JP2007188859A - Battery and center pin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery in which a short circuit can be made more surely between electrodes if it is crushed by an external force and therefore its safety is improved. <P>SOLUTION: The center pin 30 is inserted into a center of a rolled part which is formed by winding a laminated layer of a cathode and an anode with a separator in between. The center pin 30 is composed of two or more, preferably, two or three of divided parts 31 in a longitudinal direction. Each of the divided parts is of a cylindrical shape and has a cut line 32 in a longitudinal direction. If the battery is crushed by an external force, an end part 31A of the divided part 31, the cut line 32 and a cornered part 31C where the end part 31A and the cut line 32 are crossed, and the like are extruded to make a short circuit without fail. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a battery including a center pin at the center of a spiral wound body including a strip-shaped positive electrode, a separator, and a negative electrode, and a center pin used in the battery.

  In recent years, many portable electronic devices such as a camera-integrated VTR (video tape recorder), a mobile phone, or a notebook personal computer have appeared, and their size and weight have been reduced. Batteries used as portable power sources for these electronic devices, particularly secondary batteries, are actively used as key devices for research and development aimed at improving energy density. Among them, non-aqueous electrolyte secondary batteries (for example, lithium ion secondary batteries) can provide a larger energy density than conventional lead batteries and nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries. Considerations are being made in various directions.

  Various types of lithium ion secondary batteries have been developed. One of them is a stack of a positive electrode and a negative electrode with a separator interposed between them and wound in a spiral shape. Some have a center pin inserted (see, for example, Patent Document 1). Conventionally, this center pin has a cut 132 in the axial direction of a tubular main body 131 as shown in FIG. When an external force is applied to the battery, the main body 131 is crushed, and as a result, the edge of the cut 132 opens to the outside, and the open portion penetrates the separator to short-circuit between the positive electrode and the negative electrode. As a result, the battery reaction is prevented and the power generation function is safely lost.

Conventionally, in order to cause a short circuit between the electrodes regardless of the direction from which the force is applied, for example, a center pin is provided with a plurality of grooves parallel to the cut, or the edge of the cut is corrugated. Yes (see, for example, Patent Document 2). In addition, it has been proposed that a short-circuit is easily generated over a wide range by providing a concave portion in a spiral shape on the surface of the center pin or forming the center pin with a coil spring (for example, Patent Document 3 and Patent Document 4). reference).
Japanese Patent Laid-Open No. 4-332481 JP-A-8-255631 Japanese Patent No. 3178586 Japanese Unexamined Patent Publication No. Hei 8-273697

  However, in the secondary battery using the center pin of the above-described conventional structure, there is a problem that deformation at the cut portion when being crushed by an external force is not sufficient, and the positive electrode and the negative electrode cannot be short-circuited reliably. There is a demand for an effective means for ensuring safety by short-circuiting the electrodes more reliably.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery with improved safety, which can short-circuit between electrodes more reliably when crushed by an external force, and to this battery. It is to provide a center pin to be used.

  The battery according to the present invention includes a positive electrode having a positive electrode active material layer on the surface of a strip-shaped positive electrode current collector and a negative electrode having a negative electrode active material layer on the surface of the strip-shaped negative electrode current collector, with a separator interposed therebetween. The wound body is provided with a wound wound body and a tubular center pin that is disposed at the winding center of the wound body and has two or more divided portions in the longitudinal direction.

  The center pin according to the present invention is a tubular one provided at the winding center of a battery having a winding structure, and has two or more divided portions in the longitudinal direction.

  Since the battery according to the present invention or the center pin according to the present invention has two or more divided portions in the longitudinal direction, when a force is applied to the battery from the outside, the center pin is crushed and the end of the divided portion is The part and the like warp outward and project through the separator, so that the positive electrode and the negative electrode are reliably short-circuited.

  In particular, at this time, the positive electrode is provided with a positive electrode exposed region in which the positive electrode active material layer does not exist on both sides at the end of the positive electrode current collector on the winding center side, while the negative electrode is provided on the winding center side of the negative electrode current collector. When the negative electrode exposed region where the negative electrode active material layer does not exist on both sides is provided at the end of the electrode, the exposed region of the positive electrode current collector and the negative electrode current collector having a low resistance value are directly short-circuited Thus, no short circuit occurs through the positive electrode active material layer having a high resistance value, and the temperature rise in the positive electrode active material layer is suppressed.

  According to the battery of the present invention or the center pin of the present invention, since the two or more divided portions are provided in the longitudinal direction, the positive electrode and the negative electrode can be reliably connected when crushed or broken by an external force. It can be short-circuited, improving safety.

  In particular, when the negative electrode is capable of occluding and releasing electrode reactants and includes a negative electrode active material containing at least one of a metal element and a metalloid element as a constituent element, the energy density of the battery is Since a larger and higher safety is required, a higher effect can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the figure, each component schematically shows the shape, size, and arrangement relationship to the extent that the present invention can be understood, and is different from the actual size.

(First embodiment)
FIG. 1 shows a cross-sectional structure of a secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called cylindrical type, and has a wound body 20 inside a substantially hollow cylindrical battery can 11. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the wound body 20.

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

  The wound body 20 is formed by laminating a positive electrode 21 and a negative electrode 22 with a separator 23 therebetween, and is wound in a spiral shape, and a center pin 30 is inserted in the center. A positive electrode lead 24 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound body 20, and a negative electrode lead 25 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 24 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 25 is welded and electrically connected to the battery can 11.

  FIG. 2 shows a cross-sectional configuration of the positive electrode 21 shown in FIG. 1 before winding. This positive electrode 21 is obtained by providing a positive electrode active material layer 21B on both surfaces of a strip-shaped positive electrode current collector 21A. Specifically, it has a positive electrode covering region 21C where the positive electrode active material layer 21B exists on the outer peripheral surface side and the inner peripheral surface side of the positive electrode current collector 21A. In addition, in the positive electrode 21, the end portion on the winding center side is a positive electrode exposed region 21D, that is, a region where both surfaces of the positive electrode current collector 21A are exposed without the presence of the positive electrode active material layer 21B. .

  The positive electrode current collector 21A has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

The positive electrode active material layer 21B includes, for example, any one or more of positive electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a positive electrode active material. A conductive material and a binder such as polyvinylidene fluoride may be included. The positive electrode material capable of inserting and extracting lithium does not contain lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), or vanadium oxide (V ₂ O ₅ ). Examples thereof include metal sulfides, metal selenides, metal oxides, and lithium-containing compounds containing lithium.

Among these, lithium-containing compounds are preferable because some compounds can obtain a high voltage and a high energy density. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. In particular, cobalt (Co), nickel and manganese (Mn Among these, those containing at least one of them are preferred. This is because a higher voltage can be obtained. The chemical formula is represented by, for example, Li _x MIO ₂ or Li _y MIIPO ₄ . In the formula, MI and MII represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1)) or lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure. Among these, a composite oxide containing nickel is preferable. This is because a high capacity can be obtained and excellent cycle characteristics can also be obtained. Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-v Mn _v PO ₄ (v <1)). Can be mentioned.

  FIG. 3 shows the configuration of the negative electrode 22. The negative electrode 22 is obtained by providing a negative electrode active material layer 22B on both surfaces of a strip-shaped negative electrode current collector 22A. Specifically, the negative electrode covering region 22C where the negative electrode active material layer 22B exists on the outer peripheral surface side and the inner peripheral surface side of the negative electrode current collector 22A, and both surfaces of the negative electrode current collector 22A at the winding center side end. Both have a negative electrode exposed region 22D that is exposed without the negative electrode active material layer 22B.

  The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The thickness of the negative electrode current collector 22A is, for example, 5 μm to 50 μm.

  The negative electrode active material layer 22B includes, for example, a negative electrode active material, and may include other materials such as a conductive material and a binder as necessary. Examples of the negative electrode active material include a negative electrode material that can occlude and release lithium, which is an electrode reactant, and includes at least one of a metal element and a metalloid element as a constituent element. Use of such a negative electrode material is preferable because a high energy density can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of the metal element or metalloid element constituting the negative electrode material include a metal element or metalloid element capable of forming an alloy with lithium. Specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon, germanium (Ge), tin, lead (Pb), bismuth (Bi), cadmium Examples thereof include (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), and platinum (Pt).

  Among these, the negative electrode material preferably includes a group 14 metal element or metalloid element in the long-period periodic table as a constituent element, and particularly preferably includes at least one of silicon and tin as a constituent element. 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, a simple substance, an alloy, or a compound of tin, or a material having one or two or more phases thereof at least in part.

  Examples of tin alloys include silicon, nickel, copper, iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), and silver as second constituent elements other than tin. (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), and the thing containing at least 1 sort (s) of chromium (Cr) are mentioned. As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) of these is mentioned.

  Examples of the tin compound or silicon compound include those containing oxygen (O) or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

  Among these, as this negative electrode material, tin, cobalt, and carbon are included as constituent elements, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the total of tin and cobalt is A CoSnC-containing material having a cobalt ratio of 30% by mass to 70% by mass is preferable. This is because a high energy density can be obtained in such a composition range, and excellent cycle characteristics can be obtained.

  This CoSnC-containing material may further contain other constituent elements as necessary. Examples of other constituent elements include silicon, iron, nickel, chromium, indium, niobium (Nb), germanium, titanium, molybdenum (Mo), aluminum (Al), phosphorus (P), gallium (Ga), or bismuth. Preferably, 2 or more types may be included. This is because the capacity or cycle characteristics can be further improved.

  This CoSnC-containing material has a phase containing tin, cobalt, and carbon, and this phase preferably has a low crystallinity or an amorphous structure. In this CoSnC-containing material, it is preferable that at least a part of carbon as a constituent element is bonded to a metal element or a semimetal element as 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. .

  As a measuring method for examining the bonding state of elements, for example, X-ray photoelectron spectroscopy (XPS) can be cited. In XPS, the peak of the carbon 1s orbital (C1s) appears at 284.5 eV in an energy calibrated apparatus so that the peak of the gold atom 4f orbital (Au4f) is obtained at 84.0 eV if it is graphite. . Moreover, if it is surface contamination carbon, it will appear at 284.8 eV. On the other hand, when the charge density of the carbon element increases, for example, when carbon is bonded to a metal element or a metalloid element, the C1s peak appears in a region lower than 284.5 eV. That is, when the peak of the synthetic wave of C1s obtained for the CoSnC-containing material appears in a region lower than 284.5 eV, at least a part of the carbon contained in the CoSnC-containing material is a metal element or a half of other constituent elements. Combined with metal elements.

  In XPS measurement, for example, the C1s peak is used to correct the energy axis of the spectrum. Usually, since surface-contaminated carbon exists on the surface, the C1s peak of the surface-contaminated carbon is set to 284.8 eV, which is used as an energy standard. In the XPS measurement, the waveform of the C1s peak is obtained as a shape including the surface contamination carbon peak and the carbon peak in the CoSnC-containing material. For example, by analyzing using a commercially available software, the surface contamination The carbon peak and the carbon peak in the CoSnC-containing material are separated. In the waveform analysis, the position of the main peak existing on the lowest bound energy side is used as the energy reference (284.8 eV).

  As the negative electrode active material, a carbon material such as natural graphite, artificial graphite, non-graphitizable carbon, or graphitizable carbon may be used. Use of a carbon material is preferable because excellent cycle characteristics can be obtained. Moreover, lithium metal is also mentioned as a negative electrode active material. The negative electrode active material may be used alone or in combination of two or more.

  The separator 23 shown in FIG. 1 is composed of a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. A structure in which a porous film is laminated may be used.

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

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

  FIG. 4 shows the configuration of the center pin 30 shown in FIG. 1, and FIG. 5 shows its cross-sectional configuration. This center pin 30 has two or more tubular division parts 31 in the longitudinal direction, and when the battery is crushed or broken by an external force, the positive electrode 21 and the negative electrode 22 are reliably short-circuited. It is possible to improve safety.

  In particular, when the negative electrode 22 can occlude and release the electrode reactant and includes a negative electrode active material containing at least one of a metal element and a metalloid element as a constituent element, the energy density of the battery Therefore, a higher effect can be obtained because higher safety is required.

  The division part 31 is formed, for example, by rolling a thin strip-shaped plate into a tubular shape, and has a cylindrical shape with a diameter of, for example, 3.0 mm. The division parts 31 are completely separated from each other. The end portions 31A on both sides of each divided portion 31 are provided with inclined portions 31B so that they can be easily inserted into the center of the wound body 20 in the manufacturing process described later. The adjacent divided portions 31 may be in contact with each other or may be separated from each other, and may be stored in the wound body 20. The distance between the divided parts 31 is not particularly limited, but it is desirable that the distance is not too large.

  Moreover, the division part 31 has the cut | interruption 32 from one edge part of a longitudinal direction to the other edge part. The cut 32 is provided, for example, by creating a gap between the opposing long sides when the divided portion 31 is produced by rounding a thin strip-like plate into a tubular shape in the manufacturing process described later. The width of the cut 32 is, for example, 0.5 mm.

  The material and thickness of the dividing portion 31 are normally maintained at a predetermined strength, and on the other hand, when the battery is crushed by an external force, it is crushed or broken along with it. Specifically, for example, stainless steel may be used as a constituent material of the dividing portion 31. The thickness of the division part 31 is preferably 0.05 mm or more and 5 mm or less, for example. If the thickness is less than 0.05 mm, the strength may be weakened, and if it is thicker than 5 mm, it is difficult to round the tube.

  The center pin 30 preferably has two such divided portions 31 as shown in FIG. 4 or FIG. 6, or three as shown in FIG. It is because productivity may fall with four or more.

  The cut lines 32 do not necessarily have to be aligned on the same positional relationship in the circumferential direction, that is, on the same straight line L as shown in FIG. 4 or FIG. For example, the cuts 32 are preferably arranged randomly in the circumferential direction as shown in FIG. 6 or FIG. This is because the cuts 32 are arranged in a distributed manner in the circumferential direction, so that the positive electrode 21 and the negative electrode 22 can be reliably short-circuited regardless of the direction from which the external force is applied. The amount of deviation in the circumferential direction between the cuts 32 is not particularly limited.

  The length of the center pin 30, that is, the total length of the divided portions 31, varies depending on the size of the secondary battery, but is preferably 2.5 cm or more and 8.0 cm or less, for example.

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

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like material. A positive electrode mixture slurry is obtained. Subsequently, the positive electrode mixture slurry is uniformly applied to the positive electrode current collector 21A using a doctor blade or a bar coater, and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like. Then, the positive electrode 21 is produced.

  Next, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. And Subsequently, the negative electrode mixture slurry is uniformly applied to the negative electrode current collector 22A using a doctor blade or a bar coater, and the solvent is dried. Then, the negative electrode mixture layer 22B is formed by compression molding using a roll press. Then, the negative electrode 22 is produced. The roll press machine may be used by heating. Moreover, you may compression-mold several times until it becomes the target physical-property value. Furthermore, you may use press machines other than a roll press machine.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween, and wound many times in the winding direction shown in FIGS. 2 and 3 to produce the wound body 20.

  On the other hand, two thin strip-shaped plates made of, for example, stainless steel are prepared. For example, when the center pin 30 is constituted by two divided portions 31, the dimension of the plate is such that the length of the divided portion 31 is about one half of the height of the secondary battery. If it is configured by, it should be about one third. By rolling this plate and forming it into a tubular shape, a tubular divided portion 31 is formed, and end portions 31A on both sides of each divided portion 31 are tapered to provide inclined portions 31B.

  After that, the division part 31 is inserted into the center of the wound body 20. This insertion process is repeated twice when the center pin 30 is constituted by the two divided portions 31, and is repeated three times when constituted by the three divided portions 31. At that time, the cut line 32 may have a positional relationship that coincides in the circumferential direction as shown in FIG. 4 or 7, or the cut line 32 may be a circle as shown in FIG. 6 or FIG. You may make it arrange | position at random in the circumferential direction.

  After inserting the dividing portion 31, the wound body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 25 is welded to the battery can 11, and the positive electrode lead 24 is welded to the safety valve mechanism 15 to thereby wind the wound body. 20 is accommodated in the battery can 11, an electrolyte is injected into the battery can 11, and the separator 23 is impregnated. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution impregnated in the separator 23. When the discharge is performed, for example, lithium ions are released from the negative electrode 22 and inserted into the positive electrode 21 through the electrolytic solution impregnated in the separator 23. And in this secondary battery, since the center pin 30 has two or more divided parts 31 in the longitudinal direction, when an external force is applied, the divided part 31 is crushed or broken, and the end 31A becomes By projecting outward and projecting through the separator 23, the positive electrode 21 and the negative electrode 22 are reliably short-circuited.

  Further, when the dividing portion 31 is provided with a cut 32, as shown in FIG. 9, the cut 32 opens to the outside, and a sharp corner 31C where the cut 32 and the end portion 31A intersect is formed on the outside. Protrusively. When the cut 32 or the corner 31C penetrates the separator 23, the positive electrode 21 and the negative electrode 22 are further short-circuited more reliably.

  Further, in this secondary battery, a positive electrode exposed region 21D where the positive electrode active material layer 21B does not exist on both sides is provided on the winding center side of the positive electrode 21, and the negative electrode active material layer on both sides also on the winding center side of the negative electrode 22 Since the negative electrode exposed region 22D in which 22B does not exist is provided, when the end 31A, the cut 32, or the corner 31C penetrates the separator 23, the positive current collector 21A and the negative current collector 22A having a relatively low resistance value There is a direct short between them. That is, in the present embodiment, the positive electrode exposed region 21D of the positive electrode 21 and the negative electrode exposed region 22D of the negative electrode 22 are short-circuited by the end portion 31A, the cut 32, or the corner portion 31C of the divided portion 31, and the positive electrode having a high resistance value. No short circuit occurs through the active material layer 21B, and the temperature rise in the positive electrode active material layer 21B is suppressed.

  Thus, in the present embodiment, since two or more divided portions 31 are provided in the longitudinal direction of the center pin 30, when an external force is applied, the end portion 31A of the divided portion 31 protrudes outward, and the positive electrode 21 And the negative electrode 22 can be reliably short-circuited. In addition, in the wound body 20, particularly on the winding center side, the positive electrode 21 has a positive electrode exposed region 21 </ b> D in which the positive electrode active material layer 21 </ b> B is not present on both surfaces. Since the exposed region 22D is provided, when the end 31A passes through the separator 23, the positive electrode current collector 21A and the negative electrode current collector 22A having a relatively low resistance value are directly short-circuited. Therefore, the positive electrode 21 and the negative electrode 22 can be reliably short-circuited while suppressing the temperature rise of the positive electrode active material layer 21B, and safety is improved.

  In particular, when the negative electrode 22 is capable of inserting and extracting an electrode reactant and includes a negative electrode active material containing at least one of a metal element and a metalloid element as a constituent element, the battery Since the energy density is high and higher safety is required, higher effects can be obtained.

(Modification)
FIG. 10 shows a configuration of the center pin 30 of the secondary battery according to the modification of the present invention. This secondary battery is the same as that of the first embodiment except that the split portions 31 of the center pin 30 are separated from each other by a thin groove 31D provided in the circumferential direction and are continuously integrated. It has the same composition as. Therefore, the same components as those in the first embodiment will be described with the same reference numerals.

  This secondary battery is the same as that of the first embodiment except that a thin groove 31D is provided on the plate for producing the center pin 30 at a position that becomes the boundary line of the dividing portion 31 and then rolled into a cylindrical shape. It can be manufactured in the same manner as in the embodiment.

  In this secondary battery, when a force is applied to the secondary battery from the outside, the center pin 30 is crushed and bent at the thin groove 31D, the fold is projected outward, and penetrates the separator 23, thereby positive electrode. 21 and the negative electrode 22 are reliably short-circuited.

  As described above, in the present modified example, the split portions 31 of the center pin 30 are partitioned from each other by the thin grooves 31D provided in the circumferential direction and are continuously integrated. Similarly to the embodiment, the positive electrode 21 and the negative electrode 22 can be short-circuited reliably, and the safety can be improved.

(Second Embodiment)
FIG. 11 shows the configuration of the center pin 30 of the secondary battery according to the second embodiment of the present invention. The secondary battery has the same configuration as that of the first embodiment except that the center pin 30 is provided with a bent cut 33. Therefore, the same components as those in the first embodiment will be described with the same reference numerals.

  The notch 33 has a linear first portion 33A and a linear second portion 33B extending from the end of the first portion 33A in a direction different from the first portion 33A, for example, at a right angle. That is, the cut 33 has a so-called L-shape, and has a convex portion 33C at the bent portion. Thereby, in this secondary battery, when it is crushed by an external force, the notch 33 protrudes to the outside, and the bent convex portion 33C penetrates the separator 23 to more reliably short-circuit the positive electrode 21 and the negative electrode 22. Can be done. In addition, the corner | angular corner of the notch 33 does not necessarily need to be a right angle, and the corner | angular may be rounded.

  The length of the first portion 33A and the second portion 33B, that is, the dimension in the extending direction, is preferably such that the notch 33 can be reliably projected, and is, for example, about half the circumference of the center pin 30. The width of the first portion 33A and the second portion 33B, that is, the dimension in the direction orthogonal to the extending direction is preferably, for example, not less than 0.1 mm and not more than 2.0 mm. This is because a higher effect can be obtained. Note that the first portion 33A and the second portion 33B do not necessarily have the same length.

  The first portion 33A is preferably parallel to the longitudinal direction of the center pin 30, and the second portion 33B preferably extends perpendicularly from the end of the first portion 33A. This is because productivity can be improved.

  The distance D between the notches 33 is preferably 0.1 mm or more, for example. This is because productivity can be improved.

  This secondary battery can be manufactured in the same manner as in the first embodiment, except that a cut-out 33 is provided in a plate to be the center pin 30 and then rounded and molded.

  In this secondary battery, when a force is applied to the secondary battery from the outside, the center pin 30 is crushed and the notch 33 protrudes outward. The convex portion 33 </ b> C of the cut 33 penetrates the separator 23, so that the positive electrode 21 and the negative electrode 22 are further short-circuited.

  As described above, in the present embodiment, the notch 33 is provided in the center pin 30, so that the positive electrode 21 and the negative electrode 22 can be more reliably short-circuited when being crushed or broken by an external force. And safety is improved.

(Modification of the second embodiment)
FIG. 11 shows an example in which the cuts 32 are aligned on the same straight line L and have the same positional relationship in the circumferential direction. However, the cuts 32 are formed in the circumferential direction as shown in FIG. 12, for example. May be arranged at random.

  Moreover, although the case where the cuts 33 are arranged at regular intervals has been described in the present embodiment, the cuts 33 may be arranged at irregular intervals. In the present embodiment, the first portion 33A is parallel to the longitudinal direction of the center pin 30, and the second portion 33B is perpendicular to the first portion 33A. However, as shown in FIG. The first portion 33 </ b> A and the second portion 33 </ b> B may be disposed obliquely with respect to the longitudinal direction of the center pin 30.

  Furthermore, in the present embodiment, the case where the second portion 33B extends in the direction perpendicular to the end portion of the first portion 33A has been described. However, as shown in FIG. It may extend in an acute angle direction from the end of the portion 33A. Furthermore, the second portion 33B extends in an acute angle direction from the end portion of the first portion 33A, and the first portion 33A and the second portion 33B are disposed obliquely with respect to the longitudinal direction of the center pin 30. Also good.

  In addition, the cut 33 may include a linear first portion 33A and a linear second portion 33B that intersects the first portion 33A. At this time, the second portion 33B may intersect with the first portion 33A in, for example, a cross shape as shown in FIG. 15, or in a T shape as shown in FIG. May be. Further, the intersection angle between the first portion 33A and the second portion 33B is not necessarily a right angle, and may be an acute angle or an obtuse angle.

  Furthermore, the cut 33 is not necessarily limited to a straight line, and may have a rounded shape as shown in FIG. 17, for example.

  In addition, the center pin 30 may be provided with a notch 34 that intersects the cut 32 as shown in FIG. 18 in addition to the notch 33 as shown in FIG. Like the convex portion 33C of the notch 33, the positive electrode 21 and the negative electrode 22 can be more reliably short-circuited by the corner formed at the intersection of the notch 34 and the cut 32, and safety can be further improved. it can.

  In addition, the position etc. which provide the notch part 34 are not specifically limited, As shown in FIG. 18, the notch part 34 and the notch 33 do not necessarily need to be provided in the position which opposes across the cut | interruption 32. FIG. In that case, the notch 34 may be provided over both sides of the cut 32.

  The shape of the notch 33 used together with the notch 34 is not particularly limited, and the notch 33 having another shape described in the modification of the second embodiment may be provided. For example, as shown in FIG. 19, the cross-shaped cut 33 shown in FIG. 15 may be provided.

  The crossing angle of the notch 34 with respect to the cut 32 is not particularly limited, and the cut 32 may cross the cut 32 obliquely.

  Furthermore, the notch 33 does not necessarily have to be a hole that penetrates the center pin 30 in the thickness direction, and as shown in FIG. 20, a part in the thickness direction is made thinner than the surrounding region without penetrating. A thin groove may be used. The same applies to the notch 34.

  In the second embodiment and the modification thereof, the case where the center pin 30 has two divided portions 31 is illustrated as an example. However, as shown in FIG. The present invention is also applicable when the center pin 30 has three divided portions 31. Also in this case, the cuts 32 do not necessarily have to be aligned on the same straight line L as shown in FIG. 21, and may be randomly arranged in the circumferential direction, for example, as shown in FIG.

  Further, specific embodiments of the present invention will be described in detail.

(Examples 1-3)
The secondary battery described in the first embodiment was manufactured. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm and dried. Then, the positive electrode active material layer 21B was formed by compression molding with a roll press machine, and the positive electrode 21 was produced. Subsequently, a positive electrode lead 24 made of aluminum was attached to one end of the positive electrode current collector 21A.

  In addition, a CoSnC-containing material was produced as a negative electrode active material. First, cobalt powder, tin powder, and carbon powder were prepared as raw materials, and cobalt powder and tin powder were alloyed to produce a cobalt-tin alloy powder. Then, carbon powder was added to the alloy powder and dry mixed. Subsequently, this mixture was synthesized using a mechanochemical reaction using a planetary ball mill to obtain a CoSnC-containing material.

  When the composition of the obtained CoSnC-containing material was analyzed, the cobalt content was 29.3 mass%, the tin content was 49.9 mass%, and the carbon content was 19.8 mass%. . The carbon content was measured by a carbon / sulfur analyzer, and the cobalt and tin contents were measured by ICP (Inductively Coupled Plasma) emission analysis. Further, when X-ray diffraction was performed on the obtained CoSnC-containing material, a diffraction peak having a wide half-width with a diffraction angle 2θ of 1.0 ° or more was observed between diffraction angles 2θ = 20 ° to 50 °. It was. Further, when XPS was performed on the CoSnC-containing material, the C1s peak in the CoSnC-containing material was obtained in a region lower than 284.5 eV. That is, it was confirmed that carbon in the CoSnC-containing material was bonded to other elements.

  Next, 60 parts by mass of this CoSnC-containing material, 28 parts by mass of artificial graphite as a conductive agent and a negative electrode active material and 2 parts by mass of carbon black, and 10 parts by mass of polyvinylidene fluoride as a binder are mixed. The agent was adjusted. Subsequently, the negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which is applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm, and dried. The negative electrode active material layer 22B was formed by compression molding with a press. Thereafter, a negative electrode lead 25 made of nickel was attached to one end of the negative electrode current collector 22A.

  Subsequently, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm was prepared, and a positive electrode 21, a separator 23, a negative electrode 22, and a separator 23 were laminated in this order to form a laminated body. The wound body 20 was produced by winding. The maximum diameter of the body portion of the wound body 20 was 13.5 mm.

  After producing the wound body 20, after preparing the thin strip | belt-shaped board which consists of stainless steel of the dimension mentioned above as a material of the division | segmentation part 31, it rolls and shape | molds it in the cylinder shape, The inclined part 31B is set to the edge part 31A of both sides. By providing, the division part 31 was produced and this division part 31 was inserted in the center of the wound body 20, and the center pin 30 was comprised. At that time, the number of the division parts 31 constituting the center pin 30 is two in the first embodiment, three in the second embodiment, and four in the third embodiment. Moreover, when inserting the division part 31, the cut | interruption 32 was arrange | positioned on the same straight line, and it was set as the positional relationship corresponded in the circumferential direction.

After that, the wound body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 25 is welded to the battery can 11, the positive electrode lead 24 is welded to the safety valve mechanism 15, and the wound body 20 has an inner diameter of 14. It was housed inside a 0 mm battery can 11. After that, an electrolytic solution was injected into the battery can 11. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 1 mol / dm ³ in a solvent obtained by mixing 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate was used.

  After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 via the gasket 17, thereby obtaining a cylindrical secondary battery having an outer diameter of 14 mm and a height of 43 mm.

(Examples 4 to 6)
The secondary battery described in the second embodiment was manufactured. That is, as shown in FIG. 9, the fourth embodiment is the same as the first embodiment except that the notch 33 is provided in the center pin 30, and the fifth embodiment is the same as the second embodiment. Produced a secondary battery in the same manner as in Example 3.

(Examples 7 to 12)
Example 7 is the same as Example 1 except that the split portion 31 is randomly arranged in the circumferential direction when the dividing portion 31 is inserted into the winding center of the winding resistance 20. Example 8 is the same as Example 2, Example 9 is the same as Example 3, Example 10 is the same as Example 4, Example 11 is the same as Example 5, Example 12 is the Example A secondary battery was produced in the same manner as in Example 6.

  As Comparative Example 1 with respect to Examples 1 to 12, a secondary battery was obtained in the same manner as Example 1 except that a conventional center pin having only a cut 132 was used in the main body 131 as shown in FIG. Produced.

  Five secondary batteries (Battery 1 to Battery 5) of Examples 1 to 12 and Comparative Example 1 thus obtained were produced, and a crush test was performed to examine the presence or absence of ignition or rupture. Further, for Examples 1, 4, 7, and 10, the short speed (time taken until short circuit) was also examined. The short speed was determined by measuring each of the five batteries and taking the average. The obtained results are shown in Table 1.

  As can be seen from Table 1, according to Examples 1 to 12 in which two or more divided portions 31 were provided in the longitudinal direction of the center pin 30, the bursting was remarkably reduced, but a comparative example in which no divided portions were provided. In 1, the burst occurred in all of the five secondary batteries. That is, it is understood that if two or more divided portions 31 are provided in the longitudinal direction of the center pin 30, safety can be improved even when a short circuit occurs due to the battery being crushed or broken. It was.

  Further, when the first, second, fourth, fifth, seventh, eighth, tenth and eleventh embodiments are compared with the third, sixth, ninth and twelfth embodiments, the first and second embodiments in which two or three divided portions 31 are provided. 4, 4, 5, 7, 8, 10, and 11, the bursting was further reduced as compared with Examples 3, 6, 9, and 12 in which four divided portions 31 were provided. That is, it has been found that if two or three divided portions 31 are provided in the longitudinal direction of the center pin 30, the safety can be further improved.

  Further, from comparison between Example 1 and Example 4 and comparison between Example 7 and Example 10, in Examples 4 and 10 in which the notch 33 is provided in the center pin 30, Example 1 in which the notch 33 is not provided. , 7 was short-circuited earlier. That is, it was found that if the notch 33 is provided in the center pin 30, the positive electrode 21 and the negative electrode 22 can be short-circuited more quickly, and the safety can be further improved.

  In addition, from the comparison between Example 1 and Example 7 and the comparison between Example 4 and Example 10, in Examples 7 and 10 in which the cuts 32 are randomly arranged in the circumferential direction, the cuts 32 are circumferential. A short circuit occurred at an early stage as compared with Examples 1 and 4 in which the positional relationship coincided in the direction. In other words, if the cuts 32 are randomly arranged in the circumferential direction, the cuts 32 can be arranged in a distributed manner in the circumferential direction, and it is ensured that any external force is applied from any direction. It turned out that the positive electrode 21 and the negative electrode 22 can be short-circuited, and also safety can be improved.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the dividing portion 31 is not limited to the cylindrical shape described in the above embodiments and examples, and may have another cross-sectional shape such as an ellipse or a polygon.

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

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

  As the solid electrolyte, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, or an inorganic solid electrolyte made of ion conductive glass or ionic crystals can be used. At this time, as the polymer compound, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, an acrylate polymer compound alone or mixed, Alternatively, it can be used by copolymerizing in the molecule. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

  Further, in the above embodiments and examples, a cylindrical secondary battery having a winding structure has been described. However, the present invention can be applied to any shape as long as the secondary battery has a winding structure. can do. The present invention can also be applied to primary batteries.

  In addition, in the above embodiments and examples, the case where lithium is used as the electrode reactant has been described. However, other group 1 elements in the long-period periodic table such as sodium (Na) or potassium (K), or The present invention can also be applied to the case of using elements of Group 2 in the long-period periodic table such as magnesium or calcium (Ca), other light metals such as aluminum, lithium, or alloys thereof. An effect can be obtained. At that time, a negative electrode active material, a positive electrode active material, a solvent, or the like that can occlude and release the electrode reactant is selected according to the electrode reactant.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is sectional drawing showing the structure before winding of the positive electrode shown in FIG. It is sectional drawing showing the structure before winding of the negative electrode shown in FIG. It is a perspective view showing an example of composition of a center pin. It is sectional drawing of the center pin shown in FIG. It is a perspective view showing the modification of the center pin shown in FIG. It is a top view showing the other modification of the center pin shown in FIG. FIG. 10 is a plan view illustrating still another modified example of the center pin illustrated in FIG. 7. It is a figure for demonstrating the effect | action of the center pin when the secondary battery shown in FIG. 1 is crushed, and is sectional drawing along the IX-IX line of FIG. It is a perspective view showing the structure of the center pin of the secondary battery which concerns on the modification of this invention. It is a top view showing the structure of the center pin of the secondary battery which concerns on the 2nd Embodiment of this invention. It is a top view showing the other structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is sectional drawing showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a top view showing the further another structural example of a center pin. It is a perspective view showing an example of the conventional center pin.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulating plate, 14 ... Battery cover, 15 ... Safety valve mechanism, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding body, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 21C ... Positive electrode coating region, 21D ... Positive electrode exposure region, 22 ... Negative electrode, 22A ... Negative electrode current collector, 22B ... Negative electrode active material layer, 22C ... Negative electrode coating region, 22D ... Negative electrode exposure region, 23 ... Separator, 24 ... Positive lead, 25 ... Negative lead, 30 ... Center pin, 31 ... Split part, 31A ... End part, 31B ... Inclined part, 31C ... Corner, 31D ... Thin groove, 32 ... Cut, 33 ... Incision , 34 ... Notch

Claims (14)

A positive electrode having a positive electrode active material layer on the surface of the strip-shaped positive electrode current collector and a negative electrode having a negative electrode active material layer on the surface of the strip-shaped negative electrode current collector are stacked with a separator in between and wound. With round bodies,
A battery comprising: a tubular center pin disposed at a winding center of the wound body and having two or more divided portions in a longitudinal direction.   The battery according to claim 1, wherein the center pin has two of the divided portions.   The battery according to claim 1, wherein the center pin has three of the divided portions.   The battery according to claim 1, wherein the two or more divided parts are completely separated from each other.   The battery according to claim 1, wherein the center pin has a cut in a bent shape.   The positive electrode has a positive electrode exposed region in which the positive electrode active material layer does not exist on both sides at an end portion on the winding center side of the positive electrode current collector, and the negative electrode is on the winding center side of the negative electrode current collector 2. The battery according to claim 1, further comprising: a negative electrode exposed region where the negative electrode active material layer is not present on both sides at the end of the first electrode.   2. The negative electrode according to claim 1, wherein the negative electrode is capable of inserting and extracting an electrode reactant, and includes a negative electrode active material containing at least one of a metal element and a metalloid element as a constituent element. battery.   The battery according to claim 7, wherein the negative electrode includes a material containing at least one of tin (Sn) and silicon (Si) as a constituent element as the negative electrode active material.   The negative electrode includes tin, cobalt (Co), and carbon (C) as constituent elements as the negative electrode active material, and the carbon content is 9.9 mass% or more and 29.7 mass% or less, The battery according to claim 7, further comprising a CoSnC-containing material in which a ratio of cobalt to a total of tin and cobalt is 30% by mass or more and 70% by mass or less. A tubular center pin provided at the winding center of a battery having a winding structure,
A center pin having two or more divided portions in the longitudinal direction.   The center pin according to claim 10, wherein the center pin has two division parts.   The center pin according to claim 10, comprising three divided portions.   The center pin according to claim 10, wherein the two or more divided portions are completely separated from each other. The center pin according to claim 10, wherein the center pin has a bent cut.

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