JP2006107847A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of improving a charge-discharge cycle characteristic while keeping a high capacity by preventing a space from being formed in a rolled body in a charge-discharge process. <P>SOLUTION: By changing the thickness of a separator and/or the void content thereof, a hole volume ρa per unit area of the separator disposed on the rolling outer periphery side by interlaying a negative electrode is set larger than a hole volume ρb per unit area of the separator disposed on the rolling inner periphery side. The hole volume per unit area is specified by (separator unit area)×(separator thickness)×(void content). In order to improve the charge-discharge cycle characteristic, ρa/ρb should be set to 1.1-2.0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a wound body obtained by laminating and winding a positive electrode and a negative electrode via an electrolyte, and in particular, a metal, a semimetal, an alloy, and a compound capable of inserting and extracting lithium The present invention relates to a battery including a negative electrode reaction layer containing particles containing at least one member selected from the group consisting of:

  In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape recorder), a mobile phone, or a laptop computer have appeared, and their size and weight have been reduced. Accordingly, research and development for improving the energy density of batteries used as power sources for portable electronic devices, particularly secondary batteries, are being actively promoted. Among them, lithium ion secondary batteries are widely used because a large energy density can be obtained as compared with lead batteries or nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries.

  As a negative electrode active material used for a lithium ion secondary battery, a carbonaceous material such as non-graphitizable carbon or graphite exhibits a relatively high capacity and exhibits good cycle characteristics.

  However, with the recent increase in capacity, there is a problem of further increasing the capacity of the carbonaceous material. In the following Patent Document 1, a high capacity is achieved by using a carbonaceous material obtained by selecting a carbonization raw material and production conditions for a negative electrode. However, since this negative electrode has a discharge potential of 0.8 V to 1.0 V with respect to lithium, the battery discharge voltage when the battery is configured is lowered, and a significant improvement in battery energy density cannot be expected. Further, this negative electrode has a drawback that the charge / discharge curve has a large hysteresis and the energy efficiency at each charge / discharge cycle is low.

JP-A-8-315825

On the other hand, as a negative electrode active material capable of realizing a higher capacity, for example, a material that applies the reversible generation and decomposition of a certain kind of lithium metal by an electrochemical reaction has been studied. Specifically, a LiAl alloy has been known for a long time, and Patent Document 2 reports a Si alloy. Furthermore, in Non-Patent Document 1, D. Larcher et al. Introduces an intermetallic compound called Cu ₆ Sn ₅ as a negative electrode active material capable of obtaining a high capacity.

U.S. Pat. No. 4,950,566

Journal of The Electrochemical Society, 147 (5) 1658-1662 (2000)

  However, a negative electrode using an alloying reaction with lithium is greatly expanded and contracted with charge and discharge as compared with a conventionally used carbonaceous material. It was.

Therefore, in order to prevent this deterioration, a negative electrode active material in which a part of the negative electrode active material is substituted with an element that does not participate in expansion and contraction associated with insertion and extraction of lithium has been proposed. For example, Patent Document 3 discloses LiSi _a O _b (0 ≦ a, 0 <b <2), and Patent Document 4 describes Li _c Si _ld M _d O _e (M is a metal excluding an alkali metal or a group excluding silicon). Patent Document 5 describes a LiAgTe-based alloy, which represents a metal (0 ≦ c, 0 <d <1, 0 <e <2).

JP-A-6-325765

JP-A-7-230800

JP 7-288130 A

  However, even with these negative electrode active materials, the fact is that the charge / discharge cycle characteristics are greatly deteriorated due to expansion and contraction, and the characteristics of high capacity cannot be fully utilized. In particular, when the positive electrode and the negative electrode are used by being laminated and wound via an electrolyte, the charge / discharge cycle characteristics deteriorate significantly.

  As a result of intensive studies on the above problems, the inventors have found that the following structural factors cause deterioration in cycle characteristics.

  FIG. 1 is a cross-sectional view of a wound electrode body (hereinafter appropriately referred to as a wound body) in a charge / discharge process of a secondary battery. FIG. 1A shows a wound body before charging, FIG. 1B shows the wound body after charging, and FIG. 1C shows the wound body after discharging.

  When the wound negative electrode 1 as shown in FIG. 1A expands by charging, the entire wound body 10 expands due to the expansion force (FIG. 1B). At this time, since the expansion of the wound body 10 is pressed into a battery case (not shown), the negative electrode 1 and the positive electrode 2 are brought into a tight contact state with the expansion pressure.

  On the other hand, in the discharge process shown in FIG. 1C, since the negative electrode 1 contracts, the distance between the positive and negative electrodes always tends to increase. Of course, the entire wound body contracts mainly due to the contraction of each electrode of the positive electrode 2 and the negative electrode 1 and the separator 3 and the elasticity (repulsive force) of the battery case, but compared with the negative electrode expansion pressure during charging. And the force applied to the contraction is insufficient, and the distance between the positive and negative electrodes tends to increase.

  As a means for compensating for the force required to restore the wound body 10, there is a method in which the inner dimension of the battery case is made smaller than the outer dimension of the wound body 10 and the wound body is press-fitted into the battery case. However, this is not practical because the external dimensions of the battery are greatly changed by charging and discharging.

Furthermore, the spread of the distance between the positive and negative electrodes in the discharge process is as shown in FIG. 1C. The positive electrode reaction layer 2a at the inner periphery of the positive electrode facing the negative electrode reaction layer 1b through the negative electrode reaction layer 1b at the outer periphery of the negative electrode and the separator 3. The negative electrode outer peripheral electrode distance L _o including the negative electrode inner peripheral electrode distance L _i including the positive electrode outer peripheral electrode positive electrode reaction layer 2b opposed to the negative electrode inner peripheral electrode negative reaction layer 1a with the separator 3 interposed therebetween. It turned out that it always tends to be larger.

This tendency, negative outer circumference the inter-electrode gap which is represented by reference numeral G _o is always made for greater than the negative electrode in the peripheral portion between the electrodes gap represented by reference numeral G _i. This is because only the contraction of the negative electrode proceeds in the wound structure having a relatively weak restoring force from expansion to contraction in the contraction direction.

  Therefore, in the discharge process, the reaction characteristics between the negative electrode reaction layer 1b at the outer periphery of the negative electrode and the positive electrode reaction layer 2a at the inner periphery of the positive electrode are as follows. The balance is more easily degraded than the reaction characteristics between the two, and this causes a decrease in cycle characteristics.

  Accordingly, an object of the present invention is to provide a battery capable of improving charge / discharge cycle characteristics while maintaining a high capacity.

  In order to solve the above-mentioned problem, a first aspect of the present invention is a wound electrode obtained by laminating a positive electrode and a negative electrode each provided with a reaction layer on both sides of a belt-shaped metal foil via a separator and further winding the electrode. The positive electrode reaction layer of the positive electrode is made of a lithium composite oxide, and the negative electrode reaction layer of the negative electrode is selected from the group consisting of metals, metalloids, alloys and compounds capable of occluding and releasing lithium. The separator has a porosity of 30% or more and 65% or less, the pore volume per unit area of the separator disposed outside the negative electrode, and the inner side of the negative electrode The secondary battery is characterized in that the ratio (= ρa / ρb) with respect to the pore volume ρb per unit area of the separator disposed in is set to 1.1 or more and 2.0 or less.

  According to the present invention, the porosity (hole volume per unit area) of the separator disposed on the winding outer peripheral reaction surface via the negative electrode is determined by the vacancy of the separator disposed on the winding inner peripheral reaction surface. Increase the retention capacity of the electrolyte by making it larger than the porosity, and improve the reactivity of the metal foil outer periphery negative electrode, which tends to have a larger interelectrode distance than the inner periphery negative electrode through the metal foil in the discharge process Provides excellent cycle characteristics.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 2 is a perspective view showing the configuration of the secondary battery according to the embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound body 20 in which a strip-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. Have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the wound body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a thermal resistance element (Positive Temperature Coefficient: PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15a is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current, and is made of, for example, barium titanate semiconductor ceramics. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

[Positive electrode]
As the positive electrode, a belt-like electrode having a reaction layer provided on the surface of the positive electrode current collector is used. The positive electrode current collector is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil, and has a thickness of about 5 μm to 50 μm.

  The positive electrode reaction layer includes, for example, a positive electrode active material, a conductive agent such as carbon black or graphite as necessary, and a binder such as polyvinylidene fluoride. As the positive electrode active material, for example, metal oxides, metal sulfides, specific polymer materials, and the like are preferable, and one or more of them are selected according to the intended use of the battery.

Examples of the metal oxide include a lithium composite oxide mainly composed of Li _x MIO ₂ or V ₂ O ₅ . In particular, a lithium composite oxide is preferable because it can generate a high voltage and increase an energy density. In the above composition formula, MI is preferably at least one selected from the group consisting of one or more transition metals, particularly cobalt (Co), nickel and manganese (Mn). The value of x varies depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10. Specific examples of the lithium composite oxide _varies depending on the charge and discharge state of _{LiCoO 2, LiNiO 2, Li y} Ni z Co 1-z O 2 (y and z is a secondary battery, usually, 0 <y < 1, 0.7 <z <1.02), or LiMn ₂ O ₄ having a spinel structure.

Examples of the metal sulfide include TiS _{2 and} MoS _2, and examples of the polymer material include polyacetylene and polypyrrole. In addition to these positive electrode active materials, NbSe ₂ or the like can be used.

[Negative electrode]
The negative electrode has, for example, a structure in which a negative electrode reaction layer is provided on one or both surfaces of a negative electrode current collector having a pair of opposed surfaces. The negative electrode current collector is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil. The thickness of the negative electrode current collector is, for example, 5 μm to 50 μm.

  The negative electrode reaction layer includes particles of the negative electrode active material and a binder such as polyvinylidene fluoride as necessary. Examples of the negative electrode active material include metals, metalloids, alloys, and compounds capable of inserting and extracting lithium. In order to obtain a high capacity, it is preferable to include at least one of these. Note that in this specification, a metalloid refers to a single metalloid element. In this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Some of the structures include a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them.

  Metals or metalloids capable of inserting and extracting lithium include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), and bismuth (Bi). , Cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf) Is mentioned.

As the capable of intercalating and deintercalating lithium alloys and compounds, for example, those represented by the chemical formula Ma _p Mb _q Mc _r. In these chemical formulas, Ma represents at least one metal element and metalloid element capable of forming an alloy with lithium, Mb represents at least one metal element, and Mc represents a metal element and metalloid other than Ma. Represents at least one of the elements; The values of p, q, and r are p> 0, q ≧ 0, and r ≧ 0, respectively.

Among these, an intermetallic compound represented by the chemical formula MII _a N _b (MII represents at least one of tin and silicon, and N represents at least one of elements other than tin and silicon, respectively) is preferable. . These may be crystalline or amorphous.

Specific examples of the intermetallic compound represented by the chemical formula MII _a N _b are AsSn, AuSn, CaSn ₃ , CeSn ₃ , CoCu ₂ Sn, Co ₂ MnSn, CoNiSn, CoSn ₂ , Co ₃ Sn ₂ , CrCu ₂ Sn, Cu ₂ FeSn, CuMnSn, Cu ₂ MnSn, Cu ₄ MnSn, Cu ₂ NiSn, CuSn, Cu ₃ Sn, Cu ₆ Sn ₅ , FeSn ₂ , IrSn, IrSn ₂ , LaSn ₃ , MgNi ₂ Sn, Mg ₂ Sn , MnNi ₂ Sn, MnSn ₂ , Mn ₂ Sn, Mo ₃ Sn, Nb ₃ Sn, NdSn ₃ , NiSn, Ni ₃ Sn ₂ , PdSn, Pd ₃ Sn, Pd ₃ Sn ₂ , PrSn ₃ , PtSn ₂ , Pt ₃ Sn, PuSn ₃ , RhSn, Rh ₃ Sn ₂ , RuSn ₂ , SbSn, SnTi ₂ , Sn ₃ U, SnV ₃ , BeSi Zr, CoSi ₂ , β-Cr ₃ Si, Cu ₃ Mg ₂ Si, Fe ₃ Si, Mg ₂ Si, MoSi ₂ , Nb ₃ Si, NiSi ₂ , θ-Ni ₂ Si, β-Ni ₃ Si, ReSi ₂ , There are α-RuSi, SiTa ₂ , Si ₂ Th, Si ₂ U, β-Si ₂ U, Si ₃ U, SiV ₃ , Si ₂ W, SiZr ₂ and the like.

Moreover, the complex oxide containing at least one of tin and silicon disclosed in International Publication WO96 / 13873 pamphlet is also preferable. Examples of the composite oxide include a chemical formula SnMIII _c O _d (MIII represents at least one selected from the group consisting of silicon, germanium, lead, bismuth, antimony, phosphorus, boron, aluminum, and arsenic, and c is 0 to 0. 4 number, d represents each number of _{1~10.), SnMIV e O f} (MIV represents germanium, lead, bismuth, antimony, phosphorus, boron, at least one selected from the group consisting of aluminum and arsenic , C represents a number from 0 to 4, and d represents a number from 1 to 10, respectively), SnSiMgV _h O _i (MV is a group consisting of germanium, lead, bismuth, antimony, phosphorus, boron, aluminum and arsenic) At least one kind is represented, and g, h and i are numbers satisfying 0.1 ≦ g + h ≦ 4, 0.05 ≦ g ≦ 2, 1.1 ≦ i ≦ 10, respectively. There are some.).

Specific examples of such composite oxides include SnSi _0.01 O _1.02 , SnGe _0.01 O _1.02 , SnPb _0.05 O _1.1 , SnSi _0.1 Ge _0.1 Pb _0.1 O _2.6 , SnSi _0.2 Ge _0.1 O _2.6 , SnSi _0.7 O _2.4 , SnGe _0.7 O _2.4 , SnSi _0.8 O _2.6 , SnSiO ₃ , SnPbO ₃ , SnSi _0.9 Ge _0.1 O ₃ , SnSi _0.8 Ge _0.2 O ₃ , SnSi _0.8 Pb _0.2 O ₃ , SnSi _0.8 Ge _0.1 Pb _0.1 O ₃ , SnSi _1.2 O _3.4 , SnSi ₂ O ₆ , SnB _0.01 O _1.015 , SnAl _0.01 O _1.015 , SnP _0.01 O _2.015 , SnP _0.05 O _1.125 , SnB _0.05 O _1.075 , SnP _0.1 O _1.25 , SnB _0.1 O _1.15 , SnP _0.3 O _1.75 , SnB _0.7 O _{2.05 , SnP 0.8 O 3, SnPO 3.5} , SnBO 2.5, SnSi 0.25 P 0.2 B 0.2 O 3, SnSi 0.5 P 0.2 B 0.2 O 3, SnSi 0.08 P 0.2 _{3.1, SnSi 0.8 B 0.2 O 2.9} , SnSi 0.8 Al 0.2 O 2.9, SnSi 0.6 Al 0.2 B 0.2 O 2.8, SnSi 0.6 Al 0.2 P 0.2 O 3, SnSi 0.6 B 0.2 P 0.2 O 3, SnSi 0.4 Al 0.2 B 0.4 O _2.7 , SnSi _0.6 Al _0.1 B _0.1 P _0.3 O _3.25 , SnSi _0.6 Al _0.1 B _0.3 P _0.1 O _3.05 , SnSi _0.5 Al _0.3 B _0.4 P _0.2 O _3.55 , SnSi _0.5 Al _0.3 B _0.4 P _0.5 O _4.3 , or SnSi _0.8 Al _0.3 B _0.2 P _0.2 O _3.85 .

  In addition, such a negative electrode active material is produced by, for example, a mechanical alloying method or a method in which raw materials are mixed and heat-treated in an inert atmosphere or a reducing atmosphere.

Further, the negative electrode reaction layer 22b may contain other negative electrode active materials in addition to a single element, alloy or compound of a metal element or a metalloid element capable of forming an alloy with lithium. Examples of other negative electrode active materials include carbonaceous materials capable of inserting and extracting lithium, metal oxides or polymer materials, and metal composite materials. Examples of the carbonaceous material include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon or Examples thereof include carbon blacks. Among these, coke includes pitch coke, needle coke, and petroleum coke. Organic polymer compound fired bodies are carbonized by firing polymer materials such as phenol resin and furan resin at an appropriate temperature. What you did. Examples of the metal oxide include tin oxide (SnO ₂ ), and examples of the polymer material include polyacetylene and polypyrrole. Examples of the metal composite material include a composite material made of cobalt (Co), tin, indium, titanium (Ti), and carbon.

  Note that lithium may be electrochemically occluded in the negative electrode active material in the battery after the battery is manufactured, and supplied electrochemically from the positive electrode 21 or a lithium source other than the positive electrode 21 after the battery is manufactured or before the battery is manufactured. It may be occluded by the negative electrode active material. Moreover, you may make it contain in the case of the synthesis | combination of a negative electrode active material.

[Separator]
In the present invention, a wound body in which a positive electrode and a negative electrode as shown in FIG. At this time, the pore volume per unit area of the separator disposed on the winding outer peripheral reaction surface via the negative electrode is larger than the pore volume per unit area of the separator disposed on the winding inner peripheral reaction surface. By increasing the capacity of the electrolyte, the ability to retain the electrolyte is improved, and by improving the reactivity of the metal foil outer periphery negative electrode, which tends to have a larger interelectrode distance than the inner periphery negative electrode through the metal foil in the discharge process, Cycle characteristics can be obtained.

  The separator is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric, and these two or more kinds of porous films are laminated. It may be a structure.

  In general, the thickness of the separator is preferably 10 to 50 μm, more preferably 15 to 40 μm. If the separator is too thick, the filling amount of the active material is reduced and the battery capacity is reduced. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

  In the present invention, the pore volume per area of the separator is defined by [separator unit area × separator thickness × porosity]. Therefore, in order to change the pore volume between the outer peripheral side and the inner peripheral side, the thickness of the separator and / or the porosity may be changed within a suitable range.

Here, the porosity is the ratio of the vacancies in the portion facing the reaction surface. The porosity P (%) is a value obtained as [P = (1−D / ρ) × 100] from the true density ρ (g / cc) and volume density D (g / cc) of the separator. As a method for measuring the true density, a known method for measuring based on Archimedes' principle can be used. More specifically, the volume of liquid phase B excluded by solid phase A is measured by immersing solid phase A whose weight is measured using a pycnometer (hydrometer) into liquid phase B having a known specific gravity. A method using gas phase C (for example, helium gas) instead of liquid phase B is also known. In the present invention, a method using helium gas is used in which a portion in contact with the electrode reaction surface of the separator is used for measurement and a void smaller than the liquid phase can be measured.

However, in the discharge process, the problem is that the distance L _o between the negative electrode outer peripheral electrodes tends to be larger than the distance L _i between the negative electrode inner peripheral electrodes, and the thickness of the separator that acts as a cushion in the porous body It is not desirable to make the outer peripheral side thinner than the inner peripheral side. Therefore, it is more preferable to control the pore volume by making the outer peripheral side separator thicker than the inner peripheral side.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. For example, the electrolytic solution includes a solvent and a lithium salt that is an electrolyte salt. The solvent dissolves and dissociates the electrolyte salt. Solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl. 1,3 dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetic acid ester, butyric acid ester or propionic acid ester, etc., and any one of these or a mixture of two or more May be.

Examples of the lithium salt include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, or LiBr. One kind or a mixture of two or more kinds may be used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited only to these Examples.

[Production of positive electrode]
First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to obtain a positive electrode mixture slurry.

  Subsequently, it apply | coated uniformly on both surfaces of the positive electrode electrical power collector which consists of an aluminum foil with a thickness of 20 micrometers, it was made to dry, and the positive electrode reaction layer was formed by compression molding with the roll press machine, and the positive electrode was produced. After that, an aluminum positive electrode lead was attached to one end of the positive electrode current collector.

[Production of Negative Electrode A]
Copper and tin were weighed so as to be 50 parts by mass of copper and 50 parts by mass of tin, and then put into a quartz tube and melted in a high-frequency melting furnace in an argon (Ar) atmosphere. Thereafter, this was cast on a rotating disk made of copper having a diameter of 200 mm, a width of 20 mm, and a rotational speed of 3000 rpm, and rapidly cooled to obtain a ribbon-like copper tin (CuSn) alloy piece. The obtained ribbon-shaped copper tin alloy piece was pulverized in an argon atmosphere using a ball mill to obtain a particulate powder. The obtained powder was classified with a 63 μm sieve to obtain a negative electrode active material. The average particle size of the powder obtained by classification was 25 μm.

  Next, carbon black and artificial graphite particulate powder are prepared as the negative electrode active material, 60 g of the obtained copper tin alloy, 2 g of carbon black, 28 g of artificial graphite, and 10 g of porovinylidene fluoride as a binder, Were mixed to prepare a negative electrode mixture. Subsequently, the negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which is applied to both surfaces of a negative electrode current collector 22a made of a copper foil having a thickness of 15 μm, and dried. After cutting so as to be accommodated in the can 11, the negative electrode reaction layer 22 b was formed by compression molding with a roll press. After that, the negative electrode current collector 22a on which the negative electrode reaction layer 22b was formed was cut to have a width of 60 mm to produce the negative electrode 22. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a.

  Using the positive electrode and the negative electrode A thus prepared, secondary batteries of Examples 1 to 14 and Comparative Examples 1 to 6 are manufactured. Here, about the separator arrange | positioned at the inner peripheral side and the outer peripheral side of the negative electrode A, what changed the porosity and thickness as follows is used.

<Example 1>
Using a polyethylene film microporous film having a porosity of 33% and a thickness of 20 μm for the separator disposed on the outer periphery side of the winding through the negative electrode current collector, the porosity of 30 is provided for the separator disposed on the inner periphery side of the winding. %, 20 μm thick polyethylene film microporous membrane, the positive electrode and the negative electrode were laminated with these separators, and this laminate was wound many times to form a wound body 20. At this time, the lengths of the positive electrode, the negative electrode, and the separator were adjusted so that the maximum diameter of the element body portion was 17.3 mm.

<Example 2>
Using a polyethylene film microporous film having a porosity of 40% and a thickness of 20 μm for the separator disposed on the outer periphery side of the winding through the negative electrode current collector, the porosity of 30 is provided for the separator disposed on the inner periphery side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 3>
A polyethylene film microporous film having a porosity of 60% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 30 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 4>
A polyethylene film microporous film having a porosity of 40% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 5>
A polyethylene film microporous film having a porosity of 50% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 6>
A polyethylene film microporous film having a porosity of 65% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 7>
A polyethylene film microporous film having a porosity of 55% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding via the negative electrode current collector, and the porosity of 50 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 8>
A polyethylene film microporous film having a porosity of 65% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 50 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 9>
A polyethylene film microporous film having a porosity of 35% and a thickness of 22 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 10>
A polyethylene film microporous film having a porosity of 35% and a thickness of 30 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 11>
A polyethylene film microporous film having a porosity of 35% and a thickness of 40 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 12>
A polyethylene film microporous film having a porosity of 40% and a thickness of 23 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 13>
A polyethylene film microporous film having a porosity of 50% and a thickness of 25 μm is used for the separator disposed on the outer periphery side of the winding through the negative electrode current collector, and the porosity of 40 is provided for the separator disposed on the inner periphery side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 25 μm was used.

<Example 14>
A polyethylene film microporous film having a porosity of 35% and a thickness of 30 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 30 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Comparative Example 1>
The same procedure as in Example 1 was performed except that a polyethylene film microporous film having a porosity of 28% and a thickness of 20 μm was used for the separator disposed on the outer periphery and the inner periphery through the negative electrode current collector.

<Comparative example 2>
The same procedure as in Example 1 was conducted except that a polyethylene film-like microporous film having a porosity of 30% and a thickness of 20 μm was used for the separator disposed on the outer periphery and the inner periphery through the negative electrode current collector.

<Comparative Example 3>
A polyethylene film microporous film having a porosity of 65% and a thickness of 20 μm is used for the separator disposed on the outer circumferential side of the winding through the negative electrode current collector, and the porosity of 30 is provided for the separator disposed on the inner circumferential side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Comparative example 4>
A polyethylene film microporous film having a porosity of 70% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 65 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Comparative Example 5>
A polyethylene film microporous film having a porosity of 35% and a thickness of 20.5 μm is used for the separator disposed on the outer circumferential side of the winding via the negative electrode current collector, and the pores are disposed on the separator disposed on the inner circumferential side of the winding. The same procedure as in Example 1 was performed except that a polyethylene film microporous membrane having a rate of 35% and a thickness of 20 μm was used.

<Comparative Example 6>
A polyethylene film microporous film having a porosity of 35% and a thickness of 40 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 35 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 1 except that a polyethylene film microporous film having a thickness of 18 μm was used.

  Moreover, the secondary batteries of Examples 15 to 17 and Comparative Examples 7 and 8 were prepared using the positive electrode used in the above-described Examples and Comparative Examples and the negative electrode B made of the composite material produced as follows. Produced.

[Preparation of Negative Electrode B]
First, 32.0 parts by weight of cobalt powder, 59.4 parts by weight of tin powder, 3.7 parts by weight of silicon powder, 3.2 parts by weight of titanium powder, and 1.7 parts by weight of indium powder were weighed, and the quartz tube And melted in a high-frequency melting furnace in an argon (Ar) atmosphere. Thereafter, this was cast on a rotating disk made of copper having a diameter of 200 mm, a width of 20 mm, and a rotational speed of 3000 rpm, and rapidly cooled to obtain a ribbon-like material made of Co, Sn, Si, Ti, and In. The ribbon-shaped material piece was pulverized in an argon atmosphere using a ball mill to obtain a powder material A.

  Next, 16.4 g of this powder material A and 3.6 g of carbon powder were dry-mixed in an agate mortar and set in a reaction vessel of a planetary ball mill (manufactured by Ito Seisakusho) together with about 400 g of steel balls having a diameter of 9 mm. Next, the inside of the reaction vessel was replaced with an argon atmosphere, and a 10-minute operation at a rotational speed of 250 rpm and a 10-minute pause were repeated until the total operation time reached 30 hours. Thereafter, the reaction vessel was cooled to room temperature, the synthesized powder was taken out, and the coarse powder was removed through a 280 mesh sieve to obtain a ball mill synthetic powder B.

  The composition of the obtained ball mill synthetic powder B was analyzed. The carbon content was measured by a carbon / sulfur analyzer, and the contents of cobalt, tin, silicon, titanium, and indium were measured by ICP (Inductively Coupled Plasma) emission analysis. As a result, the mass ratio of Co: Sn: Si: Ti: In: C contained in this ball mill synthetic powder B is 26.2: 48.7: 3.0: 2.6: 1.4: 18.1. Yes, the half-value width of the diffraction peak of the reaction phase by X-ray diffraction analysis was 4.5 deg.

  70 parts by weight of the obtained ball mill synthetic powder B, 20 parts by weight of graphite as a conductive agent and a negative electrode active material, 1 part by weight of acetylene black as a conductive agent, and 4 parts by weight of polyvinylidene fluoride as a binder Were mixed and dispersed in a suitable solvent to form a slurry. This was coated on a 15 μm copper foil current collector, dried, cut so as to be accommodated in the battery can 11, and then compression molded with a roll press to form the negative electrode reaction layer 22b. After that, the negative electrode current collector 22a on which the negative electrode reaction layer 22b was formed was cut to have a width of 60 mm to produce the negative electrode 22. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a.

<Example 15>
Using a polyethylene film microporous film having a porosity of 33% and a thickness of 20 μm for the separator disposed on the outer periphery side of the winding through the negative electrode current collector, the porosity of 30 is provided for the separator disposed on the inner periphery side of the winding. %, 20 μm thick polyethylene film microporous membrane, the positive electrode and the negative electrode were laminated with these separators, and this laminate was wound many times to form a wound body 20. At this time, the lengths of the positive electrode, the negative electrode, and the separator were adjusted so that the maximum diameter of the element body was 17.3 mm.

<Example 16>
Using a polyethylene film microporous film having a porosity of 40% and a thickness of 20 μm for the separator disposed on the outer periphery side of the winding through the negative electrode current collector, the porosity of 30 is provided for the separator disposed on the inner periphery side of the winding. %, And the same as Example 15 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Example 17>
A polyethylene film microporous film having a porosity of 60% and a thickness of 20 μm is used for the separator disposed on the outer peripheral side of the winding through the negative electrode current collector, and the porosity of 30 is provided for the separator disposed on the inner peripheral side of the winding. %, And the same as Example 15 except that a polyethylene film microporous film having a thickness of 20 μm was used.

<Comparative Example 7>
Example 15 is the same as Example 15 except that a polyethylene film microporous film having a porosity of 30% and a thickness of 20 μm is used for the separator disposed on the outer circumference and the inner circumference via the negative electrode current collector.

<Comparative Example 8>
A polyethylene film microporous film having a porosity of 65% and a thickness of 20 μm is used for the separator disposed on the outer circumferential side of the winding through the negative electrode current collector, and the porosity of 30 is provided for the separator disposed on the inner circumferential side of the winding. %, And the same as Example 15 except that a polyethylene film microporous film having a thickness of 20 μm was used.

The wound body 20 produced as described above is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. Was accommodated in a battery can 11 having an inner diameter of 17.5 mm. After that, an electrolytic solution was injected into the battery can 11. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 1 mol / dm ³ in a solvent obtained by mixing 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate was used.

After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 via the gasket 17 to obtain a cylindrical secondary battery having an outer diameter of 18 mm and a height of 65 mm.
<Evaluation>
First, in both the examples and comparative examples, the number of batteries prepared was 50, and charging was performed until the battery voltage reached 4.2 V at a constant current of 1 A, and then the current value was set to 0.2 at a constant voltage of 4.2 V. Discharge was performed until 005A was reached. Next, after being left for 2 weeks in a charged state, batteries having an open circuit voltage (OCV) of less than 4.15 V were selected as defective OCV products.

  Subsequently, a charge / discharge cycle test was performed in a 20 ° C. environment using a good battery. The charging conditions are as described above. Discharging conditions were performed at a constant current of 1 A until the battery voltage reached 2.5V. The first discharge after aging was used for conditioning, and the cycle retention rate [%] after 300 cycles was determined starting from the second discharge capacity. The obtained results are shown in Table 1.

  As in Comparative Example 1, when the porosity of the separator is less than 30%, the cycle characteristics are remarkably deteriorated. This is because the ion permeability deteriorates. In addition, when the porosity of the separator exceeds 65% as in Comparative Example 4, the number of defective batteries increases. When the defective battery was disassembled and examined, it was found that the insulation was broken by the separator film. This is because the strength of the separator is significantly reduced.

  Therefore, the porosity is preferably 30% or more in order to ensure ion permeability. However, if it exceeds 65%, it becomes difficult to ensure the mechanical strength of the film. More preferably, it is 35 to 60%.

  Examples 1 to 8, Comparative Example 2 for pore volume ρa per unit area of the separator disposed outside the negative electrode and pore volume ρb per unit area of the separator disposed inside the negative electrode 3 when the thickness of the separator is made constant and the ratio ρa / ρb is changed, or when the separator porosity is made constant as in Examples 9 to 11 and the ratio ρa / ρb is changed, or As in Examples 12 and 13, when the ratio of ρa / ρb was changed by both the porosity and thickness, good cycle maintenance was achieved when the value of ρa / ρb was 1.1 or more and 2.0 or less. Indicates the rate. A suitable cycle maintenance rate is 72% or more.

  This is because if the ρa / ρb value is less than 1.1, the difference in reactivity in the reaction layer through the positive and negative electrodes is not sufficiently relaxed. Furthermore, if the ρa / ρb value exceeds 2.0, the electrolyte amount balance between the negative electrode outer peripheral reaction layer and the negative electrode inner peripheral reaction layer is lost, and the difference in reactivity between the inner and outer surfaces via the electrode is large. Become. For this reason, the cycle characteristics deteriorate, which is not preferable.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made.

  For example, in the above-described embodiment, the case where an electrolytic solution that is a liquid electrolyte is used as a solvent has been described. However, another electrolyte may be used instead of the electrolytic solution. Other electrolytes include, for example, a gel electrolyte in which an electrolyte is held in a polymer compound, a solid electrolyte having ionic conductivity, a mixture of a solid electrolyte and an electrolyte, or a solid electrolyte and a gel electrolyte. And a mixture thereof.

  Note that various polymer compounds can be used for the gel electrolyte as long as it absorbs the electrolyte and gels. Examples of such a polymer compound include a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, an ether-based polymer such as polyethylene oxide or a crosslinked product containing polyethylene oxide. A molecular compound, polyacrylonitrile, etc. are mentioned. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability.

  As the solid electrolyte, for example, an organic 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. At this time, as the polymer compound, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, an acrylate polymer compound alone or mixed, Alternatively, it can be used by copolymerizing in the molecule. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

  In the above-described embodiments and examples, the cylindrical secondary battery having a winding structure has been described. However, any battery having a winding structure can be applied to the present invention.

In the secondary battery used conventionally, it is a basic diagram which shows a mode that the wound electrode body produced by winding a positive electrode, a negative electrode, and a separator expand | swells and shrink | contracts in the charging / discharging process. It is a perspective view which shows sectional drawing of the secondary battery to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Negative electrode 1a ... Negative electrode inner periphery reaction layer 1b ... Negative electrode outer periphery reaction layer 2 ... Positive electrode 2a ... Positive electrode inner periphery reaction layer 2b ... Positive electrode outer periphery reaction layer 3. · The separator L _o ... negative electrode outer peripheral side interpole distance L _i ... Fukyokunai peripheral side electrode distance G _o between ... negative outer circumference electrode gap G _i ... Fukyokunai periphery inter-electrode gap 10 ... Winding body 11 ... Battery can 12 ... Insulating plate 13 ... Insulating plate 14 ... Battery lid 15 ... Safety valve mechanism 15a ... Disk plate 16 ... Heat sensitive resistance element 17 ... Gasket 20 ... Winding body 21 ... Positive electrode 22 ... Negative electrode 23 ... Separator 24 ... Center pin 25 ... Positive electrode lead 26 ... Negative electrode lead

Claims (3)

A secondary battery comprising a wound electrode body in which a positive electrode and a negative electrode provided with reaction layers on both sides of a belt-shaped metal foil are laminated via a separator and further wound,
The positive electrode reaction layer of the positive electrode is made of a lithium composite oxide,
The negative electrode reaction layer of the negative electrode is composed of a composite material containing at least one member selected from the group consisting of metals, metalloids, alloys and compounds capable of occluding and releasing lithium,
The porosity of the separator is 30% or more and 65% or less,
The ratio (= ρa / ρb) of the void volume ρa per unit area of the separator disposed outside the negative electrode to the void volume ρb per unit area of the separator disposed inside the negative electrode is 1. A secondary battery characterized by being set to 1 or more and 2.0 or less.   The secondary battery according to claim 1, wherein at least tin is included as a composite material capable of inserting and extracting lithium used in the negative electrode reaction layer.   The secondary battery according to claim 1, wherein the composite material capable of inserting and extracting lithium used in the negative electrode reaction layer includes tin, cobalt, silicon, titanium, indium, and carbon.

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