KR100327488B1 - Producing method of lithium polymer secondary battery - Google Patents

Abstract

The present invention relates to a lithium polymer secondary battery manufacturing method comprising the steps of: a) coating an electrolyte affinity polymer on at least one side of the positive electrode and the negative electrode; b) placing a porous separator between the anode and the cathode treated in step a); And c) an electrolyte affinity polymer coated on at least one side of the positive electrode and the negative electrode is gelated at room temperature by a liquid electrolyte to integrate the electrode and the porous separator.

Description

Producing method of lithium polymer secondary battery

The present invention relates to a method for manufacturing a lithium polymer secondary battery, and more particularly, to a method for manufacturing a lithium polymer secondary battery using a lithium ion conductive polymer electrolyte.

In recent years, with the development of electronic devices, in particular, miniaturization, weight reduction, and high performance of portable electronic devices, high energy density and light weight of secondary batteries used as power sources for these electronic devices are required. Currently, as the secondary batteries for public use, nickel-cadmium secondary batteries and nickel-hydrogen secondary batteries are mainly used, but interest in lithium secondary batteries having higher energy density than these is increasing day by day.

The electrolyte of a lithium secondary battery includes a liquid electrolyte in which lithium salt is dissolved in an organic solvent, and a polymer electrolyte in which the liquid electrolyte is stored in a polymer material. In the case of the liquid electrolyte, the ion conductivity is high, but due to the organic solvent dissolving lithium salt, it is necessary to install a special protective circuit to ensure safety. On the other hand, the lithium polymer secondary battery is attracting attention as a next-generation battery because there is no fear that the organic solvent is leaked out to ensure superior safety than the liquid electrolyte.

In order for a lithium polymer secondary battery to be commercially available, the following requirements must be satisfied.

First, it must be electrochemically stable over a wide voltage range to withstand overcharge and discharge,

Second, the ionic conductivity must be high (at least 1 mS / cm at room temperature),

Third, it must be chemically and electrochemically compatible with the electrode material or other compositions in the cell.

In addition, for practical applications, it is required to have excellent mechanical properties and good adhesion to the positive electrode and the negative electrode so as to have good workability. However, the conventional polymer gel electrolyte is sufficiently high that the ionic conductivity is not a problem in practical applications. Due to the weak mechanical properties, it is not easy to apply to the battery.

Methods of preparing a polymer electrolyte can be broadly classified into a hot melting method and a solvent casting method. The melting method is a method of mixing a polymer material and a liquid electrolyte to form a solution at high temperature to form a plate and cooling. In the solvent casting method, a polymer material is first dissolved in a volatile organic solvent and then a liquid electrolyte is added to uniformly mix the same. The solution is formed into a plate and then dried to remove the volatile organic solvent.

In the case of the melting method, it is difficult to use low boiling point solvents, such as dimethyl carbonate and methyl ethyl carbonate, which are widely used as organic solvents for liquid electrolyte due to the condition of high temperature processing. Since the organic solvent for liquid electrolyte is evaporated and lost in the process of drying the organic solvent added to dissolve, there is a problem that the composition of the polymer electrolyte changes as the process proceeds.

Developed to solve the above problems is a polymer electrolyte prepared using a porous support. Specifically, for example, Fuji Photo Film Co., Ltd. discloses a method of manufacturing a polymer electrolyte having good processability by impregnating a porous film with a solution mixed with a crosslinking agent and a liquid electrolyte through Japanese Patent Application Laid-Open No. 3-177410, Japan. Japanese Patent Application Laid-Open No. Hei 6-36754 introduces a method of preparing a polymer electrolyte by coating a latex material on a polyethylene porous membrane, drying the battery cell, and then injecting and gelling a liquid electrolyte.

In addition, Matsushita Electric discloses a method for preparing a gel polymer electrolyte by impregnating a curable gel solution into a porous film and curing with ultraviolet rays or heat, and in the case of Sony, Japanese Patent Application Publication No. 7-220761. Patent Application Publication No. Hei 10-162802 mentions that by applying or impregnating a gel polymer electrolyte on an insulating porous membrane such as polyethylene, the handling of the gel polymer electrolyte material can be facilitated and the manufacturability can be improved.

Mitsubishi Electric discloses a method of preparing a battery using a polyethylene separator coated with polyvinylidene fluoride on both sides through Japanese Patent Application Publication No. 10-189054, injecting a liquid electrolyte, and then applying heat to induce gelation. have.

Motorola of the United States has a number of patents related to porous supports, such as US Patent Nos. 5,681,357, 5,688,293, 5,716,421, and 5,837,015. Specifically, the polyethylene separator is immersed in a solution in which a polymer such as polyvinylidene fluoride is dissolved, and then taken out and dried to prepare a polyethylene separator coated with a polymer. Method of immersing a polyethylene separator in an emulsion in which a curable polymer such as polyvinylidene fluoride is dispersed in a liquid electrolyte, and then taken out to prepare a battery cell, followed by gelation of the polyethylene separator, coating and drying the gelable polymer on the polyethylene separator to form an electrode. And a method of manufacturing a battery by directly coating a gel polymer electrolyte solution on a polyethylene separator or an electrode surface.

As mentioned above, many studies have been conducted to improve the processability of the gel polymer electrolyte, but most of the studies adopt the method of coating the gel electrolyte on the porous support, so that the electrode and the electrolyte are compared with the interface between the gel electrolyte and the porous support. The interfacial properties between them may be poor.

Thus, examples of coating the gel electrolyte on the electrode are disclosed in US Pat. Nos. 5,861,357, 5,688,293, 5,716,421, 5,837,015, etc., which process the gel electrolyte solution coated on the electrode with heat or ultraviolet rays. Or gelled by applying a pressure at a high temperature of 80 ° C. or more while the electrolyte is in contact with the coated polymer. This process has the drawback that volatilization of the low boiling organic solvent in the electrolyte component does not keep the final electrolyte composition constant.

Accordingly, the technical problem to be achieved by the present invention is to provide a method for producing a lithium polymer secondary battery that can improve the processability and battery manufacturing processability of the gel polymer electrolyte.

1 is a view for explaining a lithium polymer secondary battery manufacturing process according to an embodiment of the present invention.

2 is a scanning electron micrograph of the cross section of the battery prepared in Example 1;

3 is a charge and discharge curve of the battery prepared in Example 2.

The present invention to achieve the above technical problem,

a) coating an electrolyte affinity polymer on at least one side of the positive electrode and the negative electrode; b) placing a porous separator between the positive electrode and the negative electrode which have passed through step a); And c) an electrolyte affinity polymer coated on at least one side of the positive electrode and the negative electrode is gelated at room temperature by a liquid electrolyte, thereby integrating the electrode and the porous separator.

According to one embodiment of the present invention, the gelling step c) is characterized in that the liquid electrolyte is injected after assembly of the battery.

According to another embodiment of the present invention, the method may further include the step of impregnating the liquid electrolyte into the porous separator before the step b), in which case the gelation of the step c) is a liquid electrolyte impregnated into the porous separator Proceed by.

Preferably, the electrolyte affinity polymer may be made of a polymer, a copolymer, or a blend thereof made of at least one monomer selected from vinyl, acrylic, alkylene oxide, alkylester, and urethane.

More preferably, the electrolyte affinity polymer may be prepared by further including monomers of acrylonitrile, vinyl acetate, acrylate, vinyl chloride, vinylpyrrolidone, styrene, and vinyl ether.

Most preferably, the electrolyte affinity polymer is a terpolymer of acrylonitrile, methyl methacrylate and styrene.

The present invention solves problems such as difficulty in maintaining the electrolyte composition of the existing gel polymer electrolyte manufacturing method, the use of low-boiling point organic solvents, the weak mechanical properties, and the like, and improve the battery manufacturing processability. In order to coat the electrolyte affinity polymer on the electrode, and then evaporate an organic solvent to prepare an electrode coated with a polymer layer, assemble a battery with a porous separator and inject the electrolyte solution to gel the electrolyte affinity polymer at room temperature It is characterized by inducing.

Method for producing a lithium polymer secondary battery according to the present invention is as follows.

First, a slurry in which a polymer material having affinity for a liquid electrolyte at room temperature is dissolved in an organic solvent is coated on at least one side of a positive electrode and a negative electrode, and then an organic solvent is volatilized to prepare an electrode coated with a polymer layer.

The electrode coated with the polymer layer is manufactured in the form of a battery by overlapping both surfaces of the porous separator. The form of the battery which can be produced by the method according to the present invention may be a rectangular battery in a stacked form, a cylindrical or rectangular battery in a wound form, and the like as a general secondary battery.

The gel polymer electrolyte is formed by injecting a liquid electrolyte into a cell assembled in the form of a cell to gel the coated polymer material on the electrode. The injected electrolyte gels the polymer layer on the electrode and then permeates into the pores in the electrode and the pores of the porous separator. The gel polymer electrolyte layer between the electrode and the porous separator serves to provide adhesion between the electrode and the porous separator and to prevent leakage of the liquid electrolyte penetrating into the pores of the electrode and the porous separator.

1 is a view illustrating a process of injecting an electrolyte after assembling a battery as an embodiment of a lithium polymer secondary battery manufacturing process according to the present invention. On the positive electrode 1 and the negative electrode 3, the slurry 4 and 6 which melt | dissolved the high molecular material which is affinity for a liquid electrolyte in the organic solvent are coated. When the organic solvent is volatilized by passing through the dryers 5 and 7, an electrode coated with a polymer material is prepared. The positive electrode and the negative electrode coated with the electrolyte affinity polymer are superimposed on both sides of the porous separator 2 and then assembled into a battery form.

When the type of battery to be assembled is a laminate type, it may be coated only on the electrode surface in contact with the porous stone separator, and in the case of the wound type, it may be coated on both sides of the electrode.

Reference numeral 8 denotes a means for applying a stacking pressure of the overlapping anode / porous separator / cathode. In the case of a stacked battery, a roller may be used, and in the case of a wound battery, a winder may be used to apply pressure.

After assembling into a battery form, a liquid electrolyte is injected to gel the polymer material coated on the electrode surface to form a gel polymer electrolyte, thereby completing a lithium polymer secondary battery.

Although not shown, as another embodiment of the present invention, the liquid electrolyte is pre-soaked in the porous separator and superimposed with the electrode coated with the polymer material so that the gelation proceeds as soon as the polymer material comes into contact with the liquid electrolyte impregnated in the porous separator. It may be.

The polymer material having affinity for the liquid electrolyte used in the method of the present invention means a polymer material which can be gelated when brought into contact with the liquid electrolyte at room temperature. Any material having such characteristics can be used.

Specifically, there may be exemplified polymers, copolymers or blends thereof made of at least one monomer selected from vinyl, acrylic, alkylene oxide, alkylester and urethane.

It is more preferable that monomers of acrylonitrile, vinyl acetate, acrylate, vinyl chloride, vinylpyrrolidone, styrene and vinyl ether are further introduced into the polymer. Most preferred are acrylonitrile-methylmethacrylate-styrene terpolymers.

The liquid electrolyte for gelling the polymer film comprises an organic solvent and a lithium salt. As the organic solvent, carbonates such as butylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethyl ethyl carbonate and vinylene carbonate And sulfolanes such as sulfolane and methyl sulfolane, ethers such as dimethoxyethane, lactones such as gamma butyrolactone, and esters such as methyl propionate, and the like. It is preferable to mix and use 2 or more types.

Lithium salts are also well known in the art, and examples thereof include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiOF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , but are not limited thereto. Lithium salts to which anions are bound can be used.

The positive electrode and the negative electrode used in the lithium polymer secondary battery according to the present invention are also well known in the art and are not particularly limited. For example, it is possible to use a lithium metal oxide such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, or a substance into which lithium can be intercalated, such as titanium sulfide or vanadium oxide, and reactive organic materials such as sulfur. In addition, it is possible to use lithium metal, lithium alloy, amorphous carbon, graphite carbon as the negative electrode.

The porous separator used in the present invention may be used as long as it is widely used in the art. For example, polyethylene, polypropylene, and the like are various, such as olefin-based, polyvinylidene fluoride, polyacrylonitrile, polysulfone, and the like for filtration membranes, polypropylene, polypropylene, polyethylene terephthalate, cellulose-based nonwoven fabrics, and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are merely examples to help understand the present invention and should not be construed as limiting or limiting the scope of the present invention.

<Example 1>

The positive electrode was a 10% by weight solution of polyvinylidene fluoride (PVdF) / N-methylpyrrolidone (NMP) after a powder mixture of an active material lithium cobalt oxide (LiCoO ₂ ) and a conductive super-P carbon. Was put in. 5Φ zirconia balls were added and mixed with a mechanical stirrer for 3 hours. The resulting slurry was cast to a thickness of 300 microns on aluminum foil, dried for 12 h in an 80 ° C. oven, vacuum dried for 24 h in an 130 ° C. oven, and then cut to 32 × 56 mm ² .

The negative electrode was charged with mesocarbon fiber as an active material in a 5% by weight PVdF / NMP solution. 5Φ zirconia balls were added and mixed with a mechanical stirrer for 3 hours. The resulting slurry was cast to a 250 micron thickness on copper foil, dried for 12 hours in an 80 ° C. oven, vacuum dried for 24 hours in an 130 ° C. oven, and then cut to 32.5 × 56.5 mm ² .

Table 1 shows the composition of the positive electrode and the negative electrode prepared as described above.

Bipolar Sonic pole Active material 93% by weight of LiCoO ₂ 92% by weight of mesocarbon fiber Challenge 3 wt% - PVdF 4 wt% 8 wt%

An acrylonitrile-methyl methacrylate-styrene (AMS) terpolymer (molar ratio 68:19:13) prepared by emulsion polymerization was used as an electrolyte solution affinity polymer material. After dissolving at 2% by weight in dimethylformamide, and coated on the positive electrode and negative electrode using a doctor blade, dried for 5 hours in an 80 ℃ oven to remove DMF and dried again at 80 ℃ vacuum to remove moisture. The thickness of the polymer layer coated on the electrode after drying was about 10 microns. A positive electrode and a negative electrode coated with an electrolyte affinity polymer were laminated on both sides of a polyethylene separator having a porosity of 40% to form a battery.

LiPF ₆ salt was dissolved in 1.2 mol of ethylene carbonate / dimethyl carbonate (2/1 volume ratio) as a liquid electrolyte, and 0.25 g was injected into the cell to gel the polymer layer on the electrode surface. The integrated cell was completed.

The photograph which observed the cross section of the cell with the scanning electron microscope is shown in FIG. It is confirmed that the polymer electrolyte layers 24a and 24b having a thickness of about 8 to 10 µm are formed between the anode 21 and the cathode 22 and the polyethylene separator 23 to uniformly and uniformly bond the anode and the cathode and the polyethylene separator. Can be. Such a structure is a preferable structure that can lower the interfacial resistance between the electrode and the electrolyte and prevent leakage of the liquid electrolyte present in the separator and the pores in the electrode.

Comparative Example

A battery was manufactured in the same manner and in the same manner as in Example 1, except that a conventional gel polymer electrolyte manufacturing method, that is, solution casting was used.

A slurry was prepared by first dissolving an AMS terpolymer and a liquid electrolyte component of the same component as in Example 1 in DMC, followed by mixing silica as an inorganic filler. After casting the slurry on a glass plate, the solvent was volatilized to obtain a gel polymer electrolyte film having a thickness of about 50 μm. The gel polymer electrolyte was composed of 17% by weight of AMS terpolymer, 70% by weight of liquid electrolyte, and 13% by weight of silica. All processes for preparing the gel polymer electrolyte film were performed in a dry box having a moisture content of 10 ppm or less.

The gel polymer electrolyte film prepared as described above was placed between 32.5 x 56.5 mm ² sized positive electrode and the negative electrode prepared in the same manner as in Example 1 to prepare a battery.

The resistance characteristics of the lithium polymer secondary battery were evaluated using the 1 kHz AC impedance measurement method widely used in the battery industry.

The impedance of the five batteries manufactured by the method of Example 1 was 0.8 Ω, and the average impedance of the five batteries manufactured by the comparative example was 1.2 Ω, which is higher than that of the example.

<Example 2>

A lithium polymer secondary battery was manufactured in the same manner as in Example 1, except that the battery was in the form of a rectangular winding, not a lamination. Therefore, the electrode coated with the electrode material on both sides of the current collector was used, AMS terpolymer was also coated on both sides of each electrode.

The widths of the positive and negative electrodes were 4 cm and 4.2 cm, respectively, and the lengths of the positive and negative electrodes were designed to be 600mAh. A positive electrode, a negative electrode, and a polyetherene separator were assembled into a battery form by winding using a rectangular winder. About 3 g of the liquid electrolyte prepared in Example 1 was injected into the assembled rectangular battery. The outer packaging material was a 5-layer aluminum laminate film known under the trade name Blue Bag, and was vacuum-packed after the battery was manufactured.

The charge and discharge characteristics of the battery prepared in Example 2 were evaluated using a charge / discharger manufactured by TOYOO, Japan. The results of charging and discharging with a constant current in the 2.75 to 4.2 V region at 60 mA current are shown in FIG. The curve shows a charge / discharge curve of a lithium secondary battery using a typical lithium cobalt oxide, the discharge capacity was 130 mAh / g or more per unit mass of the positive electrode active material.

In the lithium polymer secondary battery manufacturing method according to the present invention, since the electrolyte-compatible polymer is coated on the electrode, not the porous separator, the interface property of the electrode and the porous separator is good, and after boiling the liquid electrolyte, gelling at room temperature without heat curing process results in low boiling point organic There is no fear that the composition of the liquid electrolyte changes due to volatilization of the solvent. Therefore, the limitation of performance due to the use of low boiling point solvent can be overcome. In addition, the method of the present invention can be impregnated with a liquid electrolyte in the porous separator before injecting or injecting the liquid electrolyte after assembly of the cell, it is excellent in processability and processability.

Claims (10)

a) coating an electrolyte affinity polymer on at least one side of the positive electrode and the negative electrode; b) placing a porous separator between the positive electrode and the negative electrode which have passed through step a); And c) an electrolyte affinity polymer coated on at least one surface of the positive electrode and the negative electrode is gelated at room temperature by a liquid electrolyte to integrate the electrode and the porous separator. The method of claim 1, wherein the gelling of step c) is performed by a liquid electrolyte injected after battery assembly. The method of claim 1, further comprising the step of impregnating the liquid electrolyte into the porous separator prior to performing step b), wherein the gelling of step c) is performed by the liquid electrolyte impregnated into the porous separator. Way. The method of claim 1, wherein the electrolyte affinity polymer is characterized in that consisting of a polymer, copolymer or blends thereof made of at least one monomer selected from vinyl, acrylic, alkylene oxide, alkyl ester and urethane. Way. The method of claim 2, wherein the electrolyte affinity polymer is prepared by further comprising monomers of acrylonitrile, vinyl acetate, acrylate, vinyl chloride, vinylpyrrolidone, styrene and vinyl ether. How to. The method according to claim 5, wherein the electrolyte affinity polymer is a terpolymer of acrylonitrile, methyl methacrylate and styrene. The method of claim 1, wherein the liquid electrolyte is an aprotic organic solvent, carbonates such as butylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethylethyl carbonate or vinylene carbonate, sulfolane or methylsul And at least one solvent selected from sulfolanes such as polan, ethers such as dimethoxyethane, lactones such as gammabutyrolactone, and esters such as methylpropionate. The method of claim 1, wherein the liquid electrolyte comprises LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ or LiN (CF ₃ SO ₂ ) ₂ as a lithium salt. The method of claim 1, wherein the electrode comprises lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, titanium sulfide or vanadium oxide as a positive electrode active material. The method of claim 1, wherein the electrode comprises lithium metal, lithium alloy, amorphous carbon, or graphite carbon as an anode active material.