KR101799923B1 - Electrode active material slurry for a lithium secondary battery comprise dispersant agent and lithium secondary battery using same - Google Patents

Abstract

The present invention relates to an electrode active material slurry comprising an electrode active material, a conductive agent, a binder, a solvent and a dispersant, wherein the dispersant is one kind of compound selected from the group consisting of an isocyanate compound and a polyfunctional tertiary polyamine compound Wherein the electrode active material slurry contains at least one kind of a mixture. The electrode active material slurry according to the present invention can improve the sheet resistance by improving dispersion even when a conductive agent having a high concentration is used.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode active material slurry for a lithium secondary battery including a dispersant, and a lithium secondary battery using the electrode active material slurry.

The present invention relates to an electrode slurry for a lithium secondary battery including a dispersant and a lithium secondary battery using the same.

Demand for secondary batteries as an energy source is rapidly increasing due to the miniaturization and weight reduction of various electronic devices and the expansion of the electric automobile market. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used. In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . In recent years, studies have been actively conducted on the use of lithium secondary batteries having high energy density and discharge voltage as power sources for such electric vehicles and hybrid electric vehicles.

Generally, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated in an electrode assembly composed of a cathode including a lithium transition metal oxide as an electrode active material, a cathode including a carbonaceous active material, and a porous separator. The anode is prepared by coating a slurry of a cathode active material containing a lithium-transition metal oxide on an aluminum foil, and the anode is prepared by coating a slurry of an anode active material containing a carbonaceous active material on a copper foil.

On the other hand, in the secondary battery of high energy density, the amount of the conductive agent and the binder to be added is limited in order to increase the amount of the electrode active material contained in the slurry of the active material. When the amount of the conductive agent is increased, the amount of the binder is increased, so that the binder can act as a resistance after being applied to the electrode. In addition, when the conductive agent is not dispersed in the applied electrode, a variation in conductivity occurs, resulting in non-uniformity of inter-cell performance. Such non-uniformity in battery performance causes abnormal operation of the battery in a middle- or large-sized device in which a plurality of batteries are used, which causes many problems.

In order to improve the performance of such a secondary battery, there has been an attempt to use polyethylene oxide as a dispersant. Korean Patent Application Laid-Open No. 2003-0021112 discloses a slurry using polyethylene oxide as a dispersing agent when the surface of a positive electrode active material is coated with a conductive agent. Korean Patent Application Publication No. 2004-0087656 discloses a slurry containing polyethylene oxide Was used as a dispersing agent, it was still insignificant in terms of recognition and attainment of the effect of increasing the dispersion of the conductive agent in the whole electrode slurry.

An object of the present invention is to provide an electrode active material slurry having improved dispersibility of a conductive agent.

Another object of the present invention is to provide a lithium secondary battery comprising the electrode active material slurry.

Disclosed is an electrode active material slurry comprising an electrode active material, a conductive agent, a binder, a solvent, and a dispersing agent. The dispersant contains at least five isocyanate compounds and a multifunctional tertiary polyamine Based compound or a mixture of at least one of the foregoing compounds.

The polyfunctional polyamine compound may be represented by the following general formula (1)

[Chemical Formula 1]

(Wherein X is an integer of 1 to 50 and Y is an integer of 1 to 50).

The isocyanate compound may be at least one compound selected from compounds represented by the following general formula (2).

(2)

Here, each of R ₁ to R ₄ is independently a substituted or unsubstituted alkyl or alkylene group having 1-10 carbon atoms. Also, n is an integer of 0 to 10.

The present invention also provides a lithium secondary battery including the positive electrode for the secondary battery. The lithium secondary battery may be used as a unit battery of a battery module that is a power source of a middle- or large-sized device. The middle- or large-sized device may be a power tool, an electric vehicle (EV), a hybrid electric vehicle Electric Vehicle (HEV), and Plug-in Hybrid Electric Vehicle (PHEV); Electric motorcycle including E-bike, E-scooter; Electric golf cart; Electric truck; An electric commercial vehicle or a system for electric power storage.

The electrode active material slurry according to the present invention contains, as a dispersant, one kind of compound selected from the group consisting of an isocyanate compound and a polyfunctional tertiary polyamine compound or a mixture of at least one thereof, , And the sheet resistance can be improved through dispersion improvement.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Disclosed is an electrode active material slurry containing an electrode active material, a conductive agent, a binder, a solvent, and a dispersant. The dispersant is an isocyanate-based compound and a polyfunctional tertiary polyamine-based compound. Wherein the electrode active material slurry contains one kind of compound selected from the group consisting of one or more compounds selected from the group consisting of:

The electrode active material according to an embodiment of the present invention may be a positive electrode or a negative electrode active material.

The positive electrode active material is _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LiFePO 4, LiFe 1-x Mn x PO 4 (0≤x <1), LiNi 1-xy Mn x Co y O 2 (0≤x <1 Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Ma and / or LiNi _1-xyz Co _x M1 _y M2 _z O ₂ Mo, and x, y and z are atomic fractions of oxides, independently of each other, 0? X <1, 0? Y <1, 0? Z <1) It may be one or more selected.

The negative electrode active material may include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, hard graphitizable carbon, carbon black, carbon nanotube, fullerene, activated carbon and the like; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and lithium-containing nitrides.

The conductive agent is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 20% by weight based on the total weight of the electrode mixture. Such a conductive agent is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and may include graphite such as natural graphite and 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And a conductive material such as polyphenylene oxide and polyphenylene derivative.

As the solvent of the electrode active material slurry, it is possible to use a conventionally known cathode active material slurry and selected from the group consisting of dimethyl sulfoxide (DMSO) and N-methyl pyrrolidone (NMP) And the solvent of the cathode slurry according to an embodiment of the present invention may be N-methyl pyrrolidone. The weight of the solvent may be 70 to 80 parts by weight based on the total weight of the cathode active material according to an embodiment of the present invention.

The binder is a component that assists in bonding between the electrode active material and the conductive agent and bonding to the current collector, and is usually added in an amount of 1 to 10% by weight based on the total weight of the cathode active material, the conductive agent, and the binder. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

In general, in order to improve the conductivity in the electrode active material slurry, in order to increase the binding force between the active material and the conductive agent and the binding force with respect to the current collector, when the concentration of the conductive material is increased, Had to increase.

However, when the dispersant according to one embodiment of the present invention is used, the electrode active material slurry is improved in dispersibility and effectively retaining the binding force with the electrode collector even when a high-concentration conductive material is used, without addition of an additional binder can do.

The dispersant according to one embodiment of the present invention has a phillic property with the -OH group on the surface of the conductive agent in the electrode active material slurry, and can maintain a uniform dispersion state. More specifically, the + charge of the isocyanate group of the isocyanate compound or the nitrogen (N) portion of the polyfunctional tertiary polyamine compound binds to the -OH group on the surface of the conductive agent. Here, in the case of the polyfunctional tertiary polyamine compound, in the case of secondary and primary amines defined by the number of functional groups bonded to nitrogen atoms excluding hydrogen, the reactivity of the compound is too high, In addition, in the resulting secondary cell, other chemical side reactions may occur. The chemical bonding of such a dispersant strongly bonds to the surface of the conductive agent rather than the binder, thereby inducing the conductive agents to have easy dispersibility in the active material slurry. Therefore, the conductive agent can be easily dispersed in the slurry of the electrode active material by the dispersant, and therefore, even when the electrode active material slurry is coated on the current collector, the dispersibility of the conductive agent is improved, An electrode having a high adhesive strength to the current collector can be obtained without being mass-produced.

The dispersant may be an isocyanate compound, and a polyfunctional tertiary polyamine compound.

The polyfunctional tertiary polyamine compound may be at least one compound selected from compounds represented by the following general formula (1).

[Chemical Formula 1]

Wherein x is an integer from 1 to 50 and y is an integer from 1 to 50. [

In one embodiment of the present invention, the polyfunctional tertiary polyamine compound may be represented by the following formula (1a).

[Formula 1a]

The isocyanate compound may be at least one compound selected from compounds represented by the following general formula (2).

(2)

Here, each of R ₁ to R ₄ is independently a substituted or unsubstituted alkyl or alkylene group having 1-10 carbon atoms.

In one embodiment according to the present invention, a compound represented by the formula (2a) can be used.

(2a)

The dispersant may be contained in an amount of 0.05% by weight to 1% by weight based on the total weight of the electrode active material slurry. When the dispersant is contained in an amount of less than 0.05% by weight based on the total weight of the electrode active material slurry, the amount of the dispersant that can be bound to the surface of the conductive agent is small due to its small amount, The binding of the electrode active material slurry coated on the electrode current collector may be weakened due to the bonding force with the conductive material higher than that of the binder, when the electrode active material slurry contains 1 wt% or more based on the total weight of the electrode active material slurry.

The electrode active material slurry may further include a filler. The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like are used.

The method for producing the electrode active material slurry is not particularly limited, and a known method for producing an electrode active material slurry can be used.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode for a secondary battery can be produced by, for example, applying a slurry prepared by mixing the positive electrode active material and a conductive agent, a binder, a filler, etc. with a solvent such as N-methylpyrrolidone (NMP) Followed by drying and rolling.

After application on the current collector, the drying is carried out at a temperature of 60 to 200 캜, preferably at 60 to 150 캜. The dispersant can be decomposed at a temperature higher than 200 DEG C, so that the effect of improving battery performance can not be expected.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on its surface to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foaming agent, and a nonwoven fabric may be used.

The negative electrode is produced, for example, by applying a negative electrode mixture containing the negative electrode active material on a negative electrode collector and drying the applied mixture.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is interposed between the cathode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of a nonaqueous electrolyte and a lithium salt. Examples of the non-aqueous electrolyte include non-aqueous organic solvents, organic solid electrolytes, and inorganic solid electrolytes.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, Tetrahydrofuran, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methyltetrahydrofuran, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, methyl ethyl ketone, , Ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ A nitride of Li, a halide, a sulfate, and the like can be used.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , and LiSbF ₆ as a lithium salt. _{6, LiN (C 2 F 5} SO 2) 2, LiAlO 4, LiAlCl 4, LiSO 3 CF 3, LiClO 4, Li (CF 3 SO 2) (C 2 F 5 SO 2) N , and Li (SO ₂ F) ₂ N may be used.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle or large battery module including a plurality of battery cells.

Preferred examples of the above medium to large devices include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric motorcycle including E-bike, E-scooter; Electric golf cart; Electric truck; An electric commercial vehicle, or a system for power storage, but the present invention is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

&Lt; Production of cathode material slurry >

Example 1

, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ as a positive electrode active material was mixed with 93 wt% of the positive electrode active material, the conductive material, the binder and the dispersing agent, 3 wt% of super-p as a conductive agent, 3.8 wt% of polyvinylidene fluoride (PVdF) , 0.2 weight% of the compound represented by the above formula (1a) as a dispersant, and N-methyl-2-pyrrolidone (NMP) were added to a solvent to prepare a slurry for a cathode material.

Example 2

, LiNi _0.6 Co _0.2 Mn _0.2 O ₂ as a positive electrode active material was mixed with 93 wt% of the positive electrode active material, the conductive material, the binder and the dispersing agent, 3 wt% of super-p as a conductive agent, 3.8 wt% of polyvinylidene fluoride (PVdF) , 0.2 weight% of the compound represented by the above formula (2a) as a dispersant, and N-methyl-2-pyrrolidone (NMP) were added to a solvent to prepare a cathode slurry.

Comparative Example 1

A positive electrode mixture slurry was prepared in the same manner as in Example 1, except that only 3% by weight of super-p was added as the conductive agent and N-methyl-2-pyrrolidone (NMP) was added as a solvent.

&Lt; Preparation of electrode &

The positive electrode mixture slurry prepared in Example 1 was applied to an aluminum (Al) thin film having a thickness of about 20 mu m as a positive electrode current collector and dried to produce a positive electrode, followed by roll pressing to manufacture a positive electrode Respectively.

A negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive material to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to produce a negative electrode.

The thus prepared positive electrode and negative electrode were fabricated by polymerizing a polymer type cell together with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), followed by the addition of ethylene carbonate (EC) ) And dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) and a non-aqueous electrolytic solution containing 1 mole / liter of LiPF ₆ based on the total amount of the non-aqueous electrolytic solution as a lithium salt. The preparation of the secondary battery was completed.

<Experimental Example>

The positive electrode plates before the electrolyte solution prepared in each of Examples 1 and 2 and Comparative Example were pressed and cut at intervals of 1 cm, and the adhesion to the electrodes was measured through a 180-peel test. The results are shown in Table 1 below.

Peel strength
gf / cm Sheet resistance
mΩ / □ Example 1 84 2.52 Example 2 150 3.15 Comparative Example 2 70 5.55

As shown in Table 1, in the case of the electrodes of Examples 1 and 2, in which the compounds of Chemical Formulas 2 to 3 were used as the dispersing agent, compared with Comparative Example 1 in which the dispersing agent was not used, It was found that an excellent adhesive force can be obtained even at a low temperature.

Claims (14)

1. A cathode active material slurry for a secondary battery comprising a cathode active material, a conductive agent, a binder, a solvent, and a dispersant,
The dispersant comprises i) an isocyanate-based compound; Ii) an isocyanate compound and a polyfunctional tertiary polyamine compound; And (iii) a polyfunctional tertiary polyamine compound. In the cathode active material slurry for a secondary battery,
Wherein the isocyanate compound is at least one selected from compounds represented by the following general formula (2).
(2)

(Wherein R ₁ to R ₄ each independently represents a substituted or unsubstituted alkyl group or alkylene group having 1-10 carbon atoms, and n is an integer of 0 to 10)
The method according to claim 1,
Wherein the polyfunctional tertiary polyamine compound is at least one selected from compounds represented by the following general formula (1).
[Chemical Formula 1]

(Wherein x is an integer of 1 to 50 and y is an integer of 1 to 50)
delete The method according to claim 1,
Wherein the polyfunctional tertiary polyamine compound is represented by the following formula (1a).
[Formula 1a]

The method according to claim 1,
Wherein the isocyanate compound is a compound represented by the following formula (2a).
(2a)

The method according to claim 1,
Wherein the dispersing agent is contained in an amount of 0.05 wt% to 1 wt% based on the total weight of the electrode active material.
delete The method according to claim 1,
The positive electrode active material is _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LiFePO 4, LiFe 1-x Mn x PO 4 (0≤x <1), LiNi 1-xy Mn x Co y O 2 (0≤x <1 Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Ma and / or LiNi _1-xyz Co _x M1 _y M2 _z O ₂ Mo, and x, y and z are atomic fractions of oxides, independently of each other, 0? X <1, 0? Y <1, 0? Z <1) Wherein the cathode active material slurry is at least one kind selected from the group consisting of:
delete delete The method according to claim 1,
The conductive agent may be 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; A polyphenylene derivative, and a conductive material such as a polyphenylene derivative.
The method according to claim 1,
The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, , Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.
The method according to claim 1,
Wherein the solvent is at least one selected from the group consisting of dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), and the like.
A lithium secondary battery comprising a positive electrode produced by applying the positive electrode active material slurry according to any one of claims 1, 2, 4 to 6, 8, and 11 to 13 to a current collector.