JP2006059714A - Negative electrode and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode capable of improving cycle characteristics and a battery using the same. <P>SOLUTION: The negative electrode active material layer 12 has a tin-contained layer 12A containing Sn. A first layer 12B which contains an element capable of electrochemical reaction with Li and having a coefficient of expansion different from Sn at the time of alloy-forming with Li is provided between the tin-contained layer 12A and a negative electrode current collector 11. Furthermore, also in the tin-contained layer 12A, a second layer 12C which contains an element capable of reaction electrochemically with Li and having a coefficient of expansion different from Sn at the time of alloy-forming with Li is provided. Thereby, the stress generated by expansion and contraction accompanied with charge and discharge can be moderated, and collapse of shape of the negative electrode active material 12 and deterioration of conductivity accompanied with it can be suppressed. <P>COPYRIGHT: (C)2006,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 an urgent need to increase the capacity of secondary batteries, which are their power sources. 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. However, in order to put this negative electrode into practical use, it is necessary to improve the precipitation and dissolution efficiency of lithium and control the dendrite-like precipitation form. is there.

On the other hand, high-capacity negative electrodes using silicon (Si) or tin (Sn) have recently 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 a negative electrode active material layer is formed on a negative electrode current collector by a gas phase method, a liquid phase method, a firing method, a thermal spraying method, or the like have been studied (for example, see Patent Document 1, Patent Document 2, and Patent Document 3). ). According to this, compared with the conventional coating type negative electrode which apply | coated the slurry containing a particulate-form active material and a binder, refinement | miniaturization can be suppressed and a negative electrode collector and a negative electrode active material layer are integrated. Therefore, the electron conductivity in the negative electrode becomes extremely good, and high performance is expected in terms of capacity and cycle life. In addition, since the conductive agent, binder, voids, and the like that were conventionally present in the negative electrode can be reduced or eliminated, the negative electrode can be made essentially thin.
JP-A-8-50922 Japanese Patent No. 2948205 Japanese Patent Laid-Open No. 11-135115

  However, this negative electrode also has a problem that the battery characteristics such as the cycle characteristics are not sufficient due to the collapse of the shape such as the refinement of the negative electrode active material layer due to charge / discharge and the resulting decrease in conductivity.

  The present invention has been made in view of such problems, and an object thereof is to provide a negative electrode capable of suppressing shape collapse of the negative electrode active material layer and improving battery characteristics such as cycle characteristics and a battery using the same. There is to do.

  A negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer includes a tin-containing layer containing tin, Between the negative electrode current collector, a first layer containing an element capable of electrochemically reacting with lithium and having an expansion coefficient different from that of tin at the time of forming an alloy with lithium, lithium in the tin-containing layer, and The second layer contains an element that is electrochemically reactive and has an expansion coefficient different from that of tin at the time of forming an alloy with lithium.

  The 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 and a negative electrode active material layer provided on the negative electrode current collector, An element having a tin-containing layer containing tin, and capable of electrochemically reacting with lithium between the tin-containing layer and the negative electrode current collector, and having an expansion coefficient different from that of tin when forming an alloy with lithium And a second layer containing an element that is capable of electrochemically reacting with lithium and having an expansion coefficient different from that of tin at the time of forming an alloy with lithium. .

  According to the negative electrode of the present invention, the first layer containing an element having an expansion coefficient different from that of tin at the time of alloy formation with lithium is provided between the tin-containing layer and the negative electrode current collector. The stress applied to the negative electrode current collector can be relaxed by the expansion and contraction of the negative electrode active material layer, and the negative electrode active material layer can be prevented from peeling from the negative electrode current collector. In addition, since the second layer containing an element having an expansion coefficient different from that of tin is provided between the tin-containing layers and forming an alloy with lithium, the shape of the negative electrode active material layer is collapsed due to expansion / contraction associated with charge / discharge. Can also be suppressed. Therefore, battery characteristics such as cycle characteristics can be improved.

  In particular, as an element whose expansion coefficient at the time of alloy formation with lithium is different from that of tin, aluminum (Al), silicon (Si), zinc (Zn), silver (Ag), indium (In), antimony (Sb) and lead ( If at least one of the group consisting of Pb) is included, or if the thickness of the second layer is larger than the thickness of the first layer, a higher effect can be obtained. it can.

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

  FIG. 1 shows a schematic configuration of a negative electrode 10 according to an embodiment of the present invention. The negative electrode 10 has a structure in which, for example, a negative electrode current collector 11 is provided with a negative electrode active material layer 12. As a constituent material of the negative electrode current collector 11, for example, copper (Cu), iron (Fe), nickel (Ni), titanium (Ti), stainless steel, or reactivity with lithium including at least one of them is low. Metal materials are preferred. This is because if the reactivity with lithium is high, the negative electrode current collector 11 expands and contracts due to charge / discharge and is destroyed. Among these, from the viewpoint of price, a metal material containing copper, iron, nickel, stainless steel or at least one of them is preferable, and from the viewpoint of conductivity, a metal material containing copper or copper is more preferable. The negative electrode current collector 11 may be composed of a single layer, but may be composed of a plurality of layers.

  The negative electrode active material layer 12 has a tin-containing layer 12A containing tin. Tin may be included as a simple substance, or may be included as an alloy or a compound. These simple substances, alloys, or compounds of tin function as a negative electrode active material, so that the negative electrode 10 can obtain a high capacity. As an alloy or compound of tin, for example, an alloy or compound containing tin and an element of Group 4 to 11 in the long-period periodic table can be cited. Among them, manganese (Mn), iron, cobalt (Co), nickel And at least one selected from the group consisting of copper is preferred. This is because it has excellent conductivity and cycle characteristics, is inexpensive and has low toxicity.

  The negative electrode active material layer 12 is also capable of electrochemically reacting with lithium between the tin-containing layer 12A and the negative electrode current collector 11, and has an expansion coefficient different from that of tin when forming an alloy with lithium ( Hereinafter, the first layer 12B containing an element having an expansion coefficient different from that of tin is included. Thereby, the stress applied to the negative electrode current collector as the negative electrode active material layer 12 expands and contracts can be relieved, and the negative electrode active material layer 12 can be prevented from peeling off from the negative electrode current collector 11. ing.

  Aluminum, silicon, zinc, silver, indium, antimony or lead are preferred as the elements whose expansion coefficient is different from that of tin. Among them, aluminum, zinc, silver or antimony whose amount of reaction with lithium per atom is different from that of tin. More preferred. This is because the difference in expansion coefficient can be further increased. Furthermore, aluminum or zinc is preferable from the viewpoint of price and toxicity. An element having an expansion coefficient different from that of tin may be included as a simple substance, or may be included as an alloy or a compound. When it is contained as an alloy or a compound, it may contain two or more elements different from the above-described tin and may contain other elements.

  The negative electrode active material layer 12 further includes a second layer 12C containing an element having an expansion coefficient different from that of the above-described tin in the tin-containing layer 12A. Thereby, it is possible to suppress the negative electrode active material layer itself from being collapsed by the expansion and contraction of the negative electrode active material layer 12. The element having an expansion coefficient different from that of tin may be included as a single element, or may be included as an alloy or a compound, like the first layer 12B. The type of element having a different expansion coefficient from that of tin may be the same as or different from that of the first layer 12B. Moreover, although the case where the second layer 12C is a single layer is shown in FIG. 1, a plurality of layers may be provided in the tin-containing layer 12A at intervals.

  The thicknesses of the first layer 12B and the second layer 12C are each preferably 0.05 μm or more, and more preferably 0.5 μm or more. Further, regarding the relationship between the thickness of the first layer 12B and the thickness of the second layer 12C, when the second layer 12C is one layer, the thickness is preferably thicker than the first layer 12B. When there are a plurality of second layers 12C, the total thickness is preferably thicker than that of the first layer 12B, and each layer of the second layer 12C may be thinner or thicker than the first layer 12B. This is because the stress can be relaxed more effectively.

  Further, the ratio between the number of tin atoms in the negative electrode active material layer 12 and the number of atoms of the element having an expansion coefficient different from that of tin described above is X, and the number of atoms of the element having an expansion coefficient different from that of tin is Y. When X + Y = 100, it is preferable that Y ≧ 4 in order to obtain a sufficient stress relaxation effect.

  The negative electrode active material layer 12, that is, the tin-containing layer 12A, the first layer 12B, and the second layer 12C are preferably formed by a gas phase method, a liquid phase method, a firing method, or a thermal spray method, It may be formed by combining two or more of these. The shape collapse due to the expansion and contraction of the negative electrode active material layer 12 can be suppressed, the negative electrode current collector 11 and the negative electrode active material layer 12 can be integrated, and the electron conductivity in the negative electrode 10 can be improved. Because it can. In addition, unlike conventional coating-type negative electrodes, binders and voids can be reduced or eliminated, and a thin film can be formed.

  In addition, the negative electrode active material layer 12 includes at least part of the interface between the tin-containing layer 12A and the first layer 12B and at least part of the interface between the tin-containing layer 12A and the second layer 12C. It is preferable that they are mutually diffused and alloyed. Furthermore, it is preferable that the negative electrode active material layer 12 is alloyed by diffusing constituent elements thereof at least at a part of the interface with the negative electrode current collector 11. This is because shape collapse due to expansion and contraction of the negative electrode active material layer 12 can be further suppressed.

  That is, due to this diffusion, the tin-containing layer 12A contains an element having an expansion coefficient different from that of the above-mentioned tin, and the first layer 12B and the second layer 12C contain tin. Therefore, the tin-containing layer 12A means a layer having a higher tin content than the first layer 12B and the second layer 12C, and the first layer 12B and the second layer 12C expand with the above-described tin rather than the tin-containing layer 12A. It means a layer with a high content of elements with different rates.

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

  First, the negative electrode current collector 11 is prepared, and for example, a first layer 12B, a tin-containing layer 12A, a second layer 12C, and a tin-containing layer 12A are sequentially formed on the negative electrode current collector 11. The first layer 12B, the tin-containing layer 12A, and the second layer 12C are preferably formed by a vapor phase method, a liquid phase method, a firing method, or a thermal spray method, and two or more of these may be combined. Examples of the vapor deposition method include physical deposition method and chemical deposition method. Specifically, vacuum deposition method, sputtering method, ion plating method, laser ablation method, thermal CVD (Chemical Vapor Deposition) method. Or any of plasma CVD method etc. may be used. As the liquid phase method, either an electrolytic plating method or an electroless plating method may be used. The firing method means a method in which a particulate material is used as a raw material, mixed with a binder or a solvent as necessary, and then heated. As a firing method, any of an atmosphere firing method, a reaction firing method, a hot press firing method, and the like may be used. As the thermal spraying method, any of a plasma spraying method, a high-speed gas flame spraying method, an arc spraying method, or the like may be used.

  Next, the negative electrode current collector 11 on which the first layer 12B, the tin-containing layer 12A, and the second layer 12C are formed is heat-treated in, for example, a vacuum atmosphere, an air atmosphere, a reducing atmosphere, an oxidizing atmosphere, or an inert atmosphere. Is preferred. Thereby, the constituent elements of the negative electrode current collector 11 diffuse into the negative electrode active material layer 12, and the constituent elements of the first layer 12B, the tin-containing layer 12A, and the second layer 12C diffuse into each other. In the case of the firing method, firing and diffusion thereof may be performed simultaneously. 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 21 and the positive electrode 23 accommodated in the outer can 22 are stacked via a separator 24. is there. The peripheral portions of the outer cup 21 and the outer can 22 are sealed by caulking through an insulating gasket 25. The exterior cup 21 and the exterior can 22 are made of, for example, a metal such as stainless steel or aluminum.

  The positive electrode 23 includes, for example, a positive electrode current collector 23A and a positive electrode active material layer 23B provided on the positive electrode current collector 23A. The positive electrode current collector 23A is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 23B 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 agent 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 capacity can be increased. MI is one or more transition metals, and for example, at least one of the group consisting of cobalt, nickel and manganese 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 . As the positive electrode material capable of inserting and extracting lithium, for example, elemental sulfur or a sulfur compound is also preferable. This is because a high capacity can be obtained also by these.

  The separator 24 separates the negative electrode 10 and the positive electrode 23 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes, and is made of, for example, polyethylene or polypropylene.

  The separator 24 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 this solvent, and may contain various additives as necessary. It is preferable to use the electrolytic solution in this way because high ionic conductivity can be obtained. Examples of the solvent include organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Any 1 type may be used for a solvent and 2 or more types may be mixed and used for it.

Examples of the lithium salt include LiPF _{6 and} LiClO ₄ . Any one lithium salt may be used, or two or more lithium salts may be mixed and used.

  This secondary battery can be manufactured, for example, by laminating the positive electrode 23, the separator 24 impregnated with the electrolyte, and the negative electrode 10, placing them in the outer can 22 and the outer cup 21, and caulking them. it can.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 23 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 in the positive electrode 23 through the electrolytic solution. At that time, the negative electrode 10 has the first layer 12B and the second layer 12C containing an element having an expansion coefficient different from that of the tin between the tin-containing layer 12A and the negative electrode current collector 11 or in the tin-containing layer 12A. Therefore, the stress due to the expansion and contraction is relieved, and the structural breakdown of the negative electrode active material layer 12 and the accompanying decrease in conductivity are suppressed.

  The negative electrode according to the present embodiment may be used for a secondary battery as follows.

  FIG. 3 is an exploded view of the secondary battery. In this secondary battery, the electrode winding body 30 to which the positive electrode lead 31 and the negative electrode lead 32 are attached is accommodated in the film-shaped exterior member 40, and can be reduced in size, weight, and thickness. ing.

  The positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The positive electrode lead 31 and the negative electrode lead 32 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 40 is 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 member 40 is disposed, for example, so that the polyethylene film side and the electrode winding body 30 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 33 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 33 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 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. 4 shows a cross-sectional structure taken along line II of the electrode winding body 30 shown in FIG. The electrode winding body 30 is obtained by laminating and winding the negative electrode 10 and the positive electrode 34 via the separator 35 and the electrolyte layer 36, and the outermost peripheral portion is protected by a protective tape 37.

  The positive electrode 34 has a structure in which a positive electrode active material layer 34B is provided on one or both surfaces of a positive electrode current collector 34A. The negative electrode 10 also has a structure in which a negative electrode active material layer 12 is provided on one side or both sides of a negative electrode current collector 11. The configurations of the positive electrode current collector 34A, the positive electrode active material layer 34B, and the separator 35 are the same as those of the positive electrode current collector 23A, the positive electrode active material layer 23B, and the separator 24 described above.

  The electrolyte layer 36 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 compound. Examples of the polymer compound include polyvinylidene fluoride which is a block copolymer.

  This secondary battery can be manufactured, for example, as follows.

  First, the electrolyte layer 36 in which the electrolytic solution is held in the holding body is formed on each of the positive electrode 34 and the negative electrode 10. After that, the positive electrode lead 31 is attached to the end of the positive electrode current collector 34A by welding or the like, and the negative electrode lead 32 is attached to the end of the negative electrode current collector 11 by welding or the like.

  Next, the positive electrode 34 and the negative electrode 10 on which the electrolyte layer 36 is formed are laminated through a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the electrode winding body 30 is formed.

  Finally, for example, the electrode winding body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 33 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  The operation and effect of this secondary battery are the same as those of the coin-type secondary battery shown in FIG.

  As described above, according to the present embodiment, the first layer 12B and the second layer 12C containing an element having an expansion coefficient different from that of the tin are disposed between the tin-containing layer 12A and the negative electrode current collector 11 or the tin-containing layer 12A. Since it has in it, the stress which generate | occur | produces by the expansion / contraction accompanying charging / discharging can be relieved, and the shape collapse of the negative electrode active material layer 12 and the electroconductive fall accompanying it can be suppressed.

  In particular, the element having an expansion coefficient different from that of tin includes at least one selected from the group consisting of aluminum, silicon, zinc, silver, indium, antimony and lead, or more than the thickness of the first layer 12B. If the thickness of the second layer 12C is increased, a higher effect can be obtained.

  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.

Example 1
The negative electrode 10 shown in FIG. 1 was produced. First, a copper foil having a surface roughness (arithmetic average roughness Ra) of 0.5 μm and a thickness of 15 μm is used as the negative electrode current collector 11, and the surface of the negative electrode current collector 11 has a tin and expansion coefficient by vacuum deposition. A layer of zinc, which is a different element, was formed with a thickness of 1 μm. Next, a tin layer having a thickness of 2 μm was formed on the zinc layer by vacuum deposition. Subsequently, a zinc layer having a thickness of 1 μm was formed on the tin layer by vacuum vapor deposition, and a tin layer having a thickness of 2 μm was further formed thereon by vacuum vapor deposition. After that, heat treatment was performed in a vacuum atmosphere at 200 ° C. for 12 hours to obtain the negative electrode 10 of Example 1.

  As Comparative Examples 1-1 to 1-5 for Example 1, in Comparative Example 1-1, a 4 μm thick tin layer was vapor-deposited. In Comparative Example 1-2, a 4 μm thick tin layer and a 1 μm thick layer were used. Except that the zinc layers were deposited in this order, in Comparative Example 1-3, a 1 μm thick zinc layer and a 4 μm thick tin layer were deposited in this order, and Comparative Example 1-4 had a thickness of 2 μm. In Comparative Example 1-5, a tin layer having a thickness of 2 μm, a zinc layer having a thickness of 1 μm, a zinc layer having a thickness of 1 μm, and a thickness of 2 μm were obtained except that a tin layer of 1 μm, a zinc layer having a thickness of 1 μm, and a tin layer having a thickness of 2 μm were deposited in this order A negative electrode was produced in the same manner as in Example 1 except that the tin layer and the 1 μm thick zinc layer were deposited in this order.

  About the produced negative electrode 10 of Example 1, XPS (X-ray Photoelectron Spectroscopy; X-ray photoelectron spectroscopy), AES (Auger Electron Spectroscopy; Auger electron spectroscopy), EDX (Energy Dispersive X-Ray Spectroscope; energy dispersion type X) X-ray diffraction (X-ray diffraction) and TEM (Transmission Electron Microscope), TEM (Transmission Electron Microscope), and the constituent elements of the negative electrode current collector 11 diffused into the negative electrode active material layer 12 It was confirmed that Moreover, in the negative electrode active material layer 12, it was confirmed that tin and zinc diffused mutually. In addition, when the negative electrodes of Comparative Examples 1-1 to 1-5 were also examined, similar results were confirmed.

Further, using the produced negative electrode 10 of Example 1 and Comparative Examples 1-1 to 1-5, a coin-type secondary battery having a diameter of 20 mm and a thickness of 1.6 mm shown in FIG. 2 was produced. At that time, the positive electrode 23 was prepared by mixing lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of 5 μm, carbon black, and polyvinylidene fluoride in a mass ratio of 92: 3: 5, and mixing this with N-methyl-2-pyrrolidone. The positive electrode active material layer 23 </ b> B was formed by applying the slurry to a positive electrode current collector 23 </ b> A made of an aluminum foil having a thickness of 20 μm and drying it. As the electrolytic solution, a solution in which LiPF ₆ was dissolved at 1.0 mol / l in a solvent in which 40% by mass of ethylene carbonate and 60% by mass of dimethyl carbonate were mixed was used. As the separator 24, a polypropylene microporous film having a thickness of 25 μm was used.

For the fabricated secondary batteries of Example 1 and Comparative Examples 1-1 to 1-5, after performing constant-current constant-voltage charging under the conditions of an upper limit voltage of 4.2 V and a current density of 1 mA / cm ² , a current density of 1 mA / The charge and discharge of performing constant current discharge under the conditions of cm ² and a final voltage of 2.5 V was repeated, and the capacity retention rate at the 15th cycle was determined with the initial discharge capacity as 100%. The results are shown in Table 1.

  As can be seen from Table 1, according to Example 1, a high capacity retention rate was obtained as compared with Comparative Examples 1-1 to 1-5. That is, the first layer 12B containing an element having an expansion coefficient different from that of tin is provided between the tin-containing layer 12A and the negative electrode current collector 11, and the tin-containing layer 12A includes an element having an expansion coefficient different from that of tin. It was found that the cycle characteristics can be improved by providing the two layers 12C.

(Examples 2-1 to 2-5)
Except that the thickness of the first layer 12B and the second layer 12C was changed as shown in Table 2 in Examples 2-1 to 2-5, the negative electrode 10 and the secondary were the same as in Example 1. A battery was created. The negative electrode 10 of Examples 2-1 to 2-5 was analyzed in the same manner as in Example 1. As a result, it was confirmed that the constituent elements of the negative electrode current collector 11 were diffused in the negative electrode active material layer 12. In the active material layer 12, it was confirmed that tin and zinc were mutually diffused. Further, the thickness of the tin-containing layer 12A, the first layer 12B, and the second layer 12C was measured with a crystal oscillation type film formation controller during film formation, and the negative electrode active material layer was determined from the obtained film thickness and the theoretical density of tin and zinc. The tin and zinc contents (atomic%) in 12 were calculated.

  For the secondary batteries of Examples 2-1 to 2-5, charge and discharge were performed in the same manner as in Example 1, and the capacity retention ratio at the 15th cycle was obtained. The results are shown in Table 2 together with Example 1 and Comparative Example 1-1. In addition, about Example 1 and Comparative Example 1-1, content of tin and zinc in the negative electrode active material layer 12 was calculated in the same manner.

  As shown in Table 2, the thickness of the first layer 12B and the second layer 12C should be 0.05 μm or more, or the content of the element having an expansion coefficient different from that of tin should be 4 atomic% or more with respect to the total of tin. The effect could be clearly confirmed. Moreover, as can be seen from a comparison between Example 2-2 and Example 2-3, and Example 2-4 and Example 2-5, the thickness of the second layer 12C is made larger than the thickness of the first layer 12B. Increasing the capacity improved the capacity maintenance rate.

  That is, if the thickness of the first layer 12B and the second layer 12C is 0.05 μm or more, the number of tin atoms is X, the number of atoms of an element having a different expansion coefficient from tin is Y, and X + Y = 100, Y ≧ 4 or more It is preferable that the thickness of the second layer 12C is larger than the thickness of the first layer 12B.

(Examples 3-1 to 3-8)
In Examples 3-1 to 3-7, the negative electrode 10 and the secondary electrode were the same as in Example 2-4 except that the type of the element having an expansion coefficient different from that of tin was changed as shown in Table 3. A battery was created. Specifically, instead of the zinc layer, an aluminum layer is deposited in Example 3-1, a silicon layer is deposited in Example 3-2, and a silver layer is deposited in Example 3-3. In Example 3-4, an indium layer is deposited; in Example 3-5, an antimony layer is deposited; in Example 3-5, a lead layer is deposited; in Example 3-7, zinc and indium An alloy layer was deposited.

  In Example 3-8, the negative electrode 10 and the secondary battery were produced in the same manner as in Example 2-4, except that a copper-tin alloy layer was deposited instead of the tin layer.

  The negative electrode 10 of Examples 3-1 to 3-8 was also analyzed in the same manner as in Example 1. As a result, it was confirmed that the constituent elements of the negative electrode current collector 11 were diffused in the negative electrode active material layer 12. In the active material layer 12, it was confirmed that the constituent elements of each layer were diffused. Moreover, also about the secondary battery of Examples 3-1 to 3-8, it charged / discharged similarly to Example 2-4, and calculated | required the capacity maintenance rate of the 15th cycle. The results are shown in Table 3 together with the results of Example 2-4.

  As can be seen from Table 3, in Examples 3-1 to 3-8, a high capacity retention rate was obtained as in Example 2-4. That is, it is understood that the cycle characteristics can be improved by including at least one member selected from the group consisting of zinc, aluminum, silicon, silver, indium, antimony, and lead as an element having a coefficient of expansion different from that of tin. It was. It was also found that high cycle characteristics can be obtained even when the tin-containing layer 12A contains a tin alloy or the like.

  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 an electrolytic solution which is a liquid electrolyte or a so-called gel electrolyte is used has been described, but another electrolyte may be used. Examples of other electrolytes include solid electrolytes having ionic conductivity, a mixture of a solid electrolyte and an electrolyte solution, and a mixture of a solid electrolyte and a gel electrolyte.

  As the solid electrolyte, for example, a polymer solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, or an inorganic solid electrolyte made of ion conductive glass or ionic crystals can be used. Examples of the polymer compound of the solid polymer electrolyte include, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, and an acrylate polymer compound. Or can be copolymerized. In addition, as the inorganic solid electrolyte, one containing lithium nitride or lithium phosphate can be used.

  Moreover, in the said embodiment and Example, although the negative electrode active material layer 12 was formed in the negative electrode collector 11, it seems that another layer may be formed between a negative electrode collector and a negative electrode active material layer. Alternatively, a film having ion conductivity may be formed on the negative electrode active material layer 12.

  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, or a laminated laminate type. The present invention can be similarly applied to a secondary battery having the shape. In addition, the present invention can be applied not only to secondary batteries but also to primary batteries.

It is sectional drawing which simplifies and represents the structure of the negative electrode which concerns on the 1st Embodiment of this invention. It is sectional drawing showing the structure of the secondary battery using the negative electrode shown in FIG. It is sectional drawing 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 secondary battery shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Negative electrode, 11 ... Negative electrode collector, 12 ... Negative electrode active material layer, 21 ... Outer cup, 22 ... Outer can, 23, 34 ... Positive electrode, 23A, 34A ... Positive electrode collector, 23B, 34B ... Positive electrode active material Layer, 24, 35 ... separator, 25 ... gasket, 30 ... electrode winding, 31 ... positive electrode lead, 32 ... negative electrode lead, 33 ... adhesion film, 36 ... electrolyte layer, 37 ... protective tape, 40 ... exterior member

Claims (15)

A negative electrode current collector, and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer has a tin-containing layer containing tin, and is capable of electrochemically reacting with lithium (Li) between the tin-containing layer and the negative electrode current collector, and is an alloy with lithium. The first layer containing an element having an expansion coefficient different from that of tin (Sn) and the tin-containing layer can electrochemically react with lithium, and the expansion coefficient when forming an alloy with lithium is tin. And a second layer containing a different element.   The first layer and the second layer are formed of an element having an expansion coefficient different from that of tin at the time of forming an alloy with lithium, such as aluminum (Al), silicon (Si), zinc (Zn), silver (Ag), indium (In ), At least one selected from the group consisting of antimony (Sb) and lead (Pb).   The negative electrode according to claim 1, wherein the thickness of the second layer is larger than the thickness of the first layer.   2. The negative electrode according to claim 1, wherein constituent elements of the negative electrode current collector, the tin-containing layer, the first layer, and the second layer are diffused to each other at an interface thereof.   The tin-containing layer contains more tin than the first layer and the second layer, and the first layer and the second layer have an expansion coefficient different from that of tin when forming an alloy with lithium than the tin-containing layer. The negative electrode according to claim 4, comprising a large amount of elements.   2. The negative electrode according to claim 1, wherein the negative electrode current collector includes at least one selected from the group consisting of copper (Cu), iron (Fe), nickel (Ni), titanium (Ti), and stainless steel. . A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer has a tin-containing layer containing tin, and is capable of electrochemically reacting with lithium (Li) between the tin-containing layer and the negative electrode current collector, and is an alloy with lithium. Between the first layer containing an element having an expansion coefficient different from that of tin (Sn) and the tin-containing layer, it can electrochemically react with lithium, and the expansion coefficient when forming an alloy with lithium is tin. And a second layer containing a different element.   The first layer and the second layer are formed of an element having an expansion coefficient different from that of tin at the time of forming an alloy with lithium, such as aluminum (Al), silicon (Si), zinc (Zn), silver (Ag), indium (In ), At least one selected from the group consisting of antimony (Sb) and lead (Pb).   8. The battery according to claim 7, wherein the thickness of the second layer is larger than the thickness of the first layer.   The battery according to claim 7, wherein the constituent elements of the negative electrode current collector, the tin-containing layer, the first layer, and the second layer are diffused to each other at their interfaces.   The tin-containing layer contains more tin than the first layer and the second layer, and the first layer and the second layer have an expansion coefficient different from that of tin when forming an alloy with lithium than the tin-containing layer. The battery according to claim 10, comprising a large amount of elements.   8. The battery according to claim 7, wherein the negative electrode current collector includes at least one selected from the group consisting of copper (Cu), iron (Fe), nickel (Ni), titanium (Ti), and stainless steel. .   The battery according to claim 7, wherein the electrolyte includes a holding body, a solvent, and an electrolyte salt.   The battery according to claim 7, further comprising a film-shaped exterior member that accommodates the positive electrode, the negative electrode, and the electrolyte. The battery according to claim 7, wherein the positive electrode includes a lithium-containing metal composite oxide.

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