JP4547963B2 - Negative electrode for secondary battery, method for producing the same, and secondary battery - Google Patents

Description

  The present invention relates to a negative electrode for a secondary battery, a method for producing the same, and a secondary battery, and more specifically, a negative electrode for a secondary battery having a small irreversible capacity and excellent current collection, a method for producing the same, and a secondary battery having excellent cycle characteristics. Next battery.

  With the widespread use of mobile terminals such as mobile phones and laptop computers, the role of secondary batteries that serve as the power source has become important. Secondary batteries are required to be smaller, lighter, have higher capacity, have higher energy density, and have a longer life. In order to satisfy such a demand, researches on negative electrode active materials constituting the negative electrode of secondary batteries have been conducted.

Secondary batteries using metal lithium or lithium alloy as the negative electrode active material (also referred to as metal lithium secondary batteries) are characterized by their small size, light weight, and high energy density. Needle-like crystals (dendrites) may precipitate on the surface. Since this acicular crystal may cause an internal short circuit through a separator provided between the positive electrode and the negative electrode, a metal lithium secondary battery using metal lithium or a lithium alloy is a battery. There are problems in terms of life and safety. On the other hand, a secondary battery using a carbon material such as graphite or hard carbon capable of occluding and releasing lithium ions as a negative electrode active material has a feature that charging and discharging can be favorably repeated. It has a disadvantage that its capacity is small compared to a lithium secondary battery. In addition, as a negative electrode active material for increasing the energy density of a secondary battery, a Li storage material whose composition formula is represented by Li _X A (A is a metal element such as Al) has been studied. The secondary battery using such a Li storage material has an advantage that the lithium ion storage / release amount per unit volume of the negative electrode active material is large and the capacity is high.

  Recently, a secondary battery using silicon as a negative electrode active material has been reported (for example, see Non-Patent Document 1). Although this secondary battery has a feature of high capacity due to a large amount of occlusion and release of lithium ions per unit volume of the negative electrode active material, it has an irreversible capacity (refers to a difference between the initial charge capacity and the discharge capacity). There is a problem that the charge / discharge cycle life is short. The cause of such a problem is that when the secondary battery is charged / discharged, that is, when lithium ions are occluded in the negative electrode active material or when lithium ions are released from the negative electrode active material, the negative electrode active material itself expands. Shrinking into fine powders can be mentioned. By finely pulverizing the negative electrode active material, more active sites react with the electrolytic solution, and more electrons are consumed for the reaction with the electrolytic solution, so that the irreversible capacity of the negative electrode increases. Further, since the contact between the negative electrode active materials is deteriorated due to the pulverization of the negative electrode active material, the amount of occlusion and release of lithium ions in the negative electrode active material gradually decreases as the secondary battery is repeatedly charged and discharged. The charge / discharge cycle life of the secondary battery is shortened.

As a method for preventing such pulverization of the negative electrode active material, it has been proposed to use silicon oxide as the negative electrode active material (see, for example, Patent Document 1). In addition, it has been proposed to use silicon oxide as the negative electrode active material and to add metal powder such as Ti and Fe in order to further increase the conductivity of the negative electrode (see, for example, Patent Document 2 or Patent Document 3).
Hong Li et al., “A High Capacity Nano-Si Composite Anode Material for Lithium Rechargeable Batteries”, Electrochemical and Solid State Letters ( Electrochemical and Solid-State Letters), Vol. 2, No. 11, p547-549 Japanese Patent No. 2999741 (see claim 1) Japanese Patent No. 3010226 (refer to claim 1) Japanese Patent No. 3212018 (see claim 1)

  However, although the method described in Patent Document 1 described above could prevent pulverization of the negative electrode active material, the conductivity of the negative electrode active material of silicon oxide is low, and thus the current collecting property of the negative electrode is not sufficient. There is a fear. In addition, in the methods described in Patent Document 2 and Patent Document 3 described above, although the conductivity of the negative electrode is increased, contact between particles of silicon oxide, metal powder, and the like can be achieved by repeatedly charging and discharging the secondary battery. Alternatively, the contact property between the particles of silicon oxide or metal powder and the current collector is deteriorated, which causes a problem that the cycle characteristics of the secondary battery are deteriorated.

  The present invention has been made in order to solve the above problems, and the first object thereof is a negative electrode for a secondary battery in which the negative electrode active material is less likely to be pulverized and has excellent current collecting properties. It is in providing the manufacturing method. A second object of the present invention is to provide a secondary battery with good cycle characteristics.

  The negative electrode for a secondary battery according to the present invention for achieving the first object is a negative electrode for a secondary battery in which an active material layer is formed on a current collector, wherein the active material layer includes at least silicon oxide and Inorganic composite particles containing one kind of metal contain carbon composite particles coated with carbon.

  According to this invention, since the carbon composite particles have a structure in which the inorganic composite particles are coated with carbon, even if the silicon oxide expands and contracts during charge and discharge of the secondary battery, the carbon composite particles are difficult to be pulverized. Become. Furthermore, since the inorganic composite particles contained in the carbon composite particles contain a metal, the carbon composite particles have high conductivity. Since the negative electrode for secondary batteries of the present invention contains such carbon composite particles in the active material layer, it has a small irreversible capacity and excellent current collection.

  The negative electrode for a secondary battery of the present invention is as follows: (1) The metal is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag , Ta, W, Re, Os, Ir, Pt, Au, or La, (2) When the number of silicon atoms in the inorganic composite particles is 1, the number of metal atoms contained in the inorganic composite particles (3) When the mass of the carbon composite particles is 1, the mass of the carbon contained in the carbon composite particles is 0.05 or more, and (4) the silicon oxide It is preferable that the elemental ratio of oxygen to silicon constituting the product is 0.8 or more and less than 2, and (5) the average particle diameter of the carbon composite particles is 10 μm or less.

  The method for producing a negative electrode for a secondary battery for achieving the first object includes a step of preparing an inorganic composite particle by compounding a silicon oxide and a metal, and coating the inorganic composite particle with carbon to form a carbon. A step of producing composite particles; and a step of forming an active material layer on a current collector using a slurry containing the carbon composite particles.

  According to this invention, the carbon composite particles include a step of preparing inorganic composite particles by compounding silicon oxide and metal, and a step of preparing carbon composite particles by coating the inorganic composite particles with carbon. It is difficult to pulverize and the conductivity is increased. Further, since the method includes a step of forming an active material layer on the current collector using a slurry containing carbon composite particles, an active material layer having carbon composite particles that are difficult to be pulverized and have high conductivity is formed on the current collector. Structure. As a result, the obtained negative electrode for a secondary battery has a small irreversible capacity and an excellent current collecting property.

  The method for producing a negative electrode for a secondary battery according to the present invention is characterized in that, in the production method according to the present invention, the composite of silicon oxide and metal is performed using a pressure contact method, a sputtering method, or a vacuum evaporation method. To do.

  The method for producing a negative electrode for a secondary battery of the present invention is characterized in that, in the production method of the present invention, the inorganic composite particles are coated with carbon using a CVD method or a pressure contact method.

  According to this invention, since the coating of the inorganic composite particles with carbon is performed using the CVD method or the pressure contact method, the inorganic composite particles and the carbon are combined, and the inorganic composite particles and the carbon are separated from each other. It becomes difficult to do. As a result, the pulverization of the carbon composite particles can be suppressed.

  In order to achieve the second object, the secondary battery of the present invention includes a positive electrode containing a lithium-containing compound capable of electrochemically extracting lithium ions and an active material layer capable of inserting and extracting lithium ions. In a secondary battery having a negative electrode formed on a body and a lithium ion conductive non-aqueous electrolyte or polymer electrolyte, the active material layer is an inorganic composite containing silicon oxide and at least one metal It is characterized by containing carbon composite particles in which the particles are coated with carbon.

  According to this invention, the active material layer contains carbon composite particles in which inorganic composite particles containing silicon oxide and at least one metal are coated with carbon, and the active material layer is disposed on the current collector. Since the formed negative electrode for a secondary battery is used, the carbon composite particles are hardly pulverized even if the secondary battery is repeatedly charged and discharged. As a result, the secondary battery of the present invention is excellent in cycle characteristics because the high current collecting property of the secondary battery negative electrode is maintained even after repeated charge and discharge.

  The negative electrode for a secondary battery and the negative electrode for a secondary battery obtained by the method for producing the same according to the present invention have a small irreversible capacity because it is difficult for the negative electrode self-active material to be pulverized. Furthermore, since the negative electrode for secondary batteries obtained by the secondary battery negative electrode and the method for producing the same according to the present invention has high conductivity of the negative electrode self-active material, it is excellent in current collection. In addition, the secondary battery of the present invention is excellent in cycle characteristics because the high current collecting property of the secondary battery negative electrode is maintained even after repeated charge and discharge.

  Below, the negative electrode for secondary batteries of this invention, its manufacturing method, and the secondary battery using the negative electrode for secondary batteries are demonstrated in detail.

<Anode for secondary battery>
The negative electrode for a secondary battery of the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged cross-sectional view of a negative electrode for a secondary battery according to the present invention. As shown in FIG. 1, the negative electrode for a secondary battery of the present invention comprises an active material layer 6 and a current collector 8, and the active material layer 6 contains carbon composite particles 1, a conductivity-imparting agent and a binder. To do. When a secondary battery is produced using the negative electrode for a secondary battery of the present invention, electrons are exchanged by the electrolyte solution 7 filling the gaps in the active material layer.

  In the carbon composite particle 1, the inorganic composite particle 3 and the carbon 2 are combined (refers to partial or total fusion or partial or total vapor deposition), and the inorganic composite particle 3 is carbon. 2 is a structure covered with 2. Specifically, either a structure in which the inorganic composite particles 3 are present in a carbon matrix as shown in FIG. 2 or a structure having a layer made of carbon on the surface of the inorganic composite particles 3 as shown in FIG. be able to. The particle size of the carbon composite particles 1 is preferably 10 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Since the resistance per particle depends on the size of the particle, the intraparticle resistance of the carbon composite particle 1 can be reduced by using such a particle size. In addition, in this application, the particle size uses the value measured, for example with the particle size distribution meter based on JISZ8901.

  The carbon 2 has an effect of suppressing the pulverization of the inorganic composite particles 3 by covering the inorganic composite particles 3 and an effect of improving the conductivity of the negative electrode for secondary batteries. As the carbon 2, graphite, carbon having a layer structure like graphite, amorphous carbon, hard carbon, diamond-like carbon, carbon fiber, or the like is used. The ratio of the carbon 2 contained in the carbon composite particles 1 is preferably such that the mass of the carbon 2 is 0.05 or more and 10 or less when the mass of the inorganic composite particles 3 is 1. By setting it as such a ratio, pulverization of the carbon composite particle 1 can be suppressed and the electrical conductivity of the carbon composite particle 1 can be raised.

  The inorganic composite particle 3 is a particle in which a metal and a silicon oxide are combined, and has a structure in which the metal 5 is coated with the silicon oxide 4 as shown in FIGS. 4 and 5, and the silicon oxide 4 is the metal 5. 6 or a structure in which the silicon oxide 4 and the metal 5 are partially fused as shown in FIG. Regardless of the structure, it is desirable that the silicon oxide 4 and the metal 5 are uniformly distributed in the inorganic composite particles 3. The structure of the inorganic composite particles 3 is a crystal structure or an amorphous structure, and an amorphous structure is particularly preferable. Thus, since the inorganic composite particle 3 is a composite of metal and silicon oxide, the carbon composite particle 1 can be made difficult to be pulverized.

  The silicon oxide 4 is a high-capacity active material that absorbs and releases lithium ions. As the silicon oxide 4, an amorphous silicon oxide represented by SiOx (0.8 ≦ x <2) is preferably used. When the elemental ratio of oxygen constituting silicon oxide 4 to silicon is less than 0.8, the structure of silicon oxide 4 may be destroyed when lithium ions are occluded and released because a crystal structure may be included. There is. When the element ratio of oxygen constituting silicon oxide 4 to silicon is 2 or more, the resistance of silicon oxide 4 may increase.

The metal 5 has an effect of improving the electrical conductivity of the negative electrode for a secondary battery, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, It is a metal or alloy composed of one or more elements selected from the elements Pd, Ag, Ta, W, Re, Os, Ir, Pt, Au, and La. Examples of the alloy include FeSi, TiSi ₂ and CoSi. Of these elements, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ag, Ta, W, Pt or Au are preferable. Further, the number of atoms of the metal 5 contained in the inorganic composite particles 3 is preferably 0.05 or more and 2 or less when the number of silicon atoms in the inorganic composite particles 3 is 1. By setting it as such a ratio, the electrical conductivity of the negative electrode for secondary batteries can be raised.

  The conductivity-imparting agent can be used without particular limitation as long as it is an electron conductive material that does not cause a chemical change when the secondary battery using the negative electrode for a secondary battery of the present invention is used. For example, from conductive materials such as natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, polyphenylene derivative, polyacetylene, etc. One type or two or more types of conductive materials selected can be used. The addition amount of the conductivity-imparting agent to the active material layer 6 is, for example, about 0.01 to 50 wt%, preferably about 0.4 to 10 wt% with respect to the carbon composite particles 1 described above.

  As binders, polyacrylic acid, carboxymethylcellulose, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, starch, diacetylcellulose, hydroxypropylcellulose, polyvinylchloride, polyvinylpyrrolidone, polyethylene, polypropylene, styrene butadiene rubber (SBR) , Ethylene propylene rubber (EPDM), sulfonated ethylene propylene rubber (sulfonated EPDM), fluorine rubber, polybutadiene and polyethylene oxide, among which polyacrylic acid, carboxymethylcellulose, polytetrafluoroethylene, polyvinylidene fluoride (PVDF) is preferred.

  The active material layer 6 is formed on the current collector 8 and contains the carbon composite particles 1, a conductivity-imparting agent, and a binder. The volume filling factor of the active material layer 6 is preferably 35 to 75%. The volume filling factor of the active material layer 6 is a ratio of the active material layer 6 to the volume of the active material layer 6 including voids. For example, the thickness and weight of the electrode can be measured and calculated from the values, or can be measured by the immersion method. When the active material layer 6 is used as a secondary battery while maintaining the contact between the carbon composite particles 1 and the carbon composite particles 1 and the current collector 8 by setting the volume filling factor of the active material layer 6 to 35 to 75%. Therefore, the current collecting property of the negative electrode for the secondary battery is improved.

  The current collector 8 is for taking out electrons to the outside of the secondary battery during charging / discharging of the secondary battery, or for taking in electrons into the secondary battery from the outside. Usually, a conductive metal foil is used. Used. Examples of the material of the metal foil include aluminum, copper, stainless steel, gold, tungsten, and molybdenum. The current collector 8 has a thickness of 5 to 30 μm.

  Charging / discharging of the secondary battery is performed by inserting lithium ions into the silicon oxide 4 or releasing lithium ions from the silicon oxide 4. Since the silicon oxide 4 expands and contracts when such lithium ions are occluded and released, the particles containing the silicon oxide 4 are easily pulverized. Thus, when the particle | grains containing the silicon oxide 4 are pulverized, the active site which reacts with electrolyte solution and forms a passive film increases. Since electrons are consumed to form this passive film, the discharge capacity decreases with respect to the charge capacity, and the irreversible capacity increases.

  However, the negative electrode for a secondary battery according to the present invention has a structure in which the carbon composite particles 1 are coated with the inorganic composite particles 3 with the carbon 2, and the inorganic composite particles 3 are combined with the silicon oxide 4 and the metal 5 ( (This is the same as the following.) The silicon oxide 4 expands and contracts when lithium ions are occluded and released. Even if it occurs, the carbon composite particles 1 are not easily pulverized. Furthermore, since the inorganic composite particle 3 contained in the carbon composite particle 1 contains the metal 5, the carbon composite particle 1 has high electrical conductivity. Therefore, since the negative electrode for secondary batteries of the present invention contains such carbon composite particles in the active material layer, the irreversible capacity is small and the current collecting property is excellent.

<Method for producing negative electrode for secondary battery>
A negative electrode for a secondary battery according to the present invention includes a step of preparing inorganic composite particles by compounding a silicon oxide and a metal, a step of preparing carbon composite particles by coating the inorganic composite particles with carbon, and a carbon composite particle And applying a slurry containing the material on a current collector and drying to form an active material layer. Below, each process is demonstrated.

The process of producing inorganic composite particles by compounding silicon oxide and metal:
Since inorganic composite particles are produced by combining silicon oxide and metal, the carbon composite particles have a structure that is difficult to be pulverized.

  As a method for compounding the silicon oxide and the metal, a pressure welding method, a sputtering method, or a vacuum deposition method is preferably exemplified.

  The pressure welding method refers to a method of joining by applying pressure mechanically. Examples of the pressure welding method include a mechano-fusion method and a mechanical milling method. The mechanical milling method is a method of mechanically repeating pulverization and pressure contact using a pulverizer or the like. Examples of the pulverizer include a ball mill, a jet mill, and a mortar. These pulverizers include silicon oxide and metal. Can be pulverized and mixed to form fine particles, and pressed to form a composite. The mechano-fusion method is a method in which shearing force is applied to particles and energy is used at that time. Metal can be fused to the surface of silicon oxide, or silicon oxide can be fused to the surface of metal. Further, heat treatment may be performed after the pressure welding method.

  In the case of using the sputtering method, a film or a block is produced using silicon oxide and metal as targets. At this time, the silicon oxide and the metal may be the target at the same time, or may be the target alternately.

  In the case of using a vacuum deposition method, silicon oxide and metal are heated and evaporated to produce a film or block. At this time, the silicon oxide and the metal may be heated and evaporated at the same time, or may be alternately heated and evaporated.

  Inorganic composite particles can be produced by pulverizing the membrane or block thus obtained with, for example, the above-described pulverizer.

  Further, in addition to the pressure welding method, the sputtering method, and the vacuum deposition method, a CVD method or a plating method may be used, and inorganic composite particles may be produced by combining these methods. For example, a metal is formed by a plating method, a silicon oxide film is formed on the formed metal by a vacuum deposition method, a sputtering method, or a CVD method, and a film made of metal and a film made of silicon oxide are formed. By laminating, a film or a block can be produced, and this can be pulverized by, for example, the above-described pulverizer to produce inorganic composite particles.

A process for producing carbon composite particles by coating inorganic composite particles with carbon:
Since the carbon composite particles are produced by coating the inorganic composite particles with carbon, the carbon composite particles have a structure in which pulverization hardly occurs. Examples of a method for coating the inorganic composite particles with carbon include a CVD method and a pressure welding method. Heat treatment may be performed after the CVD method or the pressure contact method is performed. By using such a method, the inorganic composite particles and the carbon are combined, and the inorganic composite particles and the carbon are difficult to separate from each other. Therefore, the fine particles of the carbon composite particles are reduced during charging and discharging of the secondary battery. It is suppressed.

  When using the CVD method, carbon is chemically vapor-deposited on the inorganic composite particles to form a film made of carbon on the inorganic composite particles.

  When using the pressure welding method, the above-described mechano-fusion method, mechanical milling method, or the like can be used. In the case of using the mechanical milling method, inorganic composite particles and carbon can be pulverized to form fine particles, mixed and pressed to form a composite. When the mechanofusion method is used, carbon can be fused to the surface of the inorganic composite particles. Further, heat treatment may be performed after the pressure welding method.

A step of applying a slurry containing carbon composite particles onto a current collector and drying to form an active material layer:
The above-described carbon composite particles and carbon, and a conductivity-imparting agent and a binder are mixed and kneaded to prepare a slurry. The slurry is applied onto a current collector and dried, and then pressed so that the volume filling factor of the active material layer is in the above-described range to obtain a negative electrode for a secondary battery. As a method for applying the slurry onto the current collector, a known method such as a doctor blade method or spray coating can be used. As a method of drying the slurry, known methods such as vacuum drying and heat drying can be used. As a method of pressing the active material layer, a method of pressing using an apparatus such as a roller press can be used.

  As described above, according to the method for manufacturing a negative electrode for a secondary battery of the present invention, the carbon composite particles are prepared by coating inorganic composite particles with carbon, and the inorganic composite particles are formed by combining silicon oxide and metal. Therefore, even if volume expansion occurs during occlusion and release of lithium ions, the carbon composite particles are difficult to be pulverized and have high conductivity. For this reason, the negative electrode for secondary batteries which has such a carbon composite particle in an active material layer has a small irreversible capacity, and is excellent in current collection.

<Secondary battery>
The secondary battery of the present invention is produced by winding a positive electrode and the above-described negative electrode for a secondary battery in a dry air or inert gas atmosphere via a separator, and then enclosing it in a container. Is done.

A positive electrode contains the lithium containing compound which can take out lithium ion electrochemically. As such lithium-containing compound, LixMO ₂ (where M represents at least one transition metal.) Composite oxide is, for _{example, LixCoO 2, LixNiO 2, LixMn} 2 O 4, LixMnO 3, LixNiyC 1-y O ₂ etc. are mentioned. An aluminum foil obtained by dispersing and kneading such a lithium-containing compound, a conductive material such as carbon black, and a binder such as polyvinylidene fluoride (PVDF) with a solvent such as N-methyl-2-pyrrolidone (NMP) The thing apply | coated on the collectors 5, such as, can be used.

  The electrolytic solution is a lithium ion conductive non-aqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate ( EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-ethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylform Muamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- One or more solvents selected from aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, and N-methylpyrrolidone are used in combination. can do.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl and imides. Further, a polymer electrolyte may be used instead of the electrolytic solution.

  As the separator, a polyolefin film such as polypropylene and polyethylene, or a porous film such as a fluororesin can be used.

  Examples of the shape of the container include a bottomed rectangular tube shape and a bag shape in addition to the above-described bottomed cylindrical shape.

  Examples of the material of the container include a metal can and a film material. The metal can is formed from a metal plate made of aluminum, iron, stainless steel, nickel, or the like. Examples of the film material include a metal film, a resin film such as a thermoplastic resin, and a composite film including a metal layer and a resin layer. The metal film can be formed from, for example, aluminum, iron, stainless steel, nickel, or the like.

  Examples of the composite film including a metal layer and a resin layer include a laminate film having a configuration in which one or both surfaces of a flexible metal layer are covered with a resin. This laminate film is preferably used because it is lightweight and has high strength and can prevent moisture from entering from the outside. A resin layer is formed from 1 type, or 2 or more types of resin. When sealing a container produced using a composite film, the resin layer is preferably a thermoplastic resin because it is often done by heat sealing or the like. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene. The melting point of the thermoplastic resin is preferably 120 ° C. or higher, more preferably 140 ° C. to 250 ° C. In particular, it is preferable to use polypropylene having a melting point of 150 ° C. or higher because the sealing strength of the heat seal is increased. The metal layer which comprises a composite film can be formed from 1 type, or 2 or more types of metals chosen from aluminum, iron, stainless steel, nickel, etc., for example. Among these, aluminum that can prevent water from entering the secondary battery is preferable.

  The thickness of the above-described film material and metal plate is preferably 0.05 mm or more and 0.5 mm or less. When the thickness of the film material and the metal plate is less than 0.05 mm, the strength of the container is lowered, and when the thickness of the film material and the metal plate exceeds 0.5 mm, the improvement of the energy density of the secondary battery is hindered. . Thereby, thinning and weight reduction of a battery are realizable, ensuring the intensity | strength of a container.

  In the secondary battery of the present invention, the active material layer contains carbon composite particles in which inorganic composite particles containing silicon oxide and at least one metal are coated with carbon, and the active material layer is a current collector. Since the secondary battery negative electrode formed above is used, the carbon composite particles are not easily pulverized even after repeated charge and discharge, and the high current collecting property of the secondary battery negative electrode can be maintained. As a result, the secondary battery of the present invention has excellent cycle characteristics because the amount of occlusion and release of lithium ions is maintained even after repeated charge and discharge.

  Hereinafter, the present invention will be described in detail with reference to examples.

Example 1
Using silicon oxide with an average particle size of 15 μm (oxygen: silicon = 1: 1) and Fe particles with an average particle size of 1 μm as the metal, the atomic ratio of silicon to metal in the silicon oxide is 3: 1. The mixture was compounded as described above, and composite treatment was performed for 100 hours using a planetary ball mill apparatus. At this time, the ball mill container and the ball having a diameter of 10 mm in the planetary ball mill apparatus were made of zirconia. The compounding treatment and compounding treatment of silicon oxide and metal were performed in an Ar atmosphere. Next, heat treatment was performed at 1100 ° C. for 1 hour in an Ar atmosphere to obtain inorganic composite particles. Then, carbon coating was performed by CVD using methane gas to form a layer made of carbon on the inorganic composite particles, followed by classification to obtain carbon composite particles having a particle size of 10 μm. The mass ratio of the inorganic composite particles to carbon in the carbon composite particles was inorganic composite particles: carbon = 4: 1.

  Next, carbon composite particles, those obtained by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone, and a conductive agent, carbon composite particles: polyvinylidene fluoride (PVDF): conductive agent = 85: 10: 5 mass A slurry was formed by kneading to a ratio. At this time, ketjen black was used as a conductivity-imparting agent. This slurry is applied onto a current collector made of Cu foil having a thickness of 10 μm to form an active material layer, dried at 120 ° C. for 1 hour, and then the roller material presses until the volume filling rate of the active material layer reaches 60%. The negative electrode for secondary batteries was obtained by pressure molding.

Next, a lithium-containing compound, a conductivity-imparting agent, and a material obtained by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone, a mass of lithium-containing compound: conductivity-imparting agent: polyvinylidene fluoride (PVDF) = 90: 6: 4 The resulting mixture was mixed to form a slurry. At this time, LiCoO ₂ powder having an average particle diameter of 10 μm was used as the lithium-containing compound, and graphite was used as the conductivity-imparting agent. The slurry was sufficiently kneaded and then applied to an Al foil as a current collector having a thickness of 20 μm. After drying this at 120 ° C. for 1 hour, the electrode was pressure-molded with a roller press to obtain a positive electrode.

The secondary battery negative electrode and positive electrode thus produced were wound and sealed in a laminate container to prepare a secondary battery. The electrolytic solution used was a solution of LiPF ₆ dissolved in a 3: 7 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) so as to be 1 mol / liter.

  Next, a charge / discharge cycle test is performed in which the secondary battery is charged at a charge current of 1A and a charge end voltage of 4.2V, and discharged at a discharge current of 1A and a discharge end voltage of 2.5V. Evaluated. Further, impedance measurement was performed by an alternating current impedance method after 100 cycles.

(Example 2)
In Example 1, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 1 except that Ni particles having an average particle diameter of 1 μm were used as the metal.

(Example 3)
In Example 1, a secondary battery was produced in the same manner as in Example 1 except that Ti particles having an average particle diameter of 1 μm were used as the metal and the mass ratio of the inorganic composite particles to carbon was set to 1: 5. A charge / discharge cycle test and impedance measurement were performed.

Example 4
In Example 1, the same method as in Example 1 was used, except that W particles having an average particle diameter of 1 μm were used as the metal and the atomic ratio of silicon to metal in the silicon oxide was 1: 0.05. Then, a secondary battery was manufactured, a charge / discharge cycle test, and an impedance measurement were performed.

(Example 5)
In Example 1, Co particles having an average particle diameter of 1 μm were used as the metal, and the atomic ratio of silicon to metal in the silicon oxide was changed to 1: 1. Preparation of a secondary battery, a charge / discharge cycle test, and impedance measurement were performed.

( Reference Example 1 )
In Example 1, a secondary battery was produced in the same manner as in Example 1, except that V particles having an average particle diameter of 1 μm were used as the metal and the mass ratio of the inorganic composite particles to carbon was 1:10. A charge / discharge cycle test and impedance measurement were performed.

(Example 7)
In Example 1, the same method as in Example 1 was used except that Mo particles having an average particle diameter of 1 μm were used as the metal and silicon oxide having an element ratio of oxygen to silicon of 0.8 was used as the silicon oxide. Then, a secondary battery was manufactured, a charge / discharge cycle test, and an impedance measurement were performed.

(Example 8)
In Example 1, the same method as in Example 1 was used, except that Cr particles having an average particle diameter of 1 μm were used as the metal, and silicon oxide having an element ratio of oxygen to silicon of 1.9 was used as the silicon oxide. Then, a secondary battery was manufactured, a charge / discharge cycle test, and an impedance measurement were performed.

Example 9
In Example 1, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 1 except that Mn particles having an average particle diameter of 1 μm were used as the metal.

(Example 10)
In Example 1, a secondary battery was produced in the same manner as in Example 1, except that Ta particles having an average particle diameter of 1 μm were used as the metal, and the mass ratio of the inorganic composite particles and carbon was 1: 3. A charge / discharge cycle test and impedance measurement were performed.

(Example 11)
In Example 1, a secondary battery was fabricated and charged in the same manner as in Example 1 except that Nb particles having an average particle diameter of 1 μm were used as the metal and the average particle diameter of the carbon composite particles was changed to 3 μm by classification. A discharge cycle test and impedance measurement were performed.

(Example 12)
In Example 1, two Pd particles having an average particle diameter of 1 μm were used as the metal, and the atomic ratio of silicon to metal in the silicon oxide was set to 1: 2. Preparation of a secondary battery, a charge / discharge cycle test, and impedance measurement were performed.

(Example 13)
In Example 1, except that Au particles having an average particle diameter of 1 μm were used as the metal and carbon coating was performed by a mechanofusion method instead of the CVD method, the secondary battery was manufactured in the same manner as in Example 1. Fabrication, charge / discharge cycle test and impedance measurement were performed.

(Example 14)
In Example 1, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 1 except that Ag particles having an average particle diameter of 1 μm were used as the metal.

(Example 15)
In Example 1, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 1 except that Cu particles having an average particle diameter of 1 μm were used as the metal.

(Example 16)
In Example 1, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 1 except that Pt particles having an average particle diameter of 1 μm were used as the metal.

(Example 17)
In Example 1, a secondary battery was prepared and a charge / discharge cycle test was performed in the same manner as in Example 1 except that the carbon composite was prepared so that the mass ratio of inorganic composite particles to carbon was 19: 1. And impedance measurement.

(Example 18)
In Example 1, a secondary battery was prepared and a charge / discharge cycle test was performed in the same manner as in Example 1 except that the carbon composite was prepared so that the mass ratio of the inorganic composite particles to carbon was 5: 1. And impedance measurement.

(Example 19)
In Example 1, a secondary battery was prepared and a charge / discharge cycle test was performed in the same manner as in Example 1 except that the carbon composite was prepared so that the mass ratio of the inorganic composite particles to carbon was 1: 1. And impedance measurement.

(Example 20)
Silicon oxide (oxygen: silicon = 1: 1) having an average particle diameter of 5 μm was used as the silicon oxide, and Fe particles having an average particle diameter of 1 μm were used as the metal. The silicon oxide particles and the metal were blended so that the ratio of the number of Si and Fe atoms was 4: 1, and this was subjected to a composite treatment for 12 hours using a planetary ball mill apparatus to obtain inorganic composite particles. . At this time, the ball mill container and the ball having a diameter of 10 mm in the planetary ball mill apparatus were made of zirconia, and the compounding process and the compounding process were performed in an Ar atmosphere.

  Next, inorganic composite particles and carbon are blended at a mass ratio of inorganic composite particles: carbon = 5: 1, and this is subjected to a composite treatment for 5 hours in the same planetary ball mill apparatus as described above, and then in an Ar atmosphere. Heat treatment was performed at 1100 ° C. for 1 hour to obtain carbon composite particles. At this time, artificial graphite was used as carbon, and the compounding process and the compounding process were performed in an Ar atmosphere.

  Next, the carbon composite particles, those obtained by dissolving polyvinylidene fluoride (PVDF) in N-methylpyrrolidone, and a conductivity-imparting agent, carbon composite particles: polyvinylidene fluoride (PVDF): conductivity-imparting agent = 85: 10: 5 The slurry was kneaded so as to have a mass ratio. At this time, ketjen black was used as a conductivity-imparting agent. This slurry was applied on a current collector made of Cu foil having a thickness of 20 μm to form an active material layer. The active material layer was dried at 120 ° C. for 1 hour, and then pressure-molded by a roller press until the volume filling factor of the active material layer became 60%, to obtain a negative electrode for a secondary battery.

The negative electrode and a positive electrode produced in the same manner as in Example 1 were enclosed in a square can to produce a secondary battery. The electrolytic solution used was a solution of LiPF ₆ dissolved in a 3: 7 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) so as to be 1 mol / liter.

  A charge / discharge cycle test was performed in which the battery was charged at a charge current of 0.9 A and a charge end voltage of 4.2 V, and discharged at a discharge current of 0.9 A and a discharge end voltage of 2.7 V. Further, impedance measurement was performed by an alternating current impedance method after 100 cycles.

(Example 21)
In Example 20, a secondary battery was produced, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 20, except that the mass ratio of the inorganic composite particles to carbon was 1: 2.

(Example 22)
In Example 20, a secondary battery was fabricated, a charge / discharge cycle test, and impedance measurement were performed in the same manner as in Example 20 except that the mass ratio of the inorganic composite particles to carbon was 1: 3.

(Comparative Example 1)
In Example 1, in place of the inorganic composite particles, silicon oxide particles to which no metal was added were used, and in the same manner as in Example 1, production of a secondary battery, charge / discharge cycle test and impedance Measurements were made.

(Comparative Example 2)
In Example 1, the secondary battery was produced in the same manner as in Example 1 except that the inorganic composite particles were used as they were in the active material layer without carbon coating on the inorganic composite particles to produce a secondary battery negative electrode. , Charge / discharge cycle test and impedance measurement.

(result)
Table 1 shows the results of the cycle tests and impedance measurements of Examples 1 to 5 , 7 to 16 , Reference Example 1 and Comparative Examples 1 and 2. At this time, the capacity retention rate after 100 cycles was calculated by a calculation formula of (discharge capacity in each cycle) / (discharge capacity in the fifth cycle). The result of impedance measurement is shown as a result of dividing the interface resistance R after 100 cycles by the value of the interface resistance R of Comparative Example 1. The interface resistance R was a real axis value when the value of -X of the imaginary axis was the maximum value when a Cole-Cole plot was produced at a frequency from 20 KHz to 50 MHz (shown in FIG. 8).

In the secondary batteries of Examples 1 to 5, 7 to 22, the value obtained by dividing the value of the interface resistance R by the value of the interface resistance R of Comparative Example 1 is 0.2 to 0.45, and Comparative Example 1 and Comparative Example The value was lower than that of No. 2 secondary battery. In addition, the secondary batteries of Examples 1 to 5, 7 to 22 have a capacity retention rate after 100 cycles higher than that of Comparative Examples 1 and 2 by 67% or more, and can provide a battery with good cycle characteristics. I was able to prove.

It is a fragmentary sectional view which shows an example of the negative electrode for secondary batteries of this invention. It is an expanded sectional view which shows an example of the carbon composite particle which comprises the negative electrode for secondary batteries of this invention. It is an expanded sectional view which shows another example of the carbon composite particle which comprises the negative electrode for secondary batteries of this invention. It is an expanded sectional view which shows an example of the inorganic composite particle which comprises the negative electrode for secondary batteries of this invention. It is an expanded sectional view which shows another example of the inorganic composite particle which comprises the negative electrode for secondary batteries of this invention. It is an expanded sectional view which shows another example of the inorganic composite particle which comprises the negative electrode for secondary batteries of this invention. It is a colleole plot of the secondary battery of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbon composite particle 2 Carbon 3 Inorganic composite particle 4 Silicon oxide 5 Metal 6 Active material layer 7 Electrolyte solution 8 Current collector

Claims (8)

In the negative electrode for a secondary battery in which an active material layer is formed on a current collector, the active material layer is a carbon composite particle in which inorganic composite particles containing silicon oxide and at least one metal are coated with carbon. And the metal is Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, Re, Os, Ir, Pt, the negative electrode for secondary batteries, characterized Au or La der Rukoto. Wherein when the inorganic composite 1 the number of atoms of silicon in the particles, the secondary battery according to claim 1 in which the number of atoms of metal contained in the inorganic composite particles are characterized in that 0.05 to 2 Negative electrode. When set to 1 the mass of the carbon composite particles, a negative electrode for secondary battery according to claim 1 or 2, characterized in that the mass of the carbon contained in the carbon composite particles is 0.05 to 10 . The elemental ratio of silicon of oxygen included in the silicon oxide, a negative electrode for a secondary battery according to any one of claims 1 to 3, characterized in that less than 2 0.8 or more. Compounding silicon oxide and metal to produce inorganic composite particles, coating the inorganic composite particles with carbon to produce carbon composite particles, and collecting current using a slurry containing the carbon composite particles It is seen containing a step of forming an active material layer on the body, wherein the metal is, Ti, Cr, Mn, Fe , Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, A method for producing a negative electrode for a secondary battery, which is Ag, Ta, W, Re, Os, Ir, Pt, Au, or La . 6. The method for producing a negative electrode for a secondary battery according to claim 5 , wherein the composite of the silicon oxide and the metal is performed using a pressure welding method, a sputtering method, or a vacuum evaporation method. The method for producing a negative electrode for a secondary battery according to claim 5 or 6 , wherein the coating of the inorganic composite particles with carbon is performed using a CVD method or a pressure contact method. A positive electrode containing a lithium-containing compound capable of electrochemically extracting lithium ions, a negative electrode in which an active material layer capable of inserting and extracting lithium ions is formed on a current collector, and lithium ion conductive non-aqueous electrolysis In a secondary battery having a liquid or polymer electrolyte,
The active material layer includes carbon composite particles in which inorganic composite particles including silicon oxide and at least one metal are coated with carbon, and the metal includes Ti, Cr, Mn, Fe, Co, Ni , Cu, Zn, Y, Zr , Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, Re, Os, Ir, Pt, secondary batteries, characterized Au or La der Rukoto.

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