Binder composition for secondary batterry

Abstract

The present invention relates to a binder composition for a secondary battery and an electrode for a secondary battery manufactured using the same.

Description

Technology Field

[0001] The present invention relates to a binder composition for a secondary battery and an electrode for a secondary battery manufactured using the same. Background Technology

[0002] The electrodes of lithium-ion batteries consist of active materials, conductive materials, and binders; the binder is a key material that serves to bond the active and conductive materials to the metal current collector. Maximizing the adhesive strength of the binder and minimizing its content within the electrode can contribute to improving the energy density of lithium-ion batteries, which in turn affects the lifespan of batteries for electric vehicles or ESS. To enhance the energy density of lithium-ion batteries, new electrode materials with high voltage and high capacity have been continuously developed. In particular, NCM (LiNi), a representative high-capacity cathode material x Co y Mn z As O2 is being installed in electric vehicles, the need for developing binders for this purpose is increasing. In the case of existing commercial binders, polyvinylidene fluoride (PVDF) is widely used, but it lacks electrode binding strength and dispersion between active material and conductive material, so there is a need to secure source technology for a new binder that can solve these problems. Prior art literature

[0003] Republic of Korea Registered Patent Publication No. 2296582. The problem to be solved

[0004] The present invention aims to provide a binder composition for a secondary battery and an electrode for a secondary battery manufactured using the same.

[0005] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below. means of solving the problem

[0006] The first aspect of the present invention provides a binder composition comprising: a graft copolymer in which an acrylic polymer is grafted onto a polyvinylidene fluoride-based polymer main chain; and a polymer comprising amine groups.

[0007] A second aspect of the present invention provides an electrode for a secondary battery, which is manufactured using an electrode slurry comprising a binder composition, an active material, and a conductive material according to the first aspect, wherein the graft copolymer included in the binder composition and the polymer containing amine groups are cross-linked with each other.

[0008] A third aspect of the present invention provides a secondary battery comprising, as a positive electrode, an electrode for a secondary battery according to a second aspect. Effects of the invention

[0009] The binder composition according to the embodiments of the present invention and the electrode for a secondary battery manufactured using the same are characterized by adopting PVDF as the main chain to utilize the advantages of PVDF, polymerizing an acrylic polymer (polyacrylic acid, PAA) on the PVDF side chain to supplement the binding strength, and additionally crosslinking a polymer containing an amine group (polyethyleneimine, PEI) to optimize the polymer properties as a binder.

[0010] The binder composition according to the embodiments of the present invention and the electrode for a secondary battery manufactured using the same have the characteristic of improved binding strength between the active material and the conductive material due to a binder network formed by crosslinking a graft copolymer and a polymer containing amine groups. Brief explanation of the drawing

[0011] FIG. 1 shows a schematic diagram of the synthesis process of polyvinylidene fluoride (PVDF) in one embodiment of the present invention. FIG. 2 shows, in one embodiment of the present invention, PVDF, PVDFA prepared by grafting polyacrylic acid (PAA) onto PVDF, and nuclear magnetic resonance spectroscopy of intermediate-PVDFA ( 1This shows the results of the H NMR analysis. FIG. 3 is a schematic diagram of the process of forming a PVDFA-N# binder network formed by crosslinking PVDFA and polyethyleneimine (PEI) in one embodiment of the present invention. FIG. 4 shows the Fourier transform infrared spectroscopy (FT-IR) analysis results of PVDFA-N5 in one embodiment of the present invention. FIGS. 5a to 5c shows the peeling test results of electrodes with various binders applied in one embodiment of the present invention. FIG. 6 shows a peel test photograph of an electrode with various binders applied in one embodiment of the present invention. FIG. 7 shows a scanning electron microscope (SEM) image of an electrode with various binders applied in one embodiment of the present invention. FIGS. 8 and 9 show the discharge capacity according to the number of cycles of a secondary battery manufactured with an electrode to which various binders are applied, in one embodiment of the present invention. Specific details for implementing the invention

[0012] Hereinafter, embodiments and examples of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments and examples described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0013] Throughout this specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other elements interposed between them.

[0014] Throughout this specification, when a component is described as being located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0015] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0016] Terms of degree used in this specification, such as “about,” “substantially,” etc., are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0017] The terms “step of” or “step of” as used throughout this specification do not mean “step for”.

[0018] Throughout this specification, the term “combination(s) of these” included in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including one or more selected from the group consisting of said components.

[0019] Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

[0020] Throughout this specification, the term “alkyl” or “alkyl group” comprises linear or branched alkyl groups having 1 to 12 carbon atoms, 1 to 10 carbon atoms, 1 to 8 carbon atoms, or 1 to 5 carbon atoms, and all possible isomers thereof. For example, the alkyl or alkyl group may be a methyl group (Me), an ethyl group (Et), an n-propyl group ( n Pr), iso-propyl group ( i Pr), n-butyl group ( n Bu), iso-butyl group ( i Bu), tert-butyl group (tert-Bu, t Bu), sec-butyl group(sec-Bu, sec Bu), n-pentyl group ( n Pe), iso-pentyl group ( iso Pe), sec-pentyl group( sec Pe), tert-pentyl group( t Pe), neo-pentyl group( neo Examples include, but are not limited to, 3-pentyl groups, n-hexyl groups, iso-hexyl groups, heptyl groups, 4,4-dimethylpentyl groups, octyl groups, 2,2,4-trimethylpentyl groups, nonyl groups, decyl groups, undecyl groups, dodecyl groups, and isomers thereof.

[0022] Embodiments of the present invention have been described in detail below, but the present invention may not be limited thereto.

[0024] The first aspect of the present invention provides a binder composition comprising: a graft copolymer in which an acrylic polymer is grafted onto a polyvinylidene fluoride (PVDF)-based polymer main chain; and a polymer comprising amine groups.

[0025] In one embodiment of the present invention, the polyvinylidene fluoride-based polymer may comprise one or more selected from polyvinylidene fluoride (PVDF) homopolymer, polyvinylidene hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride chlorotrifluoroethylene copolymer (PVDF-TCFE), but may not be limited thereto.

[0026] In one embodiment of the present invention, the polyvinylidene fluoride-based polymer may comprise vinylidene fluoride repeating units.

[0027] In one embodiment of the present invention, the acrylic polymer may include -COOH at the terminal.

[0028] In one embodiment of the present invention, the acrylic polymer may comprise one or more selected from polyacrylic acid and polymethacrylic acid, but is not limited thereto.

[0029] In one embodiment of the present invention, the polymer containing the amine group may include one or more selected from polyethyleneimine, polyallylamine, poly(2-aminoethyl methacrylate), poly(ethylene glycol) diamine, polyaniline, polyvinylamine, and polyurea, but is not limited thereto.

[0030] In one embodiment of the present invention, the mol% of the amine group relative to the vinylidene fluoride repeating unit of the polyvinylidene fluoride-based polymer is about 0.5 mol% to about 10 mol%, about 0.5 mol% to about 9 mol%, about 0.5 mol% to about 8 mol%, about 0.5 mol% to about 7 mol%, about 0.5 mol% to about 6 mol%, about 0.5 mol% to about 5 mol%, about 1 mol% to about 10 mol%, about 1 mol% to about 9 mol%, about 1 mol% to about 8 mol%, about 1 mol% to about 7 mol%, about 1 mol% to about 6 mol%, about 1 mol% to about 5 mol%, about 2 mol% to about 10 mol%, about 2 mol% to about 9 mol%, about 2 mol% to about 8 mol%, about 2 mol% to about 7 mol%, It may be about 2 mol% to about 6 mol%, about 2 mol% to about 5 mol%, about 3 mol% to about 10 mol%, about 3 mol% to about 9 mol%, about 3 mol% to about 8 mol%, about 3 mol% to about 7 mol%, about 3 mol% to about 6 mol%, about 3 mol% to about 5 mol%, more than about 3 mol% to about 10 mol%, more than about 3 mol% to about 9 mol%, more than about 3 mol% to about 8 mol%, more than about 3 mol% to about 7 mol%, more than about 3 mol% to about 6 mol%, or more than about 3 mol% to about 5 mol%.

[0031] In one embodiment of the present invention, the binder composition may additionally include an organic solvent.

[0032] In one embodiment of the present invention, the organic solvent may comprise one or more selected from N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), pyridine, propanol, acetone, methanol, and ethanol, but is not limited thereto.

[0034] A second aspect of the present invention provides an electrode for a secondary battery, which is manufactured using an electrode slurry comprising a binder composition, an active material, and a conductive material according to the first aspect, wherein the graft copolymer included in the binder composition and the polymer containing amine groups are cross-linked with each other.

[0035] Detailed explanations have been omitted for parts that overlap with the first aspect of the present invention, but the content described in the first aspect of the present invention may be applied in the same way even if such explanations are omitted in the second aspect of the present invention.

[0036] In one embodiment of the present invention, when the electrode slurry is applied to a current collector and heat-treated, the graft copolymer of the binder composition and the polymer containing amine groups can be cross-linked with each other. More specifically, a cross-linking reaction between the carboxyl group (-COOH) of the graft copolymer and the amine group of the polymer containing amine groups can occur.

[0037] In one embodiment of the present invention, a binder network comprising the graft copolymer may be formed due to a crosslinking reaction between the graft copolymer and the polymer containing the amine group.

[0038] In one embodiment of the present invention, the binder network may include, but is not limited to, NH bonds, amide bonds, and imine bonds.

[0039] In one embodiment of the present invention, the heat treatment may be performed for about 10 hours to about 30 hours, about 10 hours to about 150°C, about 100°C to about 140°C, about 100°C to about 130°C, about 110°C to about 150°C, about 110°C to about 140°C, or about 110°C to about 130°C, for about 10 hours to about 30 hours, about 10 hours to about 20 hours, about 10 hours to about 17 hours, about 10 hours to about 16 hours, about 15 hours to about 30 hours, about 15 hours to about 20 hours, about 15 hours to about 17 hours, or about 15 hours to about 16 hours.

[0040] In one embodiment of the present invention, the active material may include Li, but is not limited thereto.

[0041] In one embodiment of the present invention, the active material is LiNi a Co b Mn c It may contain O2 (0.6≤a≤0.9, a+b+c=1), but is not limited thereto. Here, the active material may be NCM811.

[0043] A third aspect of the present invention provides a secondary battery comprising, as a positive electrode, an electrode for a secondary battery according to a second aspect.

[0044] Detailed descriptions of parts that overlap with the first and second aspects of the present invention have been omitted, but the descriptions of the first and second aspects of the present invention may be applied in the same way even if such descriptions are omitted in the third aspect of the present invention.

[0045] In one embodiment of the present invention, the secondary battery may include a lithium-ion battery, but may not be limited thereto.

[0046] In one embodiment of the present invention, the lithium-ion battery has about 90 mAh g at about 600 cycles or more. -1 It may have excellent lifespan characteristics by having a discharge capacity.

[0047] In one embodiment of the present invention, the lithium-ion battery may have excellent lifespan characteristics by maintaining a value of at least 65% of the initial discharge capacity after about 500 cycles of operation.

[0048] The present invention will be explained in more detail below using examples, but the following examples are merely illustrative to aid in understanding the present invention, and the content of the present invention is not limited to the following examples.

[0050] [Example]

[0051] 1. PVDFA Synthesis

[0052] PVDFA, in which polyacrylic acid (PAA) was grafted onto polyvinylidene fluoride (PVDF), was synthesized using the atom transfer radical polymerization (ATRP) method. PVDF (1.00 g, 15.6 mmol of VDF groups), CuCl (0.010 g, 0.100 mmol), and 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) (0.047 g, 0.21 mmol) were dissolved in 22.9 mL of tert-butyl acrylate (tBA) and then added to a single-neck flask equipped with a magnetic stirring bar. After purging the flask with argon gas for 15 minutes, the polymerization reaction was carried out for 17 hours in an oil bath controlled to a constant temperature of 100°C. The reaction was quenched using liquid nitrogen and precipitated twice in acetone. The mixture was dried overnight at 30°C under dynamic vacuum to obtain a slightly brownish powder. The obtained polymer (1.00 g, 13.1 mmol VDFA) and HCl (0.360 g, 9.90 mmol) were dissolved in 19.4 mL of 1,4-dioxane and added to a single-neck flask equipped with a magnetic stirring bar. The reaction was carried out at 60°C for 20 hours, and the crude product was precipitated twice in distilled water. PVDFA was obtained with an 80% yield by drying overnight under dynamic vacuum. Fig. 1 A schematic diagram of the PVDFA synthesis process is shown in [figure].

[0053] In order to verify whether the PVDFA modification experiment proceeded well 1 H NMR Analysis was performed ( Fig. 2In the primary reaction product (intermediate-PVDFA), a proton signal a, which is not present in the original PVDF, appeared at 1.5 ppm. This corresponds to the proton signal of -OC-(CH3)3 in tBA. In PVDFA, the proton signal a found in the intermediate-PVDFA disappeared, confirming that a hydrolysis reaction occurred and the anhydride group was converted into a carboxylic acid group.

[0054] 2. Preparation of binder solution for electrode manufacturing

[0055] A pre-binder solution was prepared by dissolving PVDFA and PEI in NMP (N-Methyl-2-pyrrolidone). The resulting pre-binder was named PVDFA-N#, where # represents the mol% of amine groups present in PEI relative to the VDF repeating units of PVDFA. The following is a representative procedure for preparing PVDFA-N5. PVDFA (0.200 g, 3.16 mmol of VDF groups) and PEI (7.00 mg, 0.158 mmol of amine groups) were dissolved in 3.97 mL of NMP and magnetically stirred at 40°C for 18 hours until a homogeneous solution was obtained.

[0056] 3. NCM Anode Manufacturing

[0057] LiNi as a cathode active material 0.8 Co 0.1 Mn 0.1O2 (NCM811) (80 wt%) was used and dispersed in NMP along with SuperP (10 wt%) and a pre-binder (PVDFA-N#) (10 wt%). The resulting slurry was uniformly applied to an aluminum (Al) current collector using a doctor blade and dried overnight at 120°C under dynamic vacuum conditions. The dried electrode was roll-pressed at room temperature to reduce its thickness by 30%, bringing it to 70% of its original thickness. The mass loading of the active material in the NCM cathode was approximately 10 mg cm⁻¹. -2 11 mg cm⁻¹ -2 It is a range.

[0058] Fig. 3 This is a schematic diagram showing the change in polymer structure during electrode fabrication. A cross-linking reaction occurs between the -COOH of PVDFA and the -NH2 of PEI, and finally, an electrode having a binder structure in the form of a PVDFA-N network was fabricated.

[0059] FT-IR to confirm whether the crosslinking experiment of PVDFA-N5 proceeded well Analysis was performed ( Fig. 4 ). The observation of a carboxylic acid C=O peak in PVDFA, which is absent in conventional PVDF, confirmed that the PVDFA modification experiment was successful. Additionally, the observation of NH, amide C=O, and C=N peaks in the crosslinking product PVDFA-N5, which are absent in PVDFA, confirmed that the crosslinking experiment proceeded successfully.

[0060] 4. Electrochemical Analysis

[0061] Charge / discharge cycle tests of Li / Celgard®2320 / NCM811 cells were performed using 2032 coin cells at 30°C in a cut-off voltage range of 3.0 V to 4.3 V (vs. Li / Li+), unless otherwise specified, where 1 C is 200 mA g -1 This corresponds to a current density. Prior to the main cycle, all cells underwent three formation cycles at 0.1 C during the charge / discharge process. Subsequently, cycling was performed under 0.5 C charge / discharge conditions. 1.2 M LiPF6 in EC:EMC (3:7 vol%) containing 2 wt% VC and 10 wt% FEC was used as the liquid electrolyte. All cell components were assembled in an argon-filled glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0063] Experimental Example 1. Evaluation of binding strength

[0064] The binding strength of the binder was evaluated by attaching 3M double-sided tape to the electrode and conducting a 180° peel test by peeling it off at a 180-degree angle. FIGS. 5a to c The measurement equipment used was a material testing machine (Lloyd-LS1+) with a crosshead speed of 30 mm / min. 3M double-sided tape was measured using a rubber roller (diameter: 95 mm, width: 45 mm, weight: 2.0 kg) at a depth of 1.2 × 2.0 cm. 2 It was attached to an electrode sample of size and maintained constant pressure throughout the experiment. Adhesion was recorded when peeled off at a 180° angle. c of Fig. 5 The value was derived as the average value of the flat portion force of each sample in Figures 5a and 5b. In the case of PVDFA, the binding strength increased by approximately 3 times compared to conventional PVDF. When PVDFA is additionally cross-linked with PEI, the binder structure becomes networked and has the effect of binding the active material and the conductive material more effectively; therefore, the binding strength showed a trend of increasing further as the PEI content increased.

[0065] Fig. 6 The images show the cathode electrode before (left) and after (center) the peel test, and the tape after the peel test (right). When using the PVDF binder, it was confirmed that the adhesion was low, as the electrode was mostly peeled off from the aluminum (Al) current collector by the 3M tape. When using the PVDFA binder, it was confirmed that the adhesion was improved due to the excellent adhesive properties of the -COOH. Additionally, when using the crosslinked PVDFA-N# binder, it was confirmed that peeling occurred in PVDFA-N1 to PVDFA-N3, which had not yet formed a crosslinked structure, due to the relatively low adhesion; however, PVDFAN-5, which had undergone significant crosslinking, exhibited superior adhesion compared to the existing PVDFA, resulting in almost no peeling.

[0066] Fig. 7 Figure 1 shows the surface SEM images of anodes prepared with PVDF, PVDFA, and PVDFA-N5, respectively. In the case of PVDF, numerous cracks were observed on the electrode surface, and some NCM active materials appeared unbound. In the case of PVDFA, although it showed improvement compared to PVDF, fine cracks and unbound active materials were still observed. In the case of PVDFA-N5, no cracks were observed, and it was confirmed that the active material and conductive material were well encapsulated and bound by the binder.

[0068] Experimental Example 2. NCM / Li Cell Test Results

[0069] Fig. 8 The following are the test results for Li / Celgard®2320 / NCM811 cells using PVDF, PVDFA, and PVDFA-N5 binders (0.5 C, 30℃). When switching from PVDF to PVDFA, the lifetime increased slightly from the existing 180 cycles to 250 cycles. In the case of the electrode with the binder applied, which was crosslinked from PVDFA to PVDFA-N5, it was confirmed that the performance significantly increased by exhibiting a long lifetime of over 500 cycles.

[0070] Fig. 9 This is the result of testing Li / Celgard®2320 / NCM811 cells using PVDFA and PVDFA-N# binders. It was confirmed that PVDFA-N5 had the best lifespan of over 600 cycles, which corresponds to the binding strength evaluation result in Fig. 5.

[0072] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical concept or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0073] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A binder composition comprising: a graft copolymer in which an acrylic polymer is grafted onto a polyvinylidene fluoride-based polymer main chain; and a polymer containing amine groups, wherein the acrylic polymer comprises one or more selected from polyacrylic acid and polymethacrylic acid, and the polymer containing amine groups comprises one or more selected from polyethyleneimine, polyallylamine, poly(2-aminoethyl methacrylate), poly(ethylene glycol) diamine, polyaniline, polyvinylamine, and polyurea. Claim 2 A binder composition according to claim 1, wherein the polyvinylidene fluoride-based polymer comprises one or more selected from polyvinylidene fluoride (PVDF) homopolymer, polyvinylidene hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride chlorotrifluoroethylene copolymer (PVDF-TCFE). Claim 3 delete Claim 4 delete Claim 5 A binder composition according to claim 1, wherein the mol% of the amine group relative to the vinylidene fluoride repeating unit of the polyvinylidene fluoride-based polymer is 0.5 mol% to 10 mol%. Claim 6 A binder composition according to claim 1, further comprising an organic solvent. Claim 7 An electrode for a secondary battery manufactured using an electrode slurry comprising a binder composition, an active material, and a conductive material according to claim 1, wherein the graft copolymer included in the binder composition and the polymer containing amine groups are cross-linked with each other. Claim 8 In claim 7, the active material is LiNi a Co b Mn c An electrode for a secondary battery containing O2 (0.6≤a≤0.9, a+b+c=1). Claim 9 A secondary battery comprising an electrode for a secondary battery according to claim 7 as a positive electrode.

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