KR102803199B1 - 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 secondary battery separator including a graphite coating layer, a lithium ion secondary battery including the same, and a method for manufacturing the same. More specifically, the present invention relates to a secondary battery separator characterized in that an anode-facing coating layer including a cathode active material is present on a cathode-facing portion of the secondary battery separator and a cathode-facing portion does not include a cathode active material, a lithium secondary battery including the same, and a method for manufacturing the same.

Description

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 secondary battery separator including a graphite coating layer, a secondary battery including the same, and a method for manufacturing the same. More specifically, the present invention relates to a secondary battery separator characterized in that a coating layer including a negative electrode active material exists on a negative electrode-facing portion of the secondary battery separator and a positive electrode-facing portion does not include a positive electrode active material, a secondary battery including the same, and a method for manufacturing the same.

Lithium secondary batteries are manufactured by mounting a rechargeable electrode assembly having a cathode/separator/negative electrode structure into a battery case. The cathode and anode are manufactured by applying a slurry containing an electrode active material to one or both sides of a metal current collector, drying, and rolling. The separator includes a porous substrate or a coating layer on at least one side of the porous substrate.

The separator isolates the positive and negative electrodes, preventing electrical short-circuiting 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 it is one of the important components that affects the performance and safety of the battery due to physical properties such as electrolyte wettability and porosity.

In general, a unit cell (10) is composed of a negative electrode having a negative active material layer (21) formed on at least one surface of a negative electrode current collector (20), as shown in FIG. 1; a separator (30); and a positive electrode having a positive electrode current collector (41) formed on at least one surface of a positive electrode current collector (40). At this time, the separator may only have a porous substrate, as shown in FIG. 1, or may have an inorganic coating layer formed on at least one surface of the porous substrate. If the adhesion between the negative electrode active material layer and the porous substrate or the inorganic coating layer of the separator is low, a phenomenon in which the separator and the negative electrode are separated may occur when an external impact occurs during the secondary battery manufacturing process or when the secondary battery is used.

When charging a lithium-ion secondary battery, lithium ions move from the positive electrode through the separator to the negative electrode. Therefore, the negative electrode and separator must remain attached to allow the movement of lithium ions.

To prevent electrical short-circuiting between the separator and the cathode due to external impact and to improve ionic conductivity, various methods are being attempted to increase the adhesive strength between the separator and the cathode.

The simplest way to improve adhesion is to use a binder. A method of placing a binder layer on the cathode surface of the separator can be considered. The amount of binder in the binder layer can be increased, or a binder with strong adhesion can be used. The binder layer itself can act as a resistor, and as the amount of binder used increases, the capacity of the entire battery decreases, which is a problem.

In order to increase the adhesive strength between the negative electrode and the separator, a method of forming the negative electrode active material in two layers and placing a material with good adhesive strength with the separator on the surface of the negative electrode facing the separator can also be considered. The method of forming two layers of active materials is complicated in its process, and the performance of the battery may be reduced due to the two layers of active materials having different compositions.

Patent Document 1 has a coating layer including 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 bonded to the electrode current collector, and the bonding force between the electrode current collector and the active material layer is not considered.

In the case of patent document 2, the surface of the separator facing the electrode current collector active material layer contains the same material as the electrode active material layer, but the adhesive strength is improved for all electrodes without distinguishing between the positive and negative electrodes, thereby improving the adhesive strength between the separator and the electrode and safety against external impact, but since an adhesive layer is formed even on the positive electrode, which already has excellent adhesive strength, there is no consideration for the performance and capacity of the battery.

In this way, it is necessary to consider a separator that improves the adhesion between each electrode and the separator to increase stability and thereby increase 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 (July 8, 2014)

The present invention is intended to solve the above problems, and aims to provide a separator capable of improving the performance of a battery by enhancing the adhesive strength between a cathode 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 provides a secondary battery separator including a porous substrate; an anode-facing coating layer formed on a portion of the porous substrate facing a cathode active material layer and including a cathode active material; wherein the cathode active material is not added to a portion of the porous substrate facing a cathode.

A portion of the above porous substrate facing the anode may have an inorganic coating layer added that does not contain a cathode active material.

The portion of the above porous substrate facing the anode may not have any coating layer added.

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

The above negative active material may be at least one of graphite such as natural graphite or artificial graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and the like.

The above cathode-facing coating layer may contain the same material as the cathode active material, or the above cathode-facing coating layer may be the same as the cathode active material layer.

Another aspect of the present invention provides a secondary battery including a positive electrode, 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 electrode active material layer facing the separator of the negative electrode, and the negative electrode coating layer of the separator may be the same.

The present invention may be a method for manufacturing an electrode assembly, including the steps of S1) preparing a cathode and anode including a cathode active material layer on a separator surface; S2) forming a cathode-facing coating layer including a cathode active material on the cathode-facing surface of a porous substrate of a separator; and S3) laminating the cathode and the separator anode so that the cathode active material layer of the cathode and the separator cathode-facing coating layer face each other and then rolling.

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

The above configurations can be used in combination 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 a negative electrode active material in the negative electrode-facing coating layer of the separator facing the negative electrode active material layer, and can obtain a separator with improved performance and capacity of the battery. In the present invention, the positive electrode active material is not added to the separator facing the positive electrode active material layer.

In addition, the adhesion between the negative electrode and the separator can be improved through a simple process of including a negative electrode active material in the coating layer of the separator, thereby simplifying the process of forming a laminate of the negative electrode, separator, and positive electrode, and reducing the defect rate during the formation of the laminate.

In addition, the adhesion between the separator and the cathode is improved, so the possibility of the separator detaching even when external impact is applied is reduced, thereby improving the safety of the battery.

Figure 1 is a schematic diagram showing a cathode, a separator, and an anode according to a first conventional example of the prior art.
Figure 2 is a schematic diagram showing a cathode, a separator, and an anode according to a second conventional example of the prior art.
Figure 3 is a schematic diagram showing a cathode, a separator, and an anode according to the first example of the present invention.
Figure 4 is a schematic diagram showing a separation membrane according to a second example of the present invention.
Figure 5 is a schematic diagram showing a separation membrane according to a third example of the present invention.
Figure 6 is a schematic diagram showing a separation membrane according to the fourth example of the present invention.

Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those with ordinary knowledge in the technical field to which the present invention pertains can easily practice the present invention. However, when describing the operating principle of a preferred embodiment of the present invention in detail, if it is determined that a specific description of a related known function or configuration may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

Also, the same drawing symbols are used for parts that have similar functions and actions throughout the drawings. Throughout the specification, when a part is said to be connected to another part, this includes not only cases where it is directly connected, but also cases where it is indirectly connected with other elements in between. Also, including a certain component does not mean excluding other components unless specifically stated otherwise, but rather means that other components can be included.

In order to help understand the present invention, the present invention will be described in more detail below. This is intended to be an example of 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, wherein the separator comprises: a porous substrate; an anode-facing coating layer formed on a portion of the porous substrate facing a cathode active material layer and containing a cathode active material; and a cathode active material is not added to a portion of the porous substrate facing a cathode.

The porous substrate may be any porous substrate used for a battery separator, but it is preferable to use a porous substrate having excellent ion conductivity. At this time, 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. As such a porous substrate, for example, a chemically resistant and hydrophobic olefin polymer such as polypropylene; a sheet or nonwoven fabric made of glass fiber or polyethylene; or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.

The negative active material layer may be formed on the negative electrode current collector. The negative electrode active material layer may be formed by applying a slurry containing a negative electrode active material, a conductive material, and a binder to one side or both sides of the negative electrode current collector. At this time, the negative electrode active material layer may be formed on the separator-facing side of the negative electrode current collector, or may be formed on both sides of the negative electrode current collector. The negative electrode active material layer of the negative electrode is formed on the separator-facing side, and the negative electrode-facing coating layer containing the negative electrode active material of the separator is formed on a portion facing the negative electrode active material layer, so that the adhesive force between the negative electrode and the separator is improved.

The above negative electrode current collector is generally made with a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the surface may be formed with fine unevenness to strengthen the bonding strength of the negative electrode active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric.

Examples of the negative active material include carbon such as non-graphitizable carbon and graphite carbon; metal composite oxides such as 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': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; Metal oxides such as 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 Bi ₂ O ₅ ; conductive polymers such as polyacetylene ; Li-Co-Ni based materials, etc. can be used.

The conductive agent is typically added in an amount of 0.1 to 30 wt% based on the total weight of the mixture including the negative active material. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and 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, summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

The binder included in the above negative electrode is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 0.1 to 30 wt% based on the total weight of the mixture including the negative electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like. However, it is preferable to use an aqueous binder such as styrene-butadiene rubber in order to prevent deterioration of the lithium secondary battery. When such an aqueous binder is used, the ratio of the active material per same volume increases, so that the battery performance, such as high capacity and long life, can be improved. However, since it is impossible to completely remove moisture when using an aqueous binder, it is difficult to use an aqueous binder when using a metal as a current collector, such as a positive electrode. In addition, considering that positive electrode active materials do not dissolve well in aqueous substances and negative electrode active materials dissolve well in aqueous substances, and considering performance according to cost, it is preferable to use a non-aqueous binder for positive electrode active materials and an aqueous binder for negative electrode active materials.

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

The negative active material present in the negative electrode-facing coating layer may contain a different material from the negative active material present in the negative electrode active material layer, but it is preferable that it contains the same material. If it contains a different material from the negative electrode active material layer, the bonding strength with the negative electrode active material layer may be reduced, and when lithium ions move from the positive electrode through the separator to the negative electrode current collector through the negative electrode active material layer, a difference in resistance may occur, so it is preferable that it contains the same material.

The above-mentioned cathode-facing coating layer may contain a conductive material and a binder included in the cathode active material layer. The above-mentioned cathode-facing coating layer may contain the same material as the cathode active material layer, and further may have the same composition as the composition of the cathode active material layer.

The cathode-facing coating layer may contain an inorganic substance to improve the mechanical strength of the separator. The inorganic substance is not particularly limited as long as it forms a uniform thickness of the coating layer and does not cause an oxidation and/or reduction reaction in the operating voltage range of the applied secondary battery. In particular, when an inorganic particle having an ion transfer capability is used, the ion conductivity within the electrochemical device can be increased, thereby improving performance. In addition, when an inorganic particle having a high permittivity is used as the inorganic particle, the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte can be increased, thereby improving the ion conductivity of the electrolyte.

Alumina (Al ₂ O ₃ ) has been widely used as the above-mentioned inorganic material, but recently, metal or metal oxide hydroxides can also be used for the purpose of improving flame retardancy.

The above metal hydroxide or metal hydrate may be selected from aluminum hydroxide (Al(OH) ₃ ), magnesium hydroxide (Mg(OH) ₂ ), aluminum oxyhydroxide (AlO(OH)), CaO?? _Al2O3 ?? _6H2O , or 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 may be at least one 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 lithium ion transfer capability.

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 .

The above piezoelectric metal oxide forms a potential difference due to positive and negative charges generated between both sides of the particle when a certain pressure is applied, and may be at least one selected from the group consisting of BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _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 a mixture thereof.

The metal oxide having the lithium ion transport capability contains a lithium element, but moves lithium ions without storing lithium, and includes 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), (LiAlTiP) _x O _y series glass (0<x<4, 0<y<13) such as 14Li ₂ O -9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ ), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), Li _3.25 Ge _0.25 P _0.75 S ₄ , and It may be at least one selected from the group consisting of lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0<x<4, 0<y<1, 0<z<1, 0<w<5) or mixtures thereof.

Additionally, in addition to the metal oxide, the composition may further include at least one selected from the group consisting of lithium nitride such as Li _{3 N} (Li _x N _y , 0<x<4, 0<y<2), SiS ₂ series glass such as Li 3 PO ₄ -Li ₂ S-SiS ₂ (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 mixtures thereof.

FIG. 3 shows a unit cell (100) including a cathode, a separator, and an anode according to the first example of the present invention.

The anode according to the present invention uses a metal such as stainless steel, aluminum, nickel, titanium, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver as the anode current collector. Among these, aluminum is most preferred.

The cathode active material used in the cathode 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 LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ having the chemical formula Li _1+x Mn _2-x O ₄ (wherein, x is 0 to 0.33); 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 expressed by the chemical 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); A lithium manganese composite oxide represented by the chemical formula LiMn _2-x M _x O ₂ (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein, M = Fe, Co, Ni, Cu or Zn); LiMn ₂ O ₄ in which a part of the Li in the chemical formula is replaced with an alkaline earth metal ion; a disulfide compound; Fe ₂ (MoO ₄ ) ₃ , etc., but is not limited thereto.

The conductive material used in the positive electrode is of the same type as the conductive material used in the negative electrode. The conductive material used in the positive electrode can be of the same type as the binder used in the negative electrode. However, considering that the positive electrode current collector is made of metal, the positive electrode active material does not dissolve well in aqueous substances, and the presence of metal elements in the active material, a non-aqueous binder is more preferable than an aqueous binder.

FIG. 2 is a schematic diagram showing a unit cell (10) including a cathode, a separator, and an anode according to a second conventional example, which is a prior art. The separator according to the second conventional example has an anode-facing coating layer (31) including a cathode active material on the cathode surface of a porous substrate (30), and an anode-facing coating layer (32) including a cathode active material on the cathode surface. In addition, an anode active material layer (21) is included on the separator surface of the cathode current collector (20), and an anode active material layer (41) is included on the separator surface of the cathode current collector (40).

However, unlike the separator of the second conventional example, the negative electrode, separator, and positive electrode according to the first example of the present invention do not have any coating layer added to the portion of the porous substrate (300) facing the positive electrode. The negative electrode surface has a negative electrode surface coating layer (310) including a negative electrode active material. This is because, due to the adhesiveness of the non-aqueous binder used in the positive electrode active material layer, if a coating layer including a positive electrode active material is formed on the positive electrode surface, the pores of the separator may be blocked, thereby reducing the performance of the battery. At this time, the negative electrode includes a negative electrode active material layer (210) on the separator surface of the negative electrode current collector (200), and the positive electrode includes a positive electrode active material layer (310) on the separator surface of the positive electrode current collector (300).

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

The second example shows a separator in which, unlike the separator of the first example, an inorganic coating layer (320) is additionally added between the cathode-facing coating layer (310) containing a cathode 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 surface of the separator of the first example.

Example 4 shows a separator in which an inorganic coating layer (320) is further added to the anode surface of the separator of Example 2.

At this time, a binder layer may be added between the cathode-facing active material layer of the separator and the cathode active material layer, but it is preferable not to add it separately because the binder itself acts as resistance.

Among the above porous substrates, the portion facing the positive electrode may be composed solely of the porous substrate, as in the first or second example of Fig. 3 or Fig. 4. When the portion facing the positive electrode is composed solely of 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 above 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 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 within the operating voltage range of the applied secondary battery. In particular, when inorganic particles having ion transfer capability are used, the ion conductivity within the electrochemical device can be increased, thereby improving performance. In addition, when inorganic particles having a high permittivity are used as the inorganic particles, the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte can be increased, thereby improving the ion conductivity of the electrolyte.

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

As in the third example of Fig. 5 and the fourth example of Fig. 6, only an inorganic coating layer (320) is present on the portion facing the anode, thereby improving the physical performance of the separator. At this time, the inorganic coating layer must not contain a cathode active material.

When an inorganic coating layer exists on the cathode-facing surface, the inorganic coating layer may exist as a separate layer from the cathode-facing coating layer. This is to improve the physical performance of the separator by using the inorganic coating layer, and to improve the adhesion between the cathode and the separator by using the cathode-facing coating layer containing the cathode active material, thereby improving the performance of each layer.

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

The inorganic coating layers formed on the anode and cathode surfaces of the above porous substrate may contain the same material, but may also contain different materials depending on the function required for each coating layer.

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

The secondary battery may be a unit cell having a structure in which a cathode, a separator, and anode are laminated, and may also be in a form in which multiple unit cells are laminated. In addition, the secondary battery may be used in a cylindrical secondary battery in which the cathode, separator, and anode are formed in a roll shape, and may be used in all forms of secondary batteries in which the cathode, separator, and anode are combined and exist.

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

This is because the thickness of the negative electrode active material layer facing the separator of the cathode and the thickness of the negative electrode coating layer of the separator are too thick, so it is desirable that they be the same in order to secure the capacity according to the efficiency and battery density of the battery.

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

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

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

The electrode assembly according to the present invention may be produced by the steps of S1) preparing a cathode and an anode including a cathode active material layer at least on a separator surface; S2) manufacturing a separator according to the above description; S3) laminating the cathode, separator, and anode so that the cathode active material layer of the cathode and the cathode-facing coating layer of the separator face each other and then rolling.

In step S1), the negative electrode including the negative active material layer on the surface of the separator is generally formed by a method for 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 onto a current collector, and the solvent is removed to manufacture an electrode having an electrode active material layer formed thereon. The binder and the electrode active material are the same as the materials mentioned above.

At this time, the solvent may include, but is not limited to, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water or a mixture thereof. These solvents provide an appropriate level of viscosity so that a slurry coating layer can be formed on the collector surface at a desired level.

The method for removing the above solvent can be done by using an oven or a heating chamber in a temperature range that takes into account the medium pressure of the solvent, or by leaving it at room temperature to allow the solvent to evaporate. At this time, the temperature range can be considered to be a temperature condition of 25°C to 100°C and a relative humidity of 40% or higher.

In the above step S1), an electrode active material layer can be formed on the non-face-to-face separator surface of the negative current collector or on one or both sides of the positive current collector by the same method as above.

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

The cathode-facing coating layer of the separator can be formed by a method in which a slurry is made by adding a coating composition containing the cathode active material and the binder to the solvent, distributing the slurry over a separator substrate, and uniformly dispersing it using a doctor blade or the like, die casting, comma coating, screen printing, etc. In addition, the slurry can be formed on a separate substrate and then bonded to the separator substrate by a pressing or lamination method. At this time, the final coating thickness can be controlled by adjusting the concentration of the solution or the number of coatings. In addition, the coating can be formed by applying the pre-dispersion liquid itself. The pre-dispersion liquid can be applied multiple times to obtain a final coating layer having a desired thickness.

In addition, a method of immersing the porous substrate in a coating composition containing the negative active material and binder or applying the composition onto the porous substrate can be used. A conventional coating method widely known in the art can be used for the method of applying or coating.

The drying process may vary depending on the solvent used. For example, it is performed in a vacuum oven at 50°C to 200°C. As a drying method, for example, drying by hot air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams may be mentioned. There is no particular limitation on the drying time, but it is usually performed in the range of 30 seconds to 24 hours.

After the above 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 can be formed on one or both sides of the porous substrate in a similar manner as described above. At this time, the inorganic coating layer does not contain a cathode active material.

The method may further include forming an inorganic coating layer on at least one surface of the porous substrate prior to the step S2).

The above inorganic coating layer may be formed together with the formation of the cathode-facing coating layer, or may be formed as a separate layer. At this time, the inorganic material may be an inorganic material according to the above description. When the inorganic coating layer is formed as a separate layer from the cathode-facing coating layer, various methods may be used, such as a method of applying slurry for forming the inorganic coating layer and then applying the cathode-facing coating layer slurry, a method of applying the slurry for forming the inorganic coating layer and the cathode-facing coating layer slurry at the same time, and a drying step may be performed after each process or after all processes are completed. At this time, the drying method may also use the same drying method as above.

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

In step S3), the cathode and the separator are arranged so that the cathode active material layer of the cathode and the cathode coating layer of the separator face each other, and then a rolling process is performed, and then the cathode is laminated and then a rolling process is performed.

Alternatively, as described above, the cathode, separator, and anode may be laminated in unit cell units or in the form of an electrode assembly in which all the cathodes, separators, and anodes are laminated at once, and then subjected to a rolling process.

In addition, the cathode non-face-to-face coating layer of the separator may be placed so as to face the anode, and then subjected to a rolling process, after which the cathode is laminated and then subjected to a rolling process.

At this time, the rolling temperature may be 90°C to 130°C. The preferred temperature is 100°C or 125°C. If the rolling temperature is less than 90°C, the adhesive strength between the electrode and the separator does not reach the desired level, and if it exceeds 130°C, the performance of the binder decreases, the adhesive strength decreases, and there is a risk that the separator may be deformed, which is not preferred.

The pressure during rolling may be about 1 to about 3 tons. At this time, the most preferable range may be about 1.5 to about 2 tons. If the pressure during rolling exceeds 3 tons, damage such as tearing of the separator may occur, and if the pressure during rolling is less than 1 ton, the desired level of adhesive strength between the electrode and the separator cannot be obtained.

The rolling time during rolling may be about 1 to about 3 minutes. At this time, the most preferable range may be about 1.5 to about 2.5 minutes. If the rolling time exceeds 3 minutes, structural deformation of the separator may occur, and if the rolling time is less than 1 minute, the adhesive strength between the electrode and the separator is not achieved at the desired level.

The present invention also provides a battery pack including unit cells as unit cells and a device including the battery pack as a power source. The unit cell of the present invention can be a power supply device used in a drone or a laptop by itself, and can be used in a form of stacking unit cells. Specifically, the battery pack can be used as a power source for a device requiring high-temperature safety, long cycle characteristics, and high-rate characteristics, and preferable examples of such devices include, but are not limited to, mobile electronic devices, wearable electronic devices, power tools powered by a battery-based motor; electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or power storage devices.

Since the structure of these devices and their manufacturing method are known in the art, a detailed description thereof is omitted in this specification.

Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the present invention pertains can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

Example 1

A 20-μm-thick negative electrode surface coating layer containing graphite as a negative electrode active material was formed on the negative electrode surface of a polypropylene substrate (total thickness of 20 μm) on which a 5-μm-thick SRS coating layer was formed on each side.

The above cathode-facing coating layer was manufactured as shown in Fig. 6 by adding 94 wt% of graphite as a cathode active material, 2 wt% of CMC as a binder, 2 wt% of SBR, and 2 wt% of carbon black as a conductive material, forming it into a slurry, and then applying it to a polypropylene substrate on which the SRS coating layer was formed.

Example 2

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

Example 3

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

Comparative Example 1

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

Comparative Example 2

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

Comparative Example 3

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

Evaluation of adhesion between electrode and separator

A cathode comprising 90 wt% of cathode active material LCO, 6 wt% of binder PVdF, and 4 wt% of conductive material carbon black in the cathode active material layer, a cathode comprising 94 wt% of cathode active material graphite, 2 wt% of binder CMC, 2 wt% of SBR, and 2 wt% of conductive material carbon black in the anode active material layer, and a separator according to Examples 1 to 3 and Comparative Examples 1 to 3 were manufactured.

The above-mentioned manufactured cathode and separator were cut to a size of 15 mm X 100 mm. The prepared separator and cathode were overlapped, sandwiched between 100 μm PET films, and bonded using a flat plate press. At this time, the conditions of the flat plate press were heating at 90°C and 8.5 MPa of pressure for 1 second. After mounting the ends of the bonded separator and cathode on a UTM device (LLOYD Instrument LF Plus), a force of 180 degrees was applied at a measurement speed of 300 mm/min to measure the force required for the cathode-facing coating layer of the cathode and separator to peel off. The above experiment was also performed identically on the cathode.

The results are shown in the table below.

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

Evaluation of membrane permeability

The air permeability was measured using the membranes according to Examples 1 to 3 and Comparative Examples 1 to 3. At this time, the measurement was made using a Gurley-type air permeability meter according to JIS P-8117. At this time, the time for 100 cc of air to pass through a diameter of 28.6 mm and an area of 645 ㎟ was measured.

As a result of the above measurement, Example 1 was measured as 610 s/100 cc, Example 2 as 600 s/100 cc, Example 3 as 700 s/100 cc, Comparative Example 1 as 570 s/100 cc, Comparative Example 2 as 1120 s/100 ml, and Comparative Example 3 as 1040 s/100 ml. Accordingly, in the case of the present invention in which a coating layer is formed on the negative electrode surface, there is no significant difference in air permeability compared to the case in which only a separator substrate is used, but when a coating layer including a positive electrode active material is formed on the positive electrode surface, it can be seen that 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 Comparative Examples 2 and 3 in considering the movement of electrolyte and ion conductivity.

When compared with the results of the adhesion between the electrode and the separator, it can be judged that if the adhesion of the separator is too high, the pores of the separator substrate are blocked, reducing the air permeability of the separator.

Battery cell performance evaluation

A positive electrode comprising aluminum as a positive current collector, 90 wt% of positive active material LCO in a positive active material layer, 6 wt% of binder PVdF, and 4 wt% of conductive material carbon black, a negative electrode comprising copper as an anode current collector, 94 wt% of negative active material graphite in a negative active material layer, 2 wt% of binder CMC, 2 wt% of SBR, and 2 wt% of conductive material carbon black, and a separator according to Examples 1 to 3 and Comparative Examples 1 to 3 were manufactured. The negative electrode, separator, and positive electrode were rolled at 90°C and a pressure of 100 MPa for 10 seconds to form a unit cell.

In order to make the amount of positive electrode active material the same in the unit cell, when using the separators of Examples 1 to 3 and Comparative Example 1, the thickness of the positive electrode active material layer of the positive electrode was manufactured to be 60 μm, and the thickness of the positive electrode active material layer of the positive electrode of Comparative Examples 2 and 3 was manufactured to be 40 μm, so that the sum of the thicknesses 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 the same at 60 μm.

In addition, in order to make the amount of the negative active material the same in the unit cell, the thickness of the negative active material layer of the negative electrode was set to 50 ㎛ in Example 1 and Comparative Example 2, 60 ㎛ in Example 2, 40 ㎛ in Example 3, and 70 ㎛ in Comparative Examples 1 and 3, so that the sum of the thicknesses of the negative active material layer used in the unit cell and the negative electrode-facing coating layer including the active material was set to the same value of 70 ㎛.

(1) Charging time evaluation

The charging time until the battery is fully charged at 3C at 25℃ is measured and shown in Table 2 below.

(2) Capacity maintenance rate

The battery was charged at 2C at 25℃ to 4.4 V, discharged at a constant current of 1C to 3.0 V, and subjected to 100 charge-discharge cycles. The discharge capacity after 1 cycle and the discharge capacity after 100 cycles were measured. Then, the capacity retention rate was measured according to the following equation (1), and the results are shown in Table 2 below.

Equation (1): Capacity retention rate (%) = {Discharge capacity after ( ) cycles / Discharge capacity after 1 cycle} X 100

As shown in Table 2 above, 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 excellent effects, and in the case of Example 3, the charging time was 36 minutes and the capacity retention rate was 94%, showing excellent effects compared to the comparative example.

While specific portions of the present invention have been described in detail above, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and that the scope of the present invention is not limited thereby. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present invention, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

10, 100: Unit Cell
20, 200 : Negative current collector
21, 210: Negative active material layer
30, 300 : Porous substrate
31, 310: Cathode-facing coating layer
32: Bipolar surface coating layer
320: Inorganic coating layer
40, 400 : Bipolar collector
41, 410: Positive active material layer

Claims (12)

porous substrate;
A negative electrode-facing coating layer formed on a portion of the porous substrate facing the negative electrode active material layer and containing a negative electrode active material;
In a secondary battery separator including:
No cathode active material is added to the portion of the porous substrate facing the cathode.
The above cathode-facing coating layer exists in the inorganic coating layer.
The above cathode-facing coating layer comprises a metal hydroxide or a metal hydrate,
A secondary battery separator having a thickness of the cathode-facing coating layer of 10 μm to 30 μm. In the first paragraph,
A secondary battery separator having an inorganic coating layer that does not contain a cathode active material added to the portion of the porous substrate facing the cathode. In the first paragraph,
A secondary battery separator in which no coating layer is added to the portion of the porous substrate facing the positive electrode. delete In the first paragraph,
A secondary battery separator in which the cathode-facing coating layer is separately present on an inorganic coating layer. In the first paragraph,
A secondary battery separator wherein the negative active material is at least one of graphite such as natural graphite or artificial graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber. In the first paragraph,
A secondary battery separator in which the negative electrode-facing coating layer contains the same material as the negative electrode active material of the negative electrode. In Article 7,
The above cathode-facing coating layer is a secondary battery separator having the same cathode active material layer. anode;
cathode;
A separator according to any one of claims 1, 2, 3, and 5 to 8 interposed between the positive and negative electrodes;
A secondary battery comprising: In Article 9,
A secondary battery in which the combined thickness of the positive electrode active material layer facing the separator of the positive electrode, the negative electrode active material layer facing the separator of the negative electrode, and the negative electrode facing coating layer of the separator are the same. S1) A step of preparing a cathode and anode including a cathode active material layer on the surface of the separator;
S2) A step for manufacturing a separation membrane according to any one of claims 1, 2, 3, and 5 to 8.
S3) A method for manufacturing an electrode assembly, comprising the steps of laminating a cathode, a separator, and an anode so that the cathode active material layer of the cathode and the cathode-facing coating layer of the separator face each other and then rolling the cathode, separator, and anode. In Article 11,
A method for manufacturing an electrode assembly further comprising a step of forming an inorganic coating layer on at least one surface of a porous substrate prior to the step S2).