Lithium secondary battery and preparation method thereof

Abstract

The present application relates to a lithium secondary battery, comprising: an electrode containing a binder having an olefin group (-C=C-); a separator substrate; and an adhesive layer comprising a thiol group (-SH), disposed between the electrode and the separator substrate so that the electrode and the separator substrate are bonded to each other.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to lithium secondary batteries and methods of making the same. Background Art

[0002] Generally, lithium secondary batteries, which include electroactive materials, have higher operating voltages and higher energy densities than lead batteries or nickel / cadmium batteries. Therefore, lithium secondary batteries are widely used as energy storage devices for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0003] Energy density of batteries is the most important issue for improving the driving range of electric vehicles. To achieve energy density, the capacity of anode and cathode materials must be increased, or the thickness of the electrodes must be increased.

[0004] During the electrode thickening process, a low-viscosity solvent is introduced into the electrolyte to maintain the performance of lithium secondary batteries. However, due to the low boiling point of low-viscosity solvents, electrolyte loss due to evaporation may occur during battery operation, which may lead to poor stability at high temperatures. In addition, there are problems such as the generation of gas in the solvent and the deintercalation between the electrode and the separator.

[0005] In currently commercially available binder-type separators, the polymer and electrode binder coated on the separator swell in the electrolyte and physically bond to each other.

[0006] However, this physical bonding method may not guarantee sufficient adhesion, and as the battery size increases, it is difficult to achieve uniform adhesion between the electrode and the separator. Therefore, it is necessary to develop a lithium secondary battery that can further improve the adhesion between the electrode and the separator to solve the above problems. Summary of the Invention

[0007] Accordingly, an aspect of the present disclosure provides a lithium secondary battery having improved adhesion between an electrode and a separator through chemical bonding using a thiol-ene click reaction, and a method of preparing the same.

[0008] According to one aspect of the present disclosure, a lithium secondary battery includes: an electrode including a binder having an olefin group (-C=C-); a separator substrate; and an adhesive layer including a thiol group (-SH) disposed between the electrode and the separator substrate such that the electrode and the separator substrate are bonded to each other.

[0009] The binder layer is prepared by mixing ceramic particles and a polymer having a mercapto group.

[0010] The adhesive layer includes a ceramic particle layer and a polymer layer disposed on the ceramic particle layer, wherein the polymer layer includes a polymer having a mercapto group.

[0011] The polymer having a thiol group can be obtained by introducing a thiol group into the polymer via a chemical reaction, wherein the polymer comprises at least one selected from polyvinylidene fluoride, polyvinyl pyrrolidone, polymethyl methacrylate, polybutyl acrylate, polyethylene fluoride and copolymers thereof.

[0012] The binder having an olefin group can be obtained by introducing the olefin group into a compound via a chemical reaction, wherein the compound is selected from styrene-butadiene rubber, carboxymethyl cellulose and polyvinylidene fluoride.

[0013] The ceramic particles include at least one ceramic selected from the group consisting of alumina, boehmite, magnesia, titanium oxide, and aluminum nitride.

[0014] The adhesive force between the separator substrate and the electrode is 30 gf / mm or more at a temperature of 70° C. or more and a pressure of 1 MPa or more.

[0015] According to one aspect of the present disclosure, a method for manufacturing a lithium secondary battery includes the following steps: preparing a separator by performing thiol modification on the surface of the separator; preparing electrodes including a cathode and an anode, with a binder layer containing carbon double bonds disposed on the electrodes; and combining the electrodes with the separator.

[0016] The steps of preparing the separator include: impregnating a binder polymer in an aqueous solution obtained by mixing potassium permanganate (KMnO4) and potassium hydroxide (KOH); and preparing a polymer having a mercapto group by reacting the impregnated binder polymer with hydrochloric acid (HCl) and 3-mercaptopropionic acid (MPA).

[0017] The binder polymer includes at least one polymer material selected from the group consisting of polyvinylidene fluoride, polyvinyl pyrrolidone, polymethyl methacrylate, polybutyl acrylate, polyethylene fluoride, and copolymers thereof.

[0018] The step of preparing the electrode includes forming carbon double bonds by immersing the binder in an aqueous solution of lithium hydroxide (LiOH).

[0019] The binder includes at least one selected from styrene-butadiene rubber, carboxymethyl cellulose and polyvinylidene fluoride.

[0020] The step of combining the electrode and the separator includes heating the separator and the electrode under static pressure while the separator and the electrode are immersed in the electrolyte.

[0021] The step of combining the electrode with the separator includes: adding an azo or peroxide compound as a reaction initiator. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and / or other aspects of the present disclosure will become more apparent and more easily understood from the following description of embodiments with reference to the accompanying drawings.

[0023] Figure 1 is a cross-sectional view of a lithium secondary battery according to a disclosed embodiment.

[0024] Figure 2 is an enlarged view of an adhesive layer of a lithium secondary battery according to a disclosed embodiment.

[0025] Figure 3 Binder polymers and electrode binders having functional group substituents according to disclosed embodiments are shown.

[0026] Figure 4 A process for producing a polymer having a mercapto group is shown.

[0027] Figure 5 A process for producing a binder having olefinic groups is shown. DETAILED DESCRIPTION

[0028] In this specification, the same numbers refer to the same elements. This specification does not describe all the elements in the embodiments, and does not describe the known information in the technical field to which the present disclosure belongs or the repeated information between the various embodiments.

[0029] Furthermore, it should be understood that the terms “comprises,” “includes,” “contains,” and / or “has” used in this specification indicate the presence of the components described, but do not exclude the presence or addition of one or more other ingredients.

[0030] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0031] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings and tables. First, a lithium secondary battery will be described, and then an adhesive-type separator for a lithium secondary battery according to the disclosed embodiment will be described in detail.

[0032] Generally, a lithium secondary battery includes a cathode, an anode, a separator, and an electrolyte. The cathode, the anode, and the electrolyte can be implemented using components generally used to manufacture lithium secondary batteries.

[0033] The electrode may be prepared by applying an electrode paste having a predetermined thickness and a conductive material to an electrode collector, and then drying and rolling the electrode paste, the electrode paste including a mixture of an electrode active material, a binder, and a solvent.

[0034] The electrode current collector may include a material having high electrical conductivity but which does not cause chemical changes in the lithium secondary battery. For example, the electrode current collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, or silver. Fine irregularities may be formed on the surface of the current collector to improve the adhesion of the cathode active material, and the irregularities may be implemented in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0035] The anode active material used to manufacture the anode can be provided using any anode active material that can intercalate and deintercalate lithium ions. The anode active material can include at least one selected from a material that can reversibly intercalate and deintercalate lithium ions, a metal material that forms an alloy with lithium, a mixture thereof, or a combination thereof.

[0036] The material capable of reversibly intercalating and deintercalating lithium ions may be at least one material selected from the group consisting of synthetic graphite, natural graphite, graphitized carbon fibers, graphitized mesocarbon microbeads (MCMB), fullerenes, and amorphous carbon.

[0037] Amorphous carbon can be hard carbon, coke, MCMB sintered at 1500°C or lower, and mesophase pitch-based carbon fiber (MPCF). In addition, the metal material capable of forming an alloy with lithium can be at least one metal selected from aluminum (Al), silicon (Si), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), nickel (Ni), titanium (Ti), manganese (Mn) and germanium (Ge). The metal material can be used alone, in combination or in the form of an alloy. In addition, the metal can also be used as a composite mixed with the carbon material.

[0038] The anode active material may include silicon. The anode active material may also include a graphite-silicon composite. Anode active materials including silicon include silicon oxide, silicon particles, silicon alloy particles, and the like. Representative examples of alloys include solid solutions of aluminum (Al), manganese (Mn), iron (Fe), titanium (Ti), and the like with silicon, intermetallic compounds, eutectic alloys, and the like, but the alloys according to the present disclosure are not limited thereto.

[0039] The cathode active material for manufacturing the cathode according to the embodiment may include a compound that allows reversible intercalation and deintercalation of lithium. More specifically, the cathode active material may be at least one composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof.

[0040] Conductive materials are used to improve electrical conductivity and include electronically conductive materials that do not cause chemical changes in lithium secondary batteries. For example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0041] Examples of the binder include aqueous binders carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) for the anode, and polyvinylidene fluoride (PVDF) for the cathode.

[0042] When the anode includes a composite of graphite and silicon, the binder may include a binder mixture containing: an aqueous binder such as CMC / SBR, which is used for graphite-based anodes to improve adhesion; and a polymer binder such as heparin, dopamine-polymerized heparin and LiPAA (lithium polyacrylate), which is used to improve the adhesion strength of silicon-based anodes and suppress the volume expansion of silicon-based anodes.

[0043] The lithium secondary battery according to the present disclosure includes an adhesive layer disposed between an electrode and a separator for bonding the electrode and the separator. The bonding between the electrode and the separator can be provided by a chemical bond between a polymer having a thiol group (-SH) and a binder having an olefin group (-C=C-) present when the adhesive layer is formed. Details will be described below.

[0044] The electrode according to the embodiment may further include other additives such as a dispersion medium, a viscosity modifier, and a filler in addition to the above-mentioned electrode active material, the conductive material, and the binder having an olefin group.

[0045] The electrolyte may include a lithium salt and a non-aqueous organic solvent, and may further include additives for improving charge / discharge performance and preventing overcharging. The lithium salt may include, for example, one or more selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI) and (CF3SO2)2NLi.

[0046] The non-aqueous organic solvent can be a carbonate, ester, ether or ketone, and can be used alone or in combination. Carbonate can include but is not limited to dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC) or vinylene carbonate (VC) etc. Esters can include but are not limited to gamma-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, n-propyl acetate etc. Ethers can include but are not limited to dibutyl ether.

[0047] In addition, the non-aqueous organic solvent may also include an aromatic organic solvent. Examples of aromatic organic solvents include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, etc., which may be used alone or in combination.

[0048] The separator is configured to provide a path for lithium ion movement in a lithium secondary battery and to physically separate the two electrodes. Any material commonly used as a separator in a lithium secondary battery can be used without any particular restrictions. In particular, the separator preferably has low resistance to electrolyte ion movement and excellent electrolyte wettability.

[0049] Conventional porous polymer membranes, for example, those made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, can be used alone or in a layered form as separator substrates.

[0050] Furthermore, according to the disclosed embodiments, a ceramic coated separator (CCS) may be used. The ceramic coating may be formed using one or more ceramics such as alumina, boehmite, magnesia, titanium oxide, and aluminum nitride.

[0051] On the other hand, a method is used in which an adhesive layer is applied between the separator and the electrode to prevent separation of the electrode and the separator and prevent leakage of the electrolyte. However, this method using physical bonding may not ensure sufficient adhesion, and as the size of the battery increases, it is difficult to achieve uniform adhesion between the electrode and the separator.

[0052] The disclosed embodiments provide a lithium secondary battery having improved adhesion between an electrode and a separator by replacing a binder polymer of a separator and a binder of an electrode with a functional group capable of chemical reaction.

[0053] Hereinafter, an adhesive-type separator for a lithium secondary battery according to the disclosed embodiment will be described in detail.

[0054] Figure 1 is a cross-sectional view of a lithium secondary battery according to a disclosed embodiment.

[0055] like Figure 1 As shown, the lithium secondary battery according to the disclosed embodiment includes a separator substrate 300; a cathode 100 and an anode 200 bonded to both sides of the separator substrate; and adhesive layers 310 and 320 provided between the electrodes and the separator substrate so that the electrodes and the separator substrate adhere to each other.

[0056] The adhesive layer includes a polymer having a thiol group (—SH). Specifically, the thiol group included in the adhesive layer and the olefin group included in the electrode binder can improve the adhesion between the electrode and the separator through a chemical bond generated by a thiol-ene click reaction.

[0057] The thiol and olefin groups are substituted functional groups (FGs) that allow the binder polymers of the separator and the binder of the electrode to undergo chemical reactions.

[0058] Adhesive layers 310 and 320 can be formed to a thickness of 0.5 to 2 μm to maintain a stable bond between the electrodes and the separator without affecting the overall volume of the lithium secondary battery. If the adhesive layer is too thin, the desired bonding strength may not be achieved. Conversely, if the adhesive layer is too thick, the capacity and output of the lithium secondary battery may decrease due to increased internal resistance.

[0059] Figure 2 is an enlarged view of an adhesive layer of a lithium secondary battery according to a disclosed embodiment.

[0060] refer to Figure 2 , the adhesive layers 310 and 320 are disposed on the separator substrate 300 and include a polymer having a mercapto group.

[0061] The adhesive layers 310 and 320 may be formed by mixing ceramic particles and a polymer having a mercapto group.

[0062] The ceramic particles may be prepared using one or more ceramics selected from the group consisting of alumina, boehmite, magnesia, titanium oxide, and aluminum nitride.

[0063] There is no particular limitation on the binder polymer as long as it can ensure adhesion between the electrode and the separator. However, it is preferred to use a material that exhibits adhesion only when the temperature is increased during the manufacture of the lithium secondary battery. For example, the binder polymer may include at least one polymer selected from polyvinylidene fluoride, polyvinyl pyrrolidone, polymethyl methacrylate, polybutyl acrylate, polyvinyl fluoride, and copolymers thereof.

[0064] The adhesive layers 310 and 320 may be formed into a multilayer structure in which a ceramic particle layer (not shown) is provided and a polymer layer (not shown) including a polymer having a thiol group is provided on the ceramic particle layer. In this case, the adhesive layers 310 and 320 may be provided by introducing a functional thiol group into the adhesive polymer.

[0065] On the other hand, the mercapto group may react with an olefin group which is a functional group included in the electrode binder.

[0066] Examples of the electrode binder include binder compounds such as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) as aqueous binders for the anode, and polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) for the cathode.

[0067] At this time, the functional groups in the separator's binder polymer and the electrode binder's functional groups should be able to react with each other. In the disclosed exemplary embodiment, the functional groups in the separator's binder polymer and the electrode binder's functional groups can react through a thiol-ene click reaction.

[0068] The thiol groups can be placed on either the electrode or the separator, and the olefin groups can be placed on the other. In the disclosed embodiment, the thiol groups are placed on the separator and the olefin groups are placed on the electrode. However, if a thiol-ene click reaction occurs, the functional groups can be arranged in a variety of different ways.

[0069] refer to Figure 2 The thiol groups on the adhesive layers 310 and 320 can react with the olefin groups in the cathode 100 and the anode 200 through a thiol-ene click reaction. The thiol-ene click reaction can proceed as a cross-linking reaction even at low energy. For example, the thiol-ene click reaction can proceed as a cross-linking reaction at a temperature of 70° C. or higher and a pressure of 1 MPa or higher.

[0070] At this time, the adhesive force between the separator substrate and the electrode may be 30 gf / mm or higher.

[0071] Figure 3 Binder polymers and electrode binders having substituted functional groups according to the disclosed embodiments are shown. Figure 3 When a normal polymer is represented by a chain, the functional group (FG) can be attached to the middle of the polymer chain or to both ends of the polymer chain. Specific functional group substitution methods will be described later.

[0072] Hereinafter, a method of preparing an adhesive-type separator according to the disclosed embodiment will be described.

[0073] The disclosed embodiment provides a method for preparing a lithium secondary battery, comprising: preparing a separator including a binder polymer by performing thiol modification on the separator surface; preparing electrodes including a cathode and an anode, the electrodes being provided with a binder layer including carbon double bonds; and combining the electrodes with the separator.

[0074] Applying an adhesive polymer to the prepared porous separator substrate. The adhesive polymer is applied to both sides of the porous separator substrate and then formed into an adhesive layer including a polymer having a mercapto group through a series of processes.

[0075] Figure 4 A process for producing a polymer having a mercapto group is shown. The binder polymer is described using polyvinylidene fluoride (PVDF) as an example.

[0076] PVDF is immersed in an aqueous solution obtained by mixing potassium permanganate (KMnO 4 ) and potassium hydroxide (KOH) to replace a certain amount of fluorine with -OH groups.

[0077] Then, the PVDF substituted with -OH groups may be immersed in an aqueous sodium bisulfite solution to neutralize the PVDF.

[0078] Then, mercapto-substituted PVDF can be synthesized by reacting the -OH group-substituted PVDF with hydrochloric acid (HCl) and 3-mercaptopropionic acid (MPA).

[0079] The separator can be prepared by coating a polymer having a mercapto group on both sides of the separator.

[0080] In one exemplary embodiment, the adhesive layer is formed on both sides of the separator substrate by applying a mixture of ceramic particles and a polymer having a mercapto group to the separator substrate.

[0081] In one exemplary embodiment, the adhesive layer may have a multi-layer structure in which ceramic particle layers are formed on both sides of the separator substrate, and a polymer layer including a polymer having a mercapto group is disposed on the ceramic particle layer.

[0082] Next, a binder compound is applied to the prepared electrode current collector. Examples of the binder compound include aqueous binders carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) for the anode, and polyvinylidene fluoride (PVDF) for the cathode.

[0083] A binder compound including an olefin group is applied to one surface of an electrode current collector, thereby preparing an electrode binder.

[0084] Figure 5A process for producing a binder having an olefin group is shown. The process for producing the binder is explained by using polyvinylidene fluoride (PVDF) as a cathode binder and using styrene butadiene rubber (SBR) as an anode binder.

[0085] refer to Figure 5 When PVDF as a cathode binder is immersed in a lithium hydroxide (LiOH) aqueous solution and reacted under stirring, fluorine and hydrogen are eliminated one by one based on the PVDF monomer to form a carbon double bond, so that PVDF substituted with olefin groups can be synthesized.

[0086] In the case of SBR, carbon double bonds (C=C) are already present and SBR does not need to be subjected to the above treatment. However, in the case of an anodic binder that does not have carbon double bonds, olefin group substitution can be achieved by applying the above treatment.

[0087] The electrode may be prepared by applying an electrode slurry obtained by mixing a binder having a synthetic olefin group, an electrode active material, a conductive material, and a solvent onto one surface of an electrode collector, and drying and rolling the electrode collector coated with the slurry.

[0088] Next, the electrodes are bonded to the separator. Specifically, the separator, manufactured according to the above method, is inserted between the cathode and anode inside a pouch. Afterward, an electrode assembly can be manufactured, in which the separator and electrodes are bonded together through electrolyte impregnation and a pressing process.

[0089] At this time, the pressing step can be performed by heating the separator and the electrodes under static pressure while being impregnated with the electrolyte. That is, a thiol-ene click reaction can be induced by increasing the temperature while applying physically constant pressure to the cathode and anode.

[0090] For example, the thiol-ene click reaction can be performed at a temperature of 70° C. or higher and a pressure of 1 MPa or higher.

[0091] As an initiator for the thiol-ene click reaction, an azo or peroxide compound may be added.

[0092] For example, the initiator can be selected from at least one of azo compounds including 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobisdimethylvaleronitrile (AMVN), etc., and peroxide compounds including benzoyl peroxide (BPO), lauroyl peroxide, octanoyl peroxide, dicumyl peroxide, etc. as a thermal initiator.

[0093] Hereinafter, the adhesiveness of the lithium secondary battery separator according to the embodiment of the present disclosure will be described with reference to Examples and Comparative Examples. However, the following examples are provided to help understand the present disclosure, and the scope of the present disclosure is not limited to the following examples.

[0094] To conduct an adhesion evaluation test, lithium secondary batteries of Examples and Comparative Examples were prepared according to the conditions shown in Table 1 below.

[0095] Example 1

[0096] 94 wt% of carbon powder as an anode active material, 2 wt% of styrene-butadiene rubber (SBR) and 1 wt% of carboxymethyl cellulose (CMC) as a binder, and 3 wt% of Super-P as a conductive material were added to water (H2O) to prepare an anode mixture slurry. This slurry was coated on both sides of a copper foil as a current collector, dried, and pressed to prepare an anode.

[0097] As the cathode active material, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, polyvinylidene fluoride (PVDF) as a binder, and carbon as a conductive material were mixed in a weight ratio of 93:3:4 and dispersed in N-methyl-2-pyrrolidone to prepare a cathode slurry. Aluminum foil was coated with the prepared cathode slurry, dried, and pressed to prepare a cathode.

[0098] A porous polyolefin was used as a separator substrate, and both surfaces of the separator substrate were coated with a slurry containing water and polyvinylidene fluoride (PVDF) having a mercapto group, and dried to prepare a separator.

[0099] A pouch-type lithium secondary battery is made by setting a separator between a cathode and an anode in a pouch, performing a pressing process, and combining the electrodes and the separator. During the pressing process, an electrolyte (ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) = 3 / 2 / 5 (volume ratio)) and 1 mol of lithium hexafluorophosphate (LiPF6) are injected and heated to 80°C under a pressure of 1 MPa for 5 minutes.

[0100] As a reaction initiator, an azo compound AIBN (2,2'-azobis(isobutyronitrile)) was added.

[0101] Example 2

[0102] A lithium secondary battery was prepared in the same manner as in Example 1, except that PVDF in which olefin groups were substituted by immersion in a LiOH aqueous solution was used as a cathode binder.

[0103] Comparative Example

[0104] A lithium secondary battery was prepared in the same manner as in Example 1, except that polyvinylidene fluoride (PVDF) was used as a binder polymer applied to the separator substrate, and AIBN (2,2′-azobis(isobutyronitrile)) was not used as a reaction initiator.

[0105] The electrode assemblies manufactured according to Examples 1 and 2 and the comparative example were cut into predetermined sizes and fixed on a glass slide, and then the peel strength between the separator and the electrode was measured using a 180° peel strength meter while peeling the separator.

[0106] Table 1

[0107]

[0108] As shown in Table 1, the peel strength between the anode and the separator of the lithium secondary battery of Example 1 using PVDF having a mercapto group as the binder polymer applied to the separator substrate was measured to be 35.3 gf / mm, and it was confirmed that the bonding strength of the lithium secondary battery of Example 1 was relatively better than the bonding strength of the lithium secondary battery according to the comparative example.

[0109] In Example 1, the PVDF with mercapto groups applied to the separator substrate was subjected to a thiol-ene click reaction with the SBR with carbon double bonds coated on the anode, but not with the existing PVDF applied to the cathode. Therefore, only the adhesion between the anode and the separator was improved.

[0110] In Example 2, in which PVDF having an olefin group was used as the cathode binder, the peel strength between the anode and the separator was measured to be 33.6 gf / mm, and the peel strength between the cathode and the separator was measured to be 37.5 gf / mm. That is, compared with the comparative example, the adhesion between the cathode and the separator and the adhesion between the anode and the separator were both improved.

[0111] In Example 2, PVDF having a mercapto group applied to the separator substrate and PVDF having a carbon double bond applied to the cathode were subjected to a thiol-ene click reaction, thereby improving the adhesion between the cathode and the separator.

[0112] As a result, the lithium secondary battery according to the disclosed embodiment can improve the adhesion between the separator and the electrode by introducing substituted functional groups into the binder polymer of the separator and the binder of the electrode. Therefore, the lithium secondary battery according to the disclosed embodiment can reduce the amount of electrolyte additives, thereby ensuring the price competitiveness of the lithium secondary battery.

[0113] The lithium secondary battery according to the disclosed embodiment can improve adhesion between an electrode and a separator by utilizing a chemical bond of a thiol-ene click reaction and reduce the amount of electrolyte additives, thereby ensuring price competitiveness of the lithium secondary battery.

[0114] Although some embodiments of the present disclosure have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for manufacturing a lithium secondary battery, comprising the following steps: The diaphragm is prepared by modifying the surface of the diaphragm with thiol, wherein the steps of preparing the diaphragm include: impregnating a binder polymer in an aqueous solution comprising potassium permanganate (KMnO4) and potassium hydroxide (KOH), wherein the binder polymer is polyvinyl fluoride; preparing a polymer having a mercapto group by reacting the impregnated binder polymer with hydrochloric acid (HCl) and 3-mercaptopropionic acid (MPA); and The polymer with mercapto groups is coated on both sides of the membrane. preparing an electrode comprising a cathode and an anode, the electrode comprising a binder containing carbon double bonds; and The electrode and the separator are combined, wherein the step of combining the electrode and the separator comprises: heating the separator and the electrode under static pressure while the separator and the electrode are immersed in an electrolyte, The obtained lithium secondary battery includes an adhesive layer placed between the electrode and the separator so that the electrode and the separator are bonded to each other, and the bonding between the electrode and the separator is provided by a chemical bond generated by a thiol-ene click reaction between a polymer having a thiol group and the binder layer having a carbon double bond when the adhesive layer is formed, and wherein an adhesive force between the separator and the electrode is 30 gf / mm or more at a temperature of 70° C. or more and a pressure of 1 MPa or more.

2. The method according to claim 1, wherein The binder polymer includes polyvinylidene fluoride.

3. The method according to claim 1, wherein The preparation of the binder containing carbon double bonds includes: forming carbon double bonds by immersing polyvinylidene fluoride in an aqueous solution of lithium hydroxide (LiOH).

4. The method according to claim 1, wherein The binder compound is styrene-butadiene rubber.

5. The method according to claim 1, wherein The step of combining the electrode and the separator comprises: Azo or peroxide compounds are added as reaction initiators.

6. A lithium secondary battery manufactured by the method according to claim 1, comprising: An electrode comprising a binder containing an olefin group -C=C-; diaphragm substrate; and an adhesive layer disposed between the electrode and the separator substrate so as to bond the electrode and the separator substrate to each other; Wherein, the adhesive layer includes mercapto group -SH, The thiol group -SH included in the adhesive layer is configured to form a chemical bond with the olefin group -C=C- included in the binder of the electrode through a thiol-ene click reaction, and wherein the adhesive force between the separator substrate and the electrode is 30 gf / mm or more at a temperature of 70° C. or more and a pressure of 1 MPa or more.

7. The lithium secondary battery according to claim 6, wherein The adhesive layer includes ceramic particles and a polymer having a mercapto group.

8. The lithium secondary battery according to claim 6, wherein The adhesive layer includes: a ceramic particle layer; and a polymer layer disposed on the ceramic particle layer, wherein the polymer layer includes a polymer having a mercapto group.

9. The lithium secondary battery according to claim 7, wherein: The polymer having a mercapto group includes polyvinylidene fluoride.

10. The lithium secondary battery according to claim 7, wherein The polymer having a mercapto group includes polyvinyl fluoride.

11. The lithium secondary battery according to claim 6, wherein The binder containing the olefin group -C=C- is styrene-butadiene rubber.

12. The lithium secondary battery according to claim 8, wherein The ceramic particles include at least one ceramic selected from the group consisting of alumina, boehmite, magnesia, titanium oxide, and aluminum nitride.

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