JP2011086503A - Lithium ion secondary battery, and negative electrode for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of improving cycle characteristics. <P>SOLUTION: The lithium ion secondary battery has a positive electrode 21, a negative electrode 22, and an electrolyte, and the electrolyte is impregnated in a separator 23 arranged between the positive electrode 21 and the negative electrode 22. A negative electrode active material layer 22B of the negative electrode 22 includes negative electrode active material particles having silicon as a constituent element. A median diameter of the negative electrode active material particles is 1.6-6.2 μm, and an arithmetic standard deviation of the median diameter is 3.1 μm or below. Loss of discharge capacity is hardly generated during charge and discharge, and the negative electrode active material layer 22B is hardly crushed or collapsed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery in which a negative electrode active material layer includes a plurality of negative electrode active material particles having silicon as a constituent element, and a lithium ion secondary battery using the negative electrode.

  In recent years, portable electronic devices such as a video camera, a digital still camera, a mobile phone, and a laptop computer have been widely used, and there is a strong demand for miniaturization, weight reduction, and long life. Accordingly, as a power source, development of a battery, in particular, a secondary battery that is small and lightweight and capable of obtaining a high energy density is in progress.

  Among them, a secondary battery (lithium ion secondary battery) that utilizes the insertion and release of lithium ions as a charge / discharge reaction is highly expected. This is because an energy density higher than that of the lead battery and the nickel cadmium battery can be obtained.

  A lithium ion secondary battery includes an electrolyte solution together with a positive electrode and a negative electrode. This negative electrode has a negative electrode active material layer on a negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material involved in a charge / discharge reaction.

  As a negative electrode active material, a carbon material is widely used. Recently, since further improvement in battery capacity is required, the use of silicon has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is much larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. In this case, not only a simple substance of silicon but also an alloy or a compound has been studied.

  However, when silicon is used as the negative electrode active material, the battery capacity increases, but some problems arise. Specifically, since the negative electrode active material expands and contracts violently during charge and discharge, the negative electrode active material layer is easily crushed and collapsed. In addition, since the negative electrode active material is highly reactive, a decomposition reaction of the electrolytic solution is likely to occur.

  Thus, various studies have been made on lithium ion secondary batteries using silicon as the negative electrode active material in order to improve various performances.

In order to improve charge / discharge characteristics, metal particles (particle size = 0.0005 μm to 10 μm) are provided on the surface of the electrode active material in the positive electrode or the negative electrode (see, for example, Patent Document 1). In order to suppress an increase in resistance and a decrease in capacity inside the battery, a metal that forms an alloy with lithium ions and a metal that does not form an alloy with lithium ions are included on the first active material layer that occludes and releases lithium ions. A second active material layer is provided (see, for example, Patent Document 2). In order to improve charge / discharge cycle characteristics, a metal is contained in the surface of a thin film mainly composed of silicon (for example, see Patent Document 3). In order to improve the cycle life, a surface coating layer made of a conductive material having a low ability to form a lithium compound is provided on an active material layer made of a silicon-based material (see, for example, Patent Document 4). In order to improve the charge / discharge cycle characteristics, the surface of silicon-containing particles (average particle diameter (D ₅₀ ) = 0.1 μm to 10 μm) is covered with a metal thin film (see, for example, Patent Document 5). In order to obtain excellent charge / discharge efficiency, a negative electrode material in which a coating part made of a metal oxide is provided on the surface of a reaction part containing silicon is used (for example, see Patent Document 6). In order to improve the electron conductivity, the negative electrode active material layer contains a ferromagnetic metal (see, for example, Patent Document 7). In this case, the negative electrode active material layer has magnetization, and the maximum magnetization obtained by the magnetization curve is 0.0006 T (Tesla) or more. In order to relax the stress concentration and improve the characteristics, a metal element is included in the negative electrode active material layer so that the concentration decreases after increasing in the thickness direction (see, for example, Patent Document 8). In order to reduce the overvoltage of the initial charge, at least a part of the surface of the active material particles is covered with a metal material having a low lithium compound forming ability (see, for example, Patent Documents 9 to 13).

JP-A-11-250896 JP 2003-217574 A JP 2003-007295 A JP 2004-228059 A Japanese Patent Laying-Open No. 2005-063767 JP 2007-141666 A JP 2007-257866 A JP 2007-257868 A JP 2008-016195 A JP 2008-016196 A JP 2008-016198 A JP 2008-066278 A JP 2008-277156 A

  In recent years, since portable electronic devices have become more sophisticated and multifunctional, their power consumption tends to increase. In addition, as a use of the lithium ion secondary battery, a large use such as an electric vehicle has been studied. Thereby, in a lithium ion secondary battery, it is anticipated that charging / discharging is repeated frequently, The cycling characteristics are in the condition which falls easily.

  The present invention has been made in view of such problems, and an object thereof is to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery that can improve cycle characteristics.

  The negative electrode for a lithium ion secondary battery of the present invention includes a negative electrode active material layer on a negative electrode current collector, and the negative electrode active material layer includes a plurality of negative electrode active material particles having silicon as a constituent element. The median diameter of the negative electrode active material particles is 1.6 μm or more and 6.2 μm or less, and the arithmetic standard deviation of the median diameter is 3.1 μm or less. Further, the lithium ion secondary battery of the present invention comprises a positive electrode having a positive electrode active material layer on a positive electrode current collector, a negative electrode having a negative electrode active material layer on a negative electrode current collector, and an electrolyte solution, The negative electrode has the above-described configuration.

  According to the negative electrode for lithium ion secondary batteries or the lithium ion secondary battery of the present invention, the negative electrode active material layer includes a plurality of negative electrode active material particles having silicon as a constituent element. The median diameter of the negative electrode active material particles is 1.6 μm or more and 6.2 μm or less, and the arithmetic standard deviation of the median diameter is 3.1 μm or less. Therefore, loss of discharge capacity is less likely to occur, and the negative electrode active material layer is less likely to be crushed and collapsed, so that cycle characteristics can be improved.

It is sectional drawing showing the structure of the negative electrode for lithium ion secondary batteries in one Embodiment of this invention. FIG. 2 is an enlarged cross-sectional view illustrating a part of the negative electrode for a lithium ion secondary battery illustrated in FIG. 1. It is sectional drawing showing the structure of the lithium ion secondary battery (square shape) using the negative electrode for lithium ion secondary batteries of one Embodiment of this invention. It is sectional drawing along the IV-IV line of the square secondary battery shown in FIG. FIG. 5 is a plan view schematically illustrating the configuration of a positive electrode and a negative electrode illustrated in FIG. 4. It is sectional drawing showing the structure of the lithium ion secondary battery (cylindrical type) using the negative electrode for lithium ion secondary batteries of one Embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body shown in FIG. It is a disassembled perspective view showing the structure of the lithium ion secondary battery (laminate film type) using the negative electrode for lithium ion secondary batteries of one Embodiment of this invention. It is sectional drawing along the IX-IX line of the winding electrode body shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The order of explanation is as follows.

1. 1. Negative electrode for lithium ion secondary battery Lithium ion secondary battery 2-1. Square type 2-2. Cylindrical type 2-3. Laminate film type

<1. Negative electrode for lithium ion secondary battery>
1 and 2 show a cross-sectional configuration of a negative electrode 10 that is a negative electrode for a lithium ion secondary battery according to an embodiment of the present invention. In FIG. 2, a part of the negative electrode 10 shown in FIG. 1 is enlarged. ing.

[Overall structure of negative electrode]
As shown in FIG. 1, the negative electrode 10 has a negative electrode active material layer 2 on a negative electrode current collector 1. The negative electrode active material layer 2 may be provided on both sides of the negative electrode current collector 1 or may be provided only on one side. In FIG. 2, only the negative electrode active material layer 2 on one side of the negative electrode current collector 1 is shown.

[Negative electrode current collector]
The negative electrode current collector 1 is made of, for example, a conductive material that is excellent in electrochemical stability, electrical conductivity, and mechanical strength. Examples of the conductive material include copper (Cu), nickel (Ni), and stainless steel. In particular, the conductive material does not form an intermetallic compound with lithium (Li) and can be alloyed with the negative electrode active material layer 2. preferable.

  The surface of the negative electrode current collector 1 is preferably roughened. This is because the adhesion of the negative electrode active material layer 2 to the negative electrode current collector 1 is improved by a so-called anchor effect. Examples of the roughening method include electrolytic treatment or sand blast treatment. The electrolytic treatment is a method in which fine particles are formed on the surface of a metal foil or the like by an electrolytic method in an electrolytic bath, and unevenness is provided on the surface. The copper foil produced by the electrolytic method is generally called “electrolytic copper foil”. In addition, the surface roughness (for example, ten-point average roughness Rz or arithmetic average roughness Ra) of the negative electrode current collector is arbitrary.

[Negative electrode active material layer]
As shown in FIG. 2, the negative electrode active material layer 2 includes a plurality of negative electrode active material particles 201 capable of occluding and releasing lithium ions, and the negative electrode active material particles 201 have silicon as a constituent element. Yes. This is because a high battery capacity can be obtained because the energy density is high. The constituent material of the negative electrode active material particle 201 is a simple substance, an alloy, or a compound of silicon, and may be a mixture of two or more kinds thereof, or may be a material having one kind or two or more kinds of phases at least in part. Good.

  Examples of the silicon alloy include materials having any one or more of the following elements as constituent elements other than silicon. Tin (Sn), Nickel, Copper, Iron (Fe), Cobalt (Co), Manganese (Mn), Zinc (Zn), Indium (In), Silver (Ag), Titanium (Ti), Germanium (Ge), Bismuth (Bi), antimony (Sb) or chromium (Cr).

  Examples of the silicon compound include a material having oxygen (O) or carbon (C) as a constituent element other than silicon. In addition, the compound of silicon may have any 1 type or 2 types or more of the series of elements demonstrated about the alloy of silicon as structural elements other than silicon, for example.

Examples of silicon alloys or compounds include the following materials. _{SiB 4, SiB 6, Mg 2} Si, Ni 2 Si, TiSi 2, MoSi 2, CoSi 2, NiSi 2, CaSi 2, CrSi 2, Cu 5 Si, are such as FeSi _2, MnSi _2, NbSi ₂ or TaSi ₂ . VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), LiSiO, or the like.

The median diameter (D ₅₀ ) of the negative electrode active material particles 201 is 1.6 μm or more and 6.2 μm or less, preferably 1.8 or more and 2.5 μm or less. The arithmetic standard deviation of the median diameter is 3.1 μm or less, preferably 0.6 μm or more and 3.1 μm or less. Since the average particle diameter of the negative electrode active material particles 201 becomes an appropriate size and the particle size distribution is concentrated in the vicinity of the average particle diameter, the electric resistance of the negative electrode active material layer 2 is reduced, and the negative electrode active material layer This is because the physical durability of 2 is improved. More specifically, since the plurality of negative electrode active material particles 201 are closely packed so as to minimize gaps between the particles (a space in which the negative electrode active material particles 201 can move) and to have a uniform size, the negative electrode active material particles 201 It becomes easy to approach. Thereby, the electrical conductivity of the negative electrode active material layer 2 is increased, and the negative electrode active material particles 201 are less likely to expand and contract during charging and discharging. In addition, since large distortion is unlikely to occur inside the negative electrode active material layer 2 during charge / discharge, the negative electrode active material layer 2 is less susceptible to distortion. Therefore, loss of discharge capacity is less likely to occur during charging and discharging, and the negative electrode active material layer 2 is less likely to be crushed and collapsed, so that cycle characteristics can be improved. The median diameter and arithmetic standard deviation can be measured using a laser diffraction / scattering particle size distribution measuring apparatus.

  Here, the influence of the median diameter and arithmetic standard deviation of the negative electrode active material particles 201 will be described in more detail as follows.

  When the median diameter is too large, the negative electrode active material particles 201 having a large particle diameter are cracked during charging and discharging, resulting in a highly reactive active surface (rare surface). As a result, a side reaction (for example, a decomposition reaction of the electrolytic solution) occurs on the active surface, so that the discharge capacity decreases as charging and discharging are repeated.

  If the median diameter is too small, the negative electrode active material particles 201 having a small particle diameter are excessively present, so that the total surface area of the negative electrode active material particles 201 is remarkably increased. In this case, although the surface of the negative electrode active material particle 201 is less reactive than the above-described active surface, the overall reactivity increases as the total surface area of the negative electrode active material particle 201 increases. . Thereby, since a large amount of side reaction occurs on the entire surface of the negative electrode active material particles 201, the discharge capacity decreases as charging and discharging are repeated.

  If the arithmetic standard deviation is too large (the negative electrode active material particles 201 having an extremely large particle size and the negative electrode active material particles 201 having an extremely small particle size are mixed), the negative electrode active material particles 201 are charged and discharged at the time of charge / discharge. A large difference occurs in the amount of expansion and contraction. Thereby, since a big distortion arises in the inside of the negative electrode active material layer 2, the negative electrode active material layer 2 will be crushed and collapsed during charging and discharging.

  The average circularity of the negative electrode active material particles 201 is not particularly limited, but is preferably 0.3 or more. This is because the plurality of negative electrode active material particles 201 are more likely to be densely packed, so that the cycle characteristics can be further improved. If the average circularity is too small, the negative electrode active material particles 201 tend to be biased in the expansion / contraction direction during charging / discharging, which may cause distortion in the negative electrode active material layer 2. The average circularity can be measured using a particle image analyzer.

  In addition, if the negative electrode active material layer 2 includes the negative electrode active material particles 201 having silicon as a constituent element, the negative electrode active material layer 2 is made of another material capable of occluding and releasing lithium ions (a material not having silicon as a constituent element). The negative electrode active material particles may be included together.

  In particular, the negative electrode active material layer 2 preferably includes a metal coating material 202 that covers the surfaces of the negative electrode active material particles 201. Since the negative electrode active material particles 201 are bound to each other via the metal coating material 202, and the negative electrode active material particles 201 and the negative electrode current collector 1 are bound to each other via the metal coating material 202, the negative electrode active material layer It is because 2 becomes difficult to crush and collapse. In addition, the negative electrode active material particles 201 can easily come into contact with each other via the metal coating material 202, and the negative electrode active material particles 201 and the negative electrode current collector 1 can easily come into contact with each other through the metal coating material 202. This is because the electrical conductivity of the material layer 2 is increased. Furthermore, since the surface of the highly active negative electrode active material particle 201 is protected by the inert metal coating material 202, the occurrence of side reactions on the surface of the negative electrode active material particle 201 is suppressed.

  In addition, when the negative electrode active material layer 2 contains the metal coating material 202, since the median diameter and arithmetic standard deviation of the negative electrode active material particle 201 are in the above-mentioned range, the following advantages are also obtained. Since extremely large gaps and extremely small gaps are not easily generated in the negative electrode active material layer 2, the size of the gaps is made uniform. In this case, if the metal coating material 202 is formed using an electrolytic plating method after the formation of the plurality of negative electrode active material particles 201, the plating film is likely to grow so as to uniformly fill the gaps. This increases the possibility that the negative electrode active material particles 201 are in contact with each other via the metal coating material 202, and the possibility that the negative electrode active material particles 201 are in contact with the negative electrode current collector 1 through the metal coating material 202. Since it becomes high, the electrical conductivity of the negative electrode active material layer 2 becomes higher.

  The metal coating material 202 preferably has a metal element that does not alloy with lithium as a constituent element. Examples of such a metal element include one or more of copper, cobalt, iron and nickel. The constituent material of the metal coating material 202 may be a single metal or an alloy. Note that the metal coating material 202 may cover only a part of the surface of the negative electrode active material particles 201 or may cover the entire surface.

  Among these, a simple substance such as copper described above is preferable, and a simple substance of copper is more preferable. This is because copper is excellent in stretchability, so that the metal coating material 202 is not easily damaged even if the negative electrode active material particles 201 expand and contract during charging and discharging.

  The formation method of the metal coating material 202 is not particularly limited, and may be a vapor phase method or a liquid phase method. Examples of the vapor phase method include a vapor deposition method, a sputtering method, and a chemical vapor deposition (CVD) method. The liquid phase method is an electrolytic plating method or an electroless plating method. Of these, the electrolytic plating method or electroless plating method which is a liquid phase method is preferable. This is because the plating film grows along the surface of the negative electrode active material particle 201, so that the metal coating material 202 is easily formed so as to cover the surface over a wide range. In addition, when the metal coating material 202 is formed after forming the plurality of negative electrode active material particles 201, the plating film easily enters the gaps between the negative electrode active material particles 201.

  Although the thickness (average thickness) of the metal coating material 202 is not particularly limited, the ratio T / D of the average thickness T of the metal coating material 202 to the median diameter D of the negative electrode active material particles 201 is 1/20. It is preferable that it is above 1/1. This is because, since the average thickness T is optimized with respect to the median diameter D, advantages such as improved binding properties can be obtained. If the ratio T / D is too small (the coating amount by the metal coating material 202 is too small), the binding property may be lowered and a side reaction may easily occur. On the other hand, if the ratio T / D is too large (the amount of coating with the metal coating material 202 is too large), lithium ions may enter and leave the negative electrode active material particles 201.

  The average thickness of the metal coating material 202 described above is measured as follows. First, the negative electrode active material layer 2 is cut using a cross session polisher to expose the cross section. Subsequently, the cross section of the negative electrode active material layer 2 is observed using a scanning electron microscope (SEM) or the like. Finally, after measuring the thickness of the metal coating material 202 for each negative electrode active material particle 201, the average value is calculated. In this case, the number of measurements (n number) is 10.

  When the negative electrode active material layer 2 includes the metal coating material 202, the metal coating materials 202 are preferably in contact with each other or bonded (alloyed or the like), and more preferably bonded. This is because the electrical conductivity between the negative electrode active material particles 201 is increased. P1 shown in FIG. 2 represents a portion where the negative electrode active material particles 201 are in contact with each other. The metal coating material 202 located in the vicinity of the negative electrode current collector 1 is preferably in contact with or bonded (alloyed or the like) to the negative electrode current collector 1, and more preferably bonded. This is because the electrical conductivity between the negative electrode active material particles 201 and the negative electrode current collector 1 is increased. P2 shown in FIG. 2 represents a portion where the negative electrode active material particles 201 are in contact with the negative electrode current collector 1 or the like.

  The negative electrode active material layer 2 may contain other materials such as a negative electrode binder or a negative electrode conductive agent as necessary.

  Examples of the negative electrode binder include synthetic rubber or a polymer material. Examples of the synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene. The polymer material is, for example, polyvinylidene fluoride or polyimide, and is not limited to polyimide but may be a material having an imide structure. These may be used alone or in combination of two or more.

  Among these, polyvinylidene fluoride or polyimide is preferable, and polyimide is more preferable. This is because high binding properties can be obtained and polyimide can also have high heat resistance.

  Examples of the negative electrode conductive agent include carbon materials such as graphite, carbon black, acetylene black, and ketjen black. These may be used alone or in combination of two or more. The negative electrode conductive agent may be a metal or a conductive polymer as long as it is a conductive material.

[Production method of negative electrode]
The negative electrode 10 is manufactured by the following procedure, for example. First, a negative electrode current collector 1 made of an electrolytic copper foil or the like is prepared. Subsequently, a plurality of negative electrode active material particles 201 as a negative electrode active material are mixed with a negative electrode binder and the like, and then dispersed in a solvent to form a slurry. Then, after apply | coating a slurry to the negative electrode collector 1, it heats as needed. Finally, the metal coating material 202 is formed so as to cover the surface of the negative electrode active material particles 201 using an electrolytic plating method or the like, and the negative electrode active material layer 2 is formed. Instead of forming the metal coating material 202 after applying the slurry, the metal coating material 202 may be formed in advance before the application. FIG. 2 shows a case where the metal coating material 202 is formed before application.

[Operation and effect of this embodiment]
According to the negative electrode 10, the negative electrode active material layer 2 includes a plurality of negative electrode active material particles 201 having silicon as a constituent element. The median diameter of the negative electrode active material particles 201 is 1.6 μm or more and 6.2 μm or less, and the arithmetic standard deviation of the median diameter is 3.1 μm or less. Therefore, when used in a lithium ion secondary battery, the loss of discharge capacity is less likely to occur, and the negative electrode active material layer 2 is less likely to be crushed and collapsed, which can contribute to improvement in cycle characteristics.

  In particular, if the average circularity of the negative electrode active material particles 201 is 0.3 or more, a higher effect can be obtained. In addition, the negative electrode active material layer 2 includes a metal coating material 202 that covers the surface of the negative electrode active material particles 201. In particular, when the ratio T / D is 1/20 or more and 1/1 or less, a higher effect can be obtained. Obtainable. Furthermore, if the negative electrode active material layer 2 contains a negative electrode binder such as polyvinylidene fluoride or polyimide, a higher effect can be obtained.

<2. Lithium ion secondary battery>
Next, a lithium ion secondary battery using the above-described negative electrode for a lithium ion secondary battery will be described.

<2-1. Square type>
3 and 4 show a cross-sectional configuration of the prismatic secondary battery, and FIG. 4 shows a cross section taken along line IV-IV shown in FIG. FIG. 5 schematically shows a planar configuration of the positive electrode 21 and the negative electrode 22 shown in FIG.

[Overall configuration of prismatic secondary battery]
This rectangular secondary battery is mainly one in which the battery element 20 is housed inside the battery can 11. The battery element 20 is a wound laminate in which a positive electrode 21 and a negative electrode 22 are laminated and wound via a separator 23, and has a flat shape according to the shape of the battery can 11.

  The battery can 11 is, for example, a square exterior member. As shown in FIG. 4, this rectangular exterior member has a rectangular or substantially rectangular shape (including a curve in part) in the longitudinal section, and is not only a rectangular shape but also an oval shape. This also applies to the square battery. That is, the square-shaped exterior member is a bottomed rectangular or bottomed oval shaped container-like member having an opening of a rectangular shape or a substantially rectangular shape (oval shape) obtained by connecting arcs with straight lines. . FIG. 4 shows a case where the battery can 11 has a rectangular cross-sectional shape.

  The battery can 11 is made of, for example, iron, aluminum, or an alloy thereof, and may have a function as an electrode terminal. Among these, iron that is harder than aluminum is preferable in order to suppress swelling of the battery can 11 by utilizing hardness (hardness to deform) during charging and discharging. In the case where the battery can 11 is made of iron, for example, nickel or the like may be plated.

  The battery can 11 has a hollow structure in which one end is opened and the other end is closed, and is sealed by an insulating plate 12 and a battery lid 13 attached to the open end. The insulating plate 12 is provided between the battery element 20 and the battery lid 13 and is made of, for example, polypropylene. The battery lid 13 is made of, for example, the same material as that of the battery can 11, and may have a function as an electrode terminal similarly to the battery can 11.

  A terminal plate 14 serving as a positive terminal is provided outside the battery lid 13, and the terminal plate 14 is electrically insulated from the battery lid 13 through an insulating case 16. The insulating case 16 is made of an insulating material such as polybutylene terephthalate, for example. A through hole is provided at substantially the center of the battery lid 13, and the through hole is electrically connected to the terminal plate 14 and is electrically insulated from the battery lid 13 through the gasket 17. A positive electrode pin 15 is inserted. The gasket 17 is made of, for example, an insulating material, and the surface thereof is coated with asphalt.

  In the vicinity of the periphery of the battery lid 13, a cleavage valve 18 and an injection hole 19 are provided. The cleavage valve 18 is electrically connected to the battery lid 13 and is disconnected from the battery lid 13 when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Is to be released. The injection hole 19 is closed by a sealing member 19A made of, for example, a stainless steel ball.

  A positive electrode lead 24 made of a conductive material such as aluminum is attached to an end portion (for example, an inner end portion) of the positive electrode 21, and nickel or the like is attached to an end portion (for example, the outer end portion) of the negative electrode 22. A negative electrode lead 25 made of a conductive material is attached. The positive electrode lead 24 is welded to one end of the positive electrode pin 15 and is electrically connected to the terminal plate 14, and the negative electrode lead 25 is welded to the battery can 11.

[Positive electrode]
The positive electrode 21 is, for example, one in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A.

  The positive electrode current collector 21A is made of, for example, a conductive material such as aluminum, nickel, or stainless steel.

  The positive electrode active material layer 21B includes one or more positive electrode materials capable of occluding and releasing lithium ions as the positive electrode active material. If necessary, the positive electrode active material layer 21B includes other materials such as a positive electrode binder and a positive electrode conductive agent. The material may be included. In addition, the detail regarding a positive electrode binder and a positive electrode electrically conductive agent is the same as that of the negative electrode binder and negative electrode electrically conductive agent which were already demonstrated, for example.

As the positive electrode material, a lithium-containing compound is preferable. This is because a high energy density can be obtained. Examples of the lithium-containing compound include a composite oxide having lithium and a transition metal element as constituent elements, or a phosphate compound having lithium and a transition metal element as constituent elements. Especially, it is preferable to have 1 type or 2 types or more of cobalt, nickel, manganese, and iron as a transition metal element. This is because a higher voltage can be obtained. The chemical formula is represented by, for example, Li _x M1O ₂ or Li _y M2PO ₄ . In the formula, M1 and M2 represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state, but are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), or lithium nickel represented by the following chemical formula: Based composite oxides. Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). Is mentioned. This is because high battery capacity is obtained and excellent cycle characteristics are also obtained. The positive electrode material may be a material other than the above.

LiNi _1-x M _x O ₂
(M is cobalt, manganese, iron, aluminum, vanadium, tin, magnesium, titanium, strontium, calcium, zirconium, molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium, ytterbium, copper, zinc, barium, boron, chromium, silicon And at least one of gallium, phosphorus, antimony, and niobium, and x is 0.005 <x <0.5.)

  Among these, as the composite oxide having lithium and a transition metal element, a lithium nickel composite oxide is preferable. This is because nickel-based composite oxides can provide better cycle characteristics than cobalt-based composite oxides.

[Negative electrode]
The negative electrode 22 has the same configuration as that of the negative electrode 10 described above. For example, the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A. The configurations of the negative electrode current collector 22A and the negative electrode active material layer 22B are the same as the configurations of the negative electrode current collector 1 and the negative electrode active material layer 2, respectively. In the negative electrode 22, the chargeable capacity of the negative electrode material capable of occluding and releasing lithium ions is preferably larger than the discharge capacity of the positive electrode 21. This is to prevent unintentional precipitation of lithium metal during charging / discharging.

  The maximum utilization rate of the negative electrode 22 in a fully charged state (hereinafter simply referred to as “utilization rate”) is not particularly limited, but is preferably 80% or less, more preferably 20% or more and 60% or less. More preferred. This is because the cycle characteristics are further improved. If the utilization rate is less than 20%, the capacity per volume is reduced, so that the merit of using silicon as the negative electrode active material cannot be utilized, and lithium ions may not easily enter and exit from the negative electrode 22. On the other hand, when the utilization rate is greater than 80%, the negative electrode active material is likely to deteriorate quickly during charge and discharge, and the negative electrode active material layer 22B may easily expand and contract.

  The “utilization rate” described above is determined by the ratio between the capacity of the positive electrode 21 and the capacity of the negative electrode 22. This utilization rate is defined as follows. When the negative electrode 22 is fully charged and the amount of lithium occluded per unit area is X, and the amount of lithium that the negative electrode 22 can store electrochemically per unit area is Y, the negative electrode Utilization rate (%) = (X / Y) × 100.

  The occlusion amount X is obtained by the following procedure, for example. First, after charging the secondary battery until it is fully charged, the secondary battery is disassembled, and a part of the negative electrode 22 (the part facing the positive electrode 21) is cut out as an inspection negative electrode. Subsequently, an evaluation battery using metal lithium as a counter electrode is assembled using the inspection negative electrode. Finally, after discharging the evaluation battery and examining the discharge capacity at the time of the first discharge, the storage capacity X is calculated by dividing the discharge capacity by the area of the inspection negative electrode. “Discharge” in this case means energization in the direction in which lithium ions are released from the inspection negative electrode.

  On the other hand, for the amount of occlusion Y, for example, after charging the above-described discharged evaluation battery at a constant current and constant voltage until the battery voltage reaches 0 V, and checking the charge capacity, the charge capacity is divided by the area of the inspection negative electrode. calculate. “Charging” in this case means energization in the direction in which lithium ions are occluded in the inspection negative electrode.

The charging / discharging conditions for obtaining the storage amounts X and Y are, for example, a current value of 1 mA / cm ² , discharging until the battery voltage reaches 1.5 V, and the current value while keeping the battery voltage at 0 V. Charge at a constant voltage until the current reaches 0.05 mA or less.

  As shown in FIG. 5, the positive electrode active material layer 21B is provided, for example, on a partial surface (for example, a central region in the longitudinal direction) of the positive electrode current collector 21A. On the other hand, the negative electrode active material layer 22B is provided on the entire surface of the negative electrode current collector 22A, for example. That is, the negative electrode active material layer 22B is provided in a region of the negative electrode current collector 22A that faces the positive electrode active material layer 21B (opposite region R1) and a region that does not oppose (non-opposite region R2). In this case, in the negative electrode active material layer 22B, the portion located in the facing region R1 is involved in charging / discharging, and the portion located in the non-facing region R2 is hardly involved in charging / discharging. In FIG. 5, the formation range of the positive electrode active material layer 21B and the negative electrode active material layer 22B is shaded.

  As described above, the negative electrode active material layer 22B includes a plurality of negative electrode active material particles whose median diameter and arithmetic standard deviation are within a predetermined range at the time of formation. However, when the negative electrode active material layer 22B expands and contracts during charge and discharge, the negative electrode active material particles are deformed or broken under the influence of the stress during the expansion and contraction, so that the median diameter and arithmetic standard deviation are the negative electrode active material layer 22B. It may vary from the value at the time of formation. In this case, the non-facing region R2 is hardly affected by charging / discharging, and the shape of the negative electrode active material particles is maintained as it is immediately after the formation of the negative electrode active material layer 22B. For this reason, when examining the median diameter and the arithmetic standard deviation, it is preferable to examine the negative electrode active material layer 22B in the non-facing region R2. This is because the median diameter and the arithmetic standard deviation can be accurately examined with good reproducibility without depending on the charge / discharge history (the presence / absence and number of times of charge / discharge).

  This is not limited to the case of measuring the median diameter and the arithmetic standard deviation, and the same applies to the case of measuring the average circularity and the ratio T / D.

[Separator]
The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass while preventing a short circuit of current caused by contact between the two electrodes. The separator 23 is made of, for example, a porous film made of synthetic resin or ceramic, and may be a laminated film in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution is obtained by dissolving an electrolyte salt in a solvent, and may contain other materials such as additives as necessary.

  The solvent contains, for example, one or more of nonaqueous solvents such as organic solvents. Examples of the non-aqueous solvent include the following materials. Ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane or tetrahydrofuran. 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane or 1,4-dioxane. Methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate or ethyl trimethyl acetate. Acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N, N-dimethylformamide, N-methylpyrrolidinone or N-methyloxazolidinone. N, N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate or dimethyl sulfoxide. This is because excellent battery capacity, cycle characteristics, storage characteristics, and the like can be obtained.

  Among these, at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferable. This is because more excellent characteristics can be obtained. In this case, a high viscosity (high dielectric constant) solvent such as ethylene carbonate or propylene carbonate (for example, a relative dielectric constant ε ≧ 30) and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate (for example, viscosity ≦ 1 mPas). -A combination with s) is more preferred. This is because the dissociation property of the electrolyte salt and the ion mobility are improved.

  In particular, the solvent preferably contains at least one of a halogenated chain carbonate and a halogenated cyclic carbonate. This is because a stable coating is formed on the surface of the negative electrode 22 during charging and discharging, so that the decomposition reaction of the electrolytic solution is suppressed. The halogenated chain carbonate is a chain carbonate having halogen as a constituent element (at least one hydrogen is replaced by a halogen). Further, the halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (at least one hydrogen is replaced by a halogen).

  The kind of halogen is not particularly limited, but among them, fluorine, chlorine or bromine is preferable, and fluorine is more preferable. This is because an effect higher than that of other halogens can be obtained. However, the number of halogens is preferably two rather than one, and may be three or more. This is because the ability to form a protective film increases and a stronger and more stable coating is formed, so that the decomposition reaction of the electrolytic solution is further suppressed.

  Examples of the halogenated chain carbonate include fluoromethyl methyl carbonate, bis (fluoromethyl) carbonate, difluoromethyl methyl carbonate, and the like. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one. This halogenated cyclic carbonate includes geometric isomers. The content of the halogenated chain carbonate and the halogenated cyclic carbonate in the solvent is, for example, 0.01 wt% or more and 50 wt% or less.

  Moreover, it is preferable that the solvent contains unsaturated carbon bond cyclic carbonate. This is because a stable coating is formed on the surface of the negative electrode 22 during charging and discharging, so that the decomposition reaction of the electrolytic solution is suppressed. The unsaturated carbon bond cyclic ester carbonate is a cyclic ester carbonate having an unsaturated carbon bond (in which an unsaturated carbon bond is introduced at any position), such as vinylene carbonate or vinyl ethylene carbonate. The content of the unsaturated carbon bond cyclic carbonate in the solvent is, for example, 0.01 wt% or more and 10 wt% or less.

  Moreover, it is preferable that the solvent contains sultone (cyclic sulfonate ester). This is because the chemical stability of the electrolytic solution is improved. Examples of sultone include propane sultone and propene sultone. The content of sultone in the solvent is, for example, 0.5% by weight or more and 5% by weight or less.

  Furthermore, it is preferable that the solvent contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of acid anhydrides include carboxylic acid anhydrides, disulfonic acid anhydrides, and carboxylic acid sulfonic acid anhydrides. Examples of the carboxylic acid anhydride include succinic anhydride, glutaric anhydride, and maleic anhydride. Examples of the disulfonic anhydride include ethane disulfonic anhydride and propane disulfonic anhydride. Examples of the carboxylic acid sulfonic anhydride include anhydrous sulfobenzoic acid, anhydrous sulfopropionic acid, and anhydrous sulfobutyric acid. The content of the acid anhydride in the solvent is, for example, 0.5% by weight or more and 5% by weight or less.

The electrolyte salt includes, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include the following materials. Lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), or lithium hexafluoroarsenate (LiAsF ₆ ). Lithium tetraphenylborate (LiB (C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) or lithium tetrachloroaluminate (LiAlCl ₄ ) . It is dilithium hexafluorosilicate (Li ₂ SiF ₆ ), lithium chloride (LiCl) or lithium bromide (LiBr). This is because excellent battery capacity, cycle characteristics, storage characteristics, and the like can be obtained.

  Among these, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate is preferable. Furthermore, lithium hexafluorophosphate and lithium tetrafluoroborate are preferable, and lithium hexafluorophosphate is more preferable. This is because the internal resistance is reduced, so that more excellent characteristics can be obtained.

  The content of the electrolyte salt is preferably 0.3 mol / kg or more and 3.0 mol / kg or less with respect to the solvent. This is because high ionic conductivity is obtained.

[Operation of prismatic secondary battery]
In this prismatic secondary battery, at the time of charging, for example, lithium ions released from the positive electrode 21 are occluded in the negative electrode 22 through the electrolytic solution impregnated in the separator 23. On the other hand, at the time of discharging, for example, lithium ions released from the negative electrode 22 are occluded in the positive electrode 21 through the electrolytic solution impregnated in the separator 23.

[Method for producing square secondary battery]
This secondary battery is manufactured by the following procedure, for example.

  First, the positive electrode 21 is produced. First, a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conductive agent are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to obtain a paste-like positive electrode mixture slurry. Subsequently, the cathode active material layer 21 is formed by applying the cathode mixture slurry to the cathode current collector 21A using a coating device such as a doctor blade or a bar coater and then drying the slurry. Finally, the positive electrode active material layer 21 is compression-molded using a roll press or the like while being heated as necessary. In this case, compression molding may be repeated a plurality of times.

  Next, the negative electrode 22 is manufactured by forming the negative electrode active material layer 22B on the negative electrode current collector 22A by the same manufacturing procedure as that of the negative electrode 10 described above.

  Next, the battery element 20 is produced using the positive electrode 21 and the negative electrode 22. First, using a welding method or the like, the positive electrode lead 24 is attached to the positive electrode current collector 21A, and the negative electrode lead 25 is attached to the negative electrode current collector 22A. Then, after laminating the positive electrode 21 and the negative electrode 22 via the separator 23, they are wound in the longitudinal direction. Finally, the wound body is molded so as to have a flat shape.

  Finally, the prismatic secondary battery is assembled. First, after storing the battery element 20 in the battery can 11, the insulating plate 12 is placed on the battery element 20. Subsequently, the positive electrode lead 24 is attached to the positive electrode pin 15 and the negative electrode lead 25 is attached to the battery can 11 using a welding method or the like. In this case, the battery lid 13 is fixed to the open end of the battery can 11 using a laser welding method or the like. Finally, after injecting the electrolyte into the battery can 11 from the injection hole 19 and impregnating the separator 23, the injection hole 19 is closed with a sealing member 19A.

[Operation and effect of prismatic secondary battery]
According to this prismatic secondary battery, since the negative electrode 22 has the same configuration as the negative electrode 10 described above, it is difficult for loss of discharge capacity to occur during charging and discharging, and the negative electrode active material layer 22 is crushed and collapsed. It becomes difficult. Therefore, cycle characteristics can be improved. Other effects are the same as those of the negative electrode 10.

<2-2. Cylindrical type>
6 and 7 show a cross-sectional configuration of the cylindrical secondary battery. In FIG. 7, a part of the wound electrode body 40 shown in FIG. 6 is enlarged. In the following, the components of the already-described prismatic secondary battery are referred to as needed.

  In the cylindrical secondary battery, a wound electrode body 40 and a pair of insulating plates 32 and 33 are mainly housed in a substantially hollow cylindrical battery can 31. The wound electrode body 40 is a wound laminated body in which a positive electrode 41 and a negative electrode 42 are laminated and wound via a separator 43.

  The battery can 31 has a hollow structure in which one end is closed and the other end is opened. For example, the battery can 31 is made of the same material as the battery can 11. The pair of insulating plates 32 and 33 are arranged so as to sandwich the wound electrode body 40 from above and below and to extend perpendicular to the wound peripheral surface.

  A battery lid 34, a safety valve mechanism 35, and a thermal resistance element (Positive Temperature Coefficient: PTC element) 36 are caulked through a gasket 37 at the open end of the battery can 31, and the battery can 31 is sealed. . The battery lid 34 is made of, for example, the same material as the battery can 31. The safety valve mechanism 35 and the thermal resistance element 36 are provided inside the battery lid 34, and the safety valve mechanism 35 is electrically connected to the battery lid 34 via the thermal resistance element 36. In the safety valve mechanism 35, when the internal pressure becomes a certain level or more due to an internal short circuit or external heating, the disk plate 35A is reversed and the electric power between the battery lid 34 and the wound electrode body 40 is reversed. Connection is cut off. The heat-sensitive resistance element 36 prevents abnormal heat generation due to a large current by increasing resistance in response to a temperature rise. The gasket 37 is made of, for example, an insulating material, and the surface thereof may be coated with asphalt.

  A center pin 44 may be inserted in the center of the wound electrode body 40. A positive electrode lead 45 made of a conductive material such as aluminum is connected to the positive electrode 41, and a negative electrode lead 46 made of a conductive material such as nickel is connected to the negative electrode 42. The positive electrode lead 45 is welded to the safety valve mechanism 35 and is electrically connected to the battery lid 34, and the negative electrode lead 46 is welded to the battery can 31.

  In the positive electrode 41, for example, a positive electrode active material layer 41B is provided on both surfaces of a positive electrode current collector 41A. The negative electrode 42 has the same configuration as that of the negative electrode 10 described above. For example, the negative electrode active material layer 42B is provided on both surfaces of the negative electrode current collector 42A. The configurations of the positive electrode current collector 41A, the positive electrode active material layer 41B, the negative electrode current collector 42A, the negative electrode active material layer 42B, and the separator 43 are the positive electrode current collector 21A, the positive electrode active material layer 21B, the negative electrode current collector 22A, and the negative electrode, respectively. The configurations of the active material layer 22B and the separator 23 are the same. The composition of the electrolytic solution is the same as the composition of the electrolytic solution in the prismatic secondary battery.

  In this cylindrical secondary battery, at the time of charging, for example, lithium ions released from the positive electrode 41 are occluded in the negative electrode 42 through the electrolytic solution. On the other hand, at the time of discharge, for example, lithium ions released from the negative electrode 42 are occluded in the positive electrode 41 through the electrolytic solution.

  This cylindrical secondary battery is manufactured, for example, according to the following procedure. First, the positive electrode active material layer 41B is formed on both surfaces of the positive electrode current collector 41A to produce the positive electrode 41 by the same production procedure as the positive electrode 21 and the negative electrode 22, and the negative electrode active material is formed on both surfaces of the negative electrode current collector 42A. The layer 42B is formed to produce the negative electrode 42. Subsequently, using a welding method or the like, the positive electrode lead 45 is attached to the positive electrode 41 and the negative electrode lead 46 is attached to the negative electrode 42. Subsequently, the positive electrode 41 and the negative electrode 42 are stacked and wound through the separator 43 to produce the wound electrode body 40, and then the center pin 44 is inserted into the winding center. Subsequently, the wound electrode body 40 is accommodated in the battery can 31 while being sandwiched between the pair of insulating plates 32 and 33. In this case, the positive electrode lead 45 is attached to the safety valve mechanism 35 using a welding method or the like, and the tip of the negative electrode lead 46 is attached to the battery can 31. Subsequently, an electrolytic solution is injected into the battery can 31 and impregnated in the separator 43. Finally, after attaching the battery lid 34, the safety valve mechanism 35, and the heat sensitive resistance element 36 to the opening end of the battery can 31, they are crimped via the gasket 37.

  According to this cylindrical secondary battery, since the negative electrode 42 has the same configuration as the negative electrode 10 described above, the cycle characteristics can be improved for the same reason as that of the square secondary battery. Other effects are the same as those of the negative electrode 10.

<2-3. Laminate film type>
FIG. 8 shows an exploded perspective configuration of a laminated film type secondary battery, and FIG. 9 is an enlarged cross section taken along line IX-IX of the spirally wound electrode body 50 shown in FIG.

  The laminate film type secondary battery is mainly one in which a wound electrode body 50 is housed inside a film-shaped exterior member 60. The wound electrode body 50 is a wound laminated body in which a positive electrode 53 and a negative electrode 54 are laminated and wound via a separator 55 and an electrolyte layer 56. A positive electrode lead 51 is attached to the positive electrode 53, and a negative electrode lead 52 is attached to the negative electrode 54. The outermost periphery of the wound electrode body 50 is protected by a protective tape 57.

  The positive electrode lead 51 and the negative electrode lead 52 are led out in the same direction from the inside of the exterior member 60 to the outside, for example. The positive electrode lead 51 is made of, for example, a conductive material such as aluminum, and the negative electrode lead 52 is made of, for example, a conductive material such as copper, nickel, or stainless steel. These materials have, for example, a thin plate shape or a mesh shape.

  The exterior member 60 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order. In this laminated film, for example, the outer peripheral edges of the two layers of the fusion layers are bonded together by an adhesive or the like so that the fusion layer faces the wound electrode body 50. The fusion layer is, for example, a film of polyethylene or polypropylene. The metal layer is, for example, an aluminum foil. The surface protective layer is, for example, a film such as nylon or polyethylene terephthalate.

  Especially, as the exterior member 60, an aluminum laminated film in which a polyethylene film, an aluminum foil, and a nylon film are laminated in this order is preferable. However, the exterior member 60 may be a laminate film having another laminated structure, a polymer film such as polypropylene, or a metal film.

  An adhesion film 61 is inserted between the exterior member 60 and the positive electrode lead 51 and the negative electrode lead 52 in order to prevent intrusion of outside air. The adhesion film 61 is made of a material having adhesion to the positive electrode lead 51 and the negative electrode lead 52. Examples of such a material include polyolefin resins such as polyethylene, polypropylene, modified polyethylene, and modified polypropylene.

  In the positive electrode 53, for example, the positive electrode active material layer 53B is provided on both surfaces of the positive electrode current collector 53A. The negative electrode 54 has the same configuration as that of the negative electrode 10 described above. For example, the negative electrode active material layer 54B is provided on both surfaces of the negative electrode current collector 54A. The configurations of the positive electrode current collector 53A, the positive electrode active material layer 53B, the negative electrode current collector 54A, and the negative electrode active material layer 54B are the same as the configurations of the positive electrode current collector 21A and the positive electrode active material layer 21B, respectively. The configuration of the separator 55 is the same as the configuration of the separator 23.

  The electrolyte layer 56 is one in which an electrolytic solution is held by a polymer compound, and may contain other materials such as additives as necessary. The electrolyte layer 56 is a so-called gel electrolyte. A gel electrolyte is preferable because high ion conductivity (for example, 1 mS / cm or more at room temperature) is obtained and leakage of the electrolyte is prevented.

  Examples of the polymer compound include one or more of the following polymer materials. Polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, polysiloxane, or polyvinyl fluoride. Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. For example, a copolymer of vinylidene fluoride and hexafluoropyrene. Among these, polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropyrene is preferable. This is because it is electrochemically stable.

  The composition of the electrolytic solution is, for example, the same as the composition of the electrolytic solution in the square secondary battery. However, in the electrolyte layer 56 which is a gel electrolyte, the solvent of the electrolytic solution is a wide concept including not only a liquid solvent but also a material having ion conductivity capable of dissociating the electrolyte salt. For this reason, when using the high molecular compound which has ion conductivity, the high molecular compound is also contained in a solvent.

  Instead of the gel electrolyte layer 56, the electrolytic solution may be used as it is. In this case, the separator 55 is impregnated with the electrolytic solution.

  In this laminated film type secondary battery, during charging, for example, lithium ions released from the positive electrode 53 are occluded in the negative electrode 54 via the electrolyte layer 56. On the other hand, during discharge, for example, lithium ions released from the negative electrode 54 are occluded in the positive electrode 53 through the electrolyte layer 56.

  The laminate film type secondary battery provided with the gel electrolyte layer 56 is manufactured, for example, by the following three types of procedures.

  In the first procedure, first, the positive electrode 53 and the negative electrode 54 are manufactured by the same manufacturing procedure as that of the positive electrode 21 and the negative electrode 22. In this case, the positive electrode active material layer 53B is formed on both surfaces of the positive electrode current collector 53A to produce the positive electrode 53, and the negative electrode active material layer 54B is formed on both surfaces of the negative electrode current collector 54A to produce the negative electrode 54. To do. Subsequently, after preparing a precursor solution containing an electrolytic solution, a polymer compound, and a solvent, the precursor solution is applied to the positive electrode 53 and the negative electrode 54 to form a gel electrolyte layer 56. Subsequently, using a welding method or the like, the positive electrode lead 51 is attached to the positive electrode current collector 53A, and the negative electrode lead 52 is attached to the negative electrode current collector 54A. Subsequently, the positive electrode 53 and the negative electrode 54 on which the electrolyte layer 56 is formed are stacked and wound via a separator 55 to produce a wound electrode body 50, and then a protective tape 57 is bonded to the outermost periphery. Finally, after sandwiching the wound electrode body 50 between the two film-shaped exterior members 60, the outer peripheral edges of the exterior member 60 are bonded to each other by using a heat fusion method or the like, and the exterior member 60 The wound electrode body 50 is encapsulated. In this case, the adhesion film 61 is inserted between the positive electrode lead 51 and the negative electrode lead 52 and the exterior member 60.

  In the second procedure, first, the positive electrode lead 51 is attached to the positive electrode 53 and the negative electrode lead 52 is attached to the negative electrode 54. Subsequently, the positive electrode 53 and the negative electrode 54 are stacked and wound through the separator 55 to produce a wound body that is a precursor of the wound electrode body 50, and then a protective tape 57 is bonded to the outermost periphery. Subsequently, after sandwiching the wound body between the two film-shaped exterior members 60, the remaining outer peripheral edge portion excluding the outer peripheral edge portion on one side is adhered by using a heat fusion method or the like, and the bag A wound body is accommodated in the interior of the outer package member 60. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared to form a bag-shaped exterior member. After injecting into the interior of the 60, the opening of the exterior member 60 is sealed using a heat fusion method or the like. Finally, the monomer is thermally polymerized to obtain a polymer compound, and the gel electrolyte layer 56 is formed.

  In the third procedure, first, a wound body is prepared in the interior of the bag-shaped exterior member 60 in the same manner as in the second procedure described above except that the separator 55 coated with the polymer compound on both sides is used. Store. Examples of the polymer compound applied to the separator 55 include a polymer (such as a homopolymer, a copolymer, or a multi-component copolymer) containing vinylidene fluoride as a component. Specifically, a binary copolymer having polyvinylidene fluoride, vinylidene fluoride and hexafluoropropylene as components, or a ternary copolymer having vinylidene fluoride, hexafluoropropylene and chlorotrifluoroethylene as components. Etc. One or two or more other polymer compounds may be used together with the polymer containing vinylidene fluoride as a component. Subsequently, after the electrolytic solution is prepared and injected into the exterior member 60, the opening of the exterior member 60 is sealed using a thermal fusion method or the like. Finally, the exterior member 60 is heated while applying a load, and the separator 55 is brought into close contact with the positive electrode 53 and the negative electrode 54 through the polymer compound. Thereby, since the electrolytic solution is impregnated into the polymer compound, the polymer compound is gelled to form the electrolyte layer 56.

  In this third procedure, battery swelling is suppressed more than in the first procedure. Further, in the third procedure, the monomer or solvent that is a raw material of the polymer compound hardly remains in the electrolyte layer 56 than in the second procedure, so that the formation process of the polymer compound is controlled well. For this reason, sufficient adhesion is obtained between the positive electrode 53, the negative electrode 54 and the separator 55 and the electrolyte layer 56.

  According to this laminate film type secondary battery, since the negative electrode 54 has the same configuration as the negative electrode 10 described above, the cycle characteristics can be improved for the same reason as that of the square type secondary battery. Other effects are the same as those of the negative electrode 10.

  Examples of the present invention will be described in detail.

(Experimental Examples 1-1 to 1-19)
The laminate film type secondary battery shown in FIGS. 8 and 9 was produced by the following procedure.

First, the positive electrode 53 was produced. First, 91 parts by mass of a positive electrode active material (lithium cobalt composite oxide: LiCoO ₂ ), 6 parts by mass of a positive electrode conductive agent (graphite), and 3 parts by mass of a positive electrode binder (polyvinylidene fluoride: PVDF) were mixed. A positive electrode mixture was obtained. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both surfaces of the positive electrode current collector 53A using a coating apparatus and then dried to form the positive electrode active material layer 53B. In this case, a strip-shaped aluminum foil (thickness = 12 μm) was used as the positive electrode current collector 53A. Finally, the positive electrode active material layer 53B was compression molded using a roll press. Note that when the positive electrode active material layer 53B was formed, the thickness was adjusted so that lithium metal was not deposited on the negative electrode 54 during full charge.

Next, the negative electrode 54 was produced. First, silicon powder (median diameter = 14 μm, arithmetic standard deviation of median diameter = 9.2 μm) was pulverized using a jet mill, and then dry-classified using a microspin. In this case, the pulverization conditions and the like were adjusted so that the median diameter, arithmetic standard deviation, and average circularity were the values shown in Table 1. In order to measure the median diameter and the arithmetic standard deviation, a laser diffraction / scattering particle size distribution measuring apparatus LA-920 (manufactured by Horiba, Ltd.) (the dispersion medium is a 1% sodium hexametaphosphate aqueous solution) was used. In order to measure the average circularity, a particle image analyzer FPIA-3000 manufactured by Hosokawa Micron Corporation was used. Subsequently, the negative electrode active material (silicon powder which is a plurality of negative electrode active material particles) and the negative electrode binder precursor (NMP solution of polyamic acid) were mixed at a dry weight ratio of 80:20, and then the amount was not exceeded. Was diluted with NMP to obtain a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector 54A using a coating apparatus, dried, and then fired in a vacuum atmosphere at 400 ° C. for 1 hour to form a negative electrode binder (polyimide: PI). Formed. In this case, a strip-shaped electrolytic copper foil (thickness = 15 μm) was used as the negative electrode current collector 54A. Finally, a metal coating material was formed using an electrolytic plating method. In this case, as shown in Table 1, copper is used as the metal coating material forming material, and the plating time (average thickness of the metal coating material) is adjusted so that the ratio T / D becomes 1/4. did. In the electrolytic plating method, an electrolytic copper plating bath (pH = 8.1 (adjusted with polyphosphoric acid), bath temperature = 50 ° C.) manufactured by Japan High Purity Chemical Co., Ltd., and current density = 0.03 mA / cm ² and Charge amount = 40 C / cm ² . The composition of this electrolytic copper plating bath is copper pyrophosphate = 105 g / dm ³ (= g / l), potassium pyrophosphate = 450 dm ³ , potassium nitrate 30 dm ³ and 10% aqueous ammonia 250 dm ³ . Note that the conditions such as the median diameter and the arithmetic standard deviation were examined for the negative electrode active material layer 54B in the non-facing region R2 described with reference to FIG.

Next, after mixing a solvent (ethylene carbonate (EC), diethyl carbonate (DEC) and vinylene carbonate (VC)), an electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) was dissolved to prepare an electrolyte solution. . In this case, the composition of the solvent was EC: DEC: VC = 30: 60: 10 by weight, and the content of the electrolyte salt was 1 mol / kg with respect to the solvent.

  Finally, a secondary battery was assembled using the electrolytic solution together with the positive electrode 53 and the negative electrode 54. First, the positive electrode lead 51 made of aluminum was welded to one end of the positive electrode current collector 53A, and the negative electrode lead 52 made of nickel was welded to one end of the negative electrode current collector 54A. Subsequently, the positive electrode 53, the separator 55, the negative electrode 54, and the separator 55 are laminated in this order and then wound in the longitudinal direction to form a wound body that is a precursor of the wound electrode body 50. The winding end portion was fixed with a protective tape 57 (adhesive tape). In this case, a laminated film (thickness = 20 μm) in which a film mainly composed of porous polyethylene was sandwiched between films mainly composed of porous polypropylene was used as the separator 55. Subsequently, after sandwiching the wound body between the exterior members 60, the outer peripheral edge portions except for one side were heat-sealed, and the wound body was housed inside the bag-shaped exterior member 60. In this case, an aluminum laminate film in which a nylon film (thickness = 30 μm), an aluminum foil (thickness = 40 μm), and an unstretched polypropylene film (thickness = 30 μm) were laminated as the exterior member 60 was used. . Subsequently, an electrolytic solution was injected from the opening of the exterior member 60 and impregnated in the separator 55 to produce the wound electrode body 50. Finally, the opening of the exterior member 60 was heat-sealed in a vacuum atmosphere, and the exterior member 60 was sealed.

  When the cycle characteristics of the secondary battery were examined, the results shown in Table 1 were obtained. In this case, first, in order to stabilize the battery state, the battery was charged and discharged for 1 cycle in an atmosphere at 23 ° C., and then charged and discharged again to measure the discharge capacity of the second cycle. Subsequently, charging and discharging were performed until the total number of cycles reached 100 in the same atmosphere, and the discharge capacity at the 100th cycle was measured. Finally, capacity retention ratio (%) = (discharge capacity at the 100th cycle / discharge capacity at the second cycle) × 100 was calculated.

In the first cycle, and a constant current charging until the voltage becomes 4.2V at a current density of 0.2 mA / cm ^2, the constant-voltage charge until further current density is 0.02 mA / cm ² at a voltage of 4.2V Then, constant current discharge was performed until the voltage became 2.5 V at a current density of 0.2 mA / cm ² . In the second cycle, charging and discharging were performed in the same manner as in the first cycle except that the voltage during constant current discharge was changed to 2.7V. In the third and subsequent cycles, charging and discharging were performed in the same manner as in the first cycle except that the current density was changed to ² mA / cm ² and the voltage during constant current discharge was changed to 2.7 V.

  When the median diameter was too small (= 1.2 μm) and too large (= 10.3 μm), the capacity retention rate was low on the whole without depending on the arithmetic standard deviation. However, when the median diameter is appropriate (= 1.6 μm to 6.2 μm), the capacity maintenance ratio changes remarkably depending on the arithmetic standard deviation, and when the arithmetic standard deviation is 3.1 μm or less, 70 A high capacity retention rate of more than 10% was obtained. In this case, the capacity retention rate was higher when the median diameter was 1.8 μm or more and 2.5 μm or less.

(Experimental examples 2-1 to 2-4)
Except that the average circularity was changed as shown in Table 2, a secondary battery was produced in the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. In this case, the pulverized and classified silicon powder was ejected by air injection, and it was made to fly with different flight trajectories in the ejection direction based on the particle drag coefficient to separate and collect particles having a desired average circularity.

  A high capacity retention ratio was obtained without depending on the average circularity, and in particular, the capacity retention ratio was higher when the average circularity was 0.3 or more.

(Experimental examples 3-1 to 3-4)
As shown in Table 3, a secondary battery was fabricated in the same procedure as in Experimental Example 1-9, except that the metal coating material forming material was changed or the metal coating material was not formed. I investigated. In the case of using cobalt, an electrolytic cobalt plating bath (pH = 8.1, bath temperature = 35 ° C.) manufactured by Japan High Purity Chemical Co., Ltd. is used, and current density = 0.05 mA / cm ² and charge amount = 40C. / Cm ² . In the case of using iron, an electrolytic iron plating bath (pH = 8.1, bath temperature = 35 ° C.) manufactured by Japan High Purity Chemical Co., Ltd. is used, and current density = 0.05 mA / cm ² and charge amount = 40C. / Cm ² . In the case of using nickel, an electrolytic nickel plating bath (pH = 3.8 to 4.2, bath temperature = 50 ° C.) manufactured by Japan High Purity Chemical Co., Ltd. is used, and current density = 0.02 mA / cm ² and Charge amount = 40 C / cm ² . The composition of this electrolytic nickel plating bath is nickel sulfate = 240 dm ³ and nickel chloride = 40 dm ³ .

  When the metal coating material was formed, the capacity retention rate was higher than when the metal coating material was not formed, and the capacity retention rate was higher when copper was used.

(Experimental examples 4-1 to 4-6)
Except that the ratio T / D was changed as shown in Table 4, a secondary battery was produced by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. In this case, the ratio T / D was adjusted by changing the formation time (plating time) of the metal coating material.

  A high capacity retention ratio was obtained without depending on the ratio T / D. In particular, when the ratio T / D was 1/20 or more and 1/1 or less, the capacity retention ratio was higher.

(Experimental examples 5-1 and 5-2)
Except for changing the type of the negative electrode binder as shown in Table 5, a secondary battery was prepared by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. When PVDF was used, the negative electrode active material (silicon powder) and the negative electrode binder (PVMP NMP solution) were mixed at a dry weight ratio of 80:20, and the firing conditions were 350 ° C. × 3 hours. When using styrene butadiene rubber (SBR), the negative electrode active material (silicon powder) and the negative electrode binder (aqueous solution of SBR) were mixed at a dry weight ratio of 80:20.

  A high capacity retention ratio was obtained without depending on the type of the negative electrode binder, and in particular, the capacity retention ratio was higher when PVDF or PI, or even PI was used.

(Experimental examples 6-1 to 6-5)
Except that the composition of the electrolytic solution was changed as shown in Table 6, a secondary battery was produced by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. The composition (weight ratio) of the main solvent is 4-fluoro-1,3-dioxolan-2-one (FEC): DEC = 50: 50, or EC: DEC: 4,5-difluoro-1, 3-dioxolan-2-one (DEEC) = 30: 65: 5. The content of sulfobenzoic anhydride (SBAH) or sulfopropionic anhydride (SPAH) in the solvent is 1% by weight. In the case of using lithium tetrafluoroborate (LiBF ₄ ), the content of LiPF ₆ was 0.9 mol / kg with respect to the solvent, and the content of LiBF ₄ was 0.1 mol / kg with respect to the solvent.

A high capacity retention ratio can be obtained without depending on the composition of the electrolytic solution. In particular, the capacity retention ratio can be further increased by using another solvent (halogenated cyclic carbonate or acid anhydride) or other electrolyte salt (LiBF ₄ ). It became high.

(Experimental examples 7-1 to 7-5)
Except that the utilization factor of the negative electrode 54 was changed as shown in Table 7, a secondary battery was produced by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. In this case, the utilization factor of the negative electrode 54 was adjusted by changing the thickness of the positive electrode active material layer 53B.

  A high capacity retention ratio was obtained without depending on the utilization ratio of the negative electrode 54. In particular, the capacity retention ratio was higher when the utilization ratio was 80% or less, and further 20% or more and 60% or less.

(Experimental example 8)
As shown in Table 8, except that the type of the positive electrode active material was changed, a secondary battery was produced by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. In this case, lithium nickel cobalt aluminum composite oxide (LiNi _0.70 Co _0.25 Al _0.05 O ₂ ) was used.

  A high capacity retention ratio was obtained without depending on the type of the positive electrode active material, and in particular, the capacity retention ratio was higher when a nickel-based positive electrode active material was used.

(Experimental examples 9-1 and 9-2)
Except that the battery structure was changed as shown in Table 9, a secondary battery was prepared by the same procedure as in Experimental Example 1-9, and the cycle characteristics were examined. When producing a square secondary battery, an aluminum or iron battery can was used.

  A high capacity retention rate was obtained without depending on the battery structure, and in particular, when the prismatic and battery cans were made of iron, the capacity retention rate was higher.

  From the results of Tables 1 to 9, in the present invention, the negative electrode active material layer of the negative electrode includes a plurality of negative electrode active material particles having silicon as a constituent element. In this case, when the median diameter of the negative electrode active material particles is 1.6 μm or more and 6.2 μm or less and the arithmetic standard deviation of the median diameter is 3.1 μm or less, it does not depend on conditions such as average circularity. Cycle characteristics are improved.

  While the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the modes described in the embodiments and examples, and various modifications can be made. For example, although the case where the capacity of the negative electrode is expressed by occlusion / release of lithium ions has been described, the present invention is not necessarily limited thereto. The present invention is also applicable to the case where the capacity of the negative electrode includes a capacity due to insertion and extraction of lithium ions and a capacity due to precipitation dissolution of lithium metal, and is expressed by the sum of these capacities. In this case, a negative electrode material capable of inserting and extracting lithium ions is used as the negative electrode active material, and the chargeable capacity of the negative electrode material is set to be smaller than the discharge capacity of the positive electrode.

  Moreover, although the case where the battery structure is a square shape, a cylindrical shape, or a laminate film type and the battery element has a winding structure has been described, the present invention is not necessarily limited thereto. The present invention is also applicable to a case where the battery structure is a square type or a button type and the battery element has a laminated structure or the like.

  In the present invention, the median diameter and arithmetic standard deviation of the negative electrode active material particles are described with respect to an appropriate range derived from the results of the examples. However, the explanation is that the median diameter and the like are outside the above-described range. The possibility is not completely denied. The appropriate range described above is a particularly preferable range in obtaining the effects of the present invention. The median diameter and the like may be slightly deviated from the above ranges as long as the effects of the present invention are obtained. The same applies to the average circularity, the ratio T / D, the utilization factor of the negative electrode, and the like.

  DESCRIPTION OF SYMBOLS 1,42A, 54A ... Negative electrode collector, 2, 42B, 54B ... Negative electrode active material layer 10, 22, 42, 54 ... Negative electrode, 20 ... Battery element, 21, 41, 53 ... Positive electrode, 21A, 22A, 41A 53A ... Positive electrode current collector, 21B, 22B, 41B, 53B ... Positive electrode active material layer, 23, 43, 55 ... Separator, 40, 50 ... Winding electrode body, 56 ... Electrolyte layer, 60 ... Exterior member, 201 ... Negative electrode active material particles, 202: metal coating material.

Claims (14)

A positive electrode having a positive electrode active material layer on a positive electrode current collector, a negative electrode having a negative electrode active material layer on a negative electrode current collector, and an electrolyte solution,
The negative electrode active material layer includes a plurality of negative electrode active material particles having silicon (Si) as a constituent element,
The median diameter of the negative electrode active material particles is 1.6 μm or more and 6.2 μm or less, and the arithmetic standard deviation of the median diameter is 3.1 μm or less.
Lithium ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein a median diameter of the negative electrode active material particles is 1.8 μm or more and 2.5 μm or less.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material particles have an average circularity of 0.3 or more.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material particles are a simple substance, an alloy, or a compound of silicon.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer includes a metal coating material that covers a surface of the negative electrode active material particles.   The lithium ion secondary battery according to claim 5, wherein the metal coating material has at least one metal element of copper (Cu), cobalt (Co), iron (Fe), and nickel (Ni) as a constituent element. .   The lithium ion secondary battery according to claim 6, wherein the metal coating material is a simple substance of copper, cobalt, iron, or nickel.   The lithium ion secondary battery according to claim 5, wherein a ratio T / D of an average thickness T of the metal coating material to a median diameter D of the negative electrode active material particles is 1/20 or more and 1/1 or less.   The lithium ion secondary battery according to claim 5, wherein the metal coating materials are in contact with or bonded to each other.   The lithium ion secondary battery according to claim 5, wherein the metal coating material is in contact with or bonded to the negative electrode current collector.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer includes a negative electrode binder.   The lithium ion secondary battery according to claim 11, wherein the negative electrode binder is polyvinylidene fluoride or polyimide.   The lithium ion secondary battery according to claim 1, wherein a utilization factor of the negative electrode is 80% or less. A negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer includes a plurality of negative electrode active material particles having silicon as a constituent element;
The median diameter of the negative electrode active material particles is 1.6 μm or more and 6.2 μm or less, and the arithmetic standard deviation of the median diameter is 3.1 μm or less.
Negative electrode for lithium ion secondary battery.

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