KR20210078747A - Separator for secondary battery comprising coating layers of carbon, secondary battery comprising the same, and method for preparing the secondary battery - Google Patents

Abstract

The present invention relates to a separator for a secondary battery including a graphite coating layer, a lithium ion secondary battery including the same, and a manufacturing method thereof, and more specifically, to a separator for a secondary battery, a lithium secondary battery including the same, and a manufacturing method thereof, wherein the separator for a secondary battery has a negative electrode-facing coating layer containing a negative electrode active material on the negative electrode-facing portion of the separator for a secondary battery, and has no positive electrode active material on a positive electrode-facing portion.

Description

A secondary battery separator comprising a graphite coating layer, a secondary battery comprising the same, and a manufacturing method thereof {Separator for secondary battery comprising coating layers of carbon, secondary battery comprising the same, and method for preparing the secondary battery}

The present invention relates to a separator for a secondary battery including a graphite coating layer, a secondary battery including the same, and a method for manufacturing the same. More specifically, a secondary battery separator comprising a coating layer containing a negative electrode active material on the negative electrode-facing portion of the secondary battery separator, and no positive electrode active material on the positive electrode-facing portion, a secondary battery including the same, and a method for manufacturing the same it's about

A lithium secondary battery is manufactured by mounting an electrode assembly capable of charging and discharging a positive electrode/separator/negative electrode structure in a battery case. The positive electrode and the negative electrode are prepared by coating a slurry containing an electrode active material on one or both surfaces of a metal current collector, drying and rolling. The separator includes a porous substrate or a coating layer on at least one surface of the porous substrate.

The separator separates the anode and the cathode to prevent an electrical short between the two electrodes while allowing electrolyte and ions to pass through. The separator itself does not participate in the electrochemical reaction of the battery, but is one of the important components that affect the performance and safety of the battery by physical properties such as electrolyte wettability and porosity.

In general, the unit cell 10 includes an anode having an anode active material layer 21 formed on at least one surface of the anode current collector 20 as shown in FIG. 1 ; separation membrane 30; and a positive electrode having a positive electrode current collector 41 formed on at least one surface of the positive electrode current collector 40 . In this case, the separator may have only a porous substrate as shown in FIG. 1 , and an inorganic coating layer may be formed on at least one surface of the porous substrate. The separator may cause separation of the separator from the negative electrode when an external impact occurs during the secondary battery manufacturing process or when using the secondary battery due to poor adhesion between the negative active material layer and the porous substrate or inorganic coating layer.

When charging a lithium ion secondary battery, since lithium ions move from the positive electrode to the negative electrode through the separator, the state in which the negative electrode and the separator are attached must be maintained for the movement of lithium ions.

In order to prevent an electrical short circuit between the separator and the negative electrode due to external impact and to improve ionic conductivity, various methods for increasing the adhesion between the separator and the negative electrode have been tried.

The simplest way to improve adhesion is to use a binder. A method of placing a binder layer on the cathode-facing surface of the separator may be considered. The amount of the binder may be increased in the binder layer, or a binder having strong adhesion may be used. The binder layer itself may act as a resistor, and as the amount of the binder increases, the overall capacity of the battery decreases.

In order to increase the adhesion between the negative electrode and the separator, a method of forming a negative electrode active material in two layers and disposing a material having good adhesion to the separator on the opposite side of the separator of the negative electrode may be considered. The method of forming the two layers of the active material is complicated, and the performance of the battery may be deteriorated due to the active material of the two layers having different configurations.

Patent Document 1 has a coating layer containing an active material corresponding to the electrode facing at least one of the surfaces facing each electrode of the separator, but the separator is directly coupled to the electrode current collector, so that the bonding force between the electrode current collector and the active material layer is not taken into account.

In the case of Patent Document 2, the same material as the electrode active material layer is included on the surface of the separator facing the electrode current collector active material layer, but the adhesive strength is improved for all electrodes without distinguishing between the positive electrode and the negative electrode, and the separator and the electrode Although the adhesion between the two and the safety due to external impact are improved, an adhesive layer is already formed on the positive electrode, which has excellent adhesion, so there is no consideration for the performance and capacity of the battery.

As such, it is necessary to consider a separator that improves the adhesion between each electrode and the separator to increase stability and thereby increases the performance and capacity of the battery.

Republic of Korea Patent Publication No. 2009-0012134 (2009.02.02) Republic of Korea Patent Publication No. 2014-0086066 (2014.07.08)

An object of the present invention is to provide a separator capable of improving battery performance by improving adhesion between an anode and a separator, a secondary battery including the same, and a method for manufacturing the same.

In order to solve the above problems, one aspect of the present invention is a porous substrate; In the separator for a secondary battery comprising a; a negative electrode facing coating layer formed on a portion facing the negative electrode active material layer of the porous substrate and comprising a negative electrode active material, the positive electrode active material is not added to the portion facing the positive electrode of the porous substrate for secondary batteries A separator is provided.

An inorganic coating layer that does not include a positive electrode active material may be added to a portion of the porous substrate facing the positive electrode.

A portion of the porous substrate facing the positive electrode may not have any coating layer added thereto.

The cathode-facing coating layer may be present in the inorganic coating layer or may be separately present on the inorganic coating layer.

The negative active material may include graphite such as natural graphite or artificial graphite; It may be at least one of carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber.

The negative electrode facing coating layer may include the same material as the negative electrode active material, or the negative electrode facing coating layer may be the same as the negative electrode active material layer.

Another aspect of the present invention is a positive electrode; Provided is a secondary battery comprising a negative electrode and a separator according to the present invention.

The combined thickness of the positive electrode active material layer facing the separator of the positive electrode, the negative active material layer facing the separator of the negative electrode, and the negative electrode facing coating layer of the separator may be the same.

The present invention comprises the steps of: S1) preparing a negative electrode and a positive electrode including an anode active material layer on the separator facing; S2) forming a negative electrode-facing coating layer comprising a negative electrode active material on the negative-electrode-facing surface of the separator porous substrate; S3) stacking the negative electrode and the separator positive electrode so that the negative electrode active material layer of the negative electrode and the separator negative electrode facing coating layer face each other, and then rolling.

In addition, the step of forming an inorganic coating layer on at least one surface of the porous substrate before the step S2); may further include.

The above components may be used in combination with each other as long as they do not conflict with each other.

The present invention improves the adhesion between the negative electrode and the separator by including the negative electrode active material in the negative electrode facing coating layer of the separator facing the negative electrode active material layer, and it is possible to obtain a separator with improved battery performance and capacity. In the present invention, the cathode active material is not added to the separator facing the cathode active material layer.

In addition, it is possible to improve the adhesion between the negative electrode and the separator by a simple process of including the negative active material in the coating layer of the separator, thereby simplifying the process of forming a laminate of the negative electrode, the separator, and the positive electrode, and reducing the defective rate when forming the laminate.

In addition, since the adhesion between the separator and the negative electrode is improved, the possibility of the separator being detached is reduced even when an external shock is applied, thereby improving the safety of the battery.

1 is a schematic view showing a negative electrode, a separator, and a positive electrode according to a first conventional example of the prior art.
2 is a schematic view showing a negative electrode, a separator, and a positive electrode according to a second conventional example of the prior art.
3 is a schematic diagram showing a negative electrode, a separator, and a positive electrode according to a first example of the present invention.
4 is a schematic view showing a separation membrane according to a second example of the present invention.
5 is a schematic view showing a separation membrane according to a third example of the present invention.
6 is a schematic view showing a separation membrane according to a fourth example of the present invention.

Hereinafter, embodiments in which those of ordinary skill in the art to which the present invention pertains can easily practice the present invention will be described in detail with reference to the accompanying drawings. However, when it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention in describing the operating principle of the preferred embodiment of the present invention in detail, the detailed description thereof will be omitted.

In addition, the same reference numerals are used throughout the drawings for parts having similar functions and functions. Throughout the specification, when a part is said to be connected to another part, this includes not only a case in which it is directly connected, but also a case in which it is indirectly connected with another element interposed therebetween. In addition, the inclusion of a certain component does not exclude other components unless otherwise stated, but means that other components may be further included.

Hereinafter, the present invention will be described in more detail for better understanding of the present invention. This is for the purpose of illustrating the present invention, and the scope of the present invention is not limited thereby.

The present invention relates to a separator for a secondary battery, the separator comprising: a porous substrate; It is formed on a portion of the porous substrate facing the negative electrode active material layer and includes a negative electrode facing coating layer including the negative electrode active material, and the positive electrode active material is not added to the portion facing the positive electrode of the porous substrate.

As the porous substrate, any porous substrate used in the separator of a battery may be used, but it is preferable to use a porous substrate having excellent ionic conductivity. In this case, the pore diameter of the porous substrate is generally 0.01 μm to 10 μm, and the thickness is generally 5 μm to 300 μm. Examples of the porous substrate include olefin-based polymers such as chemical-resistant and hydrophobic polypropylene; A sheet or nonwoven fabric made of glass fiber or polyethylene is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The anode active material layer may be formed on the anode current collector. The anode active material layer may be formed by applying a slurry including an anode active material, a conductive material, and a binder to one or both surfaces of the anode current collector. In this case, the negative electrode active material layer may be formed on the opposite side of the separator of the negative electrode current collector or on both sides of the negative electrode current collector. The negative electrode active material layer of the negative electrode is formed on the opposite side of the separator, and the negative electrode-facing coating layer including the negative electrode active material of the separator is disposed on the portion facing the negative electrode active material layer, so that the adhesion between the negative electrode and the separator is improved. .

The negative electrode current collector is generally made to have a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface. Carbon, nickel, titanium, a surface treated with silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

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

The conductive material is typically added in an amount of 0.1 to 30% by weight based on the total weight of the mixture including the negative active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The binder included in the negative electrode is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 0.1 to 30% by weight based on the total weight of the mixture including the negative active material. 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-butadiene rubber, fluororubber, and various copolymers. However, in order to prevent deterioration of the lithium secondary battery, it is preferable to use an aqueous binder such as styrene-butadiene rubber. When such an aqueous binder is used, the ratio of the active material per same volume increases, so that the battery performance improvement effect such as high capacity and long life can be obtained. However, since it is impossible to completely remove moisture when using an aqueous binder, it is difficult to use an aqueous binder when a metal is used as a current collector, such as a positive electrode. In addition, the positive active material does not dissolve well in water-based materials, and the negative active material dissolves well in water-based materials, and when considering the performance according to cost, a non-aqueous binder is used for the positive active material, and an aqueous binder is used for the negative active material. It is preferable to do

The anode active material included in the cathode-facing coating layer of the separator may include graphite such as natural graphite or artificial graphite; It may be at least one of carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber.

The negative active material present in the negative electrode facing coating layer may contain a material different from the negative active material present in the negative electrode active material layer, but preferably the same material is included. If a material different from that of the anode active material layer is included, the bonding strength with the anode active material layer may decrease, and when lithium ions move from the cathode through the separator to the anode current collector through the anode active material layer, a difference in resistance may occur. Therefore, it is preferable that they are the same material.

The negative electrode-facing coating layer may include a conductive material and a binder included in the negative electrode active material layer. The negative electrode-facing coating layer may include the same material as the negative electrode active material layer, and further may have the same composition as that of the negative electrode active material layer.

The cathode-facing coating layer may contain an inorganic material to improve the mechanical strength of the separator. The inorganic material is not particularly limited as long as the thickness of the coating layer is uniformly formed, and oxidation and/or reduction reactions do not occur in the operating voltage range of the applied secondary battery. In particular, when inorganic particles having an ion transport ability are used, the performance can be improved by increasing the ion conductivity in the electrochemical device. In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte.

_{Alumina (Al 2} O ₃ ) has been widely used as the inorganic material, but recently, a hydroxide of a metal or metal oxide may be used for the purpose of improving flame retardancy.

The metal hydroxide or metal hydrate is aluminum hydroxide (Al(OH) ₃ ), magnesium hydroxide (Mg(OH) ₂ ), aluminum oxyhydroxide (AlO(OH)), CaO??Al ₂ O ₃ ??6H2O in The selected one may be aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, nickel hydroxide, boron hydroxide, or a combination of two or more thereof.

The type of the metal oxide is not particularly limited, and for example, the metal oxide is selected from the group consisting of a metal oxide having a dielectric constant of 5 or more, a metal oxide having piezoelectricity, and a metal oxide having a lithium ion transport ability. More than one species can be used.

The metal oxide having a dielectric constant of 5 or more may be SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ or TiO ₂ .

In the metal oxide having piezoelectricity, a potential difference is formed due to positive and negative charges generated between both sides of the particle when a constant pressure is applied, BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La 1 selected from the group consisting of _x Zr _1-y Ti _y O ₃ (PLZT), Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO _{2 ), or mixtures thereof} may be more than one species.

The metal oxide having the lithium ion transport ability contains a lithium element, but moves lithium ions without storing lithium, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0<x<2, 0<y<1, 0<z<3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ such as (LiAlTiP) _x O _y based glass (0<x<4, 0<y<13), lithium lanthanide titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), lithium germanium thiophosphate such as _{Li 3.25} Ge _0.25 P _0.75 S _{4 (Li x} Ge _y P _z S _w , 0<x<4, 0<y It may be at least one selected from the group consisting of <1, 0<z<1, 0<w<5) or a mixture thereof.

Additionally, in addition to the metal oxide, lithium nitride such as _{Li 3 N (Li x} N _y , 0<x<4, 0<y<2), Li ₃ PO ₄ -Li ₂ S-SiS _{2 SiS 2} series glass such as (Li _x Si _y S _z , 0<x<3, 0<y<2, 0<z<4), _{P 2} S ₅ series glass such as _{LiI-Li 2} SP ₂ S _{5 (Li x} P _y S _z , 0<x<3, 0<y<3, 0<z<7) or a mixture thereof may further include one or more selected from the group consisting of.

3 shows a unit cell 100 including a negative electrode, a separator, and a positive electrode according to a first example of the present invention.

The positive electrode according to the present invention uses a metal such as stainless steel, aluminum, nickel, titanium, and a surface treatment of aluminum or stainless steel with carbon, nickel, titanium or silver as a positive electrode current collector. Among them, aluminum is the most preferred.

The positive electrode active material used for the positive electrode active material includes, for example, _{a layered compound such as lithium nickel oxide (LiNiO 2} ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; _{LiMn 2} O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ It may be configured, and the like, but is not limited thereto.

The conductive material used for the positive electrode is the same as the type of the conductive material used for the negative electrode. The conductive material used for the positive electrode may be of the same type as the binder used for the negative electrode, but considering that the positive electrode current collector is a metal, the positive electrode active material does not dissolve well in water-based materials, and the presence of metal elements in the active material A non-aqueous binder is more preferable than an aqueous binder.

2 is a schematic diagram showing a unit cell 10 including a negative electrode, a separator, and a positive electrode according to a second conventional example of the prior art. The separator according to the second conventional example has a cathode-facing coating layer 31 including a cathode active material on the cathode-facing surface of the porous substrate 30, and a cathode-facing coating layer 32 comprising a cathode active material on the cathode-facing surface. . In addition, the negative electrode active material layer 21 is provided on the opposite side of the separator of the negative electrode current collector 20 , and the positive electrode active material layer 41 is on the opposite side of the separator of the positive electrode current collector 40 .

However, in the negative electrode, the separator, and the positive electrode according to the first example of the present invention, no coating layer is added to the portion of the porous substrate 300 facing the positive electrode, unlike the separator of the second conventional example. A negative electrode facing coating layer 310 including a negative electrode active material is provided on the negative electrode side. This is because, due to the adhesiveness of the non-aqueous binder used for the positive electrode active material layer, when a coating layer including the positive electrode active material is formed on the positive electrode facing surface, pores of the separator are clogged, thereby reducing the performance of the battery. In this case, the negative electrode includes the negative active material layer 210 on the separator facing the negative electrode current collector 200 , and the positive electrode includes the positive electrode active material layer 310 on the separator facing the positive electrode current collector 300 .

4 is a schematic diagram showing a separation membrane according to a second example of the present invention, FIG. 5 is a third example of the present invention, and FIG. 6 is a fourth example of the present invention.

Unlike the separator of the first example, the second example shows a separator in which an inorganic coating layer 320 is further added between the anode-facing coating layer 310 including the anode active material and the porous substrate 300 .

The third example shows a separator in which an inorganic coating layer 320 is further added to the anode-facing surface of the separator of the first example.

The fourth example shows a separator in which an inorganic coating layer 320 is further added to the anode-facing surface of the separator of the second example.

At this time, a binder layer may be added between the negative electrode-facing active material layer of the separator and the active material layer of the negative electrode, but since the binder itself acts as a resistance, it is preferably not added separately.

A portion of the porous substrate facing the positive electrode may be formed of only the porous substrate as in the first or second example of FIG. 3 or FIG. 4 . When the portion facing the positive electrode consists of only the porous substrate, the separator substrate itself may directly face the positive electrode current collector or the positive electrode active material layer of the positive electrode.

The inorganic coating layer may be formed on at least one surface of the porous substrate. The inorganic coating layer may be added to supplement the physical properties of the porous substrate. The inorganic material included in the inorganic material coating layer is not particularly limited as long as it forms a uniform thickness of the coating layer and does not cause oxidation and/or reduction reactions in the operating voltage range of the applied secondary battery. In particular, when inorganic particles having an ion transport ability are used, the performance can be improved by increasing the ion conductivity in the electrochemical device. In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte.

It can selectively use the same materials as the materials that can be used for the inorganic material that can be added to the above-mentioned cathode-facing coating layer.

As in the third example of FIG. 5 and the fourth example of FIG. 6 , only the inorganic coating layer 320 is present in the portion facing the anode to improve the physical performance of the separator. At this time, the inorganic coating layer should not contain a cathode active material.

When the inorganic coating layer is present on the negative electrode-facing portion, the inorganic coating layer may be present as a separate layer from the negative electrode-facing coating layer. This is to improve the performance of each layer by improving the physical performance of the separator with the inorganic coating layer and improving the adhesion between the anode and the separator by using the cathode-facing coating layer containing the anode active material.

At this time, it is preferable that the cathode-facing coating layer 310 is present on the inorganic coating layer 320 as in the second example of FIG. 4 and the fourth example of FIG. 6 so that the anode and the cathode-facing coating layer directly meet. .

The inorganic coating layer formed on the anode-facing surface and the cathode-facing surface of the porous substrate may include the same material, but may include different materials depending on the function required for each coating layer.

The present invention may be a secondary battery having the above-mentioned separator, a positive electrode, and a negative electrode including an anode active material layer on a surface facing the separator.

The secondary battery may be a unit cell having a structure in which a negative electrode, a separator, and a positive electrode are stacked, or a plurality of the unit cells may be stacked. In addition, the secondary battery can be used in a cylindrical secondary battery in which the negative electrode, the separator, and the positive electrode are formed in a roll shape, and can be used in all types of secondary batteries in which the negative electrode, the separator, and the positive electrode are combined.

The combined thickness of the positive electrode active material layer facing the separator of the positive electrode, the negative active material layer facing the separator of the negative electrode, and the negative electrode facing coating layer of the separator may be the same.

The thickness of the negative electrode active material layer facing the separator of the negative electrode and the coating layer facing the negative electrode of the separator are too thick, so that the same is preferable in order to secure the capacity according to the battery efficiency and the battery density.

There is no limitation on the thickness of the separator-facing negative electrode active material layer of the negative electrode and the negative electrode-facing coating layer of the separator, but the thickness of the negative electrode-facing separator-facing active material layer may be greater than or equal to the thickness of the negative electrode-facing coating layer of the separator. This is because it is difficult to form an excessively thick active material layer on the cathode-facing coating layer of the separator, and if a thick active material layer is formed, pores of the separator substrate may be blocked to reduce the function of the separator.

The thickness of the cathode-facing coating layer of the separator may be the same as or greater than the thickness of the inorganic coating layer formed on the anode-facing surface.

This is to keep the amount of active material of the positive active material layer of the positive electrode of the separator and the negative active material layer of the negative electrode to be similar.

The electrode assembly according to the present invention comprises the steps of: S1) preparing a negative electrode and a positive electrode including a negative electrode active material layer on at least a separator facing; S2) manufacturing a separation membrane according to the above substrate; S3 stacking the negative electrode active material layer of the negative electrode and the negative electrode facing coating layer of the separator facing each other, and then rolling the anode, separator, and positive electrode;

In step S1), the negative electrode including the negative electrode active material layer on the opposite side of the separator is generally formed by a method of forming the negative electrode. For example, a slurry in which an electrode active material is dispersed in a binder solution in which a binder is dissolved in a solvent is applied on a current collector, and the solvent is removed to prepare an electrode having an electrode active material layer. The binder and the electrode active material are the same as those mentioned above.

At this time, the solvent is, for example, but not limited to, acetone (acetone), tetrahydrofuran (tetrahydrofuran), methylene chloride (methylene chloride), chloroform (chloroform), dimethylformamide (dimethylformamide), N-methyl-2 -Pyrrolidone (Nmethyl-2-pyrrolidone, NMP), cyclohexane (cyclohexane), water or a mixture thereof, and the like. These solvents provide an appropriate level of viscosity so that the slurry application layer can be made at a desired level on the surface of the current collector.

As a method of removing the solvent, an oven or a heating chamber may be used in a temperature range in consideration of the medium atmospheric pressure of the solvent, and a method of leaving the solvent to volatilize by leaving it at room temperature is also possible. At this time, the temperature range may consider a temperature condition of 25 ° C. to 100 ° C. and a relative humidity of 40% or more.

In step S1), the electrode active material layer may be formed on the non-facing surface of the separator of the negative electrode current collector or on one or both sides of the positive electrode current collector in the same manner as described above.

In step S2), the step of forming the above-mentioned separation film may be performed.

The cathode-facing coating layer of the separator is formed by adding a coating composition including the anode active material and the binder to the solvent, distributing it on the separator substrate, and then uniformly dispersing it using a doctor blade or the like, die casting (Die casting), comma coating (Comma coating), a method such as screen printing (Screen printing) may be mentioned. In addition, after forming on a separate substrate, the slurry may be bonded to the separator substrate by pressing or lamination. In this case, the final coating thickness can be adjusted by adjusting the concentration of the solution or the number of coatings. In addition, it can be coated by applying the pre-dispersion solution itself. By applying the linear dispersion several times, it is possible to finally obtain a coating layer having a desired thickness.

In addition, a method of immersing the porous substrate in a coating composition including the negative active material and the binder or applying on the porous substrate may be used. A method of applying or coating may use a conventional coating method well known in the art.

The drying process may vary depending on the solvent used. For example, it is carried out in a vacuum oven at 50° C. to 200° C. As a drying method, the drying method by irradiation of warm air, hot air, low-humidity wind, vacuum drying, (far) infrared rays, an electron beam, etc. is mentioned, for example. Although it does not specifically limit about drying time, Usually, it is carried out in the range of 30 second - 24 hours.

After the drying process, a cooling process may be further included, and the cooling process may be slow cooling to room temperature so that the recrystallized structure of the binder is well formed.

An inorganic coating layer may be formed on one or both surfaces of the porous substrate by a method similar to the above. In this case, the positive electrode active material is not included in the inorganic coating layer.

It may further include; forming an inorganic coating layer on at least one surface of the porous substrate before the step S2).

The inorganic coating layer may be formed together when the cathode-facing coating layer is formed, or may be formed as a separate layer. In this case, as the inorganic material, the inorganic material according to the above description may be used. When the inorganic coating layer is formed as a separate layer from the cathode-facing coating layer, a method of applying the cathode-facing coating layer slurry after applying the slurry for forming the inorganic coating layer, the slurry for forming the inorganic coating layer and the cathode-facing coating layer slurry are applied at once It can go through various methods such as how to do it, and a drying step can be performed after each process or after all processes are finished. At this time, the drying method may also use the same drying method as above.

In this case, the timing of forming the cathode-facing inorganic coating layer and the forming timing of the anode-facing inorganic coating layer may be different from each other. After forming the negative electrode-facing inorganic material coating layer, the positive electrode-facing inorganic material coating layer may be formed when the negative electrode-facing active material coating layer is formed. This is to reduce unnecessary drying time of the anode facing inorganic coating layer.

In step S3), the negative electrode and the separator are arranged to face the separator-facing negative electrode active material layer of the negative electrode and the negative electrode-facing coating layer of the separator, and then go through a rolling process, and then, after laminating the positive electrode, a rolling process may be performed.

Alternatively, as described above, the negative electrode, the separator, and the positive electrode may be laminated in a unit cell unit or in the form of an electrode assembly in which all positive electrodes, a separator, and a positive electrode are laminated at once, and then the rolling process may be performed.

In addition, the cathode non-facing coating layer of the separator may be disposed to face the anode and then subjected to a rolling process, and then the anode may be laminated and then subjected to a rolling process.

At this time, the rolling temperature may be 90 ℃ to 130 ℃. Preferred temperatures are 100°C or 125°C. When the rolling temperature is less than 90 ° C., the adhesive force between the electrode and the separator does not reach the desired level, and when it exceeds 130 ° C., the performance of the binder is reduced and the adhesive force is reduced, and there is a risk of deformation of the separator. .

The rolling pressure may be about 1 to about 3 tons. At this time, the most preferred range may be about 1.5 to about 2 tons. If the pressure during rolling exceeds 3 tons, it may cause damage such as tearing of the separator, and when the pressure is less than 1 ton during rolling, it is not possible to obtain a desired level of adhesion between the electrode and the separator.

During rolling, the rolling time may be about 1 to about 3 minutes. At this time, the most preferred range may be about 1.5 to about 2.5 minutes. If the rolling time exceeds 3 minutes, structural deformation of the separator may be caused, and if the rolling time is less than 1 minute, the adhesion between the electrode and the separator may not be achieved at a desired level.

The present invention also provides a battery pack including a unit cell as a unit cell and a device including the battery pack as a power source. The unit cell of the present invention may itself be a power supply device used in a drone or a laptop computer, and may be used in the form of stacking unit cells. Specifically, the battery pack can be used as a power source for devices that require high temperature stability, long cycle characteristics, and high rate characteristics, and preferred examples of such devices include mobile electronic devices, wearable electronic devices, and battery-based motors. moving power tools; Electric vehicle (EV), hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (Plug-in Hybrid Electric Vehicle, PHEV) or power storage device, etc., but are limited thereto no.

Since the structures of these devices and their manufacturing methods are known in the art, detailed description thereof will be omitted herein.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily carry out. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Example 1

A negative electrode-facing coating layer containing graphite as an anode active material having a thickness of 20 μm was formed on the negative side of a polypropylene substrate (total thickness of 20 μm) having an SRS coating layer having a thickness of 5 μm on both sides.

The anode facing coating layer is formed by adding 94 wt% of graphite as an anode active material, 2 wt% of CMC, 2 wt% of SBR as a binder, and 2 wt% of carbon black as a conductive material, and forming the SRS coating layer in the form of a slurry. It was prepared as shown in FIG. 6 by coating it on a propylene substrate.

Example 2

In Example 1, a separator in which the thickness of the cathode-facing coating layer was changed to 10 μm was prepared.

Example 3

In Example 1, a separator in which the thickness of the cathode facing coating layer was changed to 30 μm was prepared.

Comparative Example 1

In Example 1, a separator without a cathode-facing coating layer was used as Comparative Example 1.

Comparative Example 2

In Example 1, a coating layer containing 90% by weight of LCO as a positive electrode active material, 6% by weight of PVdF as a binder, and 4% by weight of carbon black as a conductive material was applied on the positive electrode facing surface in the same manner as the negative electrode facing coating layer to a thickness of 20 μm. added.

Comparative Example 3

In Comparative Example 2, the separator without the cathode-facing coating layer was used as Comparative Example 3.

Evaluation of adhesion between electrode and separator

The positive electrode active material layer contains 90% by weight of positive electrode active material LCO, 6% by weight of binder PVdF, and 4% by weight of conductive carbon black, and 94% by weight of graphite as negative electrode active material in the negative active material layer, 2% by weight of binder CMC, 2% by weight of SBR %, an anode containing 2 wt% of carbon black as a conductive material, and separators according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared.

The prepared negative electrode and separator were cut to a size of 15 mm X 100 mm. After overlapping the prepared separator and the negative electrode, they were sandwiched between 100 μm PET films and adhered using a flat plate press. At this time, the conditions of the flat press machine were heated for 1 second at a pressure of 8.5 MPa at 90 °C. After attaching the distal end of the bonded separator and the negative electrode to UTM equipment (LLOYD Instrument LF Plus), a force was applied at 180 degrees at a measurement speed of 300 mm/min to measure the force required to peel the negative electrode facing coating layer of the negative electrode and the separator. The above experiment was performed in the same manner for the positive electrode.

The results are shown in the table below.

As can be seen in Table 1, Examples 1 to 3 and Comparative Example 2 have excellent adhesion because the negative electrode active material is added to the negative electrode facing surface of the separator. In addition, in Comparative Examples 2 and 3 in which the positive electrode active material is added to the positive electrode facing surface, it can be seen that the adhesive strength of the positive electrode facing coating layer is excellent.

Evaluation of air permeability of the separator

The air permeability was measured using the separation membranes according to Examples 1 to 3 and Comparative Examples 1 to 3. At this time, according to JIS P-8117, it measured using the Gurley type air permeability meter. At this time, the time for 100 cc of air to pass through a diameter of 28.6 mm and an area of 645 mm 2 was measured.

As a result of the measurement, Example 1 is 610s/100cc, Example 2 is 600s/100cc, Example 3 is 700s/100cc, Comparative Example 1 is 570s/100cc, Comparative Example 2 is 1120s/100ml, Comparative Example 3 was measured as 1040s/100ml. Accordingly, in the case of the present invention in which the cathode-facing coating layer is formed, there is no significant difference in air permeability compared to the case of using only the separator substrate, but when the coating layer including the cathode active material is formed on the cathode-facing surface, the air permeability is significantly reduced. . When this is applied to an actual battery, it can be seen that the separator according to the present invention is superior to those of Comparative Examples 2 and 3 in consideration of electrolyte movement and ionic conductivity.

When compared with the result of the adhesion between the electrode and the separator, when the adhesion of the separator is too high, it can be determined that the pores of the separator substrate are blocked to reduce the air permeability of the separator.

Battery cell performance evaluation

Aluminum is used for the positive electrode current collector, the positive electrode active material layer contains 90% by weight of LCO, the binder PVdF 6% by weight, and the conductive material carbon black 4% by weight. Copper is used for the positive and negative electrode collectors, and the negative electrode active material is used for the negative electrode active material layer. A negative electrode containing graphite 94% by weight, binder CMC 2% by weight, SBR 2% by weight, and conductive carbon black 2% by weight, and separators according to Examples 1 to 3 and Comparative Examples 1 to 3 were prepared. The negative electrode, the separator, and the positive electrode were rolled at 90° C. under a pressure of 100 Mpa for 10 seconds to form a unit cell.

In order to equalize the amount of the positive active material in the unit cell, when the separators of Examples 1 to 3 and Comparative Example 1 are used, the thickness of the positive active material layer of the positive electrode is 60 μm, and the thickness of the positive active material layer of Comparative Examples 2 and 3 is 60 μm. The positive electrode active material layer of the positive electrode had a thickness of 40 μm, and the sum of the thickness of the positive electrode active material layer of the unit cell and the positive electrode facing coating layer including the active material was set to be equal to 60 μm.

In addition, in order to equalize the amount of the negative active material in the unit cell, the thickness of the negative active material layer of the negative electrode was 50 μm in Examples 1 and 2, 60 μm in Example 2, and 60 μm in Example 3 In the case of 40 μm, Comparative Examples 1 and 3, the thickness of the negative electrode active material layer used in the unit cell and the negative electrode facing coating layer including the active material was set equal to 70 μm.

(1) Evaluation of charging time

The charging time was measured at 25° C. until it was fully charged at 3 C, and is shown in Table 2 below.

(2) Capacity retention rate

Charged at 25°C until 2C, 4.4V, and discharged at a constant current of 1C until 3.0V to perform 100 charge/discharge cycles, and the discharge capacity after 1 cycle and the discharge capacity after 100 cycles were measured. Then, the capacity retention rate was measured according to Equation (1) below and shown in Table 2 below.

Equation (1): Capacity retention rate (%) = {Discharge capacity after ( ) cycle / Discharge capacity after 1 cycle}X100

As shown in Table 2, in the case of Examples 1 and 2 according to the present invention, the charging time was as short as 32 minutes, and the capacity retention rate was also 97%, showing a very excellent effect, and in the case of Example 3, the charging time was It can be seen that 36 minutes, the capacity retention rate is 94%, which shows an excellent effect compared to the comparative example.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby, and the scope of the present invention is not limited thereto. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and it is natural that such variations and modifications belong to the appended claims.

10, 100: unit cell
20, 200: negative electrode current collector
21, 210: anode active material layer
30, 300: porous substrate
31, 310: cathode facing coating layer
32: anode facing coating layer
320: inorganic coating layer
40, 400: positive electrode current collector
41, 410: positive electrode active material layer

Claims (12)

porous substrate;
a negative electrode facing coating layer formed on a portion facing the negative electrode active material layer of the porous substrate and including the negative electrode active material;
In the secondary battery separator comprising a,
A separator for a secondary battery in which a positive electrode active material is not added to a portion of the porous substrate facing the positive electrode. According to claim 1,
A secondary battery separator having an inorganic coating layer that does not include a cathode active material is added to a portion of the porous substrate facing the cathode. According to claim 1,
A secondary battery separator in which no coating layer is added to a portion of the porous substrate facing the positive electrode. According to claim 1,
The cathode-facing coating layer is a secondary battery separator present in the inorganic coating layer. According to claim 1,
The cathode-facing coating layer is a separator for a secondary battery that is separately present on the inorganic coating layer. According to claim 1,
The negative active material may include graphite such as natural graphite or artificial graphite; A separator for secondary batteries of at least one of carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber. According to claim 1,
The negative electrode facing coating layer is a secondary battery separator comprising the same material as the negative electrode active material of the negative electrode. 8. The method of claim 7,
The negative electrode facing coating layer is the same as the negative electrode active material layer for a secondary battery separator. anode;
cathode;
The separator according to any one of claims 1 to 8 interposed between the positive electrode and the negative electrode;
A secondary battery comprising a. 10. The method of claim 9,
A secondary battery having the same thickness as the positive electrode active material layer facing the separator of the positive electrode, the negative active material layer facing the separator of the negative electrode, and the coating layer facing the negative electrode of the separator. S1) preparing a negative electrode and a positive electrode including an anode active material layer on the opposite side of the separator;
S2) A step of manufacturing the separation membrane according to any one of claims 1 to 8
S3) stacking a negative electrode, a separator, and a positive electrode so that the negative electrode active material layer of the negative electrode and the negative electrode facing coating layer of the separator face each other, and then rolling. 12. The method of claim 11,
The method of manufacturing an electrode assembly further comprising; forming an inorganic coating layer on at least one surface of the porous substrate before step S2).

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