KR20020066599A - The Interface Structure of A Secondary Battery - Google Patents

Abstract

PURPOSE: Provided is a stable interfacial structure of secondary battery, which is formed by applying an ion-conductive polymer material on a cathode or anode or separator and adhering them with each other. CONSTITUTION: The secondary battery consists of a cathode(5), an anode(6), a separator(7), and a sheath. In the secondary battery, ion-conductive polymer(8) is applied to the part of cathode, anode, or separator to form a partial adhesion. Also, a part on which adhesion is not formed, provides a space which enables liquid electrolyte to uniformly penetrate. The separator consists of a single film or a composite film of polyethylene, polypropylene, or polyvinylidene fluoride. The separator has porosity of 40-80%, and thickness of 5-50 micrometer.

Description

The Interface Structure of A Secondary Battery

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

With the rapid growth of portable electronic products for information and communication such as mobile phones and notebook computers, the demand for batteries used as power sources for these products is increasing. In particular, a rechargeable battery that can be repeatedly used for charging and discharging is a key component of an electronic product for information communication. As the functions of electronic products are diversified and light and short, the demand for high-performance batteries having high energy density is increasing. In addition, due to energy depletion and environmental problems, commercialization of electric vehicles is in progress, and the importance of secondary batteries is emerging as a power source thereof.

Li-ion batteries commercialized in the early 1990s are secondary batteries with high energy density and are being used as a power source for most advanced portable electronic products, and are being actively developed for use as a power source for electric vehicles. The lithium ion battery is composed of a positive electrode, a negative electrode, a non-aqueous liquid electrolyte, a separator, and an exterior material. Lithium transition metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ are used as the positive electrode active material. These materials have a high electrochemical reaction potential that proceeds as lithium ions are inserted / desorbed into the crystal structure. As the negative electrode active material, carbon or graphite having a low potential is used. The electrolyte is mainly a polar organic solvent having a carbonate group, that is, ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, vinylidene LiPF ₆ , LiBF ₄ , LiClO ₄ , and the like are used by dissolving a mixture of carbonate (vinylidene carbonate) and gamma-butyrolactone (γ-butylo lactone). The separator electrically insulates the positive electrode and the negative electrode and provides a passage of ions. The separator mainly uses polyolefin-based polymers such as porous polyethylene, and protects the contents of the battery and provides an electrical passage to the outside of the battery. Use

Development of a lithium polymer battery using a polymer electrolyte has been steadily progressed to produce a battery that is safer and thinner than a lithium ion battery using a liquid electrolyte. When only a solid ion conductive polymer is used as an electrolyte, the ion conductivity is low at room temperature, which is not suitable for use in electronic products. A gel electrolyte in which a polymer and a liquid electrolyte are uniformly mixed, or a polymer electrolyte in which a liquid electrolyte is impregnated by forming pores in a polymer matrix has an ion conductivity of 10 ^-3 to 10 ^-4 S / cm at room temperature. It is becoming practical. The polymer electrolyte plays a role of a separator that electrically insulates the positive electrode and the negative electrode and an electrolyte that transfers ions. The polymer used here is a polymer material that is chemically and electrochemically stable in the charge / discharge voltage range of a lithium ion battery such as polyethylene oxide, polyacrylo nitrile, and polyvinylidene fluoride. admit. Lithium-ion polymer batteries have a lower risk of leakage because the liquid components in the electrolyte are trapped in the polymer matrix than lithium-ion batteries, and thus packaging materials consisting of aluminum foil and polymer layers can be used instead of metal cans. There is an advantage that the battery can be produced freely.

In the conventional polymer battery, a polymer electrolyte film is separately prepared and bound to the positive electrode and the negative electrode, or the polymer electrolyte is entirely coated on a porous polyolefin-based film such as polyethylene and polypropylene having high mechanical strength, thereby forming a multilayer film. When the polymer electrolyte film is prepared separately, the mechanical strength is weak, there is a lot of difficulty in continuous mass production, and when the electrode is bound to the electrode, it is not easy to uniformly bind the entire surface. In the case of using a multilayer film, there is a point that mass production is easy, but there is a problem in that the interface resistance increases because the movement of ions between the anode, the cathode, and the electrolyte is not smooth. Recently, a method of applying a polymer electrolyte in a form in which a polymer is dissolved in a liquid electrolyte solution has been attempted, but there are many problems due to difficulty in controlling moisture or controlling a process.

U.S. Patent No. 5,460,904 describes a film in which a positive electrode current collector is formed in a grid, and a plasticizer is added to a copolymer of vinylidene fluoride and hexapropylene fluoride. Thereafter, heat and pressure are applied to bind the electrode to form an integrated unit cell. Then, by extracting the plasticizer with the organic solvent to provide a porosity that the electrolyte solution can be impregnated. However, this technique is expensive because the current collector is used as a grid, and the manufacturing process is complicated and expensive by introducing an extraction process. In addition, in the lamination process of introducing heat and pressure, a short circuit phenomenon in which negative and positive electrodes are bonded frequently causes mass production difficulties.

U.S. Patent No. 5,837,017 uses a multi-layered polymer coated with an electrolyte affinity polymer material such as polyvinylidene fluoride on both sides of an unsaturated separator film with an electrolyte such as polyethylene, as a polymer electrolyte. to be. This form transforms the separator of a conventional lithium ion battery into a multilayer polymer layer, and after the electrolyte injection and packaging process is completed, the electrode and the polymer electrolyte can be integrated with heat and pressure. This technology has no extraction process and can be applied to existing Li-ion technology. However, in the multilayer polymer layer of the polymer material having no affinity with the electrolyte solution, there is a problem in that the ionic movement is not smooth and the interface resistance is large.

U.S. Patent No. 6,124,061 proposes a structure in which a resin layer having an overall adhesive is applied to both surfaces of a porous separator and a strong bond is formed between the electrode and the separator. This form has a disadvantage in that it is difficult to form a stable interfacial structure because it is difficult for the liquid electrolyte to be introduced later to uniformly penetrate between the electrode and the separator, and thus the ion movement is not smooth. In addition, the adhesive resin solution applied to the separator has a disadvantage that the production process is difficult and penetrates into the electrode with the remaining solvent to deteriorate the performance of the battery.

The present invention has been devised to overcome the problems of such a conventional lithium polymer battery. By using the battery structure and manufacturing method according to the present invention, the manufacturing process is simpler than the conventional polymer battery manufacturing method, the productivity is high, and by forming a stable interface between the electrode and the separator, the performance is excellent and the thickness is thin, and the area is large. A wide range of lithium polymer batteries can be produced.

The conventional manufacturing method has a disadvantage in that the manufacturing process is complicated by manufacturing a polymer electrolyte film separately and binding the positive electrode and the negative electrode, and applying a binding material to the front surface of the separator to achieve a strong binding between the electrode and the separator. This method has a problem in that uniform penetration of the electrolyte solution is difficult and the resistance at the interface is increased.

In order to solve this disadvantage, in the present invention, in an internal structure of a battery composed of a cathode / isolation membrane / cathode as a basic unit, an ion conductive polymer material is applied to a part of the surface of the cathode or the anode or the separator, and then adhesive is formed. The site where the ion conductive material is not applied provides a narrow gap between the electrode and the separator. Later when the liquid electrolyte is introduced, due to the capillary phenomenon through this narrow gap, the liquid electrolyte quickly penetrates between the electrode and the separator and is evenly distributed throughout. Due to this action, a stable interface is formed, the ions move actively, the internal resistance of the battery is low, and the charge and discharge are repeated so that the interface remains constant even if the electrode is repeatedly contracted and expanded. This improves, and there is an advantage that a battery having a thin shape or a wide area can be manufactured.

1 is a cross-sectional view of a positive electrode of a lithium polymer battery.

2 is a cross-sectional view of a negative electrode of a lithium polymer battery.

3 is a cross-sectional view of a configuration in which a unit cell is formed by laminating a positive electrode and a negative electrode through an ion conductive polymer layer on a separator;

4 is a cross-sectional view of a structure in which a plurality of cathodes are arranged on one side of a continuous separator and a plurality of anodes are arranged on the opposite side.

5 is a cross-sectional view showing a folding method of the arrangement of FIG.

6 is a cross-sectional view of a structure in which a plurality of anodes and cathodes are arranged on one side of a continuous separator;

7 is a cross-sectional view showing a method of folding the arrangement of FIG.

<Description of the code | symbol about the principal part of drawing>

1: anode current collector (aluminum foil) 2: anode composition material

3: cathode current collector (copper foil) 4: cathode composition material

5: anode 6: cathode

7: Separation membrane 8: Ion conductive polymer

Hereinafter, described in detail by the accompanying drawings as follows.

1 and 2 illustrate cross sections of the positive electrode and the negative electrode used in the present invention, respectively. The anode is a current collector by uniformly mixing a powdered active material having an oxidation / reduction potential of lithium metal with a oxidation / reduction potential of 2.0 to 5.0 volts and a conductive agent capable of transferring electrons in a solvent in which a binding polymer material is dissolved. After coating on both sides of the metal foil as a whole, the solvent is dried and compressed with a roll press to form a flat surface. The negative electrode is uniformly mixed with a powdered active material having an oxidation / reduction potential of 0.0-2.0 volts based on the oxidation / reduction potential of lithium metal and a conductive agent capable of transferring electrons in a solvent in which the binding polymer material is dissolved. After coating on both sides, the solvent may be dried and compressed with a roll press to form a flat surface, or metal lithium foil may be used.

The positive and negative electrodes thus constructed are cut to a predetermined size and sequentially stacked as shown in FIG. 3. At this time, by applying an ion conductive polymer material to a portion of the anode or cathode or separator to make the binding between the films, the liquid electrolyte containing lithium ions can penetrate uniformly on all sides of the polymer layer, the separator and the electrode. Provide space. The ion conductive polymer used here is polycyano acrylate, polyethylene acrylic acid, polymethamethyl acrylate, polyethylene oxide, polyproplylene oxide polyacrylic. It is preferably composed of one or a mixture or copolymer of polyacrylo nitrile, polyvinylidene fluoride, polyhexapropylene fluoride, and the thickness applied is 0.1 to 10 탆. Is suitable.

Hereinafter, the lithium polymer battery according to the present invention will be described in detail in Examples. However, the embodiments do not limit the scope of the present invention.

Example 1

Positive electrode production: 100 g of LiCoO2, a positive electrode active material, 5 g of carbon black as a conductive agent, and 10 g of polyvinylidene fluoride as a binder were mixed uniformly, and 50 g of N-methylpyrrolidone (NMP) as a solvent was added thereto. To prepare a slurry in a uniform state. The slurry is uniformly applied on both sides to a 20 μm thick aluminum foil and dried at 100 ° C. to evaporate NMP. The thickness of the film after drying is set to 250 탆, and the film is pressed with a roll press to have a thickness of 200 탆 to complete anode production.

Negative electrode manufacturing: uniformly mix 100 g of graphite powder as a negative electrode active material, carbon black 1 g as a conductive agent, and 10 g polyvinylidene fluoride as a binder, and add 50 g of N-methylpyrrolidone as a solvent. A slurry in a homogeneous state is prepared. The slurry is uniformly applied on both sides to a 15 μm thick copper foil and dried at 100 ° C. to evaporate NMP. The thickness of the film after drying is set to 200 µm, and the film is pressed with a roll press to have a thickness of 160 µm to complete the preparation of the negative electrode.

Battery Assembly: A solution of 1 g of polyethylene oxide (Mv = 1000,000) dissolved in 100 g of acetonitrile is prepared. The prepared positive and negative electrodes are cut to a size of 40 X 60 mm. At this time, in order to provide a terminal, which is an electrical connection passage, a portion of the aluminum foil and the copper foil is protruded, in which the material is not applied.

The polyethylene oxide solution prepared on one side of the cut anode and cathode was partially coated with a thickness of 1 μm, and then applied to a porous polyethylene separator (trade name: Celgard, thickness: 25 μm). Attached as shown in Figure 6, folded into an accordion shape to form a laminate of anode, cathode and separator, and the terminals of anode and cathode are ultrasonically fused in parallel.

The electrode is placed in an outer material consisting of polyproplyene in the innermost layer, aluminum foil in the middle layer, and nylon in the outermost layer, and 1: 1 in volume ratio of ethylene carbonate and diethyl carbonate. Into the phosphorus solvent, a liquid electrolyte dissolved at a concentration of 1 mole of LiPF ₆ is introduced, and the terminal is vacuum-packed with an exterior member in a form of protruding to the outside to complete a battery.

Example 2

Fabrication of the other components as in Example 1 is the same and the electrode is shown in the separator. After attaching in the shape as shown in Fig. 7, the parts between neighboring electrodes are folded and continuously wound to form a laminate of anode, cathode and separator.

Example 3

The manufacture of the different components from Example 1 is identical and the polyethylene oxide solution is applied to the separator to which the electrode is attached to construct the cell.

In the case of using the battery structure and the manufacturing method of the present invention, the battery can be manufactured by a simpler process than the conventional method, and the electrolyte can quickly penetrate between the electrode and the separator and evenly distribute the entire surface to form a stable interface. As a result, the internal resistance of the battery is low, and even though the electrode is repeatedly contracted and expanded due to repeated charging and discharging, the interface is kept constant, thereby improving the performance and life of the battery, and having a thin or wide area. There is an effect that can be prepared.

Claims (13)

In a secondary battery composed of a positive electrode, a negative electrode, a separator, an electrolyte, and a packaging material, A structure in which an ion conductive polymer is applied to a part of an anode, a cathode, or a separator to form a partial bond between an electrode and the separator, and a part to which the non-bonding part provides a space where the liquid electrolyte can uniformly penetrate. The separator of claim 1 consists of a single or a composite film of polyethylene, polypropylene, or polyvinylidene fluoride, having a porosity ranging from 40% to 80%, and having a thickness of 5 μm. In the range of 50 μm. The ion conductive polymer of claim 1 is polyethylene acrylic acid, polymethamethyl acrylate, polyethylene oxide, polypropylene oxide, polyacrylonitrile, When one or a mixture or copolymer or ionomer of polyvinylidene fluoride, polyhexapropylene fluoride, polystyrene. The current collector of the positive electrode of claim ₁ is aluminum foil, and the positive electrode active material coated thereon is a powder having a chemical formula of LiMO ₂ or LiM ₂ O ₄ , wherein M is cobalt (Co), nickel (Ni), manganese (Mn), When composed of one or more than two of transition metals such as tin (Sn), vanadium (V), strontium (Sr). When the positive electrode active material of claim 4 contains a Group 2 (Be) combustion or a Group 3 (Group B) element of the periodic table in an oxide state or in a compound form. In case 1, the negative electrode current collector is copper foil, and the negative electrode active material coated thereon is composed of one of lithium, carbon or graphite. The electrolyte of paragraph 1 is ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, vinylidene carbonate, gamma It is composed of two or more mixed solutions in γ-butylo lactone, and at least one of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ C ₂ F ₅ ) ₂ is dissolved in the mixed solution with lithium salt. Occation. The case 1 is made of aluminum foil and multilayer polymer. When the thickness of the porous polymer layer of 3 has a thickness in the range of 0.1 to 10㎛. The outer shell of item 8 is adjacent to the battery, and the innermost layer is made of polypropylene, the middle layer is made of aluminum foil, and the outermost layer is made of polyester or nylon. When the internal structure of the battery of claim 1 is attached to the separator continuous with a plurality of electrodes in an arrangement such as FIG. 4 or 6 to form a stacked structure overlapping the structure as shown in FIG. When the positive electrode, the negative electrode and the separator are formed in a continuous winding structure in the battery internal structure of paragraph 1. The internal structure of the battery of claim 1 is configured in the form of claims 11 and 12, the outside is fixed with a heat shrinkable film, the material of the heat shrinkable film is composed of polyvinyl chloride, polyethylene, polypropylene, polyester, etc. .