KR20170061622A - Method for preparing secondary battery - Google Patents

Abstract

The present invention relates to a method of manufacturing a secondary battery capable of improving the safety of a secondary battery by improving the bonding strength between the electrode and the separator, comprising the steps of: storing an electrode assembly in a battery case and injecting an electrolyte; A battery activating step of initially charging the battery; And a pressing step of pressing the rim of the battery case during the activation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a method of manufacturing a secondary battery.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device is one of the most attracting fields in this respect, and development of a rechargeable secondary battery is of particular interest.

BACKGROUND OF THE INVENTION [0002] Continuous research has been conducted on secondary batteries, in which various performance, particularly power, of electrode active materials has been improved. However, when the secondary battery is exposed to a high temperature, there is a problem that a short circuit occurs due to shrinkage of the separator. In addition, adhesion between the electrode and the separator is poor, and bubbles are generated on the bonding surface.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of manufacturing a secondary battery that can improve the safety of a cell by improving the bonding strength between the electrode and the separator.

According to an aspect of the present invention, there is provided a method of manufacturing an electrode assembly, comprising: storing an electrode assembly in a battery case and injecting an electrolyte; A battery activating step of initially charging the battery; And a pressing step of pressing the rim of the battery case during the activation of the electrolyte.

Preferably, the rim portion may have a width of 1 to 49% of the width of the battery case.

Preferably, the pressurization may be performed at a pressure of 50 kgf to 3000 kgf.

Preferably, the pressurization can be carried out at a temperature of 23 to 120 DEG C for 10 seconds to 3 minutes.

Preferably, the activation process may be performed in a range of 30 to 70% of SOC (State of Charge).

Preferably, the battery case may be a pouch type case.

According to an aspect of the present invention, there is also provided a secondary battery manufactured by the above method.

Preferably, the secondary battery is a lithium secondary battery.

According to the method of the present invention, it is possible to improve the safety of the secondary battery by improving the bonding strength between the electrode of the electrode assembly and the separator without changing the conventional manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
1 is a perspective view of a secondary battery according to an embodiment of the present invention.
2 is a schematic view showing a state in which a rim portion of a battery case is pressed according to an embodiment of the present invention.
3 is a photograph of the electrode assembly housed in the secondary battery manufactured according to the comparative example after storage at high temperature.
4 is a photograph of the electrode assembly housed in a secondary battery manufactured according to an embodiment of the present invention after storage at high temperature.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the constitutions described in the embodiments described herein are merely the most preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents which can be substituted at the time of application It should be understood that variations can be made.

Conventional secondary batteries have a problem in that a pressure process is performed in the process of manufacturing an electrode assembly, adhesion between the electrode and the separator is not properly performed, or bubbles are generated on the bonding surface. In addition, since the pre-compressed electrode assembly is accommodated in the battery case, there is a problem that impregnability of the electrolytic solution is lowered. According to the present invention, after the electrode assembly is housed in the battery case, by adding a pressing process, the bonding strength between the electrode and the separator can be improved, and generation of bubbles on the bonding surface can be suppressed. In addition, since the present invention performs a pressurizing process in a cell activating process for initially charging a battery, it is possible to improve the processability without requiring a separate process. In addition, The adhesion between the electrode and the separator can be improved.

According to an aspect of the present invention, there is provided a method of manufacturing a secondary battery including: storing an electrode assembly in a battery case and injecting an electrolyte; A battery activating step of initially charging the battery; And a pressing step of pressing the rim of the battery case during the activation of the electrolyte.

First, in the step of housing the electrode assembly in the battery case and injecting the electrolyte solution, the electrode assembly may be configured such that at least one anode and at least one cathode are disposed with the separator interposed therebetween.

The positive electrode and the negative electrode may be produced using a method commonly used in the art. For example, a slurry in which an electrode active material is dispersed in a binder solution in which a binder is dissolved in a solvent is coated on a current collector, and the solvent is removed to produce an electrode having an electrode active material layer. For example, forming slurry, applying slurry, and forming an electrode active material layer.

Formation of the slurry is achieved by dispersing the electrode active material in the binder solution. That is, a binder suitable for a desired electrode active material is selected, and the binder is further added to and dissolved in a suitable solvent to produce a binder solution. Then, the desired electrode active material is added to the resulting binder solution, and the mixture is further uniformly dispersed in the binder solution by stirring or the like using a mixer to prepare a slurry.

The electrode active material (that is, the positive electrode active material and the negative electrode active material) and the current collector (that is, the positive electrode collector and the negative electrode collector) are not particularly limited and they can be prepared according to a conventional method known in the art or a modified method thereof . The electrode active material may typically take the form of particles.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with at least one transition metal; A lithium manganese oxide (LiMnO ₂ ) such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, etc. represented by the formula Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33); Lithium copper oxide (Li ₂ CuO ₂ ); LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ Vanadium oxide; Nickel type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3) oxide); Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which part of the lithium in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) _3, or a composite oxide formed of a combination of these materials, and the like, and are not limited thereto.

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

The cathode active material may further be mixed with a conductive material. Such a conductive material is added, for example, in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is added to the binder in an amount of about 1 to about 50 wt% based on the total weight of the mixture including the cathode active material, for example, as a component for bonding the positive electrode active material and the conductive material and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N -methyl-2-pyrrolidone, NMP), cyclohexane, water, or a mixture thereof. These solvents provide an appropriate level of viscosity so that a slurry coating layer can be formed at a desired level on the collector surface.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode current collector. If necessary, the negative electrode may further include components such as a conductive material, a binder, a solvent, and the like described above with respect to the positive electrode.

The negative electrode collector has a thickness of, for example, about 3 to about 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides of Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The application of the slurry can be carried out continuously or discontinuously by various methods such as slot die coating, slide coating, curtain coating and the like. Particularly, in terms of productivity, it is preferable that the application is carried out continuously or simultaneously at the same time.

Formation of the electrode active material layer comprises removing solvent from the applied slurry. The solvent can be removed by drying. The slurry applied on the current collector is dried by using a drier or the like to remove the solvent to obtain an electrode.

The separator may be prepared conventionally in the art, and examples thereof include polyethylene, polypropylene, polyethyleneterephthalate, polybutyleneterephthalate, polyester ), Polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyetherketone, polyetherketone, polyetherketone, Polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide, and polyethylene naphthalene (polyethylenenaphthalene). Be a polymer or a polymer film or a multi-film, a woven or non-woven fabric formed of a mixture of two or more of these, but are not limited to.

According to an embodiment of the present invention, the electrode assembly may be manufactured by pressing one or more anodes and one or more anodes with the separator interposed therebetween, and the pressurization may be performed at a pressure of 10 kgf to 90 kgf, Lt; 0 &gt; C for 10 seconds to 3 minutes. Preferably about 100 to about 125 &lt; 0 &gt; C. When the rolling temperature falls within the above range, the adhesion between the electrode and the separator is excellent. However, when the rolling temperature exceeds 130 캜, the binder tends to form an aggregation in a direction away from the surface to be heated, thereby greatly reducing the adhesive force between the electrode and the separator, . On the other hand, if the rolling temperature is lower than 60 DEG C, the desired level of adhesion between the electrode and the separator can not be achieved. In addition, when the pressure and time during the rolling process fall within the above range, the adhesion between the electrode and the separator, particularly, the adhesion between the electrode active material layer and the separator, is excellent. However, when the pressure during rolling is more than 90 kgf, it may cause damage such as ripping of the separator. If the rolling time exceeds 3 minutes, it may cause structural deformation of the separator. On the other hand, if the pressure during rolling is less than 10 kgf or the rolling time is less than 10 seconds, the desired level of adhesion between the electrode and the separator can not be achieved.

The battery case may be a pouch type case.

The electrolytic solution A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is PF ₆ ^-, BF ₄ ^{- , Cl -, Br -, I} -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - and (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethylsulfoxide, dimethyl sulfoxide and the like. (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone (gamma -butyrolactone), or mixtures thereof, in the presence of a base such as acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, , But the present invention is not limited thereto.

Next, a cell activating step of initially charging the battery is a step of activating the electrode active material and performing an initial charging to form an SEI film on the electrode surface. In the process of forming the SEI film, gas is generated in the battery through decomposition reaction of the electrolyte, . Further, an aging step may be further performed so that the electrolytic solution injected before the activation step sufficiently penetrates the electrode and the separator.

Also, in one embodiment of the present invention, the initial charge for battery activation may be performed in the range of 30 to 70% of the state of charge (SOC).

Then, during the activation, a pressing step of pressing the rim of the battery case is performed. During the activation step, gas is generated inside the cell, and due to the internal pressure, the pressure can be performed at a higher pressure, so that the adhesion between the electrode and the separator can be improved. Preferably, the pressurization may be performed at a pressure of 50 kgf to 3000 kgf, more preferably at a pressure of 1000 kgf to 3000 kgf.

The rim portion refers to a peripheral portion of the upper surface portion or the lower surface portion of the battery case. 1 is a perspective view of a secondary battery according to an embodiment of the present invention. 1, the rim portion 102 refers to a peripheral edge portion of the upper surface portion 101 of the battery case 100, and the rim portion 102 may include at least one of the four edges. have. The rim portion 102 may have a width of 1 to 49% of the width of the battery case. Preferably, the rim portion 102 may have a width of 2 to 30 mm.

2 is a schematic view showing a state in which a rim portion of a battery case is pressed according to an embodiment of the present invention. 2, the rim portion 102 of the battery case 100 according to the present invention can be pressed by the jig 200. As shown in Fig. The shape of the jig 200 may be appropriately changed according to the shape of the rim 102 to be pressed.

The pressing step may be performed at a rolling temperature of from about 23 to about 120 DEG C, depending on the rolling temperature, for from 10 seconds to 3 minutes.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example

An anode having a predetermined size, a cathode, and an electrode assembly interposed between the anode and the cathode were prepared. After the electrode assembly was housed in the pouch-shaped case, a non-aqueous electrolyte was injected and sealed.

 Thereafter, the electrolyte was activated, and the pouch type case in which the electrode assembly was housed during the activation was pressurized at a temperature of 70 DEG C at a pressure of 1500 kgf for 30 seconds using a jig for pressing the rim.

Comparative Example

The secondary battery was manufactured in the same manner as in the above example except that the rim portion was not pressed.

High Temperature Storage Experiment

The secondary batteries prepared according to Examples and Comparative Examples were stored at 180 ° C. for 3 minutes to test whether the membranes were shrunk or not.

FIG. 3 is a photograph of the electrode assembly stored in the secondary battery manufactured according to the comparative example after high temperature storage, and FIG. 4 is a photograph of the electrode assembly stored in the secondary battery manufactured according to an embodiment of the present invention after storage at high temperature. 4 (a) is a photograph of a cathode and a separator, and (b) is a photograph of an anode and a separator.

Referring to FIGS. 3 and 4, it can be seen that the separation membrane is not shrunk in the case of performing the partial pressing, and the separation membrane is shrunk in the comparison example in which the partial pressing is not performed.

100: electrode case
101: upper surface portion
102:
200: jig

Claims (8)

Storing an electrode assembly in a battery case, and injecting an electrolyte solution;
A battery activating step of initially charging the battery; And
And a pressing step of pressing the rim of the battery case during the activation. The method according to claim 1,
Wherein the rim portion has a width of 1 to 49% of the width of the battery case. The method according to claim 1,
Wherein the pressing is performed at a pressure of 50 kgf to 3000 kgf. The method according to claim 1,
Wherein the pressing is performed at a temperature of 23 to 120 DEG C for 10 seconds to 3 minutes. The method according to claim 1,
Wherein the activation process is performed in a range of 30 to 70% of SOC (State of Charge). The method according to claim 1,
Wherein the battery case is a pouch type case. A secondary battery produced by the method of any one of claims 1 to 6. 8. The method of claim 7,
Wherein the secondary battery is a lithium secondary battery.

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