WO2017171433A1 - Method for producing secondary battery - Google Patents

Abstract

The present invention relates to a method for producing a secondary battery and a secondary battery produced by such a method, the method comprising the steps of: (step 1) providing a film layer between a separation membrane and electrodes, the film layer comprising a first solvent having melting temperature of 25°C or higher and viscosity of 1.5cP or higher; (step 2) producing an electrode assembly by means of the electrodes, film layer and separation membrane; and (step 3) storing the electrode assembly in a case, and sealing by injecting an injection solution comprising a second solvent. The method for producing a secondary battery according to the present invention can improve electrolyte wettability, and thus can further improve performance and safety of the secondary battery.

Description

Manufacturing method of secondary battery

Cross Citation with Related Application (s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0039273 dated March 31, 2016 and Korean Patent Application No. 10-2017-0039348 dated March 28, 2017. All content disclosed in the literature is included as part of this specification.

Technical Field

The present invention relates to a secondary battery manufacturing method, and more particularly to a secondary battery manufacturing method that can improve the impregnation of the electrolyte solution.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries of high energy density and high discharge voltage are commercialized and widely used.

A lithium secondary battery mainly uses a lithium-based metal oxide and a carbon material as a positive electrode active material and a negative electrode active material, respectively, and an electrode assembly in which a positive electrode plate and a negative electrode plate coated with the positive electrode active material and the negative electrode active material are disposed with a separator interposed therebetween, and the electrode An exterior material for sealingly containing the assembly together with the electrolyte solution is provided.

In the last step, the electrolyte injected into the cell is permeated by capillary force between the positive electrode plate, the negative electrode plate, and the separator constituting the electrode assembly. In order for the secondary battery to have a high capacity and a high energy density and to maintain a long lifetime, the electrode assembly interposed in the battery must be completely impregnated with the electrolyte so that lithium ion reaction between the electrodes can be actively performed.

However, impregnation of the electrolyte is not easy due to the characteristics of the porous electrode of the microstructure and the physical and chemical properties of the electrode and the elements constituting the battery. In particular, as the positive and negative electrode loads of secondary batteries gradually increase for high capacity, and as the large area electrodes of automobile batteries increase, the impregnation of electrolytes becomes more difficult. If the electrolyte solution is not sufficiently impregnated, since the charge and discharge efficiency due to lithium ions and the like is lowered, there is a disadvantage in that the performance of the secondary battery is reduced.

Recently, the use of high viscosity solvents for the safety and performance of secondary batteries has become more difficult to impregnate the electrolyte.

Accordingly, in order to improve the performance of the secondary battery and to improve the safety, there is a need for a method for improving the electrolyte impregnation of the secondary battery.

Prior art literature

Japanese Laid-Open Patent Publication No. 1996-171934A

The present invention has been made to solve such a problem,

The first technical problem to be solved by the present invention is to improve the performance and life of the lithium secondary battery by improving the electrolyte impregnation, and to provide a secondary battery manufacturing method that can improve the safety of the battery.

In addition, a second technical problem to be solved by the present invention is to provide a secondary battery manufactured by the manufacturing method.

In order to solve the above problems, in one embodiment of the present invention

Providing a film layer comprising a first solvent having a melting temperature of at least 25 ° C. and a viscosity of at least 40 cP at 40 ° C. between the separator and the electrode (step 1);

Preparing an electrode assembly using the electrode, the film layer, and the separator (step 2); And

It provides a method of manufacturing a secondary battery comprising a; receiving the electrode assembly in a case, injecting and sealing an injection solution containing a second solvent (step 3).

Providing the film layer (step 1)

(a) compressing the first solvent in a solid state at a temperature below 25 ° C. to prepare a freestanding film layer, and then providing it between the separator and the electrode, or (b) at a temperature below 25 ° C. After melting the first solvent in a solid state, it may include the step of providing a coating directly on one side or both sides of the separator.

The film layer may further include a softener.

The weight ratio of the first solvent: softener in the film layer may be 99.5: 0.5 to 90:10, specifically 99: 1 to 95: 5.

The film layer may further include a first lithium salt.

The second solvent may include a liquid at room temperature, a solvent having a viscosity of less than 1.5 cP at 25 ° C, or a solid at room temperature, and a solvent having a viscosity of at least 1.5 cP at 40 ° C.

In addition, the injection liquid may further include a second lithium salt.

The weight ratio of the first solvent to the second solvent may be 1: 0.2 to 1: 2.

In addition, in one embodiment of the present invention

Anode, cathode, separator, electrolyte, and

Provided is a secondary battery including a film layer manufactured by the method of the present invention interposed between at least one or more of the separator and the negative electrode, or between the separator and the positive electrode.

In one embodiment, the film layer is composed of a first solvent, the electrolyte may include a second solvent and a second lithium salt.

In another embodiment, the film layer may include a first solvent and a first lithium salt, and the electrolyte may include a second solvent and a second lithium salt.

In another embodiment, the film layer may include a first solvent and a first lithium salt, and the electrolyte may be composed of a second solvent.

According to the method of manufacturing a secondary battery of the present invention, by introducing a film layer containing the first solvent in the solid state at a temperature of less than 25 ℃ to the electrode assembly, and further injecting the injection solution containing the second solvent, It is possible to manufacture a secondary battery with improved impregnation and safety. Such a secondary battery can be usefully applied to high capacity and large area.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 and 2 schematically show the position and shape of the film layer containing the first solvent in the method of manufacturing a secondary battery of the present invention.

3 to 5 schematically show various configuration examples of an injection solution including a film layer and a second solvent, each including a first solvent in a method of manufacturing a secondary battery according to an embodiment of the present invention. .

Explanation of the sign

100, 200, 300, 400: electrode assembly

120, 220, 320, 420: separator

130, 230: film layer comprising a first solvent

110, 140, 210, 240, 310, 340, 410, 440: electrode

250, 350: electrolyte solution (injection solution) containing a second solvent and a second lithium salt

330 and 430: film layer comprising a first solvent and a first lithium salt

450: electrolyte solution (injection solution) containing a second solvent

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

In recent years, the positive and negative electrode loading of the battery is gradually increased to increase the capacity, and the space in the battery is decreased, and the electrolyte impregnation is becoming increasingly difficult. In particular, while a certain amount of high viscosity solvent is necessary for battery safety and cell performance, studies for further improving electrolyte impregnation have emerged.

Thus, in the present invention, the film layer formed by using a high viscosity solvent which is a solid at room temperature is first interposed between the separator and the electrode, and then a low viscosity solvent is further injected to solve the electrolyte impregnation problem.

Specifically, in one embodiment of the present invention

Providing a film layer comprising a first solvent having a melting temperature of at least 25 ° C. and a viscosity of at least 40 cP at 40 ° C. between the separator and the electrode (step 1);

Preparing an electrode assembly using the electrode, the film layer, and the separator (step 2); And

It provides a method of manufacturing a secondary battery comprising a; receiving the electrode assembly in a case, injecting and sealing an injection solution containing a second solvent (step 3).

At this time, the step (step 1) of providing the film layer in the method of the present invention

(a) compressing the first solvent in a solid state at a temperature below 25 ° C. to prepare a freestanding film layer, and then providing it between the separator and the electrode, or (b) a temperature below 25 ° C. After melting the first solvent in a solid state, it may include the step of providing a coating directly on one side or both sides of the separator.

At this time, after the coating (b), it may further comprise the step of cooling the first solvent to a solid state.

As described above, according to the method of the present invention, an injection liquid containing a second solvent is added between the separator and the electrode in a state where a film layer including the first solvent having a viscosity of 1.5 cP or more at 40 ° C. is present. By injecting into a liquid crystal, an improved electrolyte solution impregnation effect can be realized than when a mixed solvent in which a first solvent and a second solvent are mixed is injected into a battery case, which is a conventional method.

Hereinafter, a step-by-step look at the manufacturing method of the secondary battery of the present invention in detail.

First, the method of manufacturing a secondary battery according to an embodiment of the present invention, the separation membrane and the film layer comprising a first solvent in the solid state at a melting temperature of 25 ℃ or more, that is, less than 25 ℃ Providing between the electrodes (step 1).

In the step (1), a film layer in a solid form is first formed using a first solvent in a solid state at a temperature of less than 25 ° C., and then the previously formed film layer is formed between at least one of the separator and the anode, or between the separator and the cathode. It may be provided via one or more locations.

In the method of manufacturing a secondary battery of the present invention according to one embodiment, the melting temperature of the first solvent is 25 ℃ or more, specifically 25 ℃ to 200 ℃, more specifically 25 ℃ to 100 ℃, more specifically 25 ℃ To 80 ° C.

If the melting temperature of the solvent is less than 25 ℃, it may be difficult to implement a film layer of a solid because it is liquid at room temperature. That is, the first solvent is convenient for sheet production when it is in a solid state at a temperature of less than 25 ° C., for example. Sometimes, even in the case of a solvent having a melting point of room temperature or less, sheeting and electrode assembly may be possible when the temperature is kept below room temperature in the manufacturing process.

At this time, the term "room temperature" or Not cooling Not As a yearly average temperature, it means the range of 20 ± 5 ° C, and refers to a temperature of 25 ° C in this specification .

In addition, it is preferable that the first solvent is a high viscosity solvent having a viscosity of 1.5 cP or more, preferably 1.5 cP to 50 cP, more preferably 1.5 cP to 20 cP at 40 ° C. as measured by a Brookfield viscometer. If the viscosity of the first solvent is less than 1.5 cP, there may be a problem that the safety and performance of the secondary battery is reduced.

In this case, the viscosity of the first solvent is a viscosity measured at the time of liquefaction at a temperature higher than the melting temperature.

In the method of manufacturing a secondary battery of the present invention according to an embodiment, the film layer may be manufactured by various methods using a first solvent having a melting temperature of 25 ° C. or more and a viscosity of 1.5 cP or more at 40 ° C.

For example, as shown in FIG. 1, the film layer 130 may be manufactured in an appropriate size suitable for the purpose by applying pressure to a first solvent having a melting temperature of 25 ° C. or higher and a viscosity of 1.5 cP or higher at 40 ° C. .

Specifically, the film layer 130 using the first solvent is 50 Kgf / cm ² It can be formed by applying a pressure in the range of from 300 Kgf / cm ² . When the pressure range is satisfied, the film can be filmed in a state suitable for the performance of the secondary battery desired in the present invention without damage. That is, by applying an appropriate pressure to the solid materials at room temperature it can be formed into a thin film.

In the method of manufacturing a secondary battery of the present invention, the electrode assembly 100 may be formed using the negative electrode 140, the film layer 130, the separator 120, and the positive electrode 110 formed using the first solvent. In this case, the film layer 130 may be positioned between the anode 110 and the separator 120 (not shown), between the cathode 140 and the separator 120, or both (not shown).

In the method of manufacturing a secondary battery of the present invention according to an embodiment, the first solvent is a melting temperature of 25 ℃ or more, at 40 ℃ satisfies a condition of more than 1.5 cP, inhibiting the effect of the present invention Various solvents can be used in the range which is not. Specifically, the first solvent is ethylene carbonate (EC), cis-4,5-dimethyl-1,3-dioxolan-2-one (cis-4,5-Dimethyl-1,3-dioxolan-2-one ), Trans-4,5-dimethyl-1,3-dioxolan-2-one (trans-4,5-Dimethyl-1,3-dioxolan-2-one), 1,2-cyclopentylene carbonate (1 , 2-Cyclopentylene carbonate, cyclohexene carbonate, Pinacolone cyclic carbonate, 1,3-propylene carbonate, 5,5-dimethyl-1,3-dioxan-2-one (5,5- Dimethyl-1,3-dioxan-2-one), sulfolane, ethyl methyl sulfone, diethyl sulfone, ethyldimethylcarbamate, and at least one selected from the group consisting of phenyl dimethylcarbamate.

In addition, according to the method of manufacturing a secondary battery of the present invention, the film layer may further include a softener to impart ductility.

That is, in order to impart proper ductility in subsequent lamination, winding, or folding steps, ductility may be added by adding a softener that does not affect the performance of the secondary battery. The softener may be a material commonly used in the art as an electrode active material binder, and examples thereof include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) and polyvinylidene fluoride. , Polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, poly A single substance selected from the group consisting of acrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and polyacrylic acid, or a mixture of two or more thereof may be used.

At this time, the low conductivity ductile agent is present in the film layer in a simple mixture with the first solvent, it is difficult to dissolve in the second solvent additionally injected. Therefore, since only the inside of the film layer between the electrode and the separator, and does not penetrate into the electrode or the separator, there is a structural difference from the general gel electrolyte, there is a relatively small problem such as increased resistance.

The weight ratio of the first solvent: softener in the film layer may be 99.5: 0.5 to 90:10, specifically 99: 1 to 95: 5.

At this time, when the weight ratio of the softener exceeds 10, the resistance may increase, and the effect of imparting ductility to the film layer at only less than 0.5 may be insignificant.

In addition, the thickness of the film layer is preferably in the range of 10 ㎛ to 100 ㎛, when formed in the thickness range, it is possible to ensure the optimum amount of solvent for impregnation of the electrolyte solution.

The film layer may be composed of only a first solvent having a viscosity of 1.5 cP or more and a high viscosity, or may further include a first lithium salt as necessary.

The first lithium salt may be included in the first solvent at a concentration of 0.3M to 2.0M.

Examples of the first lithium salt include electrolyte salts commonly used in the art, and include, for example, Li ⁺ as a cation, and F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO ₃ ⁻ , as an anion. ^{_{N (CN) 2 -, BF}} 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 -, ( ^{_{CF 3) 2 PF 4 -,}} (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, C 4 _{^{F 9 SO 3 -, CF 3}} CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (F 2 SO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO _{^{2) 2 CH -, CF 3}} (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , at least one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N It may include one.

In the secondary battery manufacturing method of the present invention according to an embodiment, the film layer 130 is (a) freestanding by compressing the first solvent in a solid state at a temperature of less than 25 ℃ (a) After preparing a film layer having a freestanding form, it may be provided between the separator 120 and the electrode 140, or as shown in FIG. 2 (b) after melting the first solvent, the separator 120 It may be formed by directly coating on one side or both sides of, then cooling to room temperature or less.

The coating may be coated by various methods such as spraying or immersing a separator in a first solvent and then drying, but is not limited thereto.

According to another embodiment of the present invention, the film layer may be formed by sheeting the first solvent using the separator as a support layer without melting the first solvent (not shown).

In addition, the secondary battery manufacturing method of the present invention according to an embodiment may include a step (step 2) of preparing an electrode assembly using a film layer, an electrode and a separator comprising a first solvent.

Electrodes and separators for forming the electrode assembly may be prepared using a method commonly used in the art.

That is, the separator is a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer It may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of glass fibers of high melting point, polyethylene terephthalate fibers and the like can be used, but is not limited thereto.

The electrode also includes an anode and a cathode.

The positive electrode may be prepared by mixing and stirring a positive electrode active material, a binder, a conductive material, and a solvent to prepare a slurry, followed by coating (coating), compressing, and drying the positive electrode current collector.

The cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), lithium-cobalt oxide (eg, LiCoO _2, etc.), lithium-nickel oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <z1 <2) and the like), lithium-nickel Manganese-cobalt-based oxides (e.g., Li (Ni _p Co _q Mn _r1 ) O ₂ , where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2, etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (e.g. Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (excitation Where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of the independent elements, respectively, 0 <p2 <1, 0 <Q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included. Among the lithium composite metal oxides, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and lithium nickel manganese cobalt oxides (eg, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ may be improved in capacity and stability of the battery. , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ , or the like, or lithium nickel cobalt aluminum oxide (for example, Li (Ni _0.8 Co _0.15 Al _0.05 ) O _2, etc. ), And the lithium composite metal oxide may be Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , in view of the remarkable improvement effect according to the type and content ratio of the member forming the lithium composite metal oxide. _{Li (Ni 0.5 Mn 0.3 Co 0.2} ) O 2, Li (Ni 0.7 Mn 0.15 Co 0.15) O 2 or _{L (iNi 0. 8 Mn 0} . 1 Co 0. 1) O 2 and the like, any one or of which Mixtures of two or more may be used.

The cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of solids in the cathode slurry.

The binder is a component that assists in the bonding between the positive electrode active material and the conductive material and the current collector, and is generally added in an amount of 1 to 20 wt% based on the total weight of solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber Various kinds of binder polymers such as (SBR), fluororubbers, and various copolymers can be used.

The conductive material is typically added in an amount of 1 to 20% by weight based on the total weight of solids in the positive electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials 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 powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

Preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohols, N-methylpyrrolidone (NMP), acetone or water and the like, and are removed in the drying process.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the positive electrode current collector may be formed on a surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. The surface-treated with carbon, nickel, titanium, silver, etc. are mentioned. Such a positive electrode current collector generally has a thickness of 3 μm to 500 μm. The positive electrode current collector may increase the adhesion of the positive electrode active material by forming minute unevenness on the surface, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In addition, the negative electrode may be prepared by mixing and stirring a negative electrode active material, a binder, a conductive material, and a solvent to prepare a slurry, followed by coating (coating), compressing, and drying the negative electrode current collector.

The negative electrode active material is typically a carbon material such as natural graphite or artificial graphite in which lithium ions may be occluded and released; Metals (Me) that are lithium-containing titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; Alloys composed of the metals (Me); Oxides of the metals (Me); And it can be used one or two or more selected from the group consisting of a complex of the metals (Me) and carbon. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes.

The negative active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of solids in the negative electrode slurry.

The binder is a component that assists the bonding between the negative electrode active material and the conductive material and the current collector, and is generally added in an amount of 1 to 20 wt% based on the total weight of solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber Various kinds of binder polymers such as (SBR), fluororubbers, and various copolymers can be used.

The conductive material is typically added in an amount of 1 to 20% by weight based on the total weight of solids in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials 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 powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water, and the like, and are removed in a drying process.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a 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. Such negative electrode current collectors generally have a thickness of 3 μm to 500 μm. The negative electrode current collector, like the positive electrode current collector, may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material, and may be used in various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric. Can be.

According to an embodiment of the present invention, an electrode assembly may be manufactured by stacking, winding or folding the cathode, the separator including the film layer including the first solvent, and the anode in a conventional manner. The separator including the film layer including the first solvent may be located between the cathode, or optionally, both between the anode and the separator and between the cathode and the separator.

In addition, the method of manufacturing a secondary battery according to an embodiment of the present invention may include a step (step 3) of accommodating the electrode assembly in a case and injecting an injection liquid containing a second solvent.

The injection liquid may consist of only the second solvent in liquid form, or may optionally further comprise a second lithium salt or additive in the second solvent.

In this case, the second lithium salt may be included in a concentration of 0.7M to 3.0M in the second solvent.

Further, the second solvent is optionally a liquid at less than 25 ° C. and a low viscosity solvent having a viscosity of less than 1.5 cP at 25 ° C. and a solid at less than 25 ° C. as measured by a Brookfield viscometer and the first solvent is Brookfield ( Brookfield) At least one solvent selected from the group consisting of high viscosity solvents having a viscosity of 1.5 cP or higher at 40 ° C. can be used as measured by a viscometer. At this time, when the second solvent is a high viscosity solvent that is solid at less than 25 ℃ and 1.5cP or more, it may be injected after melting it.

Specifically, when the second solvent is a low viscosity solvent of less than 1.5 cP, representative examples thereof include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), butylene carbonate (BC), diethyl carbonate (DEC), dipropyl Carbonates such as carbonate (DPC) or fluoroethylene carbonate (FEC); methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP) or butyl propionate ( Esters such as BP) and lactones such as gamma-butyrolactone (GBL), or a mixture of two or more thereof.

When the second solvent is a high viscosity solvent having 1.5 cP or more, a solvent having the same high viscosity as the first solvent may be used.

At this time, when using a low viscosity solvent having a viscosity of less than 1.5 cP and a high viscosity solvent having a viscosity of 1.5 cP or more in the second solvent, a low viscosity solvent having a viscosity of less than 1.5 cP: a high viscosity solvent having a viscosity of 1.5 cP or more is 1 : 9 to 9: 1.

According to one embodiment of the present invention, the second solvent may be a solvent having a viscosity of less than 1.5 cP, in this case, when the battery is charged and stored in a high temperature environment, the low-viscosity solvent at the electrode is oxidatively decomposed carbon dioxide gas Is generated, so that expansion of the battery can be prevented, which is preferable.

According to one embodiment of the present invention, the ratio of the first solvent and the second solvent is preferably 1: 0.2 to 1: 2 by weight. If the ratio of the second solvent is less than 0.2, the ionic conductivity may be reduced, and if the ratio of the second solvent exceeds 2, not only the low temperature and high temperature output characteristics of the secondary battery, but also the capacity characteristics after high temperature storage are reduced. There may be a problem. When the first solvent and the second solvent in the above range is satisfied, the optimum effect can be achieved in the ion conductivity and the capacity and life characteristics of the secondary battery.

In general, when a solid electrolyte is used, a secondary battery is prepared including only a solid electrolyte without additional solvent. In this case, the characteristics of the solid electrolyte layer itself should be excellent. However, in the case of the solid electrolyte, since the ionic conductivity is inferior to that of the liquid electrolyte, various problems may occur in the practical application of the battery using the solid electrolyte.

On the other hand, in the present invention, problems such as ionic conductivity which may be caused by using the film layer including the high viscosity first solvent may be improved by additionally injecting the injection liquid containing the second solvent having the low viscosity. have. In addition, in the state in which the first solvent is present as a film layer between the separator and the electrode, the electrode assembly is generally contained in the battery case by injecting the injection solution including the second solvent. There is an advantage that the electrolyte solution is impregnated at a faster rate than when the nonaqueous electrolyte solution in which the first solvent and the second solvent are mixed is injected.

As described above, in the present invention, two kinds of solvents having different characteristics and shapes, that is, a film layer including a high viscosity solvent and an injection solution containing a second solvent are injected and used in different ways, so that the low temperature and In addition to the high temperature output characteristics, the optimum effect can be achieved in capacity characteristics after high temperature storage.

In addition, in one embodiment of the present invention

Anode, cathode, separator, electrolyte, and

Provided is a secondary battery including a film layer manufactured by the method of the present invention interposed between at least one or more of the separator and the negative electrode, or between the separator and the positive electrode.

The secondary battery of the present invention may be manufactured in various structures including a first solvent and a second solvent. Specifically, FIGS. 3 to 5 included in the present specification schematically show examples of various configurations of the secondary battery manufactured by the method of manufacturing the secondary battery according to the embodiment of the present invention.

That is, the secondary battery of the present invention according to an embodiment, as shown in FIG. 3, does not include the first lithium salt, the film layer 230 includes only the first solvent, the second solvent, and the second lithium salt. It may include an electrolyte (injection solution) 250 including a.

For example, the secondary battery according to the exemplary embodiment includes a solid film layer 230 made of a first solvent that is solid at room temperature or less without a first lithium salt, between the separator 220 and the electrodes 210 and 240. After positioning and manufacturing the electrode assembly 200 using them, the electrode assembly 200 is housed in a case, and an electrolyte solution (injection liquid) 250 containing a second solvent and a second lithium salt is injected and sealed. Can be prepared.

In this case, the second lithium salt may be included in 0.7M to 3.0M with respect to the second solvent.

In addition, the secondary battery of the present invention according to the embodiment, the film layer 330 including the first solvent and the first lithium salt, and the electrolyte solution containing the second solvent and the second lithium salt as shown in FIG. (Injection amount) 350.

For example, in the secondary battery according to the exemplary embodiment, the film layer 330 including the first solvent and the first lithium salt in a solid state at room temperature or less is disposed between the separator 320 and the electrodes 310 and 340. After manufacturing the electrode assembly 300 using them, the electrode assembly 300 is housed in a case, and an electrolyte solution (injection solution) 350 containing a second solvent and a second lithium salt is injected and sealed. Can be prepared.

In this case, the first lithium salt may be included in a concentration of 0.3M to 2.0M with respect to the first solvent, the second lithium salt may be included in a concentration of 0.7M to 3.0M with respect to the second solvent.

In addition, the secondary battery of the present invention according to the embodiment, as shown in FIG. 5, the film layer 430 including the first solvent and the first lithium salt, and the second solvent without the second lithium salt. It may include an electrolyte solution (injection solution) 450 to be included.

For example, in the secondary battery according to the embodiment, the film layer 430 including the first solvent and the first lithium salt having a high viscosity of 1.5 cP or more is positioned between the separator 420 and the electrodes 410 and 440. After manufacturing the electrode assembly 400 using them, the electrode assembly 400 is housed in a case and manufactured by injecting and sealing an electrolyte solution (injection solution) 450 containing only the second solvent without a second lithium salt. Can be.

In this case, the first lithium salt may be included in a concentration of 0.3M to 2.0M with respect to the first solvent.

According to an embodiment of the present invention, the first lithium salt and the second lithium salt each include Li ⁺ as a cation, and as an anion, F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO ₃ ⁻ , N ( _{^{CN) 2 -, BF 4 -}} , ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 -, (CF 3 ^{_{) 2 PF 4 -, (CF}} 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, C 4 F 9 _{^{SO 3 -, CF 3 CF 2}} SO 3 -, (CF 3 SO 2) 2 N -, (F 2 SO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) _{^{2 CH -, CF 3 (CF}} 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - at least any one selected from the group consisting of It may include.

In addition, the battery case used in the present invention may be adopted that is commonly used in the art, there is no limitation on the appearance according to the use of the battery, for example, cylindrical, square, pouch type using a can Or a coin type.

In addition, the present invention may provide a secondary battery manufactured by the method of manufacturing the secondary battery.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells. Preferred examples of the medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Example 1.

(Film layer production)

As a first solvent, ethylene carbonate (EC) having a viscosity of 1.9 cP at 40 ° C. and a melting temperature of 36.4 ° C. as measured by a Brookfield viscometer was subjected to a pressure of 200 Kgf / cm ² under a nitrogen atmosphere to 100 μm in thickness. The film layer of was formed.

(Injection liquid production)

As the second solvent, ethylmethyl carbonate (EMC) and LiPF _{6 having a} viscosity of 0.65 cP at 25 ° C. as measured by a Brookfield viscometer An injection solution containing 3M was prepared. (At this time, when the mixture was mixed with the first solvent film layer, the LiPF ₆ concentration was 1 M in total).

(Manufacture of Electrode Assembly)

89% by weight of a mixture of LiCoO ₂ as a positive electrode active material, 8% by weight of carbon black as a conductive material, and 3% by weight of polyvinylidene fluoride (PVDF) as a binder were used as a solvent, N-methyl-2-pyrrolidone ( NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and dried, followed by roll press to prepare a positive electrode.

Subsequently, a negative electrode mixture slurry was prepared by adding 97 wt%, 2 wt%, and 1 wt% of graphite black as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material, respectively, to NMP as a solvent. The negative electrode mixture slurry was applied to a thin copper (Cu) thin film, which was a negative electrode current collector having a thickness of 10 μm, and dried, followed by roll press to prepare a negative electrode.

Next, polypropylene was uniaxially stretched using a dry method to prepare a separator having a microporous structure having a melting point of 165 ° C and a width of one side of 200 mm.

The prepared negative electrode, the film layer including the first solvent, the separator and the positive electrode were sequentially stacked, and then the unit cells were placed on the long sheet polyolefin separation film and folded to form the electrode assembly of FIG. 3.

(Secondary Battery Manufacturing)

After the electrode assembly was inserted into the battery case, the injection solution was injected and sealed to complete the manufacture of a lithium secondary battery.

At this time, the weight ratio of the first solvent and the second solvent was injected to be 1: 0.5.

Example 2

LiPF ₆ as the first lithium salt in the first solvent Further adding 0.5M to prepare a solid film layer, LiPF ₆ as a second lithium salt in a second solvent Except that 0.5M was added, the electrode assembly of FIG. 4 and a lithium secondary battery having the same were manufactured in the same manner as in Example 1.

Example 3

LiPF ₆ in the first solvent The electrode assembly of FIG. 5 and the lithium secondary battery including the same were manufactured in the same manner as in Example 1, except that 1.5M was added to prepare a solid film layer, and only the second solvent was added as an injection liquid. Prepared.

Example 4

Ethylene carbonate (EC) melted at 40 ° C. was coated on the porous layer separator and then reduced to room temperature to form a separator including a 100 μm thick film layer. An electrode assembly and a lithium secondary battery including the same were manufactured in the same manner as in Example 1 except that the electrode assembly was formed by folding the separator, the cathode, and the cathode including the film layer.

Example 5

Example 1 and 1 except that the first solvent in the ethylene carbonate (EC) instead of ethylene carbonate (EC) and a sulfolane having a viscosity of 10 cP at 30 ℃ in a 1: 1 weight ratio. A lithium secondary battery was produced in the same manner.

Example 6

In Example 1, except that ethylene carbonate (EC) and 1,3-propylene carbonate were mixed in a 1: 1 weight ratio instead of ethylene carbonate (EC) as the first solvent, in the same manner as in Example 1. A lithium secondary battery was prepared.

Example 7

In Example 1, except that ethylene carbonate (EC) and 1,3-propylene carbonate were mixed in a 1: 1 weight ratio instead of ethylene carbonate (EC) as the first solvent. A lithium secondary battery was prepared.

Example 8

In Example 1, except that ethylene carbonate (EC) and 1,3-propylene carbonate were mixed in a 1: 1 weight ratio instead of ethylene carbonate (EC) as the first solvent, in the same manner as in Example 3. A lithium secondary battery was prepared.

Example 9

A lithium secondary battery was manufactured in the same manner as in Example 6, except that the first solvent and the softener (polyvinylidene fluoride) were included in a weight ratio of 97: 3 in Example 6.

Example 10

Except for using trans-4,5-dimethyl-1,3-dioxolan-2-one as the first solvent in Example 1 and using dimethyl carbonate as the second solvent. A lithium secondary battery was manufactured in the same manner as in Example 1.

Example 11

In Example 1, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 9: 1 by weight instead of ethyl methyl carbonate (EMC), and a second lithium salt LiPF _{6 was used.} A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.5 M was used.

Comparative Example 1

Without forming the film layer, the electrode assembly is assembled through a separator between the prepared positive electrode and the negative electrode and then inserted into a battery case, and then the injection liquid containing only the second solvent prepared in Example 1 was injected and sealed A lithium secondary battery was manufactured in the same manner as in Example 1, except that a lithium secondary battery was manufactured.

Comparative Example 2

Without forming the film layer, the electrode assembly was assembled through a separator between the positive electrode and the negative electrode and the prepared positive electrode and the negative electrode and inserted into the battery case, and the ethylene carbonate (EC) having a viscosity of 1.9 cP at 25 ° C. and 25 Except that a lithium secondary battery was prepared by pouring and sealing an injection solution prepared by adding LiPF ₆ 1M to a mixed solution containing an ethyl methyl carbonate (EMC) having a viscosity of 0.65 cP at a 2: 1 weight ratio. And the lithium secondary battery was manufactured by the method similar to Example 1.

Comparative Example 3

Similar to Comparative Example 2, except that the injection solution was injected with a solution in which the ratio of EC: sulforan: EMC was mixed in a 1: 1: 1 weight ratio instead of a mixed solution of ethylene carbonate (EC) and ethylmethyl carbonate (EMC). A lithium secondary battery was prepared by the method of.

Experimental Example

Experimental Example 1: Performance Test of Secondary Battery

Each of the secondary batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 3 was subjected to constant current / constant voltage condition charging and 0.05C cut off charging to 0.85C at 4.35V, and discharged at 0.5C to 3.0V. Table 1 shows the discharge capacity at this time as the initial capacity. Then, constant current / constant voltage condition charging and 0.05C cut-off charging up to 4.35V at 0.8C rate are performed, and then discharged at 0.5C 3.0V at room temperature as one cycle, and the capacity after 100 cycles is performed once. It is shown in Table 1 below as a percentage of the dose.

From the above Table 1, since the secondary batteries of Examples 1 to 11 of the present invention have a high conductivity due to the improvement of the electrolyte impregnation effect, the initial discharge amount and cycle capacity (discharge capacity remaining ratio) of the secondary batteries of Comparative Examples 1 to 3 are high. It can be seen that it is excellent in preparation. At this time, the secondary battery of Example 11 using a high viscosity solvent as an additional injection liquid as compared to the secondary batteries of Examples 1 to 10, the impregnation ability according to the increase in viscosity decreases the battery performance of the secondary batteries of Examples 1 to 10 It can be seen that it is relatively reduced compared to.

That is, in the secondary batteries of Examples 1 to 11 of the present invention, the high-viscosity solvent is sheeted with the first solvent, and the low-viscosity solvent or the mixed solvent of the low-viscosity solvent and the high-viscosity solvent is poured into the second solvent, thereby eliminating the film layer. It can be confirmed that the battery performance is superior to the secondary batteries of Comparative Examples 1 and 3 in which only the low viscosity solvent was injected and the mixed solvent in which the high and low viscosity solvents were mixed.

Claims (20)

1. Providing a film layer comprising a first solvent having a melting temperature of at least 25 ° C. and a viscosity of at least 40 cP at 40 ° C. between the separator and the electrode (step 1);

   Preparing an electrode assembly using the electrode, the film layer, and the separator (step 2); And

   And storing the electrode assembly in a case and injecting and sealing an injection solution including a second solvent (step 3).
2. The method according to claim 1,

   Providing the film layer (step 1)

   (a) compressing a first solvent in a solid state at a temperature below 25 ° C. to prepare a freestanding film layer, and then providing it between the separator and the electrode, or

   (b) melting the first solvent in a solid state at a temperature below 25 ° C., and then directly coating one or both surfaces of the separator to provide the secondary battery.
3. The method according to claim 1,

   The first solvent is ethylene carbonate, cis-4,5-dimethyl-1,3-dioxolan-2-one, trans-4,5-dimethyl-1,3-dioxolan-2-one, 1,2- Cyclopentylene carbonate, cyclohexene carbonate, pinacolon cyclic carbonate, 1,3-propylene carbonate, 5,5-dimethyl-1,3-dioxan-2-one, sulfolane, ethyl methyl sulfone, diethyl sulfone, At least one compound selected from the group consisting of ethyl dimethyl carbamate and phenyl dimethyl carbamate.
4. The method according to claim 1,

   The film layer is a secondary battery manufacturing method further comprising a softener.
5. The method according to claim 4,

   The softener is polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated From the group consisting of cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluorine rubber Method for producing a secondary battery that is a selected single substance or a mixture of two or more thereof.
6. The method according to claim 4,

   The weight ratio of the first solvent: softener in the film layer is 99.5: 0.5 to 90:10 manufacturing method of a secondary battery.
7. The method according to claim 1,

   The thickness of the film layer is a method for manufacturing a secondary battery of 10 ㎛ to 500 ㎛.
8. The method according to claim 1,

   The film layer is a method of manufacturing a secondary battery further comprises a first lithium salt.
9. The method according to claim 8,

   The first lithium salt is a method of manufacturing a secondary battery that is contained in a concentration of 0.3M to 2.0M relative to the first solvent.
10. The method according to claim 1,

    The second solvent is a liquid at room temperature, a low viscosity solvent having a viscosity of less than 1.5 cP at 25 ℃; And a solid at room temperature and at least one selected from the group consisting of a high viscosity solvent having a viscosity of 1.5 cP or higher at 40 ° C. 10.
11. The method according to claim 10,

    When the second solvent is a low viscosity solvent,

    The second solvent is a carbonate; Esters; And lactones or a single material selected from the group consisting of two or more thereof.
12. The method according to claim 11,

    The second solvent is dimethyl carbonate, ethyl methyl carbonate, butylene carbonate, diethyl carbonate, dipropyl carbonate, fluoroethylene carbonate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and Method for producing a secondary battery comprising a single substance or a mixture of two or more selected from the group consisting of gamma-butyrolactone.
13. The method according to claim 1,

    When the second solvent is a high viscosity solvent,

    The second solvent is ethylene carbonate, cis-4,5-dimethyl-1,3-dioxolan-2-one, trans-4,5-dimethyl-1,3-dioxolan-2-one, 1,2- Cyclopentylene carbonate, cyclohexene carbonate, pinacolon cyclic carbonate, 1,3-propylene carbonate, 5,5-dimethyl-1,3-dioxan-2-one, sulfolane, ethyl methyl sulfone, diethyl sulfone, Method for producing a secondary battery that is a single substance or a mixture of two or more selected from the group consisting of ethyl dimethyl carbamate and phenyl dimethyl carbamate.
14. The method according to claim 1,

    The injection solution is a secondary battery manufacturing method further comprising a second lithium salt.
15. The method according to claim 14,

    The second lithium salt is a method of manufacturing a secondary battery that is contained in a concentration of 0.7M to 3.0M relative to the second solvent.
16. The method according to claim 1,

    The weight ratio of the first solvent: the second solvent is 1: 0.2 to 1: 2 manufacturing method of the secondary battery
17. Anode, cathode, separator, electrolyte, and

    The method of claim 1 comprising a film layer comprising a first solvent having a melting temperature of 25 ° C. or higher and a viscosity of 1.5 cP or higher at 40 ° C. between at least one of the separator and the cathode or between the separator and the anode. Secondary battery produced by.
18. The method according to claim 17,

    The electrolyte is a secondary battery comprising a second solvent and a second lithium salt.
19. The method according to claim 17,

    The film layer further comprises a first lithium salt,

    The electrolyte is a secondary battery comprising a second solvent and a second lithium salt.
20. The method according to claim 17,

    The film layer further comprises a first lithium salt,

    The electrolyte is a secondary battery consisting of a second solvent.

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