KR101770869B1 - Positive electrode material slurry for a lithium secondary battery comprising at least two conductive material and lithium secondary battery using the same - Google Patents

Abstract

According to the present invention, it is possible to provide a mixed cathode material of a three-component system layer oxide and a metal oxide of a spinel structure containing two kinds of different conductive materials in a cathode active material so that particles in the mixed cathode material can be evenly mixed with a conductive material, So that the mixed cathode material slurry has a high solids content and can be easily applied to the cathode current collector while injecting a small amount of solvent. The slurry for the cathode material of a lithium secondary battery and the lithium ion secondary battery ≪ / RTI >

Description

TECHNICAL FIELD [0001] The present invention relates to a cathode slurry for a lithium secondary battery comprising at least two conductive materials, and a lithium secondary battery using the cathode slurry. 2. Description of the Related Art [0002]

The present invention relates to a slurry of a cathode material for a lithium secondary battery comprising two or more conductive materials and a lithium secondary battery using the slurry.

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.

LiCoO ₂ , which is a typical cathode active material, has reached the practical limit of power density and output characteristics. Especially, when it is used in high energy density applications, due to its structural instability, LiCoO ₂ , And generates an exothermic reaction with the electrolyte in the battery, thereby causing the explosion of the battery. In order to improve the instability of LiCoO ₂ , the use of lithium-containing manganese oxide such as LiMnO _{2 having} a layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and lithium-containing nickel oxide (LiNiO ₂ ) has been considered. Mn, and Co have been continuously studied.

However, the three-layered layered oxide has a problem of instability in composition. To improve this, there is known a technique of mixing a metal oxide of a spinel structure with a three-component cathode active material of the layered structure.

In the case of the cathode active material slurry in which the three-component layered oxide and the spinel-structured metal oxide are mixed, a large amount of solvent and a large number of conductive materials are required in mixing the conductive material for the conductive material in the mixing process. I had a problem in terms of

In the present invention, the metal oxide of the spinel structure and the Mixing of Ternary Metal Oxide The mixing process is improved by including two kinds of conductive materials having different sizes and types in the cathode active material and a small amount of conductive material and a small amount of conductive material have a high solid content The viscosity of the anode current collector can be easily maintained.

The present invention provides a cathode active material, a conductive material, a binder and a solvent, wherein the weight ratio of the cathode active material: the conductive material: the binder to the total weight of the cathode active material, To 90% by weight: 4 to 10% by weight: 1 to 10% by weight, the weight of the solvent relative to the total weight of the cathode active material is 70 to 80 parts by weight, and the conductive material includes a first conductive material and a second conductive material The cathode slurry comprising the cathode slurry.

The cathode active material may include a three-component lithium-containing metal oxide and a spinel-structured metal oxide. For example, the three-component lithium-containing metal oxide may include LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _2, and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and the metal oxide of the spinel structure may be LiMn ₂ O ₄ .

The first conductive material may be at least one selected from the group consisting of carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, carbon black of thermal black, and denka black. An example is Denka black. The first conductive material may have an average particle size of 50 to 110 nm and may be 2 to 5 wt% based on the total weight of the cathode active material, the conductive material, and the binder.

The second conductive material may be natural or artificial graphite powder, and the graphite powder may have a spherical shape and an average particle size of 4 to 6 탆 and may be 2 to 5% by weight based on the total weight of the cathode active material, the conductive material and the binder.

The present invention can also provide a positive electrode for a secondary battery including the positive electrode material slurry, and can provide a lithium secondary battery using the positive electrode material.

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 cathode active material according to the present invention provides a mixed cathode material of a three-component system layer oxide containing two different conductive materials and a metal oxide of a spinel structure, so that the particles in the mixed cathode material can be evenly mixed with the conductive material, The mixed cathode material slurry provides a slurry for a lithium secondary battery cathode material which is easy to apply to a cathode current collector while injecting a small amount of solvent.

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.

In one embodiment, the present invention provides a positive electrode active material, a conductive material, a binder, and a solvent, wherein the weight ratio of the positive electrode active material: the conductive material: , 80 to 90 wt%: 4 to 10 wt%: 1 to 10 wt% based on the total weight of the binder, the weight of the solvent relative to the total weight of the cathode active material is 70 to 90 wt parts, Wherein the second conductive material comprises a second conductive material.

The cathode active material may include a three-component lithium-containing metal oxide and a metal oxide of a spinel structure.

The three-component system lithium-containing metal oxide is _{LiNi 0 .8 Co 0 .1 Mn 0} .1 O 2, LiNi 0 .6 Co 0 .2 Mn 0 .2 O 2, and LiNi _1/3 Co _1/3 Mn _{1 / 3} O 1 all selected from the group consisting of _2, and if the embodiment of the present invention may be carried out using the _{LiNi 1/3 Co 1/3} Mn 1/3 O 2.

The metal oxide of the spinel structure may be LiMn ₂ O ₄ , preferably 30 to 80 wt%, more preferably 50 to 70 wt%, based on the total weight of the mixed cathode material with the three-component system .

When the content of the spinel is 50 wt% or less, securing the stability of the battery may be difficult due to a low content of the three-component metal oxide when the content is 70 wt% or more.

The mixed cathode material of the three-component metal oxide and the spinel-structured metal oxide generally includes a conductive material in order to improve the conductivity of the mixed cathode material. However, when one type of conductive material is added to the mixed cathode material The effect of improving the conductivity of the mixed cathode material is insufficient and furthermore, when one kind of conductive material is used for the mixed cathode material, a solvent is excessively used in order to uniformly mix the conductive material, which is a particulate material, with the two kinds of cathode active material mixture And a large amount of conductive material is required to obtain the conductivity of the cathode active material, and a long time is required in the mixing process for producing the mixed cathode material.

That is, when the particle size or surface area difference between the components to be mixed is large, the coated conductive material may be biased to one of the components having a large surface area, and the average particle diameter of the conductive material is several tens to several hundred nm. The conductive material can not be uniformly arranged between the positive electrode active materials, and can be aggregated or biased to one side, resulting in resistance and low conductivity. Such a phenomenon is the same even if the amount of the conductive material is continuously increased. Therefore, it was one of the main causes of problems in the mixing process such as using an excessive amount of solvent.

Therefore, in the present invention, in order to provide a three-component system and a spinel mixed cathode material in which a conductive material is uniformly distributed in a three-component system and a spinel mixed cathode material, Sized conductive material may be used.

Specifically, in one embodiment of the present invention, the first conductive material is a conductive material that can be generally charged into a cathode active material of a lithium secondary battery, and examples thereof include carbon black, ketjen black, channel black, furnace black, lamp black, Thermal blas, and denka black. In one embodiment of the present invention, denka black may be used.

The first conductive material may have an average particle diameter of 30 to 110 nm, preferably 60 to 100 nm. If the average particle size is less than 30 nm, the particle size is too small to disperse between the cathode active materials, and if the average particle size is larger than 110 nm, the size of the conductive material is too large in the arrangement of the conductive material according to the porosity of the cathode active material It may not be possible.

The first conductive material may be 2 to 5 wt% based on the total weight of the cathode active material, the conductive material, and the binder.

In one embodiment of the present invention, the second conductive material may be spherical graphite powder. That is, when spherical graphite powder is distributed as the second conductive material together with the first conductive material in the mixed cathode active material, the second conductive material having a size larger than that of the first conductive material is disposed in the empty space of the cathode active material, When conductive materials having different particle sizes such as conductive carbon and spherical graphite powder in a mixing process are simultaneously applied, it is possible to suppress the phenomenon that the conductive materials are biased to only one component constituting the mixed cathode material, The conductive material can be uniformly distributed in the mixed cathode material, and the conductive material is distributed not only on the surfaces of the three-component system and the spinel but also on the contact portions of the two materials, And contributes to the improvement of the conductivity with the oxide.

As a result, the electric conductivity of the mixed cathode material is increased and the resistance is lowered, thereby improving the output. In the case of the cathode active material mixed with the first and second conductive materials, in the case of the cathode active material slurry prepared from the mixed cathode active material due to the mixing of the first conductive material having a small size and the second conductive material having a relatively large size, The mixing process can be easily performed even by using a solvent.

Specifically, the graphite powder is not limited to natural or artificial graphite powder. If the amount of the graphite powder is too small, it is difficult to obtain a desired viscosity of the slurry of the cathode material by mixing two kinds of conductive materials. On the contrary, if the amount is too large, the amount of the cathode active material and the first conductive material is relatively small The capacity of the secondary battery may be reduced. The graphite powder may be 2 wt% to 5 wt% based on the total weight of the mixed cathode material.

When the positive electrode mixture slurry is prepared using the first conductive material and the second conductive material according to an embodiment of the present invention, since the average particle size and the like are different as described above, the positive electrode mixture slurry is uniformly mixed in the positive electrode active material, Can be increased. That is, the amount of the mixed slurry that can be produced per unit time increases as the solid content increases. The solid content generally means that the weight of the cathode active material, the conductive material, and the binder is 60 to 65% by weight relative to the solvent added in the cathode slurry containing the cathode active material, the conductive material, the binder and the solvent. Here, the solid content of 60 to 65% by weight refers to the viscosity within the range of 15,000 to 30,000 cp in a room temperature environment in which the cathode slurry can be easily applied on the cathode current collector. The viscosity of the slurry is increased as the solid content is increased to 65 wt% or more. When the solids content is less than 60% by weight, the viscosity of the prepared cathode material slurry becomes too low. As a result, the viscosity of the anode slurry becomes too low, Application on the current collector may not be easy.

In the embodiment of the present invention, when the first conductive material and the second conductive material are used, the viscosity of the positive electrode current collector can be easily controlled even when the solid content is high and the coating material is easily applied to the positive electrode collector Therefore, the slurry of the positive electrode active material is smoothly conveyed, and the slurry of the positive electrode material can be more efficiently coated.

In addition, the viscosity of the cathode slurry generally has a viscosity of 15,000 to 30,000 cp at room temperature (23 ° C) in order to be applied to the cathode current collector. If the viscosity is less than 15000 cp, the viscosity of the positive electrode current collector may be too low to lose the slurry of the positive electrode material or may not be properly applied. If the viscosity exceeds 30000 cp, And the thickness of the produced anode may become thick.

The method for producing the mixed cathode material slurry is not particularly limited and a known cathode material manufacturing method can be used. Specifically, a method for producing a slurry containing the binder, the cathode active material mixture, the first conductive material, and the second conductive material, But the present invention is not limited thereto.

As the solvent of the cathode active material slurry, conventionally known cathode active material slurries can be used, but the solvent of the cathode slurry according to one 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 of the slurry for a cathode material according to an embodiment of the present invention is a component that assists in bonding of a three-component system, spinel and a conductive material, and bonding to a current collector. Usually, the total weight of the cathode active material, Is added in an amount of 1 to 10% by weight. 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.

The cathode 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 present invention also provides a cathode for a secondary battery in which the mixed cathode material is coated on a current collector.

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

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

The negative electrode is prepared, for example, by applying a negative electrode mixture containing a negative electrode active material on a negative electrode collector, followed by drying.

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 anode 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 , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, lithium salts include _{LiPF 6, LiAsF 6, LiCF 3} SO 3, LiN (CF 3 SO 2) 2, LiBF 4, LiSbF 6, LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiClO _4, Li (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ) N and Li (SO ₂ F) ₂ N.

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.

≪ Production of cathode material slurry >

Example 1

As the positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was added in an amount of 61.6% by weight based on the total weight of the positive electrode active material, the conductive material and the binder, 26.4% by weight of LiMn ₂ O ₄ , 3.25% by weight of artificial graphite powder as a second conductive material, 5.5% by weight of polyvinylidene fluoride (PVdF) as a binder, 72.653 kg of N-methyl-2-pyrrolidone NMP) to prepare a positive electrode mixture slurry.

Comparative Example 1

Except that 6.5 wt% of the conductive black was added in an amount of 6.5 wt% and 89.286kg of N-methyl-2-pyrrolidone (NMP) was added as a solvent based on 100kg of the positive electrode active material. A mixture slurry was prepared.

<Experimental Example>

The solid content and viscosity of the prepared positive electrode mixture slurry were measured. The results are shown in Table 1.

The viscosity was measured at room temperature (23 캜) for 3 minutes at Brookfield LV2 +, 64Pin, 12 rpm.

Example 1 Comparative Example 1 Solids 61% 56% Viscosity 19576cP (22.8C) 22.175 (23.1 DEG C)

As described above, Example 1 in which the first conductive material and the second conductive material were charged had a higher solid content than Comparative Example 1 at 23 ° C (room temperature) and a higher solubility in the anode current collector It is possible to maintain a viscosity close to 20,000 cp, which is a level at which the polymer can be applied.

Claims (15)

1. A cathode slurry for a secondary battery comprising a cathode active material, a conductive material, a binder and a solvent,
The weight ratio of the cathode active material: the conductive material: the binder is 80 to 90 wt%: 4 to 10 wt%: 1 to 10 wt% based on the total weight of the cathode active material, the conductive material and the binder,
The weight of the solvent relative to the total weight of the cathode active material is 70 to 80 parts by weight,
Wherein the conductive material comprises a first conductive material and a second conductive material,
Wherein the first conductive material has an average particle size of 30 to 110 nm, the second conductive material has a spherical shape and an average particle size of 4 to 6 탆,
Wherein the cathode active material comprises a three-component lithium-containing metal oxide and a spinel-structure metal oxide,
Wherein the viscosity of the slurry of the cathode material is 15,000 to 30,000 cp and the solid content of the slurry of the cathode material is 60 to 65 wt% based on the total weight of the slurry of the cathode material. delete The method according to claim 1,
The three-component lithium-containing metal oxide is _one selected from the group consisting of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O _2, and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ Characterized in that the slurry of the cathode material is a secondary battery. The method according to claim 1,
Wherein the metal oxide of the spinel structure is LiMn ₂ O ₄ . The method according to claim 1,
Wherein the metal oxide of the spinel structure is contained in an amount of 50 to 70% by weight based on the total weight of the mixed cathode active material with the three-component lithium-containing metal oxide. The method according to claim 1,
Wherein the first conductive material is at least one selected from the group consisting of acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and denka black. The method of claim 6,
Wherein the first conductive material is denka black. delete The method according to claim 1,
Wherein the first conductive material is 2 to 5% by weight based on the total weight of the cathode active material, the conductive material, and the binder. The method according to claim 1,
And the second conductive material is a natural or artificial graphite powder. delete The method according to claim 1,
And the second conductive material is 2 to 5 wt% based on the total weight of the cathode active material, the conductive material, and the binder. delete A cathode material for a secondary battery comprising the slurry of the cathode material for a secondary battery according to any one of claims 1, 3 to 7, 9, 10 and 12. A lithium secondary battery comprising the cathode material for a secondary battery according to claim 14.