WO2014157987A1 - Electrode assembly for secondary battery and secondary battery using same - Google Patents

Abstract

The present invention relates to an electrode assembly for a secondary battery and a secondary battery using the same, in which a porous conductive metal layer is formed on particle surfaces of an anode active material layer and/or a cathode active material layer by a deposition method, thereby forming a metallic network formed by a porous conductive metal layer as well as an electronic conduction network formed by a conductive agent mixed with an active material inside the electrode, so that the electrode assembly can improve electrical conductivity, ion conductivity, and the capacity of the battery. The electrode assembly for the secondary battery of the present invention includes: an anode having an anode current collector and an anode active material layer formed on at least one surface of the anode current collector; a cathode having a cathode current collector and a cathode active material layer formed on at least one surface of the cathode current collector; a porous separation film formed between the cathode and the anode; and a porous conductive metal layer formed on at least one surface of the cathode active material layer and the anode active material layer, the porous conductive metal layer having a plurality of pores to allow the movement of lithium ions.

Description

Electrode assembly for secondary battery and secondary battery using same

The present invention relates to a secondary battery electrode assembly and a secondary battery using the same to form a porous conductive metal layer on the surface of the particles of the active material to improve the electrical conductivity and ion conductivity.

Lithium secondary batteries generate electrical energy by oxidation and reduction reactions when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode. A lithium secondary battery is prepared by using a material capable of reversibly intercalating / deintercalating lithium ions as an active material of a positive electrode and a negative electrode, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

A lithium secondary battery is composed of an electrode assembly in which a negative electrode plate and a positive electrode plate are wound or stacked in a predetermined form with a separator (separation membrane) interposed therebetween, and a case in which the electrode assembly and the electrolyte solution are stored.

The basic function of the separator of the lithium secondary battery is to prevent the short circuit by separating the positive electrode and the negative electrode, and furthermore, it is important to suck the electrolyte required for the battery reaction and maintain high ion conductivity. In particular, in the case of a lithium secondary battery, an additional function is required to prevent the movement of substances that inhibit battery reaction or to secure safety when an abnormality occurs.

Lithium-ion secondary batteries with high energy density and large capacity, secondary batteries including lithium-ion polymer batteries should have a relatively high operating temperature range, and the temperature rises when they are continuously used in high rate charge / discharge states. Separators are required to have higher heat resistance and thermal stability than those required by ordinary separators. In addition, it should have excellent battery characteristics such as high ion conductivity that can cope with rapid charging and discharging and low temperature.

The separator is located between the anode and the cathode of the battery to insulate it, maintains the electrolyte to provide a path for ion conduction, and when the temperature of the battery becomes too high, a part of the separator melts to block pores in order to block the current. Have

When the temperature rises further and the separator melts, a large hole is formed, which causes a short circuit between the anode and the cathode. This temperature is called SHORT CIRCUIT TEMPERATURE. In general, the separator should have a low shutdown temperature and a higher short circuit temperature.

In the case of a polyethylene separator, when an abnormal heat generation of the battery occurs, the electrode part may be contracted at 150 ° C. or more, resulting in a short circuit. Therefore, it is very important to have both the closing function and the heat resistance for high energy density and large sized secondary battery. That is, a separator having excellent heat resistance, low thermal shrinkage, and excellent cycle performance according to high ion conductivity is required.

As the material of the separator, polyolefin-based microporous polymer membranes such as polypropylene and polyethylene or multiple membranes thereof are usually used. In the conventional separator, since the porous membrane layer is in the form of a sheet or a film, there is a drawback that the sheet-like separator shrinks together with the pore blocking of the porous membrane due to heat generation due to internal short circuit or overcharge. Therefore, when the sheet-like separator collapses due to the internal heat generation of the battery, the separator is reduced and the missing part is directly in contact with the positive electrode and the negative electrode, which leads to ignition, rupture, and explosion.

Lithium secondary batteries that are currently commercialized mostly use LiCoO ₂ as a cathode active material. LiCoO ₂ is a material with excellent thermal stability and stable charge and discharge characteristics and high electron conductivity. Recently, however, there is a need for a cathode active material for a lithium secondary battery having a high voltage and a large capacity. When LiCoO ₂ is continuously charged and discharged at 4.3 V or higher, the cathode active material reacts with the electrolyte due to lattice deformation or destruction of crystal structure. By doing so, life characteristics and safety are lowered. In addition, Co, which is the starting material of the positive electrode active material, has a tendency to continuously increase in price due to the small reserves, and further development of alternative positive electrode active material is needed due to the toxicity and environmental pollution problem to the human body.

Accordingly, LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , and Li (NixCoyMnz) O ₂ may be mentioned as positive electrode active materials for lithium secondary batteries that are actively researched and developed. However, LiNiO ₂ is not only difficult to synthesize, but also difficult to commercialize due to problems of thermal stability, while LiMn ₂ O ₄ has been commercialized in low-priced products, but due to Jahn-Teller distortion due to Mn3 + The property is not good. In addition, LiFePO ₄ has a low price and excellent safety and is currently being studied for HEV, but due to low conductivity it is difficult to apply to other fields.

Therefore, Li (NixCoyMnz) O ₂ is the most recently attracting attention as an alternative cathode active material for LiCoO ₂ . This material is cheaper than LiCoO ₂ and has the advantage of being able to be used for high capacity and high voltage, but has disadvantages of poor rate characteristics and long life at high temperatures. In order to overcome these disadvantages, a method of coating a highly conductive metal on the surface of the positive electrode active material, or doping the material, such as Al, Mg, Ti, Zr, Sn, Ca, Ag and Zn therein The research has been conducted a lot, such as the coating method using a wet method, but in reality, the price has a big problem that the price increases in mass production, and now the trend of increasing the characteristics of the above metal through dry doping is a trend that is increasing to be.

In particular, in recent years, attempts have been made to improve the electrochemical properties of lithium secondary batteries through Ti doping. However, in order to dope inside the cathode active material using TiO ₂ , which is widely used to date, high plasticity of 1000 ° C. or higher is required. There is a disadvantage that a temperature and a large amount of firing time are required.

Therefore, in manufacturing a lithium secondary battery, lithium can be distributed evenly in the positive electrode active material and maximize the doping effect to improve the structural stability and electrochemical properties to prevent degradation of the battery performance as described above There is a need for research on cathode active materials for secondary batteries.

Korean Patent Application Publication No. 10-2010-56106 proposes a cathode active material for a lithium secondary battery having excellent structural stability and electrochemical properties by maximizing the doping effect of an additive element.

However, since a conventional positive electrode or negative electrode is composed of an active material, a conductive agent and a binder, an electron conduction network is formed by a conductive agent by an active material layer in the case of a large-capacity battery, and in particular, a gel polymer electrolyte battery has a poor ion conductivity. Electron conduction networks alone have limitations in ion conductivity.

An object of the present invention is to form a porous conductive metal layer on the particle surface of the electrode active material layer to form a metal network by the porous conductive metal layer in addition to the electron conductive network by the conductive material mixed with the active material inside the electrode to improve the ion conductivity accordingly It is to provide a secondary battery electrode assembly and a secondary battery using the same that can improve the performance of the battery.

Another object of the present invention is to improve the electrical conductivity of the electrode surface by adding a metal network in addition to the electron conductive network to increase the movement speed of the lithium ion, the electrode assembly for a secondary battery that can achieve high power and high capacity characteristics and It is to provide a secondary battery using the same.

The problem to be solved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description. .

In order to achieve the above object, the secondary battery electrode assembly of the present invention includes a negative electrode having a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; A positive electrode having a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector; A porous separator formed between the cathode and the anode; And a porous conductive metal layer formed on at least one surface of the negative electrode active material layer and the positive electrode active material layer and having a plurality of pores to allow the movement of lithium ions.

Each of the negative electrode and the positive electrode includes an electron conductive network by a conductive agent mixed with an active material and a metal network by the porous conductive metal layer, respectively, and as a result, the electrical conductivity, the ion conductivity, and the capacity of the battery can be improved.

The conductive metal layer is deposited on the surface of the particles of the negative electrode active material layer or the positive electrode active material layer in the form of a plurality of point particles are interconnected to form a metal network, it is preferable that pores for moving lithium ions are formed between the particles and the particles.

The conductive metal layer formed on the cathode active material layer of the present invention may be formed of Al or Ni, and the conductive metal layer formed on the anode active material layer may be formed of Cu or Ni.

The conductive metal layer is preferably set to a thickness of 30 to 400 kPa, preferably formed by a vacuum deposition method. The conductive metal layer formed on the negative electrode active material layer is set in the range of 30 ~ 300Å, the conductive metal layer formed on the positive electrode active material layer is preferably set in the range of 110 ~ 400Å.

The electrode assembly according to the present invention is assembled in a case and filled with an electrolyte to constitute a secondary battery.

The electrolyte solution comprises an organic electrolyte containing a non-aqueous organic solvent, a solute of lithium salt, a monomer for forming a gel polymer, and a polymerization initiator, and the electrolyte solution is impregnated into the porous separator and then polymerizes the gel polymer forming monomer. As a result, a gel polymer electrolyte is formed, and the porous separator serves as an electrolyte matrix in the gel polymer electrolyte.

In addition, the electrolyte solution may be an organic electrolyte solution containing a solute of a non-aqueous organic solvent and a lithium salt.

The electrode assembly according to the present invention can be applied to a secondary battery such as a lithium ion battery or a lithium polymer battery.

As described above, the electrode assembly for secondary batteries of the present invention forms a porous conductive metal layer on the surface of the particles of the negative electrode active material layer and / or the positive electrode active material layer by a deposition method, and thus conducts electrons by the conductive agent mixed with the active material in the electrode. In addition to the network, a metal network may be formed by the porous conductive metal layer, thereby improving electrical conductivity, ion conductivity, and battery capacity.

1 is a cross-sectional view illustrating an electrode assembly for a secondary battery according to a first embodiment of the present invention.

2 is a cross-sectional view illustrating an electrode assembly for a secondary battery according to a second embodiment of the present invention.

3 is an enlarged view conceptually illustrating a state in which an electrically conductive metal layer is deposited on the surface of an active material layer of the present invention.

4A is a SEM photograph taken at 2000 times magnification of a negative electrode sample of Comparative Example 1. FIG.

4B to 4E are SEM images taken at 2000 times magnification of the negative electrode samples of Examples 2 to 5. FIG.

5A is a SEM photograph taken at 2000 times magnification of the positive electrode sample of Comparative Example 2. FIG.

5B to 5C are SEM images taken at 2000 times magnification of the positive electrode samples of Examples 8 to 10. FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this process, the size or shape of the components shown in the drawings may be exaggerated for clarity and convenience of description. In addition, terms that are specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intention or custom of the user or operator. Definitions of these terms should be made based on the contents throughout the specification.

1 is a cross-sectional view showing an electrode assembly according to a first embodiment of the present invention, Figure 2 is a cross-sectional view of an electrode assembly according to a second embodiment of the present invention.

1 and 2, the electrode assembly 10 for a secondary battery according to the present invention largely includes a negative electrode 1 and a positive electrode 2.

The negative electrode 1 is disposed to face the positive electrode 2 and includes a pair of negative electrode active material layers 13a and 13b formed on both sides of the negative electrode current collector 11 to form a bicell. When the full cell is formed, the negative electrode 1 may have a structure in which a negative electrode active material layer is provided on one surface of the negative electrode current collector 11.

The positive electrode 2 includes positive electrode active material layers 23a and 23b formed on both surfaces of the positive electrode current collector 21 to form a bicell. In addition, when forming the full cell, the cathode 2 may have a structure in which a cathode active material layer is formed on one surface of the cathode current collector 21.

The cathode active material layers 23a and 23b include a cathode active material capable of reversibly intercalating and deintercalating lithium ions. Representative examples of the cathode active material include LiCoO ₂ , LiNiO ₂ , LiNiCoO ₂ , LiFeO ₄ , and the like. LiMnO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , V ₆ O ₁₃ , LiNiCoAlO ₂ , LiNi _1-xy Co _x M _y O ₂ (0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ x + y ≤ 1, M is a metal such as Al, Sr, Mg, La) or a lithium-transition metal such as Li [Ni _x Co _1-xy Mn _y ] O ₂ (where 0 <x <0.5, 0 <y <0.5) Oxides can be used.

The positive electrode active material is largely divided into five types such as lithium cobalt-based (LCO), lithium nickel cobalt manganese (NCM), lithium nickel cobalt aluminum (NCA), lithium manganese (LMO) and lithium iron phosphate (LFP) Are distinguished. In this case, it is also possible to use five types of active materials alone as the positive electrode active material or to form a hybrid form in which, for example, a layered NCM or NCA and a spinel structure LMO are mixed.

However, in the present invention, it is of course possible to use other types of positive electrode active materials in addition to the positive electrode active material.

The negative electrode active material layers 13 and 13a include a negative electrode active material capable of intercalating and deintercalating lithium ions, and the negative electrode active material includes a carbon-based negative electrode of crystalline or amorphous carbon, carbon fiber, or carbon composite material. It can be selected from the group consisting of an active material, tin oxide, lithiated thereof, lithium, lithium alloys and mixtures thereof.

The negative electrode 1 and the positive electrode 2 are prepared by mixing an appropriate amount of an active material, a conductive agent, a binder, and an organic solvent to prepare a slurry, and then, as the negative electrode and the positive electrode current collectors 11 and 21, on both sides of a copper or aluminum sheet or the like. The resulting slurry can be obtained by casting, drying and rolling.

Examples of the conductive agent include graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, metal fiber, carbon fluoride, aluminum, nickel powder, zinc oxide and potassium titanate. At least one selected from titanium oxide and polyphenylene derivatives may be used.

For example, the positive electrode is used by casting a slurry composed of LiCoO ₂ , super-P carbon, PVdF as an active material, a conductive agent, a binder on an aluminum foil, and the negative electrode is MCMB (mesocarbon microbeads), super-P carbon, PVdF The constructed slurry can be cast and used in aluminum foil. In the positive electrode and the negative electrode, after the slurry is cast, it is preferable to perform roll pressing in order to increase the adhesive force between the particles and the metal foil.

The porous separators 3a and 3b formed in the multilayer structure on the surface of the negative electrode 1 each include a first polymer made of a polymer that swells in the electrolyte so as to cover the negative electrode active material layers 13a and 13b and is capable of conducting electrolyte ions. The inorganic-porous polymer film layers 31a and 31b, and the inorganic-containing porous polymer web layers 33a and 33b made of ultrafine fibrous forms of a mixture of heat resistant polymer or heat resistant polymer and swellable polymer and inorganic particles.

In addition, the separators 3a and 3b may be separately formed without directly forming the cathode 1, and then inserted and encapsulated between the cathode and the anode when assembling the anode and the cathode.

On the surface of the particles of the negative electrode active material layer 13a and the positive electrode active material layer 23a, a metal network is formed in addition to the electron conductive network by carbon black or other conductive agent contained in the negative electrode active material layer and the positive electrode active material layer. Porous conductive metal layers 50 and 60 may be formed to improve performance.

The porous conductive metal layers 50 and 60 are formed of the porous first conductive metal layer 50 formed on the surface of the negative electrode active material layer 13a and the porous second conductive metal layer 60 formed on the surface of the positive electrode active material layer 23a. Include.

The thicknesses of the first and second conductive metal layers 50 and 60 are preferably set to 30 to 400 kPa, respectively. More preferably, the first conductive metal layer 50 is set in the range of 30 to 300 kPa, and the second conductive metal layer 60 is set in the range of 110 to 400 kPa.

When the thicknesses of the first and second conductive metal layers 50 and 60 are respectively less than 30 μs, the resistance increases, and the improvement of the electrical conductivity is insignificant. Rather, it adversely affects battery characteristics.

The first conductive metal layer 50 formed on the surface of the negative electrode active material layer 13a increases in resistance as the thickness increases or decreases, and the second conductive metal layer 60 formed on the surface of the positive electrode active material layer 23a As the thickness increases or decreases, the resistance value and the electrical conductivity tend to increase.

Here, the first conductive metal layer 50 may be formed of Cu or Ni, and the second conductive metal layer 60 may be formed of Al or Ni.

In addition, a plurality of pores 70 are formed in the porous conductive metal layers 50 and 60 to allow lithium ions to pass therethrough. That is, when the conductive metal layers 50 and 60 completely cover the particle surfaces of the active material layers 13a and 23a, the movement of lithium ions is suppressed and the performance is reduced, thereby securing pores 70 through which lithium ions can be sufficiently transferred. It is formed in one form.

To this end, as shown in FIG. 3, the conductive metal layers 50 and 60 are formed by a deposition method, for example, thermal evaporation or electron-beam evaporation, and the like. In the case of depositing 60, the deposition conditions are appropriately adjusted so that the conductive metal layers 50 and 60 are deposited in the form of point particles 80 so as to be partially interconnected, thereby depositing the particles 80 and 80. While forming a metal network of a three-dimensional structure between the) to partially secure the pores (70) to allow sufficient lithium ions to pass through.

As the deposition method for forming the conductive metal layer, a method such as sputtering, chemical vapor deposition (CVD), and physical vapor deposition (PVD) may be applied in addition to the thermal evaporation described above.

As described above, in the present embodiment, by forming the conductive metal layers 50 and 60 on the surface of the particles of the negative electrode active material layer and the positive electrode active material layer, a three-dimensional metal network having pores 70 which are passages through which lithium ions pass is formed. In addition, the electrical conductivity and the ion conductivity can be improved, thereby improving the performance of the electrode.

In particular, in the case of the gel polymer electrolyte battery, the ion conductivity is low, and the conductive metal layer is formed on the surface of the particles of the negative electrode active material layer and the positive electrode active material layer of the present embodiment in the form of dot particles to form a metal between the deposited particles 80 and the particles 80. While forming a network, the pores 70 may be partially secured to improve electrical conductivity and ion conductivity, thereby improving battery performance.

In the case of using a gel polymer electrolyte to form a flexible battery, a porous conductive metal layer is formed on the surface of the negative electrode active material layer and the positive electrode active material layer of the present embodiment to improve the electrical conductivity and the ion conductivity, thereby improving the performance of the battery. have.

 As the separators 3a and 3b, a porous polymer web obtained by electrospinning the swellable polymer instead of the first inorganic porous polymer film layers 31a and 31b may be used. For example, the porous polymer web may be formed by dissolving a swellable polymer in a solvent to form a spinning solution, and then electrospinning the spinning solution on a negative electrode active material layer to form a porous polymer web made of ultra-fine fibers. , PVDF) is obtained by calendering the porous polymer web at a temperature lower than the melting point of PVDF).

The first inorganic porous polymer film layers 31a and 31b formed to cover the negative electrode active material layers 13a and 13b in the negative electrode 1 are swelled in the electrolyte and are capable of conducting electrolyte ions, for example, PVDF. (Polyvinylidene fluoride), PEO (Poly-Ethylen Oxide), PMMA (polymethyl methacrylate), TPU (Thermoplastic Poly Urethane) can be used. In addition, the first inorganic porous polymer film layers 31a and 31b form a spinning solution by dissolving the polymer in a solvent, and then electrospinning the spinning solution on the anode active material layer to form a porous polymer web made of ultra-fine fibrous fibers. By heat-treating or calendering the porous polymer web at a temperature lower than the melting point of the polymer, the polymer film layers 31a and 31b of the inorganic pores are obtained.

In the heat treatment process, the heat treatment temperature may be performed at a temperature slightly lower than the melting point of the polymer because the solvent remains in the polymer web, and also to form the inorganic porous film while preventing the polymer web from completely melting by the heat treatment. to be.

As described above, the inorganic porous polymer film layers 31a and 31b made of a material capable of conducting electrolyte ions swelling in the electrolyte solution are directly electrospun onto the surfaces of the negative electrode active material layers 13a and 13b. When formed in close contact with 13b), swelling is performed by the electrolyte solution while maintaining conduction of lithium ions while blocking the formation of spaces between the negative electrode active material layers 13a and 13b and the film to prevent lithium ions from accumulating and depositing into lithium metal. can do. As a result, dendrite formation can be suppressed on the surface of the cathode 1 and safety can be improved.

The inorganic-containing porous polymer web layers 33a and 33b formed on the first inorganic porous film layers 31a and 31b are formed by dissolving a mixture of a heat resistant polymer or a heat resistant polymer and a swellable polymer and an inorganic particle in a solvent to form a spinning solution. Thereafter, the spinning solution is electrospun on the first non-porous polymer film layers 31a and 31b to form a porous polymer web made of ultra-fine fibrous, and the obtained porous polymer web is formed by calendering at a temperature below the melting point of the polymer.

The inorganic particles are Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , SiO ₂ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B At least one selected from ₂ O ₅ , Sn ₂ BPO _6, and mixtures thereof can be used.

When the mixture consists of a heat resistant polymer or a heat resistant polymer and a swellable polymer and inorganic particles, the content of the inorganic particles is preferably contained in the range of 10 to 25% by weight based on the total mixture when the size of the inorganic particles is between 10 and 100 nm. More preferably, the inorganic particles are contained in the range of 10 to 20% by weight, and the size is in the range of 15 to 25 nm.

In addition, when the mixture consists of a heat resistant polymer, a swellable polymer and inorganic particles, the heat resistant polymer and the swellable polymer are preferably mixed in a weight ratio of 5: 5 to 7: 3, and more preferably 6: 4. In this case, the swellable polymer is added as a binder to help bond between the fibers.

When the mixing ratio of the heat resistant polymer and the swellable polymer is less than 5: 5 by weight, the heat resistance is poor and does not have the required high temperature characteristics. When the mixing ratio is larger than 7: 3 by weight, the strength drops and the radiation trouble occurs.

The heat resistant polymer resin usable in the present invention is a resin that can be dissolved in an organic solvent for electrospinning and has a melting point of 180 ° C. or higher, for example, polyacrylonitrile (PAN), polyamide, polyimide, polyamideimide, Aromatic polyesters such as poly (meth-phenylene isophthalamide), polysulfones, polyetherketones, polyethylene terephthalates, polytrimethylene terephthalates, polyethylene naphthalates, and the like, polytetrafluoroethylene, polydiphenoxyphosphazenes Polyphosphazenes, such as poly {bis [2- (2-methoxyethoxy) phosphazene]}, polyurethane copolymers including polyurethanes and polyetherurethanes, cellulose acetates, cellulose acetate butyrates, cellulose acetate pros Cypionate and the like can be used.

The swellable polymer resin usable in the present invention is a resin that swells in an electrolyte and can be formed into ultrafine fibers by electrospinning. For example, polyvinylidene fluoride (PVDF), poly (vinylidene fluoride-co-hexa) Fluoropropylene), perfuluropolymer, polyvinylchloride or polyvinylidene chloride and copolymers thereof and polyethylene glycol derivatives including polyethylene glycol dialkyl ether and polyethylene glycol dialkyl ester, poly (oxymethylene-oligo- Oxyethylene), polyoxides including polyethylene oxide and polypropylene oxide, polyvinylacetate, poly (vinylpyrrolidone-vinylacetate), polystyrene and polystyrene acrylonitrile copolymers, polyacrylonitrile methyl methacrylate copolymers Polyacrylic containing Casting reel can be given to the copolymer, polymethyl methacrylate, polymethyl methacrylate copolymers and mixtures thereof.

In the first embodiment shown in FIG. 1, the separators 3a and 3b having a multi-layer structure are formed on the surface of the cathode 1. However, the separators 3a and 3b may be formed on the surface of the anode 2 instead of the cathode 1. In this case, preferably, the inorganic-containing porous polymer web layers 33: 33a and 33b are first formed on the surface of the anode 2, and the first inorganic porous polymer film layers 31: 31a and 31b are formed of the porous polymer web layer 33. It is formed on the surfaces of 33a and 33b to be in close contact with the cathode 1 during assembly.

In the first embodiment, the two-layer structure separation membranes 3a and 3b are formed on either the negative electrode 1 or the positive electrode 2, but the separation membrane 3 is the first as shown in the second embodiment shown in FIG. It is composed of the inorganic porous polymer film layers 31: 31a and 31b and the inorganic-containing porous polymer web layers 33: 33a and 33b, and may be formed separately from the cathode 1 and the anode 2.

For example, the first non-porous polymer film layers 31: 31a and 31b are formed on the negative electrode 1 to cover the negative electrode active material layers 13a and 13b, and the inorganic material to cover the positive electrode active material layers 23a and 23b. It is also possible that the porous polymeric web layers 33: 33a and 33b are formed on the anode 2.

It is also possible to form the second inorganic porous polymer film layer on the surfaces of the inorganic material-containing porous polymeric web layers 33a and 33b of the anode 2 in the same manner as the first inorganic porous polymer film layers 31a and 31b. In this case, when the cathode 1 and the anode 2 are assembled, the first inorganic porous polymer film layers 31a and 31b and the second inorganic porous polymer film layer are bonded to each other.

When the first inorganic porous polymer film layers 31a and 31b and the inorganic-containing porous polymer web layers 33a and 33b are integrally formed on the negative electrode 2 or are formed separately from the negative electrode 1 and the positive electrode 2, respectively. It is preferable that the thickness of the inorganic-containing porous polymer web layers 33a and 33b is set in a range of 5 to 50um, and the thickness of the first inorganic porous polymer film layers 31a and 31b is set in a range of 5 to 14um.

In this case, the function of the separator is that the inorganic-containing porous polymer web layers 33a and 33b have a higher porosity than the first inorganic-porous polymer film layers 31a and 31b, so that the first inorganic rather than the inorganic-containing porous polymer web layers 33a and 33b. Responds more sensitively to the thickness of the co-polymer film layers 31a and 31b. As will be described later, when the thickness of the first inorganic porous polymer film layers 31a and 31b is less than 5 μm, a micro short circuit occurs. When the thickness of the first inorganic porous polymer film layers 31a and 31b is greater than 14 μm, it is too thick to prevent the movement of Li ions, thereby preventing charge and discharge. The thickness of the first inorganic porous polymer film layers 31a and 31b is preferably adjusted in consideration of the ion conductivity and energy density of the film layer.

As described above, in the present invention, the first inorganic porous polymer film layers 31a and 31b and the inorganic porous polymer web layers 33a and 33b serving as separators may be formed of the cathode 1 or the anode 2 as shown in FIG. 1. It encloses with a sealing structure, or surrounds the cathode 1 and the anode 2 simultaneously with the sealing structure like FIG.

Thus, as shown in FIGS. 1 and 2, the electrode assemblies 10 and 10a of the present invention may form a unit cell by simply stacking the cathode 1 and the anode 2, for example, a large capacity for an electric vehicle. When fabricating a large size in order to construct a battery, a plurality of unit cells are simply stacked and then case assembled. Therefore, the present invention has a high assembly productivity compared to the prior art that goes through the process of folding a plurality of bi-cell with a separate membrane film.

The negative electrode 1 and the positive electrode 2 are provided with a negative electrode and a positive electrode terminal formed to protrude portions of the negative electrode and the positive electrode current collectors 11 and 21. When the electrode assemblies 10 and 10a of the present invention are laminated and assembled with a plurality of negative electrodes 1 and positive electrodes 2, the negative electrode terminal 11a of the negative electrode 1 and the positive electrode terminal 21a of the positive electrode 2 as shown in FIG. 3. ) Are stacked so that they face in opposite directions.

Conventional film type separators have a problem of shrinkage at high temperature, but in the present invention, the porous polymer web layers 33a and 33b contain an inorganic material and thus retain their shape without shrinking or melting even when heat-treated at 500 ° C.

Existing polyolefin-based film separators cause hard short-circuit as the peripheral film is continuously shrunk or melted in addition to the part damaged by initial heat generation during internal short circuit, and the film separator burns away. However, the electrode of the present invention has only a small damage in the portion where the internal short circuit occurs, and does not lead to a phenomenon in which the short circuit portion is widened.

In addition, the electrode of the present invention maintains a constant voltage between 5V and 6V and a battery temperature of less than 100 ° C by continuously consuming overcharge current by causing a very small short-circuit rather than a hard short during overcharge. Overcharge stability can also be improved.

The electrode assembly according to the present invention may constitute a lithium ion battery or a lithium polymer battery as a secondary battery.

When the electrode assembly according to the present invention constitutes a lithium ion battery (LIB), as shown in FIGS. 1 and 2, separators 3a, 3b; 3 are formed on the negative electrode 1 and the positive electrode 2, and the assembly is compressed. One electrode assembly 10, 10a contains an electrolyte solution.

The electrolyte solution includes an organic electrolyte solution containing a non-aqueous organic solvent and a solute of a lithium salt, and the lithium salt serves as a source of lithium ions in the battery to enable operation of a basic lithium battery.

In addition, when the electrode assembly according to the present invention constitutes a lithium polymer battery (LPB), the lithium polymer battery includes a negative electrode (1), a positive electrode (2) and a polymer electrolyte inserted between the negative electrode and the positive electrode, the polymer electrolyte It consists of a porous membrane and a gel polymer that serves as an electrolyte matrix.

The lithium polymer battery is formed by integrally forming a porous separator on one of the negative electrode 1 and the positive electrode 2, preferably on the surface of the negative electrode 1, or by inserting it between the negative electrode 1 and the positive electrode 2 and pressing-assembled. Including an electrolyte in the electrode assembly.

The porous membrane may serve as an electrolyte matrix, and a composite porous membrane in which a single layer porous polymer web made of nanofibers, a porous polymer web or an inorganic porous polymer film, and a porous nonwoven fabric are stacked. The electrolyte solution includes a non-aqueous organic solvent and a solute of a lithium salt, a monomer for forming a gel polymer, and a polymerization initiator.

When the electrolyte is charged while the electrode assembly is assembled to the case, the electrolyte is impregnated into the porous separator. After the gelation heat treatment, the gel polymer in the gel state is synthesized by the polymerization reaction of the monomer for forming the gel polymer. An electrolyte is formed. In this case, the porous separator serves to separate the negative electrode 1 and the positive electrode 2 while serving as an electrolyte matrix in the gel polymer electrolyte.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are merely examples of the present invention, and the scope of the present invention is not limited thereto.

(Comparative Example 1)

The negative electrode is a mixture of graphite, conductive material (CB) and binder (PVdF) of 9g, 0.5g and 0.5g, respectively, dissolved in NMP (N-Methyl pyrrolidone), which is used as a solvent, and then cast into a copper foil. In order to increase the adhesion between the particles and the metal foil, roll pressing was performed to prepare a negative electrode of Comparative Example 1.

The negative electrode sample of Comparative Example 1 was prepared in 2Ah size without metal deposition, and a SEM photograph taken at 2000 times magnification of the negative electrode sample of Comparative Example 1 is shown in FIG. 4A.

(Examples 1 to 6)

A negative electrode of Comparative Example 1 was prepared in a size of 2 Ah, a negative electrode sample of 2 Ah size was mounted on a ceramic substrate jig of a thermal evaporator, and a jig was mounted on a rotary holder of the thermal evaporator. Cu metal was weighed in proportion to the thickness to be deposited and set in a tungsten boat.

Subsequently, after rotating the holder at a speed of 2 m / s for 10 minutes with a low vacuum of 5 ^-2 torr and rotating the speed of the holder at 2 m / s for 30 minutes with a high vacuum of 5 ^-5 torr, Cu metal was deposited on the negative electrode sample by setting the thermal evaporator to 3.5 V, 120 A, and 3 min to deposit copper (Cu) at a thickness of 30 mV, 105 mV, 120 mV, 135 mV, 150 mV, and 300 mV for the negative electrode sample, respectively. Samples of 1 to 6 were prepared.

SEM pictures taken at 2000 times magnification of the samples of Examples 2 to 5 obtained are shown in FIGS. 4B to 4E.

In addition, for the samples of Examples 1 to 6, the resistance value and the electrical conductivity according to the deposition thickness of copper were measured, and are shown in Table 1 together with the characteristics of Comparative Example 1.

In addition, half-cell tests for Example 2 and Example 5 were conducted to obtain battery capacity at the time of discharge, and are shown in Table 2 below.

Table 1

Sample	Thickness	Resistance value (mΩcm)	Electrical Conductivity (S / cm)
Comparative Example 1	0	12.64	7.91 × 10
Example 1	30	8.001	1.04 × 10 2
Example 2	105	2.607	3.83 × 10 2
Example 3	120	2.648	3.77 × 10 2
Example 4	135	5.961	1.67 × 10 2
Example 5	150	6.460	1.54 × 10 2
Example 6	300	10.12	1.00 × 10 2

TABLE 2

Sample	Thickness	Capacity (mAh / g)
Comparative Example 1	0	261.9
Example 2	105	330.4
Example 5	150	273.9

As shown in Table 1, the samples of Examples 1 to 6 in which copper is deposited on the surface of the cathode according to the present invention have a resistance value and an electric conductivity characteristic compared to Comparative Example 1 in which copper is not deposited. It was found to be excellent, and the thinner the thickness of the deposited copper, the better the properties were. However, when the thickness of the deposited copper was too thin as in Example 1 or thickened as in Example 6, the resistance value increased and the electrical conductivity decreased.

In addition, as a result of the half-cell test of the samples of Example 2 and Example 5, as shown in Table 2, the capacity of the battery also showed better characteristics as the deposition thickness of copper was thinner. In particular, Example 2, in which the thickness of copper was formed to 105 kW, showed the best resistance value, electrical conductivity, and capacity.

(Comparative Example 2)

The positive electrode was mixed with 8 g, 1.5 g, and 0.5 g of a hybrid type active material, a conductive material (CB), and a binder (CMC, SBR), respectively, in which lithium nickel cobalt manganese (NCM) oxide and lithium manganese (LMO) oxide were mixed. The paste obtained by dissolving one in distilled water used as a solvent was cast on aluminum foil, and roll pressing was performed to increase the adhesion between particles and the metal foil to prepare a positive electrode of Comparative Example 2.

A positive electrode sample of Comparative Example 2 was prepared in 2Ah size without metal deposition, and a SEM photograph taken at 2000 times magnification of the positive electrode sample of Comparative Example 2 is shown in FIG. 5A.

(Examples 7 to 11)

A positive electrode of Comparative Example 2 was prepared in a size of 2 Ah, a positive electrode sample having a size of 2 Ah was mounted on a ceramic substrate jig of a thermal evaporator, and a jig was mounted on a rotary holder of the thermal evaporator. Al metal was weighed in proportion to the thickness to be deposited and set in a tungsten boat.

Subsequently, after rotating the holder at a speed of 2 m / s for 10 minutes with a low vacuum of 5 ^-2 torr and rotating the speed of the holder at 2 m / s for 30 minutes with a high vacuum of 5 ^-5 torr, A method of depositing Al metal on a positive electrode sample by setting a thermal evaporator at 2.8 V, 100 A, and 3 min to deposit Al at a thickness of 110 mW, 200 mW, 220 mW, 240 mW, and 400 mW for the positive electrode sample, respectively. Samples of were prepared.

SEM pictures taken at 2000 times magnification of the samples of the obtained Examples 8 to 10 are shown in FIGS. 5B to 5D.

In addition, for the samples of Examples 7 to 11, the resistance value and the electrical conductivity according to the deposition thickness of Al were measured, the half cell test was performed, and the ion conductivity and the voltage characteristics were obtained. It described in 3.

TABLE 3

Sample	Thickness	Resistance value (mΩcm)	Electrical Conductivity (S / cm)	Ion Conductivity (S / cm)	Capacity (mAh / g)
Comparative Example 2	0	0.264	3.87 × 10 3	2.8 × 10 -4	113.9
Example 7	110	0.191	1.09 × 10 4	5.7 × 10 -4	120.0
Example 8	200	0.048	2.08 × 10 4	6.9 × 10 -4	139.8
Example 9	220	0.094	1.87 × 10 4	6.5 × 10 -4	127.4
Example 10	240	0.181	1.24 × 10 4	6.4 × 10 -4	124.4
Example 11	400	0.210	1.01 × 10 4	5.4 × 10 -4	117.4

As shown in Table 3, the samples of Examples 7 to 11 in which aluminum is deposited on the surface of the anode according to the present invention are compared with those of Comparative Example 2 in which aluminum is not deposited. The conductivity and battery capacity were found to be good. In particular, in Example 8 in which the thickness of aluminum was formed to be 200 kPa, the resistance value, the electrical conductivity, the ion conductivity, and the capacity were all superior to those of Comparative Example 2.

However, when the thickness of the deposited aluminum was too thin as in Example 7, or thickened as in Example 11, the resistance value increased and the electrical conductivity decreased, and the ion conductivity and the capacity of the battery also decreased. If the thickness is too thin or too thick, the properties were found to be inferior.

As described above, the electrode assembly for secondary batteries of the present invention forms a porous conductive metal layer on the surface of the particles of the negative electrode active material layer and / or the positive electrode active material layer by a deposition method, and thus conducts electrons by the conductive agent mixed with the active material in the electrode. In addition to the network, a metal network may be formed by the porous conductive metal layer, thereby improving electrical conductivity, ion conductivity, and battery capacity.

In particular, in the case of using a gel polymer electrolyte to form a flexible battery, a porous conductive metal layer having a plurality of pores of three-dimensional structure is formed on the surface of the negative electrode active material layer and the positive electrode active material layer of the present embodiment to improve electrical conductivity and ion conductivity. By improving, the performance of the battery can be improved.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments, and the present invention is not limited to the spirit of the present invention. Various changes and modifications will be possible by those who have the same.

The present invention partially forms a conductive metal layer on the particle surface of the electrode active material layer to form a metal network by the porous conductive metal layer in addition to the electronic conductive network by the conductive agent mixed with the active material in the electrode, thereby forming the electrical conductivity, ion conductivity and As a technique capable of improving the capacity, it can be applied to a secondary battery such as a lithium ion battery or a lithium polymer battery.

Claims (11)

1. A negative electrode having a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector;

   A positive electrode having a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector;

   A porous separator formed between the cathode and the anode; And

   The electrode assembly for a secondary battery comprising a porous conductive metal layer formed on at least one surface of the negative electrode active material layer and the positive electrode active material layer and having a plurality of pores to allow the movement of lithium ions.
2. The method of claim 1,

   The negative electrode and the positive electrode are each an electrode assembly for a secondary battery, characterized in that it comprises an electron conductive network by a conductive agent mixed with an active material and a metal network by the porous conductive metal layer inside the electrode.
3. The method of claim 1,

   The conductive metal layer is deposited on the particle surface of the negative electrode active material layer or the positive electrode active material layer in the form of a plurality of point particles are interconnected to form a metal network, characterized in that the pores for moving lithium ions between the particles and the particles are formed Electrode assembly.
4. The method of claim 1,

   The conductive metal layer formed on the positive electrode active material layer is an electrode assembly for a secondary battery, characterized in that formed of Al or Ni.
5. The method of claim 1,

   The conductive metal layer formed on the negative electrode active material layer is a secondary battery electrode assembly, characterized in that formed of Cu or Ni.
6. The method of claim 1,

   The conductive metal layer is a secondary battery electrode assembly, characterized in that set to 30 to 400 내지 thickness.
7. The method of claim 6,

   The conductive metal layer formed on the negative electrode active material layer is set in the range of 30 ~ 300Å, the conductive metal layer formed on the positive electrode active material layer is set in the range of 110 ~ 400Å.
8. The electrode assembly of claim 1, wherein the conductive metal layer is formed by a vacuum deposition method.
9. case;

   An electrode assembly according to any one of claims 1 to 8 assembled in the case; And

   A secondary battery comprising an electrolyte solution charged in the case.
10. The method of claim 9,

    The electrolyte is composed of an organic electrolyte containing a non-aqueous organic solvent, a solute of a lithium salt, a monomer for forming a gel polymer, and a polymerization initiator,

    After the electrolyte is impregnated into the porous separator, the gel polymer electrolyte is formed by polymerizing the gel polymer forming monomer, and the porous separator serves as an electrolyte matrix in the gel polymer electrolyte. .
11. The method of claim 9,

    The electrolyte is a secondary battery, characterized in that the organic electrolyte containing a non-aqueous organic solvent and a solute of lithium salt.

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