KR20240021638A - Separator and Lithium Secondary battery comprising the same - Google Patents

Abstract

Polymer porous support; An inorganic hybrid porous layer located on one side of the polymer porous support and containing a binder polymer and an inorganic filler; And a sacrificial cathode material located on the other side of the polymer porous support or on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, and having an initial efficiency of 20% or less and a charging capacity of 500 mAh / g or more. A separator having a sacrificial cathode material layer, and a lithium secondary battery including the same are presented.

Description

Separator and Lithium Secondary battery comprising the same}

The present invention relates to a separator and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, much research is being conducted on batteries that can meet various needs.

Typically, in terms of battery shape, there is a high demand for square-shaped secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones due to their thin thickness, and in terms of materials, they have advantages such as high energy density, discharge voltage, and output stability. There is high demand for lithium secondary batteries, such as lithium metal secondary batteries, lithium-ion batteries, and lithium-ion polymer batteries.

In addition, secondary batteries are classified according to the structure of the electrode assembly of the anode/separator/cathode structure. Representative examples include jelly, which has a structure in which long sheet-shaped positive electrodes and negative electrodes are wound with a separator interposed between them. -Roll (wound type) electrode assembly, stacked (stacked) electrode assembly in which a plurality of anodes and cathodes cut into units of a predetermined size are sequentially stacked with a separator interposed between them, and a predetermined unit of anodes and cathodes interposed between a separator. Examples include a stacked/folded type electrode assembly in which bi-cells or full cells stacked in one state are wound with a separator sheet.

Generally, transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used as positive electrode active materials for lithium secondary batteries, and carbon-based materials or lithium metal are used as negative electrode active materials.

As an anode material for lithium secondary batteries, carbon-based materials such as graphite have a very low discharge potential of about -3 V relative to the standard hydrogen electrode potential, and have very reversible charge and discharge behavior due to the uniaxial orientation of the graphene layer. This shows excellent electrode lifespan characteristics, but the theoretical energy density of graphite is low at 372 mAh/g, so there is a limit to high capacity.

Compared to the previously mentioned negative electrode active materials, lithium alloys such as silicon (4,200 mAh/g) and tin (990 mAh/g) are capable of storing and releasing more lithium ions through an alloying reaction with lithium and exhibit high capacity characteristics. The material is attracting attention as an anode active material for high-capacity lithium secondary batteries.

However, in the case of negative electrode active materials such as silicon, the irreversible capacity in the initial charge/discharge cycle is large, which lowers charge/discharge efficiency. In addition, there is a problem in that volume change (contraction or expansion) occurs during the insertion and desorption process of lithium ions, which reduces mechanical stability and, as a result, cycle characteristics are impaired.

Therefore, various technologies related to prelithiation have been proposed to develop lithium secondary batteries with excellent performance, safety, and lifespan characteristics by effectively improving the shortcomings of negative electrodes containing negative electrode active materials with large irreversible capacity, but practical aspects There are still limitations.

The purpose of the present invention is to solve the above problems of the prior art and technical problems that have been requested in the past.

Specifically, the purpose of the present invention is to provide a separator that can improve the problem of low charge and discharge efficiency in the initial charge and discharge cycle between the positive electrode and the negative electrode due to the irreversible capacity of the negative electrode, and a lithium secondary battery including the same.

In order to achieve this purpose, according to one aspect of the present invention, a separation membrane of the following embodiment is provided.

According to the first embodiment,

Polymer porous support;

An inorganic hybrid porous layer located on one side of the polymer porous support and containing a binder polymer and an inorganic filler; and

A sacrificial cathode material located on the other side of the polymer porous support or on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, and having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more. A separator having a cathode material layer is provided.

According to the second embodiment, in the first embodiment,

When the sacrificial anode material layer is located on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, the separator is located on the other side of the polymer porous support, and the inorganic hybrid porous layer containing a binder polymer and an inorganic filler It may further include.

According to a third embodiment, in the first or second embodiment,

The sacrificial cathode material may have an initial efficiency of 0.1% to 20%.

According to a fourth embodiment, in any one of the first to third embodiments,

The sacrificial cathode material may have a charging capacity of 500 mAh/g to 2000 mAh/g.

According to a fifth embodiment, in any one of the first to fourth embodiments,

The sacrificial cathode material may include lithium cobalt oxide.

According to a sixth embodiment, in any one of the first to fifth embodiments,

The sacrificial cathode material may have an average particle diameter of 3 ㎛ or less.

According to a seventh embodiment, in any one of the first to sixth embodiments,

The sacrificial cathode material layer may have a thickness of 0.1 to 5 ㎛.

According to the eighth embodiment, in any one of the first to seventh embodiments,

The sacrificial cathode material layer may further include polyvinylidene-based polymer as a binder.

According to the ninth embodiment,

Comprising an anode, a cathode, and a separator interposed between the anode and the cathode,

The separator is the separator of any one of the first to eighth embodiments,

A lithium secondary battery is provided, wherein the sacrificial cathode material layer of the separator faces the cathode.

The separator according to an embodiment of the present invention includes a sacrificial anode material layer containing a sacrificial anode material having an initial efficiency of 20% or less and a charge capacity of 500 mAh/g or more on one side of the olefin polymer porous support, thereby forming such a separator. After manufacturing a lithium secondary battery, prelithiation can be performed in the initial activation process of the secondary battery.

In addition, when blending the white anode material within the electrode, there may be a risk that battery efficiency may decrease due to the occurrence of a deactivated area. However, the separator according to one embodiment of the present invention has the sacrificial anode material as a separate layer. By doing so, these risks can be prevented.

In addition, a secondary battery employing a separator according to an embodiment of the present invention has a difference in charge and discharge efficiency in the initial charge and discharge cycle even when a material with a large irreversible capacity, such as a silicon-based material, is used as the negative electrode active material. can complement it.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention along with the contents of the above-described invention. Therefore, the present invention is limited to the matters described in such drawings. It should not be interpreted in a limited way.
Figure 1A is a schematic diagram showing a cross section of a separator according to an embodiment of the present invention.
Figure 1b is a schematic diagram showing a cross section of a separator according to an embodiment of the present invention.
Figure 2 is a schematic diagram showing a cross section of a separator according to an embodiment of the present invention.
Figure 3a is a schematic diagram showing a cross section where a separator and an anode face each other according to an embodiment of the present invention.
Figure 3b is a schematic diagram showing a cross section where a separator and an anode face each other according to an embodiment of the present invention.
Figure 4 is a schematic diagram showing a cross section where a separator and an anode face each other according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

According to one aspect of the present invention,

Polymer porous support;

An inorganic hybrid porous layer located on one side of the polymer porous support and containing a binder polymer and an inorganic filler; and

A sacrificial cathode material located on the other side of the polymer porous support or on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, and having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more. A separator having a cathode material layer is provided.

1A, 1B, and 2 are schematic diagrams showing a cross section of a separator according to an embodiment of the present invention. The separator 100 according to an embodiment of the present invention includes a polymer porous support (10); An inorganic hybrid porous layer (20) located on one side of the polymer porous support (10) and containing a binder polymer and an inorganic filler; and a sacrificial anode material layer (30) located on one side of the inorganic hybrid porous layer (20) that is not in contact with the polymer porous support, and comprising a sacrificial anode material having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more. ; is provided. The separator 110 according to an embodiment of the present invention includes a polymer porous support 10; An inorganic hybrid porous layer (20) located on one side of the polymer porous support (10) and containing a binder polymer and an inorganic filler; and a sacrificial anode material layer 30 located on the other side of the polymer porous support and including a sacrificial anode material having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more.

When the sacrificial anode material layer is located on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, the separator is located on the other side of the polymer porous support, and the inorganic hybrid porous layer containing a binder polymer and an inorganic filler It may further include ;.

Therefore, referring to FIG. 2, the separator 200 includes inorganic mixed pore layers 20 and 40 located on both sides of the polymer porous support 10, and the inorganic mixed pore layer 20 A sacrificial anode material layer 30 including a sacrificial anode material having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more is provided on one side.

According to one embodiment of the present invention, the polymer porous support is not limited as long as it has a structure having pores, and may be a porous polymer substrate, and specifically may be a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

The porous polymer film substrate may be a porous polymer film made of olefin polymer such as polyethylene or polypropylene, and this olefin polymer porous polymer film substrate exhibits a shutdown function at a temperature of, for example, 80 to 130 °C.

At this time, the porous polymer film is made of olefin polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, respectively, individually or in a mixture of two or more types thereof. It may be formed from polymers or their derivatives.

Representative examples of commercially available olefin polymer porous polymer films that can be applied as such polymer porous supports include wet polyethylene series (Asahi-Kasei E-Materials, Toray, SK IE Technology, Shanghai Energy, Sinoma, Entek) and dry polypropylene series. (Shenzhen Senior, Cangzhou Mingzhu), dry polypropylene/polyethylene multilayer structure series (Polypore, Ube), etc. may be used, but are not limited to these.

Additionally, the porous polymer film substrate may be manufactured by molding into a film shape using various polymers such as polyester in addition to olefin polymer. In addition, the porous polymer film substrate may be formed in a structure in which two or more film layers are laminated, and each film layer may be formed of the above-described olefin polymer, polyester, etc., alone or a mixture of two or more types thereof. It may be possible.

In addition, the porous polymer film substrate and the porous nonwoven fabric substrate include polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide ( polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene ), etc. may be formed individually or as a mixture of polymers.

The thickness of this polymer porous support is not greatly limited, but may be 1 ㎛ or more, 5 ㎛ or more, 50 ㎛ or less, and 100 ㎛ or less. When the thickness satisfies this range, the problem of acting as a resistance layer can be improved while maintaining mechanical properties.

There is no particular limitation on the pore size and porosity of the polymer porous support, but the porosity may range from 10 to 95% and the pore size (diameter) may range from 0.1 to 50 ㎛. When the pore size and porosity satisfy these ranges, the problem of acting as a resistance layer is prevented and mechanical properties can be maintained. Additionally, the polymer porous support may be in the form of a fiber or membrane.

The inorganic hybrid porous layer is located on one side of the polymer porous support and includes a binder polymer and an inorganic filler.

In addition, this inorganic hybrid pore layer is a component of the separator and serves as an isolation layer to prevent short circuit between the anode and the cathode, and at the same time prevents the polymer porous support from coming into direct contact with lithium metal and forms the sacrificial positive electrode described above. As a result of being combined and positioned on the material layer, additional Li ions supplied from the sacrificial anode material enable pre-lithiation at the cathode, thereby supplementing the irreversible capacity of the cathode and shifting the potential working range. It can play a role.

The inorganic filler serves both as a spacer that forms micropores by enabling the formation of empty spaces between the inorganic fillers and as a kind of spacer that can maintain the physical form, and generally maintains its physical properties even at high temperatures of 200°C or higher. Because it has unchanging properties, the formed organic/inorganic composite porous film has excellent heat resistance.

Therefore, in the lithium secondary battery including the separator, even if the polymer porous support ruptures inside the battery due to excessive conditions caused by internal or external factors such as high temperature, overcharge, and external shock, both electrodes are completely protected by the inorganic mixed pore layer. It is difficult to short-circuit, and even if a short-circuit occurs, the short-circuited area is prevented from expanding significantly, thereby improving the safety of the battery.

These inorganic fillers are not particularly limited as long as they are electrochemically stable, that is, the inorganic fillers that can be used in the present invention are oxidized and / Alternatively, there is no particular limitation as long as a reduction reaction does not occur. In particular, when using an inorganic filler capable of transmitting ions, it is desirable to have as high an ionic conductivity as possible because performance can be improved by increasing the ionic conductivity within the electrochemical device. In addition, when the inorganic filler has a high density, not only is it difficult to disperse it during coating, but there is also a problem of weight increase during battery manufacturing, so it is preferable that the density is as low as possible. In addition, in the case of an inorganic material with a high dielectric constant, it can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

For the reasons described above, the inorganic filler may be a high dielectric constant inorganic filler having a dielectric constant of 5 or more, or 10 or more, an inorganic filler with piezoelectricity, an inorganic filler with lithium ion transport ability, or a mixture thereof. .

Examples of the inorganic filler having a dielectric constant of 5 or more include SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, AlO(OH), Examples include Mg(OH) ₂ , Al(OH) ₃ , AlN, or mixtures thereof, but are not limited thereto.

The inorganic filler having piezoelectricity refers to a material that is insulator at normal pressure but has the property of conducting electricity due to a change in internal structure when a certain pressure is applied. It not only exhibits high dielectric constant characteristics with a dielectric constant of 100 or more. It is a material that has the function of generating a potential difference between both sides by generating an electric charge when it is stretched or compressed by applying a certain pressure, and one side is positively charged and the other side is negatively charged.

When using an inorganic filler with the above characteristics, if an internal short circuit of both electrodes occurs due to external impact such as local crush or nail, the inorganic filler coated on the separator may cause an internal short circuit. Not only is the anode and cathode not in direct contact, but the piezoelectricity of the inorganic filler causes a potential difference within the particle, which causes electrons to move between the two electrodes, that is, a minute flow of current, resulting in a gradual decrease in battery voltage. And thus, safety can be improved.

Examples of the inorganic filler having piezoelectricity include BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1- xLa _x Zr _1-y Ti _y O ₃ (PLZT), PB(Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) hafnia (HfO ₂ ) or mixtures thereof, but are not limited thereto.

The inorganic filler having the ability to transport lithium ions refers to an inorganic filler that contains lithium element but has the function of moving lithium ions without storing lithium. The inorganic filler having the ability to transport lithium ions is present inside the particle structure. Since lithium ions can be transferred and moved due to a type of defect, lithium ion conductivity in the battery is improved, thereby improving battery performance.

Examples of inorganic fillers having the ability to transport lithium ions include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), and lithium aluminum. _{Titanium phosphate ( Li _ _ _ _ _ _ _} (LiAlTiP)xOy series glass (0<x<4, 0<y<13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), Li _3.25 Ge Lithium _germanium thiophosphate _, such _{as 0.25} P _{0.75 S 4} ( _Li Lithium nitride such as N (Li _x N _y , 0<x< ₄ , 0<y<2 ₎ , _{SiS 2} series glass ₍ Li _x Si _y S _z , P ₂ S ₅ series glass such as 0<x<3, 0<y<2, 0<z<4), LiI-Li ₂ SP ₂ S ₅ , etc. (Li _x P _y S _z , 0<x<3, 0 <y<3, 0<z<7), or mixtures thereof, but are not limited thereto.

When the above-mentioned high dielectric constant inorganic filler, piezoelectric inorganic filler, and inorganic filler with lithium ion transport ability are used together, their synergistic effect can be doubled.

The separator according to the present invention forms the pore structure of the inorganic mixed pore layer along with the pores contained in the separator substrate by controlling the size of the inorganic filler constituting the inorganic mixed pore layer, the content of the inorganic filler, and the composition of the inorganic filler and the binder polymer. This can be done, and the pore size and porosity can also be adjusted.

The average particle diameter (D50) of the inorganic filler may be 800 nm or less, or 20 to 800 nm, or 100 to 600 nm, if possible, for the formation of an inorganic mixed porous layer of uniform thickness and an appropriate porosity thereof. When the average particle diameter (D50) of the inorganic filler satisfies this range, the dispersibility of the slurry for the inorganic mixed porous layer is maintained, making it easy to control the physical properties of the separator, and the thickness of the separator increases excessively, resulting in a decrease in mechanical properties. The problem of internal short-circuiting during battery charging and discharging due to excessively large pore size can be prevented, and uniform movement of lithium ions between the positive and negative electrodes can be ensured.

The porosity of the inorganic mixed pore layer may be in the range of 40 to 80%, but is not limited thereto. The thickness of the inorganic mixed pore layer may be 0.5 to 7.0 ㎛, or 1.0 to 5.0 ㎛.

The content of the inorganic filler is not particularly limited, but may be 50% by weight or more, 60% by weight, 95% by weight or less, 97% by weight or less, and 99% by weight or less per 100% by weight based on the total weight of the inorganic mixed porous layer. there is. That is, the weight ratio of the inorganic filler and the binder polymer may be 50:50 or more, 60:40 or more, 70:30 or more, 95:5 or less, 97:3 or less, and 99:1 or less, and may be 50:50 to 99:1. , specifically 60:40 to 97:3, and more specifically 70:30 to 95:5. When the content of the inorganic filler satisfies this range, the problem of a decrease in the pore size and porosity of the inorganic mixed pore layer formed due to an excessively high content of the binder polymer can be prevented, and since the content of the binder polymer is small, The problem of weakening the peeling resistance of the inorganic mixed void layer due to a decrease in the adhesion between inorganic materials can also be solved.

In detail, the binder polymer may be used as a glass transition temperature (T _g ) as low as possible, preferably in the range of -200 to 200°C.

Additionally, the binder polymer may gel when impregnated with a liquid electrolyte solution and may have the characteristic of exhibiting a high degree of swelling of the electrolyte solution. In fact, when the binder polymers are polymers with excellent electrolyte swelling (or impregnation rate), the electrolyte injected after battery assembly permeates into the polymer, and the polymer holding the absorbed electrolyte has the ability to conduct electrolyte ions. In addition, compared to conventional hydrophobic olefin polymer-based separators, not only is the wetting property for battery electrolytes improved, but it also has the advantage of enabling the application of polar electrolytes for batteries, which were previously difficult to use. Accordingly, the solubility index of the binder polymer, that is, the Hildebrand solubility parameter, is 15 to 45 MPa ^1/2 , specifically 15 to 25 MPa ^1/2 , and more specifically 30 to 45 MPa ^{1/2. 2} range.

When the solubility index satisfies the range of 15 to 45 MPa ^1/2 , swelling can be easily achieved by a typical liquid electrolyte solution for batteries.

Specifically, the binder polymer is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, and polymethyl methacrylate. Latex, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl poly. It may include vinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose, styrenebutadiene copolymer, polyimide, or two or more of these, but is not limited thereto.

In the inorganic hybrid pore layer, the inorganic fillers are filled and bound to each other by the binder polymer in a state of contact, thereby forming an interstitial volume between the inorganic fillers, and forming an interstitial volume between the inorganic fillers. The interstitial volume becomes an empty space and forms a pore.

In other words, the binder polymer attaches the inorganic fillers to each other so that they can remain bound together. For example, the binder polymer connects and fixes the inorganic fillers. In addition, the pores of the inorganic hybrid pore layer are pores formed when the interstitial volume between the inorganic fillers becomes an empty space, which is substantially in contact with the filled structure (closed packed or densely packed) by the inorganic fillers. It is a space limited by inorganic fillers.

The sacrificial cathode material layer is located on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, and includes a sacrificial cathode material having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more.

The sacrificial cathode material is a lithium-containing compound, and has the property of releasing Li ions held during charging to the negative electrode and accepting only 20% or less of the amount released during discharging. After releasing Li ions to the negative electrode, they remain and remain. It is characterized by increasing resistance and generating gas. Therefore, it is important to reduce the initial efficiency of the sacrificial cathode material as much as possible and reduce the amount of gas generated.

The sacrificial cathode material may have an initial efficiency of 20% or less, and according to one embodiment of the present invention, the sacrificial cathode material may have an initial efficiency of 0.1 to 20%, or 0.3 to 15%. If the sacrificial cathode material has an initial efficiency of more than 20%, it is undesirable because there is a problem of continued resistance and gas generation while continuously participating in charging and discharging, and if the sacrificial cathode material has an initial efficiency of 20% or less, it is activated during battery manufacturing overload. After removing the gas generated in the step and degas process, it is advantageous in that additional gas generation can be suppressed under normal charging and discharging conditions.

The sacrificial cathode material has a charging capacity of 500 mAh/g or more, and according to one embodiment of the present invention, the sacrificial cathode material has a charging capacity of 500 mAh/g to 2000 mAh/g, or 700 to 1500 mAh/g. You can have If the sacrificial cathode material has a capacity of less than 500 mAh/g, it is undesirable because the application amount required to achieve the desired pre-lithiation effect is excessive, and if the sacrificial cathode material has a capacity of 500 mAh/g or more, pre-lithiation is possible. It is advantageous in that materials can be implemented using the separator space without additional space allocation.

At this time, the initial efficiency of the sacrificial anode material is a half-cell manufactured with an anode made of the sacrificial anode material, a cathode made of lithium metal, and a separator between the anode and the cathode, and charged up to 4.2V under charging conditions of 0.1C at room temperature. After checking the charging capacity and subsequently discharging to 3.0V under 0.1C discharge conditions at the same temperature to check the discharge capacity, the discharge capacity compared to the charging capacity at this time can be calculated and determined.

The sacrificial cathode material may include lithium cobalt oxide, specifically Li ₆ CoO ₄ .

The sacrificial cathode material may have an average particle diameter (D50) of 3 ㎛ or less, or 0.2 to 3 ㎛, or 0.3 to 2 ㎛, or 0.3 to 1.9 ㎛.

When the average particle diameter (D50) of the sacrificial cathode material satisfies this range, it is advantageous in that a desired capacity level can be achieved without excessive thickness of the isolation layer.

In this specification, “particle size Dn” means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. D50, which corresponds to the average particle size, is the particle size at 50% of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at 90% of the cumulative distribution of particle numbers according to particle size, and D10 is the cumulative distribution of particle numbers according to particle size. It is the particle size at 10% of the point.

The Dn can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the difference in diffraction patterns according to particle size is measured when the particles pass through the laser beam, thereby distributing the particle size. Calculate . D10, D50, and D90 can be measured by calculating the particle diameters at points that are 10%, 50%, and 90% of the cumulative distribution of particle numbers according to particle size in the measuring device.

When the sacrificial positive electrode layer further includes a binder material, the binder material includes polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-tetrafluoroethylene, and polyvinylidene. It may include fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, or two or more of these, but is not limited thereto.

When the sacrificial positive electrode layer further includes a binder material, the weight ratio of the sacrificial positive electrode material and the binder material is 50:50 or more, 60:40 or more, 70:30 or more, 95:5 or less, 97:3 or less, 99:99. :1 or less, 50:50 to 99:1, specifically 60:40 to 97:3, and more specifically 70:30 to 95:5.

The thickness of the sacrificial anode material layer may be 0.1 to 5 ㎛, or 0.3 to 4 ㎛, and the porosity of the sacrificial anode material layer may be 30 to 80%, or 40 to 80%.

When the thickness and porosity of the sacrificial cathode layer satisfy these ranges, it can be advantageous in terms of achieving a desired pre-lithiation level while maintaining the energy density of the battery.

The separator according to one embodiment of the present invention includes a conductive material in the sacrificial cathode material layer to form a conductive network, so that when a potential is applied to a battery including this separator, lithium ions in the sacrificial cathode material layer can move to the cathode. It can be done.

At this time, when forming a sacrificial anode material layer on the surface of the inorganic hybrid porous layer of the separator, the conductive material contained in the sacrificial anode material layer must be controlled so that it is not inserted into the pores of the inorganic hybrid porous layer and the polymer porous support. If the conductive material is inserted into the pores of the inorganic hybrid porous layer and the polymer porous support, the insulation of the separator may be destroyed. Therefore, the minimum particle size of the conductive material included in the sacrificial cathode material layer needs to be controlled to be larger than the maximum pore size of the inorganic hybrid pore layer and the polymer porous support. For example, the minimum particle diameter of the conductive material may be 50 nm or more, or 50 to 300 nm, based on secondary particles.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes 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 metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. As mentioned above, since the conductive material must be prevented from inserting into the inorganic hybrid porous layer and the pores of the polymer porous support, carbon nanotube-based conductive materials having conductive whiskers or linear structures are not desirable.

According to one embodiment of the present invention, the separator is located on the other side of the polymer porous support and may further include an inorganic hybrid porous layer containing a binder polymer and an inorganic filler.

In this case, the inorganic mixed void layer located on one side of the polymer porous support is called a first inorganic mixed void layer, and the inorganic mixed void layer located on the other side of the polymer porous support is called a second inorganic mixed void layer. It can be called

According to one embodiment of the present invention, the separator may have a structure of a second inorganic hybrid porous layer/polymer porous support/first inorganic hybrid porous layer/sacrificial anode material layer in the stacking order.

The inorganic mixed pore layer (second inorganic mixed pore layer) added to the other side of the polymer porous support prevents heat shrinkage of the polymer porous support by directly facing the polymer porous support, further strengthening the heat resistance of the separator, and further strengthening the heat resistance of the external membrane. It can play a role in maintaining the isolation function even when inserting a foreign object.

The inorganic filler and binder polymer included in the added inorganic mixed void layer (second inorganic mixed void layer) are the same as described above, and the inorganic mixed void layer (first inorganic mixed void layer) located on one side of the polymer porous support. ) may be of the same type as the inorganic filler and binder polymer, or may be different from each other.

A separation membrane according to an embodiment of the present invention includes the steps of preparing a slurry for an inorganic hybrid porous layer containing an inorganic filler, a binder polymer, and a dispersion medium (which may be a solvent for the binder polymer); Forming an inorganic hybrid porous layer by applying and drying a slurry for an inorganic hybrid porous layer on one side of a polymer porous support; Prepare a slurry for a sacrificial cathode material layer containing a sacrificial cathode material, optionally a binder material, and a dispersion medium (may be a solvent for the binder material), and apply and dry the slurry for the sacrificial cathode material layer on the inorganic hybrid porous layer. It can be manufactured by a manufacturing method including the step of forming a sacrificial anode material layer.

First, an inorganic hybrid porous layer slurry containing an inorganic filler, a binder polymer, and a dispersion medium (may be a solvent for the binder polymer) is applied and dried on one side of the polymer porous support to form an inorganic hybrid porous layer.

The slurry for the inorganic hybrid porous layer can be prepared by dissolving the binder polymer in a dispersion medium, then adding an inorganic filler and dispersing it. At this time, the inorganic fillers can be added while crushed to an appropriate size, and after adding the inorganic fillers to the binder polymer solution, the inorganic fillers can be dispersed by crushing them using a ball mill method or the like.

According to one embodiment of the present invention, the slurry for the inorganic hybrid pore layer is applied using the above-described coating device, and the applied result is dried to form the above-described interstitial volume pore structure on the upper surface of the sacrificial anode material layer. It is possible to form an inorganic mixed porous layer.

The dispersion medium may have a solubility index similar to that of the binder polymer to be used and may have a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal.

Examples of such dispersion media include, independently of one another, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, methanol, ethanol, isopropyl alcohol, and water. It may be a compound or a mixture of two or more types.

At this time, the dispersion medium may serve as a solvent for dissolving the binder polymer and a dispersion medium for dispersing it, depending on the type of binder polymer mixed together.

According to one embodiment of the present invention, methods for applying the slurry to the polymer porous support include a premetering method and a postmetering method. The total metering method is a method in which the application amount is determined in advance and introduced, for example, slot die coating, gravure coating, etc. The post-metering method is a method of applying a sufficient amount of slurry, which is a coating liquid, to a polymer porous support and then scraping off a prescribed amount. An example is bar coating. In addition, there is a direct metering coating that combines the pre-metering method and the post-metering method.

The applied result may be dried to form an inorganic hybrid pore layer having the above-described interstitial volume pore structure on at least one surface of the polymer porous support.

In addition, after the step of applying a slurry containing a binder polymer, an inorganic filler, and a dispersion medium to one surface of the polymer porous support using the above-described coating device, the cost of the binder polymer is applied to the polymer porous support to which the slurry is applied. The step of applying the falcon may further be included. When the non-solvent is applied in this way, the slurry dissolved in the solvent of the binder polymer, which is also the dispersion medium, comes into contact with the non-solvent of the binder polymer, and a phase separation phenomenon occurs. As a result, the inorganic hybrid porous layer has a plurality of nodes including the inorganic filler and a binder polymer covering at least a portion of the surface of the inorganic filler; and the binder polymer of the nodes is formed in a thread shape. It includes one or more filaments formed, wherein the filaments extend from the node and include a node connection part connecting other nodes, wherein the node connection part is formed by a plurality of filaments derived from the binder polymer crossing each other. It may have a structure forming a three-dimensional network structure.

At this time, the non-solvent application method may be a method of immersing the previously treated porous support in a composition containing a non-solvent, or a method of spraying and applying the non-solvent to the surface of the previously treated porous support by spraying, etc. . This method of forming an inorganic hybrid coating layer can also be applied when forming an additional inorganic hybrid coating layer on the other side of the polymer porous support, which will be described later.

Thereafter, a slurry for a sacrificial cathode material layer containing a sacrificial cathode material, optionally a binder material, and a dispersion medium (may be a solvent for the binder material) is prepared, and the slurry for a sacrificial cathode material layer is applied on the inorganic hybrid porous layer. and drying to form a sacrificial anode material layer.

The dispersion medium for the sacrificial cathode material layer may have a low boiling point. This is to facilitate subsequent solvent removal.

Since the sacrificial cathode material is vulnerable to water, it is necessary to use a dispersion medium other than water. Examples of such dispersion media include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, It may be one type of compound selected from methanol, ethanol, and isopropyl alcohol, or a mixture of two or more types.

At this time, the dispersion medium may serve as a solvent for dissolving the binder material and a dispersion medium for dispersing the binder material, depending on the type of binder material being selectively mixed.

The slurry for the sacrificial cathode material layer can be prepared by adding the sacrificial cathode material to a dispersion medium and dispersing it. At this time, the sacrificial cathode material can be added while crushed to an appropriate size, and the sacrificial cathode material can be dispersed by crushing it using a ball mill method or the like after adding a lithium ion-containing material to the dispersion medium.

Methods for applying the slurry for the sacrificial cathode material layer to the polymer porous support include a premetering method and a postmetering method. The total metering method is a method in which the application amount is determined in advance and introduced, for example, slot die coating, gravure coating, etc. The post-metering method is a method of applying a sufficient amount of slurry, which is a coating liquid, to a polymer porous support and then scraping off a prescribed amount. An example is bar coating. In addition, there is a direct metering coating that combines the pre-metering method and the post-metering method.

The method of drying the slurry for the sacrificial cathode material layer applied to the inorganic hybrid porous layer is applicable as long as it is a process of removing the dispersion medium in the slurry, and can be performed, for example, in an oven at 70°C to 100°C for 0.2 to 3 minutes. .

According to one embodiment of the present invention, a UV cross-linkable polymer that can be cross-linked by UV reaction is added to the slurry for the sacrificial cathode material layer, and the slurry for the sacrificial cathode material layer is applied on the inorganic mixed porous layer and then irradiated with UV. The sacrificial anode material layer can also be formed as a high-speed thin film. At this time, examples of UV cross-linkable polymers that can be used may include unsaturated polyester, polyester acrylate, polyurethane acrylate, and epoxy acrylate. Additionally, the UV irradiation conditions may be 500 to 3,000 mJ/cm ² .

In addition, the separator according to one embodiment of the present invention prepares a slurry for an additional inorganic hybrid porous layer containing an inorganic filler, a binder polymer, and a dispersion medium (may be a solvent for the binder polymer), and mixes it with the polymer porous support. It can also be applied to the other surface and dried to form an additional inorganic mixed pore layer.

According to one aspect of the present invention, a lithium secondary battery is provided including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is a separator according to an embodiment of the present invention described above, and the separator A lithium secondary battery is provided in which a sacrificial cathode material layer faces the anode.

3A, 3B, and 4 are schematic diagrams showing a cross section where a separator and an anode face each other according to an embodiment of the present invention. The separator (100, 110, 200) according to one embodiment of the present invention is located on at least one side of the polymer porous support (10) and includes an inorganic hybrid porous layer (20, 40) containing a binder polymer and an inorganic filler; And a sacrificial cathode material layer 30 located on the other side of the polymer porous support or one side of the inorganic mixed porous layer and comprising a sacrificial cathode material having an initial efficiency of 20% or less and a capacity of 500 mAh/g or more. The anode 300 faces the sacrificial anode material layer 30 of the separators 100, 110, and 200.

The lithium secondary battery may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The sacrificial cathode material layer of the separator faces the anode and has a large irreversible capacity in the initial charge and discharge cycle. Therefore, when a cathode with low initial charge and discharge efficiency is applied, the sacrificial anode material contained in the sacrificial anode material layer is charged. By releasing the Li ions held at the time to the cathode, it compensates for the irreversible capacity of the cathode and at the same time controls the working potential range of the cathode.

There is no particular limitation on the positive and negative electrodes to be applied together with the separator of the present invention, and the electrode active material can be manufactured in a form bound to the electrode current collector according to a common method known in the art. Non-limiting examples of the positive electrode active material among the above electrode active materials include common positive electrode active materials that can be used in the positive electrode of conventional electrochemical devices, especially lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof. One lithium complex oxide can be used.

Non-limiting examples of negative electrode active materials include common negative electrode active materials that can be used in the negative electrode of conventional electrochemical devices, especially lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorption materials such as graphite or other carbons, silicon, silicon oxide, silicon-carbon composite, etc. are preferred.

Non-limiting examples of the positive current collector include foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the negative current collector include foil made of copper, gold, nickel, or a copper alloy, or a combination thereof. There are foils etc. that are manufactured.

The electrolyte solution that can be used in the electrochemical device according to an embodiment of the present invention is a salt with the same structure as A ⁺ B ^- , where A ⁺ is an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or a combination thereof. Contains ions and B ^- is PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ ^- , C (CF ₂ SO ₂ ) ₃ ^- Salts containing anions such as ions or a combination thereof are propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate ( DMC), dipropylcarbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma Butyrolactone (g-butyrolactone) or mixtures thereof may be dissolved or dissociated in an organic solvent, but are not limited thereto.

The electrolyte injection may be performed at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.

Hereinafter, the present invention will be further described in detail through examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these only.

Manufacturing example

Manufacturing of anode

The conductive material pre-dispersion was prepared using N-methylpyrrolidone (NMP) as a solvent, carbon black (Denka, Li435) and dispersant (Zeon, BM740H) at a weight ratio of 10:1. At this time, the solid content of the conductive material pre-dispersion was 6%.

As a cathode active material, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM523, Jinhe Company, S740) and LiCoO ₂ (LCO, L&F Advanced Materials Company, LC10S) were mixed in a ratio of 5:5 and then polyvinylidene fluoride (Kureha Company, KF9700). was used as a binder, and mixed with the conductive material pre-dispersion to prepare a positive electrode slurry. The weight ratio of (positive electrode active material):(binder):(total weight of conductive material and dispersant in conductive material pre-dispersion liquid) was 97.1:1.25:1.65. At this time, the solid content of the positive electrode slurry was 77%.

The prepared slurry was applied on an aluminum foil, dried, and then rolled to manufacture a positive electrode. The capacity of the manufactured positive electrode was 3.696mAh/cm ² based on 4.3V charging.

Preparation of cathode

A cathode slurry was prepared by mixing water as a solvent, silicon (Wacker, developed product) as an active material, a conductive material (Imerys, Super-C65), and a binder (Li-PAA, Sigma-Aldrich) at a weight ratio of 7:2:1. was prepared, and at this time, the solid content of the cathode slurry was 42%. The prepared slurry was applied and dried on copper foil and then rolled to prepare a negative electrode. The capacity of the manufactured negative electrode was 10.64mAh/cm ² .

Example 1

The first slurry was prepared by dispersing alumina (Sumitomo, AES-11) using water as a solvent and carboxymethyl cellulose (GLChem, SG-L02) as a dispersant, and then dispersing acrylic emulsion (Toyo ink, Inc.) as a binder polymer. It was prepared by post-adding CSB130). During production, the weight ratio of alumina, carboxymethylcellulose, and acrylic emulsion was 97:1:2, and the solid content was 35%.

The second slurry used acetone as a solvent, Li ₆ CoO ₄ (LG Chemical, developed product, D50: 1.9㎛, charging capacity 687mAh/g, initial efficiency 0.9%) as a sacrificial anode material, and polyvinylidene fluoride as a binder. A slurry using tetrafluoroethylene (Daikin, VT475) and carbon black (Denka, Li435) as a conductive material was prepared. When manufacturing, the weight ratio of sacrificial anode material: binder: conductive material was 90:8:2, and the solid content was 25%.

A 6.5㎛ polyethylene porous film (Senior, SW507) was used as the substrate, and an alumina-based first slurry was applied to one side and a sacrificial anode material-based second slurry was applied to the other side by roll coating using a microgravure device. , it was dried for 2 minutes at a temperature of 80 degrees using a drying device operated by hot air. The thickness of the inorganic mixed pore layer, which was the result of the first slurry coating and drying, was 2.5 ㎛, and the thickness of the sacrificial cathode material layer, which was the result of the second slurry coating and drying, was 2.5 ㎛. The battery was assembled so that the sacrificial cathode material layer faced the anode between the prepared separator and the previously prepared anode and cathode.

The manufactured battery had a capacity of 47.9 mAh, and 300 cycles of charging and discharging were repeatedly evaluated under 1C/1C charging and discharging conditions at 45°C, and the remaining capacity compared to the initial capacity was 90.5%.

Example 2

A battery was manufactured in the same manner as in Example 1, except that the thickness of the inorganic hybrid void layer was adjusted to 1.5 μm and the thickness of the sacrificial cathode material layer was adjusted to 3.5 μm.

The manufactured battery had a capacity of 48.3 mAh, and the remaining capacity after 300 cycles was 93.3%.

Comparative Example 1

A second slurry was prepared in the same manner as in Example 1, except that the sacrificial anode material was changed to LiNiO ₂ (LNO, Ecopro, developed product, D50: 14㎛, charging capacity: 355mAh/g, initial efficiency: 28.2%). .

A separator was manufactured with the thickness of the inorganic hybrid pore layer being 1.5㎛ and the thickness of the sacrificial anode material layer being 20.0㎛, and the battery assembly was manufactured in the same manner as in Example 1.

The manufactured battery had a capacity of 47.1 mAh, the remaining capacity after 300 cycles was 24.3%, and the battery expanded due to gas generation.

The evaluation method for the sacrificial cathode material of the present invention is as follows.

Measurement of capacity and initial efficiency of sacrificial cathode material

A half-cell is manufactured containing a cathode made of lithium metal with a sacrificial cathode material, a conductive material, and a binder (weight ratio = 96:2:2) and a 20㎛ thick polyethylene separator sandwiched between the anode and the cathode. Check the charging capacity by charging to 4.2V under charging conditions of 0.1C at room temperature, and then check the discharge capacity by discharging to 3.0V under discharging conditions of 0.1C at the same temperature. Additionally, the ratio of discharge capacity to charge capacity at this time can be calculated and determined as the initial efficiency.

Measurement of average particle diameter (D50) of sacrificial cathode material

A laser diffraction particle size measurement device (Microtrac S3500) was used to calculate the particle size distribution by measuring the difference in diffraction patterns depending on the particle size when the particles passed through the laser beam. D10, D50, and D90 were measured by calculating the particle diameters at 10%, 50%, and 90% of the cumulative distribution of particle numbers according to particle size in the measuring device. At this time, D50 was defined as the average particle diameter. .

Although the present invention has been described above with reference to embodiments and drawings, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (9)

Polymer porous support;
An inorganic hybrid porous layer located on one side of the polymer porous support and containing a binder polymer and an inorganic filler; and
A sacrificial cathode material located on the other side of the polymer porous support or on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, and having an initial efficiency of 20% or less and a charging capacity of 500 mAh/g or more. A separator having a cathode material layer. According to paragraph 1,
When the sacrificial anode material layer is located on one side of the inorganic hybrid porous layer that is not in contact with the polymer porous support, the separator is located on the other side of the polymer porous support, and the inorganic hybrid porous layer containing a binder polymer and an inorganic filler A separator further comprising: According to paragraph 1,
A separator wherein the sacrificial cathode material has an initial efficiency of 0.1 to 20%. According to paragraph 1,
A separator, characterized in that the sacrificial cathode material has a capacity of 500 mAh/g to 2000 mAh/g. According to paragraph 1,
A separator, wherein the sacrificial cathode material includes lithium cobalt oxide. According to paragraph 1,
A separator, wherein the sacrificial cathode material has an average particle diameter of 3 ㎛ or less. According to paragraph 1,
A separator, characterized in that the sacrificial cathode material layer has a thickness of 0.1 to 5 ㎛. According to paragraph 1,
A separator, wherein the sacrificial cathode material layer further includes a polyvinylidene-based polymer as a binder. Comprising an anode, a cathode, and a separator interposed between the anode and the cathode,
The separator is the separator according to any one of claims 1 to 8,
A lithium secondary battery, characterized in that the sacrificial cathode material layer of the separator faces the cathode.

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