JP2005141992A - Negative electrode and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode capable of reducing stress due to expansion and constriction caused by charge and discharge of a negative electrode active material layer to improve a cycle characteristic; and to provide a battery using it. <P>SOLUTION: The negative electrode active material layer 12 contains at least one kind among a group comprising a single body, an alloy and a compound of an element, for instance, Si or Ge capable of forming an alloy with Li. A negative electrode collector 11 contains a material having superelasticity or a shape-memory effect, for instance, a Ni-Ti alloy or an alloy containing Ni, Ti and other element. Ten-point average roughness Rz of the negative electrode collector 11 is preferably 1.2 μm or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a negative electrode in which a negative electrode active material layer is provided on a negative electrode current collector, and a battery using the same.

  2. Description of the Related Art In recent years, as mobile devices have higher performance and more functions, there is a strong demand for higher capacities of secondary batteries that are power sources thereof. There is a lithium secondary battery as a secondary battery that meets this requirement. However, when lithium cobaltate is used for the positive electrode and graphite is used for the negative electrode, which is a typical form of the present lithium secondary battery, the battery capacity is in a saturated state, and it is extremely difficult to increase the capacity significantly. . Therefore, the use of metallic lithium (Li) for the negative electrode has been studied for a long time, but in order to put this negative electrode into practical use, it is necessary to improve the precipitation dissolution efficiency of lithium and control the dendrite-like precipitation form. is there.

  On the other hand, recently, a high capacity negative electrode using silicon (Si), germanium (Ge), tin (Sn), or the like has been actively studied. However, when these negative electrodes are repeatedly charged and discharged, they are pulverized and refined by vigorous expansion and contraction of the active material, current collection is reduced, or decomposition reaction of the electrolyte is promoted due to an increase in surface area, The cycle characteristics were extremely poor. Therefore, negative electrodes in which an active material layer is formed on a current collector by a vapor phase method, a liquid phase method, a sintering method, or the like have been studied (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). According to this, miniaturization can be suppressed as compared with a conventional coated negative electrode coated with a slurry containing a particulate active material and a binder, and the current collector and the active material layer are integrated. Therefore, the electron conductivity in the negative electrode is extremely good, and high performance is expected in terms of capacity and cycle life. In addition, since it is possible to reduce or eliminate the conductive material, binder, voids, and the like that existed in the conventional negative electrode, the negative electrode can be made essentially thin.

  However, even with this negative electrode, there are problems such as separation of the current collector and the active material layer due to expansion and contraction of the active material due to charge and discharge, or wrinkles in the current collector, and sufficient cycle characteristics are obtained. Couldn't get.

As a method for solving these problems, for example, an intermediate layer may be formed between the current collector and the active material layer to improve the adhesion between the current collector and the active material layer. So far, for example, the current collector is made of a metal or alloy having high mechanical strength, and an intermediate layer such as copper (Cu) that is alloyed with the active material is formed between the current collector and the active material layer. A negative electrode (see, for example, Patent Document 4) or a negative electrode in which an intermediate layer containing molybdenum (Mo) or tungsten (W) is formed between a current collector and an active material layer (see, for example, Patent Document 5). Etc. have been reported.
JP-A-8-50922 Japanese Patent No. 2948205 Japanese Patent Laid-Open No. 11-135115 JP 2002-83594 A JP 2002-373644 A

  However, as described in Patent Document 1, for example, when an intermediate layer such as copper alloyed with the active material is formed between the current collector and the active material layer, the current collector and the active material layer Although the adhesion is improved, there is a problem that the effect is small as compared with the conventional negative electrode in which the current collector is made of copper. Further, as described in Patent Document 2, for example, when an intermediate layer containing molybdenum or tungsten is provided, it is possible to suppress excessive diffusion of the constituent elements of the current collector into the active material layer. However, when such a hard metal layer is formed as an intermediate layer, there is a problem that flexibility is often lost at the bonding surface between the current collector and the active material layer.

  Furthermore, in Patent Document 1, the tensile strength of the current collector is also mentioned. However, as mechanical properties required for the current collector, flexibility such as elastic deformability is important in addition to strength. It was difficult to improve the cycle characteristics only by improving the tensile strength.

  The present invention has been made in view of such problems, and an object thereof is to relieve stress due to expansion and contraction associated with charge and discharge of the negative electrode active material layer, and to improve cycle characteristics, and a battery using the same. Is to provide.

  A first negative electrode according to the present invention includes a negative electrode current collector provided with a negative electrode active material layer, and the negative electrode current collector includes a material having superelasticity or a shape memory effect.

  The second negative electrode according to the present invention has a negative electrode current collector provided with a negative electrode active material layer, and the negative electrode current collector contains nickel (Ni) and titanium (Ti).

  A first battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode. The negative electrode is provided on a negative electrode current collector containing a material having a superelasticity or a shape memory effect, and the negative electrode current collector. And a negative electrode active material layer.

  A second battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes a negative electrode current collector containing nickel and titanium, and a negative electrode active material layer provided on the negative electrode current collector. It is equipped with.

  According to the first negative electrode and the first battery of the present invention, since the negative electrode current collector includes a material having superelasticity or shape memory effect, stress due to expansion / contraction of the negative electrode active material layer is relieved. be able to. Therefore, destruction of the negative electrode can be suppressed and cycle characteristics can be improved.

  In particular, if a material that does not form an intermetallic compound with lithium is included as a material having a superelasticity or a shape memory effect, the negative electrode current collector may be structurally destroyed by generating an intermetallic compound with lithium. Can be suppressed, and the cycle characteristics can be further improved.

  According to the second negative electrode and the second battery of the present invention, since the negative electrode current collector contains nickel and titanium, stress due to expansion / contraction of the negative electrode active material layer can be relieved, By generating lithium and the intermetallic compound, it is possible to suppress the structural destruction of the negative electrode current collector. Therefore, destruction of the negative electrode can be suppressed and cycle characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a simplified configuration of a negative electrode 10 according to an embodiment of the present invention. The negative electrode 10 includes, for example, a negative electrode current collector 11 and a negative electrode active material layer 12 provided on the negative electrode current collector 11. The negative electrode active material layer 12 may be formed on both surfaces of the negative electrode current collector 11 or may be formed on one surface.

  The negative electrode current collector 11 includes, for example, a material having superelasticity or a shape memory effect, such as an alloy, at least in part. This is because even if the negative electrode active material layer 12 expands and contracts due to charge and discharge, the stress can be relaxed and peeling of the negative electrode active material layer 12 can be suppressed. Here, the superelasticity is a property that, as defined in “JIS H7001 number 1011”, the deformation caused by the stress-induced martensitic transformation at the time of loading is recovered by the reverse transformation at the time of unloading. The shape memory effect is defined as “JIS H7001 No. 1002”. Even if an alloy having a certain shape is deformed into a different shape in the low temperature phase (martensite) state, the high temperature phase (matrix phase) can be obtained. When heated to a stable temperature, reverse transformation occurs and returns to the shape before deformation.

  In addition, as a material having superelasticity or a shape memory effect, a material that does not form an intermetallic compound with lithium is particularly preferable. When lithium and an intermetallic compound are formed, the negative electrode current collector expands and contracts with charge and discharge, structural breakdown occurs and current collecting performance decreases, and the ability to support the negative electrode active material layer 12 is reduced. This is because the active material layer 12 easily falls off the negative electrode current collector 11. Examples of such a material include an alloy containing nickel and titanium, for example, a nickel-titanium alloy, or copper, niobium (Nb), zirconium (Zr), chromium (Cr), manganese (Mn) in addition to nickel and titanium. , Alloys containing one or more other elements such as iron (Fe) or cobalt (Co). In addition, an alloy containing manganese and copper is also included.

  Among them, an alloy containing nickel and titanium has a good superelasticity or shape memory effect, does not form an intermetallic compound with lithium, and further has excellent corrosion resistance, and in addition, adhesion to the negative electrode active material layer 12. It is preferable because of its excellent properties. In particular, in the case of a nickel-titanium alloy, titanium having a content of 51 atomic% to 48 atomic% with respect to 49 atomic% to 52 atomic% of nickel is preferable, and an alloy containing other elements in addition to nickel and titanium, A titanium atom of 45 atom% to 55 atom% is preferable to nickel atom of 35 atom% to 45 atom%. Therefore, when the negative electrode current collector 11 includes these alloys, the composition ratio of nickel and titanium in the negative electrode current collector 11 is an atomic ratio of titanium 51 to 48 or nickel with respect to nickel 49 to 52. It is preferable that it is titanium 45-55 with respect to 35-45. In the case of an alloy containing other elements in addition to nickel and titanium, copper is preferable as the other elements, and may contain other elements described above in addition to copper. This is because copper can be dissolved in a nickel-titanium alloy in an amount of 30 atomic% or more, is inexpensive, and has good characteristics.

  The negative electrode current collector 11 may be composed of a single layer, but may be composed of a plurality of layers. In that case, a layer containing a material alloyed with the negative electrode active material layer 12 may be provided between the layer containing a material having superelasticity or a shape memory effect and the negative electrode active material layer 12.

  Moreover, the surface roughness in the area | region in which the negative electrode active material layer 12 of the negative electrode collector 11 is formed is 10-point average roughness (Rz) of JIS B0601 appendix 1, and is 0.8 micrometer or more. It is preferably 1.2 μm or more, more preferably 1.2 μm or more and 12.0 μm or less. Since the shape of the crack generated in the negative electrode active material layer 12 can be controlled and the stress due to expansion / contraction of the negative electrode active material layer 12 can be dispersed, cycle characteristics can be improved. is there.

In this case, the negative electrode current collector 11 may have a roughened surface by lapping, for example, or may have a protrusion formed on the surface of the substrate by plating or vapor deposition. The one is preferable because higher effects can be obtained. The material of the protrusion may be the same as or different from that of the base. For example, the material having the above-described superelasticity or shape memory effect may be used, and a metal material such as copper, nickel, titanium, iron, or chromium that does not have such characteristics, or aluminum oxide (Al ₂ O ₃ ) or silicon dioxide An oxide such as (SiO ₂ ) may be used. However, those that do not form an intermetallic compound with lithium are preferred. This is because when lithium and an intermetallic compound are produced, the protrusions expand and contract with charge / discharge, and the negative electrode current collector 11 is broken or the negative electrode active material layer 12 is easily peeled off.

  The negative electrode active material layer 12 includes, for example, at least one selected from the group consisting of simple elements, alloys, and compounds of elements capable of forming an alloy with lithium as a negative electrode active material. Among these, the negative electrode active material preferably includes at least one member selected from the group consisting of silicon, germanium, a single alloy, an alloy, and a compound. In particular, a silicon simple substance, an alloy, or a compound is preferable. These have a large ability to occlude and desorb lithium, and depending on the combination, the energy density of the negative electrode 10 can be made higher than that of conventional graphite. In particular, a simple substance, alloy or compound of silicon has low toxicity, and Because it is cheap.

Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi. ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2) or LiSiO. Examples of germanium compounds include Ge ₃ N ₄ , GeO, GeO ₂ , GeS, GeS ₂ , GeF _{4, and} GeBr ₄ .

  The negative electrode active material layer 12 is preferably formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, for example. It is possible to suppress destruction due to expansion / contraction of the negative electrode active material layer 12 due to charge / discharge, and it is possible to form the negative electrode active material layer 12 on the negative electrode current collector 11 with good adhesion. This is because the electron conductivity in the material layer 12 can be improved. Moreover, it is because a binder, a space | gap, etc. can be reduced or eliminated and the negative electrode 10 can also be thinned. As used herein, “forming an active material layer by a sintering method” means that a layer formed by mixing a powder containing an active material and a binder is heat-treated in a non-oxidizing atmosphere or the like, This means that a denser layer having a higher volume density than before the heat treatment is formed.

  The negative electrode active material layer 12 may also be formed by coating, specifically including a negative electrode active material and, if necessary, a binder such as polyvinylidene fluoride. However, as described above, those formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method are preferred.

  Further, the negative electrode active material layer 12 may be alloyed with the negative electrode current collector 11 at least at a part of the interface with the negative electrode current collector 11 so as not to drop off from the negative electrode current collector 11 due to expansion and contraction. Specifically, the constituent elements of the negative electrode current collector 11 may diffuse into the negative electrode active material layer 12, the constituent elements of the negative electrode active material layer 12 may diffuse into the negative electrode current collector 11, or they may mutually diffuse at the interface. . This alloying may occur simultaneously when the negative electrode active material layer 12 is formed by a vapor phase method, a liquid phase method, or a sintering method, but may also be caused by further heat treatment. Note that in this specification, the above-described element diffusion is also included in one form of alloying.

  This negative electrode 10 can be manufactured as follows, for example.

  First, for example, the negative electrode current collector 11 including a material having superelasticity or a shape memory effect is prepared. At that time, if necessary, the surface may be roughened by lapping or the like, or the protrusion may be formed by vapor deposition or plating.

  Next, the negative electrode active material layer 12 is formed on the negative electrode current collector 11 by, for example, a vapor phase method, a liquid phase method, a sintering method, or a combination of two or more thereof. At that time, at least a part of the interface between the negative electrode current collector 11 and the negative electrode active material layer 12 may be alloyed. In some cases, a vacuum atmosphere or a non-oxidizing atmosphere is used in order to alloy them. You may make it heat-process below.

  Examples of the vapor phase method include a physical deposition method and a chemical deposition method. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD (Chemical Vapor Deposition; Vapor phase growth method) or plasma CVD method. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used.

  Moreover, you may form the negative electrode active material layer 12 by application | coating. Specifically, for example, a negative electrode active material and a binder are mixed to prepare a mixture, and the mixture is dispersed in a dispersion medium such as N-methylpyrrolidone to prepare a mixture slurry. May be applied to the negative electrode current collector 11 and dried, followed by compression molding. However, it is preferable to use a vapor phase method, a liquid phase method, or a sintering method because adhesion between the intermediate layer 13 and the negative electrode active material layer 12 can be improved. Thereby, the negative electrode 10 shown in FIG. 1 is obtained.

  This negative electrode 10 is used for the negative electrode of the following secondary batteries, for example.

  FIG. 2 shows the configuration of the secondary battery. This secondary battery is a so-called coin-type battery, in which the negative electrode 10 accommodated in the outer cup 20 and the positive electrode 40 accommodated in the outer can 30 are stacked via the separator 50. . The peripheral portions of the outer cup 20 and the outer can 30 are sealed by caulking through an insulating gasket 60. The exterior cup 20 and the exterior can 30 are made of, for example, a metal such as stainless steel or aluminum.

  The positive electrode 40 includes, for example, a positive electrode current collector 41 and a positive electrode active material layer 42 provided on the positive electrode current collector 41, and is disposed so that the positive electrode active material layer 42 side faces the intermediate layer 13. Has been. The positive electrode current collector 41 is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 42 includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material such as a carbon material and the like as necessary. A binder such as polyvinylidene fluoride may be included. As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing metal composite oxide represented by the general formula Li _x MIO ₂ is preferable. This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that the capacity of the secondary battery can be further increased. MI is one or more kinds of transition metals, and for example, at least one of cobalt and nickel is preferable. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO _{2 and} LiNiO ₂ .

  The positive electrode 40 is prepared, for example, by mixing a positive electrode active material, a conductive material, and a binder to prepare a mixture, and dispersing the mixture in a dispersion medium such as N-methylpyrrolidone to prepare a mixture slurry. The mixture slurry is applied to a positive electrode current collector 41 made of a metal foil, dried, and then compression molded to form the positive electrode positive electrode active material layer 42.

  The separator 50 separates the negative electrode 10 and the positive electrode 40 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 50 is made of, for example, polyethylene or polypropylene.

  The separator 50 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains, for example, a solvent and a lithium salt that is an electrolyte salt dissolved in the solvent, and may contain an additive as necessary. Examples of the solvent include organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and any one of these or a mixture of two or more thereof may be used.

Examples of the lithium salt include LiPF ₆ , LiCF ₃ SO _{3, and} LiClO ₄ , and any one of these or a mixture of two or more thereof may be used.

  This secondary battery can be manufactured, for example, by laminating the negative electrode 10, the separator 50 impregnated with the electrolyte, and the positive electrode 40, placing them in the outer cup 20 and the outer can 30, and caulking them. it can.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 40 and inserted in the negative electrode 10 through the electrolytic solution. When the discharge is performed, for example, lithium ions are released from the negative electrode 10 and inserted into the positive electrode 40 through the electrolytic solution. At that time, even if the negative electrode active material layer 12 expands and contracts due to charge and discharge, the stress is relieved because the negative electrode current collector 11 contains a material having superelasticity or a shape memory effect. Therefore, cycle characteristics are improved.

  You may use the negative electrode 10 which concerns on this Embodiment for the negative electrode of the following secondary batteries.

  FIG. 3 shows the configuration of the secondary battery. In this secondary battery, the wound electrode body 120 to which the leads 111 and 112 are attached is housed in film-like exterior members 131 and 132, and can be reduced in size, weight, and thickness. Yes.

  The leads 111 and 112 are led out from the inside of the exterior members 131 and 132 to the outside, respectively, for example, in the same direction. The leads 111 and 112 are made of a metal material such as aluminum, copper, nickel, or stainless steel, respectively, and have a thin plate shape or a mesh shape, respectively.

  The exterior members 131 and 132 are made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior members 131 and 132 are disposed, for example, so that the polyethylene film side and the electrode winding body 120 face each other, and the outer edge portions are in close contact with each other by fusion or adhesive. An adhesion film 133 is inserted between the exterior members 131 and 132 and the leads 111 and 112 to prevent intrusion of outside air. The adhesion film 133 is made of a material having adhesion to the leads 111 and 112, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior members 131 and 132 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 6 shows a cross-sectional structure taken along line II of the electrode winding body 120 shown in FIG. The electrode winding body 120 is obtained by laminating and winding the negative electrode 10 and the positive electrode 121 via the separator 122 and the electrolyte layer 123, and the outermost peripheral portion is protected by the protective tape 124.

  The negative electrode 10 has a structure in which a negative electrode active material layer 12 is provided on one surface or both surfaces of a negative electrode current collector 11. The positive electrode 121 also has a structure in which a positive electrode active material layer 121B is provided on one or both surfaces of the positive electrode current collector 121A, and the positive electrode active material layer 121B side is arranged so as to face the negative electrode active material layer 12. Yes. The configurations of the positive electrode current collector 121A, the positive electrode active material layer 121B, and the separator 122 are the same as those of the positive electrode current collector 41, the positive electrode active material layer 42, and the separator 50, respectively.

  The electrolyte layer 123 is configured by a so-called gel electrolyte in which an electrolytic solution is held in a holding body. A gel electrolyte is preferable because it can obtain high ionic conductivity and can prevent battery leakage or swelling at high temperatures. The configuration of the electrolytic solution (that is, the solvent and the electrolyte salt) is the same as that of the coin-type secondary battery shown in FIG. The holding body is made of, for example, a polymer material. An example of the polymer material is polyvinylidene fluoride.

  For example, the secondary battery can be manufactured as follows.

  First, an electrolyte layer 123 in which an electrolytic solution is held in a holding body is formed on each of the negative electrode 10 and the positive electrode 121. After that, the lead 111 is attached to the end of the negative electrode current collector 11 by welding, and the lead 112 is attached to the end of the positive electrode current collector 121A by welding. Next, the negative electrode 10 on which the electrolyte layer 123 is formed and the positive electrode 121 are laminated through a separator 122 to form a laminated body, and then the laminated body is wound in the longitudinal direction to attach the protective tape 124 to the outermost peripheral portion. Thus, the electrode winding body 120 is formed. Finally, for example, the electrode winding body 120 is sandwiched between the exterior members 131 and 132, and the outer edge portions of the exterior members 131 and 132 are brought into close contact by thermal fusion or the like and sealed. At that time, an adhesive film 133 is inserted between the leads 111 and 112 and the exterior members 131 and 132. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  The operation of this secondary battery is the same as that of the coin-type secondary battery shown in FIG.

  As described above, in the present embodiment, since the negative electrode current collector 11 includes a material having superelasticity or a shape memory effect, stress due to expansion / contraction of the negative electrode active material layer 12 due to charge / discharge can be reduced. Can do. Therefore, destruction of the negative electrode 10 can be suppressed, and cycle characteristics can be improved.

  In particular, if a material that does not form an intermetallic compound with lithium is included as a material having superelasticity or a shape memory effect, the negative electrode current collector 11 expands / contracts due to charge / discharge, and the structure is destroyed. Can be suppressed. Therefore, cycle characteristics can be further improved.

  Further, if the negative electrode current collector 11 contains nickel and titanium, a higher effect can be obtained, and in particular, the composition ratio of nickel and titanium in the negative electrode current collector 11 is an atomic ratio of nickel. If it is in the range of titanium 45-55 with respect to titanium 51-48 with respect to 49-52 or titanium 35-45, a still higher effect can be acquired.

  Further, specific embodiments of the present invention will be described in detail with reference to the drawings. In the following examples, the symbols and symbols used in the above embodiment are used in correspondence with each other.

(Examples 1-1 to 1-5)
First, a nickel-titanium alloy foil having a thickness of 50 μm was prepared, and the surface was roughened by lapping, followed by degreasing and cleaning. At that time, the surface roughness was changed in Examples 1-1 to 1-5. The ten-point average roughness Rz of the nickel-titanium alloy foil after surface roughening was measured. As a result, Example 1-1 was 0.8 μm, Example 1-2 was 1.2 μm, and Example 1-3 was 2. The thickness was 0 μm, Example 1-4 was 2.5 μm, and Example 1-5 was 3.6 μm.

  Subsequently, this nickel-titanium alloy foil was used as the negative electrode current collector 11, and a negative electrode active material layer 12 having a thickness of 5 μm made of silicon was formed by a sputtering method. This obtained the negative electrode 10 of Examples 1-1 to 1-5.

Subsequently, a coin-type secondary battery having a diameter of 20 mm and a thickness of 16 mm shown in FIG. 2 was produced using the produced negative electrodes 10 of Examples 1-1 to 1-5. The positive electrode 40 is composed of lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of 5 μm as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder, lithium cobaltate: carbon black: polyfluoride. Vinylidene chloride = 92: 3: 5 is mixed at a mass ratio, and this is added to N-methylpyrrolidone as a dispersion medium to form a mixture slurry, which is applied to a positive electrode current collector 41 made of aluminum having a thickness of 15 μm and dried. The positive electrode active material layer 42 was formed by pressurizing and forming. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a lithium salt in a solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a mass ratio of 1: 1 so as to be 1.0 mol / dm ³ was used. A polypropylene film was used for the separator 50.

About the produced secondary battery of Examples 1-1 to 1-5, the charge / discharge test was done on 25 degreeC conditions, and the capacity | capacitance maintenance factor of the 50th cycle was calculated | required. In that case, charging, after performing a constant current density of 1 mA / cm ² until the battery voltage reached 4.2V, performed at a constant voltage of 4.2V until the current density reached 0.02 mA / cm ^2, discharge Was performed at a constant current density of 1 mA / cm ² until the battery voltage reached 2.5V. When charging, the negative electrode utilization rate in the first charge is set to 90% based on the charge / discharge capacities of the negative electrode 10 and the positive electrode 40 obtained in advance by actual measurement and calculation so that metallic lithium does not precipitate. did. The capacity maintenance rate at the 50th cycle was calculated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity, that is, (discharge capacity at the 50th cycle / initial discharge capacity) × 100. The obtained results are shown in Table 1.

  As Comparative Examples 1-1 to 1-4 with respect to Examples 1-1 to 1-5, except that the negative electrode current collector was changed, the negative electrode was formed in the same manner as in Examples 1-1 to 1-5 Then, a secondary battery was produced. At that time, copper foil was used in Comparative Examples 1-1 and 1-2, nickel foil was used in Comparative Example 1-3, and titanium foil was used in Comparative Example 1-4. Further, the ten-point average roughness Rz of the negative electrode current collector was 0.8 μm in Comparative Example 1-1 and 2.5 μm in Comparative Examples 1-2 to 1-4. For the secondary batteries of Comparative Examples 1-1 to 1-4, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-5, and the capacity retention ratio at the 50th cycle was obtained. The results are also shown in Table 1.

  As can be seen from Table 1, according to Examples 1-1 to 1-5 in which the negative electrode current collector 11 was formed of a nickel-titanium alloy having superelasticity or a shape memory effect, Comparative Example 1 using other materials A capacity retention rate higher than -1 to 1-4 was obtained. This is because in Comparative Examples 1-1 to 1-4, the negative electrode active material layer 12 was peeled off from the negative electrode current collector 11 due to expansion / contraction of the negative electrode active material layer 12 due to charge / discharge, In Examples 1-1 to 1-5, since the adhesion between the negative electrode current collector 11 and the negative electrode active material layer 12 is strong and the negative electrode current collector 11 has high flexibility, the negative electrode active material layer This is considered to be because the stress due to the expansion / contraction of 12 was relieved and the peeling of the negative electrode active material layer 12 could be suppressed. That is, it was found that the cycle characteristics can be improved if the negative electrode current collector 11 includes a material having superelasticity or a shape memory effect, or includes nickel and titanium.

  Further, from the results of Examples 1-1 to 1-5, a higher capacity retention ratio is obtained when the ten-point average roughness Rz of the negative electrode current collector 11 is 0.8 μm or more, and further 1.2 μm or more. I found out that If the ten-point average roughness Rz is in the above range, it is considered that cracks due to expansion / contraction of the negative electrode active material layer 12 can be controlled to an appropriate shape.

(Example 2-1)
Example 1-1, except that a nickel-titanium alloy foil having a thickness of 50 μm was degreased and washed, and then a copper protrusion was formed on the surface of the nickel-titanium alloy foil by plating to form a negative electrode current collector 11. The negative electrode 10 was formed in the same manner as ˜1-5, and a secondary battery was produced. The ten-point average roughness Rz of the negative electrode current collector 11 after the protrusions were formed was 2.4 μm.

  As Comparative Example 2-1 with respect to Example 2-1, except that a negative electrode current collector in which a copper protrusion was formed on the surface of a copper foil having a thickness of 50 μm was used, Examples 1-1 to 1 were otherwise used. A negative electrode was formed in the same manner as in −5 to produce a secondary battery. In Comparative Example 2-1, the ten-point average roughness Rz of the negative electrode current collector after the protrusions were formed was 2.4 μm.

  For the secondary batteries of Example 2-1 and Comparative Example 2-1, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-5, and the capacity retention ratio at the 50th cycle was obtained. The results are shown in Table 2.

  As shown in Table 2, also in Example 2-1, a capacity retention rate higher than that in Comparative Example 2-1 was obtained as in Examples 1-1 to 1-5. That is, even when the negative electrode current collector 11 having a protrusion formed on the substrate is used, the cycle characteristics can be improved by including a material having a superelasticity or shape memory effect, or by including nickel and titanium. I found out that

(Examples 3-1 to 3-5)
A negative electrode 10 was formed in the same manner as in Examples 1-1 to 1-5, except that the negative electrode active material 12 was formed of germanium, and a secondary battery was produced. The ten-point average roughness Rz of the negative electrode current collector 11 was 0.8 μm in Example 3-1, 1.2 μm in Example 3-2, 2.0 μm in Example 3-3, and Example 3-4. 2.5 micrometers and Example 3-5 are 3.6 micrometers. Further, as Comparative Examples 3-1 to 3-4 with respect to Examples 3-1 to 3-5, except that the negative electrode current collector was changed, other than that of Examples 3-1 to 3-5, the negative electrode To form a secondary battery. In Comparative Examples 3-1 and 3-2, a copper foil was used, in Comparative Example 3-3, a nickel foil was used, and in Comparative Example 3-4, a titanium foil was used. The ten-point average roughness Rz of the negative electrode current collector is 0.8 μm in Comparative Example 1-1 and 2.5 μm in Comparative Examples 1-2 to 1-4. For the secondary batteries of Examples 3-1 to 3-5 and Comparative examples 3-1 to 3-4, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-5, and the 50th cycle The capacity maintenance rate was obtained. The results are shown in Table 3.

  As can be seen from Table 3, Examples 3-1 to 3-5 in which the negative electrode current collector 11 was formed of a nickel-titanium alloy having superelasticity or a shape memory effect as in Examples 1-1 to 1-5. According to the above, a capacity retention rate higher than those of Comparative Examples 3-1 to 3-4 using other materials was obtained. Further, a higher capacity retention rate was obtained when the ten-point average roughness Rz of the negative electrode current collector 11 was 0.8 μm or more, and further 1.2 μm or more. That is, even when germanium is used for the negative electrode active material, the negative electrode current collector 11 is made to contain a material having a superelasticity or a shape memory effect, or to contain nickel and titanium, as in the case of using silicon. As a result, it was found that the cycle characteristics can be improved. Further, it was found that the cycle characteristics can be further improved by setting the ten-point average roughness Rz of the negative electrode current collector 11 to 0.8 μm or more, further 1.2 μm or more.

(Example 4-1)
A negative electrode 10 was formed in the same manner as in Example 2-1, except that the negative electrode active material 12 was formed of germanium, and a secondary battery was produced. That is, the negative electrode active material layer 12 of germanium was formed using the negative electrode current collector 11 having a copper protrusion formed on the surface of a nickel-titanium alloy foil having a thickness of 50 μm. The ten-point average roughness Rz of the negative electrode current collector 11 after the protrusions of Example 4-1 were formed was 2.4 μm.

  As Comparative Example 4-1 with respect to Example 4-1, except that a negative electrode current collector in which a copper protrusion was formed on the surface of a copper foil having a thickness of 50 μm was used, the others were the same as Example 4-1. Thus, a negative electrode was formed, and a secondary battery was produced. The ten-point average roughness Rz of the negative electrode current collector after the protrusions of Comparative Example 4-1 were formed was 2.4 μm.

  For the secondary batteries of Example 4-1 and Comparative Example 4-1, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-5, and the capacity retention ratio at the 50th cycle was obtained. The results are shown in Table 4.

  As shown in Table 4, also in Example 4-1, a capacity retention rate higher than that in Comparative Example 4-1 was obtained as in Examples 1-1 to 1-5. That is, even if the negative electrode current collector 11 having the protrusions formed on the base is used and germanium is used as the negative electrode active material, the negative electrode current collector 11 includes a material having superelasticity or a shape memory effect, or nickel and It has been found that the cycle characteristics can be improved by including titanium.

  In addition, although the said Example demonstrated the case where the negative electrode collector 11 contains a nickel-titanium alloy, the same result can be obtained even if it contains other materials which have a superelasticity or a shape memory effect. Further, the same result can be obtained even when the negative electrode active material layer 12 is formed by a vapor phase method other than the sputtering method, a liquid phase method, or a sintering method.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where a polymer material is used as the holding member has been described. However, an inorganic conductor containing lithium nitride or lithium phosphate may be used as the holding member. You may mix and use a conductor.

  In the above embodiment and examples, the negative electrode 10 having the negative electrode active material layer 12 in the negative electrode current collector 11 has been described. However, another layer is provided between the negative electrode current collector and the negative electrode active material layer. It may be.

  Further, in the above embodiments and examples, a coin type or wound laminate type secondary battery has been described. However, the present invention is not limited to a cylindrical type, a square type, a button type, a thin type, a large size, and a laminated laminate type. The same applies to the secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.

It is sectional drawing which simplifies and represents the structure of the negative electrode which concerns on one embodiment of this invention. It is sectional drawing showing the structure of the secondary battery using the negative electrode shown in FIG. It is a disassembled perspective view showing the structure of the other secondary battery using the negative electrode shown in FIG. It is sectional drawing showing the structure along the II line of the electrode winding body shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Negative electrode, 11 ... Negative electrode collector, 12 ... Negative electrode active material layer, 13 ... Intermediate layer, 20 ... Exterior cup, 30 ... Exterior can, 40 ... Positive electrode, 41 ... Positive electrode collector, 42 ... Positive electrode active material layer , 50 ... separator, 60 ... gasket, 111, 112 ... lead, 120 ... electrode winding body, 121 ... positive electrode, 121A ... positive electrode current collector, 121B ... positive electrode active material layer, 122 ... separator, 123 ... electrolyte layer, 124 ... Protective tape

Claims (16)

A negative electrode in which a negative electrode active material layer is provided on a negative electrode current collector,
The negative electrode current collector includes a material having superelasticity or a shape memory effect.   The negative electrode according to claim 1, wherein the material having superelasticity or shape memory effect does not form an intermetallic compound with lithium (Li). A negative electrode in which a negative electrode active material layer is provided on a negative electrode current collector,
The negative electrode current collector includes an intermediate layer containing nickel (Ni) and titanium (Ti).   The negative electrode according to claim 1, wherein the negative electrode active material layer is alloyed with the negative electrode current collector at least at a part of an interface with the negative electrode current collector.   The negative electrode according to claim 1, wherein the negative electrode active material layer is formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method.   The negative electrode according to claim 1, wherein the negative electrode active material layer includes at least one selected from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or germanium (Ge).   The negative electrode according to claim 1 or 3, wherein the ten-point average roughness of the negative electrode current collector is 1.2 µm or more.   The negative electrode current collector according to claim 1, wherein the negative electrode current collector has a protrusion on a surface thereof. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
A battery comprising: a negative electrode current collector including a material having a superelasticity or a shape memory effect; and a negative electrode active material layer provided on the negative electrode current collector.   The battery according to claim 9, wherein the material having a superelasticity or a shape memory effect does not form an intermetallic compound with lithium (Li). A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The battery comprises a negative electrode current collector containing nickel (Ni) and titanium (Ti), and a negative electrode active material layer provided on the negative electrode current collector.   The battery according to claim 9 or 11, wherein the negative electrode active material layer is alloyed with the negative electrode current collector in at least a part of an interface with the negative electrode current collector.   The battery according to claim 9 or 11, wherein the negative electrode active material layer is formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method.   The battery according to claim 9 or 11, wherein the negative electrode active material layer includes at least one selected from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or germanium (Ge).   The battery according to claim 9 or 11, wherein the negative electrode current collector has a ten-point average roughness of 1.2 µm or more. The battery according to claim 9 or 11, wherein the negative electrode current collector has a protrusion on a surface thereof.

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