KR20080074241A - Electrode material containing conductive polymer with excellent dispersibility as binder and lithium secondary battery employed with the same - Google Patents

Abstract

An electrode slurry having a conductive polymer as a binder is provided to realize excellent binding force and electroconductivity without using an additional conductive agent, and to improve the solubility to organic solvents, thereby imparting excellent cycle characteristics and high-temperature property to a secondary battery. An electrode slurry for a secondary battery comprises an electrode active material and a binder, wherein the binder is a block copolymer formed of a conductive polymer segment and a linear polymer segment having excellent solubility to organic solvents. The conductive polymer segment is at least one selected from polyacetylene, polythiophene, polypyrrole, poly(p-phenylene), polyphenylenevinylene, poly(phenylene sulfide) and polyaniline. The linear polymer segment is at least one selected from polyethylene glycol, polypropylene glycol, polydimethyl siloxane and acrylic derivatives.

Description

Electrode mixture containing a conductive polymer having excellent dispersibility as a binder and a lithium secondary battery comprising the same {Electrode Material Containing Conductive Polymer with Excellent Dispersibility as Binder and Lithium Secondary Battery Employed with the Same}

The present invention relates to an electrode mixture containing a conductive polymer as a binder, and more particularly, to a secondary battery electrode mixture containing an electrode active material and a binder, the binder has a solubility in conductive polymer segments and organic solvents. It is composed of a block copolymer composed of excellent linear polymer segments, it is possible to increase the electrical conductivity while excellent adhesion, not only need to add a separate conductive material to improve the production efficiency, but also of the secondary battery comprising the same The present invention relates to an electrode mixture for a secondary battery that can reduce resistance and improve rate and cycle characteristics.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used. Among them, lithium secondary batteries are the most used batteries due to their excellent electrode life and high fast charge and discharge efficiency.

In general, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly including a cathode including a lithium transition metal oxide, a cathode including a carbon-based active material, and a separator. The secondary battery is a non-aqueous composition, the electrode is generally manufactured by coating an electrode slurry on a metal foil, the electrode slurry is an electrode active material for storing energy, a conductive material for imparting electrical conductivity, and It is prepared by mixing an electrode mixture composed of a binder for adhering to the electrode foil in an organic solvent such as NMP (N-methyl pyrrolidone).

However, the charge and discharge cycle proceeds due to the volume change caused by the reaction with lithium during charge and discharge, the negative electrode active material is detached from the current collector during continuous charge and discharge, or the resistance increases due to the change of the contact interface between the negative electrode active materials. As a result, the capacity is drastically lowered, resulting in a shorter cycle life.

In this regard, the binder imparts a binding force between the active material and the current collector, the electrode active material and the conductive material as well as between the active materials, and has an important effect on battery characteristics by suppressing volume expansion due to charging and discharging of the battery. As such a binder resin, polyvinylidene fluoride (PVdF) has been widely used since it is preferable to use an insoluble and chemically stable material for the organic electrolysis liquid of the battery. However, if an excessive polymer is used as a binder to reduce volume change during charging and discharging, the detachment of the active material from the current collector can be reduced, but the electrical resistance of the negative electrode is increased due to the electrical insulation of the binder, and relatively As the amount decreases, problems such as capacity reduction arise.

In order to solve these problems, some prior arts propose methods of using a conductive polymer such as polyacetylene and polyaniline as a binder to improve conductivity and reduce internal resistance of a battery. same.

Japanese Patent Application Laid-Open No. 2000-067918 discloses a lithium secondary battery made by adding polyacetylene and / or polyaniline as a binder, and Japanese Patent Application Laid-Open No. 1989-132045 discloses that polyaniline performs a function of a binder and an active material at the same time. Discloses an electrode which is mixed and molded with polypyrrole. Korean Patent Application Publication No. 1999-031603 discloses a technique for minimizing interfacial resistance without attaching a polymer binder to an electrode active material by attaching an electrode and an electrode active material through a conductive polymer in a lithium polymer secondary battery. Further, Japanese Patent Application Laid-Open No. 1999-339774 discloses a positive electrode for a lithium secondary battery manufactured by applying a polyaniline / ethane disulfonic acid composite as a binder and a metal oxide as an active material to carbon fiber paper.

However, in spite of these various technical proposals, since the conductive polymers generally exhibit poor solubility in organic solvents, there is a problem that it is difficult to apply them to the process of preparing the electrodes by mixing them with an organic solvent such as NMP to prepare the electrodes. . In addition, the conductive polymer is improved in electrical conductivity as the degree of polymerization increases, and when the degree of polymerization is small, the desired conductivity cannot be exhibited. On the other hand, when the molecular weight is increased, dispersibility to the solvent is lowered. Due to these many problems, conductive polymers as binders that exhibit desired levels of physical properties have not yet been developed.

On the other hand, in order to improve the electroconductivity of an electrode, electrically conductive materials, such as graphite and carbon black, are conventionally added to the electrode mixture of a lithium secondary battery. However, when the conductive material is included in the negative electrode mixture, such a conductive material cannot penetrate into the binder, which is an insulator, and thus has a limit in improving electrical conductivity. Furthermore, since the carbon-based conductive material has a low affinity for polar solvents such as NMP, the dispersibility is poor, and the conductive material is unevenly distributed, causing a voltage drop, and blocking the movement of lithium ions, thereby lowering the rate characteristic of the positive electrode. Bring it. In addition, the mixing process of the conductive material becomes long, and the process constraints are large, while the battery repeats the charge / discharge cycle, the movement of lithium ions is disturbed, resulting in the promotion of the deposition of lithium metal on the negative electrode.

Therefore, there is a high need for a technology that can solve many problems that may occur at first by adding a conductive polymer or adding a conductive material as a binder. In this regard, in the present invention, as described below, a method of using a block copolymer composed of a conductive polymer segment and a linear polymer segment having excellent solubility in an organic solvent as a binder that does not need to add a conductive material separately. Presenting.

As a technology related to such block copolymers, US Patent Application Publication No. 2003-088032 discloses an example of an increased solubility copolymer composed of a conductive polymer block and a nonconductive polymer block, and US Patent Application Publication No. 2006-062902 No. discloses a technique comprising a block copolymer as described above as a conductive polymer in a transparent electrode of a solar cell. However, there is no example of adding a block copolymer as a binder and / or conductive material for secondary batteries as in the present invention.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After repeated studies and various experiments, the inventors of the present application have a binding force when the electrode mixture for secondary batteries includes a block copolymer composed of a segment of a conductive polymer and a segment of a linear polymer having excellent solubility in an organic solvent as a binder. Not only is this excellent, it shows excellent electrical conductivity even without the addition of a conductive material, and the solubility in organic solvents is remarkably improved. Thus, a lithium secondary battery containing such an electrode mixture has excellent cycle characteristics and excellent battery performance even at high temperatures. It has been found that the present invention can be made and the present invention has been completed.

Therefore, the electrode mixture according to the present invention is an electrode mixture for a secondary battery containing an electrode active material and a binder, the binder is composed of a block copolymer consisting of a conductive polymer segment and a linear polymer segment having excellent solubility in an organic solvent. .

The present invention includes a block copolymer having the above-described characteristic structure as a binder, wherein the segment of the conductive polymer in the block copolymer not only has excellent bonding strength but also improves electrical conductivity of the electrode, thereby providing a separate conductive material. There is no need to add it. Therefore, there is an effect that can solve the problems caused by non-uniform distribution of the conductive material, that is, problems such as lowering the rate characteristic of the battery, voltage drop, rapid precipitation of lithium metal at the negative electrode, simplifying the manufacturing process, manufacturing time and cost Can greatly reduce the production efficiency can be improved.

In addition, even in the case of the block copolymer having a sufficiently high degree of polymerization to exhibit the desired conductivity improvement due to the segment of the linear polymer, it may have excellent solubility in organic solvents and excellent dispersibility. Therefore, since the internal resistance can be reduced to facilitate the movement of lithium ions, rate characteristics and cycle characteristics can be improved, and excellent battery performance can be obtained even at high temperatures. Furthermore, the manufacturing process is very economical because it enables the use of an organic solvent that is the same as or similar to the organic solvent used in the conventional secondary battery manufacturing method, that is, the slurry manufacturing process.

The conductive polymer as a segment of the block copolymer is not particularly limited as long as it is a polymer having electrical conductivity, and may be varied. Preferably, the effect intended in the present invention, that is, the electrode active material, the electrode active material and the conductive material, and the current collector It is possible to improve the conductivity while exhibiting sufficient adhesive strength with the whole, preferably, polyacetylene, polythiophene, polypyrrole, poly (p-phenylene) (poly (p-phenylene)) , Poly (phenylenevinylene), poly (phenylene sulfide) (poly (phenylenesulfide)), and polyaniline may be one or two or more selected from the group consisting of, more preferably poly It may be a poly (3,4-ethylenedioxythiophene) (PEDOT) which is a kind of offen. Such block copolymers are typically commercially available from Aedotron ^™ and the like.

In general, conductive polymers are classified according to carriers that are supplied through electricity. The case where the carrier is an electron is called an electronically conducting polymer and the case where the carrier is an ion is an ionically conducting polymer. It is called.

The polythiophene represented by the following formula (1) and the polypyrrole represented by the following formula (2) each have an α, α'-coupling form as an electron conductive polymer, and have high electrical conductivity among the conductive polymers. This is easy.

[Formula 1]

[Formula 2]

Polyaniline is also an electronically conductive polymer, generally excellent in electrical conductivity, thermal safety, etc., and is composed of a form in which the reduced state and the oxidized state are repeated, as represented by the following Chemical Formula 3, where a total reduction type of x = 1 ( leucoemeraldine, emeraldine with x = 0.5, and pernigraniline with x = 0.

[Formula 3]

In some cases, a conductive material may be doped into the conductive polymer to induce a change in electrical conductivity.

As another segment, the linear polymer is one or two selected from the group consisting of polyesters, polysiloxanes, polyethers, and polyacrylates, as defined above, which is composed of linear polymers having excellent solubility in organic solvents. It may be more than one, more preferably may be one or two or more selected from the group consisting of polyethylene glycol, polypropylene glycol, polydimethylsiloxane and acrylic derivatives.

The length of each of the conductive and linear segments may be determined by various factors such as the type of the organic solvent, the amount of the conductive polymer added, the amount of the lithium transition metal oxide added, the stirring time and the speed. For example, when the length of the linear polymer segment is too short, solubility in organic solvents may be lowered. On the contrary, when the length of the linear polymer segment is too long, the length of the conductive polymer segment becomes relatively short in the state of being included in the positive electrode mixture. It can be difficult to provide high levels of conductivity and binding strength. Therefore, when considering these matters comprehensively, it is preferable that the linear polymer segment is included in a length of about 20 to 80% based on the total length of the copolymer.

The content of the block copolymer is not particularly limited, and may be appropriately adjusted in a range that may not adversely affect the performance of the finished battery while increasing the electrical conductivity of the electrode. That is, if the content of the block copolymer is too small, it is difficult to expect the effect of improving the binding force and electrical conductivity, and thus the resistance of the battery, the improvement of cycle characteristics, etc., on the contrary, if the content of the block copolymer is too high, the relative content of the electrode active material is reduced, so that the battery It is not preferable because its performance may be degraded. Accordingly, the block copolymer may be included in an amount of 1 to 40% by weight based on the total weight of the electrode mixture, and when used in a medium-large battery requiring high power due to low resistance rather than high capacity, a reasonable capacity may be provided. It is also possible to increase the content of the block copolymer in a sustainable state.

In the case of the conventional electrode mixture, considering that the binder and the conductive material are attached to each other, the electrode mixture according to the present invention can increase the capacity of the battery because it can increase the content of the positive electrode active material compared to the same standard by excluding one component Can be.

The block copolymer according to the present invention has excellent solubility in an organic solvent, the organic solvent in the group consisting of NMP (N-methyl pyrrolidone), DMSO (dimethyl sulfoxide), chloroform (Chloroform), alkyl carbonate and the like One or two selected may be mentioned, and among them, NMP, which is frequently used as a solvent in the production of the positive electrode slurry, is particularly preferable.

As the block copolymer, a block copolymer composed of a segment of a conductive polymer and a segment of a linear polymer having excellent solubility in an organic solvent may be used in a polymerization process of the block copolymer, such as polymerization time, temperature, type and content of a catalyst, and the like. By varying the reaction conditions, the solubility in the organic solvent can be appropriately adjusted.

Examples of the method for producing the block copolymer according to the present invention include anionic polymerization, radical polymerization and the like.

The electrode active material includes a positive electrode active material and a negative electrode active material, and examples of the positive electrode active material include lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) such as layered compounds or one or more transition metals substituted with compound; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

As said negative electrode active material, For example, carbon, such as hardly graphitized carbon and graphite type carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 of the periodic table) Metal composite oxides such as a group element, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The present invention also provides a secondary battery electrode prepared by adding the electrode mixture to a solvent such as NMP to prepare a slurry, and then applying and drying the same on a current collector.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The current collector for the cathode is generally made of a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The present invention also provides a secondary battery comprising the electrode as described above, the secondary battery may be preferably a lithium secondary battery. The lithium secondary battery is composed of an electrode of the positive and negative electrodes, a separator, and a lithium salt-containing nonaqueous electrolyte.

When the binder according to the present invention is used only for the negative electrode or the positive electrode, a general binder known in the art may be used for the remaining electrodes. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

However, preferably, by using the conductive binder according to the present invention for both the positive electrode and the negative electrode, without using the conventional binder as described above, the effect as described above can be achieved.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

As described above, the electrode mixture for secondary batteries according to the present invention includes a block copolymer composed of a segment of a conductive polymer and a segment of a linear polymer having excellent solubility in an organic solvent as a binder, thereby improving electrical conductivity while providing excellent adhesion. Since it is possible to do not need to add a separate conductive material can solve the problem caused by the non-uniform distribution of the conductive material, it is possible to improve the production efficiency. In addition, since the solubility and dispersibility in the organic solvent is excellent, it is possible to improve the rate (rate) and cycle characteristics, it is possible to increase the battery capacity compared to the same standard.

 Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (10)

An electrode mixture for a secondary battery comprising an electrode active material and a binder, wherein the binder is a block copolymer composed of a conductive polymer segment and a linear polymer segment having excellent solubility in an organic solvent. The method of claim 1, wherein the conductive polymer segment is polyacetylene, polythiophene, polypyrrole, poly (p-phenylene), polyphenylenevinylene (poly phenylenevinylene)), poly (phenylenesulfide), and polyaniline, wherein the electrode mixture is one or two or more segments selected from the group consisting of. The electrode mixture according to claim 2, wherein the conductive polymer segment is a poly (3,4-ethylenedioxythiophene) (PEDOT) segment which is a kind of polythiophene. The electrode mixture of claim 1, wherein the linear polymer segment is one or two or more segments selected from the group consisting of polyethylene glycol, polypropylene glycol, polydimethylsiloxane, and acrylic derivatives. The electrode mixture according to claim 1, wherein the linear polymer segment is included in a length of 20 to 80% based on the length of the entire copolymer. The electrode mixture of claim 1, wherein the block copolymer is included in an amount of 1 to 40 wt% based on the total weight of the electrode mixture. The electrode mixture of claim 1, wherein the organic solvent is at least one selected from the group consisting of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), chloroform, and alkyl carbonate. A secondary battery electrode prepared by applying the electrode mixture according to any one of claims 1 to 7 on a current collector and dried. A secondary battery comprising the electrode according to claim 8. The secondary battery of claim 9, wherein the battery is a lithium secondary battery.