KR20130033575A - Electrode assembly of excellent productivity and cycle capability and secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode assembly is provided to continuously maintain adhesion between a negative electrode and a separator and a negative electrode current collector and a negative electrode mixture, thereby improving processing and cycle performance. CONSTITUTION: An electrode assembly has a plurality of overlapped unit bodies each of which consists of a separator, a positive electrode, and a negative electrode. A negative electrode current collector is coated with a negative electrode mixture which comprises an active material and a binder. A continuous separator sheet is inserted into each of the overlapped part. The binder includes a polymer particle which is polymerized by using a (meth)acrylic acid ester-based monomer, vinyl-based monomer, and unsaturated carbonic acid-based monomer. The negative electrode mixture includes 1-2.5 weight% of the polymer particle based on the total weight of the negative electrode mixture.

Description

Electrode Assembly of Excellent Manufacturing Process and Cycle Characteristics and Lithium Secondary Battery Comprising the Same {Electrode Assembly of Excellent Productivity and Cycle Capability and Secondary Battery Comprising the Same}

The present invention relates to an electrode assembly having excellent manufacturing processability and cycle characteristics, and a lithium secondary battery comprising the same, and more particularly, comprising a negative electrode, a positive electrode, and a separator coated with a negative electrode mixture including an active material and a binder on a negative electrode current collector. A plurality of basic units are overlapped, and each overlapping portion has a structure in which a continuous separator sheet is interposed, and the binder is (a) 20 wt% to 79 wt% of (meth) acrylic acid ester monomer, (b A) a polymer particle polymerized using 20% to 60% by weight of a vinyl monomer, and 0.01% to 30% by weight of an unsaturated carboxylic acid monomer, and the negative electrode mixture is a negative electrode mixture. Electrode assembly, characterized in that it comprises less than 1% to 2.5% by weight relative to the total weight of the li It relates to a secondary battery.

As the price of energy sources increases due to the depletion of fossil fuels, and the interest of environmental pollution is increasing, the demand for environmentally friendly alternative energy sources becomes an indispensable factor for future life. As demand increases, demand for secondary batteries as energy sources is rapidly increasing.

Representatively, there is a high demand for rectangular secondary batteries and pouch secondary batteries, which can be applied to products such as mobile phones with a thin thickness in terms of shape of batteries, and lithium ion batteries with high energy density, discharge voltage, and output stability in terms of materials. There is a high demand for lithium secondary batteries such as lithium ion polymer batteries.

In addition, secondary batteries are classified according to the structure of the electrode assembly having a cathode / separation membrane / cathode structure. Representatively, a jelly having a structure in which long sheet-shaped anodes and cathodes are wound with a separator interposed therebetween -Roll (electrode) electrode assembly, and a plurality of positive electrode and negative electrode cut in units of a predetermined size is divided into stack-type (assembly type) electrode assembly of a structure that is sequentially stacked with a separator.

However, these conventional electrode assemblies have some problems.

First, since the jelly-roll electrode assembly is wound around a long sheet-shaped anode and cathode in a dense state to form a cylindrical or oval structure in cross section, stress caused by expansion and contraction of the electrode during charge and discharge accumulates inside the electrode assembly. If the stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. As a result of the deformation of the electrode assembly, the spacing between the electrodes becomes uneven, resulting in a sudden drop in the performance of the battery and a risk of the safety of the battery being damaged due to an internal short circuit. In addition, since the long sheet-type positive electrode and the negative electrode must be wound, it is difficult to quickly wind the coil while keeping the distance between the positive electrode and the negative electrode, which also has a problem in that the productivity is lowered.

Second, since the stack type electrode assembly has to stack a plurality of positive and negative electrode units in sequence, the electrode plate transfer process is required separately for manufacturing the unit, and the productivity is low because a lot of time and effort are required for the sequential lamination process. Has a problem.

In order to solve this problem, the electrode assembly of the advanced structure in the mixed form of the jelly-roll type and the stack type, the bi-cell (full cell) or the full cell in which the positive electrode and the negative electrode of a predetermined unit laminated with a separator; Stacked / foldable electrode assemblies have been developed in which full cells are wound using a continuous membrane sheet of long length, which is disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059 and 2001. -0082060 and the like.

1 and 2 schematically show an exemplary structure and manufacturing process of a stack / foldable electrode assembly using a full cell as a basic unit.

Referring to these drawings, a plurality of full cells 10, 11, 12, 13, 14..., In which anode / separation membrane / cathode are sequentially positioned as unit cells are superimposed, and each overlapping portion has a separator sheet ( 20 is interposed, and the separator sheet 20 has a unit length for wrapping a full cell, and is bent inward for each unit length and starts continuously from the center full cell 10 to the outermost full cell 14. It surrounds each full cell.

The stack / foldable electrode assembly may, for example, arrange the full cells 10, 11, 12, 13, 14... Stacked on the separator sheet 20 having a long length. After winding at one end 21 of the separator sheet 20 and sequentially winding, the end portion of the separator sheet 20 is heat-sealed or prepared by attaching an adhesive tape 25 or the like.

Therefore, in the stack / foldable electrode assembly, the adhesion between the electrode and the separator is important. In addition, for example, the adhesion between the negative electrode current collector and the negative electrode mixture is important because the negative electrode is manufactured by notching.

However, PVdF-based polymers are currently used as commercially available electrode binders because of their poor safety and low affinity with liquid electrolytes, which are not only a fundamental cause of deterioration of electrode performance, but also binding properties with inorganic particles such as electrode active materials. Although it is excellent, the adhesive strength with the metal current collector is not good, there is a disadvantage that a large amount must be added to exhibit and maintain sufficient adhesive strength.

In order to solve the above problems, attempts have been made to water-based binders (JP 2872354, JP 3101775, KR 2000-0075953) that use water as a dispersion medium and reduce the amount of input, but the metal current collector and electrode Not only did not obtain sufficient performance due to the lack of adhesion between the active material, but also insufficient adhesion performance when performing the thermal bonding process of the electrode and the separator to produce a stack / folding electrode assembly inevitably result in deterioration of overall battery performance It became.

On the other hand, in the case of increasing the content of the binder to increase the adhesive force, there is a problem that the content of the electrode active material and the electronic conductivity is relatively reduced to deteriorate the performance of the battery.

In order to solve this problem, a binder including a (meth) acrylic acid ester monomer, a vinyl monomer and an unsaturated carboxylic acid monomer has been developed, but conditions for optimizing cycle characteristics of a lithium secondary battery have been disclosed. There is no bar.

Therefore, there is a high need for a stack / foldable electrode assembly capable of improving cycle characteristics while preventing separation between the separator and the electrode, and between the electrode active material and the current collector with strong adhesion.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application have developed a binder containing polymer particles polymerized using a (meth) acrylic acid ester monomer, a vinyl monomer, and an unsaturated carboxylic acid monomer, under specific conditions. In the case of manufacturing the electrode assembly using, it was confirmed that the cycle characteristics and manufacturing processability is improved and the present invention was completed.

Therefore, in the electrode assembly according to the present invention, a plurality of basic units consisting of a negative electrode, a positive electrode, and a separator coated with a negative electrode mixture including an active material and a binder are stacked on a negative electrode current collector, and each overlapping portion has a continuous separator sheet. Consists of intervening structures,

The binder is (a) 20% to 79% by weight of the (meth) acrylic acid ester monomer, (b) 20% to 60% by weight of the vinyl monomer, and (c) 0.01% to 30% by weight of the unsaturated carboxylic acid monomer. Polymer particles polymerized using%,

The negative electrode mixture is characterized in that it comprises at least 1% by weight and less than 2.5% by weight relative to the total weight of the negative electrode mixture.

The electrode assembly according to the present invention has excellent adhesion between the negative electrode active materials and the negative electrode mixture and the negative electrode current collector, as compared with the conventional styrene-butadiene rubber-based binder, (a) 20 wt% to 79 wt% of the (meth) acrylic acid ester monomer, (b) 20 to 60 weight percent of vinyl monomers, and (c) 0.01 to 30 weight percent of unsaturated carboxylic acid monomers.

The inventors of the present application have experimentally confirmed that the polymer particles having the composition as described above are particularly preferable in terms of adhesion and cycle characteristics when the polymer particles are contained in an amount of 1 wt% or more to less than 2.5 wt% based on the total weight of the negative electrode mixture.

Specifically, when the content of the polymer particles is less than 1% by weight, the adhesive force between the negative electrode current collector and the negative electrode mixture is not maintained continuously, the negative electrode mixture is separated from the negative electrode current collector is not preferable for the production of the negative electrode, the polymer particles If the content of more than 2.5% by weight is not preferable because the cycle characteristics are lowered.

The basic unit may be a full cell configured so that the polarities of the electrodes constituting the uppermost end and the electrodes constituting the lower end are opposite to each other, and the full cell is an electrode at the uppermost end and the lowermost end of the unit cell opposite to each other. The structure is not particularly limited.

For example, a lamination structure of i) an anode / separation membrane / cathode, or ii) an anode / separation membrane / cathode / separation membrane / anode / separation membrane / cathode may be mentioned. The number of full cells wound up on the separator sheet may be determined by various factors such as the structure of each full cell and a desired capacity of the final manufactured battery, and may be preferably 6 to 30.

In addition, the basic unit may be a bi-cell (electrode) consisting of the same structure of the electrode of the uppermost and the lowermost of the positive electrode or the negative electrode, these bicells are the positive electrode and if the electrode on both sides of the cell has the same structure and The number of the cathode and the separator is not particularly limited.

For example, the bicell may include a stacked structure of an anode, a separator, a cathode, a separator, and an anode, and a stacked structure of a cathode, a separator, an anode, a separator, and an anode, and the bicell may be a cathode, a separator, an anode, a separator, or the like. It can be classified into a cell having a cathode stacked structure, that is, an A-type bicell having cathodes on both sides, and a cell having a cathode / separation membrane / cathode / separation membrane / cathode stacked structure, that is, a C-shaped bicell having anodes on both sides. .

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder to a portion other than a portion where a tab is to be formed on a positive electrode current collector sheet, followed by drying and pressing. Fillers, viscosity modifiers, etc. may be further added to the.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a lithium secondary battery, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; 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. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The viscosity adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include, but are not limited to, carboxymethyl cellulose, polyacrylic acid, and the like.

On the other hand, the negative electrode is manufactured by applying, drying, and pressing the negative electrode active material to the remaining portions except for the portion where the tab is to be formed on the negative electrode current collector sheet, and if necessary, the conductive material, viscosity modifier, filler, and the like may be selected. It may be further included as.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. 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 collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may be, for example, carbon such as hardly graphitized carbon or graphite 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' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; 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.

As described above, the binder used for the negative electrode according to the present invention is a polymer particle polymerized using (a) a (meth) acrylic acid ester monomer, (b) a vinyl monomer, and (c) an unsaturated carboxylic acid monomer. It includes.

The (meth) acrylic acid ester monomer is a conventional monomer known in the art that can control the battery characteristics, in particular, it improves the affinity with the electrolyte solution to improve the speed characteristics of the battery and excellent adhesion to the current collector.

Non-limiting examples of the (meth) acrylic acid ester monomers include (i) acrylic ester monomers (e.g., methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl Acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, lauryl acrylate); (ii) methacrylic acid ester monomers (e.g., methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate); Acrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, lauryl methacrylate, allyl methacrylate or these And mixtures thereof.

The content of the (meth) acrylic acid ester system is not particularly limited, but is preferably 20% to 79% by weight based on the total weight of the polymer particles. If the content of the (meth) acrylic acid ester monomer is less than 20% by weight, the adhesive properties of the binder may be significantly reduced. If the content of the (meth) acrylic acid ester monomer is greater than 79% by weight, the binder may not be able to be manufactured because the stability of the binder is decreased. .

The vinyl monomer (b) is a conventional monomer known in the art that can control battery characteristics, and in particular, controls adhesion between the active material and the active material and also has excellent ion conductivity.

Non-limiting examples thereof include styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, acrylonitrile, methacrylonitrile or mixtures thereof. In particular, the acrylonitrile monomer contains a triple bond, which can improve electrical properties with high ionic conductivity.

The content of the vinyl monomer is preferably 20 wt% to 60 wt% with respect to the total weight of the polymer particles, but is not limited thereto. When the content of the vinyl monomer is less than 20% by weight, the stability of the binder may be reduced in the manufacturing process of the binder, and the binder may not be manufactured. When the content of the vinyl monomer exceeds 60% by weight, the adhesive force may be markedly lowered due to the glass transition temperature rising effect. Can be.

The unsaturated carboxylic acid-based monomer is a monomer that can control the adhesive force, it is possible to achieve a high capacity of the battery by exhibiting excellent adhesive force only by a small amount of input during electrode production.

Non-limiting examples thereof include (i) unsaturated monocarboxylic acid monomers (e.g. acrylic acid, methacrylic acid, etc.), (ii) unsaturated dicarboxylic acid monomers (e.g. itaconic acid, fumaric acid, citraconic acid, metaconic acid, Glutamic acid, crotonic acid, isocrotonic acid, and the like, and the content is not particularly limited, but is preferably 0.01 to 30% by weight based on the total weight of the polymer particles. When the content of the monomer (c) is less than 0.01% by weight, the adhesive force is lowered, and when the content of the monomer (c) is more than 30% by weight, the stability may be reduced during the manufacturing process, thereby making it impossible to manufacture.

The binder may further include monomers commonly used in the art. In addition, the binder is preferably composed of 3 to 10 monomers of the above-described monomer components, but is not limited thereto.

The polymer particles of the present invention polymerized with the monomer component and composition ratio as described above have a final particle diameter of 100 to 400 nm, a glass transition temperature of the polymer is -30 to 50 ° C, and a gel content of 30 to 99%, More preferably, the final particle diameter is 100 nm to 400 nm, the glass transition temperature is -30 ° C to 50 ° C, and the gel content is 50% to 99%.

In fact, in this section, the binder exhibited superior properties, such as adhesion between the negative electrode and the negative electrode current collector, thermal bonding between the negative electrode and the separator, and excellent battery characteristics, such as cycle characteristics, compared with the conventional binder. It was confirmed.

When the polymer particles deviate from the above-described ranges of particle size, glass transition temperature, and gel content, the adhesion between the negative electrode mixture and the current collector may be greatly reduced, which may cause deterioration of battery characteristics.

For example, when the final particle diameter of the polymer particles is less than 100 nm, the adhesion force decreases due to a large amount of binder movement between the negative electrode active materials. When the final particle diameter exceeds 400 nm, the adhesion force decreases due to a decrease in the surface area of the polymer particles.

In addition, when the glass transition temperature of the binder is less than -30 ° C, the polymerization stability is poor, making the binder difficult, and if it exceeds 50 ° C, the adhesive force may be lowered, which is not preferable. Furthermore, if the gel content of the binder is less than 50%, it may exhibit a disadvantage of poor polymerization stability.

Since the monomers capable of controlling the battery characteristics all have inherent surface energy, the polymer formed using the same has different surface energy according to its composition ratio. Such a difference in surface energy causes a difference in affinity with the electrolyte solution, so that it is possible to disperse not only NMP used as a conventional electrode dispersion medium and a conventional organic solvent used for nonaqueous electrolyte, but also water, so that an organic solvent must be used. Not only can PVdF solve the problem, but it is also environmentally friendly.

Furthermore, in the present invention, as described above, by maximizing the content of monomers, for example, unsaturated carboxylic acid monomers, which can control adhesive properties within a range capable of achieving physical stability of the binder, a small amount of binder is added to the electrode and the collector. It is possible to maximize the effect of adhesion between the whole and the thermal bonding effect between the electrode and the separator by thermal fusion.

At this time, the effect can be expected to be exerted through the chemical bond between the carboxyl group (-COOH) contained in the unsaturated carboxylic acid-based monomer and the copper ion of the copper current collector, such as ionic bond formation.

The binder may use, in addition to the monomer components, conventional components known in the art as a polymerization additive, such as a molecular weight modifier and a crosslinking agent. The gel content of the binder particles can be controlled by adjusting the amount of the molecular weight regulator and the crosslinking agent.

The polymer particles according to the present invention may be prepared by conventional polymerization methods known in the art, such as emulsion polymerization, suspension polymerization, dispersion polymerization, and seed polymerization. In this case, the polymerization temperature and the polymerization time may be arbitrarily selected according to the polymerization method or the kind of polymerization initiator to be used. For example, the polymerization temperature may be about 50 to 200 ° C., and the polymerization time may be 0.5 to 20 hours. The binder may be dissolved in a solvent or dispersed in a dispersion medium in a conventional manner to prepare a binder composition.

The solvent or dispersion medium used in the binder composition of the present invention is not particularly limited, but at room temperature and normal pressure, which can maintain the shape of the binder polymer particles when the slurry for battery electrodes of the present invention described below is applied and dried to a current collector. It is preferable that it is a liquid.

The separator sheet used to wind the separator and the base unit interposed between the anode and the cathode of the full cell or bicell is not particularly limited as long as the separator sheet has an insulating property and a porous structure capable of moving ions. The separator sheet may or may not be the same material.

As the separator or the separator sheet, for example, an insulating thin film having high ion permeability and mechanical strength may be used, and its pore diameter is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. to be. As a raw material of such a separator or a separator sheet, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Preferably, a multilayer film produced by a polyethylene film, a polypropylene film, or a combination of these films, or a film made of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or poly A polyvinylidene fluoride hexafluoropropylene copolymer or the like, or a polymer film for a gel-type polymer electrolyte.

The separator preferably has an adhesive function by thermal fusion to form a full cell or bicell, and the separator sheet does not necessarily have such a function, but it is preferable to use an adhesive function to easily perform a winding process. desirable.

In addition, the separator sheet may have an extended length so as to wrap the electrode assembly once after winding, and the outermost end of the sheet may be fixed by heat fusion or tape. For example, a thermal welder or a hot plate is brought into contact with the finished separator sheet so that the separator sheet itself is melted by heat and adhesively fixed. This enables stable interfacial contact between the electrode and the separator sheet, allowing the pressure to be maintained continuously.

The present invention also provides a lithium secondary battery in which the electrode assembly is embedded in a battery case and impregnated with an electrolyte, and the lithium secondary battery is preferably a lithium ion polymer battery.

The electrolyte is preferably a lithium salt-containing non-aqueous electrolyte consisting of an electrolyte and a lithium salt. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

As the inorganic solid electrolyte, for example, 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 material that is readily soluble 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.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The present invention provides a battery module and a battery pack including the lithium secondary battery as a unit cell, and the battery pack is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle and the like in consideration of excellent life characteristics and safety; It can be preferably used as a power source such as an electric power storage device.

Since the structure and manufacturing method of such a lithium secondary battery, a medium-large battery module and a battery pack including the same as a unit cell are known in the art, a detailed description thereof will be omitted herein.

As described above, since the electrode assembly according to the present invention includes a negative electrode mixture including the polymer particles in an amount of 1 wt% or more to less than 2.5 wt% based on the total weight of the negative electrode mixture, between the negative electrode current collector and the negative electrode mixture and The adhesion between the cathode and the separator is continuously maintained, thereby improving the manufacturing processability and cycle characteristics.

1 is a schematic diagram of an exemplary structure of a conventional stack / foldable electrode assembly;
FIG. 2 is a schematic diagram illustrating an arrangement combination of unit cells in a manufacturing process of the stack / foldable electrode assembly of FIG. 1; FIG.
3 is a graph showing the correlation between the content of the binder and the adhesive force according to a specific embodiment of the present invention;
Figure 4 is a photograph showing the adhesive properties of the electrode assembly according to Example 1 of the present invention;
5 is a photograph showing the adhesive properties of the electrode assembly according to Comparative Example 1 of the present invention;
Figure 6 is a photograph showing the adhesive properties of the electrode assembly according to Comparative Example 2 of the present invention;
7 is a photograph showing the adhesive properties of the electrode assembly according to Comparative Example 4 of the present invention.
8 is a graph comparing the cycle characteristics of Comparative Example 1 and Comparative Example 3 of the present invention;
9 is a graph comparing the cycle characteristics of Example 2 and Comparative Examples 1 to 2 of the present invention.

Hereinafter, the present invention is further described, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

1-1. Binder Composition Preparation

93.0 g of ion-exchanged water was introduced into the reactor and the temperature was raised to 75 ° C. When the temperature of ion-exchange water reached 75 degreeC, 5.8 g of butylacrylates, 4.3 g of styrene, and 0.1 g of sodium lauryl sulfate were added. The seed 1 was completed by dissolving 0.08 g of potassium persulfate in 5.0 g of ion-exchanged water while maintaining the temperature in the reactor at 75 ° C.

A reaction product of 93.0 g of ion-exchanged water, 30.0 g of styrene, 60.1 g of butyl acrylate, 0.8 g of aryl methacrylate, 4.4 g of itaconic acid, 6 g of acrylic acid, and 0.15 g of sodium lauryl sulfate was mixed with the seed (1). Was added over 3 hours, 0.21 g of potassium persulfate was dissolved in 10.0 g of ion-exchanged water, and then added for 3 hours to complete the binder polymer. Potassium hydroxide was used to adjust the binder polymer to pH = 7 to complete the binder composition for the negative electrode. The above binder was used at the time of negative electrode manufacture.

The final particle diameter, glass transition temperature, and gel content of the binder particles were measured for physical properties of the polymerized binder. First, when the particle size was measured using a light scattering apparatus, the glass transition temperature was 195 nm, and the glass transition temperature measured at a temperature rising rate of 10 ° C / min using a DSC (Differential Scanning Calorimeter) was -5 ° C. In addition, the gel content (Gel Content) measured using toluene as a solvent was 85%.

1-2. Full Cell Manufacturing

(Anode manufacture)

After dispersing in NMP in a weight ratio of LiCoO ₂ : carbon black: PVdF = 95: 2.5: 2.5 to prepare a slurry, the slurry was coated on aluminum foil, sufficiently dried at 130 ° C., and pressed to prepare a positive electrode.

The anode to be placed on the outermost side of the outermost full cell was coated with a slurry on only one side of the aluminum foil to produce a cathode coated with an anode material on an aluminum anode current collector, and the anode of the full cell to be placed inside the slurry on both sides of the aluminum foil. The positive electrode material was coated on both sides of the aluminum positive electrode current collector to prepare a positive electrode.

(Cathode production)

Graphite: Conductive carbon (Super-P): Binder composition prepared in Example 1-1: Water-soluble polymer carboxymethylcellulose = 95.5: 1: 1: 2.5 Dispersed in water at a weight ratio of 2.5 to prepare a slurry, and then the slurry Was coated on a copper foil, sufficiently dried at 130 ° C., and pressed to prepare a negative electrode.

The negative electrode to be placed on the outermost side of the outermost full cell was coated with a slurry on only one side of the copper foil to prepare a negative electrode having a single-sided coating of the negative electrode material on the copper negative electrode current collector, and the negative electrode of the full cell to be placed inside the slurry on both sides of the copper foil. The negative electrode material was coated on both sides of the negative electrode material to prepare a negative electrode.

(Separation Membrane; Separator Membrane; Production of Polymer Film for Polymer Electrolyte)

A multilayer polymer having a polypropylene film having a thickness of 16 µm having a fine pore structure as a first polymer separator and a polyvinylidene fluoride-chlorotrifluoroethylene copolymer 32008 manufactured by Solvey Polymer as a gelling secondary polymer A film was prepared. That is, 6 g of 32008 was added to 194 g of acetone and stirred well while maintaining a temperature of 50 ° C., and after 1 hour, a transparent solution in which 32008 was completely dissolved was coated on the polypropylene first polymer separator by a coating process. The thickness of the coated 32008 was 1 μm and the final multilayer polymer film was 18 μm.

 (Production of full cell located inside)

The positive electrode current collector prepared above was cut to a positive electrode active material coated on both sides except a tab having a size of 2.9 cm x 4.3 cm, and the negative electrode active material coated on both sides of the negative electrode current collector was 3.0 cm x After cutting except for the tab to be cut into a 4.4 cm square, the multilayer polymer film prepared above was cut into 3.1 cm x 4.5 cm and placed between the anode and the cathode, and then roll laminator at 100 ° C. The inner full cell was prepared by heat bonding the electrodes and the separator to each other and bonding them.

(Manufacture of full cell located at outermost part)

The positive electrode current collector prepared above was cut into a positive electrode coated with a positive electrode active material on a single side having a rectangular size of 2.9 cm x 4.3 cm, except for a tab to be tabbed, and the negative electrode coated with a negative electrode material on both sides was 3.0 cm x After cutting, except for the tab to be cut into a 4.4 cm rectangle, the multilayer polymer film prepared above was cut to a size of 3.1 cm x 4.5 cm between the anode and the cathode, and then passed through a roll laminator at 100 ° C. Each electrode and the separator were thermally bonded to each other to prepare an outermost full cell 1.

In addition, the positive electrode active material prepared above is cut on both sides of the positive electrode current collector coated on the positive electrode current collector, except for the tabs having a rectangular size of 2.9 cm x 4.3 cm, and the negative electrode active material is double-sided on the negative electrode current collector. -0082058 p8) After cutting the coated cathode except for a tab to form a 3.0 cm x 4.4 cm rectangular tab, the multilayer polymer film prepared above is 3.1 cm x 4.5 cm between the anode and the cathode. Cut out and then placed in a roll laminator at 100 ° C. to bond each electrode to the separator by thermal bonding to prepare an outermost full cell 2.

(Overlapping of full cell)

The full cells manufactured in the above order are the outermost full cell (1), the inner full cell, the outermost full cell (2) in order, and each of the single-side coated electrodes allows the electrode current collector to be positioned at the outermost part. The multilayer polymer film prepared above was cut into 3.1 cm x 4.5 cm in size and inserted therein, and then passed through the roll laminator at 100 ° C. as it was, whereby each full cell and the separator sheet were thermally bonded to each other.

1-3. Manufacture of batteries

The overlapped full cell prepared above was put in an aluminum laminate packaging material, and a lithium ion polymer battery was prepared by injecting and packaging a liquid electrolyte having a weight composition of 1 M LiPF ₆ (Ethylene Carbonate) / EMC (Ethyl Methyl Carbonate) at a weight ratio of 1: 2. Completed.

<Example 2>

Graphite: conductive carbon (Super-P) in Example 1: the binder composition prepared in Example 1-1: water-soluble polymer carboxymethyl cellulose = 95: 1: Except that the weight ratio of 1: 1.5: 2.5 A lithium ion polymer battery was manufactured in the same manner as 1.

&Lt; Comparative Example 1 &

Example 1 except for the graphite: conductive carbon (Super-P): binder composition prepared in Example 1-1: water-soluble polymer carboxymethyl cellulose = 94: 1: 2.5: 2.5 A lithium ion polymer battery was manufactured in the same manner as 1.

Comparative Example 2

Example 1 except for the graphite: conductive carbon (Super-P): binder composition prepared in Example 1-1: water-soluble polymer carboxymethyl cellulose = 93.5: 1: 3: 2.5 except that the weight ratio A lithium ion polymer battery was manufactured in the same manner as 1.

&Lt; Comparative Example 3 &

Graphite: conductive carbon (Super-P) in Example 1: binder composition prepared in Example 1-1: water-soluble polymer carboxymethyl cellulose = 92.5: 1: 4: except that the weight ratio of 1: 2.5 A lithium ion polymer battery was manufactured in the same manner as 1.

&Lt; Comparative Example 4 &

Graphite: Conductive carbon (Super-P): styrene-butadiene rubber binder: water-soluble polymer carboxymethyl cellulose = 94: 1: 2.5: 2.5 in the weight ratio of Example 1 except that the lithium An ion polymer cell was produced.

&Lt; Comparative Example 5 &

A lithium ion polymer battery was manufactured in the same manner as in Example 1, except that the weight ratio of graphite: conductive carbon (Super-P): water-soluble polymer carboxymethylcellulose = 96.5: 1: 1: 2.5 was prepared.

<Experimental Example 1>

Adhesion Evaluation

In order to evaluate the adhesive strength, the negative electrodes of Comparative Examples 2 to 5 cut to a thickness of 1 cm were attached onto the glass plate, and then the peeling strength of the current collector was peeled off to measure 180 ° peeling strength.

Referring to FIG. 3, it can be seen that as the binder content increases, the adhesion between the negative electrode current collector (Cu-foil) and the negative electrode mixture increases. However, when the binder content is 2.5% by weight or more, as shown in Experimental Example 2, it can be seen that the cycle characteristics are reduced.

On the other hand, referring to Figures 4 to 6 showing the adhesion characteristics with the separator, in Example 1, the residue of the separator is confirmed on the negative electrode current collector, the more the residue of the separator occurs as the binder content increases It can be seen. On the other hand, in Comparative Example 5, which does not contain a binder, there is no residue, so it can be visually confirmed that the adhesive property with the separator is not shown.

Therefore, it can be seen that the content of the binder should be 1% by weight or more in order to maintain the minimum adhesive strength for manufacturing processability.

Although not shown, in the case of Comparative Example 3 containing a binder containing a styrene butadiene monomer, the adhesive properties with the separator did not appear as in the case of Comparative Example 5.

<Experimental Example 2>

Battery characteristic evaluation

Cycle characteristics were evaluated using the batteries of Example 2 and Comparative Examples 1 to 3.

Specifically, the cycle characteristics of the initial capacity, repeated charging and discharging of 400 cycles by the 0.2C constant current method is shown in Figures 8 and 9 the results.

8 and 9, it can be seen that Comparative Examples 1 and 2 have lower cycle characteristics compared to Example 2, and the cycle characteristics of Comparative Example 1 are further compared to Comparative Example 3 including a styrene-butadiene rubber-based binder. It can be seen that it is excellent.

In conclusion, the binder composition prepared in Example 1-1 shows the best cycle characteristics when included in less than 2.5% by weight relative to the total weight of the negative electrode mixture. This is in contrast to the expectation that the higher the binder content, the better the structural stability of the electrode and the better the cycle characteristics.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

A plurality of basic units composed of a negative electrode coated with a negative electrode mixture including an active material and a binder, a positive electrode, and a separator are stacked on the negative electrode current collector,
Each overlapping portion has a structure in which a continuous separator sheet is interposed.
The binder is (a) 20% to 79% by weight of the (meth) acrylic acid ester monomer, (b) 20% to 60% by weight of the vinyl monomer, and (c) 0.01% to 30% by weight of the unsaturated carboxylic acid monomer. Polymer particles polymerized using%,
The negative electrode mixture is an electrode assembly, characterized in that containing the polymer particles in an amount of more than 1% by weight to less than 2.5% by weight relative to the total weight of the negative electrode mixture. The electrode assembly of claim 1, wherein the basic unit is a full cell configured to have opposite polarities of electrodes forming a top end and electrodes constituting a bottom end. The electrode assembly of claim 2, wherein the full cell comprises an anode / separation membrane / cathode structure or an anode / separation membrane / cathode / separation membrane / anode / separation membrane / cathode structure. The electrode assembly of claim 1, wherein the basic unit is a bi-cell having a structure in which the electrodes forming the uppermost and the lowermost are both positive or negative electrodes. The electrode assembly of claim 4, wherein the bicell has a structure of an anode, a separator, a cathode, a separator, an anode, or a cathode, a separator, an anode, a separator, and a cathode. The method of claim 1, wherein the (meth) acrylic acid ester monomer is methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- amyl acrylate, iso Amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, iso Propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate At least one monomer selected from the group consisting of acrylate, hydroxypropyl methacrylate and lauryl methacrylate Electrode assembly, characterized in that the. The method of claim 1, wherein the vinyl monomer is one or more monomers selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, acrylonitrile and methacrylonitrile. Electrode assembly. According to claim 1, wherein the unsaturated carboxylic acid monomer is at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, citraconic acid, metaconic acid, glutamic acid, crotonic acid and isocrotonic acid Electrode assembly, characterized in that the. The electrode assembly according to claim 1, wherein the average particle diameter of the polymer particles is 100 to 400 nm. The electrode assembly of claim 1, wherein the binder has a glass transition temperature (Tg) of -30 to 50 ° C. The electrode assembly of claim 1, wherein the gel content of the binder is 30 to 99%. The electrode assembly of claim 1, wherein the binder is dispersible in non-aqueous and aqueous solvents. A lithium secondary battery comprising the electrode assembly according to claim 1 embedded in a battery case and impregnated with an electrolyte. The lithium secondary battery of claim 13, wherein the lithium secondary battery is a lithium ion polymer battery. A battery module comprising the lithium secondary battery according to claim 14 as a unit cell. Battery pack comprising a battery module according to claim 15. A device according to claim 16, wherein the battery pack is used as a power source.

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