JP2014071987A - Cylindrical lithium-ion secondary battery - Google Patents

Abstract

The present invention provides a high capacity cylindrical lithium ion secondary battery with high mass productivity in a small diameter battery having an outer diameter of 8.0 mm or less.
An electrode group in which a positive electrode and a negative electrode are wound so as to face each other through a separator disposed between the positive electrode and the negative electrode is housed in a case together with a non-aqueous electrolyte, a gasket, and a sealing plate The case has an outer diameter of 8.0 mm or less, the electrode group has a negative electrode disposed on the outermost periphery, and the negative electrode includes a negative electrode current collector, a negative electrode current collector, and a negative electrode current collector. A negative electrode active material layer formed on the surface of an electric conductor and containing an alloy-based negative electrode active material, and a negative electrode lead, the negative electrode lead being plasma at the negative electrode lead end and the outermost peripheral end of the negative electrode current collector It is welded, arranged on the outermost periphery of the electrode group, arranged in a range where the electrode group and the case face each other, not welded to the inner surface of the case, and electrically connected by contact Cylindrical lithium ion secondary battery.
[Selection] Figure 1

Description

  The present invention relates to a cylindrical lithium ion secondary battery having a small battery diameter, and more particularly to a current collecting system for a negative electrode of a cylindrical lithium ion secondary battery.

  The range of application of battery-based devices is expanding. In particular, lithium-ion batteries are widely used as power sources for driving personal computers, mobile phones, and portable electronic devices because of their light weight, high capacity, and high output. . Conventionally, devices having a diameter of about 20 mm and a height of about 50 mm have been widely used.

  In recent years, along with further downsizing of portable electronic devices and higher functions of glasses, hearing aids, and the like, there has been a demand for power supplies with small size, high capacity, and high output. In particular, when glasses or hearing aids are used, they may be worn for a long time in human life. In particular, there is a demand for a lightweight, compact, and high-capacity power source. The specific size is about 3 to 8 mm in diameter and about 20 to 50 mm in height. In order to increase the capacity, an alloy-based active material having a capacity higher than that of graphite that has been widely used has been developed.

  In a small-diameter battery, it is difficult to insert a welding rod into the center of the electrode group, so welding with the lead at the bottom of the case is not possible.

  It describes that the case and the electrode plate are brought into electrical contact with each other by pressure contact without using a lead (see, for example, Patent Document 1).

  Moreover, it describes that it electrically connects with an electrode by welding with a lead | read | reed on the side surface and bottom face of a case (for example, refer patent document 2, patent document 3).

  As for the alloy-based active material, silicon-based active materials such as silicon and silicon oxide are typical as negative electrodes of lithium ion batteries.

  A negative electrode containing an alloy-based active material generally includes a negative electrode current collector and a thin film of an alloy-based active material formed on the surface of the negative electrode current collector by a vapor phase method (hereinafter referred to as a “thin film-like negative electrode active material layer”). “)”.

  A conventional negative electrode is provided with a current collector exposed portion where no active material layer is formed, and a lead is welded by resistance welding or ultrasonic welding. When the active material layer is formed on the surface of the current collector, the exposed portion of the current collector does not partially form the active material layer, or after forming the active material layer on the current collector surface, It is formed by removing the part.

  The negative electrode containing an alloy-based active material can be provided with a current collector exposed portion by forming a mask layer when forming a thin film negative electrode active material layer. Extra work such as removal is required.

  In addition, it is conceivable that after the formation of the thin-film negative electrode active material layer, it is partially removed to form the current collector exposed portion. In particular, the alloy-based thin film of the silicon-based active material is vitreous and has high mechanical properties. Partial removal is very difficult because it has high strength and is firmly attached to the current collector surface.

It describes that a negative electrode current collector and a negative electrode lead are joined by an alloy layer without providing a current collector exposed portion (see, for example, Patent Document 2).

JP 2005-85556 A International Publication No. 2010/041399 Japanese Utility Model Publication No. 02-57561

  In order to bring the electrode and the case into pressure contact without using a lead as described in Patent Document 1, a positive electrode having a current collector exposed portion can be used. Is difficult. When the negative electrode is brought into pressure contact with the case, it is very difficult to provide the current collector exposed portion of the negative electrode containing the alloy-based active material. In addition, when the thin film negative electrode active material layer and the case are brought into pressure contact, the thin film negative electrode active material layer has a relatively high electric resistance, so that sufficient electric conductivity cannot be ensured.

  As described in Patent Document 2, when the negative electrode current collector and the negative electrode lead are joined by an alloy layer, the lead can be welded to the bottom of the battery case in a large-diameter battery, but in a small-diameter battery, Since it is difficult to insert a welding rod into the center of the electrode group, welding with the lead at the bottom of the case is impossible.

  In order to weld the lead on the side surface of the case as described in Patent Document 3, a space for inserting the welding rod into the case is required, which is disadvantageous for increasing the capacity. In addition, in a small-diameter battery, a thin case is used to increase the capacity. Furthermore, since the inside of the case has a small radius of curvature, the lead width must be reduced. This is because the lead does not repel between the case and the electrode group when the electrode group is inserted into the case. Therefore, the weldable area is very small, and there is a possibility that the case is perforated or the molten material is scattered during welding.

  Accordingly, an object of the present invention is to provide a high-capacity cylindrical lithium ion secondary battery with high productivity in a small-diameter battery.

  In order to solve the above-mentioned problems, the present invention has a positive electrode, a negative electrode, and an electrode group formed by facing and winding a separator disposed between the positive electrode and the negative electrode in a case together with a non-aqueous electrolyte. A cylindrical lithium ion secondary battery sealed with a gasket and a sealing plate, the case has an outer diameter of 10 mm or less, the electrode group has a negative electrode disposed on the outermost periphery, and the negative electrode is a negative electrode collector A negative electrode active material layer formed on the surface of the negative electrode current collector and containing an alloy-based negative electrode active material; and a negative electrode lead. The negative electrode lead includes a negative electrode lead end and a negative electrode current collector. Plasma welded at the outermost edge of the electrode group, arranged on the outermost circumference of the electrode group, and arranged in a range where the electrode group and the case face each other, not welded to the case inner surface, and electrically connected by contact Cylindrical shape characterized by Lithium-ion is a secondary battery.

  The cylindrical lithium ion secondary battery of the present invention has a high capacity because it uses a negative electrode provided with a thin-film negative electrode active material layer containing an alloy-based negative electrode active material.

  Further, the lead is disposed in a range where the negative electrode and the case face each other, and welding of the negative electrode lead and the case is unnecessary. Therefore, it is not necessary to provide a space for inserting the welding rod in the case.

  Furthermore, since it is not necessary to weld the negative electrode lead to the case, it is possible to avoid occurrence of a hole in the case during welding. Furthermore, the process of welding very thin leads in a small diameter case can be omitted.

  Since the present invention does not require welding between the negative electrode lead and the case in a small-sized battery having an outer diameter of 10 mm or less, the mass productivity is high. Moreover, since it has the thin film-form negative electrode active material layer containing an alloy type negative electrode active material, and the space for welding the negative electrode lead by the case opening part side is unnecessary, it is high capacity | capacitance.

1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention. Schematic longitudinal sectional view of a cylindrical lithium ion secondary battery of a comparative example The top view of the positive electrode plate which concerns on one embodiment of this invention The top view of the negative electrode which concerns on one embodiment of this invention Plan view of negative electrode (negative electrode lead welding surface) of comparative example Plan view of negative electrode (back surface of negative electrode lead weld) of comparative example

  In the present invention, a positive electrode, a negative electrode, and an electrode group that is wound while being opposed to each other through a separator disposed between the positive electrode and the negative electrode are accommodated in a case together with a non-aqueous electrolyte, and a gasket and a sealing plate It is a sealed cylindrical lithium ion secondary battery, the case has an outer diameter of 10 mm or less, the electrode group has a negative electrode disposed on the outermost periphery, and the negative electrode includes a negative electrode current collector and a negative electrode current collector The negative electrode lead is formed by plasma welding at the negative electrode lead end and the outermost peripheral end of the negative electrode current collector. The cylinder is disposed on the outermost periphery of the electrode group and is disposed in a range where the electrode group and the case face each other, and is not welded to the inner surface of the case and is electrically connected by contact. Type lithium ion secondary battery

  Since the thin-film negative electrode active material layer containing the alloy-based negative electrode active material is provided, the capacity is high.

  Since the negative electrode lead is joined by plasma welding at the end portion of the negative electrode lead and the outermost peripheral end portion of the negative electrode current collector, there is no need to provide an exposed portion of the current collector, so that mass productivity is high.

  Since the negative electrode lead and the case are electrically connected by contact, a space in the case, which is necessary for welding, becomes unnecessary, and the capacity is high.

  Further, since there is no need to weld the negative electrode lead to the case, the possibility of drilling the case at the time of welding can be avoided, and the process of welding a very thin lead in a small-diameter case can be omitted, resulting in high mass productivity.

  In the cross section in the direction perpendicular to the height direction of the battery, the cross-sectional area of the electrode group and the portion of the negative electrode lead arranged around the electrode group (hereinafter referred to as the electrode group of the negative electrode lead connection) is larger than the cross-sectional area in the case Need to be small. The smaller the electrode group connected to the negative electrode lead with respect to the cross-sectional area in the case, the more stable the insertion into the case. On the other hand, the capacity decreases.

The shape of the negative electrode lead is not particularly limited, but is preferably quadrangular because it is easy to process. In the case of a quadrilateral, the length of the plasma-welded side of the negative electrode lead (battery height direction) in the cross section perpendicular to the height direction of the battery does not affect the cross-sectional area of the electrode group connected to the negative electrode lead. The length of the other side of the welded side (direction perpendicular to the battery height direction) affects. That is, the length of the negative electrode lead in the battery height direction does not affect the insertion into the case or the battery design capacity, but the length in the direction perpendicular to the battery height direction affects.

  When the length of the plasma welded side is 1.5 mm or more and not more than the length of the negative electrode in the battery height direction, it is preferable because the welding strength with the negative electrode can be secured and the conductivity by contact with the case can be secured. . If it is less than 1.5 mm, the welding strength with the negative electrode may be insufficient, which is not preferable. If the length of the negative electrode in the battery height direction is exceeded, the portion that does not overlap the negative electrode comes into contact with the positive electrode member, causing a short circuit. This is not preferable because it may cause

  The negative electrode lead suppresses the effect of capacity reduction due to an increase in the cross-sectional area of the electrode group connected to the negative electrode lead when the other side of the plasma-welded side is not less than 1/3 and not more than 3/4 of the circumference of the case inner diameter. It is preferable because it can ensure conductivity by contact with the case. If it is less than 1/3, there is a possibility that the conductivity due to contact with the case may be insufficient. If it exceeds 3/4, the cross-sectional area of the electrode group of the negative electrode lead connection increases. It is not preferable to reduce the diameter of the electrode group in order to make insertion difficult or to insert stably, because the capacity decreases.

  The nominal capacity of the battery is preferably 5 mAh or more and 100 mAh or less. This is preferable because the electrode area can be secured and the negative electrode and the lead can be stably welded. Moreover, since sufficient electroconductivity by contact of a case and a lead is obtained at the time of charging / discharging, it is preferable. If the nominal capacity is less than 5 mAh, the area of the negative electrode lead is larger than the area of the negative electrode plate, which may make it difficult to weld the negative electrode and the lead. On the other hand, if it exceeds 100 mAh, the conductivity due to contact with the case may be insufficient during discharge exceeding 1.0 It, which is not preferable.

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

  As shown in FIG. 1, a cylindrical lithium ion secondary battery 10 of the present invention includes a bottomed cylindrical case 11, an electrode group 12 accommodated in the case 11, and a sealing plate 14 that seals the case 11. A gasket 13 and an upper ring 18 are provided.

  The electrode group 12 includes a negative electrode 15, a positive electrode 16, and a separator 17 that separates the negative electrode 15 from the positive electrode 16. The electrode group 12 is in contact with a nonaqueous electrolyte.

  The positive electrode lead 161 is electrically connected to the sealing plate 14.

  The negative electrode lead 151 is electrically connected to the case 11 by contact.

  The bottom of the case 11 and the outside of the side surface are exposed to the outside and used as an external negative electrode terminal.

  As shown in FIG. 3, the positive electrode 16 includes a positive electrode current collector 162 and a positive electrode active material layer 163 formed on both surfaces of the positive electrode current collector 162, and the positive electrode lead 161 is electrically connected.

  In the positive electrode 16, the thickness of the mixture layer formed on one surface of the positive electrode current collector is preferably 30 μm or more and 90 μm or less, and more preferably 30 μm or more and 70 μm or less. The total thickness of the positive electrode 16 is preferably 80 μm or more and 180 μm or less.

  A metal foil is used for the positive electrode current collector, and preferably an aluminum foil or an aluminum alloy foil. From the viewpoint of battery size reduction and the strength of the positive electrode current collector, the positive electrode current collector preferably has a thickness of 10 μm or more and 50 μm or less.

The positive electrode active material contained in the positive electrode 16 may be any material that can be used in a lithium ion secondary battery, and is not particularly limited. As the positive electrode active material, for example, lithium-containing transition metal oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) can be used.

From the viewpoint of battery miniaturization and high energy density, the positive electrode active material includes a general formula: Li _x Ni _y M _1-y O ₂ (where M is Na, Mg, Sc, Y, Mn, Fe). , Co, Cu, Zn, Al, Cr, Pb, Sb and B, at least one selected from the group consisting of 0 <x ≦ 1.2 and 0.5 <y ≦ 1.0) It is preferable to use the containing composite oxide.

In addition, from the viewpoint of battery miniaturization and high energy density, the positive electrode active material includes a general formula: Li _x Ni _y Co _z M _1-yz O ₂ (where M is Mg, Ba, Al, Ti). , Sr, Ca, V, Fe, Cu, Bi, Y, Zr, Mo, Tc, Ru, Ta, and W, and at least 0.9 ≦ x ≦ 1.2,. 3 ≦ y ≦ 0.9, 0.05 ≦ z ≦ 0.5, 0.01 ≦ 1-yz ≦ 0.3) is preferably used.

  As the positive electrode binder, for example, fluorine resin, styrene-butadiene rubber, fluorine rubber, polyacrylic acid, or polyvinylidene fluoride is used.

  When using a positive electrode binder, the content of the positive electrode binder in the positive electrode active material is preferably 1 to 5 parts by weight per 100 parts by weight of the positive electrode active material.

  As the positive electrode conductive agent, for example, graphites, carbon blacks, carbon fibers, metal fibers, or conductive organic materials are used.

  When the positive electrode conductive agent is used, the content of the positive electrode conductive agent in the positive electrode active material is preferably 0.5 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the positive electrode active material.

  As the material of the positive electrode lead 161, for example, aluminum is preferably used, and a metal such as titanium or nickel can also be used.

  As shown in FIG. 4, the negative electrode 15 includes a negative electrode current collector (not shown) and a thin film negative electrode active material layer 153 formed on both surfaces of a negative electrode current collector (not shown), and a negative electrode lead 151. Are connected by plasma welding. In the plasma welded portion 154, the end portion of the negative electrode lead 151 and the end portion of the negative electrode current collector (not shown) are welded. As a result, the negative electrode 15 is electrically connected to the negative electrode lead 151.

  The total thickness of the negative electrode 15 is preferably 40 μm or more and 120 μm or less.

  Since the alloy-based negative electrode active material has a high capacity density, silicon, an alloy containing silicon, and silicon oxide are preferable, and silicon oxide is particularly preferable. Alloys and silicon oxides containing silicon have a relatively large expansion / contraction during charging / discharging, but the smaller the battery size, the smaller the absolute value of expansion / contraction, so the effect is reduced. Are preferably used.

The silicon oxide is preferably SiOx (0 <x <2). The capacity of the active material increases as x decreases, but the volume change due to expansion and contraction of the active material during charge / discharge increases. Further, as x increases, the volume change due to expansion and contraction of the active material during charge / discharge decreases, but the irreversible capacity increases. In the small battery of this invention, the influence by the volume change of an active material is comparatively small. Therefore, 0 <x ≦ 1.1 is preferable from the viewpoint of volume change and reversible capacity of the active material in a small battery.

  The alloy containing silicon is preferably an alloy of silicon and at least one element selected from the group consisting of iron, cobalt, nickel, copper, and titanium.

  In addition, as the alloy-based negative electrode active material, tin, an alloy containing tin, a tin oxide, or an alloy containing lithium can be used.

  The alloy containing tin is preferably an alloy of tin and at least one element selected from the group consisting of iron, cobalt, nickel, and copper.

  The alloy containing lithium is preferably an alloy of lithium and at least one element selected from the group consisting of aluminum.

  The tin oxide is preferably SnOx (0 <x <2). The capacity of the active material increases as x decreases, but the volume change due to expansion and contraction of the active material during charge / discharge increases. Further, as x increases, the volume change due to expansion and contraction of the active material during charge / discharge decreases, but the irreversible capacity increases. In the small battery of this invention, the influence by the volume change of an active material is comparatively small. Therefore, 0 <x ≦ 1.1 is preferable from the viewpoint of volume change and reversible capacity of the active material in a small battery.

  An alloy type negative electrode active material can be used individually or in combination of 2 or more types.

  The alloy-based negative electrode active material layer can be formed by a known method. In particular, it is preferably formed in a thin film on the surface of the negative electrode current collector by a vapor phase method. Examples of the vapor phase method include a vacuum deposition method, a melt scattering method, an ion plating method, a laser ablation method, a chemical vapor deposition method, a plasma chemical vapor deposition method, and a thermal spraying method.

  A copper metal foil is used for the negative electrode current collector. By using copper as the negative electrode current collector, high output can be obtained because the resistance is low.

  The thickness of the negative electrode current collector is preferably 0.10 mm or more and 0.30 mm or less, and particularly preferably 0.15 mm or more and 0.25 mm or less. When the negative electrode current collector is 0.10 mm or more and 0.30 mm or less, the strength of the current collector is sufficient when the alloy-based negative electrode active material layer is formed, and the repulsive force against bending is sufficient. It is preferable because the negative electrode lead and the case can be brought into sufficient contact within the case. If it is less than 0.10 mm, the strength of the negative electrode current collector becomes insufficient, which is not preferable, and if it exceeds 0.25 mm, it contributes to an increase in the diameter of the electrode group, which is not preferable.

  As a material of the negative electrode lead 151, a metal such as copper or nickel can be used.

  The thickness of the negative electrode lead 151 is preferably 0.05 mm or more and 0.15 mm or less, and particularly preferably 0.1 mm or less. If it is less than 0.05 mm, the strength of the negative electrode lead 151 becomes insufficient, which is not preferable. If it exceeds 0.15 mm, it contributes to an increase in the diameter of the electrode group, which is not preferable.

  For plasma welding of the negative electrode current collector and the negative electrode lead 151, for example, conditions such as the welding current value, welding speed (moving speed of the welding torch), welding time, plasma gas, and shielding gas type and flow rate are appropriately selected. Can be implemented. By selecting these conditions, the bondability and conductivity between the negative electrode current collector (not shown) and the negative electrode lead 151 can be controlled.

  The welding current is, for example, 1A to 100A. The insertion speed of the welding torch is, for example, 1 mm / second to 100 mm / second. Argon gas or the like can be used as the plasma gas. The plasma gas flow rate is, for example, 10 mL / min to 10 L / min. Argon gas, hydrogen, or the like can be used as the shielding gas. The shield gas flow rate is, for example, 10 mL / min to 10 L / min.

  The nonaqueous electrolytic solution includes a solute and a nonaqueous solvent.

A solute is a supporting salt that dissolves in a non-aqueous solvent. Examples of the supporting salt include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis ( Trifluoromethylsulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ), lithium bis (pentafluoroethylsulfonyl) imide (LiN (C ₂ F ₅ SO ₂ ) ₂ ), lithium bis (trifluoromethylsulfonyl) (pentafluoro Ethylsulfonyl) imide (LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ )) or lithium tris (trifluoromethylsulfonyl) methide (LiC (CF ₃ SO ₂ ) ₃ ) is used. These may be used alone or in combination of two or more.

  Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,2-dimethoxyethane (DME), 1 , 2-diethoxyethane (DEE), γ-butyrolactone (γ-BL), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), N, N-dimethylformamide, tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, acetamide, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, trimethoxymethane, dioxolane, dioxolane derivatives, sulfolane, methyl Rusulfolane, a propylene carbonate derivative, or a tetrahydrofuran derivative is used. These may be used alone or in combination of two or more.

  Further, for example, a liquid electrolyte, a gel electrolyte, or a solid electrolyte (polymer solid electrolyte) may be used as the non-aqueous electrolyte.

  As the separator 17, for example, a microporous thin film, a woven fabric, or a non-woven fabric is used. These have a high ion permeability and preferably have an appropriate mechanical strength and insulating property. Examples of the material of the separator 17 include polyolefin such as polypropylene and polyethylene.

  In particular, a microporous thin film made of polyolefin is excellent in durability and has a so-called shutdown function that closes the pores when the temperature rises to a certain temperature. Therefore, it is suitable as a separator for lithium ion secondary batteries such as lithium ion batteries. Used for.

  The thickness of the separator is generally 10 μm or more and 300 μm or less, preferably 40 μm or less, more preferably 5 μm or more and 30 μm or less. The separator may be a single layer film made of one material, or a composite film or multilayer film made of two or more materials.

As the material of the gasket 13, for example, a copolymer of polypropylene, polyethylene, polyphenylene sulfide, polyether ether ketone, polyamide, polyimide, polytetrafluoroethylene, liquid crystal polymer, and perfluoroalkoxyethylene is used. These may be used alone or in combination of two or more. You may use these in combination with fillers, such as an inorganic fiber. The gasket may be coated with a sealing material to increase the airtightness of the battery.

  The composition of the electrode material and the electrolytic solution in the above embodiment is not particularly limited, and known materials and compositions may be appropriately selected.

  Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

Example 1
The cylindrical lithium ion secondary battery 10 shown in FIG. 1 was produced according to the following procedure.

(1) Production of positive electrode 100 parts by weight of lithium nickelate as a positive electrode active material, 4 parts by weight of acetylene black as a conductive agent, 4 parts by weight of polyvinylidene fluoride as a binder, N-methyl-2-pyrrolidone (as a dispersion medium) NMP) was added to prepare a positive electrode slurry. This positive electrode slurry was applied to both surfaces of a positive electrode current collector (thickness 15 μm), dried and rolled to obtain a positive electrode (thickness 0.14 mm).

  At the time of production, the positive electrode was provided with a region not having the positive electrode active material layer (a portion where the positive electrode current collector was exposed), connected to a lead, and configured as shown in FIG.

(2) Production of negative electrode Vapor deposition apparatus (manufactured by ULVAC, Inc.) having Si (99.9999% pure silicon (manufactured by High Purity Chemical Laboratories)) as a negative electrode active material and equipped with electron beam (EB) heating means. ), Oxygen gas having a purity of 99.7% was introduced, and an alloy-based negative electrode active material layer was formed on both sides of a negative electrode current collector made of a strip-shaped copper foil (thickness 30 μm, width 31 mm, and length 33 mm). The negative electrode 15 was obtained.

The obtained alloy-based negative electrode active material layer was SiOx. As a result of quantifying the amount of oxygen contained by the combustion method, the composition of the compound containing silicon and oxygen was SiO _0.5 .

Next, lithium metal was vapor-deposited on the alloy-based negative electrode active material layer using a resistance heating vapor deposition apparatus manufactured by ULVAC. At this time, lithium metal was occluded into the alloy-based negative electrode active material layer. In this way, a negative electrode active material made of SiO _0.5 was supplemented in advance with an amount of lithium corresponding to the irreversible capacity.

  Using a 1.5 mm × 3.5 mm copper lead, the end corresponding to the outermost periphery of the negative electrode current collector and the end of the lead were connected by plasma welding.

(3) Production of electrode group Using a winding core, the separator is sandwiched between the slits of the winding core and folded to form two sheets. The electrode group was configured by winding around the core such that the agent forming portions face each other. At the end of winding, a tape was applied so as not to fix the lead portion, and the group was fixed.

(4) Preparation of electrolytic solution LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) to obtain a nonaqueous electrolytic solution. The weight ratio of EC and EMC was 1: 1. The concentration of LiPF ₆ in the non-aqueous electrolyte was 1.0 mol / L.

(5) Production of cylindrical lithium ion secondary battery The configured electrode group was inserted into a case. The inner diameter of the case was 3.3 mm. At this time, the negative electrode lead and the case were connected by contact. The positive electrode lead and the sealing plate were welded and connected. An electrolyte was poured into the case and sealed to obtain a battery. In this way, a cylindrical lithium ion secondary battery (diameter 3.5 mm, height 35 mm) having a nominal capacity of 43 mAh was obtained.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that a 1.5 mm × 7.8 mm lead was used as the negative electrode lead.

(Example 3)
A battery was fabricated in the same manner as in Example 1 except that a 31.0 mm × 3.5 mm lead was used as the negative electrode lead.

Example 4
A battery was fabricated in the same manner as in Example 1 except that a 31.0 mm × 7.8 mm lead was used as the negative electrode lead.

(Example 5)
A battery was fabricated in the same manner as in Example 1 except that a 31.0 mm × 2.5 mm lead was used as the negative electrode lead.

(Example 6)
A battery was fabricated in the same manner as in Example 1 except that a 1.5 mm × 10.0 mm lead was used as the negative electrode lead.

(Comparative Example 1)
As shown in FIGS. 5 and 6, a strip-shaped copper foil (thickness 30 μm, width 29.5 mm, and length 33 mm) is used as the negative electrode current collector 252, an exposed portion is provided, and a nickel negative electrode lead 251 is used. A 32.5 mm × 1.5 mm lead was used. The negative electrode current collector 252 and the negative electrode lead 251 were electrically connected by ultrasonic welding. Further, the cylindrical lithium ion secondary battery 20 shown in FIG. 2 was produced by the same method as in Example 1 except that the negative electrode lead 251 and the case 21 were connected by resistance welding.

  In addition, when resistance welding of the negative electrode lead and the case was performed for 100 cells, two holes were formed in the case, and five pieces of melt were generated. A battery was produced using other than these.

(A) Confirmation of initial capacity Each of the three batteries of Examples and Comparative Examples produced as described above was charged and discharged in the order of (1) to (4) below.
(1) After charging for 4 hours at a constant current of 0.05 It, the battery was discharged at a constant current of 0.05 C until the closed circuit voltage of the battery reached 2.5V.
(2) After charging with a constant current of 0.1 It until the closed circuit voltage of the battery reached 4.1 V, the battery was discharged with a constant current of 0.1 It until the closed circuit voltage of the battery reached 2.5 V.
(3) After charging with a constant current of 0.1 It until the closed circuit voltage of the battery reached 4.1 V, the battery was discharged with a constant current of 0.1 It until the closed circuit voltage of the battery reached 2.5 V.
(4) After charging with a constant current of 0.1 It until the closed circuit voltage of the battery reached 4.2 V, the battery was discharged with a constant current of 0.1 It until the closed circuit voltage of the battery reached 2.5 V.

  In addition, It represents a time rate. When an amount of electricity corresponding to the design capacity C (mAh) is supplied at time t (time), the current value I (mA) is expressed as C / t.

  In the discharge of (4) above, the discharge voltage was monitored to confirm the discharge capacity. All were good products, and the discharge capacity at this time was defined as the initial capacity.

  Table 1 shows an average of the initial capacities of the three confirmed batteries.

  As shown in Table 1, in Comparative Example 1, there is welding of the negative electrode lead and the case. For the welding of the negative electrode lead equivalent to 100 cells and the case, two perforations of the case and five scatters of the melt occurred. In a battery having a thin outer diameter of 8 mm or less, a thin lead is used to suppress an increase in the diameter of the electrode group. Moreover, the thickness of the case material is thin to ensure the capacity. The welding of the negative electrode lead and the case is an elaborate operation in which a welding rod is inserted into the thin case and the thin lead is welded. From these factors, it is considered that the perforation of the case and the scattering of the melt occurred.

  In Example 1 to Example 6 of the present invention, it is not necessary to weld the negative electrode lead to the case, so that the defect as in Comparative Example 1 does not occur. Furthermore, since the process is simple, the mass productivity is high.

  Further, it can be seen that the capacities of Examples 1 to 6 are higher than those of Comparative Example 1. This is because the welding of the negative electrode lead and the case is unnecessary, and the space required for welding contributed to the capacity.

  In Example 5, as shown in Table 1, a high capacity was obtained with a discharge of 0.1 It, but a discharge with a very high load of 1.5 It or more showed a reduced capacity. The length in the winding direction of the group of negative electrode leads is ¼ of the circumferential length of the inner diameter of the case, which is considered to be due to insufficient conductivity due to contact with the case in high-load discharge.

  The battery of the present invention can be suitably used as a power source in various electronic devices, in particular, various portable electronic devices.

10, 20 Cylindrical lithium ion secondary battery 11, 21 Case 12, 22 Electrode group 13, 23 Gasket 14, 24 Sealing plate 15, 25 Negative electrode 16, 26 Positive electrode 17, 27 Separator 18, 28 Upper ring 151, 251 Negative electrode lead 252 Negative electrode current collector 153, 253 Thin film negative electrode active material layer 154 Plasma weld 161, 261 Positive electrode lead 162 Positive electrode current collector 163 Positive electrode active material layer

Claims (4)

An electrode group in which a positive electrode and a negative electrode are wound so as to face each other through a separator disposed between the positive electrode and the negative electrode is housed in a case together with a non-aqueous electrolyte, and sealed with a gasket and a sealing plate. It is a stopped cylindrical lithium ion secondary battery,
The case has an outer diameter of 8.0 mm or less,
In the electrode group, the negative electrode is disposed on the outermost periphery,
The negative electrode comprises a negative electrode current collector, a thin film negative electrode active material layer formed on the surface of the negative electrode current collector and containing an alloy-based negative electrode active material, and a negative electrode lead.
The negative electrode lead is plasma welded at the negative electrode lead end portion and the outermost peripheral end portion of the negative electrode current collector, and is disposed at the outermost outer periphery of the electrode group, and the electrode group and the case face each other. A cylindrical lithium ion secondary battery, which is disposed on the inner surface of the case, is not welded to the inner surface of the case, and is electrically connected by contact. 2. The cylinder according to claim 1, wherein the negative electrode lead has a quadrangular shape, and a length of the plasma welded side is 1.5 mm or more and not more than a length of the negative electrode in a battery height direction. Lithium ion secondary battery. The negative electrode lead is a quadrangle, and the other side of the plasma-welded side is not less than 1/3 and not more than 3/4 of the circumferential length of the case inner diameter. Cylindrical lithium ion secondary battery. The battery according to any one of claims 1 to 3, wherein a nominal capacity of the battery is 5 mAh or more and 100 mAh or less.

Images