JP2010049909A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent breakage of a cathode collector in a cylindrical nonaqueous electrolyte secondary battery. <P>SOLUTION: An insulation coating material is provided so as to cover the vicinity of a forming terminal part of a cathode active material layer placed on a winding outer peripheral side of a battery, and a lubricating layer without containing reducibility extracts is fitted between the cathode active material layer and a cathode collector. The cathode collector is put under annealing treatment beforehand so as to enable to follow expansion and contraction of the cathode active material layer accompanying charge and discharge of the battery. As the lubricating layer, silicon oil, or one at least containing either silicon system resin, acrylic acid system resin, fluorine system resin or polyolefin system resin dissolved in a solvent is used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to a cylindrical non-aqueous electrolyte secondary battery.

  In recent years, electronic devices such as mobile phones and notebook personal computers have become more cordless and portable, and thin, small and lightweight portable electronic devices have been developed one after another. There is a strong demand. At present, the cylindrical lithium ion secondary battery is most used for driving the battery.

  Generally, a cylindrical lithium ion secondary battery includes a positive electrode in which a positive electrode active material layer is formed on both sides of a strip-shaped current collector, and a negative electrode in which a negative electrode active material layer is formed on both sides of the strip-shaped current collector. And a non-aqueous electrolyte comprising a wound electrode body (battery element) wound many times and laminated with a separator interposed therebetween. In the case of such a wound battery, burrs due to cutting may occur at the positive electrode end and the negative electrode end (cut ends of the positive electrode current collector and the negative electrode current collector). The burrs generated at the positive electrode end and negative electrode end damage the adjacent separator when an impact is applied or pressed from the outside, and the positive electrode and the negative electrode are short-circuited to cause abnormal heat generation and deterioration of battery characteristics. Invite them or cause the electrode to be cut.

Therefore, in Patent Document 1 below, in order to solve the above-described problems in the winding type battery, an insulating coating material is provided at the electrode end of the winding type battery so as not to cause damage due to burrs. A method has been proposed. In Patent Document 1, in addition to the electrode end portion, an insulating covering material is provided on an electrode portion facing the electrode end portion provided with the insulating covering material with a separator interposed therebetween to improve the damage prevention effect.
JP 2001-266946 A

  In addition to the vicinity of the electrode end portion, a portion where a problem such as a short circuit may occur in the electrode terminal fixing portion or the active material layer forming end portion (boundary portion between the electrode current collector and the active material layer). In this case, it is possible to further improve the reliability by providing an insulating coating material.

  In Patent Document 1, a flat battery in which a gel-like or solid electrolyte is formed on both surfaces of each of the positive electrode and the negative electrode is used. However, recently, an insulating coating material has also been provided in a cylindrical lithium ion secondary battery. A proposed configuration has been proposed.

  By the way, in order to improve the battery capacity of the cylindrical lithium ion secondary battery, there is a method of increasing the density of the active material layer. When such a method is used, the active material layer expands during battery charging. The active material layer contracts during discharge. At this time, since the metal current collector, which is the base material on which the active material layer is formed, does not stretch, the active material layer is cracked or cracked by repeated charge and discharge, and the active material is peeled off and peeled off. .

  Therefore, in order to solve such a problem, for example, a technique of using an annealed aluminum foil as the positive electrode current collector, or heat treatment is applied to the positive electrode after forming the positive electrode active material layer on the positive electrode current collector. There is technology to apply. When the annealing treatment is performed on the aluminum foil, the elongation of the aluminum foil increases, so that the current collector can easily follow the expansion and contraction of the active material layer accompanying charge / discharge.

  For this reason, it is hard to produce a crack and a crack in an active material layer, and it can suppress peeling and peeling of an active material. Therefore, a decrease in battery capacity and a decrease in cycle characteristics can be suppressed.

  However, for example, when an insulating coating material is provided at the active material layer forming end, it has been confirmed that the winding of the current collector often occurs at the end of the insulating coating material on the battery outer periphery side by winding. It was. Further, in a battery system using an alloy-based active material mainly composed of tin (Sn) and silicon (Si) in which expansion and contraction of the active material layer due to charge and discharge are more remarkable, the problem becomes more prominent.

  Accordingly, an object of the present invention is to provide a nonaqueous electrolyte secondary battery that achieves both safety and stability of the battery.

  In order to solve the above problems, the present invention includes a strip-shaped positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector, and a strip-shaped negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector. A battery element laminated and wound via a separator is accommodated in a battery can, and an insulating coating material is provided so as to cover at least the vicinity of the formation end portion of the positive electrode active material layer positioned on the outer periphery side of the winding. A cylindrical non-aqueous electrolyte secondary battery in which a lubricating layer containing no reducing extract is provided between an insulating coating material, a positive electrode active material layer, and a positive electrode current collector.

  In the cylindrical non-aqueous electrolyte secondary battery described above, it is preferable that the positive electrode current collector is subjected to an annealing treatment.

  In the above-described cylindrical nonaqueous electrolyte secondary battery, it is preferable that the lubricating layer contains at least one of silicon oil, silicon resin, acrylic acid resin, fluorine resin, and polyolefin resin.

  The fluororesin is polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), polyvinylidene fluoride. It is preferably at least one of (PVdF). The polyolefin resin is preferably at least one of polyimide (PI), polypropylene (PP), and polyethylene (PE).

  The lubricating layer is formed by dissolving at least one of a silicon-based resin, an acrylic acid-based resin, a fluorine-based resin, and a polyolefin-based resin in a solvent. At this time, as the solvent, a solvent containing at least one of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol, toluene, and acetone can be used.

  Further, in the above-described cylindrical non-aqueous electrolyte secondary battery, the insulating coating material is composed of a base material and an adhesive layer provided by laminating the base material, and is configured such that the adhesive layer and the lubricating layer are in contact with each other. . It is preferable that the base material of the insulating coating material is a resin material formed by mixing one of a polypropylene resin and a polyimide resin, or a polypropylene resin and a polyimide resin. The pressure-sensitive adhesive layer is preferably provided on one surface of the substrate and is made of at least one of a silicon resin and an acrylic resin.

  By providing the lubricating layer as described above, adhesion between the insulating coating material, the positive electrode active material layer, and the positive electrode current collector can be reduced. Further, it is possible to prevent the surface oxide film of the positive electrode current collector from being reduced by preventing the insulating coating material and the positive electrode current collector from being in direct contact with each other.

  According to this invention, there is little difference in extensibility between a part of the positive electrode current collector to which the insulating coating material is adhered and a part of the positive electrode current collector to which the insulating coating material is not adhered, In addition, the positive electrode current collector can be prevented from being eroded by the electrolytic solution. For this reason, breakage of the positive electrode current collector can be prevented.

As a result of examining the cause of the foil breakage of the current collector in a battery using a conventional electrode, it was found that the foil breakage of the current collector occurs due to the following two combined actions.
(1) Insulating coating material (hereinafter referred to as “protective tape” as appropriate) The current collector at the attachment site and the current collector at the non-adhesion site have different extensibility during expansion of the active material at the time of charging. Due to the difference in rate, a load is applied to a part of the current collector at the end of the protective tape. In addition, although the oil film which consists of rolling oil used at the time of metal rolling is formed in the collector surface, the oil film on the collector surface will be removed by performing an annealing process or heat processing. When the current collector from which the oil film has been removed is used, the adhesion between the protective tape and the current collector is increased, and the load on a part of the current collector is further increased.
(2) Since the electric potential in the battery is increased during charging, the oxidizing atmosphere is strengthened particularly near the positive electrode. At this time, the antioxidants such as phenolic, phosphorous, and sulfur-based additives that are contained in the adhesive layer of the protective tape are eluted as reducing extracts, and the surface oxide film on the current collector is reduced. End up. For example, on the aluminum foil surface,
2Al ₂ O ₃ → 4Al + 3O ₂
The following reaction occurs. Thereby, the current collector that has lost the protective film is eroded by the electrolytic solution, and the strength of the current collector is reduced.

  In this invention, it is set as the structure which provides the lubricating layer which does not contain a reducing extract between a protective tape and a collector. This reduces the adhesion between the annealed current collector and the protective tape. In addition, since the adhesive layer of the protective tape containing the reducing extract and the current collector can be prevented from directly contacting, the surface oxide film of the current collector due to the elution of the reducing extract is reduced, The current collector can be prevented from being eroded by the electrolytic solution. Note that the lubricant layer does not contain an additive.

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

  FIG. 1 is a cross-sectional view of a lithium ion secondary battery which is an example of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. This secondary battery is called a so-called cylindrical type, and has a battery element 10 in which a strip-like positive electrode 11 and a negative electrode 12 are wound through a separator 13 inside a substantially hollow cylindrical battery can 1. is doing. The battery can 1 is made of, for example, iron plated with nickel, and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 9 a and 9 b are respectively disposed perpendicular to the winding peripheral surface so as to sandwich the battery element 10.

  Examples of the material of the battery can 1 include iron (Fe), nickel (Ni), stainless steel (SUS), aluminum (Al), titanium (Ti), and the like. The battery can 1 may be plated with nickel or the like, for example, in order to prevent corrosion due to an electrochemical non-aqueous electrolyte accompanying charging / discharging of the battery. At the open end of the battery can 1, a battery lid 2, which is a positive terminal plate, and a safety valve mechanism and a PTC element (Positive Temperature Coefficient) 4 provided inside the battery lid 2 are insulated. It is attached by caulking through a sealing gasket 5.

  The battery lid 2 is made of, for example, the same material as the battery can 1 and is provided with an opening for discharging gas generated inside the battery. In the safety valve mechanism, a safety valve 3, a disc holder 6, and a shut-off disc 7 are stacked in order. The protrusion 3 a of the safety valve 3 is connected to a positive electrode terminal 15 led out from the battery element 10 through a hole provided at the center of the shut-off disk 7. The safety valve mechanism is electrically connected to the battery lid 2 via the PTC element 4.

  In the safety valve mechanism, when the internal pressure of the battery exceeds a certain level due to internal short circuit or heating from the outside of the battery, the safety valve 3 is reversed, and the electrical connection between the protruding portion 3a, the battery lid 2 and the battery element 10 is established. To cut. That is, when the safety valve 3 is reversed, the positive electrode terminal 15 is pressed by the shut-off disk 7 and the connection between the safety valve 3 and the positive electrode terminal 15 is released. The disc holder 6 is made of an insulating material, and when the safety valve 3 is reversed, the safety valve 3 and the shut-off disc 7 are insulated.

  Further, when further gas is generated inside the battery and the internal pressure of the battery further increases, a part of the safety valve 3 is broken and the gas can be discharged to the battery lid 2 side.

  In addition, for example, a plurality of vent holes 7b are provided around the hole 7a of the shut-off disk 7, and when gas is generated from the battery element 10, the gas can be effectively discharged to the battery lid 2 side. It is configured.

  The resistance value of the PTC element 4 increases when the temperature rises, and the electric connection between the battery lid 2 and the battery element 10 is cut off to cut off the current, thereby preventing abnormal heat generation due to an excessive current. The insulating sealing gasket 5 is made of, for example, an insulating material, and the surface thereof is coated with asphalt.

  The battery element 10 accommodated in the lithium ion secondary battery is wound around the center pin 14. A positive electrode terminal 15 is connected to the positive electrode 11 of the battery element 10, and a negative electrode terminal 16 is connected to the negative electrode 12. As described above, the positive terminal 15 is welded to the safety valve 3 and electrically connected to the battery lid 2, and the negative terminal 16 is welded to the battery can 1 and electrically connected thereto.

  Hereinafter, the configuration of the battery element 10 accommodated in the battery can 1 will be described.

[Positive electrode]
In the positive electrode 11, a positive electrode active material layer 11 a containing a positive electrode active material is formed on both surfaces of a positive electrode current collector 11 b. The positive electrode current collector 11b is made of a metal foil such as an aluminum (Al) foil, a nickel (Ni) foil, or a stainless (SUS) foil. In addition, as shown in FIG. 2, a protective tape 21 is provided at the formation end of the positive electrode active material layer 11a in order to prevent a short circuit inside the battery. In addition, the lubricating layer 20 is provided between the protective tape 21 and the portion of the positive electrode active material layer 11 a to which the protective tape 21 is attached and the portion of the positive electrode current collector 11 b to which the protective tape 21 is attached. .

The positive electrode active material layer 11a includes, for example, a positive electrode active material, a conductive agent, and a binder. As the positive electrode active material, a known positive electrode active material that can be doped / dedoped with lithium ions can be used. Depending on the type of the target battery, a metal oxide, a metal sulfide, or a specific polymer can be used. Can be used. For example, metal sulfides or metal oxides not containing lithium, such as TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O ₅ , Li _x MO ₂ or Li _x M ₂ O ₄ (wherein M is one or more types) In this case, a lithium composite oxide or an intercalation compound containing lithium is mainly used, in which x is different depending on the charge / discharge state of the battery and is usually 0.05 ≦ x ≦ 1.10. As a transition metal constituting these, at least one selected from cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V), and titanium (Ti) is selected. Is done.

Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (wherein x and y vary depending on the charge / discharge state of the battery, and generally 0 <x ≦ 1. 2, 0.7 <y <1.02) or LiMn ₂ O ₄ or the like. Such a lithium composite oxide is a particularly preferable material because it can generate a high voltage when used as a positive electrode active material and has an excellent energy density.

Li _a MX _b (wherein M is one selected from the above-mentioned transition metals, X is selected from S, Se, and PO ₄ , and a and b are integers) can also be used.

  Note that, as the positive electrode active material, a plurality of the above-described positive electrode active materials can be mixed and used.

  The conductive agent is not particularly limited as long as an appropriate amount can be mixed with the positive electrode active material to impart conductivity, and for example, a carbon material such as carbon black or graphite is used. As the binder, a known binder that is usually used in a positive electrode mixture of this type of battery can be used, and preferably polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, etc. A fluorine resin is used.

  As the positive electrode current collector 11b, an annealed aluminum (Al) or the like is preferably used. Specific examples of such an aluminum (Al) material include JIS A3003P-O, JIS A8021P-O, and JIS A8079P-O. By performing the annealing treatment, the positive electrode current collector 11b can follow the expansion and contraction of the positive electrode active material layer 11a, and the positive electrode active material layer 11a can be prevented from being peeled off or peeled off.

  As the protective tape 21, a conventionally used tape can be used. For example, the adhesive tape 21b is provided on one surface of the resin base 21a.

  As the base material 21a of the protective tape 21, any material can be used as long as it is suitable for use inside the battery, such as having insulating properties, corrosion resistance to the electrolyte, and heat resistance when the battery is used. it can. Examples of such a material include polypropylene (PP) resin and polyimide (PI) resin. These may be mixed to form the substrate 21a. Further, as the adhesive layer 21b of the protective tape 21, for example, a silicon resin and an acrylic resin are used, and these may be mixed and used.

  The lubricating layer 20 serves as an oil film of the current collector removed by the annealing process, and reduces the adhesion between the protective tape 21, the positive electrode active material layer 11a, and the positive electrode current collector 11b. Moreover, it plays the role which prevents the adhesion layer 21b of the protective tape 21 and the positive electrode collector 11b from contacting directly, and prevents the surface oxide film of a collector from being reduced. For this reason, the lubrication layer 20 shall be provided between the adhesion layer 21b of the protective tape 21, and the positive electrode active material layer 11a and the positive electrode collector 11b. The lubricating layer 20 does not contain a reducing extract and is highly stable with respect to the electrolyte.

  The lubrication layer 20 exhibits fluidity when an external pressure is applied, and is a resin layer in which a resin material is made to have a fine particle size and dissolved or swellable in a solvent, or a resin material is dissolved in a solvent and gelled. It is the gel layer made into.

  As such a resin material, a silicon-based resin, an acrylic acid-based resin, a fluorine-based resin, a polyolefin-based resin, or the like can be used. Examples of the fluororesin include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and polyfluoride. And vinylidene (PVdF). Examples of the polyolefin resin include polyimide (PI), polypropylene (PP), and polyethylene (PE), and these may be used in combination.

  As the solvent, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), ethylene glycol (EG), toluene, acetone, or the like can be used.

  Note that silicon oil may be used as the lubricating layer 20.

  A positive electrode terminal 15 is connected to one end of the positive electrode 11 by spot welding or ultrasonic welding. The positive electrode terminal 15 is preferably a metal foil or a mesh-like one, but there is no problem even if it is not metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material of the positive electrode terminal 15 include aluminum (Al). The positive electrode terminal 15 is connected to the exposed portion of the positive electrode current collector 11 b provided at the end of the positive electrode 11.

[Negative electrode]
The negative electrode 12 is obtained by forming a negative electrode active material layer 12a containing a negative electrode active material on both surfaces of a negative electrode current collector 12b. The negative electrode current collector 12b is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 12a includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. As the negative electrode active material, a carbon material, crystalline, or amorphous metal oxide that can be doped / undoped with lithium is used. Specifically, examples of the carbon material that can be doped / dedoped with lithium include graphite, non-graphitizable carbon material, graphitizable carbon material, and highly crystalline carbon material with a developed crystal structure. More specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) at an appropriate temperature. Baked and carbonized), carbon materials such as carbon fiber and activated carbon, polymers such as polyacetylene, and the like can be used.

As another negative electrode active material, a metal capable of forming an alloy with lithium, or an alloy compound of such a metal can be given. Specifically, the alloy compound referred to here is M _p M ′ _q Li _r (where M ′ is 1 other than Li element and M element), where M is a metal element capable of forming an alloy with lithium. And p is a numerical value greater than 0, and q is a numerical value greater than or equal to 0). Further, in the present invention, elements such as B, Si, As, which are semiconductor elements, are also included in the metal element. Specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga). , Indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn) , Hafnium (Hf), zirconium (Zr), yttrium (Y) and their alloy compounds, for example, Li-Al, Li-Al-M (where M is a group 2A, 3B, 4B) A transition metal element), AlSb, CuMgSb, and the like.

  Among the elements described above, those containing a group 14 metal element or metalloid element in the long-period periodic table as a constituent element are preferred, and those containing at least one of silicon and tin as a constituent element are particularly preferred. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained. Specifically, for example, a simple substance, an alloy, or a compound of silicon, or a simple substance, an alloy, or a compound of tin, or a material having one or more phases thereof at least in part can be given.

In particular, the negative electrode material is preferably a CoSnC-containing material containing tin, cobalt, and carbon (C) as constituent elements, or a FeSnC-containing material containing tin, iron, and carbon as constituent elements. This is because a high energy density can be obtained and excellent cycle characteristics can be obtained. The CoSnC-containing material has a phase containing tin, cobalt, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. Similarly, the FeSnC-containing material has a phase containing tin, iron, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. In the CoSnC-containing material and the FeSnC-containing material, it is preferable that at least a part of carbon that is a constituent element is bonded to a metal element or a metalloid element that is another constituent element. The decrease in cycle characteristics is thought to be due to the aggregation or crystallization of tin or the like, but this is because such aggregation or crystallization can be suppressed by combining carbon with other elements. . Note that these CoSnC-containing material and FeSnC-containing material may further contain other constituent elements as necessary.

  The conductive agent is not particularly limited as long as an appropriate amount can be mixed with the positive electrode active material to impart conductivity, and for example, a carbon material such as carbon black or graphite is used. As the binder, for example, polyvinylidene fluoride, styrene butadiene rubber or the like is used.

  One end of the negative electrode 12 has one negative terminal 16 connected by spot welding or ultrasonic welding. The negative terminal 16 is electrochemically and chemically stable, and there is no problem even if it is not a metal as long as it can conduct electricity. Examples of the material of the negative electrode terminal 16 include copper (Cu) and nickel (Ni). Similar to the positive electrode terminal 15, the negative electrode terminal 16 is connected to the exposed portion of the negative electrode current collector 12 b provided at the end of the negative electrode 12.

[Electrolytes]
As the electrolyte, any of a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, a solid electrolyte containing an electrolyte salt, and a gel electrolyte in which an organic polymer is impregnated with a nonaqueous solvent and an electrolyte salt are used. Can do.

  The nonaqueous electrolytic solution is prepared by appropriately combining a nonaqueous solvent and an electrolyte salt, and any organic solvent can be used as long as it is a material generally used for this type of battery. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetic acid ester, tangled acid ester or propionic acid ester are preferred. Among these, Any one kind or a mixture of two or more kinds can be used.

As the electrolyte salt, one that dissolves in the non-aqueous solvent is used, and a combination of a cation and an anion is used. Alkali metal or alkaline earth metal is used as the cation, and Cl ⁻ , Br ⁻ , I ⁻ , SCN ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ or the like is used as the anion. It is done. Specifically, for example, LiCl, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, N (CnF _{2n + 1} SO ₂ ) ₂ Li and the like, and any one of these or a mixture of two or more thereof is used. Among them, it is preferable to mainly use LiPF ₆ . The electrolyte salt concentration is not a problem as long as it can be dissolved in the non-aqueous solvent, but the lithium ion concentration is 0.4 mol / kg or more and 2.0 mol / kg or less with respect to the non-aqueous solvent. A range is preferable.

  As the solid electrolyte, any inorganic solid electrolyte or polymer solid electrolyte can be used as long as the material has lithium ion conductivity. Specifically, examples of the inorganic solid electrolyte include lithium nitride and lithium iodide. The solid polymer electrolyte is composed of an electrolyte salt and a polymer compound that dissolves the electrolyte salt. Examples of the polymer compound include ether polymers such as poly (ethylene oxide) and the same cross-linked products, poly (methacrylate) esters, and acrylates. A system or the like is used alone or copolymerized or mixed in the molecule.

  As the matrix polymer of the gel electrolyte, various polymers can be used as long as they can be gelled by absorbing the non-aqueous electrolyte described above. For example, fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene), ether-based polymers such as poly (ethylene oxide) and cross-linked products thereof, and poly (acrylonitrile) Can be used. In particular, it is desirable to use a fluorine-based polymer from the viewpoint of redox stability. By containing an electrolyte salt, ionic conductivity is imparted.

  Alternatively, a polymer solid electrolyte containing a simple substance or a mixture of conductive polymer compounds or a gel electrolyte containing a swelling solvent may be used. The conductive polymer compound contained in the polymer solid electrolyte or the gel electrolyte is compatible with the electrolytic solution, specifically silicon gel, acrylic gel, acrylonitrile gel, polyphosphazene modified polymer, polyethylene oxide, Polypropylene oxide, fluorine-based polymers, composite polymers, cross-linked polymers, modified polymers, and the like thereof can be used. Examples of the fluorine-based polymer include poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), poly (vinylidene fluoride-co-trifluoroethylene), or poly (vinylidene fluoride-co-tetra). Polymer materials such as fluoroethylene) and mixtures thereof are used.

[Separator]
The separator 13 is preferably made of a porous film made of a polyolefin-based material such as polypropylene (PP) or polyethylene (PE), or a porous film made of an inorganic material such as a ceramic nonwoven fabric. Moreover, you may be set as the structure which laminated | stacked these 2 or more types of porous membranes. Among them, polypropylene and polyethylene porous films are the most effective.

  In general, the thickness of the separator 13 is preferably 5 to 50 μm, more preferably 7 to 30 μm. If the separator 13 is too thick, the filling amount of the active material is reduced to reduce the battery capacity, and the ionic conductivity is reduced to deteriorate the current characteristics. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

[Production of battery element]
First, the positive electrode 11 is produced. The above-mentioned positive electrode active material, binder, and conductive agent are uniformly mixed to form a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent and, if necessary, in a slurry state by a ball mill, a sand mill, a twin-screw kneader, etc. To. The solvent is not particularly limited as long as it is inert with respect to the electrode material and can dissolve the binder, and any of inorganic solvents and organic solvents can be used. For example, N-methyl- 2-pyrrolidone (NMP) or the like is used. Note that the positive electrode active material, the conductive agent, the binder, and the solvent only need to be uniformly dispersed, and the mixing ratio is not limited. Next, this slurry is uniformly applied to both surfaces of the positive electrode current collector 11b by a doctor blade method or the like. Furthermore, the positive electrode active material layer 11a is formed by drying at a high temperature and removing the solvent. Thereby, the positive electrode 11 is produced.

  Then, the protective tape 21 is stuck from both surfaces of the positive electrode 11 so as to protect the formation end of the positive electrode active material layer 11 a located on the winding outer peripheral side. At this time, first, the lubricant layer 20 is provided by applying a lubricant to the portion where the protective tape 21 is adhered. The lubricant can be provided by application using a tool such as a brush, application by spraying, or the like. Further, the lubricant may be applied to the adhesive layer 21b side of the protective tape 21 or to the positive electrode 11 side. And the protective tape 21 is stuck so that the formation edge part of the positive electrode active material layer 11a may be protected. Moreover, you may make it provide the protective tape 21 also in the formation edge part of the positive electrode active material layer 11a located in the winding inner peripheral side. Since the influence of the expansion of the active material layer increases as it goes to the outer periphery of the winding, it is preferable to provide the protective tape 21 at least on the outer periphery.

  Moreover, it is preferable that the protective tape 21 is attached so as to cover the positive electrode active material layer forming portion in a range of about 0.5 mm to 1 mm. The portion where the protective tape 21 and the positive electrode active material layer forming portion overlap has a thickness larger than that of the other portion, and therefore it is preferable that the overlap be as small as possible. Moreover, when an overlap is too small, the effect of the safety | security by sticking of the protective tape 21 will become thin.

  Next, the negative electrode 12 is produced. The above-described negative electrode active material, binder, and conductive agent are uniformly mixed to form a negative electrode mixture, which is dispersed in a solvent to form a slurry. At this time, a ball mill, a sand mill, a biaxial kneader or the like may be used as in the case of the positive electrode mixture. As the solvent, for example, N-methyl-2-pyrrolidone, methyl ethyl ketone, or the like is used. Note that the mixing ratio of the negative electrode active material, the conductive agent, the binder, and the solvent is not limited as in the case of the positive electrode active material. Next, this slurry is uniformly applied to both surfaces of the negative electrode current collector 12b by a doctor blade method or the like. Furthermore, the negative electrode active material layer 12a is formed by drying at a high temperature and removing the solvent. Thereby, the negative electrode 12 is produced.

  The coating apparatus is not particularly limited, and slide coating, extrusion type die coating, reverse roll, gravure, knife coater, kiss coater, micro gravure, rod coater, blade coater and the like can be used. Also, the drying method is not particularly limited, but standing drying, blower dryer, hot air dryer, infrared heater, far infrared heater, and the like can be used.

  The positive electrode 11 and the negative electrode 12 produced as described above are laminated in the order of the positive electrode 11, the separator 13, the negative electrode 12, and the separator 13, and wound to obtain the battery element 10.

  Next, the battery element 10 described above is accommodated in the battery can 1. At this time, the negative electrode terminal 16 lead-out side winding surface of the battery element 10 is accommodated so as to be covered with the insulating plate 9a made of an insulating resin. Thereafter, one electrode rod is inserted from the battery element winding center portion, the other electrode rod is disposed outside the bottom surface of the battery can and resistance welding is performed, and the negative electrode terminal 16 is welded to the battery can 1.

  After welding the negative electrode terminal 16 and the battery can 1, the center pin 14 is inserted, and the insulating plate 9 b is also disposed on the winding surface portion located on the open end side of the battery can 1 to inject the electrolyte. Further, the safety valve mechanism and the PTC element 4 are provided inside the battery lid 2 having the opening 24 and the thin wall portion 25 or the groove portion 26, and the positive electrode terminal 15 is connected to the safety valve 3. The battery lid 2 is attached by caulking through an insulating sealing gasket 5, and the inside of the battery can 1 is sealed.

  The positive terminal 15 needs to have a certain length in the manufacturing process. This is for sealing the open end of the battery can 1 after connecting the positive electrode terminal 15 to the safety valve 3 provided in the battery lid 2 in advance. The shorter the positive electrode terminal 15 is, the more the positive electrode terminal 15 is connected to the safety valve 3. Becomes difficult. For this reason, the positive electrode terminal 15 having a certain length is bent into a substantially U shape inside the battery and accommodated in the battery can 1.

  The lithium ion secondary battery produced as described above hardly breaks the positive electrode current collector 11b, and also has a short-circuit preventing effect inside the battery. For this reason, while having high safety | security, the fall of battery capacity and cycling characteristics can be suppressed, and the lithium ion secondary battery which has high quality can be obtained.

  Hereinafter, the present invention will be specifically described by way of examples. In addition, this invention is not limited only to these Examples.

<Example 1>
[Production of positive electrode]
First, 94 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 3 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder are uniformly mixed to form a positive electrode mixture Was prepared. Subsequently, the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode mixture slurry. This positive electrode mixture slurry is uniformly applied to both surfaces of an aluminum (Al) foil serving as a positive electrode current collector, dried under reduced pressure at 100 ° C. for 24 hours, and then subjected to pressure molding with a roll press machine, whereby a positive electrode active material layer Formed. As the positive electrode current collector, an annealed aluminum foil (JIS A3003P-O) was used.

  Subsequently, a protective tape having a base material made of polyimide (PI) and an adhesive layer made of silicon resin (silicon rubber) was attached to the end portion of the positive electrode active material layer on the outer periphery side of the winding. Silicone resin is suitable as a material constituting the protective tape because it hardly dissolves a reducing extract such as an antioxidant. The lubricating layer was formed by pressing the silicon rubber side, which is an adhesive layer, against a cloth soaked with a lubricant. As the lubricant, dimethyl carbonate (DMC), ethylene carbonate (EC) and propylene carbonate (PC) dissolved in 12% by weight were used.

  And the protective tape which formed the lubrication layer was stuck so that the boundary of a positive electrode active material layer formation part and a positive electrode active material layer non-formation part might be straddled. Moreover, the same protective tape was affixed on the positive electrode active material layer formation end part used as the winding inner peripheral side, without providing a lubricating layer. Thereafter, a positive electrode terminal made of aluminum (Al) was connected to the exposed portion of the positive electrode current collector.

[Production of negative electrode]
A negative electrode mixture was prepared by uniformly mixing 90 parts by weight of artificial graphite powder pulverized as a negative electrode active material and 10 parts by weight of polyvinylidene fluoride (PVdF) as a binder. Subsequently, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. The negative electrode mixture slurry is uniformly applied to both surfaces of a copper (Cu) foil serving as a negative electrode current collector, dried under reduced pressure at 100 ° C. for 24 hours, and then subjected to pressure molding with a roll press machine to thereby form a negative electrode active material layer Formed. Then, the protective tape similar to a positive electrode was affixed on the negative electrode active material layer formation edge part of winding outer peripheral side and winding inner peripheral side. At this time, no lubricating layer was provided.
Moreover, the negative electrode terminal made from nickel was connected to the one end part of the negative electrode.

  Subsequently, a separator made of a microporous polypropylene film was prepared, and a positive electrode, a separator, a negative electrode, and a separator were laminated in this order, and then wound many times in a spiral shape to produce a wound electrode body. After that, a center pin is inserted into the center of the wound electrode body, the positive terminal is joined to the safety valve joined to the battery lid, the negative terminal is joined to the battery can, and the wound electrode body is paired with a pair of insulating plates. The battery was placed inside the battery can.

Subsequently, an electrolytic solution was injected into the battery can. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt in a content of 1 mol / l in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an equal mass ratio was used. Subsequently, a safety valve mechanism including a safety valve, a disk holder, and a shut-off disk, a PTC element, and a battery lid were fixed to the open portion of the battery can by caulking through an insulating sealing gasket. Thus, a test battery having an ICR18650 size and a battery capacity of 2430 mAh at the time of manufacture described in JIS C8711 was produced.

<Example 2>
A test battery was prepared in the same manner as in Example 1 except that a resin material in which polytetrafluoroethylene (PTFE) was dissolved was used as the resin material for the lubricant.

<Example 3>
A test battery was produced in the same manner as in Example 1 except that a resin material for the lubricant was dissolved in tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA).

<Example 4>
A test battery was fabricated in the same manner as in Example 1 except that a resin material for the lubricant was prepared by dissolving a tetrafluoroethylene / hexafluoropropylene copolymer (FEP).

<Example 5>
A test battery was produced in the same manner as in Example 1 except that a material in which polyimide (PI) was dissolved was used as the resin material for the lubricant.

<Example 6>
A test battery was produced in the same manner as in Example 1 except that a material in which polypropylene (PP) was dissolved was used as the resin material for the lubricant.

<Example 7>
A test battery was prepared in the same manner as in Example 1 except that silicon oil was used as the lubricant.

<Comparative Example 1>
A test battery was produced in the same manner as in Example 1 except that a resin material in which an acrylic resin was dissolved was used as the resin material for the lubricant.

<Comparative example 2>
A test battery was produced in the same manner as in Example 1 except that the lubricant was not provided.

<Comparative Example 3>
A test battery was prepared in the same manner as in Example 1 except that the adhesive layer of the protective tape was an acrylic resin and no lubricant was provided.

<Comparative example 4>
A test battery was produced in the same manner as in Example 1 except that the protective tape and the lubricant were not provided.

<Comparative Example 5>
A test battery was produced in the same manner as in Example 1 except that the positive electrode current collector was made of an aluminum foil (JIS A3003P-H18) that was not annealed, and the lubricant was silicon oil.

  With respect to each of the test batteries described above, the battery performance was evaluated as follows.

(A) Break test After constant current charging until the battery voltage reached 4.25 V at a constant current of 1 C, constant voltage charging was performed at a constant voltage of 4.25 V until the charging time was 2.5 hours. . Thereafter, constant current discharge was performed with a constant current of 1 C and a final voltage of 3.0 V. Thereafter, the battery was disassembled, and the positive electrode current collector was confirmed to be broken. Break is
Break (Large): Current collector is completely separated into two pieces Break (Small): A part of the current collector is connected No break: Classify as no current break. In the break test, 30 test batteries of each example and comparative example were used.

(B) Cycle test After constant current charging until the battery voltage reached 4.25 V at a constant current of 1 C, constant voltage charging was performed at a constant voltage of 4.25 V until the charging time was 2.5 hours. . Then, it preserve | saved for 24 hours in 45 degreeC environment, and the constant current discharge was performed by the constant voltage of 1C and the final voltage of 3.0V. Under the same charge / discharge conditions, 500 cycles of charge / discharge were performed at room temperature, and the battery capacity at the 500th cycle was measured.

(C) Short-circuit test When assembling the test battery, about 20 50 μm square nickel (Ni) pieces were mixed in the battery can, and 10 cycles were performed under the same charging and discharging conditions as in the cycle test of (b). Charging / discharging was performed. Then, the presence or absence of a short circuit was confirmed about each battery for a test. In addition, the short circuit test was done using 10 test batteries of each Example and Comparative Example.

  The test battery has a minute gap between the positive electrode active material layer and the separator. When a metal piece enters the gap, the battery is charged and the active material layer expands, and the inner wall of the battery can and the battery element are tightly pressed to press the battery element, causing an internal short circuit.

Table 1 below shows the results of the evaluation.

  As can be seen from the examples and comparative examples, in the test battery in which the lubricating layer not containing the reducing extract was provided between the protective tape and the positive electrode current collector, the current collector was not broken and the internal short circuit did not occur. The battery capacity after 500 cycles was sufficient.

  On the other hand, in Comparative Example 1 using an acrylic resin containing a reducing extract in the lubricating layer, Comparative Example 2 and Comparative Example 3 in which the lubricating layer was not provided, the current collector was broken. This is considered to be because the surface oxide film of the current collector was reduced by the eluted reducing extract, and the current was eroded by the electrolyte solution, resulting in a decrease in strength. In Comparative Example 2 and Comparative Example 3 in which no lubricating layer was used, rupture occurred in all the test batteries, and in Comparative Example 3 in which the adhesive layer of the protective tape was an acrylic resin, most were ruptured (large). For this reason, it turned out that it is easy to produce a fracture | rupture especially when an acrylic resin is included.

  Further, in Comparative Example 4 in which the protective tape and the lubricating layer were not provided, the current collector was not broken, but an internal short circuit was likely to occur. This is presumably because, in addition to the influence of embedding the nickel piece, the protection at the active material layer forming end is lost, and therefore an internal short circuit is likely to occur at this part.

  In Comparative Example 5 in which the current collector was not annealed, the battery capacity was significantly reduced, although the current collector did not break or was internally short-circuited. This is presumably because the current collector could not follow the expansion and contraction of the active material layer accompanying charging and discharging, and the active material layer was peeled off and peeled off.

  In this way, using the positive electrode current collector that has been annealed, a lubricating layer is provided between the protective tape that covers the active material layer forming end on the winding outer periphery side of the positive electrode active material layer and the positive electrode current collector. Thereby, the current collector can easily follow the expansion and contraction of the active material layer, and the reduction of the surface oxide film of the current collector can be prevented to prevent the current collector from being broken.

  Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible.

  For example, in the above-described embodiment, the configuration using the annealed positive electrode current collector has been described. However, a positive electrode active material layer may be provided on the positive electrode current collector without the annealing treatment, and heat treatment may be performed.

It is sectional drawing which shows one structural example of the nonaqueous electrolyte secondary battery by one Embodiment of this invention. It is a basic diagram which shows the structure of the protective tape and lubricating layer in the winding outer periphery side of the positive electrode by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can 2 ... Battery cover 3 ... Safety valve 3a ... Projection part 4 ... PTC element 5 ... Insulation sealing gasket 6 ... Disc holder 7 ... Shut-off disc 7a .. Hole 7b ... Gas vent 9a, 9b ... Insulating plate 10 ... Battery element 11 ... Positive electrode 11a ... Positive electrode active material layer 11b ... Positive electrode current collector 12 ... Negative electrode 12a ... Negative electrode active material layer 12b ... Negative electrode current collector 13 ... Separator 14 ... Center pin 15 ... Positive electrode terminal 16 ... Negative electrode terminal 20 ... Lubrication layer 21 ... Protective tape 21a ... Base material 21b ... Adhesive layer

Claims (9)

A battery in which a belt-like positive electrode having a positive electrode active material layer formed on a positive electrode current collector and a belt-like negative electrode having a negative electrode active material layer formed on a negative electrode current collector are stacked and wound via a separator. The element is housed in a battery can,
An insulating coating material is provided so as to cover at least the vicinity of the formation end of the positive electrode active material layer located on the outer periphery side of the winding,
A cylindrical non-aqueous electrolyte secondary battery in which a lubricating layer containing no reducing extract is provided between the insulating coating material, the positive electrode active material layer, and the positive electrode current collector. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode current collector is annealed. The cylindrical nonaqueous electrolyte secondary battery according to claim 2, wherein the lubricating layer includes at least one of silicon oil, silicon resin, acrylic acid resin, fluorine resin, and polyolefin resin. The fluororesin is polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), polyvinylidene fluoride ( At least one of PVdF),
The cylindrical nonaqueous electrolyte secondary battery according to claim 3, wherein the polyolefin resin is at least one of polyimide (PI), polypropylene (PP), and polyethylene (PE). 5. The cylindrical nonaqueous electrolyte according to claim 3, wherein the lubricating layer is formed by dissolving at least one of the silicon resin, the acrylic resin, the fluorine resin, and the polyolefin resin in a solvent. Secondary battery. The cylindrical nonaqueous electrolyte secondary battery according to claim 5, wherein the solvent contains at least one of dimethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol, toluene, and acetone. The insulating coating material comprises a base material and an adhesive layer provided by laminating the base material,
The cylindrical nonaqueous electrolyte secondary battery according to claim 6, wherein the adhesive layer and the lubricating layer are in contact with each other. The cylindrical nonaqueous electrolyte secondary battery according to claim 7, wherein the base material is a resin material obtained by mixing one of a polypropylene resin and a polyimide resin, or a polypropylene resin and a polyimide resin. The cylindrical nonaqueous electrolyte secondary battery according to claim 8, wherein the adhesive layer is provided on one surface of the substrate and is made of at least one of a silicon resin and an acrylic resin.

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