JP5082266B2 - Negative electrode and secondary battery - Google Patents

Description

The present invention relates to a negative electrode containing silicon (Si) as a constituent element and a secondary battery using the same.

  In recent years, as mobile devices have higher performance and more functions, there is a demand for higher capacities of secondary batteries serving as power sources thereof. Secondary batteries that meet this requirement include lithium ion secondary batteries, but those currently in practical use use graphite for the negative electrode, so the battery capacity is saturated and it is difficult to achieve significant increases in capacity. . Therefore, it has been studied to use silicon or the like for the negative electrode, and recently, it has been reported that a negative electrode active material layer is formed on the negative electrode current collector by a vapor phase method or the like (see, for example, Patent Documents 1 to 3). ). Since silicon and the like have a large expansion / contraction due to charging / discharging, deterioration of cycle characteristics due to pulverization has been a problem. However, according to a vapor phase method or the like, miniaturization can be suppressed and a negative electrode current collector and Since the negative electrode active material layer can be integrated, the electron conductivity in the negative electrode becomes extremely good, and high performance is expected in terms of capacity and cycle life.

However, even in the negative electrode in which the negative electrode current collector and the negative electrode active material layer are integrated as described above, repeated charge and discharge causes the negative electrode active material layer to fall off due to severe expansion and contraction of the negative electrode active material layer. There have been problems such as deterioration of the characteristics and deformation of the negative electrode current collector due to expansion and contraction stress, causing the battery to swell. Therefore, by adding a metal element such as iron that does not alloy with lithium (Li) to the negative electrode active material layer, it has been studied to reduce the expansion and contraction of the negative electrode active material layer and improve the characteristics (for example, (See Patent Document 4).
JP-A-8-50922 Japanese Patent No. 2948205 Japanese Patent Laid-Open No. 11-135115 JP 2003-217574 A

  However, since silicon has low electrical conductivity, lithium occlusion is likely to occur locally during charging, and there is a problem in that the shape is collapsed from the portion, resulting in deterioration of cycle characteristics.

The present invention has been made in view of such problems, and an object thereof is to provide a negative electrode capable of improving the electronic conductivity of the negative electrode active material layer and a secondary battery using the same.

A negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer containing silicon as a constituent element. The negative electrode active material layer includes a ferromagnetic metal and a high-concentration metal layer having a high ferromagnetic metal concentration; And a low-concentration metal layer having a low ferromagnetic metal concentration and a maximum magnetization strength obtained by a magnetization curve of 0.0006 T or more.

A secondary 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 containing silicon as a constituent element, and the negative electrode active material layer includes a ferromagnetic metal. Including a high-concentration metal layer having a high ferromagnetic metal concentration and a low-concentration metal layer having a low ferromagnetic metal concentration, and a maximum magnetization strength obtained by a magnetization curve of 0.0006 T or more. is there.

According to the negative electrode according to the present invention, the negative electrode active material layer includes a ferromagnetic metal, and includes a high-concentration metal layer having a high ferromagnetic metal concentration and a low-concentration metal layer having a low ferromagnetic metal concentration and a maximum magnetization. Since the strength is 0.0006 T or more, the electron conductivity of the negative electrode active material layer can be improved, and an electrode reactant such as lithium can be more uniformly occluded. Therefore, stress due to expansion and contraction of the negative electrode active material layer can be relaxed, and shape collapse of the negative electrode active material layer can be suppressed. Therefore, according to the secondary battery of the present invention using this negative electrode, battery characteristics such as cycle characteristics can be improved.

  In particular, if the maximum magnetization strength of the negative electrode active material layer is 1.67 T or less, the electron conductivity can be improved and the silicon content can be increased. Therefore, the cycle characteristics can be improved while keeping the capacity high.

  Further, if a part of the ferromagnetic metal existing in the negative electrode active material layer is oxidized, the electrode reactant such as lithium is attracted to oxygen, so that the occlusion can be performed more uniformly.

  In addition, if the negative electrode active material layer contains oxygen (O) within a range of 3 atomic% to 40 atomic%, or the negative electrode active material layer includes a high oxygen concentration layer having a high oxygen concentration; If the low oxygen concentration layer having a low oxygen concentration is provided, the expansion of the negative electrode active material layer can be suppressed and the stress can be further relaxed.

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

(First embodiment)
FIG. 1 shows the configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called square type, and has a battery element 20 inside a battery can 11 having a substantially hollow prismatic shape. The battery can 11 is a metal container and is made of, for example, aluminum (Al), aluminum alloy, nickel (Ni), nickel alloy, iron (Fe), or iron alloy. The surface of the battery can 11 may be plated or may be coated with a resin or the like. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged so as to sandwich the battery element 20. One end of the battery can 11 is closed and the other end is opened, and the open end is sealed by the battery lid 14. A terminal pin 16 is disposed on the battery lid 14 via an insulating member 15. The battery lid 14 and the terminal pin 16 are made of, for example, the same metal material as the battery can 11.

  The battery element 20 has, for example, a structure in which a negative electrode 21 and a positive electrode 22 are stacked via a separator 23 and wound many times in an elliptical shape or a flat shape. A negative electrode lead 24 made of nickel or the like is connected to the negative electrode 21, and a positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 22. The negative electrode lead 24 is electrically connected to the battery can 11, and the positive electrode lead 25 is electrically connected to the terminal pin 16.

  The negative electrode 21 includes, for example, a negative electrode current collector 21A and a negative electrode active material layer 21B provided on the negative electrode current collector 21A.

  The anode current collector 21A is preferably made of a metal material containing at least one metal element that does not form an intermetallic compound with lithium. This is because when lithium and an intermetallic compound are formed, they expand and contract with charge / discharge, structural breakdown occurs, current collection performance decreases, and the ability to support the negative electrode active material layer 21B decreases. Examples of the metal element that does not form an intermetallic compound with lithium include copper (Cu), nickel, titanium (Ti), iron, and chromium (Cr).

  The negative electrode current collector 21A preferably contains a metal element that forms an alloy with the negative electrode active material layer 21B. This is because the adhesion between the negative electrode active material layer 21B and the negative electrode current collector 21A can be improved. As a metal element that does not form an intermetallic compound with lithium and forms an alloy with the negative electrode active material layer 21B, when the negative electrode active material layer 21B contains silicon as a constituent element as described later, for example, copper, nickel, Or iron is mentioned. These are also preferable from the viewpoints of strength and conductivity.

  The negative electrode current collector 21A may be formed of a single layer or may be formed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 21B may be made of a metal material alloyed with silicon, and the other layers may be made of another metal material.

  The surface of the anode current collector 21A is preferably roughened, and the surface roughness is preferably 0.1 μm or more in terms of Ra value, more preferably 0.2 μm or more. This is because the adhesion between the negative electrode active material layer 21B and the negative electrode current collector 21A can be further improved. Further, the surface roughness Ra value of the negative electrode current collector 21A is preferably 3.5 μm or less, and more preferably 3.0 μm or less. This is because if the surface roughness Ra value is too high, the negative electrode current collector 21A is likely to be cracked as the negative electrode active material layer 21B expands. The surface roughness Ra value is the arithmetic average roughness Ra specified in JIS B0601, and the surface roughness Ra of the region where at least the negative electrode active material layer 21B is provided in the negative electrode current collector 21A. Is within the above-described range.

  The negative electrode active material layer 21B contains silicon as a constituent element. This is because silicon has a large ability to occlude and release lithium, and a high energy density can be obtained. Silicon may be contained as a simple substance, may be contained as an alloy, or may be contained as a compound.

  The negative electrode active material layer 21B is preferably formed, for example, at least partially by a vapor phase method. FIG. 2 schematically shows a particle structure in a cross section in the thickness direction of the negative electrode active material layer 21B. The negative electrode active material layer 21B is formed, for example, by growing in the thickness direction, and has a plurality of active material particles 211 containing silicon as a constituent element. The active material particles 211 form a plurality of secondary particles 212 by aggregating a plurality of active material particles 211. In each secondary particle 212, the active material particles 211 are not simply adjacent to each other, but are at least partially joined to each other. Each secondary particle 212 is formed by, for example, charging / discharging, and is separated from each other by a groove 213. The groove 213 almost reaches the negative electrode current collector 21A.

  The active material particles 211 contain a ferromagnetic element such as iron, cobalt (Co), or nickel. At least a part of this ferromagnetic element is segregated without dissolving in silicon, and exists as a ferromagnetic metal inside the active material particles 211. Thus, the negative electrode active material layer 21B has magnetization, and the electron conductivity of the negative electrode active material layer 21B can be improved by setting the maximum magnetization obtained by the magnetization curve to 0.0006 T or more. It has become. When a ferromagnetic metal such as iron is present in silicon, the Fermi level changes, and the 3d electrons that normally do not move to create magnetism move like s electrons, increasing the absolute sum of the electrons and free. This is because it is considered that a behavior like an electron can be obtained. In addition, when a ferromagnetic element forms a solid solution with silicon, it exhibits paramagnetism and such characteristics cannot be obtained. The ferromagnetic metal may be a simple substance such as iron, cobalt or nickel, or an alloy containing such a ferromagnetic element. Moreover, it is preferable that the strength of the maximum magnetization obtained by the magnetization curve of the negative electrode active material layer 21B is 1.67 T or less. This is because as the content of the ferromagnetic metal increases, the content of silicon decreases and the capacity decreases. More preferably, the maximum magnetization intensity of the negative electrode active material layer 21B is 0.02T or more and 0.8T or less.

  The ferromagnetic metal may be uniformly distributed throughout the negative electrode active material layer 21B, but may have a gradient in concentration. For example, the concentration of the ferromagnetic metal is changed in the thickness direction of the negative electrode active material layer 21B, and the negative electrode active material layer 21B includes a metal high-concentration layer having a high ferromagnetic metal concentration and a metal high-concentration layer. A metal low concentration layer having a low ferromagnetic metal concentration may be laminated in the thickness direction. This is because even if the content of the ferromagnetic metal is small, a high effect can be obtained. In this case, it is preferable that one or more metal high-concentration layers are provided between the metal low-concentration layers, and more preferably a plurality of layers are provided. The concentration of the ferromagnetic metal is preferably changed stepwise or continuously between the metal high concentration layer and the metal low concentration layer.

  The active material particles 211 preferably contain oxygen as a constituent element. This is because the expansion of the negative electrode active material layer 21B can be further suppressed. It is preferable that at least a part of oxygen contained in the negative electrode active material layer 21B is bonded to a part of silicon, and the bonded state may be silicon monoxide, silicon dioxide, or other metastable state. In addition, it is preferable that at least a part of oxygen is combined with a part of ferromagnetic elements to form an oxide. That is, it is preferable that a part of the ferromagnetic metal is oxidized. This is because if oxygen is present near the portion where the electron conductivity is increased by the ferromagnetic metal, lithium is attracted to the oxygen and the lithium is more easily occluded.

  The oxygen content in the negative electrode active material layer 21B is preferably in the range of 3 atomic% to 40 atomic%. If it is less than this, a sufficient effect cannot be obtained, and if it is more than this, the capacity is reduced, the resistance value of the negative electrode active material layer 21B is increased, and it is swollen by local insertion of lithium, This is because it is considered that the cycle characteristics deteriorate. Note that the negative electrode active material layer 21B does not include a coating film that is formed on the surface of the negative electrode active material layer 21B due to decomposition of the electrolytic solution by charge and discharge. Therefore, when the oxygen content in the negative electrode active material layer 21B is calculated, oxygen contained in this coating is not included.

  The active material particles 211 preferably include a high oxygen concentration layer having a high oxygen concentration and a low oxygen concentration layer having a lower oxygen concentration than the high oxygen concentration layer stacked in the thickness direction. It is preferable that one or more oxygen high concentration layers are provided between the oxygen low concentration layers. This is because expansion / contraction associated with charge / discharge can be more effectively suppressed. The oxygen concentration in the high oxygen concentration layer is preferably 3 atomic% or more, and the oxygen concentration in the low oxygen concentration layer is preferably as low as possible. The oxygen concentration is preferably changed stepwise or continuously between the high oxygen concentration layer and the low oxygen concentration layer. This is because, when the oxygen concentration changes rapidly, the diffusibility of lithium ions decreases and the resistance may increase.

  The high oxygen concentration layer and the low oxygen concentration layer and the above-described high metal concentration layer and low metal concentration layer may exist separately as different layers, but may partially overlap each other. It may be perfectly matched. For example, it is preferable that at least a part of the high oxygen concentration layer overlaps with at least a part of the high metal concentration layer. This is because, as described above, higher effects can be obtained when oxygen is present in the vicinity of the ferromagnetic metal.

  The negative electrode active material layer 21B is preferably alloyed with the negative electrode current collector 21A at least at a part of the interface. Specifically, the constituent elements of the negative electrode current collector 21A are preferably diffused into the negative electrode active material layer 21B, the constituent elements of the negative electrode active material layer 21B are diffused into the negative electrode current collector 21A, or they are mutually diffused. This is because even if the negative electrode active material layer 21B expands and contracts due to charge / discharge, it is possible to prevent the negative electrode current collector 21A from falling off.

  The positive electrode 22 includes, for example, a positive electrode current collector 22A and a positive electrode active material layer 22B provided on the positive electrode current collector 22A, so that the positive electrode active material layer 22B faces the negative electrode active material layer 21B. Has been placed. The positive electrode current collector 22A is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 22B 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 a positive electrode material capable of inserting and extracting lithium, for example, a lithium transition metal composite oxide containing lithium and a transition metal is preferable. This is because a high voltage can be generated and a high energy density can be obtained. Examples of the lithium transition metal composite oxide include those represented by the general formula Li _x MO ₂ . M contains one or more transition metal elements, and preferably contains at least one of cobalt and nickel, for example. 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 transition metal composite oxide include LiCoO _{2 and} LiNiO ₂ .

  The separator 23 separates the negative electrode 21 and the positive electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 23 is made of, for example, polyethylene or polypropylene.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. The electrolytic solution contains, for example, a solvent and an electrolyte salt, and may contain an additive as necessary. Examples of the solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,3-dioxol-2-one, 4-vinyl-1,3-dioxolan-2-one, and 4-fluoro. Non-aqueous solvents such as -1,3-dioxolan-2-one are listed. Any one of the solvents may be used alone, or two or more may be mixed and used. For example, it is preferable to use a high boiling point solvent such as ethylene carbonate or propylene carbonate and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate because high ionic conductivity can be obtained. . In addition, a cyclic carbonate having an unsaturated bond such as 1,3-dioxol-2-one or 4-vinyl-1,3-dioxolan-2-one, or 4-fluoro-1,3-dioxolane-2 It is preferable to use a carbonic acid ester derivative having a halogen atom such as -one because the stability of the electrolytic solution can be improved.

Examples of the electrolyte salt include lithium salts such as LiPF ₆ , LiCF ₃ SO _{3, and} LiClO ₄ . Any one electrolyte salt may be used alone, or two or more electrolyte salts may be mixed and used.

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

  First, a negative electrode active material layer 21B containing silicon as a constituent element is formed on the negative electrode current collector 21A by, for example, a vapor phase method. 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 CVD (Chemical Vapor Deposition; chemical vapor deposition). ) Method or thermal spraying method may be used. At that time, for example, a ferromagnetic metal element is deposited on the negative electrode active material layer 21B by vapor-depositing a ferromagnetic metal element together with silicon or by alternately laminating a layer containing silicon and a layer containing a ferromagnetic metal element. Add. As the raw material, silicon alone, a ferromagnetic metal element alone, an alloy of silicon and a ferromagnetic metal element, an oxide of silicon, an oxide of a ferromagnetic metal element, or the like is used. When oxygen is added to the negative electrode active material layer 21B, for example, oxygen gas may be introduced into the film formation atmosphere.

  Note that after the negative electrode active material layer 21B is formed, heat treatment is performed in a vacuum atmosphere or a non-oxidizing atmosphere as necessary. This is because when the negative electrode active material layer 21B is formed, the negative electrode active material layer 21B and the negative electrode current collector 21A may be alloyed, but alloying can be promoted by heat treatment.

  Further, the positive electrode active material layer 22B is formed on the positive electrode current collector 22A. For example, it is formed by mixing the positive electrode active material and, if necessary, a conductive material and a binder, applying the mixture to the positive electrode current collector 14A, and compression molding. Next, the negative electrode lead 24 is attached to the negative electrode 22, and the positive electrode lead 25 is attached to the positive electrode 22. Subsequently, the negative electrode 21 and the positive electrode 22 are stacked via the separator 23 and wound many times, and then the tip of the negative electrode lead 24 is welded to the battery can 11 and the tip of the positive electrode lead 25 is connected to the terminal pin 16. Thus, the wound negative electrode 21 and positive electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After that, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23, and the open end of the battery can 11 is sealed with the battery lid 14. After assembling the battery in this manner, for example, charging and discharging are performed, so that the groove 213 is formed in the negative electrode active material layer 21 </ b> B and the active material particles 211 are divided into secondary particles 212. As a result, the secondary battery shown in FIGS.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 22 and inserted in the negative electrode 21 through the electrolytic solution. When discharging is performed, for example, lithium ions are extracted from the negative electrode 21 and inserted into the positive electrode 22 through the electrolytic solution. At that time, since the negative electrode active material layer 21B has magnetization and contains a ferromagnetic metal therein, the electron conductivity of the negative electrode active material layer 21B is improved, and lithium is more uniformly occluded.

  As described above, according to the present embodiment, the negative electrode active material layer 21B has magnetization, and the maximum magnetization strength obtained from the magnetization curve is 0.0006 T or more. Electron conductivity can be improved and lithium can be occluded more uniformly. Therefore, stress due to expansion and contraction of the negative electrode active material layer 21B can be relaxed, and shape collapse of the negative electrode active material layer 21B can be suppressed. Therefore, battery characteristics such as cycle characteristics can be improved.

  In particular, if the maximum magnetization strength of the negative electrode active material layer is 1.67 T or less, the electron conductivity can be improved and the silicon content can be increased. Therefore, the cycle characteristics can be improved while keeping the capacity high.

  Further, if the metal high-concentration layer and the metal low-concentration layer are provided, a high effect can be obtained even if the content of the ferromagnetic metal is reduced.

  Furthermore, if oxygen is contained as a constituent element, and if the oxygen content in the anode active material layer 21B is in the range of 3 atomic% to 40 atomic%, the oxygen high concentration layer And a low oxygen concentration layer can suppress the expansion of the negative electrode active material layer and further relax the stress.

  In addition, if a part of the ferromagnetic metal is oxidized, lithium can be attracted and occluded more uniformly.

(Second Embodiment)
FIG. 3 shows the configuration of the secondary battery according to the second embodiment of the present invention. In the secondary battery, a battery element 30 to which leads 31 and 32 are attached is housed in a film-like exterior member 40. The leads 31 and 32 are made of, for example, a metal material such as aluminum, copper, nickel, or stainless steel, and are led out from the inside of the exterior member 40 to the outside, for example, in the same direction.

  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 battery element 30 face each other, and each outer edge portion is in close contact with each other by fusion or an adhesive. An adhesion film 41 for preventing the entry of outside air is inserted between the exterior member 40 and the leads 31 and 32. The adhesion film 41 is made of a material having adhesion to the leads 31 and 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 battery element 30 shown in FIG. The battery element 30 is formed by laminating a negative electrode 33 and a positive electrode 34 via a separator 35 and an electrolyte 36 and winding them many times in an elliptical shape or a flat shape, and the outermost peripheral portion is protected by a protective tape 37. . The negative electrode 33 has a negative electrode current collector 33A provided with a negative electrode active material layer 33B, and the positive electrode 34 has a positive electrode current collector 34A provided with a positive electrode active material layer 34B. The configurations of the negative electrode current collector 33A, the negative electrode active material layer 33B, the positive electrode current collector 34A, the positive electrode active material layer 34B, and the separator 35 are the same as those of the negative electrode current collector 21A and the negative electrode active material layer 21B described in the first embodiment. , The same as the positive electrode current collector 22A, the positive electrode active material layer 22B, and the separator 23. The electrolyte 36 is obtained by holding an electrolytic solution in a polymer compound and has a so-called gel shape. The configuration of the electrolytic solution is the same as that of the first embodiment. Examples of the polymer material include polyvinylidene fluoride and a copolymer of vinylidene fluoride. For example, as shown in FIG. 6, the electrolyte 36 may be present in layers between the negative electrode 33 and the positive electrode 34 and the separator 35, but may be present by being impregnated in the separator 35. Further, as in the first embodiment, the electrolytic solution may be used as it is without being held in the polymer compound.

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

  First, after forming the negative electrode 33 and the positive electrode 34 in the same manner as in the first embodiment, the electrolyte 36 is formed on the negative electrode 33 and the positive electrode 34. Next, the leads 31 and 32 are attached to the negative electrode 33 and the positive electrode 34. Subsequently, the negative electrode 33 and the positive electrode 34 on which the electrolyte 36 is formed are stacked via the separator 35 and wound, and the protective tape 37 is adhered to the outermost peripheral portion to form the battery element 30. After that, for example, the battery element 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by thermal fusion or the like.

  Moreover, you may assemble as follows. First, after forming the negative electrode 33 and the positive electrode 34 in the same manner as in the first embodiment, the leads 31 and 32 are attached. Next, the negative electrode 33 and the positive electrode 34 are stacked with the separator 35 interposed therebetween and wound, and a protective tape 37 is adhered to the outermost peripheral portion to form a wound body. Subsequently, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge except for one side is heat-sealed into a bag shape, and then the electrolytic solution, the monomer that is the raw material of the polymer compound, the polymerization initiator, Then, an electrolyte composition containing another material such as a polymerization inhibitor is injected into the exterior member 40 as necessary. After that, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere, and heat is applied to polymerize the monomer to obtain a polymer compound, thereby forming the gel electrolyte 36.

  After assembling the battery in this manner, the grooves 213 and the secondary particles 212 are formed in the negative electrode active material layer 33B by, for example, charging / discharging, as in the first embodiment.

  This secondary battery operates in the same manner as in the first embodiment, and has the same effect as in the first embodiment.

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

( Experimental Examples 1-1 to 1-14)
A secondary battery having the structure shown in FIGS. First, a copper foil having a thickness of 12 μm is roughened and co-deposited with silicon and iron over the entire negative electrode current collector 33A having a surface roughness Ra value of 0.1 μm or more by a vacuum vapor deposition method. A material layer 33B was formed. At that time, the deposition amount of iron was changed in Experimental Examples 1-1 to 1-14. Next, heat treatment was performed in a reduced-pressure atmosphere to produce the negative electrode 33.

About the produced negative electrodes 33 of Experimental Examples 1-1 to 1-14, a cross section in the thickness direction was cut out with a focused ion beam (FIB) and observed with an SEM. It was confirmed that was growing in the thickness direction. Further, when local elemental analysis was performed on the cut section by AES (Auger Electron Spectroscopy), the negative electrode active material layer 33B and the negative electrode current collector 33A were at least partially alloyed with each other. It was confirmed that Furthermore, when the cut section was analyzed by AES line analysis and ESCA (electron spectroscopy for chemical analysis), it was confirmed that iron was present inside the active material particles 211. Note that the iron content in the negative electrode active material layer 33B was, for example, about 4.8 atomic% in Experimental Example 1-5 and about 9.8 atomic% in Experimental Example 1-6.

Further, the produced negative electrode 33 was cut out to a size of 10 mm × 10 mm, and swept with an applied magnetic field of 1194 kA / m (15 kOe) by a VSM (Vibrating Sample Magnetometer) to measure the magnetization. Table 1 shows the maximum magnetization strength obtained from the magnetization curve. FIG. 5 shows the magnetization curve of Experimental Example 1-5 as a representative.

Also, 92 parts by mass of lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of 5 μm as a positive electrode active material, 3 parts by mass of carbon black as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder are mixed. This was put into N-methyl-2-pyrrolidone as a dispersion medium to form a slurry. Next, this was applied to a positive electrode current collector 34A made of an aluminum foil having a thickness of 15 μm, dried, and then pressed to form a positive electrode active material layer 34B.

Subsequently, 37.5% by mass of ethylene carbonate, 37.5% by mass of propylene carbonate, 10% by mass of vinylene carbonate, and 15% by mass of LiPF ₆ were prepared to prepare an electrolyte solution, and 30 parts by mass of this electrolyte solution And 10 parts by mass of a copolymer of vinylidene fluoride and hexafluoropropylene were mixed and applied to both surfaces of the negative electrode 33 and the positive electrode 34 to form an electrolyte 36. After that, the leads 31 and 32 were attached, the negative electrode 33 and the positive electrode 34 were laminated and wound via the separator 35, and sealed in an exterior member 40 made of an aluminum laminate film to assemble a secondary battery.

As Comparative Example 1-1 with respect to Experimental Examples 1-1 to 1-14, except that iron was not deposited when the negative electrode active material layer was formed, the others were the same as Experimental Examples 1-1 to 1-14 Then, a secondary battery was assembled. Further, as Comparative Examples 1-2 and 1-3, the secondary battery was the same as Experimental Examples 1-1 to 1-14 except that the vapor deposition conditions were changed and silicon and iron were co-deposited over the whole. Assembled. The produced negative electrodes of Comparative Examples 1-1 to 1-3 were also analyzed and examined for magnetization curves in the same manner as in Experimental Examples 1-1 to 1-14. As a result, also in the negative electrodes of Comparative Examples 1-1 to 1-3, the plurality of active material particles grew in the thickness direction, and the negative electrode active material layer and the negative electrode current collector were alloyed at least partially. It was confirmed. In Comparative Examples 1-2 and 1-3, it was confirmed that iron was present inside the active material particles, and the content of iron in the negative electrode active material layer was about 4 in Comparative Example 1-2. The number was 5 atomic%, and Comparative Example 1-3 was about 8.8 atomic%. Further, the magnetization was not measured for Comparative Example 1-1, but was small for Comparative Examples 1-2 and 1-3. Table 1 shows the strength of the maximum magnetization.

With respect to the fabricated secondary batteries of Experimental Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-3, a charge / discharge test was performed under the condition of 25 ° C., and the capacity retention rate of the 31st cycle relative to the 2nd cycle Asked. At that time, charging is performed at a constant current density of 1 mA / cm ² until the battery voltage reaches 4.2 V, and then at a constant voltage of 4.2 V until the current density reaches 0.05 mA / cm ^2. Was performed at a constant current density of 1 mA / cm ² until the battery voltage reached 2.5V. When charging, the capacity utilization of the negative electrode 23 was set to 85% so that metallic lithium was not deposited on the negative electrode 23. The capacity retention ratio was calculated as the ratio of the discharge capacity at the 31st cycle to the discharge capacity at the 2nd cycle, that is, (discharge capacity at the 31st cycle / discharge capacity at the 2nd cycle) × 100.

Further, for the secondary batteries of Experimental Examples 1-1 to 1-14, the battery was disassembled after 31 cycles, and the discharged negative electrode 33 was taken out, and the cross section in the thickness direction at the center of the negative electrode 33 was observed by SEM. In any case, it was confirmed that a plurality of active material particles 211 aggregated to form secondary particles 212 as shown in FIG.

As shown in Table 1, according to Experimental Examples 1-1 to 1-14, the capacity retention rate was improved and the thickness increase rate was also reduced as compared with Comparative Examples 1-1 to 1-3. That is, it was found that battery characteristics such as cycle characteristics can be improved if the negative electrode active material layer 33B has magnetization and the maximum magnetization strength is 0.0006 T or more.

Further, in the results of Experimental Examples 1-1 to 1-14, the capacity retention ratio was improved as the maximum magnetization intensity was increased. That is, it was found that the maximum magnetization strength was preferably 1.67 T or less, and more preferably 0.02 T or more and 0.8 T or less.

( Experimental examples 2-1 to 2-27)
When the negative electrode active material layer 33B was formed, the same procedure as in Experimental Examples 1-1 to 1-14 was performed except that cobalt, nickel, or iron and cobalt were co-deposited over the whole instead of iron. A secondary battery was assembled. At that time, experimental examples 2-1 to 2-9 were co-deposited cobalt in by co-evaporation of nickel in Examples 2-10～2-17, co Experimental Examples 2-18～2-27 the iron-cobalt alloy Vapor deposited. In each experimental example, the deposition amount of the ferromagnetic element was changed.

For the negative electrode 33 of Experimental Example 2-1～2-27 prepared also in the same manner as in Experimental Example 1-1 to 1-14 were examined magnetization curves performs analysis. As a result, as in Experimental Examples 1-1 to 1-14, it was confirmed that the plurality of active material particles 211 grew in the thickness direction, and the ferromagnetic element was present inside the active material particles 211. It was. It was also confirmed that the negative electrode active material layer 33B and the negative electrode current collector 33A were alloyed at least partially. The maximum magnetization strength obtained from the magnetization curve was as shown in Table 2.

Regarding the secondary batteries of Experimental Examples 2-1～2-27 prepared, it was charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 were examined and the capacity retention ratio. The obtained results are shown in Table 2 together with the results of Comparative Example 1-1.

As shown in Table 2, according to Experimental Examples 2-1 to 2-27, the capacity retention rate could be improved as compared with Comparative Example 1-1. That is, it has been found that the same effect can be obtained even when other ferromagnetic elements are used.

( Experimental examples 3-1 to 3-16)
When the negative electrode active material layer 33B is formed, the ferromagnetic element is not co-deposited over the whole, but the silicon element and the ferromagnetic metal layer are alternately deposited and the ferromagnetic element is added. is a secondary battery was assembled in the same manner as in experimental example 1-1 to 1-14 or experimental example 2-1～2-27. As a result, in this experimental example, silicon and ferromagnetic elements diffuse to each other by heat treatment, but a high-concentration metal layer with a high concentration of ferromagnetic metal and a low-concentration metal layer with a low concentration of ferromagnetic metal are formed. Is done. Ferromagnetic elements iron Experimental Example 3-1 to 3-8, the experimental example 3-9～3-12 cobalt, experimental examples 3-13～3-16 is iron and cobalt. The ferromagnetic metal layer was inserted between the silicon layers, and the number of ferromagnetic metal layers was changed in each experimental example as shown in Table 3.

For the negative electrode 33 of Experimental Example 3 - 1 to 3 - prepared was also examined magnetization curve performs analysis in the same manner as in Experimental Example 1-1 to 1-14. As a result, the same results as in Experimental Examples 1-1 to 1-14 were confirmed. Further, the maximum magnetization strength obtained from the magnetization curve was as shown in Table 3. Further, for the secondary batteries of Examples 3 - 1 to 3 - prepared, it was charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 were examined and the capacity retention ratio. The obtained results are shown in Table 3 together with the results of Experimental Examples 1-5, 1-12, 2-4, 2-5, 2-20 and Comparative Example 1-1.

As shown in Table 3, according to Experimental Examples 3-1 to 3-16, the capacity retention rate could be improved as compared with Comparative Example 1-1. Further, the capacity retention ratio can be further improved as compared with Experimental Examples 1-5, 1-12, 2-4, 2-5, and 2-20 in which a ferromagnetic element is added throughout the negative electrode active material layer 33B. did it. That is, it has been found that a higher effect can be obtained by having a metal high concentration layer and a metal low concentration layer.

( Experimental examples 4-1 to 4-19)
The anode active material layer 33B oxygen gas was introduced continuously during the film formation, except that the addition of oxygen throughout the other experimental examples 1-1 to 1-14 or experimental example 2-1～2- A secondary battery was assembled in the same manner as in FIG. The amount of oxygen gas introduced was adjusted so that the oxygen content in the negative electrode active material layer 33B would be the value shown in Table 4. As for the ferromagnetic elements, Experimental Examples 4-1 to 4-8 are iron, Experimental Examples 4-9 to 4-13 are cobalt, and Experimental Examples 4-14 to 4-19 are iron and cobalt.

For the negative electrode 33 of Experimental Example 4-1～4-19 prepared it was also examined magnetization curve performs analysis in the same manner as in Experimental Example 1-1 to 1-14. As a result, the same results as in Experimental Examples 1-1 to 1-14 were confirmed. Further, the maximum magnetization strength obtained from the magnetization curve was as shown in Table 4. Further, for the secondary batteries of Experimental Examples 4-1～4-19 prepared, it was charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 were examined and the capacity retention ratio. The obtained results are shown in Table 4 together with the results of Experimental Examples 1-4, 1-5, 2-4 and 2-20.

As shown in Table 4, according to the experimental example 4-1～4-19 than Experiment 1-4,1-5,2-4,2-20, it is possible to further improve the capacity retention rate did it. In other words, it was found that it was more preferable if the negative electrode active material layer 21B contained oxygen as a constituent element.

( Experimental Examples 5-1 to 5-7)
When the negative electrode active material layer 33B was formed, iron and cobalt were co-evaporated over the whole, and oxygen gas was introduced during the film formation to form the oxygen high concentration layer and the oxygen low concentration layer. Except for the above, secondary batteries were assembled in the same manner as in Experimental Examples 1-1 to 1-14. At that time, the number of oxygen high concentration layers was changed from 1 layer to 7 layers in each experimental example.

For the negative electrode 33 of Experimental Example 5-1～5-7 prepared it was also examined magnetization curve performs analysis in the same manner as in Experimental Example 1-1 to 1-14. As a result, the same results as in Experimental Examples 1-1 to 1-14 were confirmed. Further, the strength of the maximum magnetization obtained from the magnetization curve was as shown in Table 5. Further, for the secondary batteries of Experimental Examples 5-1～5-7 prepared, it was charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 were examined and the capacity retention ratio. The obtained results are shown in Table 5 together with the results of Experimental Example 2-20.

As shown in Table 5, according to Experimental Examples 5-1 to 5-7, the capacity retention rate could be further improved as compared with Experimental Example 2-20. That is, it has been found that it is more preferable if the negative electrode active material layer 21B has a high oxygen concentration layer and a low oxygen concentration layer.

( Experimental examples 6-1 to 6-14)
When forming the negative electrode active material layer 33B, the ferromagnetic element is not co-evaporated over the whole, but the silicon layer and the ferromagnetic metal layer are alternately evaporated to add the ferromagnetic element. A secondary battery was assembled in the same manner as in Experimental Examples 1-1 to 1-14 except that oxygen gas was introduced and oxygen was added when the layers were deposited. That is, in this experimental example, a high-concentration metal layer and a low-concentration metal layer were formed, and a high-oxygen concentration layer and a low-oxygen concentration layer were formed. Ferromagnetic elements are iron and cobalt. The ferromagnetic metal layer was inserted between the silicon layers, and the number of ferromagnetic metal layers was changed in each experimental example as shown in Table 6.

For the negative electrode 33 of Experimental Example 6-1～6-14 prepared it was also examined magnetization curve performs analysis in the same manner as in Experimental Example 1-1 to 1-14. As a result, the same results as in Experimental Examples 1-1 to 1-14 were confirmed. Further, the strength of the maximum magnetization obtained from the magnetization curve is as shown in Table 6. Further, for the secondary batteries of Experimental Examples 6-1～6-14 prepared, it was charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 were examined and the capacity retention ratio. The obtained results are shown in Table 6 together with the results of Experimental Example 3-13.

As shown in Table 3, according to Experimental Examples 6-1 to 6-14, it was found that a high capacity retention rate was obtained. As it can be seen by comparing with the experimental examples 6-2,6-5,6-8,6-11,6-14 and Experimental Examples 3-13, experimental examples with the addition of oxygen 6-2,6- 5,6-8, 6-11, 6-14 could obtain higher characteristics. That is, it has been found that a higher effect can be obtained by forming a high-concentration metal layer and forming a high-oxygen concentration layer so as to at least partially overlap the high-concentration metal layer.

( Experimental examples 7-1 to 7-8)
Using a battery can 11 made of iron plated with aluminum or nickel, a secondary battery having the structure shown in FIG. 1 was produced. The negative electrode 21 and the positive electrode 22 were produced in the same manner as in Experimental Examples 1-5, 2-4, 2-12, and 2-20. As the electrolytic solution, one obtained by dissolving 1 mol / l LiPF ₆ in a solvent in which 30% by mass of ethylene carbonate, 10% by mass of vinylene carbonate, and 60% by mass of dimethyl carbonate were mixed was used.

For the secondary batteries and experimental examples 1-5,2-4,2-12,2-20 of Experimental Example 7-1 to 7-8 were prepared, charged and discharged in the same manner as in Experimental Example 1-1 to 1-14 The thickness increase rate of the battery was examined. The rate of increase in thickness is the ratio of the increase in thickness after 31 cycles to the thickness before charge / discharge, ie, [(31 Thickness after cycle−thickness before charge / discharge) / thickness before charge / discharge] × 100. The results obtained are shown in Table 7.

As shown in Table 7, than the experimental examples using the package member 40 made of aluminum laminate film, experimental examples using the battery can 11 made of aluminum, even the experimental examples using the battery can 11 made of iron However, the thickness increase rate could be reduced. That is, it was found that the battery can 11 was preferably used for the exterior, and the iron can was more preferable.

  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.

Further, in the above embodiments and examples, the case where a battery element having a structure wound in an elliptical shape or a flat shape is used is described. However, a structure wound in a circular shape may be used, and the battery element may be folded or stacked. It is good also as a structure. Furthermore, although the case of using a hollow prismatic battery can has been described, a battery can having another shape such as a cylindrical shape, a coin shape, or a button shape may be used .

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. FIG. 2 is a schematic diagram illustrating a particle structure of a negative electrode active material layer according to the secondary battery illustrated in FIG. 1. It is a disassembled perspective view showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the II line of the secondary battery shown in FIG. It is a characteristic view showing the magnetization curve of Experimental example 1-5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulating plate, 14 ... Battery cover, 15 ... Insulating member, 16 ... Terminal pin, 20, 30 ... Battery element, 21, 33 ... Negative electrode, 21A, 33A ... Negative electrode collector, 21B , 33B ... negative electrode active material layer, 22, 34 ... positive electrode, 22A, 34A ... positive electrode current collector, 22B, 34B ... positive electrode active material layer, 23, 35 ... separator, 24 ... negative electrode lead, 25 ... positive electrode lead, 31, 32 ... Lead, 36 ... Electrolyte, 37 ... Protective tape, 40 ... Exterior member, 41 ... Adhesive film, 211 ... Active material particle, 212 ... Secondary particle, 213 ... Groove

Claims (16)

A negative electrode current collector, and a negative electrode active material layer containing silicon (Si) as a constituent element,
The negative electrode active material layer includes a ferromagnetic metal and includes a high-concentration metal layer having a high ferromagnetic metal concentration and a low-concentration metal layer having a low ferromagnetic metal concentration, and has a maximum magnetization obtained by a magnetization curve. A negative electrode having a strength of 0.0006T or more.   The negative electrode according to claim 1, wherein the maximum magnetization strength obtained from the magnetization curve of the negative electrode active material layer is 1.67 T or less. The portion of the ferromagnetic metal present in the anode active material layer is oxidized, the negative electrode of claim 1, wherein. The negative electrode active material layer has active material particles containing silicon as a constituent element,
At least a portion of the active material particles, see contains the ferromagnetic metal in the particles, having a density higher metal high concentration layer of the ferromagnetic metal, and a concentration of the ferromagnetic metal is low metal low concentration layer, wherein Item 1. The negative electrode according to Item 1.   The negative electrode according to claim 1, wherein at least a part of the negative electrode active material layer is formed by a vapor phase method.   The negative electrode according to claim 1, wherein the negative electrode active material layer is alloyed at least partially with the negative electrode current collector.   The negative electrode according to claim 1, wherein the negative electrode active material layer further contains oxygen (O) as a constituent element, and the content thereof is 3 atomic% to 40 atomic%.   2. The negative electrode according to claim 1, wherein the negative electrode active material layer includes an oxygen high concentration layer having a high oxygen concentration and an oxygen low concentration layer having a low oxygen concentration in the thickness direction. With electrolyte together with positive and negative electrodes,
The negative electrode has a negative electrode current collector and a negative electrode active material layer containing silicon (Si) as a constituent element,
The negative electrode active material layer includes a ferromagnetic metal and includes a high-concentration metal layer having a high ferromagnetic metal concentration and a low-concentration metal layer having a low ferromagnetic metal concentration, and has a maximum magnetization obtained by a magnetization curve. A secondary battery having a strength of 0.0006T or more. The secondary battery according to claim 9 , wherein the maximum magnetization obtained by the magnetization curve of the negative electrode active material layer is 1.67 T or less. The secondary battery according to claim 9 , wherein a part of the ferromagnetic metal present in the negative electrode active material layer is oxidized. The negative electrode active material layer has active material particles containing silicon as a constituent element,
At least a portion of the active material particles, see contains the ferromagnetic metal in the particles, having a density higher metal high concentration layer of the ferromagnetic metal, and a concentration of the ferromagnetic metal is low metal low concentration layer, wherein Item 10. A secondary battery according to Item 9 . The secondary battery according to claim 9 , wherein at least a part of the negative electrode active material layer is formed by a vapor phase method. The secondary battery according to claim 9 , wherein the negative electrode active material layer is alloyed at least partially with the negative electrode current collector. The secondary battery according to claim 9 , wherein the negative electrode active material layer further contains oxygen (O) as a constituent element, and the content thereof is 3 atomic% to 40 atomic%. The secondary battery according to claim 9 , wherein the negative electrode active material layer includes, in the thickness direction, an oxygen high concentration layer having a high oxygen concentration and an oxygen low concentration layer having a low oxygen concentration.

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