CN110914346A - Method for improving physical properties of separator by post-treatment crosslinking and separator prepared thereby - Google Patents

Method for improving physical properties of separator by post-treatment crosslinking and separator prepared thereby Download PDF

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CN110914346A
CN110914346A CN201980003596.1A CN201980003596A CN110914346A CN 110914346 A CN110914346 A CN 110914346A CN 201980003596 A CN201980003596 A CN 201980003596A CN 110914346 A CN110914346 A CN 110914346A
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separator
group
light sources
peroxydicarbonate
crosslinking
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CN110914346B (en
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金英馥
金敏智
南宽祐
李济安
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LG Energy Solution Ltd
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LG Chem Ltd
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    • C08J5/20—Manufacture of shaped structures of ion-exchange resins
    • C08J5/22—Films, membranes or diaphragms
    • C08J5/2287—After-treatment
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H01M50/461—Separators, membranes or diaphragms characterised by their combination with electrodes with adhesive layers between electrodes and separators
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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Abstract

Disclosed are a method for improving physical properties of a separator capable of improving insulation, tensile strength and elongation and a separator having improved physical properties by the above method. In particular, the present invention is applied to a separator that has already been manufactured. After the double bonds have been formed in the already manufactured separator, the crosslinks may be formed by the double bonds or by adding a separate crosslinking initiator.

Description

Method for improving physical properties of separator by post-treatment crosslinking and separator prepared thereby
Technical Field
The present application claims priority and benefit from korean patent application No. 2018-0043356 filed on 13/4/2018 and korean patent application No. 2019-0042803 filed on 12/4/2019, the disclosures of which are incorporated herein by reference in their entireties.
The present invention relates to a method for improving physical properties of a separator by post-treatment crosslinking and a separator prepared thereby. Specifically, the present invention relates to a method comprising forming crosslinkable sites on binder molecules by post-treating a completed separator including an olefin substrate or not including an olefin substrate and crosslinking the crosslinkable sites to improve insulating properties and mechanical properties of the separator, and a separator having improved physical properties by post-treating crosslinking. The separator of the present invention is useful for batteries, particularly secondary batteries.
Background
Recently, as portable devices such as smartphones, notebook computers, tablet computers, and portable game machines tend to be reduced in weight and increased in functionality, there is an increasing demand for secondary batteries used as driving power sources thereof. In the past, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries have been used, but currently lithium secondary batteries having a high operating voltage and a high energy density per unit weight are most commonly used.
In the case of lithium secondary batteries, the demand for lithium secondary batteries increases with market growth associated with the portable device market. Lithium secondary batteries have also been used as power sources for Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV).
The lithium secondary battery is configured such that an electrode assembly having a positive electrode/separator/negative electrode structure, which can be charged and discharged, is mounted in a battery case. Each of the positive electrode and the negative electrode was manufactured by: the method includes applying a slurry including an electrode active material to one surface or both surfaces of a metal current collector, drying the slurry, and rolling the metal current collector having the dried slurry applied thereto.
The separator is one of the most important factors affecting the performance and life of the secondary battery. The separator should electrically isolate the positive and negative electrodes from each other and should allow the electrolyte solution to smoothly pass through the separator. In addition, it is desirable that the separator exhibits high mechanical strength and stability at high temperatures.
Various attempts have been made to increase the insulation resistance and mechanical strength of the separator. In the case of a lithium ion battery, a low voltage phenomenon due to self-discharge is a problem, and low insulation resistance of a separator is an important cause.
U.S. patent No. 8833354 discloses a microporous polymer layer comprising organically modified aluminum boehmite particles and an organic polymer. However, the mechanical strength is poor, which causes a problem of a high defect rate in the process.
Korean patent application laid-open No. 2016-0140211 relates to an electrolyte for a lithium battery, a negative electrode and a lithium battery, and discloses an intermediate layer including an electrolyte and a solid electrolyte and serving as a separator between the positive electrode and the negative electrode. The electrolyte is interposed between the positive electrode and the negative electrode, or may include a separator corresponding to the present invention. The difference from the invention lies in that: the surface-modified nanoparticle composite is dispersed in a block copolymer.
Korean patent application laid-open No. 2012-0093772 discloses a separator comprising an adhesive having an amine group and a separator coating layer comprising the adhesive; and a monomer unit having a crosslinkable functional group. However, this patent document does not disclose a specific step of adding a solution including an alkaline substance or a substance having an amine group.
Journal of Power Sources 144(1): 238-. However, this non-patent document does not disclose the application of PVdF-HFP/PEGDMA to the separator, but only to the polymer electrolyte.
J Appl Electrochem 46:69,2016 discloses boehmite nanoparticles and polyvinylidene fluoride polymers as separators for lithium secondary batteries. However, this non-patent document mentions that it is not sufficient to be applied to a battery cell assembly process having high stress.
Journal of Membrane Science,103,2014 discloses a porous ceramic Membrane based on magnesium aluminate as a separator for lithium secondary batteries having flexibility and thermal stability. However, this non-patent document does not disclose a method of improving strength.
RSC adv.,6,102762-. To increase the hydrophilicity of the electrospun PVDF carrier, etc., the electrospun PVDF carrier was treated with Triethylamine (TEA).
J.appl.polym.sci.8,1415,1964 discloses a crosslinking mechanism by post-treating the separator. Colloids and surfaces a Physicochem. Eng. aspects 297,267,2007 discloses the effect of improving the mechanical properties of a crosslinked separator. "Effect of cross-linking on the electrical properties of LDPE and its lighting injection Engineering", International symposium on High Voltage Engineering, Hannover, Germany,2011, August 22 discloses improved insulation properties of cross-linked separators.
In addition, the conventional method of improving the characteristics of the separator and the like improves the physical characteristics of the separator by adding an additional means or process in the manufacturing process of the separator. However, a method of improving physical properties of the separator by post-treating the already manufactured separator has not been proposed.
Disclosure of Invention
Technical problem
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of improving physical properties of a separator capable of improving insulation, tensile strength and elongation, and a separator having improved physical properties obtained thereby. In particular, the invention is characterized by applying the method to an already manufactured separator.
Technical scheme
In a first aspect of the present invention, the above and other objects can be accomplished by the provision of a method for improving physical properties of a separator through post-treatment, comprising the steps of: a) preparing a separator having a layer including an adhesive on a substrate including a polyolefin substrate or a substrate not including a polyolefin substrate; b) transforming the binder into a cross-linkable coupling moiety by de-intercalating some elements of the binder; and c) treating the separator with a crosslinking initiator and/or a reaction catalyst after the treatment of step b).
In addition to the crosslinking initiator in step c), a crosslinking agent may be added at the same time.
A separator having a coating layer including an adhesive on a substrate including a polyolefin substrate or a substrate not including a polyolefin substrate may have a coating layer including an adhesive on a polyolefin substrate. Alternatively, the separator may not include a polyolefin substrate, and include inorganic particles and a binder for coupling between the inorganic particles.
The inorganic particles may be highly dielectric inorganic particles having a dielectric constant of 1 or more, inorganic particles having piezoelectricity (piezoelectric), inorganic particles having lithium ion transport ability, hydrated alumina, or a mixture of two or more thereof.
Examples of the binder include at least one selected from the group consisting of PVdF, TFE, and polyimide.
In particular, in step b), some elements of the binder may be de-intercalated to convert a single bond to a double bond. Alternatively, in step b), a solution including a basic substance or a substance having an amine group may be added to the separator. The basic substance or the substance having an amine group may be at least one selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zeolites, limestone, sodium carbonate, ammonia, monoalkylamines, dialkylamines, trialkylamines, wherein the alkyl group may contain 1 to 10 carbon atoms.
As the crosslinking initiator, an azo (azo) -based compound or a peroxide (peroxide) -based compound can be used.
The crosslinking agent may be at least one selected from diaminoalkanes having 1 to 15 carbon atoms. Specific examples of the diaminoalkane may include 1,6-diaminohexane (1,6-diaminohexane) and 1,5-diaminopentane (1, 5-diaminopentane).
A second aspect of the present invention provides a separator having improved physical properties by the method of improving physical properties of a separator of the present invention.
A third aspect of the present invention provides an electrochemical device including a separator having improved physical properties.
The invention has the advantages of
The method of improving the physical properties of the separator according to the present invention has advantages in that: the method can provide a separator having improved insulation and tensile strength compared to conventional separators. The present invention is applicable to a separator including a polyolefin substrate or not including a polyolefin substrate. In particular, although the conventional method is applied to the process of manufacturing the separator, the present invention provides a completely different solution to improve the physical properties of the already manufactured separator. The invention has the advantages that: the composition and process conditions of the conventional mass-produced separator do not need to be changed.
Drawings
Fig. 1 is a graph showing comparative measurements of tensile strength and elongation of GEN1 separators.
FIG. 2 is a graph of comparative measurements of volume resistance and resistance of GEN1 separator plates.
Fig. 3 is a graph showing comparative measurements of tensile strength and elongation of the BA1 separator.
Fig. 4 is a graph showing comparative measurements of volume resistance and resistance of the BA1 separator.
Fig. 5 is a graph showing comparative measurements of tensile strength and elongation of the treated BA1 separator after and during coating.
Fig. 6 is a graph showing comparative measurements of volume resistance and electrical resistance of BA1 separators processed after and during coating.
Detailed Description
Hereinafter, the present invention will be described in detail. It should be noted that the terms or words used in the present specification and claims should not be construed as having ordinary meanings and dictionary-based meanings, but should be construed as having meanings and concepts consistent with the technical idea of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term in order to explain the present invention in the best way. Therefore, the embodiments described in this specification are only the most preferred embodiments and do not cover all technical ideas of the present invention, and thus it should be understood that there may be various equivalents and modifications that can replace the embodiments at the time of filing this application.
According to an aspect of the present invention, there is provided a method for improving physical properties of a separator by post-treatment, the method comprising the steps of:
a) preparing a separator having a layer including an adhesive on a substrate including a polyolefin substrate or a substrate not including a polyolefin substrate; b) transforming the binder into a cross-linkable coupling moiety by de-intercalating some elements of the binder;
and c) treating the separator with a crosslinking initiator and/or a reaction catalyst after the treatment of step b).
In step b), crosslinking sites may be formed by de-intercalation of some elements of the binder, thereby converting a single bond to a double bond. Some of the elements may be H, F or Cl.
In step b), a solution containing a basic substance or a substance including an amine group may be added to the separator.
In step c), in addition to the crosslinking initiator, a crosslinking agent may also be optionally added at the same time.
Step c) may comprise the steps of: coupling a crosslinking initiator to the coupling moiety, coupling between the binders at the coupling moiety, forming separate crosslinks between the crosslinking initiators, coupling a crosslinking agent to the coupling moiety, or forming separate crosslinks between the crosslinking agents.
In step b), H, F, Cl etc. in the binder polymer may be de-intercalated to form double bonds for conversion into cross-linkable coupling moieties. The crosslinking may be formed by coupling between the crosslinking sites formed in step b), the crosslinking initiator, the crosslinking agent and/or the reaction catalyst injected in step c) may couple the crosslinking sites, or a separate crosslinking may be formed between the crosslinking initiator and the crosslinking agent.
1) Type of separator
The separator having a layer including a binder on a substrate including or not including a polyolefin substrate may be a separator having a coating layer including a binder on a polyolefin substrate, or may be a separator not including a polyolefin substrate but including inorganic particles and a binder for coupling between the inorganic particles.
The polyolefin substrate may be polyethylene, polypropylene, and the like, as a polyolefin substrate used in a conventional separator. Technical details of the polyolefin substrate are well known to those of ordinary skill in the art, and thus a detailed description thereof will be omitted.
In the structure excluding the polyolefin-based separator substrate, the conventional separator substrate is omitted, and the separator is made of a material constituting the inorganic layer. Since the separator does not include a polyolefin separator substrate, the overall strength of a separator made of only such an inorganic layer is low. Therefore, there are the following problems: the separator interposed between the electrode assemblies may be damaged, and thus a short circuit may occur. The method of improving physical properties of a separator according to the present invention can be applied to an already-completed separator without a polyolefin-based separator substrate, thereby improving mechanical strength and insulation properties.
2) Inorganic particles
The inorganic particles according to the present invention may form empty spaces between the inorganic particles, so that micropores may be formed and maintain a physical shape as a spacer (spacer). The physical properties of the inorganic particles do not change at temperatures of 200 ℃ or higher.
The inorganic particles are not particularly limited as long as the inorganic particles are electrochemically stable. In other words, the inorganic particles that can be used in the present invention are not particularly limited as long as the inorganic particles are within the operating voltage range of the battery to which the inorganic particles are applied (e.g., based on Li/Li)+0 to 5V) is not oxidized and/or reduced. In particular, in the case of using inorganic particles having high electrolyte ion transport ability, the performance of the electrochemical device may be improved. Therefore, it is preferable that the inorganic particles have an electrolyte ion transport ability as high as possible. In addition, in the case where the inorganic particles have a high density, it may be difficult to disperse the inorganic particles when forming the porous separator, and the weight of the battery may increase when manufacturing the battery. For these reasons, it is preferable that the density of the inorganic particles is low. In addition, in the case where the inorganic particles have a high dielectric constant, the degree of dissociation of an electrolyte salt (such as a lithium salt) in the liquid electrolyte may increase, thereby improving the ion conductivity of the electrolyte solution.
For the above reasons, the inorganic particles may be highly dielectric inorganic particles having a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectricity (piezoelectricity), inorganic particles having lithium ion transport ability, hydrated alumina, or a mixture of two or more thereof.
Examples of the inorganic particles having a dielectric constant of 1 or more may include: SrTiO3、SnO2、CeO2、MgO、NiO、CaO、ZnO、ZrO2、Y2O3、Al2O3、TiO2SiC, or mixtures thereof. However, the present invention is not limited thereto.
Inorganic particles having piezoelectricity (piezoelectric) are non-conductive at normal pressure, but exhibit conductivity due to a change in the internal structure thereof when a predetermined pressure is applied thereto. In the case where the inorganic particles have a high dielectric value (for example, a dielectric constant of 100 or more) and the inorganic particles are strained or compressed at a predetermined pressure, electric charges are generated. One surface is charged as a positive electrode, and the other surface is charged as a negative electrode, thereby generating a potential difference between the two surfaces.
In the case of using inorganic particles having the above-described characteristics, if an external impact such as a local impact or a nail impact occurs, both electrodes may be short-circuited. At this time, however, the positive electrode and the negative electrode may not directly contact each other due to the inorganic particles coated on the porous separator, and a potential difference may be generated in the particles due to piezoelectricity of the inorganic particles. Accordingly, electron transfer, i.e., a minute current flow, is achieved between the two electrodes, so that the voltage of the battery is gradually lowered, and thus the stability of the battery can be improved.
Examples of the inorganic particles having piezoelectricity may include BaTiO3、Pb(Zr,Ti)O3(PZT)、Pb1-xLaxZr1- yTiyO3(PLZT)、Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT), hafnium oxide (hafnia, HfO)2) And mixtures thereof. However, the present invention is not limited thereto.
The inorganic particles having lithium ion transport ability are inorganic particles that contain lithium element and transport lithium ions without storing lithium. The inorganic particles having lithium ion transport ability can transport and transport lithium ions due to one kind of defect (defect) existing in the particle structure. Therefore, lithium ion conductivity in the battery can be improved, and thus battery performance can be improved.
Examples of the inorganic particles having lithium ion transport ability may include: lithium phosphate (Li)3PO4) (ii) a Lithium titanium phosphate (Li)xTiy(PO4)3Wherein 0 is<x<2 and 0<y<3) (ii) a Lithium aluminum titanium phosphate (Li)xAlyTiz(PO4)3Wherein 0 is<x<2,0<y<1, and 0<z<3)；(LiAlTiP)xOyBase glass (wherein 0)<x<4 and 0<y<13) Such as 14Li2O-9Al2O3-38TiO2-39P2O5(ii) a Lithium lanthanum titanate (Li)xLayTiO3Wherein 0 is<x<2 and 0<y<3) (ii) a Lithium germanium thiophosphate (Li)xGeyPzSwWherein 0 is<x<4,0<y<1,0<z<1, and 0<w<5) Such as Li3.25Ge0.25P0.75S4(ii) a Lithium nitride (Li)xNyWherein 0 is<x<4 and 0<y<2) Such as Li3N；SiS2-base glass (Li)xSiySzWherein 0 is<x<3,0<y<2, and 0<z<4) Such as Li3PO4-Li2S-SiS2；P2S5-base glass (Li)xPySzWherein 0 is<x<3,0<y<3, and 0<z<7) Such as LiI-Li2S-P2S5(ii) a And mixtures thereof. However, the present invention is not limited thereto.
The hydrated alumina may be classified into crystalline hydrated alumina or gel-type hydrated alumina according to the manufacturing method. Examples of crystalline hydrated alumina may include gibbsite i-Al (OH)3Bayerite Al (OH)3Boehmite i-AlOOH, and the gel-type hydrated alumina may be aluminum hydroxide prepared by depositing an aqueous solution containing aluminum ions using ammonia. Preferably, boehmite i-AlOOH can be used as the gel-type hydrated alumina.
In the case where inorganic particles having a high dielectric constant, inorganic particles having piezoelectricity, inorganic particles having lithium ion transport ability, and hydrated alumina are used together, the effects obtained by these components can be further improved.
The size of each inorganic particle is not particularly limited. However, in order to form a film having a uniform thickness and obtain a suitable porosity, the size of each inorganic particle may be 0.001 μm to 10 μm. In the case where the size of each inorganic particle is less than 0.001 μm, the dispersibility is reduced, whereby it is difficult to adjust the physical properties of the porous separator. In the case where the size of each inorganic particle is greater than 10 μm, the thickness of the separator manufactured at the same solid content increases, whereby the mechanical properties of the separator deteriorate. In addition, when the battery is charged and discharged, short circuits are easily generated in the battery due to excessively large pores.
3) Adhesive agent
The binder may also be generally referred to as a polymer binder, and may become gel (gel of jelly) when the binder is impregnated with a liquid electrolyte solution, whereby the binder may have characteristics of exhibiting a high impregnation rate of the electrolyte solution. In fact, for a binder polymer having a high electrolyte solution impregnation rate, an electrolyte solution injected after the battery is assembled permeates into the polymer, and the polymer impregnated with the electrolyte solution exhibits electrolyte ion transport ability. In addition, wetting of the porous separator in an electrolyte solution can be improved (wetting) compared to a conventional hydrophobic polyolefin-based separator, and a polar electrolyte solution can be used for a battery, which is conventionally difficult to use. Thus, the binder may have a solubility parameter of 15MPa1/2To 45MPa1/2Preferably 15MPa1/2To 25MPa1/2And 30MPa1/2To 45MPa1/2The polymer of (1). Solubility parameter of the adhesive is less than 15MPa1/2And greater than 45MPa1/2In case of (2), it is difficult for the conventional electrolyte solution for a battery to impregnate the binder.
Specifically, the binder may be at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile butadiene styrene copolymer, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, Styrene Butadiene Rubber (SBR), TFE, fluororubber, and polyimide. Preferably, the binder may be at least one selected from the group consisting of PVdF, TFE, and polyimide.
4) Basic substance or substance having amine group
The basic substance or the substance having an amine group is at least one selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zeolites, limestone, sodium carbonate, ammonia, monoalkylamines, dialkylamines, and trialkylamines.
5) Crosslinking initiator
The crosslinking initiator may be an azo (azo) -based compound or a peroxide (peroxide) -based compound. Specifically, the azo-based compound may be at least one selected from the group consisting of 2,2 '-azobis (2-methylbutyronitrile), 2' -azobis (isobutyronitrile), 2 '-azobis (2, 4-dimethylvaleronitrile), and 2, 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile). Preferably, the azo-based compound is 2, 2' -azobis (isobutyronitrile) (AIBN).
The peroxide-based compound may be selected from tetramethylbutyl peroxyneodecanoate, bis (4-butylcyclohexyl) peroxydicarbonate, bis (2-ethylhexyl) peroxydicarbonate, butyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate, hexyl peroxydicarbonate, dimethoxybutyl peroxydicarbonate, bis (3-methoxy-3-methoxybutyl) peroxydicarbonate, dibutyl peroxydicarbonate, dihexadecyl peroxydicarbonate, ditetradecyl peroxydicarbonate, peroxidizypivalate 1,1,3, 3-tetramethylbutyl peroxypivalate, butyl peroxypivalate, or the like, At least one of trimethylhexanoyl peroxide, dimethylhydroxybutyl peroxyneodecanoate, pentyl peroxyneodecanoate, Atofina, butyl peroxyneodecanoate, tert-butyl peroxyneoheptanoate, pentyl peroxypentanoate, tert-butyl peroxypentanoate, tert-amyl peroxy-2-ethylhexanoate, lauroyl peroxide, dilauroyl peroxide (dilauroyl), didecanoyl peroxide, benzoyl peroxide, and dibenzoyl peroxide.
The amount of crosslinking initiator, crosslinking agent and/or reaction catalyst may be greater than 0 wt% and equal to or less than 5 wt%, preferably greater than 0.2 wt% and equal to or less than 5 wt%, more preferably greater than 0.5 wt% and less than or equal to 5 wt%, and most preferably greater than 1 wt% and less than or equal to 2 wt%, based on the total weight of solids in the separator.
In the case where the amount of the crosslinking initiator, the crosslinking agent and/or the reaction catalyst in the separator is less than the lower limit, crosslinking may not be completely performed.
In the present invention, the crosslinking initiator may react at a specific temperature to cause the crosslinking agent to form a crosslinked structure. As the density of the separator of the present invention increases due to the characteristics of the cross-linked structure, physical characteristics related to the rigidity of the separator may be improved. Therefore, as the migration of electrons is affected, the insulation resistance increases.
The reaction temperature of the crosslinking initiator may be 40 ℃ to 150 ℃, preferably 50 ℃ to 130 ℃. At a temperature lower than the above reaction temperature range, the reaction rate of the crosslinking initiator is slow. When the reaction temperature of the crosslinking initiator reaches the above reaction temperature range, the crosslinking initiator reacts to form a three-dimensional network structure by crosslinking.
In the case where the reaction temperature of the crosslinking initiator is lower than 40 ℃, the crosslinking initiator hardly undergoes the crosslinking reaction, which is not desirable. In the case where the reaction temperature of the crosslinking initiator is higher than 150 ℃, the conventional separator may be deformed or melted, which is also undesirable.
5) Crosslinking agent
The crosslinking agent may be at least one selected from diaminoalkanes having 1 to 15 carbon atoms. Specifically, the crosslinking agent may be selected from at least one of 1,6-diaminohexane (diaminohexane) or 1,5-diaminopentane (diaminopentane).
6) Construction and application of electrode assemblies
The present invention also provides an electrochemical device including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Here, the electrochemical device may be a lithium secondary battery.
The positive electrode may be manufactured by applying a mixture of a positive electrode active material, a conductive agent, and a binder to a positive electrode current collector and drying the mixture. Fillers may be further added to the mixture as needed.
Generally, the cathode current collector is manufactured to have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited so long as the positive electrode current collector exhibits high conductivity while the positive electrode current collector does not cause any chemical change in a battery to which the positive electrode current collector is applied. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, or plastic carbon. Alternatively, the positive electrode current collector may be made of aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, or silver. In addition, the positive electrode current collector may have a micro-scale unevenness pattern formed on the surface thereof to increase the adhesion of the positive electrode active material. The cathode current collector may be configured in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a non-woven fabric body, and the like.
The positive active material may be, but is not limited to: such as lithium cobalt oxide (LiCoO)2) Or lithium nickel oxide (LiNiO)2) Or a compound substituted with one or more transition metals; from the formula Li1+xMn2-xO4(wherein x is 0 to 0.33) or a compound represented by the formula3、LiMn2O3、LiMnO2The lithium manganese oxide of (1); lithium copper oxide (Li)2CuO2) (ii) a Vanadium oxides, such as LiV3O8、V2O5Or Cu2V2O7(ii) a From the formula LiNi1-xMxO2(wherein M ═ Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x ═ 0.01 to 0.3) represents a Ni-site type lithium nickel oxide; represented by the chemical formula LiMn2-xMxO2(wherein M ═ Co, Ni, Fe, Cr, Zn, or Ta, and x ═ 0.01 to 0.1) or formula Li2Mn3MO8(wherein M ═ Fe, Co, Ni, Cu, or Zn); LiMn2O4Wherein Li in the formula is partially substituted with an alkaline earth metal ion; a disulfide compound; or Fe2(MoO4)3。
The conductive agent is generally added in an amount of 1 to 30% by weight, based on the total weight of the mixture including the positive electrode active material. The conductive agent is not particularly limited as long as the conductive agent exhibits high conductivity without causing any chemical change in a battery to which the conductive agent is applied. For example, the following materials may be used as the conductive agent: graphite, such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or a conductive material such as a polyphenylene derivative.
The binder is a component that facilitates the binding between the active material and the conductive agent and the binding with the current collector. The binder is generally added in an amount of 1 to 30% by weight, based on the total weight of the mixture including the cathode active material. As examples of the binder, 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, and various copolymers may be used.
The filler is an optional component for inhibiting expansion of the positive electrode. The filler is not particularly limited as long as it does not cause chemical changes in the battery to which it is applied and is made of a fibrous material. As examples of the filler, olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers.
The anode may be manufactured by applying an anode active material to an anode current collector and drying it. The above-mentioned components may be optionally further included according to need.
In general, the anode current collector is manufactured to have a thickness of 3 to 500 μm. The anode current collector is not particularly limited as long as the anode current collector exhibits high conductivity while the anode current collector does not cause any chemical change in a battery to which the anode current collector is applied. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, or plastic carbon. Alternatively, the negative electrode current collector may be made of copper or stainless steel, the surface of which is treated with carbon, nickel, titanium or silver, or may be made of aluminum-cadmium alloy. In addition, in the same manner as the cathode current collector, the anode current collector may have a micro-scale unevenness pattern formed on the surface thereof so as to increase the adhesion of the anode active material. The anode current collector may be configured in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a non-woven fabric body.
As the anode active material, for example, there can be used: carbon, such as hard carbon or graphite-based carbon; metal complex oxides, such as LixFe2O3(0≤x≤1)、LixWO2(0≤x≤1)、SnxMe1-xMe’yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of groups 1, 2 and 3 of the periodic Table of the elements, halogen; 0<x is less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8); lithium metal; a lithium alloy; a silicon-based alloy; a tin-based alloy; metal oxides, e.g. SnO, SnO2、PbO、PbO2、Pb2O3、Pb3O4、Sb2O3、Sb2O4、Sb2O5、GeO、GeO2、Bi2O3、Bi2O4Or Bi2O5(ii) a Conductive polymers such as polyacetylene; or a Li-Co-Ni based material.
According to another aspect of the present invention, there is provided a battery pack including the electrochemical device.
Specifically, the battery pack may be used as a power source for devices that require the ability to withstand high temperatures, long life, high rate characteristics, and the like. Specific examples of the apparatus may include: a mobile electronic device (mobile device); wearable electronic devices (wearable devices); a power tool driven by a battery powered motor; electric vehicles such as Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs), or Plug-in Hybrid Electric vehicles (PHEVs); an electric two-wheeled vehicle such as an electric bicycle (E-bike) or an electric scooter (E-scooter); electric golf cart (electric golf cart); and an Energy Storage System. However, the present invention is not limited thereto.
The structure and manufacturing method of the device are well known in the art to which the present invention pertains, and thus a detailed description thereof will be omitted.
Detailed description of the preferred embodiments
Hereinafter, the present invention will be described in detail with reference to the following examples and test examples; however, the present invention is not limited to these examples and test examples. The embodiments may be modified into various other forms, and the scope of the present invention should not be construed as being limited by the embodiments to be described in detail. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the invention to those skilled in the art.
< production method >
(production of separators 1 and 2)
For testing purposes, two separators which have been produced, CSP gen1 (separator 1) and BA1_ B09PA1 (separator 2), were used. CSP gen1 separator consisting of alumina Al only2O3Particles and a PVDF binder. The BA1_ B09PA1 partition board is provided with Al on a polyethylene (polyethylene) substrate2O3Inorganic particles and a PVDF binder.
Triethylamine (TEA, Triethylamine) was used as a material for forming crosslinking sites. After each separator was cut to a size of 10cm x 10cm, the separator was immersed in a 99% TEA solution at ambient temperature for 5 minutes, and then removed and dried in a fume hood.
For crosslinking, the separator having crosslinking sites was immersed in a solution in which 1.5 wt% of 2,2 '-azobis (isobutyronitrile) (AIBN,2, 2' -azobis (isobutronitril)) was dissolved in an ethanol solvent, and treated at 60 ℃ for 30 minutes. The separator was then washed with ethanol and dried in a fume hood.
< comparative test 1>
Comparative examples 1 and 2 were prepared without treating the separators 1 and 2. Examples 1 and 2 were prepared by TEA-treating only the separators 1 and 2 according to the present invention. Examples 3 and 4 were prepared by subjecting the separators 1 and 2 to TEA and AIBN treatments. The tensile strength, elongation, insulation resistance and electric resistance of the separators of comparative examples 1 and 2, and examples 3 and 4 were measured under the following conditions, respectively.
< measurement conditions for insulation resistance >
Voltage application: 100V
Measuring time: 3S
Size and shape of the electrode: 19.6cm2Circular shape
< measurement conditions for tensile Strength >
Width of the separator: 2cm
Stretching speed: 500mm/min
< test results >
Fig. 1 to 4 show the measurement results of physical properties of comparative examples 1 and 2 and examples 1, 2, 3 and 4 according to the present invention, respectively. In the Gen1 partition, Bare is comparative example 1 without treatment, TEA is example 1, and TEA + AIBN is example 3. In the BA1 partition, Bare is comparative example 2 without treatment, TEA is example 2, and TEA + AIBN is example 4.
After the TEA treatment for forming the crosslinking sites, the insulating property (volume resistance) and mechanical strength of the separator were reduced in example 1, but the insulating property (volume resistance) and mechanical strength of the separator were improved in example 2. In addition, in examples 3 and 4, the insulating property (volume resistance) and mechanical strength of the separator were increased after the AIBN solution treatment for forming the crosslinking sites. Specifically, it was confirmed that, in the case of AIBN treatment, the insulating properties and mechanical strength of all separators were improved. It can be seen that the method of improving the physical properties of a separator through post-treatment according to the present invention can be applied to a separator that has been manufactured as described above to improve the physical properties of the separator.
< comparative experiment 2>
In the presence of Al2O3Before the coating layer made of inorganic particles and PVDF binder is formed on the separator 2, the coating material is coatedComparative example 3 was prepared by adding Triethylamine (TEA, Triethylamine) as a material for forming a crosslinking site and 2,2 '-azobis (isobutyronitrile) (AIBN,2, 2' -azobis (isobutonitrile)) to prepare a slurry, and then coating the slurry on the separator 2. The separators of comparative example 3 and example 4, in which Triethylamine (TEA) and 2, 2' -azobis (isobutyronitrile) (AIBN) treatments were performed on the separator 2 according to the present invention, were measured for tensile strength, elongation, insulation resistance, and resistance, respectively, under the following conditions.
< measurement conditions for insulation resistance >
Voltage application: 100V
Measuring time: 3S
Size and shape of the electrode: 19.6cm2Circular shape
< measurement conditions for tensile Strength >
Width of the separator: 1.5cm
Stretching speed: 500mm/min
< test results >
Fig. 5 and 6 show the measurement results of physical properties of comparative example 3 (In Coating) and example 4 (After Coating) according to the present invention, respectively. Comparative example 3 was cross-linked during the procedure of BA1 separator, wherein TEA and AIBN were added during the slurry preparation procedure of the coating. Example 4 was post-treatment crosslinking in a BA1 separator, where TEA and AIBN treatments were performed after the coating was formed.
It was confirmed that the insulation property (volume resistance) and mechanical strength of example 5 in which TEA and AIBN treatments were performed after the formation of the coating layer were improved, as compared to comparative example 3 in which TEA and AIBN were added in the slurry preparation process of the coating layer. Thus, it can be seen that the separator having post-treatment crosslinking is superior to the separator that is crosslinked during the coating process.

Claims (22)

1. A method of improving the physical properties of a separator by post-treatment, the method comprising the steps of:
a) preparing a separator having a layer including an adhesive on a substrate including a polyolefin substrate or a substrate not including a polyolefin substrate;
b) transforming the binder into a cross-linkable coupling moiety by de-intercalating some elements of the binder; and
c) after the treatment of step b), treating the separator with a crosslinking initiator and/or a reaction catalyst.
2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,
wherein in step c) a cross-linking agent is added simultaneously in addition to the cross-linking initiator.
3. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,
wherein the separator has a coating layer comprising an adhesive on a polyolefin substrate, or
Wherein the separator does not include a polyolefin substrate, but includes inorganic particles and a binder for coupling between the inorganic particles.
4. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,
wherein the inorganic particles are highly dielectric inorganic particles having a dielectric constant of 1 or more, inorganic particles having piezoelectricity (piezoelectric), inorganic particles having lithium ion transport ability, hydrated alumina, or a mixture of two or more thereof.
5. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,
wherein the inorganic particles are selected from the group consisting of Al2O3、AlOOH、SiO2、MgO、TiO2And BaTiO2At least one of the group consisting of.
6. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,
wherein the binder is at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile butadiene styrene copolymer, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, Styrene Butadiene Rubber (SBR), Tetrafluoroethylene (TFE), fluororubber, and polyimide.
7. The method of claim 6, wherein the first and second light sources are selected from the group consisting of,
wherein the binder is at least one selected from the group consisting of PVdF, TFE, and polyimide.
8. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,
wherein in step b) cross-linking sites are formed by de-intercalating some elements of the binder to convert single bonds to double bonds.
9. The method of claim 8, wherein the first and second light sources are selected from the group consisting of,
wherein some of the elements are H, F or Cl.
10. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,
wherein in step b), a solution including a basic substance or a substance having an amine group is added to the separator.
11. The method of claim 10, wherein the first and second light sources are selected from the group consisting of,
wherein the basic substance or the substance having an amine group is at least one selected from the group consisting of alkali metal oxides, alkaline earth metal oxides, zeolites, limestone, sodium carbonate, ammonia, monoalkylamines, dialkylamines, and trialkylamines, and the alkyl group contains 1 to 10 carbon atoms.
12. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,
wherein step c) comprises the steps of: coupling the crosslinking initiator to the coupling moiety, performing coupling between the adhesives at the coupling moiety, forming separate crosslinks between the crosslinking initiators, coupling the crosslinking agent to the coupling moiety, or forming separate crosslinks between the crosslinking agents.
13. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,
wherein the crosslinking initiator is an azo (azo) -based compound or a peroxide (peroxide) -based compound.
14. The method of claim 13, wherein the first and second light sources are selected from the group consisting of,
wherein the azo-based compound is at least one selected from the group consisting of 2,2 '-azobis (2-methylbutyronitrile), 2' -azobis (isobutyronitrile), 2 '-azobis (2, 4-dimethylvaleronitrile), and 2, 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile).
15. The method of claim 13, wherein the first and second light sources are selected from the group consisting of,
wherein the peroxide-based compound is selected from the group consisting of tetramethylbutyl peroxyneodecanoate, bis (4-butylcyclohexyl) peroxydicarbonate, bis (2-ethylhexyl) peroxydicarbonate, butyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate, hexyl peroxydicarbonate, dimethoxybutyl peroxydicarbonate, bis (3-methoxy-3-methoxybutyl) peroxydicarbonate, dibutyl peroxydicarbonate, dihexadecyl peroxydicarbonate, ditetradecyl peroxydicarbonate, peroxypivalate (peroxipivalate) 1,1,3, 3-tetramethylbutyl peroxypivalate, butyl peroxypivalate, and the like, At least one of trimethylhexanoyl peroxide, dimethylhydroxybutyl peroxyneodecanoate, pentyl peroxyneodecanoate, Atofina, butyl peroxyneodecanoate, tert-butyl peroxyneoheptanoate, pentyl peroxypentanoate, tert-butyl peroxypentanoate, tert-amyl peroxy-2-ethylhexanoate, lauroyl peroxide, dilauroyl peroxide (dilauroyl), didecanoyl peroxide, benzoyl peroxide, and dibenzoyl peroxide.
16. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,
wherein the crosslinking agent is selected from at least one of diaminoalkanes having 1 to 15 carbon atoms.
17. The method of claim 16, wherein the first and second light sources are selected from the group consisting of,
wherein the crosslinking agent is selected from at least one of 1,6-diaminohexane (diaminohexane) or 1,5-diaminopentane (diaminopentane).
18. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,
wherein the temperature at which the crosslinking initiator, the crosslinking agent, and/or the reaction catalyst is treated is 40 ℃ to 150 ℃.
19. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,
wherein the amount of the crosslinking initiator, the crosslinking agent, and/or the reaction catalyst is greater than 0 wt% and equal to or less than 5 wt%, based on the total weight of solids in the separator.
20. A separator having improved physical properties by the method of any one of claims 1 to 19.
21. The separator for an electrochemical device according to claim 20,
wherein the separator has an air permeability of 50sec/100cc to 4,000sec/100 cc.
22. An electrochemical device comprising the separator of claim 20.
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