KR102225305B1 - Method of Manufacturing Separator Having Inorganic Coating Layer Using Phase Separation - Google Patents

Abstract

The present invention provides a method of manufacturing a separator including an inorganic coating layer, comprising: (a) preparing an inorganic slurry including a binder, inorganic particles, and a solvent; (b) applying the inorganic slurry to at least a portion of the porous substrate; And (c) adding a non-solvent having partial compatibility with the solvent to phase-separate the inorganic slurry coated on the porous substrate; About.

Description

Method of Manufacturing Separator Having Inorganic Coating Layer Using Phase Separation {Method of Manufacturing Separator Having Inorganic Coating Layer Using Phase Separation}

The present invention relates to a method of manufacturing a separation membrane including an inorganic coating layer using phase separation.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and as part of that, the fields that are most actively studied are the fields of power generation and storage using electrochemistry.

Currently, a secondary battery is a representative example of an electrochemical device that uses such electrochemical energy, and its use area is gradually expanding.

Depending on the shape of the battery case, secondary batteries are classified into cylindrical and prismatic batteries in which an electrode assembly is embedded in a cylindrical or rectangular metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch-shaped case of an aluminum laminate sheet. .

The electrode assembly built into the battery case is a power plant capable of charging and discharging composed of a stacked structure of a positive electrode/separator/cathode, and a jelly-roll type wound with a separator interposed between a long sheet-shaped positive electrode and negative electrode coated with an active material, and a predetermined It is classified into a stacked type in which a plurality of sized anodes and cathodes are sequentially stacked with a separator interposed therebetween.

As an electrode assembly of an advanced structure that is a mixture of such a jelly-roll type and a stack type, a positive electrode/separator/cathode structure full cell or positive electrode (cathode)/separator/cathode (anode)/separator/ A stack/folding electrode assembly having a structure in which a bicell having an anode (cathode) structure is folded using a long continuous separator film has been developed.

In addition, in order to improve the fairness of the existing stacked electrode assembly and meet the demand for various types of secondary batteries, a lamination/stack type electrode in which the electrode and the separator are alternately stacked and laminated unit cells are stacked. An assembly was also developed.

On the other hand, among these secondary batteries, lithium secondary batteries, which have recently been increasing in demand, have a problem of poor safety. Specifically, when the lithium secondary battery is overcharged, excess lithium is released from the positive electrode and lithium is inserted into the negative electrode, resulting in reactivity on the surface of the negative electrode. Very large lithium metal is deposited, the positive electrode is also in a thermally unstable state, and safety problems such as ignition and explosion of the battery occur due to a rapid exothermic reaction due to the decomposition reaction of the organic solvent used as an electrolyte.

In addition, when an object having electrical conductivity such as a nail penetrates the battery, the electrochemical energy inside the battery is converted into thermal energy, resulting in rapid heat generation, and the positive or negative material undergoes a chemical reaction due to the accompanying heat. , Safety problems such as ignition or explosion of the battery due to a rapid exothermic reaction occur.

In the case of such nail penetration, compression, impact, high temperature exposure, etc., a short circuit occurs locally between the positive electrode and the negative electrode inside the battery. At this time, an excessive current flows locally, and heat generation is caused by this current. Since the magnitude of the short-circuit current due to a local short-circuit is inversely proportional to the resistance, the short-circuit current flows a lot toward the lower resistance, and the current flows mainly through the metal foil used as a current collector. It can be seen that very high heat generation occurs locally around the pierced part.

When heat is generated inside the battery, the separator shrinks, causing a direct short circuit between the positive and negative electrodes again, and the short-circuit section increases due to repeated heat generation and shrinkage of the separator, resulting in thermal runaway or constituting the inside of the battery. There is a problem that the existing anode, cathode, and electrolyte react or burn with each other.

In order to solve this problem and improve safety during overcharging, there has been an attempt to use a safety separator having improved safety by applying a slurry containing inorganic particles and a binder on a porous substrate.

In the inorganic coating layer of the safety separator, when the content of the binder particles is high, the adhesion between the inorganic coating layer and the porous substrate is good, and safety is improved. However, when the content of the binder particles is high, the porosity of the inorganic coating layer is lowered, and as a result, it is difficult to move lithium ions during use of the secondary battery, and there is a problem that the internal resistance of the secondary battery is increased. U.S. Patent No. 6,432,586 discloses a safety separator having a high content of a binder in the inorganic coating layer, low porosity, and a non-porous coating layer.

On the other hand, when the content of inorganic particles is high in the inorganic coating layer of the safety separator, the porosity is improved, thereby reducing the internal resistance of the secondary battery. However, since the adhesion of the inorganic coating layer is reduced, the inorganic coating layer may be separated from the porous substrate, and the inorganic particles may be separated from the inorganic coating layer. In this case, there is a problem that the safety of the separation membrane is lowered. US Patent No. 7,662,517 discloses a separator having improved resistance characteristics by increasing the porosity of the inorganic coating layer by forming an interstitial volume due to the high content of inorganic particles.

Accordingly, there is a high need for a technology capable of improving the porosity of the inorganic coating layer while maintaining a high binder content in the inorganic coating layer of the separator.

An object of the present invention is to solve the problems of the prior art and technical problems that have been requested from the past.

After in-depth research and various experiments, the inventors of the present application added a non-solvent that is partially compatible with a solvent and coated on a porous substrate in manufacturing a separator including an inorganic coating layer, as described later. When the inorganic slurry is phase-separated, it has been confirmed that the porosity of the inorganic coating layer can be improved while maintaining the safety of the separator, and the present invention has been completed.

Therefore, the method of manufacturing a separation membrane comprising an inorganic coating layer according to the present invention,

(a) preparing an inorganic slurry containing a binder, inorganic particles, and a solvent;

(b) applying the inorganic slurry to at least a portion of the porous substrate; And

(c) phase separation of the inorganic slurry coated on the porous substrate by adding a non-solvent having partial compatibility with the solvent;

It characterized in that it comprises a.

In one specific example, the method may further include a step of forming an inorganic material coating layer by drying the inorganic material slurry phase-separated in step (d).

The solvent refers to a liquid capable of dissolving the binder, and the non-solvent refers to a liquid that does not dissolve the binder and induces phase separation of the binder.

The partial compatibility means that the solvent and the non-solvent can be interchanged through diffusion or the like.

That is, the binder is dissolved in the solvent in the inorganic slurry. When a partially compatible non-solvent is added to the inorganic slurry, the solvent and the non-solvent are interchanged, and the composition of the solvent is changed due to the mutual exchange of the solvent and the non-solvent. By adding a partially compatible non-solvent incapable of dissolving the binder, phase separation occurs in which at least a part of the binder precipitates from the solvent. Due to the phase separation, a site where a partially compatible non-solvent that cannot dissolve the binder becomes pores after drying of the liquid component, and thus, the porosity of the inorganic coating layer after drying is remarkably improved.

Therefore, according to the present invention, it is possible to form an inorganic coating layer with improved porosity by the phase separation as described above.

In one specific example, the content of the binder contained in the inorganic slurry may be in a ratio of 25:75 to 70:30 when converted into a volume ratio of the binder and the inorganic particles. When the content of the binder is less than 25 volume ratio, the amount of the binder is too small, so the mechanical properties of the separator may be deteriorated due to weakening of the adhesion between inorganic substances. On the contrary, when the content of the binder is more than 70 volume ratio, the content of the binder becomes too large and inorganic particles Pore size and porosity may be reduced due to a decrease in empty space formed between them, resulting in deterioration of the final battery performance.

As the binder, one or more binders may be used to obtain adhesive properties required for the inorganic coating layer.For example, the binder is polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoro Propylene (polyvinylidene fluoride-co-hexafluoropropylene, PVdF-HFP), polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, Polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, cellulose acetate, cellulose acetate butyrate, cellulose acetate pro Cypionate (cellulose acetate propionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carbohydrate Carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, styrene-butadiene rubber (SBR), carboxymethyl cellulose, Polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, epoxy It may be one or more selected from the group consisting of resin, polyvinyl alcohol, and hydroxypropyl cellulose, but is not limited thereto.

In one specific example, the binder may include a PVdF-based binder capable of phase separation, and the content of the PVdF-based binder may be 80% by weight or more based on the total weight of the binder. When the content of the PVdF-based binder is less than 80% by weight, it is not preferable because it is difficult to increase the porosity of the inorganic coating layer to a desired level.

Specifically, the PVdF-based binder may be at least one selected from the group consisting of PVdF and PVdF copolymers.

More specifically, the PVdF copolymers may have a PVdF monomer content of 92 mol% or more based on the total moles of monomers constituting the copolymer, and when the PVdF monomer content is less than 92 mol%, the phase separation It is difficult to increase the porosity of the inorganic coating layer to a desired level due to reduced occurrence.

Meanwhile, the inorganic particles may be at least one selected from the group consisting of inorganic particles having piezoelectricity and inorganic particles having lithium ion transfer capability.

The piezoelectricity inorganic particles are non-conductors at normal pressure, but when a certain pressure is applied, they refer to materials having physical properties that allow electricity to pass through changes in internal structure. When tensioned or compressed by applying, electric charges are generated, and one side is positively charged 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 characteristics, when an internal short circuit of the positive electrode occurs due to an external impact such as a needle-shaped conductor, not only the positive electrode and the negative electrode are in direct contact due to the inorganic particles, but also the inorganic particles Due to the piezoelectricity of, a potential difference in the particles occurs, which leads to electron movement between the positive electrodes, that is, a flow of a fine current, thereby achieving a gentle reduction in the voltage of the battery and thus improving the safety.

Examples of the piezoelectric inorganic particles include BaTiO ₃ , PZT (Pb(Zr,Ti)O ₃ ), PLZT (Pb _1-x La _x Zr _1-y Ti _y O ₃ , 0<x<1, 0<y<1), PMN-PT (Pb(Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ ), hafnium oxide (HfO ₂ ), but may be one or more selected from the group consisting of, It is not limited thereto.

The inorganic particles having a lithium ion transfer ability refer to inorganic particles containing a lithium element but not storing lithium and having a function of moving lithium ions, and the inorganic particles having a lithium ion transfer ability exist inside the particle structure. Since lithium ions can be transferred and moved due to a kind of defect, lithium ion conductivity in the battery is improved, and thus, battery performance can be improved.

Examples of the inorganic particles having the lithium ion transfer ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum 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 thiophosphate (Li _x Ge _y P _z S _w , 0<x <4, 0<y<1, 0<z<1, 0<w<5), lithium nitride (Li _x N _y , 0<x<4, 0<y<2), SiS ₂ (Li _x Si _y S _z , 0<x<3, 0<y<2, 0<z<4) series glass and P ₂ S ₅ (Li _x P _y S _z , 0<x<3, 0<y< 3, 0 <z<7) may be one or more selected from the group consisting of glass, but is not limited thereto.

The content of the inorganic particles may be 30% by volume to 75% by volume based on the total volume of the inorganic coating layer. If it is less than 30% by volume, the content of the binder becomes too high, resulting in a decrease in pore size and porosity due to a decrease in empty space formed between inorganic particles, resulting in deterioration of the final battery performance. Conversely, if it exceeds 75% by volume, the binder Since the content of is too small, mechanical properties of the separator may be deteriorated due to weakening of adhesion between inorganic substances.

The inorganic particles may have an average specific surface area of 3 m ² /g to 15 m ² /g.

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

In one example, the inorganic coating layer may further include a thickener in addition to inorganic particles and a binder, and the thickener is not particularly limited as long as it is a material capable of increasing the viscosity of the inorganic mixture slurry without causing chemical changes. No, for example, acrylic polymers and cellulose polymers can be used, and acrylic polymers include polyvinylpyrolidone (PVP) or polyvinylalcohol (PVA), etc. Polymers include hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), and methyl cellulose. , MC), carboxymethyl cellulose (CMC), and may be at least one selected from the group consisting of hydroxyalkyl methyl cellulose.

Meanwhile, the solvent is not particularly limited as long as it dissolves the binder and has partial compatibility with a non-solvent. For example, acetone, methylethyl ketone (MEK), tetrahydrofuran , THF), methylene chloride (MC), chloroform, dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl It may be one or more selected from the group consisting of acetamide (dimethylacetamide, DMAc) and cyclohexane.

The non-solvent is not particularly limited as long as it does not dissolve the binder and has partial compatibility with the solvent, and may be, for example, one or more selected from the group consisting of water, methanol, ethanol, isopropanol, and butanol.

In one specific example, when adding a partially compatible non-solvent to the inorganic slurry in the process (c), the non-solvent may be introduced in a gaseous state. When the gaseous non-solvent is introduced and added, it is possible to perform phase separation using a small amount of non-solvent, and drying of the inorganic slurry is easier.

In the process (c), the temperature at which the non-solvent in the gaseous state is added may be 15°C to 60°C, and when the temperature is less than 15°C, the non-solvent is difficult to maintain the gaseous state, and the drying rate of the inorganic slurry is low, resulting in low productivity. In the case of more than 60° C., the drying rate of the solvent and the non-solvent is too fast, so that phase separation is difficult to sufficiently occur.

In addition, in the process (c), a non-solvent is added so that the vapor pressure of the non-solvent is 30% to 80% of the saturated vapor pressure, and a process of phase separation may be sequentially performed. When the vapor pressure of the non-solvent is less than 30% of saturated water vapor, the amount of the non-solvent is too small to sufficiently cause phase separation, and when it exceeds 80%, it is difficult to obtain a uniform coating due to too much phase separation.

In order to perform phase separation by adding a non-solvent in a gaseous state, it is advantageous that evaporation occurs easily because the boiling point of the solvent is low. That is, when the temperature is lowered while the solvent evaporates, the non-solvent in the gaseous phase is condensed and exchange with the solvent may be facilitated. In one specific example, when a non-solvent in a gaseous state is added, the solvent may have a boiling point of 30°C to 80°C. In addition, the solvent of the inorganic slurry to which the gaseous non-solvent is added may be, for example, one or more selected from the group consisting of acetone and MEK.

In another example, when adding a partially compatible non-solvent to the inorganic slurry in step (c), the non-solvent may be added in a liquid state. When the non-solvent is added in a liquid state, the process of adding the non-solvent is easier, and various types of solvents that can be used are advantageous.

In one specific example, in the process (c), the addition of a non-solvent in a liquid state may be performed by immersing the inorganic slurry coated on a porous substrate in a non-solvent in a liquid state.

In addition, in the case of adding a liquid non-solvent in the process (c), a non-solvent in a liquid state may be added after partially drying the solvent included in the initial inorganic slurry. This is because when a non-solvent in a liquid state is added while the solvent is not dried, it may be difficult to obtain a uniform coating due to excessive phase separation.

Specifically, in the process (c), 30% to 70% of the solvent included in the initial inorganic slurry may be partially dried, and then a liquid non-solvent may be added. When the degree of drying is less than 30%, it may be difficult to achieve uniform coating due to excessive phase separation, and when it is more than 70%, it may be difficult to sufficiently improve the porosity of the inorganic coating layer.

Meanwhile, when a liquid non-solvent is added, the solvent may be, for example, one or more selected from the group consisting of water, NMP, DMF, and DMAc.

The present invention also provides a separator manufactured by the above method and a secondary battery including the separator.

The secondary battery may be a lithium secondary battery, a lithium ion battery, or a lithium ion polymer battery.

The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, and other components of the secondary battery will be described below.

The positive electrode may be prepared, for example, by coating a positive electrode mixture in which a positive electrode active material, a conductive material, and a binder are mixed on a positive electrode current collector, and if necessary, a filler may be further added to the positive electrode mixture.

The positive electrode current collector is generally manufactured to a thickness of 3 to 300 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium , And one selected from among those surface-treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel may be used, and in detail, aluminum may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

The positive electrode active material may include, 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 formula Li _1+x Mn _2-x O ₄ (wherein x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _2; 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; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (here, 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, Zn or Ta, and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, A lithium manganese composite oxide represented by Ni, Cu, or Zn); _{LiMn 2} O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ etc. are mentioned, but it is not limited only to these.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; 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 may be used.

The binder included in the positive electrode and the negative electrode is a component that assists in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such a binder 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, and various copolymers.

The filler is selectively used as a component that suppresses the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefin-based polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

Meanwhile, the negative electrode may be manufactured by applying a negative electrode mixture including a negative electrode active material, a conductive material, and a binder to the negative electrode current collector, and a filler may be optionally further included therein.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

In the present invention, the thicknesses of the negative electrode current collectors may all be the same within the range of 3 to 300 μm, but may have different values in some cases.

The negative active material may include, for example, carbon such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogen, metal complex oxides such as 0<x≦1;1≦y≦3;1≦z≦8); Lithium metal; Lithium alloy; 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.

In one specific example, the porous substrate may be a polyolefin-based separation film commonly used in the art, for example, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polyethylene terephthalate (polyethyleneterephthalate), polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone , Polyethersulfone (polyethersulfone), polyphenylene oxide (polyphenyleneoxide), polyphenylene sulfidero (polyphenylenesulfidro), polyethylene naphthalene (polyethylenenaphthalene) It may be a sheet consisting of one or more selected from the group consisting of a mixture thereof.

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 μm. When the pore size and porosity are less than 0.1 μm and 10%, respectively, it acts as a resistance layer, and when the pore size and porosity exceed 50 μm and 95%, it is difficult to maintain mechanical properties.

The electrolyte may be a lithium salt-containing non-aqueous electrolyte, and the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and as the non-aqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc. are used. It is not limited to only.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyllactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile , Nitromethane, methyl formate, methyl acetate, phosphate tryester, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ions A polymerization agent or the like containing an active dissociation group 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, and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS _{2 may be used.}

The lithium salt is a material that is easily 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 ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4 phenyl borate, imide, etc. may be used.

In addition, in the non-aqueous electrolyte, for the purpose of improving charge/discharge properties and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), and the like may be further included.

In one specific example, _{lithium salts such as LiPF 6} , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ are used in the cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC as a low viscosity solvent. The lithium salt-containing non-aqueous electrolyte can be prepared by adding it to a mixed solvent of linear carbonate.

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

The device includes, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, an MP3, a wearable electronic device, a power tool, an electric vehicle (EV), and a hybrid electric vehicle (HEV). , Plug-in Hybrid Electric Vehicle (PHEV), electric bicycle (E-bike), electric scooter (E-scooter), electric golf cart (electric golf cart), or power storage system However, of course, it is not limited to these only.

Since the structure and manufacturing method of such a device are well known in the art, detailed descriptions thereof are omitted herein.

As described above, the method of manufacturing a separator according to the present invention includes a step of phase-separating an inorganic slurry coated on a porous substrate by adding a non-solvent that is partially compatible with a solvent, when using the same amount of a binder. The porosity of the inorganic coating layer can be further improved.

In addition, it is possible to improve the mobility of lithium ions by improving the porosity of the inorganic coating layer while maintaining the mechanical properties of the separator by maintaining a high content of the binder.

Hereinafter, it will be described with reference to the embodiments of the present invention, but this is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

_{BaTiO 3} as inorganic particles, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP, PVdF monomer content 92 mol%) as a binder were mixed in a volume ratio of 72.5:27.5, and acetone was mixed as a solvent to prepare an inorganic slurry. I did.

The inorganic slurry thus prepared was coated on both sides with a thickness of 5 μm on a porous polyethylene substrate (porosity 45%, ventilation time 120sec/100cc, separator resistance 0.49 ohm) having a thickness of 12 μm. In a drying oven at 40°C, water vapor in a gaseous state as a partially compatible non-solvent was added until the vapor pressure compared to the saturated vapor pressure reached 60%, and phase separation and drying were performed in a drying oven at 40°C for 3 hours to prepare a separator. I did.

<Comparative Example 1>

A separator was prepared in the same manner as in Example 1, except that the process of phase separation by adding a partially compatible non-solvent in Example 1 was omitted and dried under dry room conditions.

<Example 2>

In Example 1, a separator was prepared in the same manner as in Example 1, except that inorganic particles and a binder were mixed in a volume ratio of 60:40 when preparing an inorganic slurry.

<Comparative Example 2>

A separator was prepared in the same manner as in Example 2, except that the process of phase separation and drying by adding a partially compatible non-solvent in Example 2 was omitted.

<Example 3>

In Example 1, a separator was prepared in the same manner as in Example 1, except that inorganic particles and a binder were mixed in a volume ratio of 35:65 when preparing an inorganic slurry.

<Comparative Example 3>

A separator was prepared in the same manner as in Example 3, except that the process of phase separation and drying by adding a partially compatible non-solvent in Example 3 was omitted.

<Example 4>

_{BaTiO 3} as inorganic particles, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP, PVdF monomer content 92 mol%) as a binder were mixed in a volume ratio of 35:65, and NMP as a solvent was mixed to prepare an inorganic slurry. I did.

The inorganic slurry thus prepared was coated on both sides at a thickness of 5 μm each on a 12 μm thick porous polyethylene substrate (porosity 45%, ventilation time 120sec/100cc, separator resistance 0.49 ohm), and in a drying oven at 40°C for 1 hour After drying, 40% of the solvent contained in the initial inorganic slurry was dried.

As a partially compatible non-solvent, a 40% dry inorganic slurry was immersed in liquid water for 30 seconds and removed, followed by phase separation and drying in a drying oven at 40° C. for 4 hours to prepare a separator.

<Comparative Example 4>

A separator was prepared in the same manner as in Example 4, except that the process of phase separation by immersion in a partially compatible non-solvent was omitted in Example 4.

<Comparative Example 5>

In Example 1, a separator was prepared in the same manner as in Example 1, except that inorganic particles and a binder were mixed in a volume ratio of 22.5:77.5 when preparing an inorganic slurry.

<Comparative Example 6>

In Example 1, a separator was prepared in the same manner as in Example 1, except that inorganic particles and a binder were mixed in a volume ratio of 85:15 when preparing an inorganic slurry.

<Experimental Example 1>

Breathability experiment

The separation membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 6 were measured using a permeability measuring device (Asahi), and the results are shown in Table 1 below.

<Experimental Example 2>

Membrane resistance measurement experiment

The resistance of the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 6 were measured, and the results are shown in Table 1 below. Separator resistance was carried out in such a way that the coin cell was mounted with a separator, and then the electrolyte was sufficiently impregnated and the EIS was measured.

<Experimental Example 3>

Adhesion test

In order to measure the adhesion to the electrodes of the separators prepared in Examples 1 to 4 and Comparative Examples 1 to 6, respectively, after attaching to the prepared separator electrode, the separator was peeled off and a 180 peel test was performed, The results are shown in Table 1. In Table 1, when the adhesive force is 20 gf/cm or more, it is indicated as "normal", and when it is less than 20 gf/cm, it is indicated as "abnormal".

Inorganic particles: Binder
(Volume ratio) Breathable
(Second / 100 cm ³ ) Membrane resistance
(ohm) Adhesion
(gf/cm) Example 1 72.5:27.5 201 0.77 normal Comparative Example 1 72.5:27.5 3,620 1.62 normal Example 2 60:40 244 0.81 normal Comparative Example 2 60:40 5,130 1.83 normal Example 3 35:65 282 0.96 normal Comparative Example 3 35:65 infinity 2.27 normal Example 4 35:65 264 0.94 normal Comparative Example 4 35:65 infinity 2.33 normal Comparative Example 5 22.5:77.5 198 0.75 normal Comparative Example 6 85:15 350 1.19 abnormal

Referring to Table 1, the noticeability tends to decrease as the content of the binder increases, but when the phase separation is performed by adding a non-solvent when forming the inorganic coating layer, the breathability is improved by at least about 15 times compared to the other case. I can confirm. In addition, when the phase separation is performed by adding a partially compatible non-solvent, it can be seen that the resistance is reduced by about 50% or more as compared to the comparative example in which the phase separation process is omitted.

On the other hand, in the case of Comparative Example 5 in which the content of the binder is low, the adhesive strength is measured to be significantly low, and since there is a high possibility of being easily separated from the electrode, it is not evaluated as suitable as a separator.

Although the above has been described with reference to the embodiments of the present invention, a person of ordinary skill in the field to which the present invention belongs will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (24)

(a) preparing an inorganic slurry containing a binder, inorganic particles, and a solvent;
(b) applying the inorganic slurry to at least a portion of the porous substrate; And
(c) phase separation of the inorganic slurry coated on the porous substrate by adding a non-solvent having partial compatibility with the solvent;
(d) drying the phase-separated inorganic slurry to form an inorganic coating layer;
In the method for manufacturing a separation membrane comprising an inorganic coating layer, characterized in that it comprises,
The volume ratio of the binder and the inorganic particles is 25:75 to 70:30,
The process (c) proceeds at 15 ℃ to 60 ℃,
The binder includes a PVdF-based binder, the content of the PVdF-based binder is 80% by weight or more based on the total weight of the binder, and the PVdF-based binder has a PVdF monomer content based on the total moles of Method for producing a separator, characterized in that 92 mol% or more. delete delete delete delete delete The method of claim 1, wherein the inorganic particles are at least one selected from the group consisting of inorganic particles having piezoelectricity and inorganic particles having lithium ion transfer capability. The method of claim 1, wherein the inorganic particles have a specific surface area of 3 m ² /g to 15 m ² /g. The method of claim 1, wherein the solvent is acetone, methylethyl ketone (MEK), tetrahydrofuran (THF), methylene chloride (MC), chloroform, dimethylformamide. (dimethylformamide, DMF), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc) and one or more selected from the group consisting of cyclohexane Method for producing a separation membrane, characterized in that. The method of claim 1, wherein the non-solvent is at least one selected from the group consisting of water, methanol, ethanol, isopropanol, and butanol. The method of claim 1, wherein the non-solvent added in the step (c) is in a gaseous state. delete 12. The method of claim 11, wherein in the step (c), a non-solvent is added and phase separated so that the vapor pressure of the non-solvent is 30% to 80% of the saturated vapor pressure is sequentially performed. The method of claim 11, wherein the solvent of the inorganic slurry to which the gaseous non-solvent is added has a boiling point of 30°C to 80°C. The method of claim 14, wherein the solvent is at least one selected from the group consisting of acetone and MEK. The method of claim 1, wherein the non-solvent added in the step (c) is in a liquid state. The method of claim 16, wherein the addition of the liquid non-solvent is performed by immersing the inorganic slurry coated on the porous substrate in the liquid non-solvent. The method of claim 16, wherein in the step (c), a non-solvent in a liquid state is added after partially drying the solvent contained in the initial inorganic slurry. 19. The method of claim 18, wherein 30% to 70% of the solvent contained in the initial inorganic slurry is dried. The method of claim 16, wherein the method of producing a separation membrane, characterized in that at least one selected from the group consisting of cost tying water, methanol, ethanol, isopropanol and butanol, the inorganic slurry cost-solvent in the liquid state is added. A separation membrane, characterized in that produced by the method of manufacturing the separation membrane according to claim 1. A secondary battery comprising the separator according to claim 21. A battery pack comprising the secondary battery according to claim 22 as a unit battery. A device comprising the battery pack according to claim 23 as a power source.