear that various changes or modifications can be made within the scope of the technical idea described in the claims by those of ordinary skill in the field of the technology to which the present invention belongs. It should be understood as belonging to the technical scope of the present invention.

10: lithium secondary battery
20: positive electrode
21: current collector
22: positive electrode active material layer
30: cathode
31: current collector
32: anode active material layer
40: separator layer

Claims (17)

A negative active material comprising a silicon-based active material and a carbon-based active material, and
Binder comprising polyacrylic acid amine salt prepared by mixing polyacrylic acid and tris(hydroxymethyl)aminomethane
A negative active material layer for a lithium secondary battery comprising a.
In claim 1,
The polyacrylic acid amine salt is a negative active material layer for a lithium secondary battery prepared by mixing polyacrylic acid and tris(hydroxymethyl)aminomethane in a weight ratio of 1:1.
delete In claim 1,
The polyacrylic acid amine salt is an anode active material layer for a lithium secondary battery having a network structure.
In claim 1,
The silicon-based active material is an anode active material layer for a lithium secondary battery that is included in an amount of 3 mass% to 80 mass% with respect to the total mass of the anode active material.
In claim 1,
The silicon-based active material is Si, SiO _m , Si-C composite, Si-Q alloy, or a combination thereof, the negative active material layer for a lithium secondary battery.
(wherein m is 0<m≤2, and Q is an alkali metal, alkaline earth metal, a group 13 to 16 element, a transition metal, a rare earth element, or a combination thereof, and Si is excluded from Q)
In claim 1,
The carbon-based active material is artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or a combination thereof.
In claim 1,
The negative active material layer for a lithium secondary battery is a negative active material layer for a lithium secondary battery further comprising a conductive material.
Applying a slurry comprising a silicon-based active material, a carbon-based active material, and a polyacrylic acid amine salt prepared by mixing polyacrylic acid and tris(hydroxymethyl)aminomethane on a current collector, and
drying the slurry on the current collector at a temperature of 150° C. or higher
A method of manufacturing an anode active material layer for a lithium secondary battery comprising a.
In claim 9,
The polyacrylic acid amine salt is prepared by mixing polyacrylic acid and tris(hydroxymethyl)aminomethane in a weight ratio of 1:1.
delete In claim 9,
The polyacrylic acid amine salt is a method of manufacturing a negative active material layer for a lithium secondary battery having a network structure.
In claim 9,
The method of manufacturing a negative active material layer for a lithium secondary battery, wherein the silicon-based active material is contained in an amount of 3% by mass to 80% by mass based on the total mass of the slurry.
In claim 9,
The silicon-based active material is Si, SiO _m , Si-C composite, Si-Q alloy, or a combination thereof, a method of manufacturing a negative active material layer for a lithium secondary battery. (wherein m is 0<m≤2, and Q is an alkali metal, alkaline earth metal, a group 13 to 16 element, a transition metal, a rare earth element, or a combination thereof, and Si is excluded from Q)
In claim 9,
The carbon-based active material is artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or a combination thereof.
In claim 9,
The negative active material layer for a lithium secondary battery is a method of manufacturing a negative active material layer for a lithium secondary battery further comprising a conductive material.
A negative electrode comprising the negative active material layer according to any one of claims 1, 2, and 4 to 8;
anode; and
separator layer
A lithium secondary battery comprising a.

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