Binder for secondary batteries, slurry containing the same, electrodes and secondary batteries

Abstract

The present invention includes a water-soluble polymer and a conductive polymer, the water-soluble polymer includes a first copolymer, the conductive polymer includes a second copolymer and a polymer of a conductive monomer, the second copolymer has a degree of hydrolysis of 50% or more, and has a peak at 3250 cm in an FT-IR spectrum. -1 Or 3350cm -1 The present invention provides a binder for secondary batteries, in which an absorbance peak appears at 22% or more, and a slurry, electrode, and secondary battery each containing the binder.

Description

[Technical Field]

[0001] The present invention relates to a binder for secondary batteries containing a conductive polymer, a slurry containing the same, an electrode, and a secondary battery. Specifically, the present invention relates to a binder for secondary batteries containing a conductive polymer that can exhibit excellent properties by adjusting the degree of hydrolysis of the water-soluble monomer used in the production of the conductive polymer for secondary batteries, a slurry containing the same, an electrode, and a secondary battery. [Background technology]

[0002] Lithium batteries are used as power sources for portable electronic devices such as video cameras, mobile phones, and laptop computers. Rechargeable lithium secondary batteries have an energy density more than three times higher per unit weight compared to existing lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and enable fast charging.

[0003] Generally, lithium secondary batteries are manufactured by using materials capable of reversible intercalation and deintercalation of lithium ions as the positive electrode active material and the negative electrode active material, and by filling the space between the positive electrode containing the positive electrode active material and the negative electrode containing the negative electrode active material with an electrolyte.

[0004] On the other hand, while binders in electrode materials play a major role in maintaining the electrode plate structure, they can also affect the properties of electrodes and lithium secondary batteries manufactured using them. Water-soluble conductive polymers are sometimes added to improve binder performance. However, existing water-soluble monomers used in the production of water-soluble conductive polymers have drawbacks: as the PEDOT content relative to the polymer increases, aggregation occurs and dispersion power decreases, resulting in poor processability and reduced electrical conductivity. Furthermore, as the PEDOT content increases during slurry production, viscosity decreases, negatively impacting slurry rheology. Additionally, conductive polymers with excellent dispersion power are easy to process, but their low electrical conductivity can reduce electrical conductivity within the electrode, affecting electrode performance. Therefore, there is a need for research into conductive polymers that can overcome these disadvantages. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to solve the problems of the conventional technology described above, and to provide a binder for secondary batteries containing a conductive polymer that can embody excellent properties by adjusting the degree of hydrolysis of the water-soluble monomer used in the production of conductive polymers for secondary batteries, a slurry containing the same, an electrode, and a secondary battery. [Means for solving the problem]

[0006] A binder for a secondary battery according to one embodiment of the present invention comprises a water-soluble polymer and a conductive polymer, the water-soluble polymer comprising a first copolymer, and the conductive polymer comprising a second copolymer and a polymer of conductive monomers, the second copolymer having a degree of hydrolysis of 50% or more and an FT-IR spectrum of 3250 cm⁻¹ -1 or 3350cm -1 The absorbance peak that appears may be 22% or higher.

[0007] The first copolymer is a copolymer of a polymer containing polar functional groups and PAA, and may have an uncontrolled degree of hydrolysis. The first copolymer may also be PVA-PAA with an uncontrolled degree of hydrolysis.

[0008] The second copolymer is a copolymer of a polymer containing polar functional groups and PAA, and may have a controlled degree of hydrolysis. The second copolymer may be a PVA-PAA copolymer with a controlled degree of hydrolysis.

[0009] The conductive monomer may be one or more selected from the group consisting of EDOT (3,4-Ethylenedioxythiophene), thiophene monomers, polyacetylene, polyaniline, and polypyrrole.

[0010] The conductive polymer may contain conductive monomers in a weight ratio of 1:0.5 to 20 relative to the second copolymer. The conductive polymer may also be contained in a ratio of 4 to 6:1 relative to the water-soluble polymer.

[0011] A slurry according to one embodiment of the present invention may include an electrode active material and the aforementioned binder.

[0012] The total slurry may contain 95 to 99% by weight of electrode active material and 1 to 5% by weight of binder, based on 100% by weight of the total slurry.

[0013] An electrode according to one embodiment of the present invention may be formed by applying and drying the aforementioned slurry on the surface of a current collector.

[0014] A secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, an electrolyte interposed between them, and a separator membrane inserted between the positive electrode and the negative electrode, wherein one or more of the positive and negative electrodes may be the aforementioned electrodes. [Effects of the Invention]

[0015] The binder for secondary batteries containing a conductive polymer according to the embodiment of the present invention has the characteristics of high dispersion and high electrical conductivity. The slurry according to the embodiment of the present invention has excellent dispersion stability. The electrodes according to the embodiments of the present invention have excellent electrode conductivity. Furthermore, the secondary battery according to the embodiments of the present invention has improved battery internal resistance and life characteristics. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a graph showing the degree of hydrolysis of PAA-1 and PAA-5 produced by the manufacturing example of the present invention, measured via FT-IR. [Figure 2] Figure 2 is a photograph confirming the presence or absence of phase separation in the conductive polymer binder of Example 2 and Comparative Example 2 of the present invention. [Figure 3] Figure 3 shows photographs of the evaluation of the dispersion stability of the slurries of Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of the present invention using a grind gauge. [Figure 4] Figure 4 is a graph showing the electrochemical evaluation results for the lithium secondary batteries of Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of the present invention. [Modes for carrying out the invention]

[0017] The terms First, Second, Third, etc., are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Thus, the First Part, component, region, layer, or section described below may be referred to as the Second Part, component, region, layer, or section, to the extent that it does not fall outside the scope of the invention. The technical terms used herein are merely for the purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes the plural form unless the text explicitly indicates the opposite. The meaning of “including” as used in this specification is to embody a particular characteristic, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other characteristics, regions, integers, steps, operation, element, and / or component. When one part is said to be “on top of” or “on top of” another part, this means that it is directly on top of or on top of the other part, or that the other part may be between them. In contrast, when one part is said to be "directly above" another part, there is no other part intervening between them. Unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent. Although not defined differently, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have a meaning consistent with the relevant technical literature and the present disclosure, and are not interpreted in their ideal or highly formal sense unless otherwise defined. Embodiments of the invention are described below in detail so that they can be easily implemented by a person of ordinary skill in the art to which this invention pertains. However, the invention can be embodied in a variety of different forms and is not limited to the embodiments described herein.

[0018] A binder for a secondary battery according to one embodiment of the present invention comprises a water-soluble polymer and a conductive polymer, the water-soluble polymer comprises a first copolymer, and the conductive polymer comprises a second copolymer and a polymer of conductive monomers, the second copolymer having a degree of hydrolysis of 50% or more and an FT-IR spectrum of 3250 cm⁻¹ -1 or 3350cm -1 The absorbance peak that appears may be 22% or higher.

[0019] Water-soluble polymers are added for the binding force between the active material and electrodes, and conductive polymers are added to improve the electrical conductivity of the binder. In one embodiment of the present invention, a functional binder with improved binding and electrical conductivity can be obtained by using a mixture of water-soluble polymers and conductive polymers for a secondary battery.

[0020] A binder for a secondary battery according to one embodiment of the present invention may include a polymer of a second copolymer and a polymer of a conductive monomer. By including a polymer of a second copolymer and a polymer of a conductive monomer, dispersibility and electrical conductivity can be improved.

[0021] The second copolymer can have a degree of hydrolysis of 50% or more. Specifically, the second copolymer can have a degree of hydrolysis of 60% or more, and more specifically, a degree of hydrolysis of 70% or more. If the degree of hydrolysis of the second copolymer is excessively low, the dispersibility of the manufactured conductive polymer will be low, resulting in poor slurry stability and potentially causing problems with reduced electrode performance.

[0022] A binder for a secondary battery according to one embodiment of the present invention has an FT-IR spectrum of 3250 cm⁻¹ of the second copolymer. -1 or 3350cm -1The absorbance peak that appears may also be 22% or more. In the FT-IR spectrum, the size of the peak can be quantified by the absorbance, the area of the peak, and the shape of the peak. Specifically, it can be said that the larger the absorbance (%) (= 100% - transmittance (%)), the wider the area of the peak, and the sharper the shape of the peak, the larger the size of the peak. As the degree of hydrolysis of the second copolymer increases, more polar functional groups such as -OH and -COOH in the chain structure are included, so the absorbance increases and the O-H peak size increases in the range of 3250 cm -1 to 3350 cm -1 Specifically, the absorbance peak that appears in the FT-IR spectrum at 3250 cm -1 to 3350 cm -1 may also be 23% or more.

[0023] The first copolymer is a copolymer of a polymer containing a polar functional group and PAA, and may not have its degree of hydrolysis adjusted. By using a copolymer of a polymer containing a polar functional group and PAA as the first copolymer, an effect of improving the adhesion and dispersibility of the active material and the electrode can be obtained compared to the case of using PAA or PSS alone. Specifically, the first copolymer may be one or more selected from the group consisting of PVA-PAA, PEO-PAA, PPO-PAA, HEA-PAA, PHEA-PAA, PVP-PAA, PAM-PAA, PAN-PAA, PVAM-PAA, etc. whose degree of hydrolysis is not adjusted. More specifically, the first copolymer may be PVA-PAA whose degree of hydrolysis is not adjusted. Also, when using a first copolymer with an adjusted degree of hydrolysis, there may be a problem that the adhesion and dispersibility of the binder become low. In the case of the first copolymer whose degree of hydrolysis is not adjusted, it can show a degree of hydrolysis of 0% to 10%.

[0024] The second copolymer is a copolymer of a polymer containing polar functional groups and PAA, and its degree of hydrolysis may be controlled. By using a copolymer of a polymer containing polar functional groups and PAA as the second copolymer, the binding strength and dispersibility of the active material and electrodes are improved compared to when PAA or PSS is used alone. Specifically, the second copolymer may be one or more selected from the group consisting of PVA-PAA, PEO-PAA, PPO-PAA, HEA-PAA, PHEA-PAA, PVP-PAA, PAM-PAA, PAN-PAA, and PVAM-PAA, with controlled degrees of hydrolysis. More specifically, the second copolymer may be PVA-PAA with controlled degrees of hydrolysis. If a second copolymer with an uncontrolled degree of hydrolysis is used, problems such as reduced dispersibility and electrical conductivity may occur.

[0025] The conductive monomer may be one or more selected from the group consisting of EDOT (3,4-Ethylenedioxythiophene), thiophene monomers, polyacetylene, polyaniline, and polypyrrole, but is not limited thereto. Specifically, the conductive monomer may be EDOT.

[0026] The conductive polymer may contain conductive monomers in a weight ratio of 1:0.5 to 20 relative to the second water-soluble monomer. Specifically, it may contain conductive monomers in a ratio of 1:0.5 to 10 relative to the second water-soluble monomer. More specifically, it may contain conductive monomers in a ratio of 1:0.5 to 2 relative to the second water-soluble monomer. If the ratio of the second copolymer (PAA-x) is excessively low compared to the conductive monomer (EDOT), a problem may arise in which the electrical conductivity decreases. Conversely, if the ratio of the second copolymer is excessively high compared to the conductive monomer, a problem may arise in which the dispersibility decreases.

[0027] The conductive polymer may be included in a ratio of 4 to 6:1 to the water-soluble polymer. If the ratio of the water-soluble polymer (PVA-PAA) is excessively low compared to the conductive polymer (PEDOT:PAA-x), problems may arise such as reduced active material and electrode binding strength. Conversely, if the ratio of the water-soluble polymer is excessively high compared to the conductive polymer, problems may arise such as reduced electrical conductivity of the electrode.

[0028] A slurry according to one embodiment of the present invention may contain an electrode active material and the aforementioned binder. A slurry according to one embodiment of the present invention may further contain a solvent, a conductive material, etc., as needed. Specifically, a slurry according to one embodiment of the present invention may contain 95 to 99% by weight of electrode active material and 1 to 5% by weight of binder, based on 100% by weight of the total slurry. More specifically, based on 100% by weight of the total slurry, it may contain 96 to 98% by weight of electrode active material and 2 to 4% by weight of binder. If the amount of electrode active material included is excessively low, there is a possibility that the electrochemical performance of the battery will decrease, and if the amount of electrode active material included is excessively high, there is a possibility that the electrodes cannot be manufactured (decreased bonding strength). Furthermore, if the amount of binder included is excessively low, there is a possibility that the adhesion strength between the active material and the electrode will be low, and if the amount of binder included is excessively high, there is a possibility that the resistance of the battery will increase.

[0029] The electrode active material may be either a positive electrode active material or a negative electrode active material. The positive electrode active material can be any lithium-containing metal oxide commonly used in the industry, without limitation. For example, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used, and a specific example is Li a A 1-b B 1 b D 12 (In the above equation, 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b B 1 b O 2-c D 1 c (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b B 1 b O 4-c D 1 c (In the above equation, 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B 1 c D 1 α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 2 (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Mn b B 1 c D 1 α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 α(In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 2(In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1.); Li a Ni b Co c Mn d G e O2(In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1.); Li a NiG b O2(In the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1.); Li a CoG b O2(In the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1.); Li a MnG b O2(In the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1.); Li a Mn2G b O4(In the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1.); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI 1 O2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Any one of the compounds represented by the chemical formulas of Fe2(PO4)3(0 ≤ f ≤ 2); LiFePO4 can be used.

[0030] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof, and B 1is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof, D 1 is O, F, S, P, or combinations thereof, E is Co, Mn, or combinations thereof, F 1 is F, S, P, or combinations thereof, G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof, Q is Ti, Mo, Mn, or combinations thereof, I is Cr, V, Fe, Sc, Y, or combinations thereof, J is V, Cr, Mn, Co, Ni, Cu, or combinations thereof.

[0031] Specifically, LiCoO2, LiMn x O 2x (x = 1, 2), LiNi 1-x Mn x O 2x (0 < x < 1), LiNi 1-x-y Co x Mn y O2(0 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.5), LiFePO4, etc.

[0032] Of course, compounds having a coating layer on their surface can also be used, or a mixture of the compound and a compound having a coating layer can be used. This coating layer may contain coating element compounds of oxide, hydroxide, oxyhydroxy, oxycarbonate, or hydroxycarbonate of the coating element. These compounds forming the coating layer may be amorphous or crystalline. As the coating elements included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof can be used. The coating layer formation step can be carried out using any coating method that does not adversely affect the physical properties of the positive electrode active material using these elements (e.g., spray coating, immersion method, etc.), and since this is well understood by those engaged in this field, a detailed explanation will be omitted.

[0033] The negative electrode active material can be any material that can be used as a negative electrode active material for lithium secondary batteries in the art. For example, it may include one or more materials selected from the group consisting of lithium metal, metals alloyable with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0034] Specifically, the metals that can form an alloy with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element or a combination of these elements, and is not Si), Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element or a combination of these elements, and is not Sn), etc. As the element Y, it may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

[0035] Specifically, the transition metal oxides may be lithium titanate, vanadium oxide, lithium vanadate, etc.

[0036] Specifically, the non-transition metal oxides may be SnO2, SiO x (0 < x < 2), etc.

[0037] Specifically, the carbon-based material may be crystalline carbon, amorphous carbon or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, etc. More specifically, the carbon-based material may be graphite.

[0038] As the solvent, N-methylpyrrolidone, acetone, water, etc. can be used, but it is not limited thereto, and any solvent that can be used in the technical field can be used.

[0039] While carbon black and graphite nanoparticles can be used as conductive materials, the materials are not limited to these; any material that can be used as a conductive material in the relevant technical field can be used.

[0040] An electrode according to one embodiment of the present invention may be formed by applying and drying the aforementioned slurry on the surface of a current collector.

[0041] A secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, an electrolyte interposed between them, and a separator membrane inserted between the positive electrode and the negative electrode, wherein one or more of the positive electrode and the negative electrode may be the aforementioned electrodes.

[0042] Any separation membrane commonly used in lithium batteries can be used. A membrane with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity can be used. Specifically, it can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or combinations thereof, and may be in nonwoven or woven fabric form. Specifically, for lithium-ion batteries, a rollable polyolefin separation membrane such as polyethylene or polypropylene can be used, and for lithium-ion polymer batteries, a separation membrane with excellent organic electrolyte impregnation capacity can be used.

[0043] The electrolyte may be an organic electrolyte. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

[0044] Any organic solvent that can be used as an organic solvent in the art may be used. Specifically, it may include one or more selected from the group consisting of ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), butylene carbonate, ethyl propionate, ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, gamma-valerolactone, gamma-butyrolactone, and tetrahydrofuran, but is not limited thereto, and any organic solvent that can be used as an organic solvent in the art may be used.

[0045] Any lithium salt that can be used as a lithium salt in the relevant art can be used. Specifically, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are natural numbers), LiCl, LiI, or mixtures thereof, etc.

[0046] Furthermore, the electrolyte may be solid. Specifically, it may be boron oxide, lithium oxynitride, etc., but is not limited to these, and any material that can be used as a solid electrolyte in the art can be used. The solid electrolyte may be formed on the negative electrode by methods such as sputtering.

[0047] The embodiments of the present invention will be described below in detail so that they can be easily implemented by a person with ordinary skill in the art to which the invention pertains. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein. [Examples]

[0048] [Manufacturing Example - Synthesis and Hydrolysis of PVA-PAA Polymer]

[0049] (1) Synthesis of PVA-PAA polymers with uncontrolled degree of hydrolysis

[0050] 1050 g of distilled water and 10 g of emulsifier (dowfax) were added to the reactor as solvents. After stirring under a nitrogen atmosphere for 1 hour, 2.5 g of initiator (KPS, potassium persulfate) was added. 140 g of vinyl acetate and 350 g of ethyl acrylate were added dropwise to the reactor as monomers for 3 hours, and polymerization was carried out at 65°C for 1 hour to produce a PVA-PAA (Polyvinylacetate-Polyethylacrylate) copolymer. (Hereafter, the PVA-PAA copolymer with an unadjusted degree of hydrolysis will be referred to as "PVA-PAA".)

[0051] (2) Hydrolysis of PVA-PAA polymer

[0052] Hydrolysis of PVA-PAA was carried out using 150g of ethanol and 17g of NaOH (sodium hydroxide) at 65°C, with the hydrolysis reaction time adjusted. The hydrolyzed PVA-PAA was dissolved in distilled water and washed several times to produce hydrolyzed PVA-PAA copolymers. (Hereafter, PVA-PAA copolymers with a degree of hydrolysis of 30% will be referred to as "PAA-1", PVA-PAA copolymers with a degree of hydrolysis of 70% as "PAA-3", and PVA-PAA copolymers with a degree of hydrolysis of 90% as "PAA-5".)

[0053] [Example 1]

[0054] (1) Manufacturing of conductive polymer binders

[0055] Using 300g of water as the solvent, 5g of the solid content of the acceptor PAA-3 produced in the above production example and 5g of the conductive monomer EDOT (ethylenedioxythiophene) were mixed in a 1:1 ratio, and 10g of an initiator (APS, ammonium persulfate) was added to produce the conductive polymer binder "PEDOT:PAA-3".

[0056] (2) Production of slurry

[0057] A slurry was prepared by mixing 97% by weight of graphite as the electrode active material, 2.5% by weight of PVA-PAA and 0.5% by weight of PEDOT:PAA-3 as binders, adding the mixture to distilled water, and stirring with a mechanical agitator.

[0058] (3) Manufacturing of electrodes (negative electrode)

[0059] The manufactured slurry was coated to a thickness of 300-400 μm onto a 10 μm copper foil film, which served as the negative electrode current collector. After drying in a hot air dryer at 110°C for 1 hour, the negative electrode was manufactured by rolling it in a roll press.

[0060] (4) Manufacturing of secondary batteries

[0061] The positive electrode, electrolyte (a non-aqueous electrolyte containing lithium), and separation membrane used in the secondary battery manufacturing process were purchased and used as NCM 622 (South Korea, Welcos Co., Ltd.), 1M LiPF6 DEC / EC+FEC 1% (South Korea, Soulbrain), and polyolefin separation membrane Celgard 2325 (USA, Celgard), respectively. A lithium secondary battery was manufactured using the negative electrode manufactured in (3) above, along with the positive electrode, electrolyte, and separation membrane.

[0062] [Example 2]

[0063] In the production of the conductive polymer binder, the conductive polymer, slurry, electrode, and secondary battery were manufactured in the same manner as in Example 1, except that "PEDOT:PAA-5" was produced by using PAA-5 produced in the above production example as the acceptor.

[0064] [Comparative Example 1]

[0065] In the slurry preparation, 97% by weight of graphite was used as the electrode active material and 3.0% by weight of PVA-PAA was used as the binder. Except for the absence of conductive polymers, the slurry, electrodes, and secondary battery were manufactured in the same manner as in Example 1.

[0066] [Comparative Example 2]

[0067] The conductive polymer, slurry, electrode, and secondary battery were manufactured in the same manner as in Example 1, except that PAA (aldrich) was used as the acceptor to produce "PEDOT:PAA" in the production of the conductive polymer binder.

[0068] [Comparative Example 3]

[0069] In the production of the conductive polymer binder, the conductive polymer, slurry, electrode, and secondary battery were manufactured in the same manner as in Example 1, except that "PEDOT:PAA-1" was produced by using PAA-1 produced in the above production example as the acceptor.

[0070] [Experimental Example 1]

[0071] The degree of hydrolysis of PAA-1 and PAA-5 produced in the above manufacturing example was confirmed by FT-IR and is shown in Figure 1. As the degree of hydrolysis increases, the chain structure contains more polar functional groups such as -OH and -COOH, so PAA-5, which has a higher degree of hydrolysis, is 3300 cm⁻¹ higher than PAA-1. -1 We confirmed that the size of the nearby OH peak was large.

[0072] [Experimental Example 2]

[0073] To investigate the dispersion safety of conductive polymers based on the degree of hydrolysis, the conductive polymer binders from Example 2 and Comparative Example 2 were placed in empty cans and observed for stability and the presence or absence of phase separation at 25°C for 15 days, as shown in Figure 2. In Example 2, which used a receptor adjusted to have a high degree of hydrolysis, excellent dispersion stability was confirmed without phase separation. However, in Comparative Example 2, which used a receptor whose degree of hydrolysis was not adjusted, the dispersion stability was poor and phase separation occurred.

[0074] [Experimental Example 3]

[0075] The viscosity of the slurries of Comparative Example 1, Comparative Example 2, Example 1, and Example 2 was observed and compared visually, and the dispersion stability was evaluated using a grind gauge, as shown in Figure 3. Visual comparison of the viscosity of Examples 1 and 2, which contain conductive polymers, with Comparative Example 1, which does not contain conductive polymers, confirmed that the viscosity of the slurry did not increase or decrease. This indicates that the conductive polymer does not affect the viscosity of the slurry. Furthermore, as shown in Figure 3, in Examples 1 and 2, which contain conductive polymers, no particles were observed even below 30 μm on the grind gauge, confirming excellent slurry dispersion stability. However, in the case of Comparative Example 2, particles were observed above 90 μm, confirming poor slurry dispersion stability. This is thought to be because the conductive polymer was manufactured using a acceptor with an uncontrolled degree of hydrolysis, resulting in low dispersion safety of the conductive polymer binder.

[0076] [Experimental Example 4]

[0077] The electrical conductivity of the electrodes manufactured in the above examples and comparative examples was measured using a surface resistance meter and is shown in Table 1 below. Furthermore, the lithium secondary batteries manufactured in the above examples and comparative examples were subjected to five charge-discharge cycles under 25°C charging conditions (0.1~0.5C) and discharge conditions (0.1~0.5C), and the battery resistance and battery life characteristics (≧500 cycles) were evaluated under a SOC of 50% and are shown in Table 1 below.

[0078] [Table 1]

[0079] As shown in Table 1 above, in the case of electrodes of Examples 1 and 2, which contain a conductive polymer manufactured using a receptor that satisfies the hydrolysis degree range of the present invention, it can be confirmed that the electrical conductivity of the electrodes is superior to that of Comparative Examples 1 to 3, which either do not contain a conductive polymer, use a receptor whose degree of hydrolysis is not adjusted, or use a receptor that does not satisfy the hydrolysis degree range of the present invention. Furthermore, it can be confirmed that the secondary batteries of Examples 1 and 2 show improved battery characteristics, with reduced battery resistance and increased battery life compared to the comparative examples. Comparing Comparative Example 3, Examples 1 and 2, it can be confirmed that the electrical conductivity, battery resistance, and battery life characteristics of the electrodes improve as the degree of hydrolysis of the receptor increases. This indicates that as the degree of hydrolysis increases, the dispersibility of the conductive polymer binder improves, it is distributed more uniformly within the electrode, the electrical conductivity increases, and this affects the performance improvement of the secondary battery.

[0080] [Experimental Example 5]

[0081] After fabricating the lithium secondary batteries of Comparative Example 1, Comparative Example 2, Example 1, and Example 2 into coin cell 2032 form, they were charged and discharged under the same conditions as in Experimental Example 4, and the electrochemical evaluation results of measuring the battery resistance by the EIS method are shown in Figure 4.

[0082] In Examples 1 and 2, similar to the internal resistance results in Experimental Example 4, a significant decrease in resistance was observed compared to Comparative Examples 1 and 2, and it was confirmed that the greater the degree of hydrolysis of the receptor, the greater the decrease in resistance.

[0083] The present invention is not limited to the embodiments described herein and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the present invention pertains will understand that the invention can be implemented in other specific forms without altering the technical idea or essential features of the invention. Therefore, the embodiments described above should be understood to be illustrative and not limiting in any way.

Claims

1. It contains water-soluble polymers and conductive polymers, The water-soluble polymer includes the first copolymer, The conductive polymer comprises a polymer of a second copolymer and a conductive monomer. The second copolymer has a degree of hydrolysis of 50% or more and an FT-IR spectrum of 3250 cm⁻¹. －１ or 3350cm －１ The absorbance peak that appears is 22% or higher. The first copolymer is a copolymer of a polymer containing polar functional groups and PAA, and has a degree of hydrolysis of 0% to 10% that is not controlled. The second copolymer is a copolymer of a polymer containing polar functional groups and PAA, and its degree of hydrolysis is controlled. The conductive monomer is one or more selected from EDOT (3,4-ethylenedioxythiophene) or thiophene monomers. Binder for rechargeable batteries.

2. The binder for a secondary battery according to claim 1, wherein the first copolymer is PVA-PAA whose degree of hydrolysis has not been controlled.

3. The binder for a secondary battery according to claim 1, wherein the second copolymer is PVA-PAA with a controlled degree of hydrolysis.

4. The conductive polymer is A binder for a secondary battery according to claim 1, comprising a conductive monomer in a weight ratio of 1:0.5 to 20 with respect to the second copolymer.

5. The binder for secondary batteries according to claim 1, comprising a conductive polymer in a ratio of 4 to 6:1 to the water-soluble polymer.

6. A slurry comprising an electrode active material and a binder according to any one of claims 1, 2, 3, and 4.

7. Based on a total slurry of 100% by weight, The electrode active material contains 95 to 99% by weight, The slurry according to claim 6, comprising 1 to 5% by weight of the binder.

8. An electrode formed by applying and drying the slurry described in claim 6 onto the surface of a current collector.

9. It includes a positive electrode, a negative electrode, an electrolyte interposed between them, and a separation membrane inserted between the positive and negative electrodes. A secondary battery in which one or more electrodes selected from the positive and negative electrodes are the electrodes described in claim 8.

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