KR20170052838A - Separator Having Buffer Binder Layer and Electrode Assembly Comprising the Same - Google Patents

Abstract

The present invention relates to a jelly-roll type electrode assembly, comprising a sheet-type positive electrode; a sheet-type negative electrode; and a separation film interposed between the positive electrode and the negative electrode, and having a buffer binder layer formed on at least one surface of a sheet-type porous substrate to prevent twisting of the positive electrode or the negative electrode, due to repetitive charge and discharge, wherein a buffer binder contained in the buffer binder layer has a swelling ratio of 150% or more, with respect to an electrolyte of a secondary battery.

Description

TECHNICAL FIELD [0001] The present invention relates to a separation membrane having a buffer type binder layer and an electrode assembly including the separator.

The present invention relates to a separator having a buffer type binder layer and an electrode assembly comprising the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

The secondary battery is classified into a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-shaped battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

The electrode assembly incorporated in the battery case is a charge / dischargeable power generating element formed of a laminate structure of a positive electrode / separator / negative electrode. The electrode assembly is composed of a jelly-roll type in which a separator is interposed between a positive electrode and a negative electrode coated with an active material, Sized positive and negative electrodes are stacked in a stacked state in a state in which a separator is interposed therebetween.

A full cell or anode / separator / cathode / separator / separator / separator / cathode assembly having a positive electrode / separator / negative electrode structure with a constant unit size, which is a progressive structure of a jelly- A stack / folding type electrode assembly having a structure in which a bicell having a positive (negative) electrode structure is folded by using a continuous long separating film has been developed.

Further, in order to improve the processability of the conventional stacked electrode assembly and meet the demands of various types of secondary batteries, a lamination / stacked electrode structure in which unit cells alternately laminated and laminated are laminated Assemblies have also been developed.

On the other hand, the jelly roll type electrode assembly repeatedly shrinks and expands during charging and discharging, and twisting occurs in the anode or the cathode. When a twist phenomenon occurs, a space may be generated between the electrode and the separator, and the active material may be desorbed from the collector. As a result, there is a problem that the internal resistance of the secondary battery rises and the capacity decreases.

In order to fundamentally solve such a problem, it is desirable to prevent shrinkage and expansion of the electrode. However, due to the characteristics of the secondary battery, shrinkage and expansion of the electrode are inevitably generated.

As a next step, there has been an effort to improve the adhesion between the electrode and the separator to reduce the twisting phenomenon. However, when the charging / discharging cycle is progressed, the adhesion between the electrode and the separator becomes weaker and the performance of the secondary battery is deteriorated. A problem has occurred.

Therefore, in the jelly roll type electrode assembly, there is a high need for a technique capable of preventing the twisting phenomenon and improving the life characteristics and the output characteristics.

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

The inventors of the present application have conducted intensive research and various experiments, and have found that, as will be described later, the present inventors have found that when a positive electrode or a negative electrode twisted due to repetitive charge and discharge on at least one surface of a sheet- it is possible to prevent the twisting phenomenon of the jelly roll type electrode assembly and improve the life characteristics and the output characteristics when the separator includes a buffer layer for preventing twisting. .

Accordingly, the jelly roll type electrode assembly according to the present invention includes: a sheet-like positive electrode; A sheet-like negative electrode; And a separator interposed between the anode and the cathode and having a cushioning binder layer formed on at least one surface of the sheet-like porous substrate to prevent twisting of the anode or the cathode due to repetitive charge and discharge , And the cushioning binder contained in the cushioning binder layer has a swelling ratio of 150% or more with respect to the electrolyte of the secondary battery.

During charging and discharging, a force is generated which causes twisting by shrinkage and expansion of the anode and cathode. At this time, the buffer type binder layer adhered to the positive electrode or the negative electrode absorbs the force causing twisting, so that the adhesion state of the positive electrode or the negative electrode and the separation membrane is maintained, and thus the twisting phenomenon is prevented in the electrode assembly.

At this time, in order to sufficiently absorb the force causing the twisting of the positive electrode or the negative electrode to prevent twisting, the buffer type binder contained in the buffer type binder layer may have a swelling ratio of 150% or more with respect to the electrolyte of the secondary battery have. Specifically, the swelling degree of the buffer type binder may be from 150% to 300%, and more particularly, the swelling degree may be from 170% to 250%. When the swelling ratio is less than 150%, the force causing the twisting can not be sufficiently absorbed, so that the life characteristics and the output characteristics of the secondary battery are not greatly increased. When the degree of swelling is 300% or more, It may be melted and lost, and the swelling of the electrolytic solution may be too large to reduce the energy density, or excessive force may be applied to the electrode or the battery case to cause the shape deformation.

In one specific example, the degree of swelling is determined by measuring a film made of a buffer binder at 25 DEG C in a solvent such as ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP ) Is immersed in a solvent mixed in a weight ratio of EC: PC: PP = 3: 1: 6 for 24 hours and can be measured based on volume change before and after immersion. Combination of solvents other than EC, PC, and PP is not unavoidable. When the degree of swelling is measured in combination ratio and mixing ratio of the solvent, there is a very high correlation between swelling degree and prevention of twisting phenomenon.

The swelling degree can be calculated according to the following formula 1 when the volume of the film before immersion in the solvent is V1 and the volume of the film after immersion is V2.

Swelling degree (%) = (V2-V1) / V1 * 100 (One)

On the other hand, the buffer binder is not limited as long as it can provide an adhesive force to the separator and the electrode and prevent the twisting phenomenon through buffering action. For example, the buffer binder may be a fluorine-based binder or an acrylate- And an acrylate-based binder.

In one specific example, the fluorine-based binder may be at least one selected from the group consisting of PVdF and PVdF copolymers.

In detail, the PVdF copolymer is prepared by mixing polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-co-trichlorethylene And may be one or more selected from the group consisting of

At this time, the PVdF copolymer can control the adhesive force and the degree of swelling by controlling the content of the vinylidene fluoride monomer. More specifically, the vinylidene fluoride monomer vinylidene fluoride, VdF) monomer may be from 70 mol% or more to less than 95 mol%, and more specifically from 80 mol% or more to 90 mol% or less.

In one specific example, the acrylate-based binder comprises, based on the total weight of the monomer mixture, i) 50 to 90 wt% of a (meth) acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms, ii) 1 to 40% by weight of at least one monomer selected from the group consisting of esters, unsaturated acetates and unsaturated nitriles, and iii) 0.5 to 20% by weight of at least one monomer selected from the group consisting of unsaturated carboxylic acids Polymer.

In one specific example, the monomer of i) is selected from the group consisting of methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (Meth) acrylate, isodecyl acrylate, decyl (meth) acrylate, isopropyl (meth) acrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl acrylate, isooctyl acrylate, octyl methacrylate, Acrylate, methacrylate, dodecyl methacrylate, isobornyl methacrylate, and lauryl (meth) acrylate.

If the monomer of i) is contained in an amount of less than 50% by weight based on the total weight of the monomer mixture, the initial adhesion of the acrylate-based pressure sensitive adhesive can not be secured. If the monomer is contained in an amount exceeding 90% by weight, The transfer of the pressure-sensitive adhesive to the complex is largely undesirable.

The number of carbon atoms of the alkyl group in i) may be 1 to 14, more specifically, 2 to 14, and if it is less than 1, the cohesive force of the acrylate- By weight, the acrylate-based pressure-sensitive adhesive becomes too soft and adhesive properties deteriorate, which is not preferable.

In one specific example, the monomer of ii) may be at least one selected from the group consisting of vinyl acetate, vinyl butanoate, vinyl propionate, vinyl laurate, vinyl pyrrolidone, acrylonitrile and methacrylonitrile , Specifically, vinyl acetate, vinyl butyrate, or acrylonitrile.

When the monomer of ii) is contained in an amount of less than 1% by weight based on the total weight of the monomer mixture, the acrylate-based pressure-sensitive adhesive becomes too soft and can not secure sufficient adhesive property. If it exceeds 40% by weight, The rate-based pressure-sensitive adhesive becomes excessively firm so that a remarkable decrease in cohesive strength occurs.

In one specific example, the monomer of iii) may be at least one selected from the group consisting of acrylic acid, itaconic acid, maleic anhydride, fumaric acid, crotonic acid, methacrylic acid, and ethyl methacrylic acid.

When the monomer of iii) is contained in an amount of less than 0.5% by weight based on the total weight of the mixture, the acrylate-based pressure-sensitive adhesive becomes too soft and can not secure sufficient adhesive property. When the monomer is contained in an amount exceeding 20% by weight, The adhesive agent is excessively firmly adhered to cause a remarkable deterioration in adhesive strength.

The monomer mixture may further comprise other monomers and crosslinking agents as needed. In one specific example, the monomer mixture further comprises a crosslinking agent, which is present in an amount of from 0.1 to 3 wt% based on the total weight of the monomer mixture %, More specifically from 0.1 to 2% by weight. If the content of the crosslinking agent is less than 0.1% by weight, the degree of swelling may be too high, and if it is more than 3% by weight, the degree of swelling may be low.

The crosslinking agent is added to reinforce the cohesive force of the acrylate adhesive. In one specific example, the crosslinking agent may be a compound having 5 to 15 alkylene oxide groups and having an acrylate group or a vinyl group, May be a compound having 6 to 12 alkylene oxide groups and having an acrylate group or a vinyl group, and within the above range, room temperature, aging tackiness, and stability are all excellent.

For reference, the number of alkylene oxide groups means the average number of alkylene oxide groups contained in the cross-linking agent used, and when the number of alkylene oxide groups is less than 5 in the cross-linking agent, the pressure- And when the number of alkylene oxide groups is more than 15, the pressure-sensitive adhesives to be produced tend to be more flexible than necessary, resulting in deteriorated adhesive properties.

In one specific example, the crosslinking agent is an organic crosslinking agent such as polyethylene glycol diacrylate, polypropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylpropane triacrylate, Trimethylolpropyl methacrylate, vinyltrimethoxysilane and divinylbenzene, and the like, and an inorganic crosslinking agent such as aluminum acetyl (meth) acrylate such as tripropylene glycol diacrylate, 1,3-butanediol diacrylate, pentatrytol triacrylate, Acetone, zinc acetate, zirconium carbonate and the like, and specifically may be at least one selected from the group consisting of polyethylene glycol diacrylate and polypropylene glycol diacrylate.

In one specific example, the monomer mixture may further contain an epoxy group-containing unsaturated monomer, and the epoxy group-containing unsaturated monomer specifically includes glycidyl (meth) acrylate, alpha methyl glycidyl (meth) (Meth) acrylate, glycidyl ether, oxocyclohexyl (meth) acrylate and 3,4-epoxycyclohexylmethyl (meth) acrylate, and more particularly, glycidyl Or an allyl glycidyl ether.

The epoxy group-containing unsaturated monomer may be contained in an amount of 0.1 to 3% by weight based on the total weight of the monomer mixture, and the pressure-sensitive adhesive composition has sufficient cohesion within the above range.

Meanwhile, the buffer type binder layer may further include inorganic particles to improve thermal stability and resistance to foreign matter.

The buffer layer may contain inorganic particles in an amount of 10% by weight to 90% by weight, more preferably 20% by weight to 60% by weight based on the total weight of the buffer layer. When the content of the inorganic particles is less than 10% by weight, it is difficult to provide sufficient resistance against foreign matter and thermal stability. When the content of the inorganic particles exceeds 90% by weight, the degree of swelling of the buffer type binder layer becomes low and it may be difficult to provide sufficient adhesion.

In one specific example, the inorganic particles may be at least one selected from the group consisting of inorganic particles having piezoelectricity and inorganic particles having lithium ion transferring ability.

The piezoelectricity inorganic particle means a non-conductive material at normal pressure or a material having electrical conductivity due to a change in internal structure when a certain pressure is applied, and exhibits a high permittivity with a dielectric constant of 100 or more, The charge is generated in the case of applying tensile or compressive force, so that one side is charged positively and the other side is negatively charged, thereby generating a potential difference between both sides.

In the case of using inorganic particles having the above-described characteristics, when an internal short-circuit of both electrodes occurs due to an external impact such as a needle-shaped conductor, not only the anode and the cathode are in direct contact with each other due to the inorganic particles, A potential difference is generated in the particle due to the piezoelectricity of the electrode. As a result, electrons move between the two electrodes, that is, a minute current flows, so that the voltage of the cell can be reduced smoothly and safety can be improved.

Examples of the inorganic particles having piezoelectricity include BaTiO ₃ , PZT (Pb (Zr, Ti) O ₃ ), PLZT (Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ , PT (PB ₃ (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ ), and hafnium oxide (HfO ₂ ). However, it is preferable that at least one selected from the group consisting of 0 <x <1, 0 <y <1, PMN- But is not limited thereto.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect, the lithium ion conductivity in the battery can be improved and the battery performance can be improved.

Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) x O y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3), lithium germanium Mani help thiophosphate _{(Li x Ge y P z S} w, 0 <x (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si (0 <y <1, 0 <z < _{y S z, 0 <x <} 3, 0 <y <2, 0 <z <4) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 <y <3, 0 < z < 7) series glass, but the present invention is not limited thereto.

The buffer layer may further include other commonly known additives in addition to the inorganic particles and the buffer binder described above.

In one specific example, the buffer type binder layer may further include a thickening agent, and the thickening agent is not particularly limited as long as it is a material capable of raising the viscosity without causing chemical change. For example, Acrylic polymers and cellulosic polymers may be used. Examples of the acrylic polymer include polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA). Cellulose polymers include hydroxyethyl cellulose A cellulose ester such as hydroxyethyl ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethylcellulose Carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and the like. The.

Meanwhile, the electrode assembly may have a structure in which the cathode is positioned on the inner surface side of the electrode assembly and the anode is wound on the outer surface side of the electrode assembly.

With this structure, the stability of the secondary battery can be improved by placing the positive electrode having relatively high stability against the external impact on the outer surface of the electrode assembly.

The present invention also provides a separator for use in a jellyroll-type electrode assembly.

Wherein the separator has a cushioning binder layer formed on at least one side of the sheet-like porous substrate to prevent twisting of the positive electrode or the negative electrode due to repetitive charging and discharging, and the cushioning binder contained in the cushioning- Of the electrolytic solution may be 150% or more.

The present invention also provides a method of manufacturing a jellyroll-type electrode assembly.

The method of manufacturing the jelly roll type electrode assembly includes:

(a) a buffer type binder layer for preventing twisting of the positive electrode or the negative electrode due to repetitive charging and discharging is formed on at least one surface of the sheet-like porous substrate, and the buffer type binder contained in the buffer type binder layer is a secondary battery Preparing a separator having a swelling degree of 150% or more with respect to an electrolyte;

(b) laminating a sheet-like anode, a sheet-like cathode, and the separator; And

(c) winding the stacked positive electrode, negative electrode, and separator;

. &Lt; / RTI &gt;

In one specific example, in the step (a), a first separator having a cushion-type binder layer formed on both surfaces of a sheet-like porous substrate; And a second separation membrane in which a buffer layer is formed only on one surface of the sheet-like porous substrate.

As described above, the product cost can be reduced by using the first and second separation membranes having different structures from each other.

At this time, a binder layer having a property different from that of the buffering type binder layer can be formed on the other surface of the second separation film on which the buffering type binder layer is formed. For example, a binder layer having a higher content of inorganic particles than the buffer type binder layer can be formed in order to increase mechanical rigidity and improve stability against external impact.

In one specific example, in the step (b), a first separator having a buffer layer on both sides of the porous substrate is disposed between the anode and the cathode, and on the outer surface of the anode or the cathode, The buffer layer of the second separator may be laminated so that the buffer layer of the second separator faces the anode or the cathode.

In one specific example, in the step (c), the negative electrode may be positioned on the inner surface side of the electrode assembly, and the positive electrode may be wound on the outer surface side of the electrode assembly.

The present invention also provides a secondary battery in which such an electrode assembly is embedded in a battery case together with an electrolytic solution.

Hereinafter, other components of the secondary battery will be described.

The electrode is collectively referred to as a negative electrode and a positive electrode. The positive electrode may be prepared, for example, by applying a positive electrode mixture mixed with a positive electrode active material, a conductive material and a binder to a positive electrode collector, A filler may be further added.

The cathode current collector is generally formed to a thickness of 3 to 201 탆 and 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 , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can 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, 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 , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where 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} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; 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 positive electrode material mixture containing the positive electrode 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 whiskey 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 binder contained in the positive electrode is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the positive electrode active material, as a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

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.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture containing a negative electrode active material, a conductive material, and a binder to a negative electrode collector, and a filler or the like may further be optionally included.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or 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.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 201 탆, but may have different values depending on the case.

The negative electrode active material may include, for example, carbon such as non-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 alloy; Silicon-based alloys; Tin alloy; _{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 Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

In one specific example, the porous substrate may be a polyolefin-based separation film commonly used in the art and may be, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate but are not limited to, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, , Polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylene naphthalene, and mixtures thereof. [0034] The term &quot; polyolefin &quot;

The pore size and porosity of the porous substrate are not particularly limited, but the porosity may be in the range of 10 to 95% and the pore size (diameter) may be in the range of 0.1 to 50 탆. When the pore size and porosity are 0.1 μm or less and 10% or less, respectively, it acts as a resistive layer. If the pore size and porosity are more than 50 μm and 95%, it is difficult to maintain the mechanical properties.

The electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, The present invention is not limited thereto.

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 derivatives, Tetrahydrofuran derivatives, ether, 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 acid dissociation group and the like may 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a substance that is soluble in the nonaqueous electrolyte and includes, 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 ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. 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), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

The present invention also provides a battery pack including such a secondary battery as a unit cell, and a device including such a battery pack as a power source.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , A plug-in hybrid electric vehicle (PHEV), an electric bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

The structure and manufacturing method of such a device are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the electrode assembly according to the present invention includes a separator having a cushioning binder layer formed on at least one surface of a sheet-like porous substrate to prevent twisting of the anode or the cathode due to repeated charge and discharge The jelly roll type electrode assembly can be prevented from being twisted, and life characteristics and output characteristics can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but it should be understood that the scope of the present invention is not limited thereto.

&Lt; Preparation Example 1 &

Manufacture of Secondary Battery

LiCoO _2, based on the weight of the acrylic binder, and a conductive agent (LGC CNT), 99.0: 0.75 : after mixed with 025, and the N- methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry, the thickness 12 ㎛ amount of coating on an aluminum foil, dried and rolled by loading a positive electrode was prepared in the 20.9 mg / cm ² sheet.

97.0, based on the weight of the artificial graphite and an acrylic binder: mix to 3.0, and then mixed with water as a solvent, prepare the cathode slurry coated on a copper foil having a thickness of 10 ㎛, dried, the amount of rolling load 11.1 mg / cm ² A sheet-like negative electrode was prepared.

A buffer layer was coated on both sides of a porous polyethylene substrate (porosity: 45%) having a thickness of 18 μm to a thickness of 5 μm to form a buffer layer to prepare a separator.

A negative electrode / separator / anode / separator in this order, and the negative electrode was wound on the inner surface side of the electrode assembly to manufacture a jelly roll type electrode assembly.

An electrolytic solution prepared by dissolving a LiPF ₆ electrolyte at a concentration of 1 M in a mixed solvent of EC: PC: PP = 3: 1: 6 by weight was prepared.

The thus prepared jelly-roll type electrode assembly and the electrolyte solution were put in a cylindrical battery case and sealed to manufacture a cylindrical secondary battery.

&Lt; Example 1 >

According to Production Example 1, a secondary battery was produced using polyvinylidene fluoride-nuclear fluoropyrene (PVdF-HFP, VdF monomer content: 83 mol%, Arkema Kynar 2500) having a molecular weight of about 250,000 as a buffer type binder.

&Lt; Example 2 >

According to Production Example 1, a secondary battery was produced using an acrylic copolymer (Zeon PX-LP25) as a buffer type binder.

&Lt; Example 3 >

According to Production Example 1, an acrylic copolymer (Zeon BM-L302) was used as a buffer type binder to prepare a secondary battery.

<Example 4>

According to Production Example 1, a secondary battery was produced using an acrylic copolymer (LGC H79 as a buffer type binder.

&Lt; Comparative Example 1 &

According to Production Example 1, a secondary battery was produced using polyvinylidene fluoride-nuclear fluoropyrene (PVdF-HFP, VdF monomer content: 95 mol%, Arkema LBG) having a molecular weight of about 800,000 as a buffer type binder.

&Lt; Comparative Example 2 &

According to Production Example 1, a secondary battery was prepared using polyvinylidene fluoride-nuclear fluoropyrene (PVdF-HFP, VdF monomer content: 97 mol%, Kureha 8200) having a molecular weight of about 1,000,000 as a buffer type binder.

&Lt; Comparative Example 3 &

According to Production Example 1, a secondary battery was produced using an acrylic copolymer (Zeon PX-LP17) as a buffer type binder.

&Lt; Comparative Example 4 &

According to Production Example 1, an acrylic copolymer (LGC H78) was used as a buffer type binder to prepare a secondary battery.

<Experimental Example 1>

A film having a thickness of 1 mm was prepared using the buffer binders used in Examples 1 to 4 and Comparative Examples 1 to 4, respectively. Each of the films thus prepared was mixed with ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) at a weight ratio of EC: PC: PP = 3: 1: 6, for 24 hours, and the volume change before and after immersion was measured. When the volume of the film before immersion in the solvent was V1 and the volume of the film after immersion was V2, the swelling degree of the buffer type binder was calculated according to the following formula 1. The results are shown in Table 1 below.

Swelling degree (%) = (V2-V1) / V1 * 100 (One)

Swelling (%) Example 1 235 Example 2 210 Example 3 179 Example 4 164 Comparative Example 1 134 Comparative Example 2 114 Comparative Example 3 71 Comparative Example 4 126

<Experimental Example 2>

The secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were charged at a rate of 0.1 C from 3 V to 4 V, discharged at a rate of 0.1 C, and the initial capacity was measured. Thereafter, the battery was charged at a 0.1 C-rate and discharged at 0.5 C-rate, and the discharge capacity after about 100 cycles was measured. Based on this, the capacity retention rate (capacity after 100 cycles relative to initial capacity) was calculated. The results are shown in Table 2 below.

Initial Capacity
(mAh / g) Capacity after 100 cycles
(mAh / g) Capacity retention rate
(%) Example 1 120 116.5 97.1 Example 2 119 117.3 98.6 Example 3 124 120.9 97.5 Example 4 123 118.6 96.4 Comparative Example 1 114 101.7 89.2 Comparative Example 2 118 103.8 88 Comparative Example 3 119 101.2 85 Comparative Example 4 122 107.1 87.8

The results are shown in Table 2. Referring to Table 2, Examples 1 to 4 include a cushion-type binder having a swelling degree of 150 or more and a capacity retention rate of 95% or more after 100 cycles of charging and discharging, And the capacity retention rate does not reach 90%.

In particular, referring to Examples 1 to 3, it can be confirmed that when the swelling degree is from 170 to 240, the capacity retention ratio is not less than 97%.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (23)

A jelly-roll type electrode assembly comprising:
A sheet-like positive electrode;
A sheet-like negative electrode; And
A separator interposed between the anode and the cathode and having a cushioning binder layer formed on at least one surface of the sheet-like porous substrate to prevent twisting of the anode or the cathode due to repetitive charging / discharging;
Lt; / RTI &gt;
Wherein the cushioning binder contained in the cushioning binder layer has a swelling ratio of 150% or more with respect to the electrolyte of the secondary battery. The electrode assembly according to claim 1, wherein the buffer type binder has a swelling degree of 150% to 300%. The electrode assembly according to claim 1, wherein the buffer binder has a swelling degree of 170% to 250%. The method according to claim 1, wherein the degree of swelling is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) ) Is immersed in a solvent mixed in a weight ratio of EC: PC: PP = 3: 1: 6 for 24 hours and measured based on the change in volume before and after immersion. The electrode assembly according to claim 4, wherein the degree of swelling is calculated according to the following formula 1 when the volume of the film before immersion in the solvent is V1 and the volume of the film after immersion is V2:
Swelling degree (%) = (V2-V1) / V1 * 100 (1) The electrode assembly according to claim 1, wherein the buffer binder is a fluorine-based binder, an acrylate-based binder, or a mixture of a fluorine-based binder and an acrylate-based binder. The electrode assembly according to claim 6, wherein the fluorine-based binder is at least one selected from the group consisting of PVdF and PVdF copolymers. The method of claim 7, wherein the PVdF copolymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-co-trichlorethylene ). &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; [7] The PVdF copolymer according to claim 7, wherein the PVdF copolymer has a vinylidene fluoride (VdF) monomer content of 70 mol% or more to less than 95 mol% based on the total mole of the monomers constituting the copolymer The electrode assembly comprising: [7] The acrylate binder according to claim 6, wherein the acrylate binder comprises i) 50 to 90% by weight of a (meth) acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms, ii) 1 to 40% by weight of at least one monomer selected from the group consisting of esters, unsaturated acetates and unsaturated nitriles, and iii) 0.5 to 20% by weight of at least one monomer selected from the group consisting of unsaturated carboxylic acids &Lt; / RTI &gt; wherein the polymer is a polymer. 11. The electrode assembly of claim 10, wherein the monomer mixture further comprises a crosslinking agent, wherein the crosslinking agent is present in an amount of from 0.1 to 3% by weight based on the total weight of the monomer mixture. The electrode assembly of claim 1, wherein the buffer layer further comprises inorganic particles. 13. The electrode assembly according to claim 12, wherein the buffer layer comprises inorganic particles in an amount of 10% by weight to 90% by weight based on the total weight of the buffer layer. 13. The electrode assembly according to claim 12, wherein the inorganic particles are at least one selected from the group consisting of inorganic particles having piezoelectricity and inorganic particles having lithium ion transporting ability. The electrode assembly according to claim 1, wherein the negative electrode is positioned on the inner surface side of the electrode assembly and the positive electrode is wound on the outer surface side of the electrode assembly. A separation membrane for use in a jelly roll type electrode assembly,
A buffer type binder layer is formed on at least one surface of the sheet-like porous substrate to prevent twisting of the positive electrode or the negative electrode due to repetitive charge and discharge, and the buffer type binder contained in the buffer type binder layer is a Wherein the swelling degree of the separator is 150% or more. A method of manufacturing a jelly roll-type electrode assembly,
(a) a buffer type binder layer for preventing twisting of the positive electrode or the negative electrode due to repetitive charging and discharging is formed on at least one surface of the sheet-like porous substrate, and the buffer type binder contained in the buffer type binder layer is a secondary battery Preparing a separator having a swelling degree of 150% or more with respect to an electrolyte;
(b) laminating a sheet-like anode, a sheet-like cathode, and the separator; And
(c) winding the stacked positive electrode, negative electrode, and separator;
&Lt; / RTI &gt; 18. The method of claim 17, wherein in the step (a)
A first separator having a cushioning binder layer formed on both surfaces of a sheet-like porous substrate; And a second separation membrane having a cushioning-type binder layer formed on only one surface of the sheet-like porous substrate. 18. The method of claim 17, wherein in step (b)
Between the anode and the cathode is disposed a first separator having a buffer layer on both sides of the porous substrate,
A second separator having a buffer layer formed on only one surface of the porous substrate is disposed on the outer surface of the anode or the cathode,
Wherein the buffer layer of the second separation membrane is laminated so as to face the anode or the cathode. 18. The method according to claim 17, wherein in step (c), the cathode is positioned on the inner surface side of the electrode assembly and the anode is wound on the outer surface side of the electrode assembly. The secondary battery according to claim 1, wherein the electrode assembly is embedded in the battery case together with the electrolyte solution. A battery pack comprising a secondary battery according to claim 21 as a unit cell. 23. A device comprising the battery pack according to claim 22 as a power source.